JPH05338547A - Four-wheel steering device - Google Patents

Abstract

PURPOSE:To provide a four-wheel steering device which prevents the increase of the load applied to an engine and an alternator, even if the steering angle of a front wheel and rear wheel becomes max. CONSTITUTION:The steering mechanism of a four-wheel steering device consists of a front wheel power steering 11 and a rear wheel power cylinder 30. Both are operated by receiving a hydraulic pred6&e from a DC motor driven type hydraulic pump. The control unit 10 of the four-wheel steering device detects each steering angle of a front wheel and rear wheel from a steering angle sensor 50 and a car speed sensor 51, and when the actual steering angle for the front wheel or rear wheel is nearly close to the allowable max. steering angle, the supply of electric current to the corresponding hydraulic pump, i.e., DC motor is restricted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system equipped with power steering.

[0002]

2. Description of the Related Art A power steering device has been conventionally mounted on a large automobile or the like, but in recent years, it has been naturally mounted on a small automobile due to the good operability of a steering wheel. .. This power steering system is designed to supplement the driving force of a hydraulic cylinder to a tie rod driven by a rotating operation of a steering wheel so that steering of front wheels can be performed lightly and quickly. For example, this hydraulic cylinder can be driven by hydraulic pressure from an electric motor-driven hydraulic pump.

On the other hand, the four-wheel steering system imparts steering to the rear wheels in the same phase or opposite phase to the front wheels according to the steering angle of the front wheels, the vehicle speed, etc. to improve the stability of lane change at high speed. Alternatively, it improves the performance such as entering a narrow side road or turning in a narrow place. For example, steering of the rear wheels is performed by a power cylinder, which can be driven by hydraulic pressure from an electric motor driven hydraulic pump. This hydraulic pump is provided on the front wheel side, that is, separately from the hydraulic pump for the power steering device.

[0004]

In a four-wheel steering system equipped with a power steering system, when the front wheels or the rear wheels reach the maximum allowable steering angle, the hydraulic pressure that can be supplied to the hydraulic cylinder or the power cylinder is limited. However, since the hydraulic pump tries to supply the hydraulic pressure, the hydraulic pump is loaded, and the electric motor driving this hydraulic pump is also loaded, and the supply current of the electric motor increases.

In particular, when the front wheels are stationary while the vehicle is stopped, or when the front wheels are steered significantly at extremely low speeds, both the front wheels and the rear wheels may have the maximum allowable steering angle. In many cases, since the supply currents of the two electric motors on the front wheel side and the rear wheel side both increase, the sum of the supply currents to these electric motors becomes quite large. In addition, in the above-mentioned state, the engine speed is low, so the amount of power generated by the alternator is small, and the loads on the alternator and the engine are increased, which is not preferable.

The present invention has been made in consideration of the above-mentioned problems, and an object thereof is a four-wheel steering system which prevents an increase in loads on an alternator and an engine even when steering angles of front wheels and rear wheels are maximized. To provide.

[0007]

According to the present invention, in order to achieve the above object, a four-wheel steering system supplies a hydraulic pressure to the power steering system for assisting the steering force of the front wheels and the power steering system. An electric motor driven first hydraulic pump, a power cylinder for steering the rear wheels, an electric motor driven second hydraulic pump for supplying hydraulic pressure to the power cylinder, and steering angles of the front and rear wheels are allowed. The detection means for detecting whether or not it is at the maximum steering angle, and the current supplied to the electric motor in the corresponding hydraulic pump when the maximum steering angle of the actual steering angle of the front wheels or the rear wheels is reached by this detection means. Is equipped with a means for limiting

[0008]

The detecting means detects that the front wheels and the rear wheels have reached the maximum allowable steering angle. Based on this detection result, the supply current of the electric motor of the hydraulic pump corresponding to the steering of the front wheels or the rear wheels is limited.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS. As shown in FIG. 1, the four-wheel steering system (4WS) mainly includes a front wheel steering mechanism, a rear wheel steering mechanism, a control unit (C / U) 10, and each sensor.

The front wheel steering mechanism includes a power steering 11 composed of a hydraulic cylinder, and both piston rods 12 of the power steering 11 are connected to knuckle arms 13 and 13 supporting the front wheels, respectively. The power steering 11 has a pair of pressure chambers 14 and 15 inside thereof.
Is connected to an electrically driven first hydraulic pump 17 and an oil reservoir 18 via a steering valve 16. First
The hydraulic pump 17 can be driven by a first DC motor 19, and the first DC motor 19 is connected to the control unit 10 via a first driver unit 20.

The first driver unit 20 is electrically chopper-controlled by the controller unit 10. Therefore, the controller 10 controls the DC power source 25 of the vehicle.
(Alternator and battery) to first DC motor 19
It controls the current supplied to the. The steering valve 16 is composed of a 4-port 3-position directional switching valve with a throttle, and is incorporated in the steering column. When the steering handle 22 is operated, the steering valve 16 connects one pressure chamber corresponding to the direction to the first hydraulic pump 17 side to supply hydraulic pressure to this pressure chamber and the other pressure chamber Switching operation is performed so as to connect to the oil reservoir 18 side. Therefore, by operating the power steering 11 with the operation of the steering wheel 22,
The operation power will be helped.

The rear wheel steering mechanism includes a double rod type power cylinder 30 and a rear lock device. Both piston rods 31 of the power cylinder 30 are respectively connected to knuckle arms 32, 32 supporting the rear wheels. The power cylinder 30 has a pair of pressure chambers 3 therein.
The pressure chambers 33 and 34 are connected to the oil passage control valve 38 and the oil reservoir 18 via the steering angle control valve 37. A pair of center springs 35 and 36 are provided inside the pressure chambers 33 and 34, respectively.
Maintains the rear wheels in the neutral position (the steering angle of the rear wheels is zero) when the hydraulic pressure is not supplied to the pressure chambers 33, 34, that is, when the rear wheels are not being steered. At this time, the rear lock device operates and the power cylinder is fixed at its neutral position.

As shown in FIG. 1, the rudder angle control valve 37 is composed of an electromagnetically driven 4-port 3-position direction switching valve, and an electric signal is supplied from the control unit 10 to switch its direction. Be done. As shown in FIG. 1, the oil passage control valve 38 is also composed of an electromagnetically driven 4-port 3-position directional switching valve, and an electric signal is supplied from the control unit 10 to switch its direction. An accumulator 42 is connected to the oil passage control valve 38, and the accumulator 4 is connected to the oil passage control valve 38.
A pressure sensor 43 is provided in the oil passage between the oil pressure control valve 38 and the oil passage control valve 38. The pressure sensor 43 detects the hydraulic pressure stored in the accumulator 42 and supplies the sensor signal to the control unit 10.

Further, from the oil passage control valve 38 to the oil passage 4
4 and 45 extend, and these oil passages 44 and 45 are joined and connected on the way, and are connected to the electrically driven second hydraulic pump 40 via a way check valve 47. A check valve 46 is inserted in the oil passage 44. The second hydraulic pump 40 is driven by the second DC motor 41, and the second DC motor 41 drives the second DC motor 41.
The motor 41 is connected to the control unit 10 via the second driver unit 21.

The second driver unit 21 is electrically chopper-controlled by the controller unit 10, and accordingly,
The controller unit 10 controls the supply current from the DC power supply 25 of the vehicle to the second DC motor 41. On the other hand, the control unit 10 is composed of a microcomputer and the like, and various sensors and switches are connected to the control unit 10 in addition to the pressure sensor 43. That is, the steering wheel angle sensor 50, the vehicle speed sensor 51, the pressure sensor 43, the ignition key switch 52, and the mode switch 53 are electrically connected to the control unit 10.

The steering wheel angle sensor 50 is arranged in the steering column and detects the steering wheel angle θ _H.
The sensor signal is supplied to the control unit 10. The vehicle speed sensor 51 is incorporated in, for example, a circuit of a speedometer unit (not shown), and supplies the sensor signal to the control unit 10. The ignition key switch 52 supplies an ON signal to the control unit 10 when the engine is driven, whereas it supplies an OFF signal to the control unit 10 when the engine is stopped.

When the mode switch 53 is turned on, it supplies an on signal to the control unit 10, and as a result, the control unit 10 enables steering of the rear wheels. On the other hand, when the mode switch 53 is turned off and the control unit 10 receives the off signal, the control unit 10 prohibits the steering of the rear wheels.

Next, power steering and rear wheel steering of the four-wheel steering system will be described with reference to the graph shown in FIG. FIG. 2 shows the first D with respect to the steering wheel angle θ _H when the vehicle is stopped or in an extremely low speed traveling state.
Shown are a current supply characteristic C1 to the C motor 19, a steering angle characteristic C2 of the rear wheels, and a current supply characteristic C3 to the second DC motor 41.

Therefore, the following description will be made assuming that the vehicle is in a stopped state. First, the control unit 10
When an ON signal is supplied from the ignition key switch 52, the main routine becomes operable. At the same time, the input signals from the steering wheel angle sensor 50, the vehicle speed sensor 51 and the pressure sensor 43 are supplied to the control unit 10. Then, at this time, if the mode switch 53 is switched to the ON side or has already been switched, the ON signal is supplied to the control unit 19, the rear lock device is released, and the steering of the rear wheels can be operated. Becomes

When the steering wheel 22 is operated clockwise, that is, to the right, a sensor signal from the steering wheel angle sensor 50 is supplied to the control unit 10, and the control unit 10 supplies a control signal to the first driver unit 20. , DC power supply 25 to 1D
A current is supplied to the C motor 19. Then, the first hydraulic pump 17 is driven, and the power steering 11 becomes operable. At the same time, one pressure chamber 14 of the power steering 11 is connected to the first hydraulic pump 17 side by the steering valve 16, and hydraulic pressure is supplied to this pressure chamber 14. The other pressure chamber 15 is connected to the oil reservoir 18 side. As is clear from the supply current characteristic C1 of the first DC motor 19 shown in FIG. 2, when the steering wheel angle θ _H is zero, the supply current to the first DC motor 19 is zero. The operation of the hydraulic pump 17 is stopped.

Looking at the supply current characteristic C1, a large current change peak of the supply current can be seen immediately to the right of the zero position of the steering wheel angle θ _H. This is generally D
This is because, as a characteristic of the C motor, a large starting current is required to generate torque from a stopped state. In addition, in the above situation, in addition to the first DC motor 19 being stopped, the maximum static friction force is generated between the tire surface of the front wheel and the road surface during steering of the front wheels. Since a higher hydraulic pressure needs to be supplied in order to give an overwhelming force to the front wheels, the torque of the first DC motor 19 is further increased.

Looking at the rear wheel steering angle characteristic C2 in FIG. 2, when the steering wheel 22 is further operated in the same direction and the steering wheel angle θ _H becomes 260 °, for example, the rear wheels are steered in the opposite phase direction to the front wheels. Start being done. That is, at this time, the control signal is supplied from the control unit 10 to the steering control valve 37 and the oil passage control valve 38, and the steering control valve 3
In FIG. 7, 7 is switched from its neutral position to the right switching position, while the oil passage control valve 38 is also switched from its neutral position to the right switching position. Therefore, the hydraulic pressure from the accumulator 42 is supplied to one pressure chamber 33 of the power cylinder 30 via the steering control valve 37 and the oil passage control valve 38, and the other pressure chamber 34 is connected to the oil reservoir 18 side. As a result, the rear wheels are steered via the power cylinder 30. Here, the steering angle θ _R of the rear wheels is set based on the steering wheel angle θ _H.

When the hydraulic pressure of the accumulator 42 drops from the initial pressure and the value of the sensor signal reaches a predetermined value, the control unit 10 supplies a supply current to the second DC motor 41 to drive the second hydraulic pump 40. After that, when the discharge pressure of the second hydraulic pump 40 reaches or exceeds the residual pressure of the accumulator 42, the hydraulic pressure from the second hydraulic pump 40 is supplied to the pressure chamber 33 of the power cylinder 30. The supply current of the second DC motor 41, that is, the pressure chamber 34
The hydraulic pressure to be raised to is set according to the magnitude of the steering angle θ _R.

When the steering wheel 22 is returned,
The control unit 10 returns the steering control valve 37 to the neutral position, while switching the oil passage control valve 38 to the left switching position. Therefore, in this case, the power cylinder 3
Both pressure chambers 33 and 34 of 0 are connected to the oil reservoir 18, so that the rear wheels have their center springs 35 and 36.
Thus, the neutral position, that is, the straight traveling state is restored. On the other hand, at this time, the second hydraulic pump 40 is connected to the accumulator 42 side and stores the hydraulic pressure in the accumulator 42. Then, when the hydraulic pressure is sufficiently accumulated in the accumulator 42 and the sensor signal of the pressure sensor 43 reaches a predetermined value corresponding to the initial pressure, the second hydraulic pump 40 is stopped. After this, the control unit 10 turns the oil passage control valve 38
To the neutral position.

Looking at the supply current characteristic C3 of FIG. 2, a large supply current peak is seen even when the steering wheel angle θ _H slightly exceeds 260 °, which is similar to the peak of the supply current characteristic C1. It depends on the reason. On the other hand, in addition to the above-described rear wheel steering angle control, the control unit 10
The supply current suppression routine shown in FIG. 3 is also executed. This routine is processed in parallel with the main routine described above, and the supply current suppression routine will be described below.

This supply current suppression routine is executed at the same time when the ON signal is supplied from the ignition key switch 52 to the control unit 10, and this execution is executed from the ignition key switch 52 to the control unit 1.
It is repeated until the OFF signal is supplied to 0. In step S1, the steering wheel angle θ _H calculated in the main routine of the control unit 10 is read based on the sensor signal from the steering wheel angle sensor 50.

In the next step S2, the vehicle speed calculated in the main routine of the control unit 10 is read based on the sensor signal from the vehicle speed sensor 51, and
Step S3 is executed. In step S3, the steering angle θ _{R of the} rear wheels is calculated based on the steering wheel angle θ _H and the vehicle speed.

In the next step S4, based on the result of step S3, the absolute value of the steering angle θ _R of the rear wheels, that is, | θ _R | is equal to or greater than a predetermined maximum steering angle α (α is, for example, 5 °). It is determined whether there is any. This judgment result is positive (Yes)
When it is, step S5 is performed and it progresses to step S6, and conversely, when it is no (No), step S6 is performed as it is.

The condition in which the result of the determination in step S4 is positive means that the steering wheel 22 is largely operated and the steering angle θ _{R of the} rear wheel becomes the maximum steering angle α. At this time, the piston of the power cylinder 30 of the rear wheel is Is in a state where its movement is blocked. In this state, hydraulic oil cannot be sent to the pressure chamber 33 of the power cylinder 30. In this case, the second hydraulic pump 40 is loaded, and the second DC motor 41 driving the second hydraulic pump 40 is also loaded. Therefore, the supply current of the second DC motor 41 is C5 indicated by a broken line in FIG. It will increase rapidly as shown.

However, when step S5 is executed, the control unit 10 causes the second driver unit 21 to supply the current I _R to the second DC motor 41 driving the second hydraulic pump 40 on the rear wheel side. To limit.
Specifically, the supply current I _R of the second DC motor 41 is I _R1
Limited to −ΔI _R (ΔI _R ≧ 0). This means that the supply current I _R of the second DC motor 41 is ΔI _R (≧ 0) from I _R1 at the time when the steering angle θ _{R of the} rear wheels is maximum, as seen from the supply current characteristic C3 of FIG. It can be seen that the reduced value is maintained. The supply current I _R is _calculated from I _R1 to ΔI.
Even if it is reduced by _R , the steering angle of the rear wheels does not go back due to the hysteresis effect due to the frictional force between the tire and the road surface.

In step S6, it is determined whether or not the absolute value of the steering wheel angle θ _H , that is, θ _H is equal to or larger than the maximum steering angle. When this determination result is positive, step S7 is executed and the process returns to step S1. Conversely, step S6 is performed.
If the result of the determination is NO, then step S1
Return to. The situation in which the result of the determination in step S6 is positive is
The steering handle 22 is operated until the end of rotation, and at this time, the piston of the power steering 11 for the front wheels is in contact with the stopper. In this case, since the hydraulic oil cannot be sent to the pressure chamber 14 of the power steering 11, the load is applied to the first hydraulic pump 17 and the first DC motor 19 that drives the first hydraulic pump 17 is also loaded. become. Therefore, also in this case, the supply current of the first DC motor 19 rapidly increases as indicated by the broken line C4 in FIG.

However, as in step S5, the step
When step S7 is executed, the control unit 10
Through the first driver unit 20 to the first front wheel side.
To the first DC motor 19 that drives the hydraulic pump 17.
Supply current I_F, The determination result of step S6 becomes positive.
Point I_F1To ΔI_F(ΔI_F≧ 0). This
In the case of the supply current characteristic C1 of FIG.
Supply current I of the motor 19 _FIs I_F1After reaching_F1−
ΔI_FIt can be seen that it has been lowered and maintained. In addition,
Supply current I_FIs I_F1-ΔI_FTires, even if limited to
Due to the hysteresis effect due to frictional force with the road surface, etc.
Therefore, the steering angle of the front wheels does not return.

Since the graph in FIG. 3 is symmetrical with respect to the left and right with respect to the vertical axis, even when the steering handle 22 is operated in the counterclockwise direction, that is, to the left, the first and the first described above. The supply current of the 2DC motor is likewise limited. The relationship between the front wheel steering and the rear wheel steering in the state where the vehicle is stopped and the vehicle is traveling at an extremely low speed has been described above.However, the maximum steering angle for both the front wheels and the rear wheels cannot be obtained during normal traveling and high speed traveling of the vehicle. Also, at this time, the engine speed is higher than when idling, and
Since the supply current from the C power supply 25 is sufficiently secured, it is not necessary to limit the supply current of the DC motor.

Therefore, in a vehicle equipped with the power steering 11 and the steering mechanism for the rear wheels, when the front wheels are stationary while the vehicle is stopped or the front wheels are largely steered in the low speed running state, And the steering angle of the rear wheels becomes the maximum allowable steering angle, and the first and second hydraulic pumps 17,
40, that is, even in a situation where the loads on the first and second DC motors 19 and 41 increase rapidly, the supply current of these DC motors can be limited to the necessary minimum by the control from the controller unit 10. In the state where the current supplied from the DC power source 25 is small, such as when the vehicle is stopped or running at an extremely low speed, the effect obtained industrially, such as preventing an increase in the load of the alternator and the engine, is very large.

The present invention is not limited to the above-described embodiment, but various modifications are possible. For example,
In the routine of FIG. 3, the steering angle θ _R of the rear wheels is calculated and calculated based on the steering wheel angle θ _H and the vehicle speed. However, a steering angle sensor is provided on the rear wheel side, and the steering angle sensor is used to detect the rear wheels. It may be determined whether or not the steering angle θ _R has reached the maximum value.

In one embodiment, the supply currents of the first and second DC motors are reduced to I _R1 -ΔI _R or I _F1 -ΔI _F , but these supply currents are limited to I _R1 and I _F1 . Even if the same effect is obtained.

[0037]

As described above, according to the four-wheel steering system of the present invention, the power steering system and the power cylinder are detected by detecting that the steering angles of the front wheels and the rear wheels have reached the maximum allowable steering angles. Since the drive source of the hydraulic pump that supplies the hydraulic pressure, that is, the supply current of the electric motor is limited, even if the steering angle of the front wheels and the rear wheels reaches the maximum allowable steering angle,
Industrially significant effects such as the prevention of an increase in the load on the DC power supply, that is, the alternator and the engine are very large.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a four-wheel steering system.

FIG. 2 is a graph showing a supply current characteristic and a rear wheel steering angle characteristic of the first and second DC motors with respect to a steering wheel angle.

FIG. 3 is a flowchart of a supply current suppression routine.

[Explanation of symbols]

 10 Control Unit 11 Power Steering 16 Steering Valve 17 First Hydraulic Pump 18 Oil Reservoir 19 First DC Motor 20 First Driver Unit 21 Second Driver Unit 22 Steering Handle 25 DC Power Supply 30 Power Cylinder 37 Steering Angle Control Valve 38 Oil Path Control Valve 40 Second hydraulic pump 41 First DC motor 42 Accumulator 43 Pressure sensor 50 Handle angle sensor 51 Vehicle speed sensor 52 Ignition switch 53 Mode switch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B62D 123: 00

Claims (1)

[Claims] 1. A power steering device for assisting the steering force of the front wheels, an electric motor driven first hydraulic pump for supplying hydraulic pressure to the power steering device, a power cylinder for steering the rear wheels, and a power cylinder. A second hydraulic pump driven by an electric motor that supplies hydraulic pressure, detection means for detecting whether or not the steering angles of the front wheels and the rear wheels are at an allowable maximum steering angle, and the detection means for detecting the front wheels or the rear wheels. A four-wheel steering system comprising means for limiting a current supplied to an electric motor in a corresponding hydraulic pump when the actual steering angle reaches a maximum allowable steering angle.