JPH0224271A - Device for controlling steering of vehicle - Google Patents

Abstract

PURPOSE:To improve traveling stability at the time when a vehicle is traveling on an uneven road by detecting the uneven condition of the road surface and correcting the assistingly steering quantity command value of a steering control means based on the detected value. CONSTITUTION:The steering control device of a vehicle for assistingly steering at least one part of front wheels or rear wheels has an assistingly steering mechanism A for assistingly steering at least one part of the front and rear wheels. This assistingly steering mechanism A is controlled based on an assistingly steering quantity command value generated by a steering control means B in accordance with the steering input values of a steering angle, steering angular velocity, steering torque, etc. In this case, by providing a road surface condition detecting means C for detecting the uneven condition of a road surface (a bad road or a rough road) and, based on the detected value of a road surface condition detected by the detecting means C, the assistingly steering quantity command value is corrected so as to select a smaller value than that at the time of traveling on a good road by an assistingly steering quantity correcting means D, to improve the traveling stability at the time of traveling an uneven road.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a steering control device for a vehicle that performs auxiliary steering of at least one of a front wheel and a rear wheel.

[Conventional technology]

As a conventional steering control device for a vehicle capable of auxiliary steering, there is, for example, a vehicle steering control device described in Japanese Unexamined Patent Publication No. 61-287867.

This conventional steering control device includes a front wheel steering mechanism and a rear wheel steering mechanism, and the rear wheel steering mechanism varies the ratio of the rear wheel steering angle to the front wheel steering angle according to a predetermined steering ratio characteristic. a steering ratio variable means, a detection means for detecting vertical vibration of the vehicle body, and receiving an output signal from the detection means, adjusting the ratio of the rear wheel steering angle to the front wheel steering angle in the same phase according to an increase in the vertical vibration of the vehicle body. It is equipped with a correction means for correcting in the direction.

According to this conventional steering control device, when driving on an uneven road (bad road or bumpy road), the rear wheels are steered in the same phase direction as the front wheels, and the turning of the vehicle is restricted, compared to when driving on a good road. As a result, it prevents the vehicle from skidding due to a decrease in grip on the road surface, improving driving stability.

[Problem to be solved by the invention]

However, in such conventional steering control devices, the control gain for rear wheel steering in the same phase direction increases, so when driving on an uneven road, the steering is steered (kickback) due to road surface disturbance. If this happens, it will be mistakenly assumed that the driver has turned the steering wheel, and the rear wheels will be assisted with a large steering angle even though the driver is not actively steering the vehicle, impairing the vehicle's driving stability. There was an unresolved problem.

SUMMARY OF THE INVENTION In order to solve these problems, it is an object of the present invention to provide a steering control device for a vehicle that can improve running stability even when running on an uneven road.

[Means for solving problems]

In order to solve the above problems, as shown in FIG. A vehicle steering control device comprising a steering control means for controlling based on an auxiliary steering amount command value corresponding to a steering input value such as angular velocity or steering torque, comprising: a road surface condition detection means for detecting an irregular state of a road surface; The present invention is characterized by comprising an auxiliary steering amount correction means for correcting an auxiliary steering amount command value of the steering control means based on a detection value of the road surface condition detection means.

[For production]

According to this invention, when the road surface condition detection means detects that the road surface on which the vehicle is traveling is uneven, the auxiliary steering amount correction means sets the auxiliary steering amount command value to a value smaller than that when the vehicle is traveling on a good road. By selecting this, the amount of auxiliary steering can be reduced. As a result, even if a front wheel kick-hack steering angle occurs when driving on an uneven road, at least one of the front wheels and rear wheels will not be significantly steered, which improves the running stability of the vehicle when driving on an uneven road. can be improved.

【Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a schematic diagram showing an embodiment of the present invention.

In the figure, IL and IR are front wheels, and 2L and 2R are rear wheels. The front wheels IL and IR have tie rods 3L at the knuckles (not shown).
, 3R are connected, the other ends of the tie rods 3L and 3R are connected to the rack shaft 4a of the rack and pinion type steering device 4, and the steering shaft 5 of the rack and pinion type steering device W4 is connected to the steering wheel 6, By steering the steering wheel 6, the front wheels IL are moved in the same direction as the steering direction.

IR is steered. A piston rod 7a of a front wheel auxiliary steering cylinder 7 that generates a steering auxiliary force is connected to a rack housing 4b that is elastically supported by a mount insulator (not shown) so as to be movable laterally relative to the vehicle body.

On the other hand, the rear wheels 2L and 2R have a piston rod 9a of a rear wheel auxiliary steering cylinder 9 connected to knuckles (not shown) via tie rods 8L and 8R.

The driving force of the engine 10 is transmitted to the rear wheels 2L, 2R via axle shafts 14L, 14R connected to the variable speed gear, propeller shirt 12, differential device 13, and the output side of the differential device 13.

Further, in the front wheel auxiliary steering cylinder 7 and the rear wheel auxiliary steering cylinder 9, pressure chambers Tl, 1r and 91°9r defined by pistons 7b and 9b are connected to closed center type servo valves 2o and 21, respectively. ing. The servo valves 2o and 21 have their input ports connected to each other and are connected to the discharge side of a hydraulic pump 23 which is rotationally driven by the engine 10 via an unload valve 22, and have drain ports connected to each other to supply a reservoir tank 24. It is connected. Note that 425 is an accumulator that accumulates line pressure.

The servo valves 20 and 21 are driven and controlled by control signals from a controller 31 including a microcomputer. A vehicle speed detector 33 is attached to detect the vehicle speed of the vehicle, and a front wheel steering angle detector 34 detects a front wheel steering angle as a front wheel auxiliary steering amount by detecting the amount of movement of the piston 7b of the front wheel auxiliary steering cylinder 7. , a rear wheel steering angle detector 35 that detects a rear wheel steering angle as a rear wheel auxiliary steering amount by detecting the amount of movement of the piston 9b of the rear wheel auxiliary steering cylinder 9; Detection signals from the vehicle height detector 60 for calculating the degree of irregularity of the running road surface are input, and predetermined arithmetic processing is executed based on these detection signals to form control signals for each servo valve 20 and 21.

That is, based on the vehicle speed detection value V of the vehicle speed detector 33, a proportionality constant is determined according to the following formula +11, and a differential coefficient τ2. At the same time, the degree of irregularity of the traveling road surface is detected, and based on this, a storage table corresponding to the relationship between the degree of irregularity of the traveling road surface and the correction coefficient α shown in FIG. 3, which is stored in advance in the storage device, is created. A correction coefficient α is determined by referring to the correction coefficient α, each proportionality constant Kt, and a differential coefficient τ1. τ,
The corrected proportional constant K fen K re and the corrected differential coefficients τ, , τ, C are calculated by multiplying by
) and the steering angle θ(3), and the transfer function H, (s) between the rear wheel steering angle δ, (s) and the steering angle θ(s).
), and calculate these transfer functions Hr(s) and H,(s)
The front wheel steering angle δf(s) and the rear wheel steering angle δ, (s) are calculated from the following equations (6) and (7) from the steering angle θ(s) and are used as the front wheel auxiliary steering amount command value. A front wheel steering angle command value δ and a rear wheel steering angle command value δ as a rear wheel auxiliary steering amount command value are calculated, and these front wheel steering angle command value δ, rear wheel steering angle command value δ, and front wheel steering angle are calculated. Each servo valve 20 and 2 is adjusted so that the difference value between the detected value δf4 and the rear wheel steering angle detected value δr4 becomes zero.
A control signal is output to 1.

・・・・・・・・・(11 C, IV ・・・・・・・・・(2) C, IV ・・・・・・・・・(3) H, (s)=, c+r , cS...”
...”'(4) H, (s)=, c-τr CS
”'”'”' (5) Hr(s)−δr(s
)/θ(s)・・・・・・(6)H,(s)=
δ, (s)/θ(s) −...Old...(7
) Here, C7 is the front wheel cornering power, c, is the rear wheel cornering power, l is the wheel base, a is the distance between the front wheels and the center of gravity, b is the distance between the rear wheels and the center of gravity, M is the vehicle M amount, is the vehicle yaw moment of inertia, ■ is the vehicle speed, and S is the Laplace operator.

In the present embodiment described above, the degree of irregularity of the running road surface can be determined by using the vehicle height detector 60 as the amount of variation in vehicle height from the vehicle height reference value.

This vehicle height detector 60 is composed of an ultrasonic distance measuring device attached to the lower surface of the front end of the vehicle body, and ultrasonic waves emitted from the ultrasonic receiver at predetermined intervals are reflected on the road surface. The reflected waves are received by an ultrasonic receiver, the time from the time of ultrasonic emission to the time of ultrasonic wave reception is measured, and by multiplying this by the speed of sound and multiplying this by 2, the distance between the vehicle body and the road surface can be calculated. The distance is measured and the measured value is output as a digital vehicle height detection signal H.

The vehicle speed detector 33 is constituted by optical, magnetic, or other means for detecting the rotation of a speedometer flexible wire that is connected to the transmission connected to the engine and rotates in accordance with the transmission output. A vehicle speed detection signal consisting of a corresponding pulse signal is output.

The steering angle detector 32 is, for example, a rotation detector consisting of a disc with a slit attached to the steering shaft l and a photocoupler having two sets of detectors facing the slit, and detects the rotation of the steering shaft. It outputs a steering angle detection signal consisting of a pulse signal depending on the direction and rotation speed.

Next, the operation of the above embodiment will be explained with reference to the flowchart of FIG. 4 showing the processing procedure of the controller 31.

The controller 31 executes the interrupt processing program l shown in FIG. 4, which is executed every predetermined time, for example, every 20 m5ec.

When the ignition switch is turned on, the controller is powered on and the program shown in the figure is started.

In step (2), the vehicle height detection value H from the vehicle height detector 60 is read.

Next, the process moves to step (2), where it is determined whether the vehicle is running (■≠0) or stopped (V=0). This determination is made depending on whether a pulse signal is output from the vehicle speed detector 33. If it is determined that the vehicle is stopped (V=O), the process moves to step (2).

In step ■, the information read and stored in step ■,
The vehicle height detection value H while the vehicle is stopped is updated and stored in a predetermined area of the storage device RAM as a vehicle height reference value (■) which is a reference value when detecting the degree of irregularity of the running road surface.

The reason why the vehicle height while the vehicle is stopped is set as the vehicle height reference value H is because passengers have boarded the vehicle and cargo has been loaded before the vehicle starts, and this may be adopted as the vehicle height reference value ■. be.

If it is determined in step (2) that the vehicle is running (■≠O), the process moves to step (2).

In step (2), the steering angle detection value θ from the steering angle detector 32 and the vehicle speed detection value (2) from the vehicle speed detector 33 are read, and then the process proceeds to step (2), where the above (11 to (11) 3) Calculate the equation to obtain the proportionality constant Kf,
and differential coefficient τ1. Calculate τ.

Next, the process moves to step (2), and the absolute value (ΔH) of the difference between the vehicle height value H read in step (2) and the vehicle height reference value H stored in step (2) is calculated.

Next, the process moves to step (2), where a moving average value H3 of ΔH is calculated, and this is stored as the road surface irregularity degree H5. This moving average value H3 corresponds to the degree of road surface irregularity, and the value of H3 increases as the degree of irregularity (degree of unevenness and degree of continuity of unevenness) of the traveling road surface increases.

Then, the process moves to step (2), and the correction coefficient α is determined based on the road surface irregularity level H8 with reference to the memory table corresponding to FIG. 3.
, and then proceed to step (3) to select the correction coefficient α, the proportionality constant, , and the differential coefficient τ1. τ, and the correction proportionality constant is multiplied by 1. .

Krc and corrected differential coefficient τfe+τre are calculated.

Next, proceeding to step 0, the correction proportionality constant K fc
+ KrC and correction differential coefficient τfen τ1. Based on the equations (4) and (5), the front wheel transfer function Hf(s) and the rear wheel transfer function H,(s) are calculated.

Next, the process moves to step 0, and the above equations (6) and (7) are calculated based on the detected steering angle value θ, the front wheel side transfer function Hr(s), and the rear wheel side transfer ratio Hr(s). to calculate the front wheel steering angle δ, (S) and the rear wheel steering angle δ(S), and perform inverse Laplace transform to calculate the front wheel steering angle command value δ and the rear wheel steering angle command value δ. Then, the process moves to step @, and reads the detected front wheel steering angle value δf4 and the detected rear wheel steering angle value δ14 from the front wheel steering angle detector 34 and the rear wheel steering angle detector 35, and calculates the difference value Δδ between the two.

δ1-δ1. Calculate,
When the difference values Δδ and Δδr are zero, the control signals C3r-, C3tb and C8r for the servo valves 20 and 21,
, C8,, b to logical value II O'', difference value Δδ, 〉O2
When Δδ,〉O, the control signals cs, , csr, are set to the logical value II II II, the control signals C3rb, C3,b are set to the logical value “′O゛,” and when the difference value Δδ,<O5Δδ, is 0, Control signals cs, , cs, , are set to logical value +i 0
++, the control signals C3tb, C3, b are respectively set to the logical value "l" and the servo valves 20 and 21 are controlled to feedback-control the front wheel auxiliary steering cylinder 7 and the rear wheel auxiliary steering cylinder 9. do.

In this embodiment, the processes in steps ■, ■ to @ correspond to the steering control means, the processes in steps ■, ■, ■■ correspond to the road surface condition detection means, and the processes in steps ■ and ■ correspond to the auxiliary steering amount. Compatible with correction means.

Now, when you turn on the ignition switch of the vehicle, since the vehicle is stopped, the process moves to step ■ through step ■ in Figure 4, and the detected vehicle height while the vehicle is stopped, which was detected and stored in step ■, is the vehicle height. It is updated and stored as the reference value ■. Next, when the vehicle starts running, in step ■, ■≠0, so the process moves to step ■ without proceeding to step ■, and the detected vehicle height value H immediately before the start of driving remains constant during the subsequent driving. The vehicle height standard value is H.

Therefore, assuming that all vehicles are traveling on good roads, the correction coefficient will be a large value because the degree of road surface irregularity is small.
Accordingly, the correction coefficient α, the proportionality constant, , and the differential constant τ1. The correction proportionality constant K tc, which is multiplied by τ,
Krc and correction differential coefficient τ10. τ and C also become large values, and the finally calculated front wheel steering angle command value δ, as shown by the solid line in FIG. 5(a), is different from the actual steering angle θ shown by the chain line.
As the rise becomes steeper, the steering angle also increases, and the rear wheel steering angle command value δ also has a larger negative phase bone as shown by the solid line in Figure 5(b), resulting in the overall response of the vehicle. can improve sex.

On the other hand, when the vehicle is traveling on an uneven road surface, the variation of the vehicle height detection value H detected in step (2) with respect to the vehicle height reference value H becomes large, and as a result, ΔH becomes large in step (2). Therefore, in step ■, the moving average value of ΔH, that is, the degree of road surface irregularity H1 increases, and the value of the correction coefficient α in step ■ becomes a small value as shown in FIG. 3, and accordingly, the correction proportionality constant K ,c,K,
c and the corrected differential coefficient τ,. , τ1c are also small values, so the actual front wheel steering angle approaches the actual steering angle θ, as shown by the broken line in FIG.
At bl, as shown by the broken line, the negative phase bone and the positive phase component decrease, and the overall auxiliary steering amount of the vehicle is reduced by the irregularity variation of the road surface, resulting in a decrease in the responsiveness of the vehicle.

Therefore, even if the vehicle runs over an uneven road surface and a steering angle θ based on kickback of the front wheels occurs when driving on an uneven road, the front and rear wheels will not be steered significantly. The driving stability can be improved.

In the above embodiment, the proportionality constants for the front wheels and the rear wheels are , , and the differential coefficient τ1. We have explained the case where τ and τ are changed simultaneously according to the irregularity of the road surface.
The invention is not limited to this, and either the proportionality constant or the differential coefficient may be changed depending on the road surface irregularity. Specifically, only the differential coefficient that has a large effect on the transient behavior of the vehicle may be changed. Furthermore, the auxiliary steering mechanism is not limited to the case where the auxiliary steering mechanism is provided on both the front wheel side and the rear wheel side, but the auxiliary steering mechanism may be provided on either the front wheel side or the rear wheel side. Furthermore, as the control element for the auxiliary steering, in addition to the one having a proportional element and a differential element as in this embodiment, any other control element may be used, such as only a proportional element, only a differential element, or an integral element with a delay. You can have it.

Furthermore, in the above embodiment, a case has been described in which the front wheel auxiliary steering cylinder 7 and the rear wheel auxiliary steering cylinder 9 are feedback-controlled using the closed center type servo valves 20 and 21, but the present invention is not limited to this. Instead, open center type servo valves are applied in place of the closed center type servo valves 20 and 21, and the piston ron door of each cylinder 7 and 9 is accordingly changed.
Control may be performed by inserting a return spring that returns 9a to the neutral position.

Further, in the above embodiment, a case has been described in which the rear wheels 2L and 2R are steered by the rear wheel side auxiliary steering cylinder 9, but the present invention is not limited to this. The same effect as in the above embodiment can be obtained even if the hydraulic cylinders are supported by lateral rods, and hydraulic cylinders are inserted in the middle of one of the lateral rods so as to change the toe angle, and these hydraulic cylinders are controlled by the controller 21. effect can be obtained.

In the above embodiment, a case has been described in which the amount of auxiliary steering of the front and rear wheels is continuously decreased according to the degree of irregularity of the road surface.
However, the present invention is not limited to this, and for example, the level of road surface irregularity may be set to one or more patterns, and the front and rear wheel auxiliary steering amounts may be reduced in stages in accordance with the degree of irregularity in each pattern.

Further, in the above embodiment, an ultrasonic detector which is a vehicle height detector is used as the irregularity detector, but it is not necessarily limited to this. For example, a piezoelectric element assembled to a suspension device may be used. The degree of road surface irregularity can also be detected by full-wave rectifying the output signal from the element and smoothing it. Other potentiometers can also be used.

Furthermore, in this embodiment, the steering angle (
θ), but when the steering torque generated as a reaction force of the driver's steering wheel operation and corresponding to the lateral acceleration when the vehicle turns is used as the steering input value, and the front and rear wheel auxiliary steering amounts are controlled based on this. Alternatively, the steering angular velocity may be used as the steering command value.

Furthermore, in the above-mentioned embodiment, in the road surface irregularity degree calculation (steps ■, ■), the vehicle height reference value H is set to the vehicle height detection value H from when the vehicle is stopped to just before starting. The moving average value of the high detection value H may be used as the vehicle height reference value ■.

[Effects of the Invention] As explained above, according to the present invention, the degree of irregularity of the traveling road surface is detected by the road surface condition detection means, and the auxiliary steering amount command value is corrected based on the detection result. Even if a kickback steering angle is ordered for the front wheels when driving on an uneven road, the amount of auxiliary steering for at least one of the front and rear wheels can be made smaller than when driving on a good road. This has the effect that one side is not significantly steered, and the running stability of the vehicle when running on an uneven road can be improved.

[Brief explanation of the drawing]

Fig. 1 is a diagram corresponding to the claims of the present invention, Fig. 2 is a schematic configuration diagram showing an embodiment of the invention, Fig. 3 is a characteristic diagram showing the relationship between the degree of road surface irregularity and the correction coefficient (α), FIG. 4 is a flowchart showing the processing procedure of the controller in the embodiment of FIG. 2, and FIGS. 5A and 5B are characteristic diagrams showing the relationship between the front wheel steering angle and the rear wheel steering angle with respect to time, respectively. Inside, IR, IR are front wheels, 2L, 2R are rear wheels, 4 is a rack-and-binion steering device, 6 is a steering wheel, 7 is a cylinder for front wheel auxiliary steering, 9 is a cylinder for rear wheel auxiliary steering, IO is an engine, 11 is a transmission, 2
0 and 21 are servo valves, 23 is a hydraulic pump, 31 is a controller, 32 is a steering angle detector, 33 is a vehicle speed detector, 3
4 is a front wheel steering angle detector, 35 is a rear wheel steering angle detector, and 36L. 36R, 37L, and 37R are front wheel rotation speed detectors, and 60 is a vehicle height detector. Patent applicant: Nissan Motor Co., Ltd. Patent attorney: Tetsuya Mori

Claims (1)

[Claims] (1) An auxiliary steering mechanism that auxiliarily steers at least one of the front wheels and rear wheels, and an auxiliary steering amount command value that sets the auxiliary steering amount of the auxiliary steering mechanism according to steering input values such as steering angle, steering angular velocity, and steering torque. A steering control device for a vehicle, comprising: a road surface condition detection means for detecting an irregular state of the road surface; A vehicle steering control device comprising: auxiliary steering amount correction means for correcting a steering amount command value.