JP4359315B2 - All-wheel steering device for vehicle - Google Patents

Description

  The present invention relates to an all-wheel steering device for a vehicle that controls the turning angle of a rear wheel based on the turning angle and the vehicle speed of a front wheel, and more particularly, a vehicle that is combined with an electric power steering device that assists the turning of a front wheel. The present invention relates to an all-wheel steering apparatus.

  In all-wheel steering devices for vehicles that control vehicle characteristics by means of rear wheel steering angle drive control (RTC: Rear Toe Control), drive control by RTC may fail. In this case, the rear wheels cannot be controlled, and the toe angle of the rear wheels is fixed, so that a change occurs in the yaw rate gain of the vehicle. In particular, in the case of a failure in a state with a high yaw rate gain such as toe-out or reverse phase failure, the vehicle is likely to become unstable, and thus it is necessary to achieve stabilization of the vehicle.

It is already known that vehicle stability is achieved by feeding back vehicle characteristics such as yaw rate and performing control by an electric power steering device using a reaction force by the feedback (see, for example, Patent Document 1). ).
JP 2003-81117 A

  However, in the conventional technology such as Patent Document 1, in the feedback such as the yaw rate, the reaction force value by the feedback is simply determined for each vehicle speed. Therefore, the reaction force value due to feedback that should be originally set according to the vehicle characteristics cannot be appropriately changed. If the vehicle characteristics change due to the failure of drive control by RTC, the vehicle is likely to become unstable, but the conventional technology can no longer cope with the change, and the vehicle is Stable stabilization could not be achieved.

  Accordingly, an object of the present invention is to achieve stabilization of the vehicle even in a state where the vehicle is likely to become unstable due to a failure in drive control of the steering angle of the rear wheels.

  In order to solve the above problems, the present invention provides an electric power steering device in which an electric motor generates an auxiliary torque according to at least a steering torque and transmits the auxiliary torque to a steering system of a front wheel, and a turning angle of at least a front wheel. And a rear wheel steering device that controls the turning angle of the left and right rear wheels based on the vehicle speed, and a steering control device that controls the electric power steering device and the rear wheel steering device. The steering control device includes means for detecting a yaw rate of the vehicle, means for determining a failure state of the rear wheel steering device, means for calculating a yaw rate gain in the failure state, the yaw rate, the vehicle speed. And calculating a yaw rate feedback torque correction value in the failed state based on the yaw rate gain in the failed state When the target value of the assist torque, characterized in that it comprises a means for modifying in the yaw rate feedback torque correction value.

  According to the present invention, it is possible to achieve stabilization of the vehicle even in a state where the vehicle is likely to become unstable due to a failure in driving control of the steering angle of the rear wheels.

  Hereinafter, the best mode for carrying out the all-wheel steering device for a vehicle of the present invention (hereinafter referred to as “embodiment”) will be described. In the description, the accompanying drawings are referred to as appropriate. 1 is a schematic view of a four-wheel vehicle to which the all-wheel steering device according to the present embodiment is applied, FIG. 2 is a configuration diagram of an electric power steering device, and FIG. 3 is a rear wheel steering on the left rear wheel side. It is a block diagram of an apparatus, FIG. 4 is a block diagram of the actuator of a rear-wheel steering apparatus.

1. Configuration of All-Wheel Steering Device As shown in FIG. 1, the all-wheel steering device 100 includes an electric power steering device 110 that assists steering by the steering handle 3 that steers the front wheels 1L and 1R, and the steering of the front wheels 1L and 1R. Steering control devices (hereinafter referred to as “steering”) for controlling the rear wheel steering devices 120L and 120R, the electric power steering device 110, and the rear wheel steering devices 120L and 120R that independently steer the rear wheels 2L and 2R according to the angle and the vehicle speed. Control ECU (Electronic Control Unit) ”) 130, vehicle speed sensor S _V , yaw rate sensor S _Y , lateral acceleration sensor S _{GS, and} other various sensors.

2. Configuration of Electric Power Steering Device The electric power steering device 110 includes a main steering shaft 3a provided with a steering handle 3, a shaft 3c, and a pinion shaft 7 as shown in FIG. ) The pinion gear 7a connected by 3b and provided at the lower end of the pinion shaft 7 meshes with the rack teeth 8a of the rack shaft 8 which can reciprocate in the vehicle width direction. The left and right front wheels 1L and 1R are connected via tie rods 9,9. With this configuration, the electric power steering apparatus 110 can change the traveling direction of the vehicle when the steering handle 3 is steered. Here, the rack shaft 8, the rack teeth 8a, and the tie rods 9 and 9 constitute a turning mechanism. The pinion shaft 7 is supported by the steering gear box 6 through bearings 3d, 3e, and 3f at its upper, middle, and lower portions.

  In addition, the electric power steering device 110 includes an electric motor 4 that supplies auxiliary steering force (auxiliary torque) for reducing the steering force (steering torque) by the steering handle 3, and is provided on the output shaft of the electric motor 4. The worm gear 5a thus engaged meshes with the worm wheel gear 5b provided on the pinion shaft 7. That is, the worm gear 5a and the worm wheel gear 5b constitute a speed reduction mechanism. The worm gear 5a, the worm wheel gear 5b, the pinion shaft 7, the rack shaft 8, the rack teeth 8a, the tie rods 9, 9 and the like connected to the rotor of the motor 4 and the motor 4 constitute a steering system.

The electric motor 4 is a three-phase brushless motor including a stator (not shown) having a plurality of field coils and a rotor (not shown) that rotates inside the stator, and mechanically transfers electric energy. It is converted into energy (P _M = ωT _M ). Here, omega is the rotational speed of the electric motor 4, T _M is the torque generated by the motor 4. Further, the relationship between the generated torque T _M and the output torque T _M ^* that can actually be extracted as an output is expressed by the following equation. (I: Reduction ratio between the worm gear 5a and the worm wheel gear 5b)
T _M ^* = T _M − (c _m dθ _m / dt + J _m d ² θ _m / dt ² ) i ² (1)
From this equation, the relationship between the output torque T _M ^* and the motor rotation angle θ _m is defined by the inertia moment J _m of the rotor of the motor 4 and the viscosity coefficient _cm, and is independent of the vehicle characteristics and the vehicle state.

Here, the steering torque applied to the steering wheel 3 Ts, the coefficients of the assist amount A _H, which assists the torque of the motor 4 which is boosted through a reduction mechanism (auxiliary torque), for example, a function of the vehicle speed V As k _A (V). In this case, since A _H = k _A (V) × Ts, the pinion torque that is the road surface load Tp is
Tp = Ts + A _H
= Ts + k _A (V) × Ts
It becomes. From this, the steering torque Ts is
Ts = Tp / (1 + k _A (V)) (2)
It is expressed.

Therefore, the steering torque Ts is reduced to 1 / (1 + k _A (V)) times the pinion torque Tp (load). For example, if k _A (0) = 2 when the vehicle speed V = 0, the steering torque Ts is controlled to be 1/3 lighter than the pinion torque Tp, and k _A when the vehicle speed V = 100 km / h. If (100) = 0, the steering torque Ts becomes equal to the pinion torque Tp, and the steering feeling is controlled to a solid weight equivalent to that of manual steering. That is, by controlling the steering torque Ts according to the vehicle speed V, a light and stable steering feeling can be imparted lightly at low speeds and firmly at high speeds.

In general, the steering torque Ts is
Ts = J · d ² θ _S / dt ² + C · dθ _S / dt + K (θ _S −θ _F ) (3)
I know that
Here, θ _S is a steering rotation angle, and θ _F is a value obtained by dividing the motor rotation angle θ _m by the rotation ratio n _M of the speed reduction mechanism. J is the inertia coefficient (inertia) of the steering system, C is the viscosity coefficient (damper) of the steering system, and K is the base signal coefficient. This formula is also irrelevant to the vehicle characteristics and the vehicle state, like the formula (1).

At this time, in evaluating the steering feeling, paying attention to the difference in the steering reaction force due to the presence or absence of the moment of inertia, the moment of inertia can be evaluated using the ratio Ev between the input torque and the reaction torque (inertia torque) as an evaluation function. it can. From the evaluation results using this evaluation function, it was found that there is a region where the steering feeling evaluation is high in the vicinity of the inertia coefficient J of the steering system and the point Ev0 where the viscosity around the steering system is ignored.
Here, the ratio Ev is
Ev = Tdet / Ts = K (θ _S −θ _F ) / Ts (4)
It is. Thereby, it is possible to obtain a compensator H (S) that makes the gain characteristic of the transfer function from Ts to Tdet = K (θ _S −θ _F ) equal to or less than Ev0.

Since the compensator obtained by the H∞ control is determined by the target model and the order of the frequency weighting function, it becomes a high-order compensator that is difficult to realize with a normal microcomputer. Therefore, the order of the compensator was reduced by focusing on the frequency band necessary for controlling the steering system.
For example, the transfer function Hf (S) is set to have four zeros and four poles.
Hf (S) = 8.88 (S + 140) (S + 65.1) (S + 30.1) (S + 1.77) / {(S + 1730) (S + 209) (S + 37.1) (S + 15.6)}
Can be set to Note that the gain characteristic of the transfer function Hf (S) has a differential characteristic.

Moreover, amplification electric power steering apparatus 110 includes a motor drive circuit 23 for driving the electric motor 4, a resolver 25, a torque sensor S _T for detecting the pinion torque Tp applied to the pinion shaft 7, the output of the torque sensor S _T a differential amplifier circuit 21, and a vehicle speed sensor S _V. Then, the steering control ECU 130 of the all-wheel steering device 100 drives and controls the electric motor 4, which is a functional unit that is not separated from the electric power steering device 110, and the front wheel turning angle control unit 130a and the rear wheel turning angle control unit 130b (see FIG. 5).

The motor drive circuit 23 includes a plurality of switching elements such as a three-phase FET bridge circuit, for example, and uses a DUTY (DU, DV, DW) signal from the front wheel turning angle control unit 130a to generate a rectangular wave voltage. The motor 4 is generated and driven. The motor drive circuit 23 has a function of detecting a three-phase motor current I (IU, IV, IW) using a hall element (not shown). The resolver 25 detects an electric motor rotation angle θ _m of the electric motor 4 and outputs an angle signal θ. For example, a magnetic sensor provided with a plurality of uneven portions at equal intervals in the circumferential direction is provided as a sensor for detecting a change in magnetoresistance. There is something close to the rotating body.

Torque sensor S _T is used to detect the pinion torque Tp applied to the pinion shaft 7, a magnetic film so that the opposite direction of the anisotropy in the axial direction two portions of the pinion shaft 7 is deposited, the magnetic A detection coil is inserted on the surface of the membrane so as to be separated from the pinion shaft 7. The differential amplifier circuit 21 amplifies the difference in permeability change between the two magnetic films detected by the detection coil as an inductance change, and outputs a torque signal T.

A vehicle speed sensor S _V is for detecting the vehicle speed V of the vehicle as a pulse number per unit time, and outputs a vehicle speed signal VS.
The functional configuration of the steering control ECU 130 will be described later together with the control of the electric power steering device 110 and the control of the rear wheel steering devices 120L and 120R.

3. Configuration of Rear Wheel Steering Device Next, the configuration of the rear wheel steering device will be described with reference to FIGS. 3 and 4.
FIG. 3 is a plan view showing the rear wheel steering device on the left rear wheel side, and FIG. 4 is a schematic sectional view showing the structure of the actuator of the rear wheel steering device.

  The rear wheel steering devices 120L and 120R are respectively attached to the left and right rear wheels 2L and 2R of the vehicle. FIG. 3 shows the rear wheel steering device 120L taking the left rear wheel 2L as an example. The rear wheel steering devices 120L and 120R include an actuator 30 and a rear wheel steering drive control device (hereinafter referred to as “rear wheel steering drive control ECU”) 37. Note that FIG. 3 shows only the left rear wheel 2L, but the right rear wheel 2R is also attached in the same manner (symmetrical).

  An end portion in the vehicle width direction of the cross member 12 extending substantially in the vehicle width direction is elastically supported by the rear side frame 11 of the vehicle body. The front end of the trailing arm 13 extending substantially in the vehicle longitudinal direction is supported near the end of the cross member 12 in the vehicle width direction. A rear wheel 2L is fixed to the trailing end of the trailing arm 13.

  The trailing arm 13 is configured by connecting a vehicle body side arm 13a attached to the cross member 12 and a wheel side arm 13b fixed to the rear wheel 2L via a rotation shaft 13c in a substantially vertical direction. Yes. Thereby, the trailing arm 13 can be displaced in the vehicle width direction.

  One end of the actuator 30 is attached to the front end portion on the front side from the rotating shaft 13c of the wheel side arm 13b via the ball joint 16, and the other end is attached to the cross member 12 via the ball joint 17.

As shown in FIG. 4, the actuator 30 includes an electric motor 31, a speed reduction mechanism 33, a feed screw portion 35, and the like.
The electric motor 31 includes a brush motor or a brushless motor that can rotate in both forward and reverse directions.
The speed reduction mechanism 33 is configured by combining, for example, a two-stage planetary gear (not shown).
The feed screw portion 35 is movable in the axial direction by meshing with the rod 35a formed in a cylindrical shape, a nut 35c formed with a screw groove 35b and inserted into the rod 35a, and the screw groove 35b. And a screw shaft 35d to be supported. The screw shaft 35d is housed in an elongated case body 34 together with the speed reduction mechanism 33 and the electric motor 31, and one end of the speed reduction mechanism 33 is connected to the output shaft of the electric motor 31 and the other end is connected to the screw shaft 35d.
The power from the electric motor 31 is transmitted to the screw shaft 35d via the speed reduction mechanism 33, and the screw shaft 35d rotates, so that the rod 35a can be extended and retracted in the horizontal direction (axial direction) in the figure with respect to the case body 34. It is supposed to be. Further, a boot 36 is attached to the actuator 30 so that foreign matter such as dust and water from the outside does not enter.

  Further, the actuator 30 is provided with a stroke sensor 38 for detecting the position (expansion / contraction amount) of the rod 35a. The stroke sensor 38 includes, for example, a magnet and can detect the position using magnetism. Thus, by detecting the position using the stroke sensor 38, the steering angle (toe angle) of the toe-in and toe-out of the rear wheels 2L and 2R can be individually detected with high accuracy.

  In the actuator 30 configured in this manner, the ball joint 16 provided at the distal end of the rod 35a is rotatably connected to the wheel side arm 13b (see FIG. 3) of the trailing arm 13, and the base end of the case main body 34 is connected. Is connected to the cross member 12 (see FIG. 3) in a freely rotatable manner. When the screw shaft 35d is rotated by the power of the electric motor 31 and the rod 35a extends (left direction in FIG. 4), the wheel side arm 13b is pressed outward in the vehicle width direction (left direction in FIG. 3), and the rear wheel 2L When the vehicle turns leftward and the rod 35a contracts (rightward in FIG. 4), the wheel side arm 13b is pulled inward in the vehicle width direction (rightward in FIG. 3), and the rear wheel 2L turns rightward. .

  The place where the ball joint 16 of the actuator 30 is attached is not limited to the wheel side arm 13b as long as the toe angle of the rear wheel 2L can be changed, such as a knuckle. In the present embodiment, the rear wheel steering devices 120L and 120R are shown as examples applied to a semi-trailing arm type independent suspension type suspension. However, the present invention is not limited to this, and other suspension type suspension devices may be used. It can also be applied to suspensions.

The actuator 30 is integrally configured with a rear wheel steering drive control ECU 37. The rear wheel steering drive control ECU 37 is configured to be fixed to the case body 34 of the actuator 30 and connected to the stroke sensor 38 via a connector or the like.
The rear wheel steering drive control ECU 37 is supplied with electric power from a power source such as a battery (not shown) mounted on the vehicle. The steering control ECU 130 and the motor drive circuit 23 are also supplied with electric power from a power source such as a battery (not shown) in a separate system.

4). Functional Configuration of Steering Control ECU Next, functions of the steering control ECU will be described with reference to FIGS.
FIG. 5 is a functional block diagram of the entire steering control ECU showing the functional relationship between the steering control ECU and the rear wheel steering drive control ECU, and FIG. 6 is a diagram showing the characteristics of the base signal calculation unit and the damper compensation signal calculation unit. 7 is a detailed functional block diagram of the yaw rate feedback torque correction calculation unit in FIG. 5, and FIG. 8 is a diagram showing characteristics of the yaw rate feedback torque correction calculation unit.

The steering control ECU 130 includes a computer and a program including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a peripheral circuit, and the like, and has functions described in the functional configuration diagram of FIG. Realize.
As shown in FIG. 5, the steering control ECU 130 includes a front wheel turning angle control unit 130a that controls the electric power steering device 110, and a rear wheel turning angle control unit 130b that controls the toe angles of the rear wheels 2L and 2R. .

4.1. Front Wheel Turning Angle Control Unit First, the front wheel turning angle control unit 130a will be described with reference to FIGS.
The front wheel turning angle control unit 130a includes a base signal calculation unit 51, a damper compensation signal calculation unit 52, an inertia compensation signal calculation unit 53, a Q axis (torque axis) PI control unit 54, and a D axis (magnetic pole axis). A PI control unit 55, a two-axis three-phase conversion unit 56, a PWM conversion unit 57, a three-phase two-axis conversion unit 58, an electric motor speed calculation unit 67, and an excitation current generation unit 59 are provided.

The three-phase two-axis converter 58 detects the three-phase currents IU, IV, and IW of the motor 4 (see FIG. 2) detected by the motor drive circuit 23, the D axis that is the magnetic pole axis of the rotor of the motor 4, and the is intended to convert the two axes of the Q axis is an axis rotated 90 electrical degrees with respect to the D-axis, Q-axis current IQ is proportional to the generated torque T _M of the motor 4, D-axis current ID is energized Proportional to current. The motor speed calculator 67 differentiates the angle signal θ of the motor 4 to generate an angular speed signal ω. The excitation current generator 59 generates a target signal for the excitation current of the electric motor 4 (see FIG. 2), and can perform field-weakening control by making the D-axis current and the Q-axis current substantially equal if necessary. .

The base signal calculation unit 51 generates a base signal D _T that serves as a reference for the target signal IM of the output torque T _M ^* from the torque signal T and the vehicle speed signal VS. This signal generation is performed by referring to the base table 51a set in advance by experimental measurement based on the torque signal T and the vehicle speed signal VS, and the base signal stored in the base table 51a in FIG. 6 (a). The function of _DT is shown. When the value of the torque signal T is small, the base signal calculation unit 51 is provided with a dead band N1 in which the base signal _DT is set to zero. When the value of the torque signal T becomes larger than the dead band N1, the base signal calculation unit 51 is linear with a gain G1. It has an increasing characteristic. Further, the base signal calculation unit 51 has a characteristic that the output increases with the gain G2 within a predetermined torque value range, and the output is saturated when the torque value further increases.
In general, since the load on the road surface (road reaction force) varies depending on the traveling speed, the vehicle has a gain adjusted by the vehicle speed signal VS. The load is heaviest during stationary operation at zero vehicle speed, and the load is relatively light at medium and low speeds. For this reason, the base signal calculation unit 51 sets the gain (G1, G2) to be low and the dead zone N1 to be large as the vehicle speed V increases and increases to increase the manual steering area and to provide road surface information to the driver. To give. That is, as the vehicle speed V increases, a firm feeling of steering torque Ts is given. At this time, it is necessary to perform inertia compensation also in the manual steering region.

Returning to FIG. 5, the damper compensation signal calculation unit 52 is provided to compensate for the viscosity of the steering system and to have a steering damper function for compensating for a decrease in convergence when the vehicle travels at a high speed. This is performed by referring to the damper table 52a based on the angular velocity signal ω. FIG. 6B is a diagram illustrating a characteristic function of the damper table 52a. The compensation value I increases linearly as the rotational speed ω of the electric motor 4 (see FIG. 2) increases, and the compensation value is increased at a predetermined speed. It has characteristics that increase rapidly. Further, as the value of the vehicle speed signal VS is higher, that is, as the vehicle speed V is larger, the gain is increased to attenuate the output torque T _M ^* of the electric motor 4 according to the rotational speed of the electric motor 4, that is, the turning speed. Yes. In other words, the damper compensation signal calculation unit 52 controls the rotation speed of the motor 4 to be suppressed in order to avoid a large current being supplied to the motor 4 to increase the rotation speed. Due to this steering damper effect, the convergence of the steering wheel can be improved and the vehicle characteristics can be stabilized.

Returning to FIG. 5 again, the adder 61 subtracts the output signal (compensation value I) of the damper compensation signal calculation unit 52 from the output signal _DT of the base signal calculation unit 51. The adder 62 The output signal 61 and the output signal of the inertia compensation signal calculation unit 53 are added.
The base signal calculation unit 51, the damper compensation signal calculation unit 52, and the adder 61 perform assist control.

The inertia compensation signal calculation unit 53 compensates for the influence of inertia of the steering system, the torque signal T is calculated by referring to the inertia table 53a, and the transfer function Hf (S) of the stored table is For example,
Hf (S) = 8.88 (S + 140) (S + 65.1) (S + 30.1) (S + 1.77) / {(S + 1730) (S + 209) (S + 37.1) (S + 15.6)}
It is.

Further, the inertia compensation signal calculation unit 53 compensates for a decrease in responsiveness due to the inertia of the rotor of the electric motor 4. In other words, when switching the rotation direction from the normal rotation to the reverse rotation or from the reverse rotation to the normal rotation, the electric motor 4 tries to maintain the state by inertia, so the rotation direction is not switched immediately. Therefore, the inertia compensation signal calculation unit 53 performs control so that the switching of the rotation direction of the electric motor 4 coincides with the timing at which the rotation direction of the steering handle 3 is switched. In this manner, the inertia compensation signal calculation unit 53 improves the response delay of the steering due to the inertia and viscosity of the steering system and provides a clean steering feeling.
It is also practical for vehicle characteristics such as front engine front wheel drive (FF), front engine rear wheel drive (FR), recreation vehicle (RV), and sedan, and steering characteristics that vary depending on vehicle conditions such as vehicle speed and road surface. Sufficient properties are imparted.

The output signal IM ₁ of the adder 62 is a Q-axis current target signal that defines the torque of the electric motor 4 (see FIG. 2).
The adder 63 outputs a yaw rate set according to the current front wheel turning angle (also referred to as tire angle) δ, yaw rate γ, etc., output from the yaw rate feedback torque correction calculation unit 72 with respect to the output signal IM ₁ . A yaw rate feedback torque correction value I _Y (hereinafter simply referred to as “correction value I _Y ”) calculated based on the yaw rate γ and the vehicle speed V is subtracted to reflect the gain, and the output signal IM ₂ is subtracted. The result is output to the adder 64.
A detailed description of the yaw rate feedback torque correction calculation unit 72 will be given later.

The adder 64 subtracts the Q-axis current IQ from the output signal IM _2, and generates a deviation signal IE. The Q-axis (torque axis) PI control unit 54 performs P (proportional) control and I (integral) control so that the deviation signal IE decreases.
The adder 65 subtracts the D-axis current ID from the output signal of the exciting current generator 59. The D-axis (magnetic pole axis) PI control unit 55 performs PI feedback control so that the output signal of the adder 65 decreases.

The two-axis three-phase conversion unit 56 converts the two-axis signal of the output signal VQ of the Q-axis (torque axis) PI control unit 54 and the output signal VD of the D-axis (magnetic pole axis) PI control unit 55 into a three-phase signal UU / UV. -Convert to UW. The PWM converter 57 generates a duty signal (DU, DV, DW) that is an ON / OFF signal [PWM (Pulse Width Modulation) signal] having a pulse width proportional to the magnitude of the three-phase signals UU, UV, UW. .
In addition, the angle signal θ of the electric motor 4 (see FIG. 2) is input to the biaxial three-phase conversion unit 56 and the PWM conversion unit 57, and a signal corresponding to the magnetic pole position of the rotor is output.

4.2. Rear wheel turning angle control unit Next, the rear wheel turning angle control unit 130b will be described with reference to FIGS. As shown in FIG. 5, the rear wheel turning angle control unit 130 b includes a front wheel turning angle calculation unit 68, a rear wheel target turning angle diagnosis unit 73, a rear wheel target turning angle calculation unit 71, and a yaw rate feedback torque correction calculation unit 72. Have

4.2.1. Front wheel turning angle calculation unit The front wheel turning angle calculation unit 68 calculates the turning angle δ of the front wheels from the rotation angle output from the resolver 25, and the rear wheel target turning angle calculation unit 71 and the yaw rate feedback torque correction calculation unit. 72.
The rear wheel target turning angle calculation unit 71 calculates the toe of each of the rear wheels 2L and 2R from the vehicle speed signal VS, the turning angle δ of the front wheels 1L and 1R, and the rotational speed ω of the electric motor 4 proportional to the turning angular speed. Generate a target value for the corner. This target value generation is performed by referring to a preset rear wheel turning angle table 71a based on the turning angle δ, the vehicle speed VS, and the rotational speed ω.
In a range where the vehicle speed is a predetermined low speed, a target value of the toe angle of each rear wheel is generated so that the rear wheels 2L and 2R can be easily turned in an opposite phase according to the turning angle δ.

In a high speed range exceeding the predetermined low speed range, when the absolute value of the rotational speed ω is equal to or less than a predetermined value and the turning angle δ is within a predetermined range on the left and right, depending on the turning angle δ The target value of the toe angle of each rear wheel is set in the same phase. That is, the target value of the toe angle of each rear wheel is set so as to reduce the side slip angle β in the lane change. However, when the absolute value of the rotational speed ω exceeds a predetermined value in a high speed range exceeding the predetermined low speed range, or the turning angle δ exceeds a predetermined range on the left and right, the turning angle δ The target value of the toe angle of each rear wheel is set to the opposite phase according to The target value of the toe angle generated by the rear wheel target turning angle calculation unit 71 is input to the yaw rate feedback torque correction calculation unit 72 and the rear wheel turning drive control ECU 37 of each of the rear wheel turning devices 120L and 120R.
It should be noted that the target value of the toe angle generated by the rear wheel target rudder angle calculation unit 71 follows the geometry of Ackerman Jant.

4.2.2. Yaw rate feedback torque correction calculation unit 72
A detailed configuration of the yaw rate feedback torque correction calculation unit 72 will be described with reference to FIG. The yaw rate feedback torque correction calculation unit 72 includes a yaw rate gain calculation unit 72a, a yaw rate feedback torque correction value calculation unit 72b, and a yaw rate feedback map 72c.

Yaw rate gain calculating part 72a, the vehicle speed V, the yaw rate gamma, front wheel steering angle [delta], and on the basis of the failure signal received α from wheel target steering angle diagnostic unit 73 after which later, the rear wheel steering device 120R · calculating a yaw rate gain _{G Y} in failure condition of 120L. The calculation of the yaw rate gain G _Y, by receiving a failure signal alpha, rear wheel steering device 120R · 120L is started when it is determined that the failure condition, the vehicle speed V, the yaw rate γ and the front wheel of the rolling This is performed based on the steering angle δ. In other words, the yaw rate gain calculating section 72a, in order to determine the yaw rate target in failure state, while changing the vehicle speed V as appropriate, to calculate the yaw rate gain G _Y from the relationship between the front wheel turning angle δ and the yaw rate gamma. Calculated yaw rate gain G _Y is outputted to the yaw rate feedback torque correction value calculating section 72b, is used to calculate a later-described correction value I _Y. Further, the calculated yaw rate gain G _Y is outputted to the yaw rate feedback map 72c, it is used to create and update the map.

The yaw rate feedback torque correction value calculation unit 72b is based on the vehicle speed V, the yaw rate γ, the yaw rate gain G _Y , and the failure signal α. The yaw rate feedback torque correction value I acts as a reaction force of the assist force by the electric power steering device 110. _Y is calculated. The calculation of the yaw rate feedback torque correction value I _Y is started when it is determined that the rear wheel steering devices 120R and 120L are in a failure state by receiving the failure signal α, and the vehicle speed V, the yaw rate γ, It is performed on the basis of the yaw rate gain G _Y. That is, the yaw rate feedback torque correction value calculation unit 72b is input to correct the torque of the electric motor 4 (see FIG. 2) defined by the output signal IM ₁ (see FIG. 5) according to the failure state. For the yaw rate γ, the yaw rate feedback torque correction value I _Y is calculated with reference to the yaw rate feedback map 72c determined according to the vehicle speed V. The calculated yaw rate feedback torque correction value I _Y is output to the adder 63 as a torque correction current of the electric motor 4 (see FIG. 2).

The yaw rate feedback map 72c defines the correspondence between the yaw rate γ and the yaw rate feedback torque correction value I _Y by the yaw rate gain G _Y and the vehicle speed V. FIG. 8 shows an example of the characteristics of the yaw rate feedback torque correction calculation unit 72 that defines the corresponding relationship.

In FIG. 8A, within a predetermined range including the origin O, the yaw rate feedback torque correction value I _Y increases linearly with a predetermined slope as the yaw rate γ increases in the positive direction. The yaw rate gain _GY is a value that determines the inclination. The positive direction of the yaw rate γ means that when the cornering vehicle is viewed from above, the direction of the speed at which the rotation angle changes in the turning direction of the vehicle is the same as the direction of the change in the rotation angle. It means that the speed is increasing.
When the yaw rate γ increases in the positive direction and exceeds a predetermined range, the yaw rate feedback torque correction value I _Y is set to maintain a constant value without increasing. By setting in this way, excessive correction to the torque of the electric motor 4 (see FIG. 2) is suppressed, and the function of assist control by the power steering device 110 is ensured.

The slope of the straight line in FIG. 8A increases as the vehicle speed V increases. That is, the yaw rate feedback torque is set so as to increase as the vehicle speed V increases. Thus set, when the vehicle is traveling at high speed, in order to emphasize driving stability, by increasing the yaw rate feedback torque correction value I _Y as a reaction force of the torque of the electric motor 4 (see FIG. 2) Thus, the assist force by the power steering device 110 is reduced, and the steering of the steering handle 3 (see FIG. 1) is increased. When the vehicle is traveling at a low speed, in order to emphasize the steering feeling of the steering handle 3 (see FIG. 1), the correction value _IY is decreased to increase the assist force by the power steering device 110, and the steering operation is performed. Lightly steer the direction handle 3 (see FIG. 1).

In conditions of a vehicle speed V, the yaw rate gain G _Y in a state where the rear wheel steering device 120R · 120L is defective is not defective, the yaw rate gain G in normal state (see FIG. 8 (b)) _When it becomes larger than _Y0 , the yaw rate feedback torque is increased as shown in (A) of FIG. 8B to increase the running stability of the vehicle. Yaw rate gain G _Y in a state where the failure to opposition, not defective, when it becomes smaller than the yaw rate gain G _Y0 in normal (see FIG. 8 (b)), FIG. 8 (b As in (B), the yaw rate feedback torque is reduced and the steering force is reduced to improve operability (maneuverability).

4.2.3. Rear wheel target turning angle diagnosis unit Next, the rear wheel target turning angle diagnosis unit 73 will be described. When the rear wheel target turning angle diagnosis unit 73 receives the failure signal α from the self-diagnosis unit 81d (see FIG. 9), which will be described later, of the rear wheel turning drive control ECU 37 of the rear wheel turning devices 120L and 120R, the rear wheel turning device It is determined that 120R and 120L are in a failure state. Then, the rear wheel target turning angle diagnosis unit 73 performs a correction calculation of the yaw rate feedback torque together with the failure signal α to the yaw rate feedback torque correction calculation unit 72 according to the determination, and a correction signal (correction value I _Y ) is commanded to be output. In addition, the rear wheel target turning angle diagnosis unit 73 transmits the failure signal α to the base signal calculation unit 51, and performs calculation related to the base signal D _T according to the failure state of the rear wheel turning devices 120R and 120L. It is possible.

4.3. Rear wheel steering drive control ECU
Next, details of the rear wheel steering drive control ECU will be described with reference to the functional block diagram of FIG.
As shown in FIG. 9, the rear wheel steering drive control ECU 37 has a function of driving and controlling the actuator 30, and includes a control unit 81 and an electric motor drive circuit 83. Each rear wheel steering drive control ECU 37 is connected to the steering control ECU 130 via a communication line, and is also connected to the other rear wheel steering drive control ECU 37 via a communication line.

The control unit 81 includes a CPU, a RAM, a ROM, and the like, and includes a target current calculation unit 81a, a correction current setting unit 81b, an electric motor control signal generation unit 81c, and a self-diagnosis unit 81d.
The target current calculation unit 81a calculates a target current signal based on the signal of the target value of the toe angle of the rear wheel 2L (or the rear wheel 2R) input from the rear wheel target turning angle calculation unit 71 of the steering control ECU 130. And it outputs to the motor control signal generation part 81c via the adder 81e. The target current signal is a current signal necessary for setting the actuator 30 to a desired operation amount (the amount of expansion / contraction that makes the rear wheels 2L and 2R a desired toe angle), and is supplied to the correction current setting unit 81b as a reference signal. Is also entered.
Based on the toe angle target value signal, the position information input from the stroke sensor 38, and the target current signal as a reference signal, the correction current setting unit 81b obtains the target current signal from the deviation from the toe angle indicated by the target current. A correction current signal for correction is output to the adder 81e. The adder 81e subtracts the corrected current signal from the target current signal, and outputs the corrected target current signal to the electric motor.
In this way, by correcting the target current signal from the target current calculation unit 81a, the current value required for turning the rear wheel 2L (or 2R) becomes the vehicle speed V, the road surface environment, the vehicle motion state, the tire wear state, and the like. It is possible to feed back the change according to the value and control to set the target toe angle.

The motor control signal generation unit 81 c receives the target current signal from the target current calculation unit 81 a via the adder 81 e and outputs a motor control signal to the motor drive circuit 83. This electric motor control signal is a signal including the current value supplied to the electric motor 31 and the direction in which the electric current flows.
The motor drive circuit 83 is configured by a FET (Field Effect Transistor) bridge circuit or the like, and applies a motor voltage to the motor 31 based on a motor control signal.

  Further, as shown in FIG. 9, in the all-wheel steering device 100 for a vehicle according to the present embodiment, the self-diagnosis unit 81 d of the control unit 81 includes the position information of the stroke sensor 38, the signal of the state of the motor drive circuit 83, The target current signal from the calculation unit 81a and the correction current signal from the correction current setting unit 81b are received, and the failure signal α from the other rear wheel steering drive control ECU 37 to which the user does not belong is received. Check if it is not. That is, while receiving and monitoring the signal which shows whether the electric motor 31 and the electric motor drive circuit 83 corresponding to own rear wheel steering drive control ECU37 are operating | moving soundly, the other rear wheel steering drive control ECU37 is sent. A signal indicating whether or not the corresponding electric motor 31 or electric motor drive circuit 83 is operating soundly is monitored. From the monitored signal, the self-diagnosis unit 81d is in a failure state in which at least one of the motor 31, the stroke sensor 38, the motor drive circuit 83, the target current calculation unit 81a, or the correction current setting unit 81b is not operating soundly. If it judges, self-diagnosis part 81d will send failure signal alpha to self-diagnosis part 81d of the other rear-wheel steering drive control ECU37 which is not rear-wheel steering drive control ECU37 to which it belongs. Further, the failure signal α is transmitted to the rear wheel target turning angle diagnosis unit 73 of the steering control ECU 130 through the signal line. For example, the failure state that is not soundly moving as determined by the self-diagnosis unit 81d is, for example, a state in which the toe angle indicated by the stroke sensor 38 is more than a predetermined value with respect to the toe angle corresponding to the target current signal Refers to a state in which has continued for a predetermined time. Such a state may occur due to a decrease in the steering function of the actuator 30 due to overheating of the electric motor 31 or the like.

  In the present embodiment, the rear wheel steering drive control ECU 37 calculates the target current, is configured integrally with the actuator 30, and is disposed separately from the steering control ECU 130, thereby detecting the detected value (position) from the stroke sensor 38. The position control and current control feedback processing can be performed in the rear wheel steering drive control ECU 37 without returning the information to the steering control ECU 130. Therefore, since a feedback loop is formed only on the rear wheel steering devices 120L and 120R, it is possible to set according to the variation of each actuator 30 (it is not necessary to set according to the steering control ECU 130), and processing It becomes possible to increase the speed. That is, the steering control ECU 130 only outputs a signal of the target toe angle without giving an instruction as to how much the rear wheel steering drive control ECU 37 wants to move, so that the load on the steering control ECU 130 is minimized. It becomes possible to. This also facilitates replacement with the rear wheel steering drive control ECU 37 having the electric motor drive circuit 83 corresponding to the actuator 30 having the steering force according to the type of vehicle.

  Further, when the electric motor 31 of the actuator 30 and the steering control ECU 130 are connected, the feedback loop becomes very long, and there is a problem that the phase delay becomes large due to the length of the feedback loop and the control accuracy is lowered. On the other hand, in the present embodiment, since the control unit 81 of the rear wheel steering drive control ECU 37 can calculate the target current, the feedback loop can be minimized and the control accuracy can be improved. become.

5. Summary As described above, according to the present embodiment, in the vehicle to which the all-wheel steering device 100 using the electric power steering device 110 is applied, the rear wheel steering devices 120R and 120L are in a failed state and the vehicle is not Even if the vehicle becomes stable, the vehicle can be stabilized by performing the assist control according to the failure state by the electric power steering device 110. In the yaw rate feedback torque correction calculating unit 72 calculates the yaw rate gain G _Y when the rear wheel steering device 120R · 120L is in a failure state previously learned, the yaw rate feedback torque calculated by using the yaw rate gain G _Y This is because the correction value I _Y is input to the adder 63 and is controlled so as to act as a reaction force of the assist force by the electric power steering device 110.

In particular, in a vehicle that originally has a high yaw rate gain, if the steering input of the steering handle 3 (see FIG. 1) is increased, a larger yaw rate is generated and the vehicle is likely to be unstable. This is even more so if you are in a failed state. Therefore, by increasing the yaw rate gain G _Y that determines the yaw rate feedback torque correction value I _Y that acts as a reaction force of the assist force by the electric power steering device 110, the assist force is suppressed and the steering handle 3 (see FIG. 1) is controlled. By reducing the steering input, the vehicle can be stabilized even in such a vehicle.

  In addition, although the above-mentioned form is the best thing for implementing this invention, it is not the meaning limited to this form. Therefore, various modifications can be made to the implementation form without departing from the scope of the present invention.

  For example, instead of correcting the auxiliary torque using the correction value of the feedback torque related to the yaw rate of the vehicle in the failed state as in the above embodiment, the vehicle characteristics such as the lateral acceleration and the side slip angle of the vehicle in the failed state The auxiliary torque may be corrected using a feedback torque correction value relating to a parameter that represents

  The determination that the rear wheel steering devices 120R and 120L are in a failure state in the yaw rate feedback torque correction calculation unit 72 is generated not only by the reception of the failure signal α but also by the rear wheel target turning angle calculation unit 71. The determination may be made using the target value of the toe angle. That is, when receiving the failure signal α, if the toe angle set by the rear wheel steering devices 120R and 120L does not reach the target value, it may be determined that the vehicle is in a failure state.

1 is a schematic view of a four-wheel vehicle to which an all-wheel steering device according to an embodiment is applied. It is a block diagram of an electric power steering device. It is a lineblock diagram of the rear wheel steering device on the left rear wheel side. It is a block diagram of the actuator of a rear-wheel steering apparatus. It is a functional block diagram of the whole steering control ECU which also shows the functional relationship between steering control ECU and rear-wheel steering drive control ECU. It is a figure which shows the characteristic of a base signal calculating part and a damper compensation signal calculating part. It is a detailed functional block diagram of a yaw rate feedback torque correction calculation unit. It is a figure which shows the characteristic of a yaw rate feedback torque correction calculating part. It is a functional block diagram of rear-wheel steering drive control ECU.

Explanation of symbols

1L, 1R Front wheel 2L, 2R Rear wheel 3 Steering handle 4 Electric motor S _GS Lateral acceleration sensor S _T Steering torque sensor S _V Vehicle speed sensor S _Y Yaw rate sensor 11 Rear side frame 12 Cross member 13 Trailing arm 13a Car body side arm 13b Wheel side Arm 13c Rotating shaft 16, 17 Ball joint 23 Electric motor drive circuit 30 Actuator 31 Electric motor 33 Deceleration mechanism 34 Case main body 35 Feed screw part 35a Rod 35b Screw groove 35c Nut 35d Screw shaft 36 Boot 37 Rear wheel steering drive control ECU
38 Stroke sensor 100 All-wheel steering device 110 Electric power steering device 120L, 120R Rear wheel steering device 130 Steering control ECU
130a Front wheel turning angle control unit 130b Rear wheel turning angle control unit 61, 62, 63, 64, 65 Adder 68 Front wheel turning angle calculation unit 71 Rear wheel target turning angle calculation unit 72 Yaw rate feedback torque correction calculation unit 72a Yaw rate Gain calculation unit 72b Yaw rate feedback torque correction value calculation unit 72c Yaw rate feedback map 73 Rear wheel target turning angle diagnosis unit

Claims (1)

An electric power steering device that generates an auxiliary torque according to at least the steering torque and transmits the auxiliary torque to the steering system of the front wheels, and steering of the left and right rear wheels based on at least the turning angle and vehicle speed of the front wheels In an all-wheel steering device for a vehicle comprising a rear wheel steering device for controlling an angle, and a steering control device for controlling the electric power steering device and the rear wheel steering device,
The steering control device includes:
Means for detecting the yaw rate of the vehicle;
Means for determining a failure state of the rear wheel steering device;
Means for calculating a yaw rate gain in the failed state based on the turning angle of the front wheels, the yaw rate, and the vehicle speed ;
Means for calculating a yaw rate feedback torque correction value in the failed state based on the yaw rate, the vehicle speed, and the yaw rate gain in the failed state;
Means for correcting the target value of the auxiliary torque with the yaw rate feedback torque correction value;
An all-wheel steering device for a vehicle, comprising:

Images