JP7380438B2 - steering device - Google Patents

Description

The present invention relates to a steering device for steering steering wheels of a vehicle.

Conventionally, so-called steer-by-wire steering devices are known in which power transmission between a steering wheel and steered wheels is mechanically separated. For example, in the steering device of Patent Document 1, two motors are provided coaxially with respect to a steering shaft that steers steered wheels. A ball nut is integrally provided on each of the rotors of the two motors, and these ball nuts are screwed into a ball screw provided on a steered shaft via a large number of balls. The rotational motion of the two motors is converted into linear motion of the steered shaft via a ball screw mechanism including a ball nut.

There are various types of mechanisms that transmit the rotation of a motor to a steered shaft. Depending on the product specifications, for example, a belt transmission mechanism may be employed as the transmission mechanism. In this case, pulleys are provided on the output shaft of the motor and the ball nut, respectively, and an endless belt is wound around these pulleys. The rotation of the motor is transmitted from a pulley provided on its output shaft to a pulley provided on a ball nut via a belt. As the ball nut rotates in conjunction with the drive of the motor, the steered shaft moves in its axial direction.

Japanese Patent Application Publication No. 2006-347209

In a steering device, when a belt transmission mechanism is adopted as a mechanism for transmitting the rotation of the motor to the steering shaft, a toothed pulley is used as the pulley in order to more appropriately transmit the rotation of the motor to the steering shaft. Also, a toothed belt is sometimes used as the belt. In this way, the teeth of the two pulleys and the teeth of the belt mesh with each other, so that the rotation of the motor is transmitted to the steered shaft without slipping. However, when using a toothed pulley and a toothed belt, the following concerns arise.

That is, a large reverse input load may act on the steered shaft due to the vehicle running onto a curb or the like. In this case, as the steered shaft moves in its axial direction, the end of the steered shaft may come into contact with the housing, which is a so-called end abutment. In this case, rotation of the ball nut and belt is restricted by physically restricting movement of the steered shaft. On the other hand, the motor and drive pulley tend to continue rotating due to their inertia. For this reason, there is a risk that so-called tooth skipping may occur in the belt. Teeth skipping refers to a phenomenon in which the teeth of the belt and the teeth of the pulley cross over the teeth of the pulley due to the teeth of the belt not meshing properly.

If this belt tooth skipping occurs repeatedly, the wear of the belt teeth progresses, and there is a concern that the quiet performance or torque transmission performance of the belt transmission mechanism will eventually deteriorate. Therefore, in order to take some measures against the occurrence of belt tooth skipping, it has been required to detect belt tooth skipping.

An object of the present invention is to provide a steering device that can detect belt tooth skipping.

A steering device capable of achieving the above object includes a steering shaft that has two ball screw parts and steers a steered wheel by linear motion, and two ball nuts that are screwed into the two ball screw parts, respectively. and two transmission mechanisms having two motors that generate driving force, toothed belts that transmit the driving force of the two motors to the corresponding ball nuts, and rotation angles of the two motors, respectively. The motor includes two detection devices that perform detection, and a control device that controls each of the two motors. The control device detects tooth skipping of the belt based on rotation angles of the two motors detected through the two detection devices.

For example, if tooth skipping occurs in one of the belts of two transmission mechanisms, the rotation amount of the motor connected to the transmission mechanism where the tooth skipping occurred, and the rotation amount of the motor connected to the transmission mechanism where the tooth skipping did not occur. The amount of rotation of the motor differs depending on the degree of tooth skipping. Therefore, as in the above-mentioned steering device, it is possible to detect occurrence of tooth skipping in one of the belts of the two transmission mechanisms based on the rotation angles of the two motors.

In the above steering device, the control device is configured to calculate a first absolute position of the steered shaft based on a rotation angle of the first motor detected through the first detection device, and a second absolute position of the steered shaft. The tooth skipping of the belt may be detected through comparison with a second absolute position of the steered shaft calculated based on a second rotation angle of the motor detected through the detection device.

If tooth skipping occurs on the belt of either one of the two transmission mechanisms, the amount of rotation of the motor connected to the transmission mechanism where tooth skipping occurs, and the motor connected to the transmission mechanism where tooth skipping does not occur. The amount of rotation differs depending on the degree of tooth skipping. Therefore, if tooth skipping occurs in the belt of either one of the two transmission mechanisms, the first absolute position of the steered shaft calculated based on the rotation angle of the first motor, and the position of the second motor. The second absolute position of the steered shaft calculated based on the rotation angle also has different values depending on the degree of tooth skipping. Therefore, as in the above steering device, the first absolute position of the steered shaft is calculated based on the rotation angle of the first motor, and the steered shaft is calculated based on the rotation angle of the second motor. By comparing the second absolute position with the second absolute position, tooth skipping of the belt can be appropriately detected.

In the above-mentioned steering device, the control device is configured such that the absolute value of the difference between the first absolute position of the steered shaft and the second absolute position of the steered shaft determines tooth skipping of the belt. When the value is equal to or greater than a predetermined threshold value, it may be determined that tooth skipping has occurred in the belt.

If tooth skipping occurs in the belt of either one of the two transmission mechanisms, the first absolute position of the steered shaft calculated based on the rotation angle of the first motor and the rotation angle of the second motor The second absolute position of the steered shaft calculated based on this will have different values depending on the degree of tooth skipping. Therefore, the absolute value of the difference between the first absolute position and the second absolute position of the steered shaft is a value corresponding to the degree of tooth skipping. For example, the greater the degree of tooth skipping, the greater the absolute value of the difference between the first absolute position and the second absolute position of the steered shaft. Conversely, the smaller the degree of tooth skipping, the smaller the absolute value of the difference between the first absolute position and the second absolute position of the steered shaft. Therefore, as in the above-mentioned steering device, the absolute value of the difference between the first absolute position and the second absolute position of the steering shaft is equal to or greater than the threshold value determined for determining tooth skipping of the belt. When this occurs, it can be determined that tooth skipping has occurred in the belt. Further, by setting the threshold value according to the detection accuracy of tooth skipping required of the steering device, it is possible to appropriately detect tooth skipping of the belt.

In the above steering device, the first detection device and the second detection device may have different shaft angle multipliers. In this case, as an initialization process at the time of starting execution of steering control for steering the steered wheels, the control device detects a first rotation angle of the motor detected through the first detection device, and a second rotation angle of the motor detected through the first detection device. The absolute position of the steered shaft may be calculated based on the rotation angle of the second motor detected through the detection device. After the initialization process, the control device converts the amount of change in the rotation angle of the first motor detected through the first detection device into the amount of movement of the steered shaft, The current value of the first absolute position of the steered shaft can be calculated by adding the amount of movement of the steered shaft to the absolute position acquired through the initialization process. Further, the control device converts the amount of change in the rotation angle of the second motor detected through the second detection device into the amount of movement of the steered shaft, and the converted movement of the steered shaft. The current value of the second absolute position of the steered shaft can be calculated by adding the amount to the absolute position obtained through the initialization process.

The steering device described above may include a shaft that rotates in conjunction with the steering shaft, and an absolute angle sensor that detects an absolute rotation angle of the shaft. In this case, as an initialization process at the start of execution of steering control for steering the steered wheels, the control device includes an absolute rotation angle of the steered shaft based on an absolute rotation angle of the shaft detected through the absolute angle sensor. The position may also be calculated. After the initialization process, the control device converts the amount of change in the rotation angle of the first motor detected through the first detection device into the amount of movement of the steered shaft, By adding the amount of movement of the rudder shaft to the absolute position acquired through the initialization process, the current value of the first absolute position of the steered shaft can be calculated. Further, after the initialization process, the control device converts the amount of change in the rotation angle of the second motor detected through the second detection device into the amount of movement of the steered shaft, and By adding the amount of movement of the steered shaft to the absolute position acquired through the initialization process, the current value of the second absolute position of the steered shaft can be calculated.

In the above-mentioned steering device, when it is determined that the vehicle is traveling straight by satisfying a predetermined determination condition, the control device determines the absolute position of the steering shaft at that time. You may make it set as a steering neutral position which becomes a reference point when calculating a position. After the steering neutral position of the steering shaft is set, the control device converts the amount of change in the rotation angle of the first motor detected through the first detection device into the amount of movement of the steering shaft. The current value of the first absolute position of the steered shaft can be calculated by converting and adding the converted movement amount of the steered shaft to the steered neutral position. Further, the control device converts the amount of change in the rotation angle of the second motor detected through the second detection device into the amount of movement of the steered shaft, and The current value of the second absolute position of the steered shaft can be calculated by adding the amount of movement to the steered neutral position.

In the above steering device, the control device may execute a predetermined warning operation when the number of times the tooth skipping is detected is equal to or greater than a number threshold.
According to this configuration, it is possible to appropriately warn that tooth skipping has occurred on the belt.

According to the steering device of the present invention, tooth skipping of the belt can be detected.

FIG. 1 is a configuration diagram of a first embodiment of a steering device. FIG. 2 is a block diagram of a control device in the first embodiment. 5 is a flowchart showing the procedure of abnormality detection processing in the first embodiment. FIG. 2 is a block diagram of a control device in a second embodiment. FIG. 7 is a configuration diagram of a third embodiment of a steering device. FIG. 3 is a block diagram of a control device in a third embodiment. FIG. 7 is a block diagram of a control device in a fourth embodiment.

<First embodiment>
A first embodiment of a vehicle steering device will be described below.
As shown in FIG. 1, the steering device 10 has a housing 11 fixed to a vehicle body (not shown). A steering shaft 12 extending along the left-right direction of the vehicle body (left-right direction in FIG. 1) is housed inside the housing 11. Steered wheels 14, 14 are connected to both ends of the steered shaft 12 via tie rods 13, 13, respectively. By moving the steered shaft 12 along its axial direction, the steered angles θw, θw of the steered wheels 14, 14 are changed.

The steered shaft 12 is provided with a first ball screw portion 12a and a second ball screw portion 12b. The first ball screw portion 12a is a portion provided with a right-handed thread over a predetermined range near the first end (left end in FIG. 1) of the steered shaft 12. The second ball screw portion 12b is a portion provided with a left-hand thread over a predetermined range near the second end (the right end in FIG. 1) of the steered shaft 12.

The steering device 10 has a first ball nut 15 and a second ball nut 16. The first ball nut 15 is screwed onto the first ball screw portion 12a of the steered shaft 12 via a plurality of balls (not shown). The second ball nut 16 is screwed onto the second ball screw portion 12b of the steered shaft 12 via a plurality of balls (not shown).

The steering device 10 has a first motor 17 and a second motor 18. The first motor 17 and the second motor 18 are sources of steering force, which is the power for steering the steered wheels 14, 14, and are, for example, three-phase brushless motors. The first motor 17 and the second motor 18 are each fixed to an outer part of the housing 11. The output shaft 17a of the first motor 17 and the output shaft 18a of the second motor 18 each extend parallel to the steered shaft 12.

The steering device 10 has a first transmission mechanism 21 and a second transmission mechanism 22.
The first transmission mechanism 21 includes a driving pulley 23, a driven pulley 24, and an endless belt 25. The drive pulley 23 is fixed to the output shaft 17a of the first motor 17. The driven pulley 24 is fitted and fixed to the outer peripheral surface of the first ball nut 15 . The belt 25 is stretched between the drive pulley 23 and the driven pulley 24. Therefore, the rotation of the first motor 17 is transmitted to the first ball nut 15 via the drive pulley 23, belt 25, and driven pulley 24.

The drive pulley 23 is a toothed pulley having teeth 23a on its outer peripheral surface. The tooth traces of the teeth 23a of the drive pulley 23 are inclined with respect to the axis of the drive pulley 23. The driven pulley 24 is also a toothed pulley having teeth 24a on its outer peripheral surface. The tooth traces of the teeth 24a of the driven pulley 24 are inclined with respect to the axis of the driven pulley 24 in the same direction as the tooth traces of the drive pulley 23. Further, the belt 25 is a toothed belt having teeth 25a provided on its inner peripheral surface. The tooth traces of the teeth 25a of the belt 25 are inclined according to the tooth traces of the drive pulley 23 and the driven pulley 24.

Like the first transmission mechanism 21, the second transmission mechanism 22 includes a drive pulley 26, a driven pulley 27, and an endless belt 28. The drive pulley 26 is fixed to the output shaft 18a of the second motor 18. The driven pulley 27 is fitted and fixed to the outer peripheral surface of the second ball nut 16. The belt 28 is stretched between the drive pulley 26 and the driven pulley 27. Therefore, the rotation of the second motor 18 is transmitted to the second ball nut 16 via the drive pulley 26, belt 28, and driven pulley 27.

The drive pulley 26 is a toothed pulley with teeth 26a provided on its outer peripheral surface. The tooth traces of the teeth 26a of the drive pulley 26 are inclined with respect to the axis of the drive pulley 26. The driven pulley 27 is also a toothed pulley having teeth 27a on its outer peripheral surface. The tooth traces of the teeth 27a of the driven pulley 27 are inclined with respect to the axis of the driven pulley 27 in the same direction as the tooth traces of the drive pulley 26. Further, the belt 28 is a toothed belt having teeth 28a provided on its inner peripheral surface. The tooth traces of the teeth 28a of the belt 28 are inclined in correspondence with the tooth traces of the drive pulley 26 and the driven pulley 27.

Incidentally, the reduction ratio between the first motor 17 and the steered shaft 12 and the reduction ratio between the second motor 18 and the steered shaft 12 have the same value. Further, the lead of the first ball screw portion 12a and the lead of the second ball screw portion 12b of the steered shaft 12 are the same value. Therefore, the amount of movement of the steered shaft 12 when the first motor 17 makes one rotation is the same as the amount of movement of the steered shaft 12 when the second motor 18 makes one rotation.

The steering device 10 includes a first detection device 30a that detects the rotation angle of the first motor 17, and a second detection device 30b that detects the rotation angle of the second motor 18. The first detection device 30a is provided in the first motor 17 and includes a first rotation angle sensor 31 and a second rotation angle sensor 32. The second detection device 30b is provided on the second motor 18 and includes a third rotation angle sensor 33 and a fourth rotation angle sensor 34. For example, resolvers are employed as these four rotation angle sensors (31 to 34). Further, the detection range of the four rotation angle sensors (31 to 34) is 360° corresponding to one cycle of the electrical angle of the first motor 17 or the second motor 18.

The first rotation angle sensor 31 detects the rotation angle α1 of the first motor 17. The first rotation angle sensor 31 generates a first sine signal (sin signal) that changes in a sine wave shape as an electrical signal according to the rotation of the first motor 17, and a cosine wave shape as an electric signal that changes in a sine wave shape according to the rotation of the first motor 17. A first cosine signal (cos signal) that changes to is generated. The first rotation angle sensor 31 calculates the arctangent based on the first sine signal and the first cosine signal as the rotation angle α1 of the first motor 17. This rotation angle α1 changes in a sawtooth waveform at a period corresponding to the shaft angle multiplier of the first rotation angle sensor 31. That is, the rotation angle α1 changes in accordance with the rotation of the first motor 17, repeating a rise and a steep fall.

The second rotation angle sensor 32 detects the rotation angle α2 of the first motor 17. The second rotation angle sensor 32 has the same configuration and the same function as the first rotation angle sensor 31, and together with the first rotation angle sensor 31, it is a redundant system of rotation angle sensors for the first motor 17. Configure.

The third rotation angle sensor 33 detects the rotation angle β1 of the second motor 18. The third rotation angle sensor 33 receives a third sine signal that changes in a sine wave shape as an electric signal corresponding to the rotation of the second motor 18, and a third sine signal that changes in a cosine wave shape in accordance with the rotation of the second motor 18. Generate a cosine signal of 3. The third rotation angle sensor 33 calculates the arctangent based on the third sine signal and the third cosine signal as the rotation angle β1 of the second motor 18. This rotation angle β1 changes in a sawtooth waveform at a period corresponding to the shaft angle multiplier of the third rotation angle sensor 33.

The fourth rotation angle sensor 34 detects the rotation angle β2 of the second motor 18. The fourth rotation angle sensor 34 has the same configuration and the same function as the third rotation angle sensor 33, and together with the third rotation angle sensor 33, it forms a redundant system of rotation angle sensors for the second motor 18. Configure.

The first rotation angle sensor 31 and the third rotation angle sensor 33 have different shaft angle multipliers. Further, the second rotation angle sensor 32 and the fourth rotation angle sensor 34 have different shaft angle multipliers. The shaft angle multiplier refers to the ratio of the electrical angle of the electrical signal to the rotation angle (mechanical angle) of the first motor 17 and the second motor 18. For example, when the first rotation angle sensor 31 generates one period of electrical signals while the first motor 17 makes one rotation, the shaft angle multiplier of the first rotation angle sensor 31 is one angle (1X). Further, when the first rotation angle sensor 31 generates four cycles of electrical signals while the first motor 17 rotates once, the shaft angle multiplier of the first rotation angle sensor 31 is four times the angle (4X). .

The first rotation angle sensor 31 and the third rotation angle sensor 33 have mutually different shaft angle multipliers, and the second rotation angle sensor 32 and the fourth rotation angle sensor 34 have mutually different shaft angle multipliers. There is. Therefore, the number of cycles of the rotation angles α1, α2 per rotation of the first motor 17 and the rotation angles β1, β2 per rotation of the second motor 18 are different from each other. Furthermore, the value of the rotation angle represented by the mechanical angle of the first motor 17 per period of the electric signal generated by the first rotation angle sensor 31 and the second rotation angle sensor 32, and the third rotation angle The values of the rotation angle indicated by the mechanical angle of the second motor 18 per period of the electric signal generated by the sensor 33 and the fourth rotation angle sensor 34 are different from each other.

The first motor 17 is connected to the steered shaft 12 and, in turn, to the steered wheels 14 , 14 via a first transmission mechanism 21 . Further, the second motor 18 is connected to the steered shaft 12 and, in turn, to the steered wheels 14, 14 via a second transmission mechanism 22. Therefore, the rotation angles α1, α2 of the first motor 17 and the rotation angles β1, β2 of the second motor 18 are the absolute positions in the axial direction of the steered shaft 12, and the steered angles of the steered wheels 14, 14, respectively. It is a value that reflects the

The steering device 10 has a first control device 41 and a second control device 42. Note that the first control device 41 includes (1) one or more processors that operate according to a computer program (software), and (2) an application-specific integrated circuit (ASIC) that executes at least part of various processes. or (3) a combination thereof. A processor includes a CPU and memory, such as RAM and ROM, where the memory stores program codes or instructions configured to cause the CPU to perform processing. Memory or non-transitory computer-readable media includes any available media that can be accessed by a general purpose or special purpose computer. The configuration of the second control device 42 is also similar to that of the first control device 41.

The first control device 41 controls the first motor 17 . The first control device 41 takes in a target steering angle θ ^* calculated by, for example, a higher-level control device mounted on the vehicle according to the steering state of the vehicle or the running state of the vehicle. The first control device 41 also controls the rotation angle α1 of the first motor 17 detected through the first rotation angle sensor 31 and the rotation angle α1 of the first motor 17 detected through the second rotation angle sensor 32. Take in the angle α2. The first control device 41 also controls the rotation angle β1 of the second motor 18 detected through the third rotation angle sensor 33 and the rotation angle β1 of the second motor 18 detected through the fourth rotation angle sensor 34. The angle β2 is taken in via the second control device 42.

The first control device 41 performs steering control to steer the steerable wheels 14, 14 according to the steering state through drive control of the first motor 17. As an initialization process at the start of execution of steering control, the first control device 41 detects the rotation angle α1 of the first motor 17 detected through the first rotation angle sensor 31 and the third rotation angle sensor 33. The actual absolute position of the steered shaft 12 is calculated using the rotation angle β1 of the second motor 18 detected through the rotation angle β1. After the initialization process, the first control device 41 converts the amount of change in the rotation angle α1 into the amount of movement of the steered shaft 12 based on the rotation angle α1 of the first motor 17, and converts the amount of change in the rotation angle α1 into the amount of movement of the steering shaft 12. The current value of the absolute position of the steered shaft 12 is calculated by adding the amount of movement of the steered shaft 12 to the absolute position of the steered shaft 12 acquired during the initialization process. The first control device 41 also calculates the target absolute position of the steered shaft 12 based on the target steered angle θ ^* . The first control device 41 determines the difference between the target absolute position and the actual absolute position of the steered shaft 12, and controls the power supply to the first motor 17 so as to eliminate this difference.

The second control device 42 controls the second motor 18 . The second control device 42 takes in the current command value generated by the first control device 41. The second control device 42 also controls the rotation angle β1 of the second motor 18 detected through the third rotation angle sensor 33 and the rotation angle β1 of the second motor 18 detected through the fourth rotation angle sensor 34. Take in the angle β2. The second control device 42 also controls the rotation angle α1 of the first motor 17 detected through the first rotation angle sensor 31 and the rotation angle α1 of the first motor 17 detected through the second rotation angle sensor 32. The angle α2 is taken in via the first control device 41.

The second control device 42 executes steering control to steer the steerable wheels 14, 14 according to the steering state through drive control of the second motor 18. As an initialization process at the start of execution of steering control, the second control device 42 detects the rotation angle α1 of the first motor 17 detected through the first rotation angle sensor 31 and the third rotation angle sensor 33. The actual absolute position of the steered shaft 12 is calculated using the rotation angle β1 of the second motor 18 detected through the rotation angle β1. After the initialization process, the second control device 42 converts the amount of change in the rotation angle β1 into the amount of movement of the steered shaft 12 based on the rotation angle β1 of the second motor 18, and converts the amount of change in the rotation angle β1 into the amount of movement of the steering shaft 12. The current value of the absolute position of the steered shaft 12 is calculated by adding the amount of movement of the steered shaft 12 to the absolute position of the steered shaft 12 acquired during the initialization process. Further, the second control device 42 controls power supply to the second motor 18 based on the current command value generated by the first control device 41.

Incidentally, as the first ball nut 15 and the second ball nut 16 rotate relative to the steered shaft 12, torque around the shaft acts on the steered shaft 12. When trying to move the steered shaft 12 in a specific direction, the first ball nut 15 and the second ball nut 16 rotate in opposite directions, and as the ball nuts rotate, the rotation occurs. The operations of the first motor 17 and the second motor 18 are controlled so that the magnitude of the torque acting on the rudder shaft 12 has the same value. Therefore, the torque acting on the steered shaft 12 due to the rotation of the first ball nut 15 and the torque acting on the steered shaft 12 due to the rotation of the second ball nut 16 are torques in opposite directions. are canceled out. Therefore, no torque around the shaft acts on the steered shaft 12.

<Control device>
Next, the first control device 41 and the second control device 42 will be explained in detail.
As shown in FIG. 2, the first control device 41 includes a position detection circuit 51, a position control circuit 52, and a current control circuit 53.

As an initialization process at the start of execution of steering control, the position detection circuit 51 detects the rotation angle α1 of the first motor 17 detected through the first rotation angle sensor 31 and the rotation angle α1 detected through the third rotation angle sensor 33. The rotation angle β1 of the second motor 18 is taken in, and the absolute position P1 of the steered shaft 12 is calculated based on these rotation angles α1 and β1. The shaft angle multiplier of the first rotation angle sensor 31 and the shaft angle multiplier of the third rotation angle sensor 33 are the rotation angle α1 detected by the first rotation angle sensor 31 and the rotation detected by the third rotation angle sensor 33. The angle β1 is set so that it does not coincide with the angle β1 within the maximum movement range of the steered shaft 12. Therefore, the combination of the value of the rotation angle α1 and the value of the rotation angle β1 corresponds to the absolute position P1 of the steered shaft 12 on a one-to-one basis. Therefore, it is possible to detect the absolute position P1 of the steered shaft 12 based on the combination of the two rotation angles α1 and β1. After the initialization process, the position detection circuit 51 converts the amount of change in the rotation angle α1 of the first motor 17 into the amount of movement of the steered shaft 12, and performs the initialization process on the converted amount of movement of the steered shaft 12. The current value of the absolute position P1 of the steered shaft 12 is calculated by adding it to the absolute position of the steered shaft 12 acquired at the time. The center point of the calculation range of the current value of the absolute position P1 calculated by the position detection circuit 51 is the origin, that is, the steering neutral position (steering angle θw) which is the position of the steering shaft 12 when the vehicle is traveling straight. = 0°).

Incidentally, the position detection circuit 51 may calculate the absolute position P1 of the steered shaft 12 using a first table stored in the storage device of the first control device 41. This first table shows the combination of the value of the rotation angle α1 detected by the first rotation angle sensor 31 and the value of the rotation angle β1 detected by the third rotation angle sensor 33, and the absolute value of the steering shaft 12. It defines the relationship with position.

The position control circuit 52 calculates the target absolute position of the steered shaft 12 based on the target steered angle θ ^* calculated by the above-mentioned higher-level control device. Since the steered shaft 12 and the steered wheels 14, 14 are interlocked with each other, there is a correlation between the steered shaft 12 and the steered angle θw of the steered wheels 14, 14. Using this correlation, the target absolute position of the steered shaft 12 can be determined from the target steered angle θ ^* . The position control circuit 52 determines the difference between the target absolute position of the steered shaft 12 and the actual absolute position P1 of the steered shaft 12 calculated by the position detection circuit 51, and controls the first motor 17 to eliminate this difference. A current command value I ₁ ^* for the second motor 18 and a current command value I ₂ ^* for the second motor 18 are calculated. Normally, the current command value I ₁ ^* and the current command value I ₂ ^* are set to the same value. However, depending on the product specifications, the current command value I ₁ ^* and the current command value I ₂ ^* may be set to different values.

The current control circuit 53 supplies the first motor 17 with electric power according to the current command value I ₁ ^* calculated by the position control circuit 52 . Thereby, the first motor 17 generates torque according to the current command value I ₁ ^* .

As shown in FIG. 2, the second control device 42 includes a position detection circuit 61 and a current control circuit 63.
As an initialization process at the start of execution of steering control, the position detection circuit 61 detects the rotation angle β1 of the second motor 18 detected through the third rotation angle sensor 33 and the rotation angle β1 detected through the first rotation angle sensor 31. The rotation angle α1 of the first motor 17 is taken in, and the absolute position P2 of the steered shaft 12 is calculated based on these rotation angles β1 and α1. The shaft angle multiplier of the third rotation angle sensor 33 and the shaft angle multiplier of the first rotation angle sensor 31 are the rotation angle β1 detected by the third rotation angle sensor 33 and the rotation detected by the first rotation angle sensor 31. The angle α1 is set so as not to coincide with the angle α1 within the maximum movement range of the steered shaft 12. Therefore, the combination of the value of the rotation angle β1 and the value of the rotation angle α1 corresponds to the absolute position P2 of the steered shaft 12 on a one-to-one basis. Therefore, it is possible to detect the absolute position P2 of the steered shaft 12 based on the combination of the two rotation angles β1 and α1. After the initialization process, the position detection circuit 61 converts the amount of change in the rotation angle β1 of the second motor 18 into the amount of movement of the steered shaft 12, and performs the initialization process on the converted amount of movement of the steered shaft 12. The current value of the absolute position P2 of the steered shaft 12 is calculated by adding it to the absolute position of the steered shaft 12 acquired at the time.

Incidentally, the position detection circuit 61 may calculate the absolute position P2 of the steered shaft 12 using a second table stored in the storage device of the second control device 42. This second table shows the combination of the value of the rotation angle β1 detected by the third rotation angle sensor 33 and the value of the rotation angle α1 detected by the first rotation angle sensor 31, and the This defines the relationship with the absolute position P2. Further, the midpoint of the calculation range of the absolute position P2 calculated by the position detection circuit 61 is set as the origin (turning angle θw=0°).

The current control circuit 63 supplies the second motor 18 with electric power according to the current command value I ₂ ^* calculated by the position control circuit 52 . Thereby, the second motor 18 generates torque according to the current command value I ₂ ^* .

<Abnormality detection circuit>
Here, as described above, the steering device 10 employs a belt transmission mechanism as a transmission mechanism that transmits the rotation of the first motor 17 and the second motor 18 to the steering shaft 12, respectively. For this reason, in the steering device 10, the following concerns arise.

That is, when a large reverse input load acts on the steering shaft 12 due to a vehicle running onto a curb, etc., the end of the steering shaft 12 hits the housing 11 as the steering shaft 12 moves in the axial direction. There is a risk that a so-called end contact may occur. In this case, by physically restricting the movement of the steered shaft 12, the rotation of the belt 25 in the first ball nut 15 and the first transmission mechanism 21, and the rotation of the belt 25 in the first ball nut 15 and the second transmission mechanism 21 are restricted. Rotation of the belt 28 in the mechanism 22 is restricted. On the other hand, the drive pulley 23 of the first motor 17 and the first transmission mechanism 21 and the drive pulley 26 of the second motor 18 and the second transmission mechanism 22 will continue to rotate due to their inertia forces. shall be. Therefore, there is a risk that so-called tooth skipping may occur in the belts 25, 28. If this tooth skipping occurs repeatedly, there is a risk that the teeth 25a, 28a of the belts 25, 28 will wear out more.

Therefore, in this embodiment, the following configuration is adopted in order to detect tooth skipping.
As shown in FIG. 2, the first control device 41 has an abnormality detection circuit 54. The second control device 42 has an abnormality detection circuit 64. These abnormality detection circuits 54 and 64 detect the current value of the absolute position P1 of the steered shaft 12 calculated by the position detection circuit 51 and the current value of the absolute position P2 of the steered shaft 12 calculated by the position detection circuit 61. Incorporate each. Abnormality detection circuits 54 and 64 detect tooth skipping of belts 25 and 28 by comparing absolute positions P1 and P2 of steered shaft 12, respectively.

This is based on the following viewpoint. That is, for example, when tooth skipping occurs in the belt 25 of the first transmission mechanism 21 or the belt 28 of the second transmission mechanism 22, the rotation amount of the motor connected to the transmission mechanism where the tooth skipping occurs and the tooth skipping occur. The amount of rotation of a motor connected to a transmission mechanism in which no tooth skip occurs has a different value depending on the degree of tooth skipping. Therefore, the current value of the absolute position of the steered shaft 12 calculated based on the rotation angle of the motor connected to the transmission mechanism in which tooth skipping has occurred, and the rotation of the motor connected to the transmission mechanism in which tooth skipping has not occurred. The current value of the absolute position of the steered shaft 12 calculated based on the angle also differs depending on the degree of tooth skipping. Therefore, the current value of the absolute position P1 of the steered shaft 12 is calculated based on the rotation angle α1 of the first motor 17, and the absolute position of the steered shaft 12 is calculated based on the rotation angle β1 of the second motor 18. By comparing the current value of P2 with the current value, it is possible to detect that tooth skipping has occurred in either one of the two belts 25, 28.

When tooth skipping of the belts 25, 28 is detected, the abnormality detection circuit 54 generates a notification command signal S1 for a notification device 70 provided in the vehicle interior, for example. Further, the abnormality detection circuit 64 generates a notification command signal S2 to the notification device 70 when tooth skipping of the belts 25 and 28 is detected. The notification command signals S1 and S2 are commands for causing the notification device 70 to perform a predetermined notification operation. The notification device 70 performs a notification operation based on the notification command signal S1 or the notification command signal S2. Examples of the notification operation include emitting a warning sound and displaying a warning on a display.

<Procedure of abnormality detection process>
Next, the procedure of abnormality detection processing executed in each of the abnormality detection circuits 54 and 64 will be explained according to the flowchart of FIG. 3. The processing in this flowchart is executed at a predetermined control cycle.

As shown in the flowchart of FIG. 3, the abnormality detection circuit 54 detects the current value of the absolute position P1 of the steered shaft 12 calculated by the position detection circuit 51 and the absolute The current value of position P2 is taken in (step S101).

Next, the abnormality detection circuit 54 determines whether the absolute value of the difference between the absolute position P1 and the absolute position P2 is greater than or equal to the tooth skip determination threshold Pth (step S102). The tooth skipping determination threshold Pth is set according to the tooth skipping detection accuracy required of the steering device 10. Here, the tooth skipping determination threshold Pth is based on the viewpoint of detecting tooth skipping of one or more teeth 25a, 28a of the belts 25, 28. This is set based on the amount of movement of the steered shaft 12 when the steering shaft 12 rotates by the same amount.

When the abnormality detection circuit 54 determines that the absolute value of the difference between the absolute position P1 and the absolute position P2 is not greater than or equal to the tooth skipping determination threshold value Pth (NO in step S102), the abnormality detection circuit 54 detects that there is no tooth skipping in the belts 25 and 28. Assuming that no occurrence has occurred (step S103), the process ends.

In the previous step S102, the abnormality detection circuit 54 detects two Assuming that tooth skipping has occurred on one of the belts 25 and 28 (step S104), the process moves to the next step S105.

In step S105, the abnormality detection circuit 54 increments a count value N, which is the number of times tooth skipping of the belts 25 and 28 has been detected. Increment means adding a predetermined number (here, "1") to the count value N.

Next, the abnormality detection circuit 54 determines whether the count value N is greater than or equal to the number of times threshold Nth (step S106). There is a possibility that wear of the teeth 25a, 28a of the belts 25, 28 may progress due to tooth skipping occurring repeatedly on the belts 25, 28, but the number of times threshold value Nth is determined by the number of times, for example, when tooth skipping occurs on the belts 25, 28. This is set based on the number of times a warning should be issued.

If the count value N is not equal to or greater than the number of times threshold Nth (NO in step S106), the abnormality detection circuit 54 ends the process.
If the count value N is equal to or greater than the number threshold Nth (YES in step S106), the abnormality detection circuit 54 generates a notification command signal S1 for the notification device 70 (step S107), and ends the process. The notification device 70 performs a predetermined notification operation upon receiving the notification command signal S1. The driver of the vehicle can recognize through the notification operation of the notification device 70 that tooth skipping of the belts 25 and 28 is repeatedly occurring.

Incidentally, the abnormality detection circuit 64 of the second control device 42 also executes each process in the flowchart of FIG. 3, similarly to the abnormality detection circuit 54. If the count value N is equal to or greater than the number threshold Nth (YES in step S106), the abnormality detection circuit 64 generates a notification command signal S2 to the notification device 70 (step S107), and ends the process.

<Effects of the first embodiment>
Therefore, according to the first embodiment, the following effects can be obtained.
(1) When tooth skipping occurs in the belt 25 of the first transmission mechanism 21 or the belt 28 of the second transmission mechanism 22, the absolute value of the steered shaft 12 calculated based on the rotation angle α1 of the first motor 17 The current value of the position P1 and the current value of the absolute position P2 of the steered shaft 12 calculated based on the rotation angle β1 of the second motor 18 differ depending on the degree of tooth skipping. Therefore, the absolute value of the difference between the current value of the absolute position P1 and the current value of the absolute position P2 is a value that corresponds to the degree of tooth skipping. Therefore, if the absolute value of the difference between the current value of the absolute position P1 and the current value of the absolute position P2 is greater than or equal to the tooth skipping determination threshold Pth determined for determining the tooth skipping of the belts 25 and 28, the belt It can be determined that tooth skipping has occurred at 25 and 28. Further, by setting the tooth skipping determination threshold Pth according to the tooth skipping detection accuracy required for the steering device 10, the tooth skipping of the belts 25 and 28 can be appropriately detected.

(2) Also, by utilizing the rotation angle α1 of the first motor 17 detected through the first detection device 30a and the rotation angle β1 of the second motor 18 detected through the second detection device 30b. , tooth skipping of the belts 25, 28 can be detected more accurately. Depending on the setting of tooth skip determination threshold Pth, it is also possible to detect tooth skip for one tooth 25a, 28a of belts 25, 28. This is due to the following reason. For example, there are rotation angle sensors that detect multiple rotation angles exceeding 360 degrees, such as steering angles, in absolute values, but this type of rotation angle sensor detects the rotation angles of the first motor 17 and the second motor 18. The resolution may be lower than that of the rotation angle sensors (31 to 34) for detection. Therefore, by using the rotation angle sensors (31 to 34) of the motor with higher resolution, it is possible to ensure accuracy in detecting tooth skipping.

(3) When the count value N, which is the number of times tooth skipping has been detected, reaches the number threshold value Nth, a warning is given that tooth skipping has occurred. Therefore, the occurrence of tooth skipping on the belts 25, 28 is not excessively reported.

<Second embodiment>
Next, a second embodiment of the steering device will be described. This embodiment basically has the same configuration as the first embodiment shown in FIGS. 1 and 2, and the same configurations are the same as the first embodiment. Reference numerals are given and explanations thereof are omitted. However, as the second control device 42, a configuration in which the position detection circuit 61 shown in FIG. 2 is omitted is adopted. Although this embodiment differs from the first embodiment in the method for detecting belt tooth skipping, belt tooth skipping is detected through execution of an abnormality detection process according to the flowchart of FIG. 3 described above.

As shown in FIG. 4, the abnormality detection circuit 54 of the first control device 41 detects not the absolute positions P1 and P2 of the steered shaft 12, but the first motor 17 detected through the first rotation angle sensor 31, for example. The rotation angle α1 of the second motor 18 and the rotation angle β1 of the second motor 18 detected through the third rotation angle sensor 33 are taken in. The abnormality detection circuit 54 detects tooth skipping of the belts 25 and 28 when the absolute value of the difference between the rotation angle α1 of the first motor 17 and the rotation angle β1 of the second motor 18 is equal to or higher than a tooth skipping determination threshold. Detect. The abnormality detection circuit 64 of the second control device 42 detects tooth skipping of the belts 25 and 28 in the same manner as the abnormality detection circuit 54 of the first control device 41. The abnormality detection circuits 54 and 64 generate notification command signals S1 and S2 to the notification device 70 when the count value, which is the number of times tooth skipping has been detected, is equal to or greater than the number threshold.

The tooth skipping determination threshold is set according to the tooth skipping detection accuracy required of the steering device 10. The tooth skipping determination threshold is based on the viewpoint of detecting tooth skipping of one or more teeth 25a, 28a of the belts 25, 28, for example, when the belts 25, 28 rotate by one tooth 25a, 28a. The rotation amount of the first motor 17 and the second motor 18 at that time is set as a reference.

When tooth skipping occurs in the belt 25 of the first transmission mechanism 21 or the belt 28 of the second transmission mechanism 22, the rotation amount of the motor connected to the transmission mechanism where the tooth skipping occurs and the amount of tooth skipping occur. The rotation amounts of motors connected to a transmission mechanism different from each other depending on the degree of tooth skipping. Therefore, the absolute value of the difference between the rotation angle α1 of the first motor 17 and the rotation angle β1 of the second motor 18 is a value corresponding to the degree of tooth skipping. Therefore, it can be determined that tooth skipping has occurred in the belts 25 and 28 based on the absolute value of the difference between the rotation angle α1 of the first motor 17 and the rotation angle β1 of the second motor 18. Further, by setting the tooth skipping determination threshold according to the tooth skipping detection accuracy required for the steering device 10, the tooth skipping of the belts 25 and 28 can be appropriately detected.

Incidentally, the abnormality detection circuits 54 and 64 detect the rotation angle α2 of the first motor 17 and the rotation angle α2 of the second motor 18 instead of the rotation angle α1 of the first motor 17 and the rotation angle β1 of the second motor 18. The angle β2 may be taken in and the tooth skipping of the belts 25 and 28 may be detected based on the value of the difference between these rotation angles α2 and β2.

Therefore, according to the second embodiment, in addition to the same effects as (1) to (3) of the first embodiment, the following effects can be obtained.
(4) By directly utilizing the rotation angle α1 of the first motor 17 detected through the first rotation angle sensor 31 and the rotation angle β1 of the second motor 18 detected through the third rotation angle sensor 33. Tooth skipping of belts 25 and 28 is detected. Therefore, tooth skipping of the belts 25, 28 can be easily detected without calculating the absolute positions P1, P2 of the steered shaft 12, for example.

(5) As the second control device 42, a configuration in which the position detection circuit 61 shown in FIG. 2 is omitted can be adopted. Therefore, the configuration of the second control device 42 can be simplified.

<Third embodiment>
Next, a third embodiment of the steering device will be described. This embodiment basically has the same configuration as the first embodiment shown in FIGS. 1 and 2, and the same configurations are the same as the first embodiment. Reference numerals are given and explanations thereof are omitted. This embodiment differs from the first embodiment in the method of calculating the absolute positions P1 and P2 of the steered shaft 12.

As shown in FIG. 5, the steering device 10 has a pinion shaft 71. The pinion shaft 71 is rotatably supported by the housing 11. The pinion shaft 71 is provided so as to intersect with the center portion of the steered shaft 12, that is, the portion between the first ball screw portion 12a and the second ball screw portion 12b. The pinion teeth 71a of the pinion shaft 71 are engaged with rack teeth 12c provided in the center portion of the steered shaft 12. The pinion shaft 71 rotates in conjunction with the movement of the steered shaft 12. The amount of movement of the steered shaft 12 per rotation of the pinion shaft 71 is called a specific stroke.

The pinion shaft 71 is provided with an absolute angle sensor 72. Absolute angle sensor 72 is supported by housing 11 . The absolute angle sensor 72 detects the rotation angle θp of the pinion shaft 71 over multiple rotations of more than 360° as an absolute angle.

The first control device 41 controls the steering axis based on the rotation angle θp of the pinion shaft 71 detected through the absolute angle sensor 72 and the rotation angle α1 of the first motor 17 detected through the first rotation angle sensor 31. The current value of the absolute position P1 of 12 is calculated. The second control device 42 controls the steering axis based on the rotation angle θp of the pinion shaft 71 detected through the absolute angle sensor 72 and the rotation angle β1 of the second motor 18 detected through the third rotation angle sensor 33. The current value of the absolute position P2 of 12 is calculated.

As shown in FIG. 6, the position detection circuit 51 of the first control device 41 performs initialization processing at the start of execution of steering control based on the rotation angle θp of the pinion shaft 71 detected through the absolute angle sensor 72. The absolute position P1 of the steered shaft 12 is calculated. Specifically, the position detection circuit 51 calculates the rotation of the pinion shaft 71 by dividing the rotation angle θp of the pinion shaft 71 detected through the absolute angle sensor 72 by 360°, and by multiplying the divided value by the specific stroke. The angle θp is converted into the position of the steered shaft 12, and the converted value is set as the initial value of the absolute position P1 of the steered shaft 12. After the initialization process, the position detection circuit 51 converts the amount of change in the rotation angle α1 of the first motor 17 into the amount of movement of the steered shaft 12, and performs the initialization process on the converted amount of movement of the steered shaft 12. The current value of the absolute position P1 of the steered shaft 12 is calculated by adding it to the absolute position P1 of the steered shaft 12 obtained at the time.

Further, the position detection circuit 61 of the second control device 42 adjusts the position of the steered shaft 12 based on the rotation angle θp of the pinion shaft 71 detected through the absolute angle sensor 72 as an initialization process at the start of execution of the steered control. Calculate absolute position P2. After the initialization process, the position detection circuit 61 converts the amount of change in the rotation angle β1 of the second motor 18 into the amount of movement of the steered shaft 12, and performs the initialization process on the converted amount of movement of the steered shaft 12. The current value of the absolute position P2 of the steered shaft 12 is calculated by adding it to the absolute position P2 of the steered shaft 12 obtained at the time.

The abnormality detection circuits 54 and 64 detect tooth skipping of the belts 25 and 28 through execution of the abnormality detection process shown in the flowchart of FIG. 3, respectively. Therefore, according to the third embodiment, the same effects as (1) to (3) of the first embodiment can be obtained.

<Fourth embodiment>
Next, a fourth embodiment of the steering device will be described. This embodiment basically has the same configuration as the first embodiment shown in FIGS. 1 and 2, and the same configurations are the same as the first embodiment. Reference numerals are given and explanations thereof are omitted. This embodiment differs from the first embodiment in the method of calculating the absolute positions P1 and P2 of the steered shaft 12. The steering device 10 is applied to a by-wire type steering device in which power transmission between a steering wheel and steered wheels 14, 14 is separated.

As shown in FIG. 7, the position detection circuits 51 and 61 learn the steering neutral position, which is the position of the steering shaft 12 when the vehicle is traveling straight. For example, the position detection circuits 51 and 61 determine that the vehicle is traveling straight when all of the following three determination conditions (A1) to (A3) are satisfied. However, the conditions for determining whether the vehicle is running straight ahead may be changed as appropriate depending on product specifications and the like.

(A1) Vehicle speed V is greater than or equal to the vehicle speed threshold. Vehicle speed V is detected through a vehicle speed sensor 81 mounted on the vehicle.
(A2) The amount of time change in the rotation angle α1 of the first motor 17 or the rotation angle β1 of the second motor 18, that is, the absolute value of the rotation speed of the first motor 17 or the second motor 18 is less than or equal to a predetermined value. The condition continues for more than the set time.

(A3) The state in which the steering torque τ applied to the steering shaft 83 through the operation of the steering wheel 82 remains below the torque threshold continues for a set time or longer. The steering torque τ is detected through a torque sensor 84 provided on the steering shaft 83.

When it is determined that the vehicle is traveling straight, the position detection circuits 51 and 61 determine the position of the steering shaft 12 when the steering angle θw becomes zero according to a learning algorithm stored in a storage device (not shown). A steering neutral position is calculated, and the calculated steering neutral position is stored in a storage device as the latest learned value.

After the steering neutral position of the steering shaft 12 is calculated, the position detection circuit 51 uses the steering neutral position as a reference point and calculates the absolute position P1 of the steering shaft 12 based on the amount of position change from the reference point. Calculate the current value. That is, the position detection circuit 51 converts the amount of change in the rotation angle α1 of the first motor 17 into the amount of movement of the steered shaft 12, and converts the converted amount of movement of the steered shaft 12 into the amount of movement of the steered shaft 12. The current value of the absolute position P1 of the steered shaft 12 is calculated by adding it to the rudder neutral position.

Further, after the steering neutral position of the steering shaft 12 has been calculated, the position detection circuit 61 uses the steering neutral position as a reference point to determine the absolute position of the steering shaft 12 based on the amount of change in position from the reference point. Calculate the current value of P2. That is, the position detection circuit 61 converts the amount of change in the rotation angle β1 of the second motor 18 into the amount of movement of the steered shaft 12, and converts the converted amount of movement of the steered shaft 12 into the amount of movement of the steered shaft 12. The current value of the absolute position P2 of the steered shaft 12 is calculated by adding it to the rudder neutral position.

Incidentally, the position detection circuit 51 uses the rotation angle α2 of the first motor 17 detected through the second rotation angle sensor 32 instead of the first rotation angle sensor 31 to determine the absolute position P1 of the steered shaft 12. The current value may also be calculated. Further, the position detection circuit 61 uses the rotation angle β2 of the second motor 18 detected through the fourth rotation angle sensor 34 instead of the third rotation angle sensor 33 to determine the absolute position P2 of the steered shaft 12. The current value may also be calculated.

The abnormality detection circuits 54 and 64 detect tooth skipping of the belts 25 and 28 through execution of the abnormality detection process shown in the flowchart of FIG. 3, respectively. Therefore, according to the fourth embodiment, the same effects as (1) to (3) of the first embodiment can be obtained.

<Other embodiments>
Note that the first to fourth embodiments may be implemented with the following modifications.
- In the first, third, and fourth embodiments, tooth skipping of the belts 25 and 28 was detected through comparison of the absolute positions P1 and P2 of the steered shaft 12. However, the state quantities used for detecting tooth skipping are not limited to the absolute positions P1 and P2 of the steered shaft 12, but the tooth skipping of the belts 25 and 28 is detected through comparison of state quantities that can be converted into absolute positions P1 and P2. You may. The state quantities that can be converted into the absolute positions P1 and P2 of the steered shaft 12 include, for example, the rotation angle of the output shaft 17a of the first motor 17, which represents the rotation angle over multiple rotations exceeding 360°, and An example is an absolute angle that is the rotation angle of the output shaft 18a of the second motor 18 and represents a rotation angle over multiple rotations exceeding 360 degrees.

In this case, for example, the position detection circuit 51 calculates the current value of the absolute angle θm1 of the output shaft 17a of the first motor 17 based on the rotation angle α1. Further, for example, the position detection circuit 61 calculates the current value of the absolute angle θm2 of the output shaft 18a of the second motor 18 based on the rotation angle β1. In this case, the midpoint of the calculation range for the absolute angle θm1 and the midpoint of the calculation range for the absolute angle θm2 are set at the same position. As such a midpoint, for example, an absolute angle when the vehicle is traveling straight is used. Then, the position detection circuits 51 and 61 detect tooth skipping of the belts 25 and 28 by comparing the absolute angles θm1 and θm2, similarly to when comparing the absolute positions P1 and P2 of the steered shaft 12.

In addition, as state quantities that can be converted into the absolute positions P1 and P2 of the steered shaft 12, in addition to the absolute angles of the output shaft 17a of the first motor 17 and the output shaft 18a of the second motor 18, for example, the steered wheel 14 The steering angle θw or the rotation angle θp of the pinion shaft 71 may be used, and can be changed as appropriate.

- In each embodiment, the first ball screw portion 12a may be a left-handed screw, and the second ball screw portion 12b may be a right-handed screw. It is only necessary that the first ball screw portion 12a and the second ball screw portion 12b have a reverse screw relationship. Further, both the first ball screw portion 12a and the second ball screw portion 12b may be right-handed or left-handed. However, when this configuration is adopted, the steered shaft 12 is provided with a rotation regulating portion for suppressing relative rotation of the steered shaft 12 with respect to the housing 11.

- In each embodiment, the tooth jump determination threshold Pth is set based on the amount of movement of the steered shaft 12 when the belts 25, 28 rotate by one tooth 25a, 28a. The amount of movement of the steered shaft 12 when rotated by two, three or more teeth of the teeth 25a, 28a may be set as a reference. The tooth skipping determination threshold Pth is set to an appropriate value depending on the tooth skipping detection accuracy required of the steering device 10.

- In each embodiment, the higher-level control device mounted on the vehicle calculates not the target steering angle θ ^* but the target absolute position of the steering shaft 12 according to the steering state of the vehicle or the running state of the vehicle. You can. In this case, the first control device 41 takes in the target absolute position of the steered shaft 12 calculated by the higher-level control device, and sets the current command value I ₁ ^* to the first motor 17 based on the taken-in target absolute position. And a current command value I ₂ ^* for the second motor 18 is calculated.

- In each embodiment, the processes of step S105 and step S106 in the flowchart of FIG. 3 may be omitted depending on the product specifications. In this case, the abnormality detection circuits 54 and 64 immediately generate notification command signals S1 and S2 when tooth skipping of the belts 25 and 28 is detected (YES in step S102).

- In each embodiment, the first control device 41 and the second control device 42 may be provided as a single control device.
- In each embodiment, a configuration having only one of the first rotation angle sensor 31 and the second rotation angle sensor 32 may be adopted as the first detection device 30a. Furthermore, a configuration having only one of the third rotation angle sensor 33 and the fourth rotation angle sensor 34 may be adopted as the second detection device 30b.

- In each embodiment, the conditions for generating the notification command signals S1 and S2 in the abnormality detection circuits 54 and 64 may be set as follows. That is, the abnormality detection circuits 54 and 64 store the history of the absolute positions P1 and P2 of the steered shaft 12 calculated by the position detection circuits 51 and 61. Specifically, the position detection circuits 51 and 61 store, for example, the absolute positions P1 and P2 of the steered shaft 12 at the time when tooth skipping is detected. The abnormality detection circuits 54 and 64 generate notification command signals S1 and S2 to the notification device 70 when tooth skipping occurs a predetermined number of times or more at a specific rotational position in the belts 25 and 28. The rotational positions of the belts 25 and 28 where tooth skipping repeatedly occurs can be determined by, for example, changing the absolute positions P1 and P2 of the steered shaft 12 at the time when the tooth skipping is detected to the movement of the steered shaft 12 per rotation of the belts 25 and 28. It is obtained as the remainder after dividing by the quantity. In this way, it is possible to detect at which position on the belts 25, 28 tooth skipping occurs.

- In each embodiment, when the position detection circuits 51 and 61 have a learning function of the steering neutral position of the steering shaft 12, the abnormality detection circuits 54 and 64 detect tooth skipping of the belts 25 and 28 as follows. may be detected. That is, the abnormality detection circuits 54 and 64 receive information that the position detection circuits 51 and 61 have calculated the steering neutral position. Each abnormality detection circuit 54, 64 compares the absolute position P1 before and after calculation of the steering neutral position by the position detection circuit 51 while the vehicle is traveling straight. In other words, the abnormality detection circuits 54 and 64 determine whether or not the value of the absolute position P1 changes by storing the steering neutral position calculated by the position detection circuit 51 in the storage device as the latest learned value. do. Further, the abnormality detection circuits 54 and 64 compare the absolute position P2 before and after the calculation of the steering neutral position by the position detection circuit 61. That is, the abnormality detection circuits 54 and 64 determine whether or not the value of the absolute position P2 changes by storing the steering neutral position calculated by the position detection circuit 61 in the storage device as the latest learned value. do. Then, each abnormality detection circuit 54, 64 determines that tooth skipping has occurred in the belt on the side where the absolute position of the steered shaft 12 is changing before and after calculating the steered neutral position.

This is because the position detection circuit 5 The value of the absolute position P1 of the steered shaft 12 calculated by or the value of the absolute position P2 of the steered shaft 12 calculated by the position detection circuit 61 is different before and after calculating the neutral position of the steered shaft 12. Based on high probability. The abnormality detection circuits 54 and 64 determine that tooth skipping has occurred in the belt 25 when the absolute position P1 changes before and after calculating the steering neutral position. The abnormality detection circuits 54 and 64 determine that tooth skipping has occurred in the belt 28 when the absolute position P2 changes before and after calculating the steering neutral position. In this way, it is possible to determine which of the two belts 25 and 28 tooth skipping has occurred.

- In each embodiment, the abnormality detection circuits 54 and 64 may detect tooth skipping of the belts 25 and 28 in the following manner. That is, the abnormality detection circuits 54 and 64 store the absolute positions P1 and P2 of the steered shaft 12 at the time when the first end contact occurs due to a normal steering operation other than when the vehicle runs on a curb. The occurrence of end contact of the steered shaft 12 is detected based on, for example, whether the position of the steered shaft 12 has reached the limit position of its movable range. Thereafter, when the second end contact due to normal steering operation occurs on the same side as the first end contact, the abnormality detection circuits 54 and 64 detect the steering shaft 12 at the time when the second end contact occurs. , and the stored absolute positions P1 and P2 at the time when the first end contact occurred are compared. The abnormality detection circuits 54 and 64 detect that tooth skipping has occurred in the belt on the side where the absolute position of the steered shaft 12 is changing between the time when the first end contact occurs and the time when the second end contact occurs. Judgment is made. The abnormality detection circuits 54 and 64 determine that tooth skipping has occurred in the belt 25 when the absolute position P1 has changed. The abnormality detection circuits 54 and 64 determine that tooth skipping has occurred in the belt 28 when the absolute position P2 has changed. In this way, it is possible to determine which of the two belts 25 and 28 tooth skipping has occurred.

- In each embodiment, the abnormality detection circuits 54 and 64 may detect which of the belts 25 and 28 has skipped teeth in the following manner. That is, the abnormality detection circuits 54, 64 detect the rotation speed and rotation direction of the motors (17, 18). The rotation speeds of these motors can be obtained, for example, by differentiating the rotation angles α1, α2 of the first motor 17 and the rotation angles β1, β2 of the second motor 18. Further, the rotation directions of these motors are obtained based on changes in the rotation angles α1, α2 and rotation angles β1, β2, for example. Abnormality detection circuits 54, 64 monitor whether the rotational speeds of first motor 17 and second motor 18 exceed predetermined speed thresholds. This speed threshold is set, for example, based on a rotational speed at which there is a high probability that tooth skipping will occur. Further, the abnormality detection circuits 54 and 64 store the rotation direction when the rotation speed of the motor exceeds the speed threshold. When tooth skipping of the belts 25, 28 is detected, the abnormality detection circuits 54, 64 move the belts 25, 28 in a direction corresponding to the rotational direction of the motor that rotated at a rotation speed exceeding the speed threshold before the tooth skipping was detected. It is determined that tooth skipping has occurred in the belts 25, 28 on the side where the absolute positions P1, P2 have changed. This is based on the fact that the faster the rotational speed of the motor, the more likely tooth skipping occurs in the belts 25, 28. In this way, it is possible to determine which of the two belts 25 and 28 tooth skipping has occurred.

- When the abnormality detection circuits 54, 64 can determine which of the two belts 25, 28 the tooth skipping has occurred, the abnormality detection circuits 54, 64 detect the belt on the side where the tooth skipping has been detected. The current supplied to the first motor 17 or the second motor 18 may be limited. For example, the abnormality detection circuits 54 and 64 generate limit signals for the current control circuits 53 and 63 of the control device (41, 42) that controls the motor (17, 18) on the side where tooth skipping has been detected. The current control circuits 53 and 63 limit the value of the current supplied to the motor on the side where tooth skipping has been detected to a value smaller than the current that should originally be supplied, based on the limit signal generated by the abnormality detection circuits 54 and 64. do. Since the rotation of the motor on the side where tooth skipping has been detected is suppressed by the current limit, the life of the belt where tooth skipping has occurred can be extended.

- Each embodiment of the steering device 10 may be applied to a by-wire type steering device in which power transmission between the steering wheel and the steered wheels is separated. A by-wire steering device has a reaction force motor that is the source of the steering reaction force applied to the steering shaft, and a reaction force control device that controls the drive of the reaction force motor. There is a system that calculates a target steering angle of the steering wheel based on the state or the driving state of the vehicle. In this case, the first control device 41 takes in the target steering angle calculated by the reaction force control device as a higher-level control device as the target turning angle θ ^* .

DESCRIPTION OF SYMBOLS 10... Steering device, 12... Steered shaft, 12a... First ball screw part, 12b... Second ball screw part, 14... Steered wheel, 15... First ball nut, 16... Second ball nut , 17...first motor, 18...first motor, 21...first transmission mechanism, 22...first transmission mechanism, 25, 28...belt, 30a...first detection device, 30b...second Detection device, 41... First control device, 42... Second control device, 72... Absolute angle sensor, N... Count value, Nth... Number of times threshold, P1... Absolute position of steered axis (first absolute position), P2...Absolute position of the steered shaft (second absolute position), Pth...Tooth jump determination threshold, α1, α2...Rotation angle of the first motor, β1, β2...Rotation of the second motor corner.

Claims (7)

a steering shaft that has two ball screw parts and steers a steered wheel by moving in a straight line;
two ball nuts screwed into the two ball screw parts, respectively;
Two motors that generate driving force,
two transmission mechanisms each having a toothed belt that transmits the driving force of the two motors to the corresponding ball nut;
two detection devices that respectively detect rotation angles of the two motors;
A control device that controls each of the two motors,
The control device is a steering device that detects tooth skipping of the belt based on rotation angles of the two motors detected through the two detection devices. The control device detects a first absolute position of the steered shaft calculated based on a rotation angle of the first motor detected through a first detection device, and a first absolute position of the steered shaft detected through a second detection device. The steering device according to claim 1, wherein tooth skipping of the belt is detected through comparison with a second absolute position of the steering shaft calculated based on a rotation angle of the second motor. The control device is configured such that the absolute value of the difference between the first absolute position of the steered shaft and the second absolute position of the steered shaft is greater than or equal to a threshold value determined for determining tooth skipping of the belt. 3. The steering device according to claim 2, wherein it is determined that tooth skipping has occurred in the belt. The first said detection device and the second said detection device have mutually different shaft angle multipliers,
As an initialization process at the time of starting execution of steering control for steering the steered wheels, the control device detects a first rotation angle of the motor detected through the first detection device, and a second rotation angle of the motor detected by the first detection device. calculating the absolute position of the steered shaft based on the rotation angle of the second motor detected through the device;
After the initialization process, the amount of change in the rotation angle of the first motor detected through the first detection device is converted into the amount of movement of the steered shaft, and the converted amount of movement of the steered shaft is converted. is added to the absolute position obtained through the initialization process to calculate the current value of the first absolute position of the steered shaft, and
The amount of change in the rotation angle of the second motor detected through the second detection device is converted into the amount of movement of the steered shaft, and the converted amount of movement of the steered shaft is processed through the initialization process. The steering device according to claim 2 or 3, wherein the current value of the second absolute position of the steered shaft is calculated by adding it to the acquired absolute position. a shaft that rotates in conjunction with the steered shaft;
an absolute angle sensor that detects the absolute rotation angle of the shaft,
The control device calculates the absolute position of the steered shaft based on the absolute rotation angle of the shaft detected through the absolute angle sensor as an initialization process at the start of execution of steering control for steering the steered wheels. death,
After the initialization process, the amount of change in the rotation angle of the first motor detected through the first detection device is converted into the amount of movement of the steered shaft, and the converted amount of movement of the steered shaft is converted. is added to the absolute position obtained through the initialization process to calculate the current value of the first absolute position of the steered shaft, and
The amount of change in the rotation angle of the second motor detected through the second detection device is converted into the amount of movement of the steered shaft, and the converted amount of movement of the steered shaft is processed through the initialization process. The steering device according to claim 2 or 3, wherein the current value of the second absolute position of the steered shaft is calculated by adding it to the acquired absolute position. When it is determined that the vehicle is traveling straight due to the satisfaction of a predetermined determination condition, the control device sets the position of the steered shaft at that time as a reference for calculating the absolute position of the steered shaft. Set as the steering neutral position,
After the steering neutral position of the steering shaft is set, the amount of change in the rotation angle of the first motor detected through the first detection device is converted into the amount of movement of the steering shaft, and this conversion is performed. calculating the current value of the first absolute position of the steered shaft by adding the amount of movement of the steered shaft to the steered neutral position;
The amount of change in the rotation angle of the second motor detected through the second detection device is converted into the amount of movement of the steered shaft, and the converted amount of movement of the steered shaft is determined as the amount of change in the rotation angle of the second motor. The steering device according to claim 2 or 3, wherein the current value of the second absolute position of the steered shaft is calculated by adding the second absolute position to the position. The steering device according to any one of claims 1 to 6, wherein the control device executes a predetermined warning operation when the number of times the tooth skipping is detected is equal to or greater than a number threshold.