JP4582057B2 - Vehicle steering system - Google Patents

Description

  The present invention relates to a vehicle steering apparatus.

  In recent years, the steering angle of the steered wheels (steering angle) to control the yaw moment of the vehicle based on the vehicle model (vehicle motion model) that models the relationship between the vehicle state quantity such as the vehicle speed and the yaw rate and the motion state of the vehicle. There has been proposed a steering control system having a so-called active steering function for controlling the vehicle.

  In general, the vehicle model is simplified by a two-wheel model that assumes that the front and rear wheels of the vehicle have the same left and right tire characteristics as shown in FIG. 13, and the moment about the center of gravity axis shown in equation (1) and equation (2) It is expressed by the balance of force in the vehicle lateral direction shown in FIG. The change amount per unit time of the target value of the vehicle state quantity (target state quantity, target yaw rate and target slip angle) can be expressed by the following expression (3) from these two expressions. Is obtained by integrating the amount of change. Specifically, as shown in equation (4), the change amount for one calculation cycle (sampling time) is added to the target value of the vehicle state quantity (previous value of the target state quantity) calculated in the previous vehicle model calculation. It is calculated by adding.

これを利用して、例えば、特許文献１に記載の車両用操舵装置では、センサにより検出された車両状態量の実際値とその目標値との比較により車両のステアリング特性（ステア特性）を判定する。そして、オーバーステア状態にある場合には、目標値と実際値との偏差に基づくフィードバック制御により、ヨーモーメントと逆方向に転舵角を変更するよう、即ち所謂カウンタステアをあてるように同転舵角を制御することで、車両姿勢の安定化を図るようになっている。
特開２００５−８８６４８号公報

By utilizing this, for example, in the vehicle steering apparatus described in Patent Document 1, the steering characteristic (steer characteristic) of the vehicle is determined by comparing the actual value of the vehicle state quantity detected by the sensor and its target value. . When the vehicle is in the oversteer state, the turning angle is changed in the direction opposite to the yaw moment by feedback control based on the deviation between the target value and the actual value, that is, so-called counter steering is applied. By controlling the angle, the vehicle posture is stabilized.
JP 2005-88648 A

  However, on low μ roads such as frozen roads, the stable region in which the vehicle posture can be kept stable, that is, the range in which the yaw moment of the vehicle can be stably controlled is narrow. . For this reason, on such low μ roads, there is a tendency for a delay in the stabilization of the vehicle posture, and in particular, when the driver performs counter steering together, a large counter amount is generated as a whole. The trend tends to be even more pronounced, and there is still room for improvement in this regard.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a vehicle steering apparatus that can quickly stabilize the vehicle posture even on a low μ road. .

  In order to solve the above problems, the invention according to claim 1 is directed to a vehicle based on a drive unit capable of changing the turning angle of the steered wheels, a control unit for controlling the operation of the drive unit, and a vehicle model. Vehicle model calculation means for calculating a target value of the vehicle state quantity related to the yaw moment of the vehicle, and steer characteristic determination means for determining the steering characteristic of the vehicle, wherein the control means is when the vehicle is in an oversteer state And performing oversteer control for operating the driving means to change the turning angle in a direction opposite to the yaw moment by feedback calculation based on a deviation between the target value and the actual value of the vehicle state quantity. The vehicle model calculation means calculates the new target value every predetermined period by adding the amount of change for one period to the previous value of the calculated target value. Counter steering detecting means for detecting counter steering during the oversteer control, and when the vehicle model calculating means detects the end of the counter steering, The gist is to replace the value with a value indicating a counter-counter direction rather than the previous value.

  According to the above configuration, the target value of the vehicle state quantity calculated after the next time also indicates the counter-counter direction more than the value when the previous value is not replaced. As a result, in the oversteer control performed to eliminate the oversteer occurring in the opposite direction to the initial oversteer, the deviation used for the feedback calculation becomes large, and a large value (absolute value) as the control starts. A command value having is generated. As a result, the start of the control can be accelerated and the oversteer state in the opposite direction due to the occurrence of the overshoot can be quickly eliminated, and the vehicle posture can be stabilized quickly.

The gist of the invention described in claim 2 is that the vehicle model calculation means replaces the vehicle model calculation means with a steady circle turning value calculated based on a steady circle turning formula.
That is, in the vehicle model calculation, the target value of the vehicle state quantity is obtained by integrating the amount of change per unit time (sampling period). Therefore, in the so-called “return” process of returning from counter steering to normal steering, the steady circle turning value calculated by the steady circle turning formula has a counter-counter direction that is less than the target value obtained by normal vehicle model calculation. It will be shown. Therefore, the target value after the previous value is replaced with the steady circle turning value by the above configuration shows the counter-counter direction more than the value when the previous value is not replaced. Furthermore, it is not known what route changes will occur when the vehicle is traveling. In this regard, if the vehicle model calculation is performed based on the steering angle steady circle turning value corresponding to the current steering angle, it is possible to flexibly cope with the subsequent course change.

  According to a third aspect of the present invention, there is provided estimation means for estimating a steering angle after returning from the counter steering to normal steering, and the vehicle model calculation means is configured to perform the steady circular turning based on the estimated steering angle. The gist is to calculate the value.

  According to the above configuration, the steady circle turning value is calculated using the estimated steering angle after the return of normal steering (the turning angle calculated based on the steering angle), thereby replacing the previous value of the target state quantity. By doing so, the target value after quickly returning to normal steering can be calculated. As a result, the vehicle posture can be stabilized more promptly.

The gist of the invention described in claim 4 is that the vehicle model calculation means performs a filtering process on the target value calculated after the replacement.
According to the above configuration, the target value can be smoothly changed even when the previous value is replaced. As a result, this makes it possible to prevent instability of the vehicle posture and to suppress a variation in the steering reaction force to ensure a good steering feeling.

  According to the present invention, it is possible to provide a vehicle steering apparatus that can quickly stabilize the vehicle posture even on a low μ road.

Hereinafter, an embodiment in which the present invention is embodied in a vehicle steering apparatus provided with a variable gear ratio system 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. As shown in the figure, a steering shaft 3 to which a steering (handle) 2 is fixed is connected to a rack 5 via a rack and pinion mechanism 4, and the rotation of the steering shaft 3 accompanying the steering operation is The pinion mechanism 4 converts the rack 5 into a reciprocating linear motion. Then, by changing the rudder angle of the steered wheels 6, that is, the steered angle, by the reciprocating linear motion of the rack 5, the traveling direction of the vehicle is changed.

  The vehicle steering apparatus 1 of the present embodiment includes a gear ratio variable actuator 7 serving as a transmission ratio variable apparatus that varies the transmission ratio (gear ratio) of the steered wheels 6 with respect to the steering angle (steering angle) of the steering 2, and the gear ratio. And an IFSECU 8 for controlling the operation of the variable actuator 7. In the present embodiment, the gear ratio variable actuator 7 constitutes drive means, and the IFSECU 8 constitutes control means.

  More specifically, the steering shaft 3 includes a first shaft 9 to which the steering 2 is connected and a second shaft 10 to be connected to the rack and pinion mechanism 4. The variable gear ratio actuator 7 includes the first shaft 9 and the first shaft 9. A differential mechanism 11 that couples the two shafts 10 and a motor 12 that drives the differential mechanism 11 are provided. The gear ratio variable actuator 7 adds the rotation driven by the motor to the rotation of the first shaft 9 associated with the steering operation and transmits it to the second shaft 10, 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. 2 and 3, the gear ratio variable actuator 7 has the steered angle (ACT angle θta) of the steered wheels based on the motor drive to the steered angle (steer steered angle θts) of the steered wheels 6 based on the steering operation. ) Is added, the ratio of the turning angle θt of the steered wheels 6 to the steering angle θs, that is, the transmission ratio (gear ratio) is varied. The IFSECU 8 controls the control of the gear ratio variable actuator 7 through the supply of driving power to the motor 12, thereby controlling the transmission ratio (gear ratio) between the steering angle θs and the turning angle θt (gear ratio). Variable control).

  In this case, “addition” is defined to include not only addition but also subtraction, and so on. Further, when the “gear ratio of the steering angle θt to the steering angle θs” is expressed as an overall gear ratio (steering angle θs / steering angle θt), the ACT angle θta in the same direction as the steering angle θts should be added. Thus, the overall gear ratio becomes small (large turning angle θt, see FIG. 2). Then, the overall gear ratio is increased by adding the ACT angle θta in the reverse direction (small turning angle θt, see FIG. 3). In this embodiment, the steer turning angle θts constitutes the first rudder angle, and the ACT angle θta constitutes the second rudder angle.

  As shown in FIG. 1, the vehicle steering apparatus 1 includes an EPS actuator 17 that applies an assist force for assisting a steering operation to the steering system, and an EPS ECU 18 that controls the operation of the EPS actuator 17. Yes.

  The EPS actuator 17 of the present embodiment is a so-called rack assist type EPS actuator in which a motor 22 as a driving source is provided in the rack 5, and assist torque generated by the motor 22 is generated by a ball screw mechanism (not shown). Is transmitted to the rack 5. The EPS ECU 18 controls the assist force applied to the steering system by controlling the assist torque generated by the motor 22 (power assist control).

  In the present embodiment, the IFSECU 8 that controls the gear ratio variable actuator 7 and the EPSECU 18 that controls the EPS actuator 17 are connected via an in-vehicle network (CAN: Controller Area Network) 23. Are connected to a plurality of sensors for detecting the vehicle state quantity. Specifically, a steering angle sensor 24, a torque sensor 25, wheel speed sensors 26a and 26b, a lateral G sensor 28, a vehicle speed sensor 29, a brake sensor 30, and a yaw rate sensor 31 are connected to the in-vehicle network 23. A plurality of vehicle state quantities detected by the sensors, that is, steering angle θs, steering torque τ, wheel speed Vtr, Vtl, turning angle θt, slip angle θsp, vehicle speed V, brake signal Sbk, and yaw rate Ry are as follows: The data is input to the IFSECU 8 and the EPSECU 18 via the in-vehicle network 23.

  In this embodiment, the turning angle θt is obtained by multiplying the steering angle θs by the base gear ratio of the rack and pinion mechanism 4, that is, by adding the ACT angle θta to the steering angle θts, and the slip angle θsp is obtained based on the lateral acceleration detected by the lateral G sensor 28 and the yaw rate Ry. The IFSECU 8 and EPSECU 18 transmit and receive control signals by mutual communication via the in-vehicle network 23. The IFSECU 8 and EPSECU 18 perform the gear ratio variable control and the power assist control in an integrated manner based on the vehicle state quantities and control signals input via the in-vehicle network 23.

Next, the electrical configuration and control mode of the steering apparatus according to the present embodiment will be described.
FIG. 4 is a control block diagram of the vehicle steering apparatus 1 of the present embodiment. As shown in the figure, the IFSECU 8 includes a microcomputer 33 that outputs a motor control signal and a drive circuit 34 that supplies drive power to the motor 12 based on the motor control signal.

  In the present embodiment, the motors 12 and 22 that are drive sources of the gear ratio variable actuator 7 and the EPS actuator 17 are both brushless motors, and the drive circuit 34 and the drive circuit 44 of the EPS ECU 18 described later are input. Based on the motor control signal, three-phase (U, V, W) driving power is supplied to the corresponding motors 12, 22 respectively. Each control block shown below is realized by a computer program executed by the microcomputer 33 (43).

  The microcomputer 33 includes an IFS control calculation unit 35, a gear ratio variable control calculation unit 36, and a Lead Steer control calculation unit 37. Each of these control calculation units is a control target component of the ACT angle θta based on the input vehicle state quantity. (And control signal) is calculated.

  More specifically, the steering angle θs, the turning angle θt, the vehicle speed V, the wheel speeds Vtr and Vtl, the brake signal Sbk, the yaw rate Ry, and the slip angle θsp are input to the IFS control calculation unit 35. The IFS control calculation unit 35 calculates the control target component of the ACT angle θta for controlling the yaw moment of the vehicle based on the so-called active steering function, that is, the vehicle model, based on these vehicle state quantities, and related items. Perform control signal calculations. Specifically, the IFS control calculation unit 35 calculates the IFS_ACT command angle θifs * as a control target component of the ACT angle θta for realizing the active steer function, and indicates the vehicle steering function as the control signal. The characteristic value Val_st is calculated (IFS control calculation).

  Here, the vehicle posture in the yaw direction is expressed as “steer characteristic (steering characteristic)”. The steer characteristic is a characteristic regarding a difference between a vehicle turning speed assumed by the driver and an actual vehicle turning speed when the driver performs a steering operation. The case where the actual vehicle turning speed is larger than the assumed vehicle turning speed is referred to as oversteer (OS), the case where the actual vehicle turning speed is small is referred to as understeer (US), and the case where there is no difference is referred to as neutral steer (NS). This “vehicle turning speed assumed by the driver” can be replaced with the target yaw rate in the vehicle model, and when the vehicle is in a steady circular turning state and the steering characteristic is neutral steering, the turning direction Can also be rephrased as the vehicle traveling direction.

  In the present embodiment, the IFS control calculation unit 35 applies a yaw moment to the steered wheel 6 to reduce the turning angle of the steered wheel 6 when the steer characteristic is understeer, and when the steer characteristic is oversteer. The IFS_ACT command angle θifs * is calculated as a control target component of the ACT angle θta for giving a rudder angle (counter steer) in the opposite direction. Note that the OS / US characteristic value Val_st is used for internal calculation processing in the IFS control calculation unit 35, transmitted to the EPSECU 18 via the in-vehicle network 23, and used for power assist control by the EPSECU 18.

  A steering angle θs, a turning angle θt, and a vehicle speed V are input to the gear ratio variable control calculation unit 36. Then, the gear ratio variable control calculation unit 36 uses the gear ratio variable ACT command angle θgr * as a control target component for varying the gear ratio according to the vehicle speed V based on these vehicle state quantities (and control signals). Calculate (gear ratio variable control calculation).

  The vehicle speed V and the steering speed ωs are input to the lead steer control calculation unit 37. The steering speed ωs is calculated by differentiating the steering angle θs (the same applies hereinafter). Then, the Lead Steer control calculation unit 37 calculates the LS_ACT command angle θ ls * as a control target component for improving the responsiveness of the vehicle based on the vehicle speed V and the steering speed ω s (Lead Steer control calculation). ).

  The IFS control calculation unit 35, the gear ratio variable control calculation unit 36, and the Lead Steer control calculation unit 37 are each control target component calculated by the above calculation, that is, IFS_ACT command angle θifs *, gear ratio variable ACT command angle θgr *, and The LS_ACT command angle θls * is output to the adder 38a. In the adder 38a, the IFS_ACT command angle θifs *, the gear ratio variable ACT command angle θgr *, and the LS_ACT command angle θls * are superimposed, whereby the ACT command angle θta * that is the control target of the ACT angle θta is obtained. Calculated.

  The ACT command angle θta * calculated by the adder 38 a is input to the F / F control calculation unit 39 and the F / B control calculation unit 40. Further, the ACT angle θta detected by the rotation angle sensor 41 provided in the motor 12 is input to the F / B control calculation unit 40. The F / F control calculation unit 39 calculates the control amount εff by feedforward calculation based on the input ACT command angle θta *, and the F / B control calculation unit 40 calculates the ACT command angle θta * and the ACT angle θta. The control amount εfb is calculated by feedback calculation based on the above.

  The F / F control calculation unit 39 and the F / B control calculation unit 40 output the calculated control amount εff and control amount εfb to the adder 38b, and these control amount εff and control amount εfb are output to the adder 38b. By being superposed, it is input to the motor control signal output unit 42 as a current command. The motor control signal output unit 42 generates a motor control signal based on the input current command and outputs it to the drive circuit 34.

  That is, as shown in the flowchart of FIG. 5, when the microcomputer 33 fetches sensor values from the respective sensors as vehicle state quantities (step 101), first, IFS control calculation is performed (step 102), and then gear ratio variable control is performed. An operation (step 103) and a lead steer control operation are performed (step 104). Then, the microcomputer 33 superimposes the IFS_ACT command angle θifs *, the gear ratio variable ACT command angle θgr *, and the LS_ACT command angle θls *, which are calculated by executing the calculation processes of the above steps 102 to 104, To calculate the ACT command angle θta * which is the control target. The microcomputer 33 calculates a current command by performing a feedforward calculation (step 105) and a feedback calculation (step 106) based on the calculated ACT command angle θta *, and performs motor control based on the current command. A signal is output (step 107).

  On the other hand, as shown in FIG. 4, the EPS ECU 18 includes a microcomputer 43 and a drive circuit 44 in the same manner as the IFSECU 8. The microcomputer 43 includes an assist control unit 45, a torque inertia compensation control unit 46, a steering return control unit 47, and a damper compensation control unit 48, and each of these control units has the motor 22 based on the input vehicle state quantity. A control target component of the generated assist torque is calculated.

  More specifically, the vehicle speed V and the steering torque τ are input to the assist control unit 45 and the torque inertia compensation control unit 46, respectively. The assist control unit 45 calculates a basic assist current command Ias * as a base control target component, and the torque inertia compensation control unit 46 is an inertia compensation current command Iti that is a control target component for compensating the inertia of the motor 22. Calculate *.

  The vehicle speed V, the steering torque τ, and the turning angle θt are input to the steering return control unit 47, and the vehicle speed V and the steering speed ωs are input to the damper compensation control unit 48. The steering return control unit 47 calculates a steering return current command Isb *, which is a control target component for improving the return characteristic of the steering 2, and the damper compensation control unit 48 improves the power assist characteristic during high speed running. A damper compensation current command Idp *, which is a control target component for the calculation, is calculated.

  The microcomputer 43 includes an IFS torque compensation control unit 49 that calculates an IFS torque compensation gain Kifs for improving the steering feel during IFS control, in addition to the control units described above. In the present embodiment, the IFS torque compensation control unit 49 includes the steering torque τ, the steering angle θs, and the steering speed ωs, the IFS_ACT command angle θifs * calculated by the IFS control calculation unit 35, and the OS / US characteristic value Val_st. Is entered. Then, the IFS torque compensation controller 49 calculates the IFS torque compensation gain Kifs based on each vehicle state quantity, the IFS_ACT command angle θifs *, and the OS / US characteristic value Val_st.

  In the present embodiment, the IFS torque compensation gain Kifs is multiplied by the basic assist current command Ias * calculated by the assist control unit 45, and the corrected basic assist current command Ias ** is the inertia compensation current command Iti. *, The steering return current command Isb *, and the damper compensation current command Idp * are input to the adder 50. Then, by superimposing these control target components, a current command that is a control target of the assist torque generated by the motor 22 is calculated.

  The current command calculated by the adder 50 is input to the motor control signal output unit 51. In addition, the motor control signal output unit 51 receives an actual current and a rotation angle detected by a current sensor 52 and a rotation sensor 53 provided in the motor 22. The motor control signal output unit 51 generates a motor control signal by performing feedback control based on the current command, the actual current, and the rotation angle, and outputs the motor control signal to the drive circuit 44.

Next, IFS control calculation processing in the IFS control calculation unit will be described in detail.
FIG. 6 is a control block diagram of the IFS control calculation unit. As shown in the figure, the IFS control calculation unit 35 includes a vehicle model calculation unit 61, a crossing road determination unit 62, a steer characteristic calculation unit 63, an OS control calculation unit 65, a US control calculation unit 66, and a control ON / OFF determination unit. 67, and an IFS_ACT command angle calculation unit 68.

  The turning angle θt and the vehicle speed V are input to the vehicle model calculation unit 61 as vehicle model calculation means. Then, the vehicle model calculation unit 61 performs vehicle model calculation based on the turning angle θt and the vehicle speed V, and the target value of the vehicle state quantity related to the yaw moment of the vehicle, that is, the target yaw rate Ry0 as the target state quantity and The target slip angle θsp0 is calculated.

  Specifically, the vehicle model calculation unit 61 includes a previous value storage unit 71. The previous value storage unit 71 includes target state quantities calculated by the vehicle model calculation unit 61, that is, a target yaw rate Ry0 and a target slip. The angle θsp0 is stored as the previous values Ry0_b and θsp0_b of the target state quantities. Then, the vehicle model calculation unit 61 executes the next vehicle model calculation based on the previous values Ry0_b and θsp0_b stored in the previous value storage unit 71 (see the above formula (4)).

  Wheel speeds Vtr and Vtl, a turning angle θt, a vehicle speed V, and a brake signal Sbk are input to the crossing road determination unit 62. Based on these vehicle state quantities, the crossing road determination unit 62 determines whether or not the vehicle is on a crossing road, that is, whether the left and right wheels of the vehicle are on two road surfaces (μ split road surfaces) with significantly different road resistances. Judgment is made. Specifically, it is determined whether braking is in the μ split state, that is, whether the vehicle is in the μ split braking state (crossing road determination).

  The steering angle θs, the vehicle speed V, the yaw rate Ry, and the target yaw rate Ry0 calculated by the vehicle model calculation unit 61 are input to the steering characteristic calculation unit 63 serving as a steering characteristic determination unit. Based on these vehicle state quantities, the steer characteristic calculation unit 63 calculates the steer characteristic of the vehicle, that is, whether the vehicle is in oversteer, understeer, or neutral steer, and indicates the characteristic. An OS / US characteristic value Val_st is calculated (steer characteristic calculation). In this embodiment, the OS / US characteristic value Val_st is output as an analog signal based on the following equation: Val_st = (L × Ry / V−θt) × Ry, L: wheel base.

  The OS control calculation unit 65 includes a yaw rate F / B calculation unit 72 and a slip angle F / B calculation unit 73. The yaw rate F / B calculation unit 72 and the slip angle F / B calculation unit 73 correspond to each other. A feedback calculation is performed so that the actual value of the vehicle state quantity follows the target value. Based on the feedback calculation in each of these F / B calculation units, the OS control calculation unit 65 controls the control target component of the ACT angle θta when the steer characteristic is oversteer, that is, the steering angle in the direction opposite to the yaw moment ( As a control target component for generating (countersteer), an ACT command angle θos * during OS control is calculated (OS control calculation).

  More specifically, the yaw rate Ry and the target yaw rate Ry0 are input to the yaw rate F / B calculation unit 72, and the yaw rate F / B calculation unit 72 performs a feedback calculation based on the deviation ΔRy. Specifically, the yaw rate F / B calculating unit 72 calculates the yaw rate proportional F / B command angle θRyp * by multiplying the deviation ΔRy by the proportional F / B gain KP, and the differential F / B is calculated as the differential amount of the deviation ΔRy. The yaw rate differential F / B command angle θRyd * is calculated by multiplying by the gain KD (yaw rate F / B calculation). Similarly, the slip angle θsp and the target slip angle θsp0 are input to the slip angle F / B calculation unit 73, and the slip angle F / B calculation unit 73 multiplies the deviation Δθsp by the slip angle F / B gain Kslip. Thus, the slip angle F / B command angle θsp * is calculated (slip angle F / B calculation).

  In addition to the yaw rate F / B calculation unit 72 and slip angle F / B calculation unit 73, the OS control calculation unit 65 of this embodiment calculates a control component for ensuring stability during so-called μ split braking. A yaw angle F / B calculation unit 74 is provided. Then, the yaw angle F / B calculation unit 74 executes the yaw angle F / B calculation based on the target yaw angle θy0 and the yaw angle θy using the determination result in the crossing road determination unit 62 as a trigger, and the yaw angle is calculated based on the deviation Δθy. By multiplying the gain Kyaw, the yaw angle F / B command angle θy * is calculated.

  The yaw rate F / B command angle θRyp * and yaw rate differential F / B command angle θRyd * calculated by the yaw rate F / B calculation unit 72, and the slip angle F / B command calculated by the slip angle F / B calculation unit 73. The angle θsp * and the yaw angle F / B command angle θy * calculated by the yaw angle F / B calculation unit 74 are input to the adder 76. Then, the OS control calculation unit 65 calculates an ACT command angle θos * during OS control by superimposing these control target components in the adder 76 (OS control calculation).

  The US control calculation unit 66 receives the steering angle θs, the steering speed ωs, and the OS / US characteristic value Val_st calculated by the steering characteristic calculation unit 63. Then, the US control calculation unit 66 calculates the ACT command angle θus * during US control based on these vehicle state quantities (US control calculation).

  The vehicle speed V, the steering angle θs, the yaw rate Ry, and the OS / US characteristic value Val_st are input to the control ON / OFF determination unit 67. Then, the control ON / OFF determination unit 67 performs oversteer control (OS control) based on the OS control ACT command angle θos * calculated by the OS control calculation unit 65 or the US calculated by the US control calculation unit 66. It is determined whether to perform understeer control (US control) based on the ACT command angle θus * during control, and the determination result is output as a control ON / OFF signal Sc (control ON / OFF determination).

  The IFS_ACT command angle calculator 68 includes an OS control ACT command angle θos * calculated by the OS control calculator 65, a US control ACT command angle θus * calculated by the US control calculator 66, and control ON / OFF. A control ON / OFF signal Sc output from the determination unit 67 is input. When the input control ON / OFF signal Sc indicates “OS control ON”, the IFS_ACT command angle calculator 68 determines the OS control time ACT command angle θos * as the control ON / OFF signal Sc. When “US control ON” indicates “US control ON”, the ACT command angle θus * during US control is output as the IFS_ACT command angle θifs * (IFS_ACT command angle calculation). In the present embodiment, when the control ON / OFF signal Sc is “NS”, that is, indicates that the steering is neutral, the IFS_ACT command angle calculator 68 sets the IFS_ACT command angle θifs * to “0”. And

  That is, as shown in the flowchart of FIG. 7, the IFS control calculation unit 35 first executes vehicle model calculation (step 201), and then executes crossover determination (step 202). Then, a steer characteristic calculation is executed (step 203).

  Next, the IFS control calculation unit 35 executes the yaw rate F / B calculation and the slip angle F / B calculation based on the target yaw rate Ry0 and the target slip angle θsp0 calculated in the vehicle model calculation in step 201. ACT command angle θos * is calculated during OS control (OS control calculation, step 204). If it is determined in step 202 that the μ split braking state is in effect, the yaw angle F / B calculation is executed using the determination result as a trigger. Then, the US control calculation ACT command angle θus * is calculated by executing the US control calculation (step 205), and then the control ON / OFF determination is executed (step 206). Then, the OS control ACT command angle θos * or the US control ACT command angle θus * (or “0”) is output as a control target component for realizing the active steering function, that is, the IFS_ACT command angle θifs * (IFS_ACT command). Angle calculation, step 207), counter steering detection and target state quantity previous value replacement calculation described in detail below are executed (step 208).

(Counter steering detection and target state quantity previous value replacement control)
Next, counter steering detection and target state quantity previous value replacement control in the vehicle steering system of the present embodiment will be described.

  As shown in FIG. 6, in this embodiment, the IFS control calculation unit 35 includes a counter steering detection unit 77 as counter steering detection means for detecting counter steering by the driver during the OS control. The counter steering detection unit 77 receives the yaw rate Ry, the steering angle θs, the steering speed ωs, and the OS / US characteristic value Val_st calculated by the steering characteristic calculation unit 63. Further, the counter steering detection unit 77 stores a steering angle (OS generation steering angle θs_oss) and a maximum counter steering angle (maximum counter steering angle θs_cmax) when the OS state is reached. The counter steering detection unit 77 detects the start and end of counter steering by the driver based on these state quantities (and control signals), and generates a counter signal S_cs indicating the presence or absence of the counter steering. In the present embodiment, the counter signal S_cs is configured such that its output is “ON” when there is counter steering, and its output is “OFF” when there is no counter steering.

  More specifically, as shown in the flowchart of FIG. 8, the counter steering detection unit 77 acquires the above-described state quantities, that is, the yaw rate Ry, the steering angle θs, the steering speed ωs, and the OS / US characteristic value Val_st (step). 301) Subsequently, it is determined whether or not the vehicle is in the OS state (step 302). If it is determined that the vehicle is in the OS state (step 302: YES), it is determined whether or not a counter steering flag indicating that the driver is performing counter steering is set (step 303). ) If the counter steering flag is not set (step 303: NO), the driver determines whether to start counter steering (steps 304 to 306).

  Specifically, the counter steering detection unit 77 first determines whether or not a steering operation in a direction opposite to the direction of the yaw moment has occurred, depending on whether or not the signs of the yaw rate Ry and the steering speed ωs are inconsistent (step S1). 304). Next, it is determined whether or not the steering speed ωs (absolute value) is faster than a predetermined threshold value ωs0 (step 305). Subsequently, the amount of change in the steering angle from the steering angle θs_oss at the time of OS generation becomes a predetermined threshold value θs0. It is determined whether it exceeds (step 306). When all of the requirements of Step 304 to Step 306 are satisfied, that is, the signs of the yaw rate Ry and the steering speed ωs are inconsistent (Step 304: YES), and the steering speed ωs (absolute value) is from a predetermined threshold ωs0. Is faster (| ωs |> ωs0, step 305: YES), and the amount of change in steering angle from the steering angle θs_oss at the time of OS generation exceeds a predetermined threshold θs0 (| θs_oss−θs |> θs0, step 306: YES) Then, it is determined that the counter steering by the driver has been started. If it is determined that the counter steering is started in this way, the counter steering flag is set (step 307), and the output of the counter signal S_cs is turned on (step 308).

  If any of the determination conditions of step 304 to step 306 is not satisfied (step 304: NO, step 305: NO, or step 306: NO), the processing of steps 307 and 308 is not executed. . If it is determined in step 302 that the vehicle is not in the OS state (step 302: NO), the processing from step 304 to step 308 and step 309 and subsequent steps are not executed.

  On the other hand, when it is determined in step 303 that the counter steering flag is set (step 303: YES), the counter steering detection unit 77 performs the counter steering end determination (steps 309 to 311). .

  Specifically, the counter steering detection unit 77 first determines whether or not the yaw moment of the vehicle has changed in the stable direction, that is, the neutral steering direction, based on the differential value dRy of the yaw rate Ry (step 309). Next, it is determined whether or not the steering speed ωs is “0” or is generated in the counter-counter direction (step 310), and then whether the steering angle change amount from the maximum counter steering angle θs_cmax exceeds a predetermined threshold θs1. It is determined whether or not (step 311). When all the requirements of Step 309 to Step 311 are satisfied, that is, the yaw moment of the vehicle changes in a stable direction (Step 309: YES), and the steering speed ωs is “0” or occurs in the counter-counter direction. (Step 310: YES) and if the steering angle change from the maximum counter steering angle θs_cmax exceeds a predetermined threshold θs1 (| θs_cmax−θs |> θs1, Step 311: YES), the counter steering is completed. judge. If it is determined that the counter steering is completed in this way, the counter steering flag is reset (step 312), and the output of the counter signal S_cs is set to “off” (step 313). Note that if any of the determination conditions of Step 309 to Step 311 is not satisfied (Step 309: NO, Step 310: NO, or Step 311: NO), the processing of Steps 312 and 313 is not executed. .

  In the present embodiment, the counter signal S_cs generated by the counter steering detection unit 77 is input to the vehicle model calculation unit 61. When the counter signal S_cs indicates the end of the counter steering, that is, when the vehicle signal is switched from “ON” to “OFF”, the vehicle model calculation unit 61 determines the target state quantity ( The previous values Ry0_b and θsp0_b of the target yaw rate Ry0 and the target slip angle θsp0) are replaced with values indicating the counter-counter direction rather than the previous values (target state quantity previous value replacement control).

  More specifically, the vehicle model calculation unit 61 of the present embodiment includes a steady circle turning value calculation unit 78 that calculates target state quantity values (steady circle turning values Ry0_cy, θsp0_cy) when the vehicle is in a steady circle turning. ing. Specifically, the steady circle turning value calculation unit 78 calculates the steady circle turning values Ry0_cy and θsp0_cy based on the “steady circle turning equation” shown in the following equations (5) to (7). Note that “β” obtained by the equation (5) is a steady circular turning value θsp0_cy of the slip angle, and “γ” obtained by the equation (6) is a steady circular turning value Ry0_cy of the yaw rate. “A” in each of these formulas is “stability factor”.

そして、車両モデル演算部６１は、カウンタ操舵検出部７７の出力するカウンタ信号Ｓ_csが「オン」から「オフ」に切り替わった場合には、この定常円旋回値Ｒy0_cy，θsp0_cyにより前回値Ｒy0_b，θsp0_bを置換する。つまり、目標ヨーレイトＲy0及び目標スリップ角θsp0を演算する際、上記（４）式の「β（Ｋ），γ（Ｋ）」に代入する値を、本来の値である前回値Ｒy0_b，θsp0_bから、定常円旋回値Ｒy0_cy，θsp0_cyへと置換する。

When the counter signal S_cs output from the counter steering detection unit 77 is switched from “ON” to “OFF”, the vehicle model calculation unit 61 obtains the previous values Ry0_b and θsp0_b from the steady circular turning values Ry0_cy and θsp0_cy. Replace. That is, when calculating the target yaw rate Ry0 and the target slip angle θsp0, the values to be substituted for “β (K), γ (K)” in the above equation (4) are changed from the previous values Ry0_b and θsp0_b which are the original values. Replace with steady circle turning values Ry0_cy, θsp0_cy.

  That is, as shown in the flowchart of FIG. 9, the vehicle model calculation unit 61 first determines whether or not the counter signal S_cs output from the counter steering detection unit 77 has been switched from “on” to “off” (step 401). When it is determined that the counter signal S_cs has been switched from “ON” to “OFF” (step 401: YES), the steady circle turning value calculation is executed (step 402). Then, the previous values Ry0_b and θsp0_b are replaced by the steady circle turning values Ry0_cy and θsp0_cy (step 403), and the vehicle model calculation is executed (step 404).

(Action / Effect)
Next, the operation and effect of the vehicle steering apparatus of the present embodiment configured as described above will be described. For convenience of explanation, only the yaw rate Ry (target yaw rate Ry0) will be described, but it goes without saying that the same tendency applies to the slip angle θsp (target slip angle θsp0).

  10A to 10C show changes in the steering angle θs, the yaw rate Ry and the target yaw rate Ry0, and the OS time ACT command angle θos * when the driver performs counter steering during the OS control on the low μ road. FIG. In the figure, the waveform M shows the transition of the yaw rate Ry, the waveform M0 shows the transition of the target yaw rate Ry0, and the broken lines M ′ and M0 ′ (parts after detection of the end of the counter) of these waveforms M and M0 are shown. The transition of the yaw rate Ry and the target yaw rate Ry0 when the above-described target state quantity previous value replacement control is performed is shown. The waveform N shows the transition of the OS time ACT command angle θos * when the target state quantity previous value replacement control is not performed, and the waveform N ′ shown by the broken line is the case where the target state quantity previous value replacement control is performed. The transition of the ACT command angle θos * at the time of OS is shown.

  As shown in the figure, during the OS control, the steering angle θs in the counter direction (below the reference line in the figure) is generated by the driver's counter steering, so that the steering angle θs (steering angle θt) is obtained. The target yaw rate Ry0 calculated based on the value also indicates the counter direction. Therefore, when there is counter steering by the driver, the target yaw rate Ry0 may coincide with the yaw rate Ry in a state where the target yaw rate Ry0 is at a value indicating the counter direction.

  However, on a low μ road such as an icy road, the stable region in which the vehicle posture can be kept stable, that is, the range in which the yaw moment of the vehicle can be stably controlled is narrow, so the yaw rate Ry is difficult to converge to the target yaw rate Ry0. Overshoot is likely to occur. Therefore, in the above case, the yaw rate Ry exceeds the target yaw rate Ry0 and becomes larger in the counter direction, so that an oversteer in the direction opposite to the oversteer that appears first occurs. As described above, a delay occurs in the stabilization of the vehicle posture.

  In this regard, in this embodiment, the end of the counter steering by the driver, that is, the return timing to the normal steering is detected, and when the end of the counter steering is detected, the target yaw rate Ry0 and the basis of the vehicle model calculation are detected. The previous values Ry0_b and θsp0_b of the target slip angle θsp0 are replaced with the steady circular turning values Ry0_cy and θsp0_cy calculated based on the steady circular turning expressions shown in the above formulas (5) to (7) (see FIG. 6).

  That is, as shown in the above equations (3) and (4), the target yaw rate Ry0 and the target slip angle θsp0 are obtained by integrating the amount of change per unit time (sampling period). Therefore, in the so-called “returning” process in which the counter steering is returned to the normal steering, the target yaw rate Ry0 and the target slip angle θsp0 obtained by the above equation (4) are calculated based on the steady circular turning formula. The value indicates the counter direction rather than the values Ry0_cy and θsp0_cy.

  That is, the steady circle turning values Ry0_cy and θsp0_cy indicate the counter-counter direction (upward direction in FIG. 10) from the previous values Ry0_b and θsp0_b replaced by the steady circular turning values Ry0_cy and θsp0_cy. The value Ry0_rp of the target yaw rate Ry0 calculated in the model calculation indicates the counter counter direction than the value Ry0_or when the previous values Ry0_b and θsp0_b are not replaced. As a result, in the OS control performed to eliminate the oversteer in the direction opposite to the previous oversteer, the deviation ΔRy (deviation from the yawrate Ry) used in the yaw rate F / B calculation becomes large, and the OS At the start of control, an OS control ACT command angle θos * having a large value (absolute value) is output. As a result, the start of the control can be accelerated and the oversteer state in the opposite direction due to the occurrence of the overshoot can be quickly eliminated, and the vehicle posture can be stabilized quickly.

  Furthermore, it is not known what route changes will occur when the vehicle is traveling. In this regard, as described above, if the target yaw rate Ry0 and the target slip angle θsp0 are calculated on the basis of the steering angle steady circle turning values Ry0_cy and θsp0_cy corresponding to the current steering angle θs, However, it can respond flexibly.

In addition, you may change this embodiment as follows.
In the present embodiment, the present invention is embodied in the vehicle steering apparatus 1 that realizes an active steering function by changing the ACT angle θta of the gear ratio variable actuator 7. However, the present invention is not limited to this, and the present invention may be embodied in what uses other actuators as driving means, for example, a so-called steer-by-wire vehicle steering device in which steered wheels and steering are mechanically separated.

  In the present embodiment, the vehicle steering apparatus 1 includes the EPS actuator 17 that uses the motor 22 as a drive source. However, the power assist apparatus may be hydraulic. Further, the present invention may be embodied in a vehicle steering device that does not include a power assist device.

  The target yaw rate Ry0 and the target slip angle θsp0 may be changed smoothly by filtering the target values (target yaw rate Ry0 and target slip angle θsp0) calculated after the target state quantity previous value replacement control. As a result, it is possible to prevent the vehicle posture from becoming unstable due to the sudden change in the ACT angle θs, and to suppress the fluctuation of the steering reaction force to ensure a good steering feeling.

  The determination condition in the counter steering start determination, “when the steering angle change amount from the steering angle θs_oss at the time of OS generation exceeds a predetermined threshold θs0” is “from the maximum steering angle after the vehicle is in an oversteer state” … ”.

  Further, an estimation means for estimating the steering angle θs ′ after returning from the counter steering to the normal steering is provided, and the estimated steering angle θs ′ (the turning angle θt calculated based on the steering angle θs ′) is provided. The steady circle turning value may be calculated on the basis of this. With such a configuration, the steady circular turning value is calculated using the estimated steering angle θs ′ after returning to normal steering (the turning angle θt calculated based on the steering angle θs ′), and thereby By replacing the previous value of the target state quantity, the target state quantity after quickly returning to normal steering can be calculated. As a result, the vehicle posture can be stabilized more promptly.

  Specifically, for example, the counter steering amount Δθs_cs given by the driver is obtained by obtaining the difference between the steering angle θs_oss at the time of OS generation and the steering angle at the end of the counter steering (the steering angle θs_cse at the end of the counter) ( Δθs_cs = | θs_oss−θs_cse |). In addition, a counter steering amount correction gain Ks having a larger value is calculated as the steering speed ωs (absolute value) at the time when the end of the counter steering as shown in FIG. 11 is detected is faster (Ks = “ 1 "to" 0 "). Then, the steering angle θs ′ after returning to normal steering is calculated by subtracting the value obtained by multiplying the counter steering amount Δθs_cs and the counter steering amount correction gain Ks from the steering angle θs (θs ′ = θs− (Δθs_cs × Ks). ).

  That is, in the so-called “return” process of returning from counter steering to normal steering, the larger the initial counter steering amount Δθs_cs, the larger the return amount, and the larger the return amount, the higher the steering speed ωs. Get faster. Therefore, by multiplying the initial counter steering amount Δθs_cs by the counter steering amount correction gain Ks corresponding to the steering speed ωs, an appropriate return amount for returning to normal steering can be obtained. Since the steering angle θs at the end of the counter steering is opposite to the steering angle θs ′ after the normal steering return, the steering angle θs ′ after the normal steering return is estimated by subtracting this from the steering angle θs. It can be done.

  The processing procedure when such a configuration is applied to the target state quantity previous value replacement control may be performed as follows, for example. That is, as shown in the flowchart of FIG. 12, it is first determined whether or not the end of the counter steering is detected (step 501). If the end of the counter steering is detected (step 501: YES), the counter steering amount is determined. Calculation (Δθs_cs = | θs_oss−θs_cse |, step 502) and calculation of the counter steering amount correction gain Ks (step 503) are executed. Then, the counter steering amount correction gain Ks and the counter steering amount Δθs_cs obtained thereby are used to estimate the steering angle θs ′ after returning to the normal steering (θs ′ = θs− (Δθs_cs × Ks), step 504).

  Next, in step 504, it is determined whether or not the estimated steering angle θs ′ after returning to normal steering is between the current steering angle θs and the OS-generated steering angle θs_oss (step 505). If the condition is satisfied (step 505: YES), the steady circle turning value is calculated using the estimated steering angle θs ′ after the normal steering return (step 506). This is to ensure the validity of the estimated steering angle θs ′ after returning to normal steering. If the determination condition of step 505 is not satisfied (step 505: NO), the steady circle turning value may be calculated using the current steering angle θs (step 507). Then, the previous value of the target state quantity is replaced with the steady circle turning value calculated in step 506 or step 507 (step 508), and vehicle model calculation is executed (step 509).

  If the end of counter steering is not detected in step 501 (step 501: NO), the vehicle model calculation in step 509 is executed without executing the processing in steps 502 to 508.

The schematic block diagram of the steering apparatus for vehicles. Explanatory drawing of gear ratio variable control. Explanatory drawing of gear ratio variable control. The control block diagram of the steering device for vehicles. The flowchart which shows the process sequence of the arithmetic processing in IFSECU. The control block diagram of an IFS control calculating part. The flowchart which shows the process sequence of the calculation process in an IFS control calculating part. The flowchart which shows the process sequence of counter steering detection. The flowchart which shows the process sequence of target state quantity last value replacement control. (A)-(c) The waveform diagram which shows transition of a steering angle, a yaw rate, a target yaw rate, and an OS time ACT command angle when the driver performs counter steering during OS control. Explanatory drawing which shows the determination method of the counter steering amount correction | amendment gain according to a steering speed. The flowchart which shows the process sequence of the target state amount last value replacement control of another example. Explanatory drawing of a vehicle model.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering device for vehicles, 2 ... Steering, 6 ... Steered wheel, 7 ... Variable gear ratio actuator, 8 ... IFSECU, 35 ... IFS control calculating part, 61 ... Vehicle model calculating part, 63 ... Steer characteristic calculating part, 65 ... OS control calculation unit, 71 ... previous value storage unit, 77 ... counter steering detection unit, 78 ... steady circle turning value calculation unit, θs, θs' ... steering angle, ωs ... steering speed, θt ... turning angle, θts ... steer Steering angle, θta ... ACT angle, θifs * ... IFS_ACT command angle, θos * ... ACT command angle during OS control, Val_st ... OS / US characteristic value, S_sc ... Counter signal, Ry ... Yaw rate, Ry0 ... Target yaw rate, θsp ... Slip angle, θsp0, target slip angle, Ry0_b, θsp0_b, previous value, Ry0_cy, θsp0_cy, steady circular turning value, Δθs_cs, counter steering amount, Ks, counter steering amount correction gain.

Claims (4)

Driving means capable of changing the turning angle of the steered wheels, control means for controlling the operation of the driving means, and vehicle model calculation for calculating a target value of the vehicle state quantity related to the yaw moment of the vehicle based on the vehicle model And a steering characteristic determining means for determining a steering characteristic of the vehicle, wherein the control means is based on a deviation between a target value and an actual value of the vehicle state quantity when the vehicle is in an oversteer state. By performing feedback calculation, oversteer control is performed to operate the drive means to change the turning angle in a direction opposite to the yaw moment, and the vehicle model calculation means sets the previous value of the calculated target value to A vehicle steering apparatus that calculates a new target value every predetermined period by adding a change amount for one period,
Counter steering detection means for detecting counter steering during the oversteer control,
When the vehicle model calculation means detects the end of the counter steering, the vehicle model calculation means replaces the previous value serving as the basis of the calculation with a value indicating a counter-counter direction rather than the previous value;
A vehicle steering apparatus characterized by the above. The vehicle steering apparatus according to claim 1,
The vehicle steering apparatus according to claim 1, wherein the vehicle model calculation means replaces the vehicle model calculation means with a steady circle turning value calculated based on a steady circle turning formula. The vehicle steering apparatus according to claim 2,
An estimation means for estimating a steering angle after returning from the counter steering to normal steering;
The vehicle steering apparatus according to claim 1, wherein the vehicle model calculation means calculates the steady circle turning value based on the estimated steering angle. In the steering device for vehicles according to any one of claims 1 to 3,
The vehicle model calculation means performs a filtering process on the target value calculated after the replacement.

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