JPS62218282A - Four-wheel steering gear for vehicle - Google Patents

Abstract

PURPOSE:To improve stability and safety of a vehicle for its running, by fixing the steering ratio to a predetermined value mainly by an actuator while by a mechanical urging means only when the actuator is inoperative, when abnormality is generated in an electrical system. CONSTITUTION:A rear wheel steering mechanism generates auxiliary power of steering by pressure oil supplied to and discharged from right and left pressure oil chambers of a power cylinder 15. Here a solenoid valve 37, which is closed in the normal time, is mounted interposing between bypass passages 38 connecting the both pressure oil chambers, and said valve 37 is controlled by an electrical system fail-safe mechanism 34 in a controller 28. Said fail-safe mechanism 34, which sets the first fail mode resetting the rear wheel steering mechanism slowly to a predetermined position by driving a pulse motor 25 and the second fail mode resetting the steering mechanism faster than the first fail mode, is constituted so as to control the valve 37 after the above described modes are decided in a mode decision part 35 in accordance with a signal from a trouble condition detecting means 45.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a four-wheel steering system for a vehicle that improves steering stability and safety when an abnormality occurs in the electrical system of a rear wheel steering mechanism. Regarding.

[Prior art]

Conventionally, as a four-wheel steering system for a vehicle such as an automobile, for example, as disclosed in Japanese Patent Laid-Open No. 59-128054, the steering angle of the rear wheels is adjusted in accordance with the traveling speed of the vehicle and the steering angle of the front wheels. It is known that the steering wheel is controlled by an electrically driven actuator such as a pulse motor, and the steering operation of the actuator is assisted by a hydraulic device having a double-acting hydraulic cylinder. In such a four-wheel steering system for a vehicle, it is necessary to ensure safety against failure of the electrical system including the actuator and a control means for controlling the actuator.

The electrical system failures listed above include mechanical locking of the alternator, disconnection or short circuit within the alternator, loosening or disconnection of the belt that transmits engine rotation to the alternator, battery life, or disconnection within the battery. Also, there was a problem that the actuator did not operate normally.

Conventionally, in order to ensure safety against failures in the electrical system, a pair of springs have been provided that return the piston of the hydraulic cylinder to, for example, a neutral position. When a failure is detected by the failure detection means and the electric system failure detection means, the hydraulic pressure of the hydraulic circuit is removed, or the pressure receiving chambers on both sides of the piston are communicated with each other to eliminate the differential pressure acting on both sides. Control means are provided for this purpose. In such a four-wheel steering system for a vehicle, the operation of the control means and the action of the spring ensure that the pistons are returned to the neutral position or the maximum position on the same phase side, even if any electrical system failure occurs. It is returned and held in that position. For example, when the piston returns to the neutral position, the steering ratio of the rear wheels becomes 0, and the steering of the vehicle depends only on the two front wheels. This operation was intended to ensure safety in the event of a failure of the control circuit while the vehicle is running.

However, when the piston of a hydraulic cylinder is held in a neutral position etc. by the force of a spring in this way, it is not possible to control the operating speed of the piston, so the rear wheel suddenly returns to the neutral position etc. Improvement is required.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned conventional circumstances, and the present invention fixes the steering ratio to a predetermined value mainly by using an actuator when an abnormality occurs in the electrical system. By fixing the steering ratio to a predetermined value using mechanical biasing means only in the case of operation,
The object of the present invention is to provide a four-wheel steering device for a vehicle that improves running stability and safety.

[Structure of the invention]

In order to achieve the above object, a four-wheel steering device for a vehicle according to the present invention includes a rear wheel steering mechanism that steers the rear wheels with a steering ratio characteristic that changes depending on the driving condition of the vehicle, and A four-wheel steering system for a vehicle comprising an actuator that variably controls a ratio, a first fail mode in which the actuator fixes the steering ratio to a predetermined value, and a mechanical urging means to fix the steering ratio to a predetermined value. and a second fail mode in which the four-wheel steering device is fixed, and a mode determination section is provided for determining whether the four-wheel steering device is in the first fail mode or the second fail mode in response to a signal from a failure state detection means for detecting a failure state of the four-wheel steering device. , when the drive power of the actuator is sufficient, the rear wheel steering mechanism is returned to the predetermined position relatively slowly, and only when the drive power of the actuator is insufficient, the rear wheel steering mechanism is returned to the predetermined position more quickly. It is characterized by being configured so that it can be restored.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 to 4.

The front wheel steering device 1 is configured to transmit rotation of a steering wheel 3 to left and right front wheels 2 via a rack and pinion mechanism 4, left and right tie rods 5, and knuckle arms 6. The rear wheel steering device 7 includes a rear wheel steering rod 9 slidably supported on the vehicle body, a pair of left and right tie rods 10, and a pair of left and right knuckle arms 11 in order to steer the left and right rear wheels 8 in coordination with each other. It is equipped with A rank (not shown) is formed on the rear wheel steering rod 9, and a binion 13 formed on a pinion shaft 12 is meshed with this rack, and the rack and binion 13 constitute a steering gear mechanism 14. A piston 15a of a power cylinder 15, which is a double-acting hydraulic cylinder, is fixed to the rear wheel steering rod 9, and the cylinder of the power cylinder 15 is fixed to the vehicle body. Each pressure oil chamber 15 of this power cylinder 15
b are connected to a control valve 18 disposed around the pinion shaft 12 via pressure oil passages 16 and 17, respectively. The control valve 18 is connected to a hydraulic pump 22 driven by, for example, an electric motor 21 via a pressure oil supply passage 19 and a return oil passage 20. The control valve 18 selects one of the repressurized oil chambers 15b of the power cylinder 15 in response to the rotation of the pinion shaft 12 in order to control the assist force and its direction of the rear wheel steering device 7. The other pressure oil chamber 15b is connected to the return oil passage 20, and the piston 15a and the rear wheel steering rod 9 are connected to the pressure oil supply passage 19, and the piston 15a and the rear wheel steering rod 9 are connected to the pressure oil supply passage 19. Room 1
It is configured to be driven toward the 5b side. The pinion shaft 12 is connected via a pair of bevel gears 23 and 24 to a pulse motor 25 as an actuator that controls the turning angle of the rear wheel steering device 70. The pinion shaft 12 is rotated in either the forward or reverse direction by the pulse motor 25, and the rear wheel steering rod 9 is moved while being assisted by the power cylinder 15, thereby steering the rear wheels 8 left and right. ing. In order to control the steering angle of the rear wheel steering device 7 in accordance with the steering angle of the front wheel steering device 1 and the traveling speed, a front wheel steering angle sensor 26 that detects the steering angle of the front wheels 2 and a vehicle speed sensor are provided. A vehicle speed sensor 27 for detecting the vehicle speed and a controller 28 for controlling the electric motor 21 by inputting their outputs are provided. As shown in FIG. 1, this controller 28 includes a characteristic storage section 29 that stores preset steering angle characteristics (characteristics of rear wheel steering angle with respect to front wheel steering angle), the front wheel steering angle sensor 26, and A target steering angle calculation unit 30 that compares the output signal of the vehicle speed sensor 27 with the memory in the characteristic storage unit 29 and calculates a target steering angle in that state, and generates a pulse number signal corresponding to the calculation result. Pulse generator 31
and a driver 32 that drives the pulse motor 25 in response to pulse signals from the pulse generator 31. Further, 5V power is supplied from the battery 33 to the controller 28 via the 5V constant voltage circuit 46, and 12V power is supplied to the drivers 32 and 40 that drive the pulse motor 25 and the solenoid valve 37. , the battery 33 is connected to a battery voltage sensor 44 which is one of the fault state detection means 45 for detecting the battery voltage .

Furthermore, in the four-wheel steering system of this vehicle, when a failure such as a short circuit or disconnection occurs in the circuit components related to four-wheel steering including the drive power source in the electrical system of this vehicle, the steering ratio is set to O1. An electrical fail-safe device 34 is provided for switching to a two-wheel steering state or returning the steering ratio to the maximum value on the same phase side or an intermediate value on the same phase side. This electrical fail-safe device 34 is configured to change the steering ratio at a speed corresponding to the nature of the failure. That is, the pulse motor 25 is driven to operate the rear wheel steering device 7 relatively slowly in order to provide a sense of stability in steering in the event of a failure while driving and to prevent an inexperienced driver from making a sudden and dangerous steering operation. It has two return modes: a mode in which the rear wheel steering device 7 is returned to the predetermined position (first fail mode), and a mode in which the rear wheel steering device 7 is returned to the predetermined position faster than this mode (second fail mode). The electrical fail-safe device 34 includes the above-mentioned panteri voltage sensor 44 and an alternator output voltage sensor 43 which is connected to the alternator terminal and is one of the fault state detection means 45 for detecting the output voltage vA of the alternator.
A mode determining section 35 is provided which determines which of the above return modes is to be selected based on the output of and outputs a slow return command or a rapid return command in accordance with the result of the determination. Further, in the controller 28, in response to the slow speed return command, the target turning angle of the target turning angle calculating section 30 is stored.
For example, in the case of Oo, a neutral return command section 36 is provided. Furthermore, the side pressure oil chamber 1 of the power cylinder 15
5b and a bypass oil passage 38 with a normally closed solenoid valve 37 interposed therebetween, and a side pressure oil chamber 15b.
A spring 39 is inserted into the controller 28 to return the piston 15a to a neutral position, etc., and a driver 40 is provided in the controller 28 to open the solenoid valve 37 in response to the quick return command. There is.

Note that the steering angle characteristics stored in the characteristic storage section 29 are as follows:
For example, at low vehicle speeds, as the front wheel steering angle increases, the rear wheel steering angle changes from the same phase (the front and rear wheels are steered in the same direction) to the opposite phase (the front and rear wheels are steered in opposite directions).
At high vehicle speeds, as the front wheel steering angle increases, the rear wheel steering angle increases in the same phase, but the ratio of the rear wheel steering angle to the front wheel steering angle changes depending on the lateral G and yaw rate depending on the vehicle driving condition. It should be changed so that it occurs.

In the above configuration, when the engine starts operating,
As shown in FIG. 3, the battery voltage VB is detected by the battery voltage sensor 44 (F1), and the alternator L terminal voltage (2) is detected by the alternator output voltage sensor 43 (F2).

Next, based on the output signals from the battery voltage sensor 44 and the alternator output voltage sensor 43, the mode determination unit 35 determines whether the battery voltage VB is higher than a predetermined voltage V (F3) and whether the alternator terminal voltage vA is It is determined whether the voltage is higher than a predetermined voltage v2 (F4). Here, if either answer is negative, the side voltage v8
- vA is measured, while if both answers are positive, the main routine is started (F5). In this main routine, first, the mode determination unit 3 determines whether or not the alternator output voltage ■ is higher than the predetermined voltage ■3.
5 (F6). Here, if the alternator terminal voltage V is higher than the predetermined voltage V3, then the mode determination unit 35 determines whether the battery voltage V6 is higher than the predetermined voltage V4 (Fl). If the battery voltage VB is higher than the predetermined voltage V4, normal control is achieved (F8).
, again both mold pressures VA -V! Measure l. If the battery voltage (8) is lower than the predetermined voltage (4), for example, if there is a disconnection in the battery, a slow return command is output from the mode determination unit 35 to the neutral return command unit 36, which causes the target steering angle to change. The target turning angle of the calculating section 30 is set to O''. The target turning angle calculating section 30 outputs a signal corresponding to the calculation result to the pulse generator 31, and the pulse generator 31 sends a pulse to the driver 32. A signal is output. In response to this pulse signal, the driver 32 drives the pulse motor 25 toward the neutral position, slowly returns the rear wheel steering device 7 to the neutral position, and performs two-wheel steering (
2WS) (F9).

Next, a sensor provided on the pulse motor 25 detects whether the rear wheel steering device 7 is at the 2WS position (FIO). If the position is 2WS, the pulse motor 25 is fixed (Fl]). Further, if the driver 4 is not in the 2WS position, the mode determination unit 35 sends the driver 4
Outputs a quick return command to 0. As a result, the solenoid valve 37 is opened and the repressurization oil chamber 15b of the power cylinder 15 is connected via the bypass oil passage 38, and the pressure difference in the repressurization oil chamber 15b is eliminated, so that the piston 15a is moved by the spring 39. will be returned to the neutral position. As a result, the rear wheel steering device 7 is returned to the neutral position (F12). Also, when the alternator output voltage V is lower than the predetermined voltage ■3, the battery voltage ■8
The battery voltage sensor 44 detects whether or not the voltage is higher than a predetermined voltage (4) (F13). If the battery voltage V is lower than the predetermined voltage V4, the solenoid valve 3
7 is opened to return the rear wheel steering device 7 to the neutral position (Fl4). If the battery voltage (2) is higher than the predetermined voltage v4, it is detected whether the vehicle speed was greater than 10 seconds (Fl5).

If the vehicle speed is low for more than 10 seconds, it is determined that the engine has stalled, and normal control is performed (Fl5), and both mold pressures are increased again.
・Detect ■8. If the vehicle speed exceeds 10 seconds,
The abnormality detection signal is input to the mode determination section 35, which drives the pulse motor 25 to slowly return the rear wheel steering device 7 to the neutral position.

Note that it is preferable that the fixation of the pulse motor 25, which is the actuator, to the neutral position is released by turning off all power when the engine is stopped or turning on the power when starting the next engine.

Furthermore, in the explanation of the above flowchart, the pulse motor 25 or the piston 15a is fixed at the neutral position in the event of an abnormality in the power supply system, but the pulse motor 25 or the piston 15a is not limited to the neutral position. , or an intermediate position on the same phase side, etc., as required, of course.

〔Effect of the invention〕

As described above, the four-wheel steering system for a vehicle according to the present invention has a first fail mode in which the steering ratio is fixed at a predetermined value by an actuator, and a first fail mode in which the steering ratio is fixed at a predetermined value by a mechanical urging means. 2 fail modes, and is provided with a mode determination unit that determines whether the four-wheel steering device is in the first fail mode or the second fail mode in response to a signal from the failure state detection means that detects the failure state of the four-wheel steering device. If the drive power of the actuator is sufficient, the rear wheel steering device is returned to the specified position relatively slowly, and only when the drive power of the actuator is insufficient, the rear wheel steering device is returned relatively quickly by mechanical biasing means. can be returned to the predetermined position. Thereby, there is no possibility that the steering becomes unstable, and there is an effect that safety can be further improved.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the main parts of an electrical system related to four-wheel steering according to an embodiment of the present invention, Fig. 2 is a general schematic diagram of an embodiment of the present invention, and Fig. 3 is a diagram showing the above-mentioned embodiment. FIG. 3 is a flowchart when the four-wheel steering system of the vehicle is activated. 7 is a rear wheel steering mechanism (rear wheel steering device), 15 is a power cylinder, 15b is a cylinder chamber, 25 is an actuator (pulse motor), 28 is a controller, 35 is a mode determination section, 37 is a solenoid valve, 43 is an alternator output Voltage sensor, 44, battery voltage sensor, 4
5 is a fault state detection means, which in this embodiment includes an alternator output voltage sensor 43 and a battery voltage sensor 4.
4 constitutes a failure state detection means 45.

Claims (1)

[Claims] 1. A four-wheel steering system for a vehicle, comprising a rear wheel steering mechanism that steers the rear wheels with a steering ratio characteristic that changes depending on the driving condition of the vehicle, and an actuator that variably controls the steering ratio. A first fail mode in which the steering ratio is fixed at a predetermined value by an actuator and a second fail mode in which the steering ratio is fixed at a predetermined value by a mechanical urging means are set, and a failure state of the four-wheel steering device is set. 1. A four-wheel steering system for a vehicle, comprising a mode determination section that determines whether the mode is a first fail mode or a second fail mode in response to a signal from a failure state detection means that detects a failure state.