JPH04135975A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To make a device small in size, and thereby speedily steer rear wheels as well as to assure safety by steering the rear wheels with steering force equivalent to the magnitude of multiplication of the driving quantity of two motors, making the driving force the other motor zero when one motor fails, and thereby making the steering angle of the rear wheels zero. CONSTITUTION:A steering mechanism 49 transmits component steering force which is given by the driving quantity of a first motor 37 multiplied by the driving quantity of a second motor 48, to the sides of rear wheels, so that the rear wheels 2L and 2R are thereby steered. A motor failure judging means 61 is made up within a control unit 15 to make judgment that either of the motors is at fault while the other motor is operated with the driving momentum of one motor made zero. In this case, a sensor failure judging means 62 is made up, which judges that an encoder 27 or a gear ratio sensor 28 for the motor the driving momentum of which is made zero, is at fault, if each rear wheel steering angle is changed when the other motor is operated in a state that the driving momentum of one motor is made zero while a rear wheel steering angle sensor 29 is being monitored.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a rear wheel steering device for a vehicle, and particularly to a device that steers the rear wheels using the driving force of a motor.

(Prior art) Conventionally, as a rear wheel steering device of a vehicle, for example,
As disclosed in No. 7-44568 and Japanese Unexamined Patent Publication No. 61-46763, etc., an electric motor, a steering mechanism that transmits the driving force of the motor to the rear wheels to steer the rear wheels, and a steering wheel are disclosed. Vehicles that include a controller that controls the operation of the electric motor according to the steering angle, vehicle speed, etc. are known.

This type of rear wheel steering device transmits the steering force of the front wheels to the rear wheels via a rod or the like to steer the rear wheels. The advantage is that there is a large degree of freedom in rear wheel steering control, such as being able to steer the rear wheels.

In this type of rear wheel steering system, as a countermeasure against electric motor failure, the steering mechanism usually includes a clutch that cuts off power transmission from the electric motor to the rear wheels, and a clutch that biases the rear wheels to a neutral position. A centering spring is provided.

(Problem to be solved by the invention) However, in this case, the preset load of the centering spring is set to a fairly large value, so if the electric motor breaks down during turning, the rear wheels may be returned to the neutral position suddenly. There are concerns about safety. Further, there is a problem in that the electric motor becomes larger and has a higher output in response to a larger preset load, and the steering of the rear wheels becomes less prompt.

Therefore, in order to solve this problem, it is conceivable to provide two electric motors in parallel so that when one electric motor fails, the other electric motor is used as a backup. However, this requires a clutch to switch the power transmission system of the electric motor, so
Increase the size of the device. In addition, the spare drive motor is rarely used, and there are problems in managing its operation.

The present invention has been made in view of these points, and its purpose is to reduce the size of the device and speed up rear wheel steering by appropriately combining two motors. In addition to detecting failures in the electric motor at an early stage when starting rear wheel steering without putting any load on the motor or engine, in the event of a failure, safety is ensured by setting the rear wheels to a two-wheel steering state with zero steering angle. It is an object of the present invention to provide a rear wheel steering device for a vehicle.

(Means for solving the problem) In order to achieve the above object, the invention described in claim (1):
The rear wheel steering device of the vehicle includes a first motor that is controlled according to at least the steering angle of the steering wheel, a variable gear ratio mechanism that changes the gear ratio, and a second motor that drives the variable gear ratio mechanism to control the gear ratio. a motor; a steering mechanism that transmits a steering force obtained by multiplying the drive amount of the first motor by the drive amount of the second motor to the rear wheels to steer the rear wheels; and the first and second motors. A motor enemy side discriminating means for determining whether the motor is malfunctioning by operating the other motor while the drive amount of one of the motors is set to zero, and a motor that is not malfunctioning when the discriminating means determines that the motor is malfunctioning. and control means for controlling both motors so that the amount of drive of the two motors is zero.

In addition to the structure of the invention described in claim (1), the invention according to claim (2) further includes a rear wheel steering angle sensor that detects a rear wheel steering angle, and a rear wheel steering angle detected by the sensor. When the rear wheel steering angle changes when the drive amount of one motor is set to zero and the other motor is operated, the sensor that detects the operation of the motor whose drive amount is set to zero changes. It is provided with a sensor failure determination means for determining when a failure has occurred.

(Function) With the above configuration, in the present invention, prior to the start of rear wheel steering, the drive amount of one of the first and second motors is set to zero, and the other motor is operated, so that the other motor operates normally. The motor enemy side determining means determines whether the motor is out of order or not. In this case, the multiplication amount of the drive amount of the first motor and the drive amount of the second motor is zero and the steering force is not transmitted to the rear wheels. There is no load on it.

Furthermore, when the drive amount of one motor is set to zero and the other motor is operated, the rear wheel steering angle remains zero and does not change. The failure determination means determines that when this changes, a failure occurs in which a center shift has occurred in the sensor that detects the operation of the motor whose drive amount is desired to be reduced to zero.

When both of the above motors operate normally, both motors are controlled as appropriate under the control of the control means, and a steering force corresponding to the multiplication of the driving forces of these two motors is transmitted via the steering mechanism. The signal is transmitted to the rear wheels, and the rear wheels are steered.

On the other hand, when it is determined that one of the two motors has failed, the drive amount of the other motor is reduced to zero by the control means, and the steering force, which is the amount multiplied by the drive amount of both motors, also becomes zero. , a two-wheel steering state is realized in which the steering angle of the rear wheels is zero.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows the overall configuration of a steering system for a vehicle equipped with a rear wheel steering device according to an embodiment of the present invention. The steering system of this vehicle includes a front wheel steering device A that steers the left and right front wheels IL and IR;
It is constituted by a rear wheel steering device B that steers the left and right rear wheels 2L and 2R.

The front wheel steering device A includes a pair of left and right knuckle arms 3L and 3R and tie rods 4L and 4R, a relay rod 5 that connects the pair of left and right tie rods 4L and 4R, and a rack tooth formed on the relay rod 5. (not shown) A steering shaft 8 is provided with a pinion 6 provided at one end and a steering wheel 7 provided at the other end, and when the steering wheel 7 is operated, the relay rod 5 is moved in the vehicle width direction. Displaced,
The configuration is such that the front wheels are steered by IL or IR.

On the other hand, the rear wheel steering device B has a pair of left and right knuckle arms 1. IL, IIR and tie tips 12L, 1
2R, and a rear wheel steering mechanism section 14 that steers the left and right rear wheels 2L and 2R by displacing a relay rod 13 that connects the pair of left and right tie rods 1.2L and 12H in the axial direction (that is, in the vehicle width direction). , and a control unit 5 constituting a control section that controls the rear wheel steering mechanism section 14 (in detail, the operation of first and second motors 37 and 48, which will be described later).

Further, 21 is a steering wheel steering angle sensor that detects the steering wheel steering angle, 22 is a vehicle speed sensor that detects vehicle speed, 23 and 24 are lateral acceleration sensors that detect lateral acceleration of the front and rear parts of the vehicle body, respectively, and 25 is a brake switch; 26 is an accelerator switch, and signals from these sensors 21 to 24 and switches 25 and 26 can be input to the control unit 15. In addition, control unit 1
5 includes various sensors of the rear wheel steering mechanism section 14, that is, an encoder 27, a gear ratio sensor 28, and a rear wheel steering angle sensor 29.
Signals from the are also input.

The specific structure of the rear wheel steering mechanism section 4 is shown in FIGS. 2 to 6. In these figures, the relay rod 13
Both left and right ends of the relay rod are connected to tie rods 12L and 12H via hole joints 31, respectively, and a sector gear 32 is attached to the relay rod 13 by spline connection so as to be relatively movable in the axial direction and to rotate integrally. . The sector gear 32 meshes with a gear portion 34a formed on the outer periphery of a ball screw 34 provided on the shaft 33, and the shaft 33 is connected to the first motor 37 via a set of bevel gears 35 and 36. Drive connected. Thus, the ball screw 34 moves in the axial direction on the shaft 33 by the forward and reverse rotation of the first motor 37, and the relay rod 13 rotates around its axis via the sector gear 32. An encoder 27 is attached to the first motor 37, and the garlic 2
7 outputs operating information of the first motor 37 to the control unit 15.

Reference numeral 41 denotes a variable gear ratio mechanism that changes the gear ratio, and the variable gear ratio mechanism 41 includes an arm member 42 that is integrally formed with the relay rod 13 and extends radially from its axis; An annular ring member 43 is provided on the outer periphery of the relay rod 13 in correspondence with the member 42 . The ring member 43 has shaft portions 43a and 43b extending in a direction perpendicular to the axis of the relay rod 13,
The shaft portions 43a and 43b are rotatably supported within a predetermined angular range relative to the housing 44 with the shaft portions 43a and 43b as central axes. Further, a ball bushing 45 is slidably provided on the inner peripheral surface of the ring member 43, and the tip of the arm member 42 is engaged with the ball bushing 45.

A sector gear 46 is attached to the shaft portion 43a of the ring member 43.
The sector gear 46 is engaged with a gear 47a of a reduction gear 47, and the reduction gear 47 is connected to a second motor 48. The ring member 43 or its shaft portion 43 is then driven by the driving force of the second motor 48.
a and 43b, and the gear ratio is determined according to the magnitude of the inclination angle of the link member 43 with respect to the axis of the relay rod 13 (FIG. 2 shows a state where this inclination angle is zero). Further, when the ring member 43 is inclined at a predetermined angle, that is, when the gear ratio is a value other than zero, the first
When the relay rod 13 is rotated by the operation of the motor 37, the ball bush 45 on the tip side of the arm member 42 slides along the inner peripheral surface of the ring member 43, and the relay rod 1
3 is adapted to move in its axial direction (vehicle width direction), and the amount of axial movement of this relay rod 13 is proportional to the value obtained by multiplying the above gear ratio and the rotation angle of the relay rod 13. Therefore, the relay rod 13 and tie rod 1
2L, 12R, etc., the steering force obtained by multiplying the drive amount of the first motor 37 by the drive amount of the second motor 48 is transmitted to the rear wheel side.

A steering mechanism 49 for steering 2R is also configured.

Further, a gear ratio sensor 28 is connected to the shaft portion 43a of the ring member 43 via a joint 51, and the gear ratio sensor 28 detects the gear ratio based on the inclination angle of the ring member 43. Ratio information is output from the gear ratio sensor 28 to the control unit 15. Further, a gear portion 52 is formed on the outer peripheral surface of the relay rod 13, and a pinion 53 connected to the rear wheel steering angle sensor 29 meshes with the gear portion 52. The rear wheel steering angle is detected based on the amount of axial movement of the relay rod 13, and the rear wheel steering angle information is output from the rear wheel steering angle sensor 29 to the control unit 15.

Next, the operation control of the first motor 37 and the second motor 48 by the control unit 15 will be explained.
According to the flow shown in the figure, failure determination of both the motors 37 and 48, the encoder 27, and the gear ratio sensor 28 is performed.

That is, first, after waiting for the system to start in step S1, the driving amount of the first motor 37 is made zero in step S2, and the driving force of the first motor 37 is made zero based on the signal from the encoder 27 in step S3. Check to see if it has happened. After waiting for it to become zero, the drive amount of the second motor 48 (that is, the gear ratio of the variable gear ratio mechanism 41) is changed by one cycle between the maximum value and the minimum value in step S4. In S5, it is determined whether the second motor 48 has operated based on the signal from the gear ratio sensor 28.

When the determination in step S5 is YES, it is determined in step S6 whether the rear wheel steering angular velocity θR is equal to the substantially zero value θRO (=0) based on the signal from the rear wheel steering angle sensor 29. Here, when the drive amount of the first motor 37 is set to zero, the multiplication amount of the drive amount of the first motor 37 and the drive amount of the second motor 48 is always zero, so the second motor 48
Even when the rear wheel steering angle is activated, no steering force is transmitted to the rear wheels and the rear wheel steering angle remains zero and does not change. However, if this rear wheel steering angle changes and the rear wheel steering angle speed changes to a value other than zero. This is because there is a shift in the center position of the encoder 27 and the amount of drive of the first motor 37 is not actually zero. Therefore, step S6 ultimately determines whether or not the encoder 27 is out of center or malfunctioning.

Then, when the determination in step S6 is YES (when there is no failure in the encoder 27 and there is no shift in the center position),
In step S7, the drive amount of the second motor 48 is set to zero, and in step S8, the drive amount of the second motor 48 is set to zero based on the signal from the gear ratio sensor 28.
Check whether the driving force of the motor 48 has become zero. After waiting for the drive amount to become zero, the drive amount of the first motor 48 is changed by one cycle between the maximum value and the minimum value in step S9, and the drive amount of the first motor 48 is changed by one cycle between the maximum value and the minimum value in step SIO. 1. It is determined whether or not the motor 37 has operated.

When the determination in step S10 is YES, it is determined in step Sll based on the signal from the rear wheel steering angle sensor 29 whether the rear wheel steering angular velocity θR is equal to the substantially zero value θRO (=0). Here, when the drive amount of the second motor 48 is zero, the drive amount of the first motor 37 and the second motor 4
Since the amount multiplied by the drive amount of 8 is always zero, even if the first motor 37 is activated, no steering force is transmitted to the rear wheels, and the rear wheel steering angle remains zero and does not change. Or, this rear wheel steering angle changes and the rear wheel steering angle speed becomes a value other than zero.
This is because there is a shift in the center position of the gear ratio sensor 28, and the amount of drive of the second motor 48 is not actually zero.

Therefore, step Sll ultimately determines whether or not there is a failure in the gear ratio sensor 28 due to a shift in the center position.

If the determination in step Sl② is YES (when there is no failure in the gear ratio sensor 28 and there is no shift in the center position), the process returns.

On the other hand, when the determination in step S5 is No (when the second motor 48 is malfunctioning and does not operate), when the determination in step S6 is NO (when the encoder 27 is out of center position), the determination in step SIO is No. (when the first motor 37 does not operate) or when the determination in step Sll is No (when the gear ratio sensor 28 is out of center position), in step S12 the first and second motors 3
Both drive amounts of 7°48 are set to zero, and in step S13, the fail-safe determination is stopped and the control is ended.

Among the above flows, especially steps S2 to S5 and S
7 to SlO constitute a motor failure determination means 61 that operates one of the first and second motors 37, 48 with the drive amount of the other motor set to zero and determines a failure of the motor. ing. Also, steps S6 and S
ll monitors the rear wheel steering angle detected by the rear wheel steering angle sensor 29, and operates the other motor with the drive amount of one of the first and second motors 37, 48 set to zero. A sensor failure determination means 62 is configured to determine that when the rear wheel steering angle changes when the rear wheel steering angle changes, it is determined that the encoder 27 or the gear ratio sensor 28, which is a sensor that detects the operation of the motor whose drive amount is zero, has failed. has been done. Both of the discrimination means 61 and 62 are provided within the control unit 15.

According to such a flow, the first and second motors 37,
48, the first and second motors 37
, 48, when the drive amount of one motor is set to zero and the other motor is operated, the motors 37, 48
The multiplication amount between the drive amounts of is zero, and the steering force is not transmitted from the steering mechanism 49 to the rear wheels, so no load is applied to the motor or engine, and the motors 37, 4
8 can be quickly and reliably determined. Furthermore, when determining the failure of the motors 37 and 48, it is possible to easily determine the failure of the garlic 27 and the gear ratio sensor 28, which are the sensors of the rear wheel steering mechanism section 14, at the same time, so that the rear wheel steering can be controlled. The above is very effective.

Then, as a result of the failure determination, if there is no failure in either the motors 37, 48 or the sensors 27, 28, the control unit 15 controls the operation of the first motor 37 and the second motor 48, respectively, as follows. .

That is, the operation control of the first motor 37 is such that the rotation angle θl of the relay rod 13 due to its operation is expressed by the following formula (1).
It is done to vary based on.

θl −−Kl ・2 to θH+ ・■・ψ ・
...(1) However, θH is the steering angle, ■ is the vehicle speed, and ψ is the yaw rate. In addition, the coefficients Kl and 2 are variables that are changed based on the vehicle speed, and are determined depending on the characteristics of the vehicle.To give a specific example, K1 is a variable that is changed based on the vehicle speed. Due to nature, it is approximately 0.35 up to around 10 Km/h, but as the vehicle speed V increases beyond 10 KII/h, it gradually increases to approximately 1 at around 40 Km/h. When the speed exceeds 80 km/h, in order to ensure straight-line stability at high speeds, it is gradually decreased as the vehicle speed increases, making the reaction to changes in the front wheel steering angle slower.

In addition, when driving backwards, the 5KII/
Below 5km/h, the value is about 0.35, but when the speed exceeds 5km/h, it is decreased as the vehicle speed increases to ensure stability. On the other hand, K2 is 10 km as shown in Figure 9.
When it exceeds /h, it gradually increases and changes to increase to 0.005 around 30 km/h.

FIG. 10 shows an example of the change characteristics of the steering wheel steering angle θH and the rear wheel steering angle θR when the gear ratio is constant and the rotation angle θ1 of the relay rod 13 is controlled based on the above equation (1). As can be seen from this figure, the rear wheel steering angle θR is
Since the yaw rate ψ and the vehicle speed V are used as functional elements in addition to the steering wheel angle θH, there is not necessarily a proportional relationship with the steering wheel angle θH and the front wheel steering angle.

Further, the operation control of the second motor 48 and the variable control of the gear ratio in the variable steering ratio mechanism 41 are performed in accordance with the vehicle speed, and a specific example thereof is shown in FIG. 11. That is, in the case of this specific example, the gear ratio e is a low value and approximately constant in the low vehicle speed region of 30Km/h or less, and when the speed exceeds 30Km/h, the gear ratio e increases rapidly, reaching 60 around +e/h. reaches the maximum value.

In the medium vehicle speed range from 60 km/h to 80 km/h, the gear ratio e is constant at the maximum value, and at 80 + a/h
In a high vehicle speed range exceeding 200 m, the gear ratio e gradually decreases. In this variable gear ratio control, as shown by the broken line in FIG. Hysteresis is provided to prevent the gear ratio e from decreasing unless the speed is reduced. Furthermore, hysteresis is provided so that when the vehicle speed decreases in a high vehicle speed region, the gear ratio e increases quickly.

On the other hand, when either one of the first and second motors 37, 48 is out of order, the control unit 15 controls the drive amount of the other motor that is not out of order to be zero. In other words, when the first motor 37 fails, the drive amount of the second motor 48 and the gear ratio of the variable gear ratio mechanism 41 become zero, and when the second motor 48 breaks down, the drive amount of the first motor 37 and the relay rod become zero. 13 rotation amount becomes zero. As a result, even in the event of a failure of either the first or second motor 37°48, a two-wheel steering state is achieved in which the steering angle of the rear wheels 2L and 2R is zero, so safety can be ensured. .

Furthermore, when the steering angle of the rear wheels 2L and 2R is set to zero, the drive amount of the non-faulty motor 37 or 48 gradually decreases from a certain value at the time of motor failure, so the preset load of the centering spring causes the relay rod 13 The rear wheels 2L and 2R are not returned suddenly like when returning to the neutral position.
Safety can be further improved.

Furthermore, when moving the relay rod 13 in the axial direction to steer the rear wheels 2L and 2R, there is no need for a large steering force to resist the preset load as in the conventional case, so the motors 37 and 48 are It is possible to achieve smaller size and lower output, and to improve the speed of rear wheel steering. Also, there is no need for centering springs or clutches, etc.
This can also contribute to downsizing of the rear wheel steering device.

Incidentally, when one of the first and second motors 37 and 48 is out of order, the control command of the control unit 15 is as follows.
The drive amount of both motors 37 and 48 is reduced to zero (step 512 in the flow shown in FIG. 7), but since the failed motor does not operate even if it receives the command, only the drive amount of the non-faulty motor is reduced to zero. becomes zero. Furthermore, even when the encoder 27 or the gear ratio sensor 28 fails, the drive amount of both motors 37 and 48 is reduced to zero and the two-wheel steering state is maintained, just as when the motors 37 and 48 fail. This will be ensured.

(Effects of the Invention) As described above, according to the rear wheel steering device of the present invention, a steering force corresponding to the multiplication of the drive amount of the first motor and the drive amount of the second motor is transmitted to the rear wheels. and steer the rear wheels,
When one motor fails, the driving force of the other motor is reduced to zero, thereby reducing the steering angle of the rear wheels to zero. This ensures safety in the event of a motor failure, and also reduces the center spring and clutch. By omitting this, it is possible to downsize the device and speed up rear wheel steering. It also has the effect of being able to quickly and reliably determine a motor failure without imposing any load on the motor or engine.

Furthermore, in the case of the invention set forth in claim 21, failure determination of the sensor can be performed at the same time as failure determination of the motor, which is very advantageous in controlling rear wheel steering.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is an overall configuration diagram of a vehicle steering system, Fig. 2 is a sectional view of a rear wheel steering mechanism,
Figures 3 and 4 are the ■-■ line and IV of Figure 2, respectively.
5 is a sectional view taken along line -IV in FIG. 4, FIG. 6 is a sectional view taken along line Vl-Vl in FIG. 3, and FIG. Flow chart diagrams, Figures 8 and 9 are diagrams showing changes in the coefficient Kl of 2, Figure 10 is a diagram showing changes in the steering angle of the steering wheel and rear wheel steering angle, and Figure 11 is a diagram showing changes in the gear ratio. FIG. 15... Control unit (control means) 29...
Rear wheel steering angle sensor 37...first motor 41...variable gear ratio mechanism 48...second motor 49...steering mechanism 61...motor failure determination means 62...sensor failure determination means 15 Control unit 29 Rear wheel steering angle setter 37 First motor 4 Gear ratio variable mechanism 48-Second motor 49 Steering mechanism 6 controller failure determination means 62-Sensor failure determination means (control means) Brown'-1st section 1 Figure 5 Figure 6 Figure 8 Figure 9

Claims (2)

[Claims] (1) At least the first control unit controlled according to the steering angle
a motor, a variable gear ratio mechanism that changes the gear ratio, and a second motor that drives the variable gear ratio mechanism to control the gear ratio;
a steering mechanism that steers the rear wheels by transmitting a steering force obtained by multiplying the drive amount of the first motor and the drive amount of the second motor to the rear wheels; motor failure determination means for determining whether the motor is at fault by operating the other motor with the drive amount of one motor being zero, and when the determination means determines that the motor is at fault, the motor that is not at fault; A rear wheel steering device for a vehicle, comprising: control means for controlling both motors so that the amount of drive of the motors is zero. (2) A rear wheel steering angle sensor detects the rear wheel steering angle, and the rear wheel steering angle detected by the sensor is monitored, and the drive amount of one motor is set to zero while the other motor is operated. The rear wheel of the vehicle according to claim (1), further comprising a sensor failure determination means for determining that when the rear wheel steering angle changes, a failure occurs in a sensor that detects the operation of the motor whose drive amount is zero. Steering device.