JPS62146777A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To prevent a stepping motor from generating its step out, by detecting supply voltage to the stepping motor, which adjusts steering ratio of a rear wheel to a front wheel, and decreasing a driving speed of said motor corresponding to a decrease of the detected voltage. CONSTITUTION:The captioned device has a front wheel steering mechanism A equipped with a power steering mechanism F controlled by a steering mechanism C and a rear wheel steering mechanism B equipped with a power steering mechanism D related to said mechanism C through the front wheel steering mechanism A and a steering ratio change gear E. The steering ratio change gear E, having a stepping motor 44, is controlled by a control unit 51 so that a preset steering ratio characteristic is obtained. Here the device provides a voltage sensor 54 detecting supply voltage to the stepping motor 44. And the device performs a correction to decrease a driving speed of the stepping motor 44 corresponding to a decrease of the supply voltage detected by the voltage sensor 54.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a four-wheel steering system for a vehicle.

(Prior Art) Some vehicles are designed to steer both the front wheels and the rear wheels, so-called four-wheel steering, as disclosed in Japanese Unexamined Patent Publication No. 199771/1983.

In this four-wheel steering, since the ratio of the rear wheel steering angle to the front wheel steering angle, that is, the steering ratio, is changed depending on the driving condition of the vehicle, the steering of the rear wheels is controlled electrically. Common.

(Problems to be Solved by the Invention) By the way, as mentioned above, when controlling the steering of the rear wheels electrically, from the viewpoint of ease of control, etc., an actuator for adjusting the steering ratio is used. It is conceivable to use a stepping motor (pulse motor). This stepping motor has its stepping number (pulse a)
Therefore, the rotation angle is uniformly determined, and the desired rotation position, that is, the steering ratio, can be easily and accurately controlled by the number of steppings with a certain reference position neck as the origin. This is extremely advantageous in that open control of the steering ratio can be used to speed up the responsiveness of the control, that is, the steering ratio can be changed quickly to follow changes in the vehicle's driving conditions. Even when the steering ratio is feedback-controlled, the actual steering ratio can be quickly converged to the target steering ratio.

However, when the supply voltage of this stepping motor decreases, its driving torque decreases, so it is not rotated by the rotation angle corresponding to the input stepping number, and as a result, the rotational position according to the stepping number This results in a ``deviation'' between the actual rotational position and the actual rotational position, which becomes an obstacle to obtaining the desired steering ratio. In particular, the voltage supplied to the stepping motor is subject to considerable fluctuations since it is powered by a battery mounted on the vehicle, and some kind of countermeasure is desired in this regard.

Therefore, an object of the present invention is to deal with changes in the supply voltage to the stepping motor, especially when the supply voltage decreases, on the premise that a stepping motor is used as an actuator for adjusting the steering ratio. To provide a four-wheel steering system for a vehicle that can prevent the vehicle from collapsing.

(Means and effects for solving the problem) In order to achieve the above-mentioned object, in the present invention, even if the supply voltage is the same, the stepping motor can increase the driving torque by decreasing the driving speed. This was done by focusing on the following points.

In other words, by lowering this drive speed when the supply voltage decreases, the desired drive torque can be secured and the
This is to prevent "step-out".

Specifically, as shown in Fig. 1, a four-wheel steering system for a vehicle that steers both the front wheels and the rear wheels includes a stepping motor for adjusting the steering ratio of the rear wheels to the front wheels; steering ratio control means for controlling the stepping motor based on a predetermined steering ratio characteristic; voltage detection means for detecting the voltage supplied to the stepping motor; and in response to a decrease in the voltage supplied to the stepping motor, A drive speed correction means for reducing the drive speed of the stepping motor.

(Example) Embodiments of the present invention will be described below with reference to the accompanying drawings.

In Fig. 2, IR is the right front wheel, IL is the left front wheel, 2R is the right rear wheel, and 2L is the left front wheel.The left and right front wheels IR and IL are linked by a front wheel steering mechanism A, and the left and right rear wheels 2R1
2L is linked by rear wheel steering mechanism B.

In the embodiment, the front wheel steering mechanism A includes a pair of left and right knuckle arms 3R13L and a tie rod 4R14L, and a relay rod 5 that connects the pair of left and right tie rods 4R14L. A steering mechanism C is linked to the front wheel steering mechanism A, and the steering mechanism C is of a rack-and-binion type in this embodiment. In other words, the rack 6 is attached to the relay rod 5.
is formed, while the pinion 7 that meshes with the rack 6 is
It is connected to a handle 9 via a shaft 8. As a result, when the handle 9 is turned to the right, the relay rod 5 is displaced to the left in FIG. The steering wheel is steered clockwise in the figure by an amount corresponding to the amount of operation displacement 9, that is, the steering angle of the steering wheel. Similarly, when the steering wheel 9 is operated to turn to the left, the left and right front wheels IR1IL are steered to the left in accordance with the amount of displacement of this operation.

Similarly to the front wheel steering mechanism A, the rear wheel steering mechanism B also has a pair of left and right knuckle arms 10R, 1OL and a tie rod IIR1IIL, and a relay rod 12 that connects the tie rods 4R14L. The wheel steering mechanism B is configured to include a hydraulic power steering mechanism. To explain this power steering mechanism, a cylinder device 13 is attached to the relay rod 12, and the cylinder 13a is fixed to the vehicle body, while a piston 13d defines the inside of the cylinder 13a into two chambers 13b and 13c. It is integrated into the relay rod 12. Two chambers 13b, 13 within this cylinder 13a
c is connected to a control valve 16 via a pipe 14 or 15. Further, pipes 18 and 19 extending from the reservoir tank 17 are connected to each of the control valves 16, and an oil pump 20 driven by an engine (not shown) is connected to one of the pipes 18, which serves as an oil supply pipe. There is. The control valve 16 is of a so-called booster valve type (spool type) in which the control rod 21 is a sliding type, and the input portion 21a of the control rod 21 is also used as a moving member of a steering ratio changing device E to be described later. Further, the output portion 21b of the control rod 21 is integrated with the relay rod 12 of the rear wheel steering mechanism B.

In such a power steering mechanism, as is known, when the control rod 21 is displaced to the left in FIG. 2, the relay rod 12 is displaced to the left in FIG. The arm l0R110L rotates WfJz around its rotation center lOR', 10L'.
The rear wheels 2R and 2L are rotated clockwise in the figure and steered to the right. During this steering, oil is supplied into the chamber 13b of the cylinder device 13 according to the amount of displacement of the control rod 21 to assist in driving the relay rod 12 (boosting effect). Similarly, control rod 2
1 is displaced to the right in FIG. 2, the rear wheel 2R12L is steered to the left while receiving the boosting action of the cylinder device 13 (oil is supplied to the chamber 13b) according to the amount of displacement. will be done. In addition, 13e and 13f in FIG.
This is a spring that biases the rear wheel 2R12L toward the neutral position.

The front wheel steering mechanism A also has a power steering mechanism F like the rear wheel steering mechanism B. This power steering mechanism F includes a cylinder device 65 attached to the relay rod 5 of the front wheel steering mechanism A, and the cylinder 65a is fixed to the vehicle body.
A piston 65d that defines two chambers 65b and 65c inside a is integrated with the relay rod 5. This cylinder 6
The two chambers 65b and 65c in 5a are connected to piping 66 or 67.
is connected to a rotary control valve 68 provided on the shaft 8 of the steering mechanism C. This control valve 68 is connected to a pipe 70 extending from a branch valve 69 connected to the discharge side of the oil pump 20.
, and a pipe 71 branched from the pipe 19 are connected.

Such a power steering mechanism F boosts the operating force of the handle 9 (chamber 65b or 6 of the cylinder device 65).
5c) and transmits it to the relay rod 5.The function of such a power steering mechanism F itself is basically the same as that of the power steering mechanism described above, so no further details will be given. Further explanation will be omitted.

The steering mechanism C and the rear wheel steering mechanism B are linked via the front wheel steering mechanism A and the steering ratio changing device E.

An input rod 22 extends forward from the steering ratio changing device E, and a binion 23 attached to the front end of the input rod meshes with a rack 24 formed on the relay rod 5 of the front wheel steering mechanism A. Note that the output terminal of the steering ratio changing device E is also used by the input portion 21a of the control rod 21 in the control valve 16, as described above.

An example of the steering ratio changing device E will be explained with reference to FIG. 3, and the embodiment has substantially the same configuration as that shown in the above-mentioned Japanese Patent Application Laid-open No. 199771/1983. That is, the input portion 21a of the control rod 21 is held slidably in the vehicle width direction with respect to the vehicle body, and its axis of movement is shown as letter 1. Further, this steering ratio changing device E has a swinging arm 31, and the base end of the swinging arm 31 is connected to the bin 33 with respect to the holder 32.
It is pivotally mounted to allow free movement. This Holter 32 is
The rotation axis 32a is the movement axis Jomon 1 of the input section 21a.
It is held in the vehicle body so as to be rotatable about an orthogonal line 112 that is orthogonal to . The bin 33 is located at the intersection of the two sides 1 and 2, and the orthogonal Jomon 2
It extends in a direction perpendicular to. Therefore, the swinging arm 31 is made to swing around the bin 33, but by rotating the holder 32, the angle of inclination between the bin 33 and the movable shaft edge stand 1, that is, the bin 33 A plane perpendicular to the moving axis of the orbital plane centered on Jomon 1 (reference plane)
The angle of inclination relative to the surface is variable.

The tip of the swing arm 31 and the input section 21a are connected by a connecting rod 34. That is, the connecting member 34 connects to the swing arm 31 via the pole joint 35.
The input section 21a is connected to the input section 21a via a pole joint 36. With such a connecting rod 34, the distance between the pole joints 35 and 36 at each end of the swing arm 31 is always maintained constant. Therefore, the above pole joint 35
If is displaced in the left and right direction in Figure 5S3, then according to this displacement,
The input section 21a will be displaced in the left-right direction in FIG.

The swinging of the swinging arm 31 about the pin 33 is performed according to the operational displacement of the steering mechanism C, that is, the steering angle of the steering wheel. A rotating plate 37 is connected thereto. This rotating plate 37 is rotatably held on the vehicle body so that its rotating shaft 37a is on the movement axis 11, and the connecting rod 34 is connected to the pole joint with respect to the eccentric portion of this rotating plate 37. 38, and is slidably penetrated therethrough.

A bevel gear 39 connected to the input rod 22 is meshed with a rotating plate 37 made of a bevel gear.

Due to such a rotating plate 37, the swinging arm 31 is swung around the bin 33 by an amount corresponding to the steering angle of the steering wheel, but the axis of the bin 33 and the moving axis Jomon 1 are tilted. 3, the pole joint 35 is displaced in the horizontal direction in FIG. 3, that is, in the direction of the moving axis Jomon 1.
The signal is transmitted to the input section 21a via the input section 21a, and the input section 21a is displaced. Even if the swing angle of the swing arm 31 about the bottle 33 is the same, the displacement of the pole joint 35 in the left-right direction in FIG. When the angle changes, it will be changed (steering ratio change).

In order to change the inclination angle, the rotation shaft 32a of the holder 32
A sector gear 40 as a worm wheel is attached to the worm wheel, and a worm gear 41 mated with the sector gear 40 is rotationally driven by a stepping motor 44 as an inclination angle changing means via a pair of bevel gears 42 and 43. It has become so. And this holder 3
The rotation angle, ie, the tilt angle, of the rotation shaft 32a is detected by a steering ratio detection sensor 45, which includes a potentiometer or the like, provided for the rotation shaft 32a.

Here, the above-described swing angle of the swing arm 31 about the bin 33 and the inclination angle of the swing arm 31 (the inclination angle of the bin 33) are determined by the moving axis edge of the pole joint 35 (input section 21 a). The influence on displacement in the vertical direction will be explained. Now, the swing angle of the swing arm 31 about the bin 33 is 0, the reference plane orthogonal to the movement axis It is δ, and the inclination angle that the swing orbital surface of the swing arm 31 makes with the reference plane δ is α. ,
If the eccentric distance of the pole joint 35 from the bin 33 is r, the displacement X of the pole joint 3 in the moving axis Jomon 1 direction is X = r tan a * 51nO, with α and θ as parameters. It becomes a function. Therefore, if the inclination angle α is fixed to a certain value, X is 0
That is, it is a function of the steering angle of the steering wheel, and if the value of this inclination angle α is changed, the value of X will change even if the steering angle of the steering wheel is the same. Then, this change in the inclination angle α directly results in a change in the steering ratio.

As described above, there is a case as shown in FIG. 4 as an example of changing the steering ratio by adjusting the inclination angle. In this Figure 4, the steering ratio is changed according to the vehicle speed, and when the front wheel steering angle in Figure 4 is set to a certain value, the change in the rear wheel steering angle with respect to the front wheel steering angle is shown. FIG. 5 shows how the steering ratio changes depending on the vehicle speed.

Both swing stroke ends of the sector gear 40 driven by the stepping motor 44 are regulated by a pair of stoppers 48, 49 (see Figure i3). The necessary rotation range of the stepping motor 44 over the entire swing range of the sector gear 40 (from the stroke end on the same phase side to the stroke end on the opposite phase side) is r580J in terms of the number of steps.

In FIG. 2, 51 is a control unit composed of a microcomputer, for example, and this control unit 51 includes:
In addition to the output from the steering ratio sensor 45, the vehicle speed sensor 53
Also, outputs from a voltage sensor 54 that detects the voltage supplied to the stepping motor 44 are input. Further, the control unit 51 outputs an output to the stepping motor 44.

Next, the content of control by the above-mentioned control 22) 51 will be explained based on the flowcharts shown in FIGS. 6 to 10. In this embodiment, the stepping motor 44 is
In consideration of the possibility that "step-out" (deviation between the number of steppings and the corresponding actual positional relationship) may occur, the reference position adjustment, that is, "motor position initialization" is performed at any time. This "motor position initialization" involves bringing the sector gear 40 into contact with one of the stoppers 48 or 49 (in the embodiment, the stopper 49 is on the opposite phase side when each member operates in the direction of the arrow in FIG. 3). This time is set as the origin position of the stepping number "0", and the stepping number driven from this origin position is set as the motor position "MP" at that time.
``Motor position initialization'' is performed at the start of control (immediately after starting the engine) and every time the vehicle speed becomes zero. Also,
In the flowchart shown in this embodiment, "flag 1", "
Two types of flags, ``Flag 2'', are used, and the meanings of each flag are as follows.

■Flag l This flag is used to distinguish whether "motor position initialization" is in progress or not. When rQJ, it means that initialization has ended, and rlJ means that initialization is in progress.

■Flag 2 When "Initialize motor position" is executed one time, it is set as rlJ, and it is set as "rlJ" only once every time the vehicle speed changes from non-zero to zero.
This is used to initialize the motor position.

Based on the above, either the interrupt processing for the main routine as shown in FIG. This will be explained starting from Figure).

Interruption place Fl! , 1 (FIG. 8) The interrupt routine shown in FIG. 8 is for driving the stepping motor 44, and is for every required period of time set by a timer (for example, the stepping motor 44 is driven 10 times per second).
If you want to drive at a rate of 0 steps, use 10ms e c
6), an interrupt is made to the main routine of FIG. Then, each interrupt is driven by the number of l steppings. Therefore, the driving speed of the stepping motor 44 is reduced as the interrupt time (T) becomes longer, and as shown in FIG. 7, which will be described later, the supply voltage (V ). In addition, rCPJ in the figure is the target rear wheel steering angle, that is, the target stepping number, necessary to achieve the steering ratio characteristic determined by a map with vehicle speed as a parameter, as shown in FIG. 4 (FIG. 5), for example. ,
In addition, as mentioned above, rMPJ is the reverse phase side stopper 49.
The swinging position of the sector gear 40 (the steering position of the rear wheel 2R12L) from the origin position is shown by the number of steppings when the origin position is taken as the origin position.

Based on the above, first, in step S41, it is determined whether or not the target stepping number CP and the current position MP match, and when CP=MP, the rear wheels 2R12L are set to a predetermined steering ratio characteristic. In step S42, the stepping motor 4
After that, in step 343, a timer is set to a predetermined time T, which will be described later, in preparation for the next interrupt.

When it is determined in step S41 that CP=MP is not true, the current supplied to the stepping motor 44 is increased (current town is canceled) in preparation for driving the stepping motor 44, and then in step S45, C
It is determined whether P>MP. And CP>M
When it is determined that it is not P, stepping motor 4
Since the current position of No. 4 is located on the same phase side with respect to the target stepping number CP, in step S46, the stepping motor 44 is driven by one step toward the opposite phase side. Then, in accordance with this "one stepping" operation, the current position MP is updated by one stepping in step 547, and then the process moves to step S43. On the other hand, when it is determined in step 345 that it is CPOMF, in step 348 the stepping motor 44 is driven by one step toward the same phase side, and then step S
The current position MP is updated in step S49, and the process moves to step S43.

Interrupt (Fig. 9) This interrupt processing is performed every time this pulse is generated (at the rise or fall of the pulse) because the vehicle speed sensor 53 is supposed to generate a pulse as the speedometer meter cable rotates. Then, the main routine of FIG. 6 is interrupted. The vehicle speed sensor 53 is, for example, a 20 pulse sensor (a sensor in which the number of pulses generated when the meter cable rotates once is 20).
Therefore, the number of pulses generated when traveling 1km is r12740 pulses. The pulses generated by the vehicle speed sensor 53 are sequentially counted and integrated in step S51, and then P CNT
is stored as.

Odan, 1%3 (IT construction zone) This interrupt processing is performed by the vehicle speed sensor set as described above so that the cumulative count pulse number explained in the fJSG diagram above can be used as it is as the vehicle speed (km/h). 5
3 and meter cable, 282,575m
An interrupt is made to the main routine shown in FIG. 6 every 5ec.

That is, after the P CNT is directly set as a vehicle speed value (km/h) in step 552, the integrated count value P GMT in step 551 in FIG. 9 is cleared in step S53.

Note that FIGS. 9 and 10 are merely examples of vehicle speed detection, and vehicle speed can be detected by any conventionally known appropriate means.

Main routine (Fig. 6) First, in step S1, the entire system is initialized, and in step S2, MP=0. CP=-
580, flag 1=rlJ, timer set time T for interrupt for driving the stepping motor 44 is set to the initial value. That is, setting CP=-580 means forcibly performing the process from step S45 to step S46, as is clear from the explanation of FIG. This is to return the sector gear 40 until it makes contact, that is, to "initialize the motor position." The reason for setting it to the value r580J is that no matter what position the sector gear 40 is currently in, if it is returned by 580 steps, the phase will always be reversed. This is because it can be brought into contact with the side stopper 49 and returned to the original position.

Thereafter, in step S3, a voltage check, which will be described later, is performed, and then in step S4, it is determined whether flag 1 is rlJ. In this step S4,
Since flag 1 is initially set to "1" in step S2, the process moves to step S5. This step S5
Then, it is determined whether CP=MP or not, but CP=
If it is not MP, step S4 is performed again from step S3.
During this loop, the stepping motor 44 shown in FIG. 8 is driven (MP approaches -580), and eventually CI''=
Becomes an MP. And when this CP=MP,
Since "motor position initialization" is completed, MP = 01
CP=O, flag 1=o, and flag 2=1.

When it is determined in step S4 that flag 1 is not rlJ, it is determined in step S7 whether or not the current vehicle speed is zero.

In this determination, if it is determined that the vehicle speed is not zero, that is, the vehicle is running, then in step S8, CP is set to a value corresponding to the vehicle speed based on the map shown in FIG. 4 (FIG. 5). . After this, in step S9, flag 1 and flag 2 are both set to "0", and the process returns to step S3.

Further, when it is determined in step S7 that the current vehicle speed is zero, in step 510 flag 2 or "
0", and if flag 2 is not "0", that is, "1", the stepping motor 44 is not driven after "motor position initialization", so this "motor position initialization" is performed. It is not necessary to repeat the process ``'' again, and the process returns to step S3. Also, step S1
If it is determined that the flag 2 is "0", the process moves to step Sll to perform "motor position initialization" (same as setting in step S2).

Voltage Check (FIG. 7) This voltage check is performed by first reading the supply voltage V to the stepping motor 44 in step S21, and then calculating the timer set time T according to this supply voltage V in step S22. This time T is set to a constant value when the supply voltage V is equal to or higher than a predetermined voltage.In this way, by increasing the time T as the supply voltage V becomes smaller, it becomes clear from the explanation of FIG. By lowering the driving speed of the stepping motor 44, which means that the time required to drive the stepping motor 44 one stepping number (interrupt time in FIG. 8) becomes longer, the stepping motor 44 can be driven as follows. A similar predetermined large drive torque is always ensured before and after the supply voltage V decreases, and "step-out" is prevented. Note that the supply voltage V is the same as the supply voltage to the stepping motor 44. Although it may be detected directly, it may also be detected indirectly by checking the battery voltage.

Although the embodiments have been described above, if the control unit 51 is configured by a computer, it may be of either a digital type or an analog type.

(Effects of the Invention) As is clear from the above description, the present invention prevents step-out of the stepping motor for adjusting the steering ratio in the event of a voltage drop and always maintains the steering ratio at a predetermined steering ratio. It becomes possible to control for adjustment.

Of course, in the present invention, the driving speed of the stepping motor is set to be low when the supply voltage decreases, in other words, the driving speed of the stepping motor is set to be high when the supply voltage is normal. It is possible to ensure control accuracy while ensuring control response as fast as possible.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the present invention. FIG. 2 is an overall plan view showing one embodiment of the present invention. FIG. 3 is a skeleton diagram showing the rear wheel steering mechanism. FIG. 4 and FIG. 5 are graphs showing an example of steering ratio characteristics. FIG. 6 to FIG. 1O are flowcharts showing control examples according to the present invention. A: Front wheel steering mechanism B: Rear wheel steering mechanism C steering mechanism E: Steering ratio changing device IRlIL: Front wheel 2R12L: Rear wheel 9 steering wheel 44 Ni steering motor 51: Control unit 54: 'i' [pressure sensor

Claims (1)

[Claims] (1) A four-wheel steering system for a vehicle that steers both the front wheels and the rear wheels includes a stepping motor for adjusting the steering ratio of the rear wheels relative to the front wheels, and a steering ratio based on predetermined steering ratio characteristics. steering ratio control means for controlling the stepping motor by using the following steps; voltage detection means for detecting the voltage supplied to the stepping motor; and a drive for reducing the driving speed of the stepping motor in response to a decrease in the voltage supplied to the stepping motor. A four-wheel steering device for a vehicle, comprising: a speed correction means;