JP4359317B2 - Steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a sense of incongruity from being applied to the hand of the driver by the steering torque of an electric power steering device combined with a rear wheel toe angle changer. <P>SOLUTION: This steering system comprises the electric power steering device 110 which includes a base signal calculation part 51, a damper compensation signal calculation part 52, and n inertia compensation signal calculation part 53, having a motor driven by a target signal IM<SB>1</SB>determined by compensating a damper compensation signal, an inertia compensation signal, and a base signal, and applying a steering support force. An abnormal state detection signal is received from a self-diagnosing part 81d to determine that predetermined actual toe angles &alpha;<SB>SL</SB>, &alpha;<SB>SR</SB>received simultaneously do not indicate the toe-in state of rear wheels or &alpha;<SB>SL</SB>=&alpha;<SB>SR</SB>=0, and a vehicle speed is equal to or lower than a predetermined value V<SB>low</SB>. When the requirements above are satisfied, an abnormal state supporting torque limiting part 63 so controls that a signal IM<SB>1</SB>input into an abnormal state supporting torque limiting part 63 is lowered by &Delta;IM and output as a signal IM<SB>2</SB>. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a steering system that operates and controls a toe angle of a rear wheel based on a turning angle and a vehicle speed of a front wheel, and more particularly to a steering system that combines an electric power steering device that assists the turning of a front wheel.

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. Patent Document 1 discloses a technology of 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. Further, in Patent Literature 2, in a steer-by-wire vehicle steering apparatus, when an abnormality (failure) related to steering occurs, the electronic control unit determines the steering torque based on the steering torque conversion table with respect to the steering angle. A technique for notifying the driver of the occurrence of an abnormality is described in which the map is changed by adopting a large (so-called, heavy) map, and the steering torque for the driver's steering wheel operation is set to a larger steering torque than normal. ing.
Japanese Examined Patent Publication No. 6-47388 (FIG. 2) Japanese Patent Laying-Open No. 2005-199955 (FIG. 6)

  However, if the toe angle changing device that makes it possible to change the toe angle of the left and right rear wheels, for example, if the toe angle changing device is stuck in a toe-out or reverse-phase control state, the vehicle behavior becomes unstable if the vehicle runs at high speed as it is. Become.

Further, even if the above-described sticking occurs during low-speed traveling, the driver may feel the same as in the normal state due to the effect of assisting the auxiliary torque of the electric power steering device.
Therefore, when an abnormality occurs in the toe angle changing device, it is conceivable to combine techniques for increasing the steering torque as compared with the normal time and informing the driver of the occurrence of abnormality as described in Patent Document 2. However, detecting an abnormality in the toe angle changing device and suddenly changing the steering torque makes the driver feel confused.

  An object of the present invention is to provide a steering system that solves the above problems.

In order to solve the above problems, an invention according to claim 1 is directed to an electric power steering device in which an electric motor generates an auxiliary torque in accordance with at least a steering torque and transmits the auxiliary torque to a steering system of a front wheel, and at least a front wheel rotation. Toe angle change in a steering system comprising a toe angle changing device capable of changing the toe angle of left and right rear wheels based on the rudder angle and the vehicle speed, and an electric power steering device and a steering control device for controlling the toe angle changing device In the case of having an abnormality detection means for detecting an abnormal state of the device and an auxiliary torque calculation means for calculating a target value of the auxiliary torque, and receiving an abnormal state detection signal from the abnormality detection means , the vehicle speed is not more than a predetermined value In this case, the calculated target value of the auxiliary torque is reduced.

According to the invention of claim 1, when receiving an abnormal condition detection signal from the abnormality detection means, the further, when the vehicle speed is below a predetermined value, so decreasing the target value of the assist torque, traveling at relatively high speed There is no sudden increase in steering torque response.

The invention according to claim 2 is based on 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 at least a turning angle and a vehicle speed of the front wheel. An abnormality state of a toe angle changing device is detected in a steering system including a toe angle changing device capable of changing the toe angles of left and right rear wheels, and an electric power steering device and a steering control device for controlling the toe angle changing device. The toe angle changing device has an abnormality detecting means and an auxiliary torque calculating means for calculating a target value of the auxiliary torque. the toe angle is fixed, the steering control apparatus, when receiving the abnormal condition detection signal from the abnormality detection means, the further the vehicle speed is below a predetermined value, and, after the left and right At least one of the abnormal state fixed toe angle according to the while showing the toe-out, and wherein reducing the target value of the calculated assist torque.

According to the invention of claim 2, steering rudder controller, when receiving the abnormal condition detection signal from the abnormality detection means, the further the vehicle speed is below a predetermined value, and the toe angles of the right and left rear wheels at least Only when one of them is fixed with toe-out, the calculated target value of the auxiliary torque is lowered.

According to a third aspect of the present invention, there is provided an electric power steering device in which an electric motor generates an auxiliary torque in accordance with at least a steering torque and transmits the auxiliary torque to a steering system of a front wheel, and at least a steering angle and a vehicle speed of the front wheel. In a steering system comprising a toe angle changing device capable of changing the toe angles of left and right rear wheels, and an electric power steering device and a steering control device for controlling the toe angle changing device, an abnormal state of the toe angle changing device is determined. It has an abnormality detection means for detecting, and when an abnormal state detection signal is received from the abnormality detection means, the auxiliary torque is set to zero.

According to the third aspect of the present invention, when the abnormality detecting means detects an abnormal state of the toe angle changing device, the auxiliary torque amount becomes 0, and the response feeling of the steering torque can be increased.

The invention according to claim 4 is the steering system of claim 3, when receiving an abnormal condition detection signal from the abnormality detection means, the further, when the vehicle speed is below a predetermined value, the assist torque 0 It is characterized by doing.

According to the invention of claim 4, when receiving an abnormal condition detection signal from the abnormality detection means, the further, when the vehicle speed is below a predetermined value, so that the assist torque to zero, running at relatively high speed There is no sudden increase in steering torque response.

According to a fifth aspect of the present invention, in the configuration of the third aspect of the present invention, the toe angle changing device detects the toe angles of the left and right rear wheels according to the abnormal state when the abnormality detecting means detects the abnormal state. fixed, the steering control apparatus, when receiving the abnormal condition detection signal from the abnormality detection means, the further the vehicle speed is below a predetermined value, and a fixed toe angle in accordance with the abnormal state of the left and right rear wheels at least When one of them shows toe-out, the auxiliary torque is set to zero.

According to the invention of claim 5, the steering control apparatus, when receiving the abnormal condition detection signal from the abnormality detection means, the further the vehicle speed is below a predetermined value, and, at least one of the toe angles of the right and left rear wheels The auxiliary torque is set to 0 only in a state where is fixed with toe-out.

According to the first and fourth aspects of the present invention, when the toe angle changing device is in an abnormal state and the vehicle speed is equal to or lower than the predetermined value, the auxiliary torque is reduced or reduced to zero. In addition, it is possible to prevent a driver from feeling confused by telling the driver a sudden change in the response of the steering torque .

Further, according to the invention described in claim 3, the toe angle changer is in an abnormal state, for example, when the toe angles of the rear wheels is fixed, since the assist torque to zero, the change in a responsive feeling from the steering torque Thus, it is possible to provide a steering system that makes it easy for the driver to feel the abnormal state of the toe angle changing device .

According to the inventions of claim 2 and claim 5 , when the toe angle changing device is in an abnormal state, at least one of the left and right rear wheels indicates toe out and is fixed, and the vehicle speed is equal to or less than a predetermined value , Since the auxiliary torque is reduced or set to 0, when the left and right rear wheels are fixed at a toe angle that gives stable turning performance that does not show toe-out, the auxiliary torque is reduced to unnecessary or 0. It is possible to provide a rational steering system that does not have to do.

<Embodiment>
An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is an overall conceptual diagram of a four-wheel vehicle to which a steering system according to an embodiment of the present invention is applied, and FIG. 2 is a configuration diagram of an electric power steering apparatus.

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. the controller 130 (hereinafter, referred to as a steering control ECU), front wheel steering angle sensor _{S S,} is configured to include a variety of sensors such as a vehicle speed sensor _{S V.}

(Electric power steering device)
In the electric power steering apparatus 110, as shown in FIG. 2, a main steering shaft 3a provided with a steering handle 3, a shaft 3c, and a pinion shaft 7 are 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 and 9 are connected to 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. Here, the rack shaft 8, the rack teeth 8a, and the tie rods 9 and 9 constitute a turning mechanism. Further, the front wheels 1L from the moving amount of the vehicle width direction of the rack shaft 8, the front wheel turning angle sensor S _S for detecting the orientation of the 1R are provided in the steering 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 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 motor 4, the motor 4, and the like 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 angular 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 taken out 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 _cm, and is independent of vehicle characteristics and vehicle conditions. is there.

Here, varying the steering torque applied to the steering wheel 3 Ts, the coefficients of the assist amount A _H, which assists the booster has been generated torque of the motor 4 via a reduction mechanism, for example, as a function of vehicle speed VS k _A (VS). In this case, since A _H = k _A (VS) × Ts, the pinion torque Tp, which is a road load, is expressed by the following equation (2).
Tp = Ts + A _H
= Ts + k _A (VS) × Ts (2)
Thus, the steering torque Ts is expressed as the following equation (3).
Ts = Tp / (1 + k _A (VS)) (3)

Therefore, the steering torque Ts is reduced to 1 / {1 + k _A (VS)} times the pinion torque Tp (load). For example, if k _A (0) = 2 when the vehicle speed VS = 0, the steering torque Ts is controlled to be 1/3 lighter than the pinion torque Tp, and k _A when the vehicle speed VS = 100 km / h. If (100) = 0, the steering torque Ts becomes equal to the pinion torque Tp, and is controlled to feel the steering torque with a firm weight equivalent to that of manual steering. In other words, by controlling the steering torque Ts in accordance with the vehicle speed VS, a sense of responsiveness of a stable and stable steering torque is imparted lightly during low-speed traveling and firmly during high-speed traveling.

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 amplifier circuit 21 which amplifies, and a vehicle speed sensor S _V for detecting the speed of the vehicle (vehicle speed).
The steering control ECU 130 of the steering system 100 includes an electric power steering control unit 130a (see FIG. 5) to 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 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 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 the vehicle speed VS 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 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.
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). 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.

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 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. 8) 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 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 operates to expand and contract in the horizontal direction (axial direction) in the figure with respect to the case body 34. It is supposed to do. 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 changing control ECU 37 is fixed to the case main body 34 of the actuator 30 and connected to the stroke sensor 38, the temperature sensor 31a, and a connector. 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 a communication line.
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. 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.

(Steering control ECU)
Next, functions of the steering control ECU will be described with reference to FIGS.
FIG. 5 is a schematic control function configuration diagram of the steering control ECU and the 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, ROM, RAM, 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 (see FIGS. 1 and 2), and a rear wheel toe that calculates target toe angles of the rear wheels 2L and 2R. An angle control unit 130b is provided.

(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) 51, a damper compensation signal calculation unit (auxiliary torque calculation unit) 52, an inertia compensation signal calculation unit (auxiliary torque calculation unit) 53, a Q Axis (torque axis) PI control unit 54, D axis (magnetic pole axis) PI control unit 55, two-axis three-phase conversion unit 56, PWM conversion unit 57, three-phase two-axis conversion unit 58, and motor speed calculation A unit 67 and an exciting 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 manner and converts the two axes of the Q axis is an axis obtained by rotating 90 degrees, the Q-axis current IQ is proportional to the generated torque T _M of the motor 4, D-axis current ID is proportional to the exciting 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 the base table 51a, which is set in advance by experimental measurement for a vehicle having the same steering function as that of the present embodiment and having the 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 _DT 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 VS increases and increases, thereby increasing the manual steering area and providing road surface information to the driver. To give. That is, a firm feeling of steering torque Ts is given as the vehicle speed VS increases. 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. The angular velocity signal ω is obtained by referring to the damper table 52a.
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 value of the vehicle speed signal VS is higher, the gain (G3, G5) is increased to attenuate the output torque T _M ^* of the electric motor 4 according to the angular speed of the electric motor 4, that is, the turning speed. In other words, when a large current is supplied to the motor 4 and the angular velocity ω increases, the angular velocity ω does not decrease immediately due to the inertia of the motor 4. In order to avoid this phenomenon, the damper compensation signal calculation unit 52 suppresses and controls the angular velocity 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.

Returning to FIG. 5 again, the adder 61 subtracts the output signal I of the damper compensation signal calculation unit 52 from the output signal _DT of the base signal calculation unit 51, and the adder 62 outputs the output signal of the adder 61. and in which by adding the output signal of the inertia compensation signal computing part 52 and the 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 the torque signal T is calculated 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.
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, and is input to the abnormal auxiliary torque limiting unit 63.
Abnormal assist torque limiting part 63, the output signal IM ₁ of the adder 62 is input, when the correction command signal from the toe angle change control diagnostic part 73 to be described later is input, the as shown in FIG. 7 The signal IM _{1 is} temporally changed to decrease the signal IM ₁ by a predetermined correction amount ΔIM, and the output signal IM ₂ is output to the adder 64.
The correction amount ΔIM is a percentage of the signal IM _1, for example, to 80%. Originally, the signal IM ₁ has a positive / negative current at the time of left / right steering, so the auxiliary torque is reduced to be understood by the driver by reducing it to 80% of the input value as well as the positive / negative of the input signal IM _1. Let
Abnormal assist torque limiting part 63, when the correction command signal from the toe angle change control diagnostic part 73 is not input, and outputs a signal IM ₁ which is input to the adder 64 as it is as the output signal IM _2.

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 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. .
The biaxial three-phase converter 56 and the PWM converter 57 receive the angle signal θ of the electric motor 4 and output a signal corresponding to the magnetic pole position of the rotor.

(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 target toe angle calculation unit 71 and a toe angle change control diagnosis unit 73.

Front-wheel steering angle sensor S _S detects the front wheels 1L, turning angle of 1R [delta], and inputs the target toe angle computing unit 71.
The target toe angle calculation unit 71 calculates the rear wheels 2L, 2R from the vehicle speed signal VS, the turning angle δ, and the turning angular velocity δ ′ (which can be easily obtained by time differentiation of the turning angle δ). The target toe angles α _TL , α _TR are generated, and the target toe angles α _TL , α _TR are input to the toe angle change control ECUs 37, 37 that control the change of the respective toe angles of the left and right rear wheels 2 L, 2 R ( (See FIG. 8). The target toe angles α _TL and α _{TR are} generated by referring to the toe angle table 71a set in advance for each of the left and right rear wheels 2L and 2R based on the turning angle δ, the turning angular velocity δ ′, and the vehicle speed VS. Done.
For example, the following equations (4) and (5) are set.
α _TL = K _L (VS, δ ′, δ) · δ (4)
α _TR = K _R (VS, δ ′, δ) · δ (5)
Here, K _L (VS) and K _R (VS) are front and rear wheel steering ratios depending on the vehicle speed VS, the turning angle δ, and the turning angular velocity δ ′, and the rear wheel target toe angles α _TL , α _TR are In a range where the vehicle speed is a predetermined low speed, target toe angles α _TL , α _{TR for the} rear wheels are generated so that the rear wheels 2L, 2R are easily turned in the 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 turning angular velocity δ ′ 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 δ is set. Accordingly, the target toe angles α _TL and α _{TR of the} rear wheels 2L and 2R are set to the same phase. That is, the target toe angles α _TL and α _{TR of the} rear wheels 2L and 2R are set so as to reduce the side slip angle β in the lane change.
However, in a high speed range that exceeds the predetermined low speed range, the absolute value of the steering angular velocity δ ′ exceeds a predetermined value, or a large steering angle δ that exceeds the predetermined range on the left and right In this case, the target toe angles α _TL , α _TR of each rear wheel are set in the opposite phase according to the turning angle δ.
Note that 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.

Next, the toe angle change control diagnosis unit 73 will be described. The toe angle change control diagnosis unit 73 receives an abnormal state detection signal described later from a self-diagnosis unit 81d (see FIG. 8) described later after the toe angle change control ECU 37 of the toe angle change devices 120L and 120R, and receives it together with the abnormal state detection signal. The predetermined actual toe angles α _SL and α _SR described later do not indicate the toe-in state of the rear wheels 2L and 2R, or α _SL = α _SR = 0 (that is, indicate that at least one rear wheel is in the toe-out state). ) And whether the vehicle speed is equal to or lower than a predetermined value V _low , and when this condition is satisfied, the signal IM ₁ input to the abnormal auxiliary torque limiting unit 63 is reduced by ΔIM as described above. and outputs to the time of the correction command signal abnormality assist torque limiting part 63 to output a signal IM _2. When the above conditions are not satisfied, for example, in the case of fixing in the rear wheel toe-in state, in the case of fixing in a predetermined actual toe angle α _SL = α _SR = 0 described later, both toe angle changing devices 120L and 120R are normal. In this case, the correction command signal is not output to the abnormal auxiliary torque limiter 63.

(Toe angle change control ECU)
Next, a detailed configuration of the toe angle changing control ECU will be described with reference to FIG. FIG. 8 is a block diagram of the control function of the toe angle changing control ECU of the toe angle changing device.
As shown in FIG. 8, 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 communication line, and is also connected to the other toe angle change control ECU 37 via a communication line.

The control unit 81 includes a microcomputer including a CPU, RAM, ROM, and peripheral circuits, and includes a target current calculation unit 81a, a motor control signal generation unit 81c, and a self-diagnosis unit (abnormality detection means) 81d. ing.
The target current calculation unit 81a of one (right rear wheel 2R side) toe angle change control ECU 37 obtains the target toe angle α _TR of the rear wheel 2R input from the steering control ECU 130 via the communication line and the stroke sensor 38. current after based on the toe angle alpha _R of wheel 2R to be, to calculate a target current signal, and outputs the motor control signal generation part 81c.
The target current calculation unit 81a of the other (left rear wheel 2L side) toe angle change control ECU 37 obtains the target toe angle α _TL of the rear wheel 2L input from the steering control ECU 130 via the communication 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 at a desired speed and a desired operation amount (amount of expansion / contraction that makes the rear wheels 2L and 2R have desired toe angles α _TL and α _TR ). It is.
In this way, 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). It is possible to quickly set the target toe angles α _TL and α _TR by feeding back that the current value required for turning the vehicle changes depending on the vehicle speed VS, road surface environment, vehicle motion state, tire wear state, and the like. .
In addition, in the target current calculation part 81a, responsiveness may be improved by adding feedforward control.

  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. 8, 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 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 (winding temperature high mode) and determines a predetermined actual toe angle α _SL (or actual toe). The angle α _SR ), for example, 0 ° is input to the target current calculation unit 81a. Here, the actual toe angle α _SL is an actual toe angle realized by being injected to the left rear wheel 2L at the time of abnormality detection, and the actual toe angle α _SR is injected to the right rear wheel 2R at the time of abnormality detection. This is the actual toe angle realized.

The self-diagnosis unit 81d monitors the target current value of the target current calculation unit 81a and the detection signal of the actual current from the hall element of the electric motor drive circuit 83, and also fixes the actuator 30 based on the position signal from the stroke sensor 38. If it is determined that the motor is fixed (fixed mode), the motor drive circuit 83 is instructed to stop power supply to the motor 31, and the current toe angle α _L (or the toe angle α _{R is} transmitted to the target current calculator 81a). ) As the actual toe angle α _SL (or the actual toe angle α _SR ). Then, an abnormal state detection signal and an abnormal state signal are detected and transmitted to the self-diagnosis unit 81d of the other toe angle change 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 of the control unit 81 is detected, the motor drive circuit 83 is supplied with power to the motor 31. The stop may be instructed, and an abnormal state detection signal may be output to the self-diagnosis unit 81d of the other toe angle change control ECU 37.

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 actual toe angle α _SL (or the actual toe angle α _SR ) is input to the target current calculation unit 81a based on the signal of the mode that has been dealt with.
That is, while receiving and monitoring the 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 properly, the other toe angle changing device 120L A signal indicating whether or not the toe angle changing device 120R (or toe angle changing device 120L) corresponding to the angle changing control ECU 37 is operating properly is monitored, and if either side is abnormal, both toe angles are monitored. The change control ECUs 37 and 37 deal with a predetermined same mode.
Then, each self-diagnosis unit 81d performs toe angle change control on the abnormal state detection signal, the signal of the mode that has been dealt with by detecting the abnormality, and the predetermined actual toe angle α _SL (or the predetermined actual toe angle α _SR ). The data is sent to the diagnosis unit 73.

Next, the control in the toe angle change control diagnosis unit 73 will be described with reference to FIG. FIG. 9 is a flowchart showing the flow of control in the toe angle change control diagnostic unit. This process is control performed at a constant cycle.
In step S11, the vehicle speed VS, the abnormal state detection signal from the self-diagnosis unit 81d of the left and right toe angle change control ECU 37, and predetermined actual toe angles α _SL and α _SR are read as needed.
In step S12, it is checked whether or not an abnormal state detection signal has been received (abnormality detection?). If an abnormality is detected (Yes), the process proceeds to step S13. If no abnormality is detected (No), the process within one cycle is terminated.

In step S13, the predetermined actual toe angles α _SL and α _SR read in step S11 are checked to determine whether both the left and right rear wheels 2L and 2R are in a toe-in state or α _SL = α _SR = 0. If both the rear wheels 2L and 2R are in the toe-in state or α _SL = α _SR = 0 (Yes), the processing within one cycle is terminated. If both the rear wheels 2L and 2R are not in the toe-in state or α _SL = α _SR = 0 (No), the process proceeds to step S14 to check whether the vehicle speed VS is equal to or lower than the predetermined vehicle speed V _low . When the vehicle speed VS is higher than the predetermined vehicle speed V _low (No), the process within one cycle is terminated. When the vehicle speed VS is equal to or lower than the predetermined vehicle speed V _low (Yes), a correction command signal is output to the abnormal time auxiliary torque limiting unit 63. That is, the auxiliary torque is reduced and a series of control is finished.

Then, the abnormal time supplementary torque limiting part 63 to the signal IM ₁ input, is lowered to assist torque gradually predetermined proportion to have a predetermined time delay, as shown in FIG. 7, hereinafter, is input A predetermined ratio of the signal IM ₁ , in this case, 20% of the output signal IM ₂ is output to the adder 64.
By the way, the vehicle speed V _low is a sufficiently low vehicle speed, and even if the driver is confused by a sudden change in steering force while the vehicle is running against a sudden decrease in auxiliary torque, for example, 80% cut, the vehicle speed The vehicle speed does not affect driving. For example, the vehicle speed is 10 km / hr at the slowest speed.

As described above, according to the present embodiment, the steering control ECU 130 receives the rear wheel turning function abnormal state detection signal from the toe angle change control ECU 37 in the toe angle change control diagnosis unit 73, and the rear wheel When both 2L and 2R are not in the toe-in state or α _SL = α _SR = 0, it is confirmed that the vehicle speed is equal to or lower than the vehicle speed V _low and the adder 64 is output so as to reduce the auxiliary torque. In such a state, the auxiliary torque is reduced, and the driver feels that the response feeling of the steering torque is increased, so that it is easy to sense that the steering function is abnormal.
Therefore, it is possible to prevent the driver from being confused due to the sudden reduction of the sudden assist torque during traveling.

If the vehicle is traveling at a vehicle speed exceeding the vehicle speed V _low , the gain is originally set so that the auxiliary torque decreases as the speed increases. It is easy to feel and the driver feels uncomfortable in the steering performance and reduces the vehicle speed. When the vehicle speed becomes V _low or lower, the auxiliary torque is reduced, and the driver is informed that the toe angle changing devices 120L and 120R are abnormal. It can be clearly detected.
At this time, since the auxiliary torque is reduced with a time delay, it is possible to prevent the driver from being surprised by the rapid reduction of the auxiliary torque.

When the signals from the toe angle change control ECU 37 indicate that both the rear wheels 2L and 2R are in a toe-in state or α _SL = α _SR = 0, the rear wheels 2L and 2R may not be reduced. When fixed at α _SL = α _SR = 0, the steering performance and the turning performance are the same as those of the steering vehicle with only the normal front wheels 1L, 1R, and the vehicle behavior shows a stable characteristic in the toe-in state. Therefore, it is sufficient to light the alarm lamp for notifying the abnormality of the toe angle changing devices 120L and 120R provided on the console to alert the driver.

  Incidentally, when the self-diagnosis unit 81d of one toe angle change control ECU 37 detects an abnormal state, an abnormal state detection signal is transmitted to the other toe angle change control ECU 37, and both toe angle change devices 120L and 120R are transmitted. Therefore, it is possible to prevent only one of the toe angles of the rear wheels 2L and 2R from being changed and controlled, and the running performance when the toe angle changing devices 120L and 120R are in an abnormal state is stable. Maintained.

(Modification)
The present invention is not limited to the above-described embodiment, and for example, the following various modifications are possible.
(1) Although the electric power steering control unit 130a in the above embodiment sets the target current and controls the current flowing through the electric motor 4, the voltage applied to the electric motor 4 can also be set as the target voltage. It is also possible to control the current flowing through the electric motor 4 by setting the torque output by the motor to the target torque. This target voltage or target torque is also included in the target signal.
(2) In the present embodiment, and the toe angle change control diagnostic part 73 outputs a correction command signal to the abnormal assist torque limiting part 63, lowering the current target value IM ₂ in abnormal assisting torque limiting part 63 However, it is not limited to that.
As shown in FIG. 10, the relay switch 60 may be arranged on the downstream side of the PWM conversion unit 57, and the relay switch 60 may be turned off by a command from the toe angle change control diagnosis unit 73 to cut the auxiliary torque. .
(3) In the present embodiment, as shown in FIG. 6A, the base signal calculation unit 51 uses the vehicle speed VS as a parameter as a reference from the torque signal T to the base signal IM _{1 for} the output torque T _M ^*. The signal _DT is calculated, but the present invention is not limited to this. An operation angle signal from an operation angle sensor provided on the steering handle 3 and a yaw rate signal from a yaw rate sensor provided on the vehicle body are input to the steering control ECU 130, and predetermined based on the vehicle speed VS and the operation angle. The present invention is also applicable to an electric power steering apparatus that calculates a reference yaw rate and feedback-controls a reaction force to the steering handle 130 based on a difference between the reference yaw rate and the actual yaw rate.

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. It is a schematic control function block diagram of steering control ECU of a steering system, and a toe angle change apparatus. It is a figure which shows the characteristic of a base signal calculating part and a damper compensation signal calculating part. It is a diagram illustrating an output signal IM ₂ to the input signal IM ₁ when subjected to the correction instruction signal at an abnormal time of the auxiliary torque limiting part. It is a control functional block block diagram of toe angle change control ECU of a toe angle changing apparatus. It is a flowchart which shows the flow of control of a rear-wheel steering function diagnostic part. It is a schematic control function block diagram of steering control ECU and toe angle changing device of a steering system in a modification.

Explanation of symbols

1L, 1R Front wheel 2L, 2R Rear wheel 3 Steering handle 4 Electric motor 25 Resolver 30 Actuator 31 Electric motor 31a Temperature sensor (abnormality detection means)
33 Deceleration mechanism 35 Feed screw part 37 Toe angle change control ECU (steering control device)
38 Stroke sensor 51 Base signal calculation unit (auxiliary torque calculation means)
51a Base table 51b Backup table 52 Damper compensation signal calculation unit (auxiliary torque calculation means)
53 Inertia compensation signal calculation unit (auxiliary torque calculation means)
54 Q-axis (torque axis) PI control unit 60 Relay switch 61, 62 Adder 63 Abnormal auxiliary torque limiting unit 67 Motor speed calculation unit 71 Target toe angle calculation unit 71a Toe angle table 73 Toe angle change control diagnosis unit 81 Control unit 81a Target current calculation unit 81c Motor control signal generation unit 81d Self-diagnosis unit (abnormality detection means)
83 Electric motor drive circuit 100 Steering system 110 Electric power steering device 120L, 120R Toe angle changing device 130 Steering control ECU (steering control device)
130a Electric power steering control unit 130b Rear wheel toe angle control unit S _S Front wheel steering angle sensor S _T torque sensor S _V vehicle speed sensor

Claims (5)

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 at least the toe angles of the left and right rear wheels based on the turning angle and vehicle speed of the front wheels In a steering system comprising a toe angle changing device that can change the power, a steering control device that controls the electric power steering device and the toe angle changing device,
An abnormality detection means for detecting an abnormal state of the toe angle changing device;
Auxiliary torque calculating means for calculating a target value of the auxiliary torque,
When the abnormal state detection signal is received from the abnormality detection means, and further when the vehicle speed is equal to or lower than a predetermined value, the calculated target value of the auxiliary torque is reduced. 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 at least the toe angles of the left and right rear wheels based on the turning angle and vehicle speed of the front wheels In a steering system comprising a toe angle changing device that can change the power, a steering control device that controls the electric power steering device and the toe angle changing device,
An abnormality detection means for detecting an abnormal state of the toe angle changing device;
Auxiliary torque calculating means for calculating a target value of the auxiliary torque,
The toe angle changing device fixes the toe angles of both the left and right rear wheels according to the abnormal state when the abnormality detecting means detects the abnormal state,
The steering control apparatus, when receiving the abnormality detection means or found abnormal state detection signal, in addition, the vehicle speed is below a predetermined value, and the toe angle fixed in accordance with the abnormal state of the left and right rear wheels steering system characterized Occasionally, reducing the target value of the calculated assist torque, at least one of indicates the toe-out of. 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 at least the toe angles of the left and right rear wheels based on the turning angle and vehicle speed of the front wheels In a steering system comprising a toe angle changing device that can change the power, a steering control device that controls the electric power steering device and the toe angle changing device,
Having an abnormality detection means for detecting an abnormal state of the toe angle changing device;
The steering system according to claim 1, wherein the auxiliary torque is set to 0 when an abnormal state detection signal is received from the abnormality detection means. The steering system according to claim 3 , wherein when the abnormal state detection signal is received from the abnormality detection means , the auxiliary torque is set to 0 when the vehicle speed is equal to or lower than a predetermined value. The toe angle changing device fixes the toe angles of both the left and right rear wheels according to the abnormal state when the abnormality detecting means detects the abnormal state,
The steering control apparatus, when receiving the abnormal condition detection signal from the abnormality detection means, the further the vehicle speed is below a predetermined value, and a fixed toe angle according to the abnormal state of the left and right rear wheels The steering system according to claim 3 , wherein the auxiliary torque is set to 0 when at least one of them indicates toe-out.

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