JPS62146778A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To suppress a step out of a stepping motor to a minimum limit, by detecting the step out of the stepping motor, which adjusts steering ratio of a rear wheel to a front wheel, and decreasing a driving speed of the stepping motor when its step out is detected. 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 has a stepping motor 44 controlled by a control unit 51 so that a preset steering ratio characteristic is obtained. Here the device, when it detects a step out of the stepping motor 44, that is, a deviation of a control value of the motor 44 from the actual steering ratio, performs correction decreasing a driving speed of the stepping motor 44.

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 number)
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 steps with a certain base position as the origin. This is extremely advantageous in that it is possible to perform steering ratio oven control to speed up the responsiveness of the control, that is, to quickly follow changes in vehicle driving conditions and change the steering ratio. Even when the steering ratio is feedback-controlled, the actual steering ratio can be quickly converged to the target steering ratio.

However, for example, if an unexpected large external force is applied to this stepping motor, the stepping motor will not be rotated by the rotation angle corresponding to the input stepping number, and as a result, the rotational position will differ from the actual rotational position depending on the stepping number. This results in a "°'deviation" or "out-of-step", which becomes an obstacle to obtaining the desired steering ratio.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a four-wheel steering system for a vehicle that can prevent large "step-out" of the stepping motor, assuming that a stepping motor is used as an actuator for adjusting the steering ratio. It's about doing.

(Means and operations for solving the problem) In order to achieve the above-mentioned object, the present invention has been developed with the focus on the fact that the stepping motor can increase its driving torque by decreasing its driving speed. be. That is, when step-out is detected, the drive speed is reduced to ensure a large drive torque and prevent "step-out" from progressing. 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; step-out detection means for detecting step-out of the stepping motor; and when step-out of the stepping motor is detected. , and 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 IR1IL 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 pair of left and right tie rods 4R.

It is composed of a relay rod 5 that connects the 4Ls. A steering mechanism C is linked to the front wheel steering mechanism A, and the steering mechanism C is of a rack and pinion type in this embodiment. That is, a rack 6 is formed on the relay rod 5, and a pinion 7 that meshes with the rack 6 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 vehicle is steered clockwise in the figure by an amount corresponding to the amount of operational displacement of the handle 9, that is, the steering angle. Similarly, when the steering wheel 9 is turned to the left, the left and right front wheels IR1I
L will be steered to the left.

The rear wheel steering mechanism B is similar to the front wheel steering mechanism A.

A pair of left and right knuckle arms l0R110L and tie rods IIR, IIL, and the tie rods 11R,
11L, and a relay rod 12 that connects the rear wheel steering mechanism B. In the embodiment, the rear 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 attached to the relay rod 12.
is fixed to the vehicle body, while the inside of the cylinder 13a is divided into two chambers 13.
A piston 13d defined at L3c and L3c is integrated with the relay rod 12. Two chambers 13b and 13c within this cylinder 13a are connected to a control valve 16 via piping 14 or 15. Further, each of the control valves 16 includes a reservoir tank I7.
Pipes 18 and 19 extending further are connected, 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. 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, 1. The relay rod 12 is displaced to the left in FIG.
rotates clockwise in FIG. 2 about the rotation centers 10R' and IOL', and the rear wheel 2R22L is 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 21
When the rear wheel 2R12L 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. That will happen. Note that 13e and 13f in FIG. 2 are springs that bias 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 inspected 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 lot of the steering ratio changing device H is shared 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 manpower section 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 pivoted more freely. This Holter 32 is
The rotation axis 32a is the moving axis edge stand 1 of the human power section 21a.
It is held in the vehicle body so as to be rotatable around an orthogonal line 2 that is perpendicular to . Then, the bin 33 has both Mlt
It is located at the intersection of and sentence 2, and extends in a direction perpendicular to the orthogonal line 12. Therefore, the swing arm 3
1 is able to swing freely around the bottle 33, but by rotating the holder 32, the inclination angle between the bottle 33 and the movement axis m, i.e., the swinging around the bottle 33 can be changed. The inclination angle of the raceway surface with respect to a plane (reference plane) perpendicular to the moving axis edge stand 1 is variable.

The tip of the swing arm 31 and the input section 21a are]!
! They are connected by a connecting rod 34. That is, the connecting member 34 is connected to the tip of the swing arm 31 via a pole joint 35, and is also 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, if the ball joint 35 is displaced in the left-right direction in FIG. 3, the input section 21a will be displaced in the left-right direction in FIG. 3 in accordance with this displacement.

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 KLt, 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 about 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 shaft edge stand l are If it is tilted, the pole joint 35 is displaced in the left-right direction in Eg3 diagram, that is, in the direction of the movement axis fLt, as the pole joint 35 swings about the bin 33, and this displacement is transmitted to the input section via the connecting rod 34. 21a, and the input unit 21
a will be displaced. The displacement of the pole joint 35 in the left-right direction in FIG.
When the inclination angle of the bin 33, that is, the rotation angle of the holder 32 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 meshing 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 looks like this. 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 based on the movement axis 1 of the pole joint 35 (input section 21 a). The effect on displacement in the construction direction will be explained. Now, the swinging angle of the swinging arm 31 about the bin 33 is θ, the reference plane orthogonal to the moving shaft edge stand 1 is δ, and the inclination angle that the swinging orbital surface of the swinging arm 31 makes with the reference plane δ is If α is the eccentric distance of the pole joint 35 from the bin 33, then the displacement The function is Therefore, if the inclination angle α is fixed to a certain value, X will be a function of θ, that is, depending on the steering angle, and this inclination angle α
If the value of is changed, the value of X will change even if the steering wheel angle is the same. And this inclination angle α
A change in the above results in a change in the steering ratio.

An example of changing the steering ratio by adjusting the inclination angle as described above is the case shown in Figure 4 of the Edict. 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 FIG. 3). The necessary rotation range of the stamping 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 as follows.
The stepping number is r580J.

Reference numeral 51 in FIG. 2 denotes a control unit composed of, for example, a microcomputer, and this control unit 51 includes:
In addition to the output from the steering ratio sensor 45, the vehicle speed sensor 53
The output from is now input. Further, from this control unit 51, the stepping motor 44
The signal is output to an alarm device 54 consisting of a lamp, a buzzer, etc.

Next, the details of the control by the control unit 51 will be explained based on the flowcharts shown in Figures 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 l", "
Three types of flags, ``Flag 2'' and ``Flag 3,'' are used, and the meaning of each flag is as follows.

-Flag 1 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 to "l", and it is set to "l" only once every time the vehicle speed goes from non-zero to zero.
This is used to initialize the motor position.

■Flag 3 Set to “1” when step-out of the stepping motor 44 is detected.
When this step-out is detected once, it is used to prohibit step-out checking until "motor position initialization" is completed.

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

Interrupt processing 1 (Fig. 8) The interrupt routine shown in Fig. 8 is for driving the stepper blowfish motor 44, and is performed every predetermined time set by a timer (for example, the stepper motor 44 is activated at 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, it is designed to be driven by one stepping number for each interrupt. Therefore, the driving speed of the stepping motor 44 is reduced as the interrupt time (T) becomes longer, and as explained in FIG. The length is gradually increased each time a degree is detected. 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. , rMPJ is, as described above, the swinging position M of the sector gear 40 from the origin position (the steering position of the rear wheels 2R12L) when the reverse phase side stopper 49 is set to the origin position, expressed as a stepping number. be.

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 S43, 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 or not it is a POMF. 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 S47, and then the process moves to step S43. On the other hand, when it is determined in step S45 that CP>MP, the stepping motor 44 is driven by one step toward the same phase in step S4B, and then step S45 is determined.
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. ``Such puzzles generated by the vehicle speed sensor 53 are sequentially counted and integrated in step S51, and the P CW
It is stored as T.

Interrupt 3 (FIG. 10) This interrupt processing is performed by the vehicle speed sensor 53 and the vehicle speed sensor 53 set as described above so that the cumulative count pulse number explained in FIG. Due to the relationship with the meter cable, 282.575m5e
An interrupt is made to the main routine shown in No. 61A every c.

That is, after the PGMT is directly set as the vehicle speed value (km/h) in step S52, the integrated count value PGMT of step S51 in FIG. 9 is cleared in step S53.

Note that FIG. 9 and FIG. 1O are merely examples of vehicle speed detection, and the 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, MPPO2CP=-
580, flag 1 = rlJ, the table number N of the table in which the stepping motor 44 drive interrupt time T is set is set to the initial value O, and this interrupt time T
Assume that corresponds to the above table number N=0. In addition, in the embodiment, the table number N of the above table is 0.
, l, 2.3..., the driving speed of the stepping motor 44 increases to 100PPS, 90PPS, etc.
S, 80PPS, etc., the speed is decreased by 10PPS, and the maximum speed is 100PPS corresponding to N=0. Moreover, setting Cp=-sao is, as is clear from the explanation of FIG. 8 mentioned above, step S4.
5 through step S46,
This is to return the sector gear 40 until it comes into contact with the opposite phase side stopper 49, that is, to perform "motor position initialization". This is because even if it is returned by 580 steps, it will definitely come into contact with the opposite phase side stopper 49 and return to the original position.

After this, in step S3, it is determined whether the flag l is "1". In this step S3, since flag 1 is initially set to "l" in step S2, the process moves to step S4. In this step S4, it is determined whether CP=MP.
If it is not P, a loop returns from step S3 to step S4 again, and as the stepping motor 44 shown in FIG. 8 is driven during this loop (MP approaches -580), eventually CP=MP
becomes. Then, when this CP=MP, "motor position initialization" is completed, and MP=O1CP=
0, flag 1=0, flag 2=1, and flag 3=0.

When it is determined in step S3 that flag 1 is not rlJ, it is determined in step S6 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, it is determined that the vehicle is running, then in step S7, CP is set to a value corresponding to the vehicle speed based on the map shown in FIG. 4 (FIG. 5). . After this, after flag 1 and flag 2 are both set to "0" in step S8, a step-out check is performed in step S9, which will be described later.
Return to step S3.

Further, when it is determined in step S6 that the current vehicle speed is zero, flag 2 is set to r in step SlO.
QJ or not is determined, and if flag 2 is not "0", that is, rlJ, the stepping motor 44 has not been driven after "motor position initialization", so this "motor position initialization" is performed again. As it is unnecessary to do so.

The process directly returns to step S3. If flag 2 is determined to be "0" in step S10, the process moves to step Sll to perform "motor position initialization" (same as setting in step S2).

First, in step 521, it is determined whether or not flag 3 = 0, that is, whether or not step-out has occurred after completion of "motor position initialization". If it is determined that a key is not occurring, the process moves to step S22. In this step S22, the actual steering ratio detected by the steering ratio sensor 45 is
0 read as the converted value θS, then step S23
, the stepping number corresponding to this θS is MPX
After the IMP
- Whether or not MPX l is smaller than a predetermined setting value, that is, whether the actual steering ratio (MP It is determined whether or not the value is within "5"].

In step S24, if IMP-MPXl is larger than the set value, it means that "r step-out" has occurred, and in this case, the process moves to step 525. In this step S25, among the tables in which the driving speed of the stepping motor 44 is set, a table number corresponding to the current driving speed is selected than the table number N (the upper limit value of N) in which the slowest driving speed is set. It is determined whether N is smaller. Then, in step S44, if the current table number N is smaller than the upper limit value, the process moves to step 526, where the table number N is a table number for which a driving speed is set one step slower than the current driving speed. will be updated to.

Then, in step 527, a time T corresponding to the updated table number is set (reduction in driving speed), and then flag 3 is set to 1 in step S28.

In step S24, if IMF-MPXl is smaller than the set value, it means that step-out has not occurred.
Return as is. In addition, if it is determined in step S21 that 7 lag 3 is not 0, there is no need to check for synchronization until "motor position initialization" is completed after one synchronization, so in this case as well, finish.

Here, in this embodiment, in step S25,
When it is determined that the table number N is not smaller than the upper limit value, it means that there is no table for setting the drive speed of the stepping motor 44 to a smaller value. In this case, the process moves to step S29, where it is determined that it is no longer possible to prevent step-out, and the alarm 54 is activated and the interrupt time T is set such that the driving torque of the stepping motor 44 becomes extremely large. CP is set to a set value of , that is, an extremely low speed, and CP is set to a value corresponding to a steering ratio of 0 at which the rear wheels 2R12L are in the neutral position. After that, the detected value θS of the steering ratio sensor 45 is read (step 532), and this θS is set to MP (step 533), and in step 534, the value θS is set to MP.
After waiting for the time when and CP substantially match (the time when the rear wheels 2R12L are returned to the substantially neutral position), in step S35, all interrupts are prohibited and control of the steering ratio is stopped.

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.

(Effect of the invention) As is clear from the above description, the present invention has been made.

When a step-out occurs in the stepping motor for adjusting the steering ratio, the drive speed is reduced to make it less likely to occur. This is preferable for controlling the steering ratio to a predetermined steering ratio sensor.

Of course, in the present invention, the driving speed of the stepping motor is set as fast as possible unless step-out occurs in the stepping motor, so that control accuracy is ensured while ensuring control response as fast as possible. can be secured.

[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. 6 to 10 are flowcharts showing control examples according to the present invention. A: Front wheel steering mechanism B: Rear wheel steering mechanism C Ni steering mechanism E: Steering ratio changing device IR, IL: Front wheel 2R12L: Rear wheel 9: Handle 44 Nischy 2 pin motor 45: Steering ratio sensor 51; Control unit Figure 6 Figure 8

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 a steering ratio; step-out detection means for detecting step-out of the stepping motor; and reducing the driving speed of the stepping motor when step-out of the stepping motor is detected. A four-wheel steering device for a vehicle, comprising: a drive speed correction means;