JP5189780B2 - Steering system - Google Patents

Description

  The present invention relates to a vehicle steering system.

In the electric power steering apparatus, the electric motor generates an auxiliary torque corresponding to the magnitude of the steering torque, and transmits the auxiliary torque to the steering system to reduce the steering force that the driver steers. A technique is disclosed in which a base current (assist torque) determined by steering torque and vehicle speed is compensated by inertia (inertia) and damping (viscosity) of a steering system, and the motor is controlled using the compensated current as a target current ( (See Patent Documents 1 and 2).
Patent Document 3 discloses a technique for an all-wheel independent steering device that independently controls the operation of all traveling wheels based on the operation angle of the steering wheel and the vehicle speed.

  The characteristics of damping, inertia, and base current described in Patent Document 1 are calculated using an inertia table having a base table, a damper table, and a substantially differential characteristic. Here, a method for setting each table, which is a function of the steering torque, the vehicle speed, and the motor angular velocity, will be considered. The base table lowers the gain as the vehicle speed increases, increases the dead zone, increases the manual steering area, and gives the driver road surface information. In addition, the inertia table is used to improve the response delay of the steering due to the inertia and viscosity of the electric motor, thereby providing a clean steering feeling.

  In the damping control, the road surface reaction force decreases during high-speed traveling, so that the movement of the electric motor at a high rotational speed is suppressed and controlled to give a sense of stability to the steering feeling. For this purpose, the damping control performs a correction for attenuating the target current with a compensation value corresponding to the damping gain.

However, in the conventional electric power steering apparatus, since the damping gain is set based on the turning angle of the front wheel, the rear wheel is turned corresponding to the turning of the front wheel in a vehicle capable of turning the rear wheel. When steered, there is a difference between the yaw rate generated in the vehicle and the damping correction. As a result, the driver may feel an unnatural steering feeling.
JP 2002-59855 A (FIG. 2) Japanese Patent Laid-Open No. 2000-177615 (FIG. 2) Japanese Examined Patent Publication No. 6-47388 (FIG. 2)

  Accordingly, an object of the present invention is to provide a steering system capable of realizing a natural steering feeling even when the rear wheels are steered.

In order to solve the above-mentioned problem, an invention according to claim 1 is directed to 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; A toe angle changing device capable of changing the toe angles of the left and right rear wheels based on a turning angle and a vehicle speed; and the steering control device for controlling the electric power steering device and the toe angle changing device. The control device includes auxiliary torque calculation means for calculating a target value of the auxiliary torque, and a target signal for driving the electric motor output from the auxiliary torque calculation means is determined based on the toe angle of the rear wheel. The steering system is corrected with the compensation value calculated by the steering control device. When the vehicle equipped with the steering system turns, at least when the rear wheels outside the turn toe out, the compensation value is set larger than when at least the rear wheels outside the turn toe in, and the compensation value Is a signal that realizes a steering damper function by being subtracted from the base signal serving as a reference of the target signal as the angular speed of the electric motor increases and the rate of change relative to the change in angular speed increases as the vehicle speed increases. Features.

  According to the first aspect of the present invention, when the rear wheel outside the turn is toe-out, the target signal for driving the motor can be corrected with a larger compensation value than when the rear wheel outside the turn is toe-in.

The invention according to claim 2, before Symbol steering system calculates the compensation value, a correction operation unit for outputting a reaction force correction instruction signal based on the compensation value, abnormality in the toe angle changer An abnormality detection means for detecting occurrence and notifying the correction calculation section, and a path for transmitting the reaction force correction instruction signal calculated by the correction calculation section to the steering control device, the correction calculation section And a blocking means for blocking the transmission of the reaction force correction instruction signal according to the drive signal from. When no abnormality occurs in the toe angle changing device, the steering control device adds or subtracts the reaction force correction instruction signal transmitted through the route to the target signal. When the abnormality calculation means is notified by the correction calculation unit that an abnormality has occurred in the toe angle changing device, the correction calculation unit provides a drive signal to the blocking means to pass the route. And the steering control device does not correct the target signal with the reaction force correction instruction signal.

According to the invention of claim 2 , when the correction calculation unit outputs a reaction force correction instruction signal corresponding to the toe angle of the rear wheel and an abnormality occurs in the toe angle changing device, the reaction force correction instruction signal is controlled by the steering control. Transmission to the device can be blocked.
The invention according to claim 3 is characterized in that the toe angle changing device includes an actuator for independently changing the toe angles of the two rear wheels.

  According to the present invention, it is possible to provide a steering system capable of realizing a natural steering feeling even when the rear wheels are steered.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings as appropriate.

<< First Embodiment >>
FIG. 1 is an overall conceptual diagram of a four-wheel vehicle to which a steering system according to a first embodiment of the present invention is applied, and FIG. 2 is a configuration diagram of an electric power steering device.

As shown in FIG. 1, the steering system 100 includes an electric power steering device 110 that assists the steering by the steering handle 3 that steers the front wheels 1L and 1R by the electric motor 4, and the front wheels 1L and 1R by the electric power steering device 110. Steering for controlling the toe angle changing devices 120L and 120R, the electric power steering device 110, and the toe angle changing devices 120L and 120R that change the toe angles of the rear wheels 2L and 2R independently by the actuator 30 in accordance with the steering angle and the vehicle speed. controller (hereinafter, referred to as steering control ECU) 130, it is configured to include a variety of sensors such as a vehicle speed sensor S _V.

(Electric power steering device)
As shown in FIG. 2, 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 connected by two universal joints (universal joints) 3b. A pinion gear 7 a provided at the lower end of the pinion shaft 7 meshes with the rack teeth 8 a of the rack shaft 8 that can reciprocate in the vehicle width direction, and tie rods 9, 9 are provided at both ends of the rack shaft 8. The left and right front wheels 1L, 1R are connected. With this configuration, the electric power steering apparatus 110 can change the traveling direction of the vehicle when the steering handle 3 is operated.
The pinion shaft 7 is supported by a steering gear box (not shown) 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 an auxiliary steering force for reducing the steering force by the steering handle 3, and a worm gear 5a provided on the output shaft of the electric motor 4 is connected to a pinion shaft. 7 is meshed with a worm wheel gear 5b.
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 electric motor 4 and the electric 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, ω is the angular velocity of the electric motor 4, and T _M is the torque generated by the electric motor 4. Further, the relationship between the generated torque T _M and the output torque T _M ^* that can actually be extracted as output is expressed by the following equation (1).
T _M ^* = T _M − (c _m dθ _m / dt + J _m d ² θ _m / dt ² ) i ² (1)
Here, i is a reduction ratio between the worm gear 5a and the worm wheel gear 5b.
From the equation (1), 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 c _m, and is independent of vehicle characteristics and vehicle conditions. is there.

The 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 T _P applied to the pinion shaft 7, the output of the torque sensor S _T A differential amplifying circuit 21 for amplifying and a vehicle speed sensor S _V for detecting the speed (vehicle speed) of the vehicle are provided.
The steering control ECU 130 of the steering system 100 (see FIG. 1) has an electric power steering control unit 130a (see FIG. 5) which will be described later for driving and controlling the electric motor 4 that is a functional unit of the electric power steering device 110. .

The electric 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 electric power steering control unit 130a (see FIG. 5), A rectangular wave voltage is generated and the electric motor 4 is 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 sensor for detecting a change in magnetoresistance includes a plurality of irregularities at equal intervals in the circumferential direction of a rotor (not shown). Some of them are close to a magnetic rotating body provided with a portion.

Torque sensor S _T is used to detect the pinion torque T _P 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 A detection coil is inserted on the surface of the magnetic film so as to be separated from the pinion shaft 7.
The differential amplifier circuit 21 amplifies the difference in permeability change between the two magnetostrictive 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 a vehicle speed as a pulse number per unit time, and outputs a vehicle speed signal VS.
The steering control ECU 130, the motor drive circuit 23, and each sensor are driven by power (not shown) supplied from a power source such as a battery.
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 toe angle changing devices 120L and 120R.

(Toe angle changing device)
Next, the configuration of the toe angle changing device will be described with reference to FIGS.
FIG. 3 is a plan view showing the toe angle changing device on the left rear wheel side, and FIG. 4 is a schematic sectional view showing the structure of the actuator of the toe angle changing device.
The toe angle changing devices 120L and 120R are respectively attached to the left and right rear wheels 2L and 2R of the vehicle. FIG. 3 shows the toe angle changing device 120L taking the left rear wheel 2L as an example. The toe angle changing device 120L includes an actuator 30 and a toe angle changing control device (hereinafter referred to as a toe angle changing control ECU) 37.
3 shows only the left rear wheel 2L, the actuator 30 and the toe angle change control ECU 37 are also attached to the right rear wheel 2R in the same manner (symmetrical). Incidentally, the steering control ECU 130 and the toe angle change control ECUs 37 and 37 constitute a steering control device of the present invention.

Further, the end portion of the cross member 12 extending 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 in the longitudinal direction of the vehicle body 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 substantially vertical rotation shaft 13c. 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 of the wheel side arm 13b on the front side of the rotating shaft 13c 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. And it has the temperature sensor 31a which detects the coil | winding temperature of a coil, and inputs a detected temperature signal into the self-diagnosis part 81d (refer FIG. 7) mentioned later of toe angle change control ECU37.
The speed reduction mechanism 33 is configured by combining, for example, a two-stage planetary gear (not shown). Here, the self-diagnosis unit 81d and the temperature sensor 31a constitute an abnormality detection means of the present invention.

The feed screw portion 35 is engaged with the rod 35a formed in a cylindrical shape, a nut 35c inserted into the rod 35a to have a cylindrical shape, and a screw groove 35b formed on the inner peripheral side, and the screw groove 35b. The screw shaft 35d supports the rod 35a so as to be movable in the axial direction.
The feed screw portion 35 is accommodated in an elongated, substantially cylindrical case main body 34 together with the speed reduction mechanism 33 and the electric motor 31. A boot 36 is attached to the feed screw 35 side of the case body 34 so as to cover between the end of the case body 34 and the end of the rod 35a, and is exposed from the end of the case body 34. Dust and foreign matter do not adhere to the outer peripheral surface of the rod 35a, and dust, foreign matter and water do not enter the case main body 34 from the outside.

  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. The toe angle of the rear wheel is kept constant even when the motor 31 is not energized and driven by the frictional force of engagement between the screw shaft 35d and the screw groove 35b of the nut 35c.

  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 rear wheels 2L, 2R toe-in and toe-out rudder angles (toe angles) 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. A ball joint 17 provided on the right end in FIG. 4 is rotatably connected to the cross member 12 (see FIG. 3). 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 toe angle changing devices 120L and 120R are shown as examples applied to a semi-trailing arm type independent suspension type suspension, but the present invention is not limited thereto, and other suspension type suspensions are used. It can also be applied to.
For example, it can be realized by incorporating the actuator 30 into a side rod of a double wishbone suspension or a side rod of a strut suspension.

In addition, the actuator 30 is integrally configured with a toe angle change control ECU 37. The toe angle change control ECU 37 is fixed to the case main body 34 of the actuator 30 and connected to the stroke sensor 38 and the temperature sensor 31a via a connector or the like. Further, the toe angle change control ECUs 37 and 37 and the toe angle change control ECU 37 and the steering control ECU 130 are connected by signal lines.
The toe angle changing control ECU 37 is supplied with electric power from a power source such as a battery (not shown) mounted on the vehicle.

(Steering control ECU)
Next, functions of the steering control ECU will be described with reference to FIGS.
FIG. 5 is a schematic configuration diagram of a steering control ECU and a toe angle changing device of the steering system. FIG. 6 is a diagram illustrating characteristics of the base signal calculation unit and the damper compensation signal calculation unit.

The steering control ECU 130 includes a microcomputer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (not shown) and peripheral circuits.
As shown in FIG. 5, the steering control ECU 130 includes an electric power steering control unit 130a that controls the electric power steering device 110 and a rear wheel toe angle control unit 130b that calculates target toe angles of the rear wheels 2L and 2R. .

(Electric power steering controller)
First, the electric power steering control unit 130a will be described with reference to FIG. 2 as appropriate with reference to FIGS.
The electric power steering control unit 130a includes a base signal calculation unit (auxiliary torque calculation unit, target current signal calculation unit) 51, a damper compensation signal calculation unit (auxiliary torque calculation unit, correction value calculation unit) 52, and inertia compensation. A signal calculation unit (auxiliary torque calculation means) 53, a Q-axis (torque axis) PI control unit 54, a D-axis (magnetic pole axis) PI control unit 55, a 2-axis three-phase conversion unit 56, a PWM conversion unit 57, A three-phase two-axis converter 58, an electric motor speed calculator 67, and an excitation current generator 59 are provided.

The three-phase two-axis converter 58 converts the three-phase currents IU, IV, and IW of the electric motor 4 detected by the electric motor drive circuit 23 into the D axis that is the magnetic pole axis of the rotor of the electric motor 4 and the D axis The Q-axis current IQ is proportional to the generated torque T _M of the electric motor 4, and the D-axis current ID is proportional to the excitation current. The motor speed calculator 67 differentiates the angle signal θ of the motor 4 to generate an angular speed signal ω. The exciting current generating unit 59 generates a target signal for the exciting current of the electric motor 4, but 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 ₁ 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 a base table 51a, which has been set in advance by experimental measurement for a vehicle having the same steering function as that of the present embodiment and having a front wheel steering function, based on the torque signal T and the vehicle speed signal VS. FIG. 6A shows a function of the base signal D _T stored in the base table 51a. 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 at a predetermined torque value, 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 _S increases and increases to drive the road surface information with a large manual steering area. Give to the person. That is, a firm feeling of steering torque T _S is given as the vehicle speed V _S increases. At this time, it is necessary to perform inertia compensation also in the manual steering region.

The base signal calculation unit 51 has a backup table 51b. When the toe angle changing devices 120L and 120R are abnormal in accordance with a command from the toe angle changing control diagnosis unit 73 described later, the torque signal T And a vehicle speed signal VS, a base signal (target value) D _{T serving} as a reference for the target signal IM ₁ of the output torque T _M ^* is generated.
In this backup table 51b as well, it is a function of the torque signal T and the vehicle speed signal VS as shown in FIG. 6A, but the gains (G1, G2) for the same vehicle speed are reduced in FIG. Therefore, the setting is such that the gain (G1, G2) is significantly different from the base table 51a, the auxiliary torque is small, and the driver feels abnormal.

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. The steering damper function is realized by referring to the damper table 52a corresponding to the angular velocity ω.
FIG. 6B is a diagram showing a characteristic function of the damper table 52a. The compensation value I increases linearly as the angular velocity ω of the motor 4 increases, and the compensation value I increases rapidly at a predetermined speed. It has characteristics. Further, as the vehicle speed signal VS is larger, the damping gain is increased to attenuate the output torque T _M ^* of the electric motor 4 according to the angular speed ω of the electric motor 4, that is, the turning speed. In other words, when a large current is supplied to the electric motor 4 to increase the angular velocity ω, the damper compensation signal calculation unit 52 controls to suppress the angular velocity ω of the electric motor 4. Due to this steering damper effect, the convergence of the steering wheel 3 can be improved and the vehicle characteristics can be stabilized.
Further, the first embodiment is characterized in that the damper table 52a corresponds to the target toe angle of the rear wheel 2 (see FIG. 1), as will be described in detail later.

Returning to FIG. 5 again, the adder (correction means) 61 subtracts the output signal I of the damper compensation signal calculator 52 from the output signal _DT of the base signal calculator 51. The adder 62 is an adder. The output signal 61 is added to the output signal of the inertia compensation signal calculation unit 53 to obtain an output signal IM ₁ .
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 the inertia of the steering system, and can output an output signal corresponding to the input torque signal T by referring to the inertia table 53a.

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.
Also, it is practically sufficient for vehicle characteristics such as FF (Front engine Front wheel drive), FR (Front engine Rear wheel drive), RV (Recreation Vehicle) and sedan, and steering characteristics that vary depending on vehicle speed, road surface, etc. Steering feeling is given.

The output signal IM ₁ of the adder 62 is a current target signal that defines the torque of the electric motor 4.

The adder 64 subtracts the Q-axis current IQ from the output signal IM ₁ of the adder 62 to generate 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 converter 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 three-phase signals 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 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.

(Rear wheel toe angle controller)
Next, the rear wheel toe angle control unit 130b will be described with reference to FIG. As shown in FIG. 5, the rear wheel toe angle control unit 130 b includes a front wheel turning angle calculation unit 68, a target toe angle calculation unit 71, and a toe angle change control diagnosis unit 73.

The front wheel turning angle calculation unit 68 calculates the turning angle δ of the front wheels 1L and 1R from the angle signal θ output from the resolver 25 (see FIG. 2), and inputs it to the target toe angle calculation unit 71.
The target toe angle calculation unit 71 is based on the vehicle speed signal VS, the turning angle δ and the turning angular velocity obtained by differentiating the turning angle δ (which is proportional to the angular velocity ω of the motor 4 and can be easily obtained). The target toe angles α _TL , α _TR of the rear wheels 2L, 2R are generated, and the toe angle change control ECUs 37, 37 for controlling the change of the toe angles of the left and right rear wheels 2L, 2R are supplied to the target toe angles α _TL , α _TR is input (see FIG. 7). The target toe angles α _TL and α _{TR are} generated based on the turning angle δ, the angular velocity δ ′ of the turning angle δ, and the vehicle speed V _S based on the toe angle table 71a set in advance for each of the left and right rear wheels 2L and 2R. For example, the following equations (2) and (3) are set.
α _TL = K _L (V _S , δ ′, δ) · δ (2)
α _TR = K _R (V _S , δ ′, δ) · δ (3)
Here, K _L (V _S , δ ′, δ) and K _R (V _S , δ ′, δ) are the front and rear wheel steering ratios that depend on the vehicle speed V _S , the turning angle δ, and the angular speed δ ′ of the turning angle. In the range where the vehicle speed is a predetermined low speed, the target toe angles α _TL , α _{TR of the} rear wheels are generated so that the rear wheels 2L, 2R are in reverse phase and easily turn around according to the turning angle δ. The Here, the fact that the rear wheel 2 is in an opposite phase indicates that at least the rear wheel 2 on the outside of the turn toes out when the vehicle V turns.

When the absolute value of the angular velocity δ ′ of the turning angle is equal to or less than a predetermined value and the turning angle δ is within a predetermined range on the left and right, the turning angle is within a high speed range that exceeds the predetermined low speed range. The target toe angles α _TL and α _TR of each rear wheel are set in the same phase according to δ. Here, the fact that the rear wheels 2 are in phase indicates that at least the rear wheels 2 on the outside of the turn toe-in when the vehicle V turns.
However, in a high speed range that exceeds the predetermined low speed range, the absolute value of the angular velocity δ ′ of the turning angle exceeds a predetermined value, or a large turning angle where the turning angle δ exceeds a predetermined range on the left and right In the case of the angle δ, the target toe angles α _TL and α _TR of each rear wheel are set in the opposite phase according to the turning angle δ.
The target toe angles α _TL and α _TR generated by the target toe angle calculation unit 71 do not necessarily follow the Ackermann-Jantt geometry from the viewpoint of turning stability. Further, when the turning angle δ is 0 °, the target toe angles α _TL and α _TR may each be set to a toe-in of 2 °, for example.

(Configuration of steering control ECU)
The steering control ECU 130 (see FIG. 1) is connected to the motor drive circuit 23 of the electric power steering device 110 and the left and right toe angle changing devices 120L and 120R, and controls each of them and is connected to each sensor, and each sensor outputs It is a device that inputs information to be used.

  The toe angle change control diagnostic unit 73 (see FIG. 5) receives an abnormality detection signal from a self-diagnosis unit 81d (see FIG. 7) which will be described later on the toe angle change control ECUs 37 and 37 of the toe angle changing devices 120L and 120R.

(Toe angle change control ECU)
Next, a detailed configuration of the toe angle change control ECU will be described with reference to FIG. FIG. 7 is a configuration diagram of a toe angle changing control ECU of the toe angle changing device.
As shown in FIG. 7, the toe angle change control ECU 37 has a function of controlling the drive of the actuator 30 and includes a control unit 81 and an electric motor drive circuit 83. Each toe angle change control ECU 37 is connected to the steering control ECU 130 via a signal line, and is also connected to the other toe angle change control ECU 37 via a signal line.

The control unit 81 includes a microcomputer (not shown) including a CPU, RAM, ROM, and peripheral circuits, and the like, and includes a target current calculation unit 81a, a motor control signal generation unit 81c, and a self-diagnosis unit (abnormality detection means) 81d. Have.
The target current calculation unit 81a of the toe angle change control ECU 37 on the one (right rear wheel 2R side) obtains the target toe angle α _TR of the rear wheel 2R input from the steering control ECU 130 via the signal line and the stroke sensor 38. Based on the current toe angle α _R of the rear wheel 2R, a target current signal is calculated and output to the motor control signal generator 81c.
The target current calculation unit 81a of the toe angle change control ECU 37 on the other side (left rear wheel 2L side) obtains the target toe angle α _TL of the rear wheel 2L input from the steering control ECU 130 via the signal line and the stroke sensor 38. Based on the current toe angle α _L of the rear wheel 2L, a target current signal is calculated and output to the motor control signal generator 81c.

Here, the target current signal is a current signal necessary for setting the actuator 30 to a desired operation amount at a desired speed (the amount of expansion / contraction to make the rear wheels 2L, 2R desired toe angles α _L , α _R ). It is.
As described above, the target current calculation unit 81a feeds back the current toe angles α _L and α _R to the target toe angles α _TL and α _TR to correct the target current signal, thereby correcting the rear wheel 2L (or 2R). The current value required for turning the vehicle is fed back to changes in the vehicle speed V _S , road environment, vehicle motion state, tire wear state, and the like, so that the target toe angles α _TL and α _TR can be quickly set.

  The motor control signal generator 81 c receives the target current signal from the target current calculator 81 a 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 supplies a motor current to the motor 31 based on a motor control signal.

Further, as shown in FIG. 7, the self-diagnosis unit 81d has a position signal of the stroke sensor 38 of the toe angle changing device 120L or toe angle changing device 120R on the side to which it belongs, a detection signal from a hall element of the motor drive circuit 83, Based on the temperature signal from the temperature sensor 31a and the state monitoring of the target current calculator 81a, it is determined whether or not an abnormal state has been detected.
For example, when the signal from the temperature sensor 31a exceeds a predetermined value, the self-diagnosis unit 81d determines that the winding temperature of the electric motor 31 is abnormal, and determines a predetermined target toe angle α _TL (or target toe angle α _TR ), for example, 0 ° is input to the target current calculation unit 81a. Here, the target toe angle α _TL is a target toe angle for the left rear wheel 2L when an abnormality is detected, and the target toe angle α _TR is a target toe angle for the right rear wheel 2R when an abnormality is detected.

The self-diagnosis unit 81d monitors detection signals from the target current calculation unit 81a and the Hall elements of the motor drive circuit 83, determines whether the actuator 30 is fixed based on the position signal from the stroke sensor 38, and fixes Is determined, the motor drive circuit 83 is instructed to stop power supply to the motor 31, and the current toe angle α _L (or toe angle α _R ) is set to the target toe angle α _TL (or target toe angle) to the target current calculation unit 81a. Enter as angle α _TR ). Then, the abnormal state detection signal and the signal of the mode dealt with are detected by detecting the abnormal state to the self-diagnosis unit 81d of the other toe angle changing control ECU 37.

  As an abnormality detection means, not only the self-diagnosis unit 81d but also a watchdog circuit is provided as a peripheral circuit to monitor the control unit 81. When an abnormality is detected in the control unit 81, the motor drive circuit 83 supplies power to the motor 31. The stop may be instructed, and the self-diagnosis unit 81d of the other toe angle change control ECU 37 may output an abnormal state detection signal.

Further, the self-diagnosis unit 81d checks whether an abnormality detection signal is received from the self-diagnosis unit 81d of the toe angle change control ECU 37 of the toe angle change device 120R (or toe angle change device 120L) on the other side, When the abnormality detection signal is received, the target toe angle α _TL (or the target toe angle α _TR ) is input to the target current calculation unit 81a based on the signal of the handled mode.
That is, the self-diagnosis unit 81d receives and monitors a signal indicating whether or not the toe angle changing device 120L (or toe angle changing device 120R) corresponding to its own toe angle changing control ECU 37 is operating normally. And a signal indicating whether or not the toe angle changing device 120R (or toe angle changing device 120L) corresponding to the other toe angle changing control ECU 37 is operating normally, and either side is abnormal Causes both toe angle change control ECUs 37, 37 to deal with a predetermined same mode.
The self-diagnosis unit 81d transmits an abnormality detection signal to the toe angle change control diagnosis unit 73.

The vehicle V including the steering system 100 including the above components includes a toe angle changing device 120 in addition to the steering of the front wheels 1 by the operation of the steering handle 3 (see FIG. 1) by the driver. The toe angles α _L and α _R of the rear wheels 2L and 2R (see FIG. 1) are changed by (see FIG. 1), and the vehicle V (see FIG. 1) is steered. Hereinafter, the operation of the vehicle V accompanying the operation of the steering handle 3 will be described with reference to FIGS.

When the driver operates the steering handle 3 to steer the front wheel 1, the target of the rear wheels 2L and 2R is determined based on the steering angle δ, the angular velocity δ ′ of the steering angle δ, and the vehicle speed V _S as described above. The toe angles α _TL and α _TR are set, and the toe angles α _L and α _R of the rear wheels 2L and 2R are set to the set target toe angles α _TL and α _TR . FIGS. 8A and 8B show measurement results in a situation where the vehicle V travels in a slalom where the vehicle speed (V _S ) is 100 km / h, and the left and right are continuously turned 10 ° at a rate of 0.5 Hz. (A) is a graph showing the relationship between the turning angle and the yaw rate corresponding to the toe angle of the rear wheel, and (b) is a graph showing the relationship between the turning angle and the steering torque.
As shown by the broken line in FIG. 8 (a), the rear wheels 2L, toe angles of the 2R alpha _L, alpha when _R is set to toe, the rear wheels 2L, toe angles of the 2R alpha _L, alpha _R is 0 ° In this case (shown by a solid line in the figure), the yaw rate with respect to the turning angle δ of the front wheel 1 becomes smaller. That is, the yaw rate gain Gγ indicated by the magnitude of the yaw rate with respect to the turning angle δ is low.

  As described above, the yaw rate gain Gγ is the magnitude of the yaw rate of the vehicle V corresponding to the turning angle δ. Therefore, the lower the yaw rate gain Gγ, the more the yaw rate of the vehicle V with respect to the operation of the steering handle 3 by the driver. The followability will be low.

Here, when the damping control corresponding only to the turning angle δ of the front wheel 1 is executed, the damping control is performed assuming that the toe angles α _L and α _R of the rear wheels 2L and 2R are 0 °. Control is advanced beyond the low yaw rate gain Gγ when the toe angles α _L and α _{R of the} wheels 2L and 2R are set to toe-in.

FIG. 8B shows that when the turning angle δ is changed, the steering torque T _S changes along a trajectory that traces the graph clockwise as indicated by the arrow. As shown in FIG. 8B, when the rear wheel 2 is toe-in (indicated by a broken line in the figure), the toe angles α _L and α _{R of} the rear wheels 2L and 2R are 0 ° (in the solid line in the figure). It becomes a locus on the outer side than in the case of (shown).

Here, consider a case where the turning angle δ rotates in the positive direction. Further, the point A on the broken line and the point B on the solid line have the same steering torque T _S. At this time, the turning angle δ at point B is larger than the turning angle δ at point A. That is, the steering torque T _S corresponding to an arbitrary turning angle δ (point B) when the toe angle of the rear wheel 2 is 0 ° is greater when the rear wheel 2 is toe-in than when the toe angle is 0 °. This corresponds to a small turning angle δ (point A). Point A and point B are points on the locus for steering the turning angle δ in the positive direction, that is, in the direction of increasing the steering angle δ. Therefore, when the rear wheel 2 is toe-in, steering with respect to the change in the turning angle δ is performed. The follow-up of the torque T _S indicates that the phase advances more than when the toe angles α _L and α _R of the rear wheels 2L and 2R are 0 °.

Thus, by tracking the phase of the steering torque T _S with respect to the change of the steering angle δ is shifted, the driver will feel an unnatural steering feeling.

Therefore, in the first embodiment, when the rear wheel 2 is toe-in, a smaller compensation value I is set in the damper table 52a shown in FIG. 5 than when the rear wheel 2 has a toe angle of 0 °. And
That is, when the rear wheel 2 is toe-in and the phase of the steering torque T _S advances with respect to the turning angle δ, it is necessary to delay the phase of the steering torque T _S. Therefore, when the rear wheel 2 is toe-in, as shown in FIG. 6C, the angular velocity ω of the electric motor 4 is set to a smaller compensation value I than when the rear wheel 2 has a toe angle of 0 °. Reduce the effectiveness of damping. FIG. 6C is a diagram illustrating a characteristic function of the damper table at the same vehicle speed V _S.
As shown in FIG. 6 (c), when the rear wheel 2 is toe-in, the increase in the compensation value I accompanying the increase in the angular velocity ω is smaller than when the rear wheel 2 has a toe angle of 0 °. Accordingly, the compensation value I may be set.

On the other hand, when the toe angles α _L and α _{R of} the rear wheels 2L and 2R are set to toe-out, the yaw rate gain Gγ is high.

  As described above, the yaw rate gain Gγ is the magnitude of the yaw rate of the vehicle V corresponding to the turning angle δ. Therefore, the higher the yaw rate gain Gγ, the more the yaw rate of the vehicle V with respect to the operation of the steering handle 3 by the driver. The followability will be high.

Here, when the damping control corresponding only to the turning angle δ of the front wheel 1 is executed as described above, the damping control is performed assuming that the toe angles α _L and α _R of the rear wheels 2L and 2R are 0 °. Therefore, control is performed later than the high yaw rate gain Gγ when the toe angles α _L and α _{R of} the rear wheels 2L and 2R are set to toe-out. That is, as shown in FIG. 8B, when the rear wheel 2 is toe-out (indicated by a one-dot chain line in the figure), the toe angles α _L and α _{R of} the rear wheels 2L and 2R are 0 ° (FIG. 8). (Indicated by the solid line) This is because when the rear wheel 2 is toe-out, the tracking of the steering torque T _S with respect to the change in the turning angle δ has a phase more than when the toe angles α _L and α _R of the rear wheels 2L and 2R are 0 °. It shows that it is late.

As described above, the phase of the follow-up of the steering torque T _S with respect to the change in the turning angle δ shifts, so that the driver feels an unnatural steering feeling.

Therefore, in the first embodiment, when the rear wheel 2 is toe-out, a larger compensation value I is set in the damper table 52a shown in FIG. 5 than when the rear wheel 2 has a toe angle of 0 °. And
That is, when the rear wheel 2 toes out and the phase of the steering torque T _S with respect to the turning angle δ is delayed, the phase of the steering torque T _S needs to be advanced. Therefore, when the rear wheel 2 is toe-out, as shown in FIG. 6C, the angular velocity ω of the electric motor 4 increases the compensation value I than when the toe angle of the rear wheel 2 is 0 °. Increase the effectiveness of damping.
That is, as shown in FIG. 6C, when the rear wheel 2 is toe-out, the increase in the compensation value I accompanying the increase in the angular velocity ω is larger than when the toe angle of the rear wheel 2 is 0 °. The compensation value I may be set according to the characteristics to be performed.

Thus, in the first embodiment, the damper table 52a has a configuration corresponding to the toe angles α _L and α _R of the rear wheels 2L and 2R. Then, by damping control of the steering damper corresponding to the toe angles α _L and α _R of the rear wheels 2L and 2R, when the rear wheel 2 is toe-out when the vehicle V is turning, the electric motor 4 Since the angular velocity ω of the rotor quickly decreases, it is possible to follow the high yaw rate gain Gγ of the vehicle V, and when the rear wheel 2 is toe-in, the angular velocity ω of the rotor of the electric motor 4 gradually decreases. Therefore, an excellent effect of following the low yaw rate gain Gγ of the vehicle V is achieved.

The graph shown in FIG. 6C shows the state transition at the same vehicle speed V _S , and as shown in FIG. 6B, the damping gain increases as the vehicle speed V _S increases. Set.

<< Second Embodiment >>
The second embodiment is characterized by including a reaction force correction control unit that calculates a reaction force correction instruction signal corresponding to the toe angle of the rear wheel.
In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
FIG. 9 is a diagram illustrating a configuration of the steering control ECU according to the second embodiment. As shown in FIG. 9, the steering control ECU 131 includes a reaction force correction control unit 72 in the rear wheel toe angle control unit 131b. The reaction force correction control unit 72 includes a CPU 72a, a computer including a ROM, a RAM, and the like (not shown), a program, peripheral circuits, and the like.

The reaction force correction control unit 72 is connected to the toe angle changing devices 120L and 120R, and receives the toe angles α _L and α _{R of} the rear wheels 2L and 2R. Further, the reaction force correction control unit 72 receives the angular velocity ω of the electric motor 4 and the turning angle δ of the front wheels 1. The reaction force correction control unit 72 calculates a compensation value based on the input toe angles α _L and α _R , the angular velocity ω, and the turning angle δ, and uses the calculated compensation value as a reaction signal such as an electric signal. The force correction instruction signal IM _R is output.

FIG. 10A is a block diagram showing a mode in which a reaction force correction instruction signal is added from the target signal. As shown in FIG. 10A, in the electric power steering control unit 130a, the base signal calculated by the base signal calculation unit 51 based on the torque signal T and the vehicle speed signal VS is converted into an inertia compensation signal calculation unit 53, The target signal IM ₁ is output after being corrected by the damper compensation signal calculation unit 52. Then, in the adder (correction means) 63, a reaction force correction instruction signal IM _R the reaction force correction control unit 72 is output is added or subtracted, the output signal IM ₂ is output.

FIG. 10B is a block diagram illustrating a configuration of the reaction force correction control unit. As shown in FIG. 10B, the reaction force correction control unit 72 generates the reaction force correction instruction signal IM _R based on the angular velocity ω of the electric motor 4 and the toe angles α _L and α _R of the rear wheels 2L and 2R. Has a function to output.
Here, a large motor current is supplied to the electric motor 4, as the angular velocity ω becomes faster, in order to significantly attenuate too effectiveness of the assist, the reaction force correction instruction signal IM _R may be large enough angular velocity ω increases.
Therefore, in the second embodiment, the compensation value I constituting the reaction force correction instruction signal IM _R is a value proportional to the angular velocity ω. That is, the proportional constant as a damping gain G _D, the compensation value I is shown by the following formula (4).
I = G _D · ω (4)

To achieve the above functions, reaction force modification control section 72 includes an integration means 72b for integrating an angular velocity ω and the damping gain G _D.
The integrating means 72b can be realized by being incorporated in a program for driving the CPU 72a of the reaction force correction control unit 72, for example. In that case, the angular velocity ω may be input to the CPU 72a of the reaction force correction control unit 72. Incidentally, the damping gain G _D, as described later, may be configured to calculate at CPU72a the reaction force modification control section 72.

Further, the yaw rate gain Gγ increases as the rear wheels 2L, 2R largely toe out, and the yaw rate gain Gγ decreases as the rear wheels 2L, 2R steered to the front wheel 1 in the same phase increase. The value I may be associated with a larger value as the toe angles α _L and α _R of the rear wheels 2L and 2R are larger. That may be increased damping gain G _D. Therefore, the reaction force modification control section 72, 2L, toe angle alpha _L of 2R, the conversion unit 72c for converting the alpha _R to a predetermined damping gain G _D provided.

In the second embodiment, as shown in FIG. 10C, the damping gain G _D has a value from 0 to the maximum value MAX, and the toe angles α _L and α _{R of the} rear wheels 2L and 2R are 0 ° damping gain G _D is zero when the rear wheels 2L, toe angle alpha _L of 2R, when alpha _R is the maximum of the toe angle alpha _MAX, damping gain G _D was set to be MAX. The damping gain G _D is the rear wheel 2L, toe angles of the 2R alpha _L, and a value proportional to the alpha _R. Then, the conversion unit 72c has a function of outputting the wheel 2L, toe angles of the 2R alpha _L, damping gain G _D corresponding to alpha _R after being entered. Here, the value of the maximum value MAX of the damping gain G _D is not a value that is limited, for example, the rear wheels 2L, toe angles of the 2R alpha _L, when alpha _R is the maximum of the toe angle alpha _MAX, steering feeling May be set to a damping gain G _D that is optimal.
The conversion means 72c can be realized by being incorporated in a program for driving the CPU 72a of the reaction force correction control unit 72, for example. In this case, the toe angles α _L and α _R of the rear wheels 2L and 2R may be input to the CPU 72a of the reaction force correction control unit 72.

Thus, the compensation value I is a value proportional to the angular velocity ω and the damping gain G _D, and the damping gain G _D, it was a value proportional to the toe angle of the rear wheels 2, the reaction force modification control section 72 The calculation in the CPU 72a is simplified, and the load on the CPU 72a of the reaction force correction control unit 72 can be reduced.

The reaction force correction control unit 72 converts the calculated compensation value I into an electric signal such as a current and outputs it as a reaction force correction instruction signal IM _R. Then, as shown in FIG. 10 (a), the electric power steering control unit 130a adds or subtracts the reaction force correction instruction signal IM _R to the target signal IM ₁ by the adder 63 to obtain the output signal IM ₂ . Generate.

That is, when the rear wheel 2 is toe-in, the reaction force correction instruction signal IM _R is added to the target signal IM ₁ to reduce the effect of damping, and when the rear wheel 2 is toe-out, the target signal by subtracting the reaction force correction instruction signal IM _R from IM _1, it may be increased effectiveness of damping.

Incidentally, the correlation between the toe angle and the damping gain G _D of wheel 2 after the is merely an example, and in consideration of the motion characteristics of the vehicle V, may be appropriately set.

  For example, the correlation between the compensation value I and the angular velocity ω shown in FIG. 6C may be converted into data and stored in a storage device (not shown) provided in the reaction force correction control unit 72. Then, the reaction force correction control unit 72 may be configured to calculate the compensation value I by reading the compensation value I corresponding to the input toe angle of the rear wheel 2.

  As described above, by damping control of the steering damper, when the rear wheel 2 is toe-out when the vehicle V turns, the angular speed ω of the rotor of the electric motor 4 is quickly reduced. When the rear wheel 2 is toe-in, the angular velocity ω of the rotor of the electric motor 4 gradually decreases, so that it follows the low yaw rate gain Gγ of the vehicle V. An excellent effect equivalent to that of the first embodiment can be achieved.

In the second embodiment, the reaction force correction instruction signal IM _R is calculated based on the toe angles α _L and α _R of the rear wheels 2L and 2R input from the toe angle changing device 120. As a result, for example, even if the rear wheels 2L and 2R are not set to the same toe angle as the target toe angles α _TL and α _TR , they correspond to the actual toe angles α _L and α _R of the rear wheels 2L and 2R. A reaction force correction instruction signal IM _R is output. Therefore, the driver can obtain an excellent effect that the steering feeling corresponding to the behavior of the vehicle V can be obtained.

  In addition, as shown in FIG. 11, a path 72e connecting the reaction force correction control unit 72 and the adder 63 is provided with a blocking means 72d such as a relay driven by a drive signal output from the reaction force correction control unit 72. Also good. For example, when it is detected that an abnormality has occurred in the toe angle changing device 120, the path 72e may be blocked.

  As described above, the toe angle change control ECU 37 includes the self-diagnosis unit 81d, and the self-diagnosis unit 81d can detect that an abnormality has occurred in the toe angle change device 120. Therefore, the abnormality detection signal generated by the self-diagnosis unit 81d is input to the CPU 72a of the reaction force correction control unit 72. Then, the reaction force correction control unit 72 that has received the abnormality detection signal outputs a drive signal to drive the blocking means 72d, and blocks the path 72e between the reaction force correction control unit 72 and the adder 63.

Thus, when an abnormality occurs in the toe angle changing device 120, the reaction force correction instruction signal calculated by the reaction force correction control unit 72 is cut off by blocking the path between the reaction force correction control unit 72 and the adder 63. do not enter the IM _R to the adder 63. Therefore, when an abnormality occurs in the toe angle changing device 120, the reaction force correction instruction signal IM _R is not added to the target signal IM ₁ .

When an abnormality occurs in the toe angle changing device 120, the toe angles α _L and α _R set for the rear wheels 2L and 2R are different from the target toe angles α _TL and α _TR calculated by the target toe angle calculating unit 71. It is conceivable that the toe angle is set. Then, if the correction instruction signal IM _R is calculated based on the toe angles α _L and α _R different from the target toe angles α _TL and α _TR set by the toe angle changing device 120 in which an abnormality has occurred, it is unnatural for the driver. May give a good steering feeling.

When an abnormality occurs in the toe angle changing device 120, the path between the reaction force correction control unit 72 and the adder 63 is blocked, and the reaction force correction instruction signal IM _R is not added to the target signal IM _1. Thus, a steering feeling equivalent to that of the power steering without the reaction force correction control unit 72 is obtained, and an excellent effect that the unnaturalness of the steering feeling given to the driver can be reduced is achieved.

The reaction force correction control unit 72 to which the abnormality detection signal is input may be configured to always set the output reaction force correction instruction signal IM _R to “0”. If comprised in this way, the influence at the time of abnormality generate | occur | producing in the toe angle changing apparatus 120 can be excluded, without providing the interruption | blocking means 72d.
<Modification>

Further, as a modified example, a case where the rear wheels are steered to the same phase or the opposite phase corresponding to the steering of the front wheels can be considered. In a vehicle V shown in Figure 1, when the rear wheel 2 is steered front wheels 1 and opposite phase, by increasing the reaction force against the motor 4 to increase the damping gain G _D, the angular velocity of the electric motor 4 omega, i.e., rolling The output torque T _M ^* of the electric motor 4 is greatly attenuated according to the steering speed. In other words, as shown in FIG. 6C, the increase rate of the compensation value I is increased to suppress the increase in the output torque T _M ^* of the electric motor 4, and the angular velocity ω of the rotor of the electric motor 4 is quickly reduced.
On the other hand, when the rear wheel 2 is steered to the front wheel 1 and the same phase is to reduce the damping gain G _D reduces the damping reaction force against the motor 4, the angular velocity of the electric motor 4 omega, i.e., the motor according to the steering speed 4 to decrease the attenuation of the output torque T _M ^* . In other words, as shown in FIG. 6C, the output torque T _M ^* of the electric motor 4 is increased by suppressing the increasing rate of the compensation value I, and the angular velocity ω of the rotor of the electric motor 4 is changed to the opposite phase. Decrease more slowly than the case.

Further, when the vehicle V is turning, for example, a configuration in which the toe angles α _L and α _R set for the left and right rear wheels 2L and 2R are different, such as changing the toe angle only for the rear wheel 2 outside the turn, is also conceivable.
For example, in the configuration in which the toe angle is changed only for the rear wheel 2 on the outside of the turn, the effect of the change in the toe angle on the yaw rate gain Gγ is considered to be small compared to the case where both the rear wheels 2 are steered. it may be set small damping gain G _D than when both wheels of the wheel 2 is steered.

  As described above, even when the rear wheel 2 is steered in response to the steering of the front wheel 1, the rear wheel 2 is toe-in when the rear wheel 2 is steered in the same phase as the front wheel 1. When the rear wheel 2 is steered in the opposite phase to the front wheel 1, the damping control is performed with the same characteristics as when the rear wheel 2 is toe-out. Steering feeling can be given.

1 is an overall conceptual diagram of a four-wheel vehicle including a steering system according to an embodiment of the present invention. It is a block diagram of the electric power steering apparatus of a steering system. It is a block diagram of the toe angle changing device on the left rear wheel side of the steering system. It is a schematic sectional drawing which shows the structure of the actuator of a toe angle change apparatus. 1 is a schematic configuration diagram of a steering control ECU and a toe angle changing device of a steering system. It is a figure which shows the characteristic of a base signal calculating part and a damper compensation signal calculating part. It is a block diagram of the toe angle change control ECU of the toe angle changing device. (A) is a graph showing the relationship between the steering angle and the yaw rate corresponding to the toe angle of the rear wheel, and (b) shows the relationship between the steering angle and the steering torque when the vehicle is driven in slalom. It is a graph. It is a figure which shows the structure of steering control ECU concerning 2nd Embodiment. (A) is a block diagram which shows the aspect which adds a reaction force correction instruction signal to a target signal, (b) is a block diagram which shows the structure of a reaction force correction control part. It is a figure which shows having provided the interruption | blocking means in the path | route between a reaction force correction control part and an adder.

Explanation of symbols

1 (1L, 1R) Front wheel 2 (2L, 2R) Rear wheel 3 Steering handle 4 Electric motor (steering system)
5a Worm gear (steering system)
5b Worm wheel gear (steering system)
7 Pinion shaft (steering system)
8 Rack shaft (steering system)
8a Rack teeth (steering system)
9 Tie rod (steering system)
31a Temperature sensor (abnormality detection means)
37 Toe angle change control ECU (steering control device)
51 Base signal calculation unit (auxiliary torque calculation means, target current signal calculation means)
52 Damper compensation signal calculation unit (auxiliary torque calculation means, correction value calculation means)
53 Inertia compensation signal calculation unit (auxiliary torque calculation means)
61, 63 Adder (correction means)
68 Front wheel turning angle calculation unit 71 Target toe angle calculation unit 72 Reaction force correction control unit (correction calculation unit)
72d blocking means 72e route 81 control part 81d self-diagnosis part (abnormality detection means)
DESCRIPTION OF SYMBOLS 100 Steering system 110 Electric power steering apparatus 120 (120L, 120R) Toe angle change apparatus 130 Steering control ECU (steering control apparatus)
IM _R reaction force correction instruction signal V Vehicle

Claims (3)

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;
A toe angle changing device capable of changing the toe angles of the left and right rear wheels based on at least the steering angle of the front wheels and the vehicle speed;
A steering control device for controlling the electric power steering device and the toe angle changing device,
The steering control device has auxiliary torque calculation means for calculating a target value of the auxiliary torque, and outputs a target signal for driving the electric motor output from the auxiliary torque calculation means,
A steering system that corrects with a compensation value calculated by the steering control device based on a toe angle of the rear wheel,
When the vehicle equipped with the steering system turns, at least when the rear wheels outside the turn toe out, the compensation value is made larger than at least when the rear wheels outside the turn toe in, the compensation value is The greater the angular velocity of the motor, the larger the value, and the higher the vehicle speed, the greater the rate of change with respect to the change in angular velocity, and a signal that realizes a steering damper function by being subtracted from the base signal that serves as a reference for the target signal. Steering system. The steering system
A correction calculator that calculates the compensation value and outputs a reaction force correction instruction signal based on the compensation value;
An abnormality detecting means for detecting that an abnormality has occurred in the toe angle changing device and notifying the correction calculating section;
A blocking means for blocking the transmission of the reaction force correction instruction signal by a drive signal from the correction calculation section in a path for transmitting the reaction force correction instruction signal calculated by the correction calculation section to the steering control device; Further comprising
When no abnormality occurs in the toe angle changing device,
The steering control device includes:
The target signal is corrected by adding or subtracting the reaction force correction instruction signal transmitted via the path to the target signal,
When the correction calculation unit is notified from the abnormality detection means that an abnormality has occurred in the toe angle changing device,
The correction calculation unit provides a driving signal to the blocking unit to block the path,
The steering control device includes:
The steering system according to claim 1, wherein the target signal is not corrected by the reaction force correction instruction signal. The steering system according to claim 1 or 2 , wherein the toe angle changing device includes an actuator that independently changes the toe angles of the two rear wheels.

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