JP4872366B2 - Vehicle steering system - Google Patents

Description

  The present invention relates to a vehicle steering apparatus including a transmission ratio variable device.

  Conventionally, by adding a second rudder angle (ACT angle) of a steered wheel based on motor drive to the first rudder angle of a steered wheel based on a steering operation, the steering angle of the steering wheel (steering angle) and the rudder of the steered wheel There is a vehicle steering apparatus including a transmission ratio variable device that varies a transmission ratio (gear ratio) between an angle (steering angle). In such a vehicle steering apparatus, control of the motor that is a drive source is normally performed by feedback control so that the ACT angle follows the command value.

However, in the feedback control based on the deviation between the ACT angle and its command value, when the deviation is small, the amount of current flowing to the motor is also small, and the response of the steered wheels and the steering reaction force with respect to the steering operation are reduced. That is, there is a problem that so-called steering rigidity is lowered. This tendency becomes particularly noticeable during straight running in which the steering angle is maintained substantially constant near the steering neutral position. For this reason, conventionally, in order to solve such problems, when the steering angle is within a predetermined range near the steering neutral position, the energization phase to the motor is fixed and locked, or the feedback gain within the predetermined range is increased. Measures such as setting it high (see, for example, Patent Document 1) are taken.
JP 2005-170129 A

  However, in any of the above conventional methods, as long as steering neutrality is maintained, a large amount of driving power is continuously supplied to the motor. For this reason, there is a problem that not only the energy efficiency is deteriorated but also heat is generated in the power supply path including the motor coil and the drive circuit. In this respect, there is still room for improvement.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a vehicle steering apparatus capable of improving the steering rigidity without causing deterioration in energy efficiency or heat generation in the power supply path. Is to provide.

In order to solve the above problem, the invention according to claim 1 is characterized in that the second rudder angle of the steered wheel based on motor drive is added to the first rudder angle of the steered wheel based on a steering operation. A transmission ratio variable device that varies a transmission ratio between the steering angle of the steering wheel and the steering angle of the steered wheels, and a control unit that controls the operation of the transmission ratio variable device, wherein the control unit includes a command value, A vehicle steering apparatus that controls a motor by feedback control based on a deviation from an actual value, wherein the control means switches the control of the motor to a regeneration mode when the deviation is equal to or less than a predetermined threshold , The gist is that the control means changes the threshold value to a larger value as the vehicle speed increases .

According to the above configuration, even when the deviation between the command value and the actual value is small, for example, during straight running, the steering rigidity feeling can be improved by the regenerative braking action of the motor. And since a large current is not energized to a motor, the heat_generation | fever of a power supply path (a motor coil, a drive circuit, etc.) can be suppressed.
Further, as the vehicle speed increases, the driver tends to demand a higher steering rigidity feeling. Therefore, by changing the threshold value to a larger value as the vehicle speed increases, it is possible to achieve both a steering rigidity feeling required during high speed traveling and excellent responsiveness to steering operation during low and medium speed traveling.

The gist of the invention described in claim 2 is that the control means does not switch to the regeneration mode when the steering angle is larger than a predetermined value.
In other words, heat generation in the power supply path is most likely to be a problem during straight running when the steering operation is substantially constant over a long period of time. Therefore, when the steering angle is not in the vicinity of the steering neutral position, the responsiveness to the steering operation can be ensured by performing the normal feedback control without setting the regeneration mode.

  ADVANTAGE OF THE INVENTION According to this invention, the steering apparatus for vehicles which can improve a steering rigidity feeling without causing the deterioration of energy efficiency and the heat_generation | fever in an electric power supply path | route can be provided.

Hereinafter, an embodiment in which the present invention is embodied in a vehicle steering apparatus including a transmission ratio variable device will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a vehicle steering apparatus 1 according to the present embodiment, FIG. 2 is a control block diagram thereof, and FIGS. 3A and 3B are operation explanatory diagrams of transmission ratio variable control. As shown in FIG. 1, the steering shaft 3 to which the steering wheel 2 is fixed is connected to a rack 5 via a rack and pinion mechanism 4. Is converted into a reciprocating linear motion of the rack 5. Then, the steering angle of the steered wheels 6, that is, the steered angle is varied by the reciprocating linear motion of the rack 5, so that the vehicle traveling direction is changed. The vehicle steering apparatus 1 according to the present embodiment is a so-called rack assist type electric power steering apparatus (EPS), and generates an assist torque generated by a motor 7 as a drive source via a ball screw mechanism (not shown). By transmitting to the rack 5, an assist force is applied to the steering system.

  Further, the vehicle steering apparatus 1 of the present embodiment has a variable transmission ratio that varies the transmission ratio (gear ratio) between the steering angle (steering angle) of the steering 2 and the steering angle (steering angle) of the steered wheels 6. A device 8 and an IFSECU 9 as a control means for controlling the operation of the transmission ratio variable device 8 are provided.

  More specifically, the steering shaft 3 includes a first shaft 10 to which the steering 2 is connected and a second shaft 11 to be connected to the rack and pinion mechanism 4, and the transmission ratio variable device 8 includes the first shaft 10 and the first shaft 10. A differential mechanism 12 for connecting the two shafts 11 and a motor 13 for driving the differential mechanism 12 are provided. The transmission ratio variable device 8 adds the rotation driven by the motor to the rotation of the first shaft 10 accompanying the steering operation and transmits it to the second shaft 11, thereby inputting the steering shaft to the rack and pinion mechanism 4. The rotation of 3 is increased (or decelerated).

  That is, as shown in FIGS. 3A and 3B, the transmission ratio variable device 8 uses the steering angle of the steered wheels based on the motor drive (the steered steer angle θts) based on the steering operation (steer steered angle θts). By adding the ACT angle θta), the transmission ratio between the steering angle θs and the turning angle θt is varied.

  In this case, “addition” is defined to include not only addition but also subtraction, and so on. Further, when the “transmission ratio between the steering angle θs and the turning angle θt” is expressed as an overall gear ratio (steering angle θs / steering angle θt), the ACT angle θta in the same direction as the steering turning angle θts is By adding it, the overall gear ratio becomes small (large turning angle θt, see FIG. 3A). Then, the overall gear ratio is increased by adding the ACT angle θta in the opposite direction (small turning angle θt, see FIG. 3B).

  Further, the motor 13 of the present embodiment is a brushless motor, and rotates when three-phase (U, V, W) driving power is supplied from the IFSECU 9. The IFSECU 9 controls the operation of the transmission ratio variable device 8, that is, the ACT angle θta (transmission ratio variable control) by controlling the rotation of the motor 13 through the supply of the driving power.

Next, the electrical configuration and control mode of the vehicle steering apparatus of the present embodiment will be described.
As shown in FIG. 1, the steering angle θs (steering speed ωs) detected by the steering angle sensor 16 and the vehicle speed V detected by the vehicle speed sensor 17 are input to the IFSECU 9. Then, the IFSECU 9 controls the rotation of the motor 13 based on the steering angle θs (steering speed ωs) and the vehicle speed V, thereby executing the operation of the transmission ratio variable device 8, that is, the transmission ratio variable control.

  More specifically, as shown in FIG. 2, the IFSECU 9 includes a microcomputer 21 that outputs a motor control signal and a drive circuit 22 that supplies drive power to the motor 13 based on the motor control signal.

  The microcomputer 21 includes a gear ratio variable control calculation unit 23 and a differential steer control calculation unit 24, and the steering angle θs and the vehicle speed V are input to the gear ratio variable control calculation unit 23. Is input with the vehicle speed V and the steering speed ωs. The gear ratio variable control calculation unit 23 calculates a gear ratio variable command angle θgr *, which is a control target component for changing the gear ratio (transmission ratio) according to the vehicle speed V, and the differential steer control calculation unit 24 Then, the differential steering command angle θls *, which is a control target component for improving the responsiveness of the vehicle, is calculated according to the steering speed ωs.

  The gear ratio variable command angle θgr * and the differential steer command angle θls * calculated by the gear ratio variable control calculation unit 23 and the differential steer control calculation unit 24 are input to the adder 25. The adder 25 calculates the ACT command angle θta * by superimposing the gear ratio variable command angle θgr * and the differential steer command angle θls *.

  Further, the rotation angle sensor 26 provided in the motor 13 is connected to the IFSECU 9, and the ACT command angle θta * calculated by the adder 25 is calculated based on the motor rotation angle θm output from the rotation angle sensor 26. The ACTθta is input to the subtractor 27. Then, the position control calculation unit 28 calculates the current command ε by feedback calculation based on the deviation Δθta between the ACT command angle θta * which is the command value and the actual value of the ACT command angle θta *, and supplies it to the motor control signal output unit 29. The motor control signal output unit 29 outputs the motor control signal based on the current command ε.

  On the other hand, in the present embodiment, the drive circuit 22 is configured by a plurality (2 × 3) of switching elements (FETs) corresponding to each phase of the motor 13, and between the in-vehicle power supply (battery) 30 and the motor 13. It is provided in the middle of the power supply path. Specifically, the drive circuit 22 is formed by connecting in parallel a series circuit of each set of FETs 31a and 31d, FETs 31b and 31e, and FETs 31c and 31f. 32u, 32v, and 32w are connected to each phase motor coil of the motor 13, respectively. The gate terminals of the FETs 31a to 31f are connected to the microcomputer 21, and the FETs 31a to 31f are turned on / off in response to a motor control signal output from the microcomputer 21 (motor control signal output unit 29). The DC power of the in-vehicle power supply 30 is converted into three-phase drive power and supplied to the motor 13.

(Regenerative control)
As described above, in the feedback control based on the deviation Δθta between the ACT angle θta and the ACT command angle θta *, when the deviation Δθta is small, the amount of current supplied to the motor 13 is also reduced, and the steering rigidity feeling is lowered. There is a problem of doing.

  In consideration of this point, in the present embodiment, the microcomputer 21 short-circuits the motor control signals output to the drive circuit 22 between the phases of the motor 13 when the deviation Δθta (the absolute value thereof) is equal to or less than the predetermined threshold value α. The regenerative mode is set so that the motor 13 functions as a generator. The regenerative braking action improves the steering rigidity feeling.

  Specifically, the microcomputer 21 of the present embodiment includes a switching determination unit 33, and a deviation Δθta in the feedback control (transmission ratio variable control) is input to the switching determination unit 33. When the deviation Δθta is equal to or smaller than the predetermined threshold value α, the switching determination unit 33 outputs the switching signal Sc to the motor control signal output unit 29, and the motor control signal output unit 29 outputs the lower FETs 31d and 31e. , 31f are output to the drive circuit 22 as motor control signals that should be turned on.

  That is, as shown in the flowchart of FIG. 4, when the microcomputer 21 obtains the deviation Δθta between the ACT angle θta and the ACT command angle θta * (step 101), the deviation Δθta is subsequently less than or equal to a predetermined threshold value α. Is determined (step 102). When the deviation Δθta is equal to or smaller than the threshold value α (| Δθta | ≦ α, step 102: YES), the motor control signal output to the drive circuit 22 is switched to a circuit that short-circuits between the phases of the motor 13 to generate the regeneration mode. When the deviation Δθta is larger than the threshold value α, the motor control signal generated based on the feedback control is output to the drive circuit 22 (normal mode, step 104).

  As described above, according to the configuration of the present embodiment, even when the deviation Δθta between the ACT angle θta and the ACT command angle θta * during a straight running or the like is small, the regenerative braking action of the motor 13 provides the steering rigidity feeling. Can be improved. And since a large current is not passed through the motor 13, heat generation in the power supply path (motor coil, drive circuit, etc.) can be suppressed.

In addition, you may change this embodiment as follows.
When the steering angle θs (absolute value thereof) is larger than a predetermined value, the switching to the regeneration mode may not be performed. In other words, heat generation in the power supply path is most likely to be a problem during straight running when the steering operation is substantially constant over a long period of time. Therefore, when the steering angle θs is not in the vicinity of the steering neutral position, it is possible to ensure excellent responsiveness to the steering operation by performing normal feedback control.

  -It is good also as a structure which varies the threshold value (alpha) in switching determination to regeneration mode according to the vehicle speed V. FIG. That is, as the vehicle speed V increases, the driver tends to demand a higher steering rigidity feeling. Therefore, by changing the threshold value α to a larger value as the vehicle speed V increases, it is possible to achieve both a steering rigidity feeling required during high speed driving and excellent responsiveness to steering operation during low and medium speed driving.

The schematic block diagram of the steering apparatus for vehicles. The control block diagram of the steering device for vehicles. (A) (b) Action explanatory drawing of transmission ratio variable control. The flowchart which shows the process sequence of switching determination to regeneration mode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vehicle steering device, 2 ... Steering, 6 ... Steered wheel, 8 ... Transmission ratio variable device, 9 ... IFSECU, 13 ... Motor, 21 ... Microcomputer, 22 ... Drive circuit, 30 ... In-vehicle power supply, θta ... ACT angle, θta *: ACT command angle, Δθta: deviation, α: threshold, θs: steering angle, V: vehicle speed, Sc: switching signal.

Claims (2)

The transmission ratio between the steering angle of the steering wheel and the steering angle of the steered wheel is obtained by adding the second rudder angle of the steered wheel based on the motor drive to the first rudder angle of the steered wheel based on the steering operation. A vehicle steering apparatus comprising: a variable transmission ratio variable device; and control means for controlling the operation of the variable transmission ratio device, wherein the control means controls the motor by feedback control based on a deviation between a command value and an actual value. Because
When the deviation is equal to or less than a predetermined threshold, the control means switches the motor control to a regeneration mode ,
The vehicle steering apparatus according to claim 1, wherein the control means changes the threshold value to a larger value as the vehicle speed increases . The vehicle steering apparatus according to claim 1,
The vehicle steering apparatus according to claim 1, wherein the control means does not switch to the regeneration mode when the steering angle is larger than a predetermined value .

Images