JP2699585B2 - Auxiliary steering angle control device for front wheel drive vehicles - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an auxiliary steering angle control device for a front wheel drive vehicle that obtains an optimum turning performance by auxiliary steering of at least one of a front wheel and a rear wheel during front wheel steering. About.

2. Description of the Related Art Conventionally, as a rear wheel steering angle control device for a front-rear-wheel steering vehicle using a drive wheel slip as a control input, for example, Japanese Patent Application Laid-Open No. Sho 62-71
An apparatus described in Japanese Patent No. 761 is known.

According to this conventional source, a driving wheel slip state occurring at the time of vehicle acceleration is detected based on a rotational speed difference between a driving wheel and a non-driving wheel, and the rear wheels are subjected to auxiliary steering control in accordance with the rotational speed difference to drive the vehicle during turning. There is disclosed a technique for preventing a change in steer characteristics due to slip (reduction in cornering force).

Specifically, the rear wheels are auxiliary-steered to the same phase or opposite phase according to the increase in the front and rear wheel rotation speed difference, and the target steering angle ratio is K ^* = K * f (g) = K * (α * G) However, K ^* ; target steering angle ratio K; vehicle speed corresponding steering angle ratio α; proportionality constant g; given by front / rear rotation speed difference, and changes front / rear wheel steering angle ratio at the same time as occurrence of front / rear wheel rotation speed difference. It has a configuration.

However, according to the conventional control described above, although the gain of the target steering angle ratio changes depending on the vehicle speed, in the case of an all-vehicle drive vehicle, the rear wheels are corrected to the opposite phase during the drive slip, In the case of a wheel drive vehicle, the rear wheels are corrected to the same phase during a drive slip.

Here, comparing the correction of the rear wheels to the in-phase side and the correction of the rear wheels to the opposite phase, when the latter is reversed, a moment in the oversteer direction is given, and the vehicle is made unstable. Needless to say,

Needless to say, the higher the vehicle speed, the higher the maneuverability of the vehicle.

From the above points, when evaluating the above-described conventional technology, in the case of a front-wheel drive vehicle in which the drive wheel slip is required to have the opposite phase, when the drive slip amount is erroneously detected larger than the actual amount, the reverse phase is more than necessary. Corrected and the vehicle becomes unstable.
In particular, at high speeds in which maneuverability is important, the above-described reverse phase correction may cause a vehicle spin, which is not preferable.

In the case where the drive slip amount is erroneously detected larger than the actual one, for example, in a general front heavy front wheel drive vehicle, the front tire diameter of the front and rear tire radius becomes smaller due to the wheel load, and the drive slip amount is detected. The value is erroneously detected as a value larger than the true drive slip amount.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problem. In an auxiliary steering angle control device for a front wheel drive vehicle that assists steering of at least one of a front wheel and a rear wheel during front wheel steering, excessive drift-out occurs. It is an object of the present invention to secure small turnability during low-speed turning and to ensure stability during high-speed turning while preventing the occurrence of a vehicle.

(Means for Solving the Problems) In order to solve the above problems, the front wheel drive vehicle auxiliary steering angle control device of the present invention increases the drive slip amount detected by the difference between the front and rear wheel drive rotation speeds, and increases the value as the vehicle speed increases. A means for performing auxiliary steering angle control for preventing drift based on a difference from the set offset value.

That is, as shown in the claim correspondence diagram of FIG. 1, a front wheel drive vehicle having front wheels as drive wheels, a front wheel steering mechanism a for steering the front wheels in response to a steering operation by a driver, and a drive command from outside An auxiliary steering mechanism b for providing an auxiliary steering angle control amount to at least one of the front wheel and the rear wheel, a front wheel steering amount detecting means c for detecting the front wheel steering amount, and a basic auxiliary steering angle control for providing a front wheel steering amount. Basic auxiliary steering angle control amount determination means d for determining the amount, front and rear wheel rotation speed difference detection means e for detecting a difference between the front wheel rotation speed and the rear wheel rotation speed, vehicle speed detection means f for detecting the vehicle speed, The offset value of the wheel rotational speed difference is set to a small value at which the steering angle is easily corrected to the oversteer side at low speed, and is set to a value that gradually increases as the vehicle speed increases, and the steering angle is hardly corrected to the oversteer side at high speed. An offset value setting means g for setting a correct auxiliary steering angle control amount for correcting the oversteer side as the difference between the front and rear wheel rotational speed difference detection value and the vehicle speed corresponding offset setting value increases. Angle control amount determining means h; auxiliary steering angle control amount determining means i for determining an auxiliary steering angle control amount based on a sum of the basic auxiliary steering angle control amount and the corrected auxiliary steering angle control amount; And output means j for outputting a drive command for obtaining the amount to the auxiliary turning mechanism b.

(Operation) When the front wheels are steered through the front wheel steering mechanism a by the driver's steering operation, the front wheel steering amount is detected by the front wheel steering amount detecting means c, and the basic auxiliary steering angle control amount determining means d determines the front wheel steering amount. The basic auxiliary steering angle control amount to be given is determined accordingly.

On the other hand, if there is a difference between the front and rear wheel rotational speed difference detection means e and the vehicle speed corresponding offset set value by the offset value setting means g, the correction auxiliary steering angle control amount determining means h As the two values increase, the correction auxiliary steering angle control amount to be corrected to the oversteer side is determined.

In the auxiliary steering angle control amount determining means i, the auxiliary steering angle control amount is determined by the sum of the basic auxiliary steering angle control amount and the corrected auxiliary steering angle control amount, and the determined auxiliary steering angle is output from the output means j. A drive command for obtaining the control amount is output to the auxiliary steering mechanism b.

Accordingly, during low-speed slip turning, the vehicle speed corresponding offset setting value is a small value, and the steering wheel is corrected to the oversteer side from the time when a small difference between the front and rear wheel rotation speeds exceeding this value is generated. The characteristics change in the oversteer direction, and a small turn is enabled.

Also, at the time of high-speed slip turning, the vehicle speed corresponding offset setting value is a large value, and if a large difference in front and rear wheel rotation speed exceeding this value does not occur, the auxiliary steered wheels are not corrected to the oversteer side because the steering angle is not corrected. In the slip range where the offset does not exceed the set value, the change in the steering characteristics is suppressed, ensuring stability during high-speed turning.In the slip range exceeding the offset set value, excessive cornering caused by cornering force reduction due to drive slip is caused. Drift-out is prevented from occurring.

(Examples) Hereinafter, instructions of the present invention will be described with reference to the drawings.

 First, the configuration will be described.

FIG. 2 is an overall view of a front wheel drive vehicle to which a rear wheel steering angle control system (auxiliary steering angle control device) according to the embodiment is applied. Front steering unit 2 (front wheel steering mechanism) for steering front wheels 1 and 1, and rear wheels that are non-drive wheels in response to an external drive command during front wheel steering.
A hydraulic actuator 4 (auxiliary steering mechanism) that provides the rear wheel steering angle δ _r (auxiliary steering angle control amount) to 3, 3 is provided.

The hydraulic actuator 4 includes an oil pump 41 for supplying pressurized hydraulic oil, a hydraulic cylinder 42 for holding the rear wheels 3, 3 at a steering angle neutral position by a biasing force of a spring when the hydraulic pressure is cut off, and an oil pump 41. A control valve 45 provided in the middle of oil passages 43 and 44 connecting the hydraulic cylinder 42 and
The piston stroke of the hydraulic cylinder 42 is changed to the rear wheel steering angle δ.
_It has steering linkages 46, 46 for converting into _r .

A rear wheel steering angle control system for controlling the operation of the control valve 45 includes a front wheel steering angle sensor 5 (front wheel steering amount detecting means) for detecting a front wheel steering angle θ (front wheel steering amount) as a sensor for detecting necessary information by an electric signal. and), a front wheel rotational speed sensor 6 for detecting a front wheel rotational speed N _f, a wheel rotation speed sensor 7 after detecting a rear wheel rotational speed N _f, a vehicle speed sensor 8 for detecting a vehicle speed V, used as feedback information A rear wheel steering angle sensor 9 for detecting a rear wheel steering angle _{δr based} on a cylinder stroke is provided.

Further, inputs the detection signals from these sensors 5, 6, 7, 8, this rear wheel steering angle target value [delta] _r ^* with determining the rear wheel steering angle target value [delta] _r ^* by a predetermined calculation process As means for applying the obtained output signal to the control valve 45, a rear wheel steering angle controller 10 is provided.

Then, the rear wheel steering angle controller 10 sets the front and rear wheel rotational speed difference calculating section (front and rear wheel rotational speed difference detection means), a front wheel steering angular velocity calculating section, a vehicle speed corresponding gain K ₁ for front-wheel steering angle θ a first gain setting unit, a front wheel and a second gain setting unit that sets a vehicle speed corresponding gain K ₂ to the steering angular velocity, an offset value setting unit that sets a larger value to the offset value of the front and rear wheels rotational speed difference ΔN with increasing vehicle speed V (Offset value setting means), a basic rear wheel steering angle determining section (basic auxiliary steering angle control amount determining means) for determining a basic rear wheel steering angle δ _ro given according to K ₁ , θ, K ₂ , A corrected wheel steering angle determination unit (corrected auxiliary steering angle control) that determines a corrected wheel steering angle δ _r ′ to be corrected to oversteer as the difference N between the wheel rotation speed difference ΔN and the vehicle speed corresponding offset set value N _OFF increases. Amount determining means) and the basic rear wheel steering angle δ wheel steering angle target value determiner after determining the rear wheel steering angle target value [delta] _r ^* by the sum of the _ro and modification rear wheel steering angle [delta] _{r 'and} (the auxiliary steering angle control quantity determining means),
An output unit (output means) for outputting a drive command to obtain the determined rear wheel steering angle target value δ _r ^* to the control valve 45 is incorporated as a control program.

 Next, the operation will be described.

FIG. 3 is a flowchart showing a flow of a rear wheel steering angle control process operation repeatedly performed by the rear wheel steering angle controller 10 with a predetermined control time as a cycle. Each step will be described below.

In step 31, the vehicle speed V, the front wheel steering angle θ, the front wheel rotation speed
N _f and the rear wheel rotation speed N _f are input.

In step 32, the front and rear wheel rotational speed difference ΔN is calculated by the following equation.

In ΔN = N _f -N _r step 33, by the steering angle change per unit time obtained by differentiating the front wheel steering angle θ time steering angular speed is calculated.

theta _0; 1 cycle before theta Delta] t: the control time step 34, the vehicle speed corresponding gain K ₁ for the front wheel steering angle theta is calculated.

The arithmetic expression is K ₁ = f ₁ (V). As shown in FIG. 4, the gain K ₁ is set to the opposite phase in the low vehicle speed range, and the gain K _{1 is} almost 0 in the middle speed range. It is set to the gain K ₁ is set to the in-phase side in the high speed range.

That is, the gain K ₁ to ensure low speed maneuverability and fast stability is set.

In step 35, the vehicle speed-basis gain K ₂ for the front wheel steering angular speed is calculated.

The calculation formula is _{K 2 = f 2 (V)} , as shown in FIG. 5, in the low middle speed range gain K ₂ is set to 0, the gain K ₂ in the opposite phase side in the high speed range Is set. That is, the setting is made so as to improve the turning performance of the vehicle at the beginning of a turn when traveling at high speed.

In step 36, a vehicle speed corresponding offset set value N _{OFF of} the front and rear wheel rotation speed difference ΔN is calculated.

The operation formula is N _OFF = f ₃ (V), and N _OFF is gradually set to a larger value as the vehicle speed V increases, as shown in FIG.

In step 37, the rear wheel steering angle target value [delta] _r ^* is, [delta] _r Z ^* =
It is calculated by the formula of f ₄ (K ₁ , θ, K ₂ , θ, ΔN, N _OFF ).

Rear wheel steering angle target value [delta] _r ^* this, those obtained by Enzan by the sum of the base rear-wheel steering angle [delta] _ro the corrected wheel steering angle [delta] _{r ',} the base rear-wheel steering angle [delta] _ro, the following Given by the formula.

_{δ ro = K 1 * θ +} K 2 * , and the absolute value of the front and rear wheel rotational speed difference .DELTA.N | .DELTA.N | and the vehicle speed corresponding offset setting value N absolute value of the _OFF | N _OFF | opposite phase side according to the difference N increases the ( The corrected wheel steering angle δ _r ′ to be corrected to the oversteer side is given by the following equation.

δ _r ′ = −K ₃ * N where N = MAX (| ΔN | − | N _OFF |, 0) K ₃ is a proportionality constant, and when K ₃ * N is shown as a characteristic diagram, FIG. K ₃ * N> 0 indicates the in-phase direction, and the corrected wheel steering angle δ _r ′ becomes a value in the opposite phase direction by adding a minus to this.

Note that | ΔN | and | N _OFF | mean that the front wheels 1,1 are also decelerated by decelerating the accelerator pedals, etc., even when the front wheels 1,1 are excessively rotating due to excessive driving force due to depression of the accelerator. Is also included in the drive slip when performing a deceleration slip that tends to lock.

In step 38, the output signal-wheel steering angle target value [delta] _r ^* is obtained after being calculated in step 37 is applied to the control valve 45.

Next, the operation will be described separately for grip turning and slip turning.

(A) When turning the grip When turning the grip, such as when turning at a constant speed or when changing lanes, the difference between the rotational speeds of the front and rear wheels, usually representing the drive clip, Δ
N does not reach the vehicle speed corresponding offset set value N _OFF , the corrected rear wheel steering angle δ _r ′ becomes 0, and the rear wheel steering angle target value δ _r ^* is given by the following equation using only the basic rear wheel steering angle δ _ro. Can be

^{_{δ r * = K 1 * θ}} + K 2 * ...... Therefore, during low speed turning, the characteristic of the gain K ₁ shown in FIG. 4, since the rear wheels 3 are steered in opposite phase, the low-speed maneuverability properties obtained Can be

Further, at the time of high speed turning, when the operation incision in the handle pivot initial, since the rear wheels 3 are steered momentarily reversed phase the characteristics of the gain K ₂ shown in FIG. 5, turning the initial vehicle When the turning performance is improved and the steering is maintained, the rear wheels 3, 3 are steered in phase with respect to the front wheels 1, _{1 by} the characteristic of the gain K1 shown in FIG. Nature is secured.

(B) Slip turning An area where the difference between the front and rear wheel rotation speeds ΔN representing the driving slip does not reach the vehicle speed corresponding offset setting value N _OFF during a slip turning such as a turning accompanied by an acceleration / deceleration operation or a tight corner turning. in Although the rear wheel steering angle target value [delta] _r ^* is given based on the equation shown above, in a region where the front and rear wheel rotational speed difference ΔN is greater than the vehicle speed corresponding offset setting value N _OFF, the rear wheel steering angle target value [delta] _r ^* Is a value obtained by correcting the basic rear wheel steering angle δ _{ro in the} opposite phase direction by the corrected rear wheel steering angle δ _r ′, that is, given by the following equation.

^{_{δ r * = δ ro + δ}} r '= K 1 * θ + K 2 * -K 3 * (| ΔN | - | N OFF |) ...... during (low speed slip turning) slow slip turning offset of Figure 6 As shown in the set value characteristics, the value of N _OFF is a small value of N ₀ or −N ₂ , and the rear wheels 3, 3 are in the opposite phase from the time when a small front and rear wheel rotational speed difference ΔN exceeding this value occurs. , The steer characteristic becomes the oversteer side, and a small turn is possible.

For example, when turning around a tight corner at about 30 km / h or less,
The front wheel rotation speed N _f is changed to the rear wheel rotation speed due to the difference in turning miracle between the front and rear wheels.
Faster than N _r, although the front and rear wheel rotational speed difference ΔN exceeds the value of the offset value N _OFF is generated, this time, since the rear wheels 3 is corrected in the opposite phase side, the bulging of the swivel according to understeer This makes it possible to make a small turn.

Further, as compared with a four-wheel steering vehicle that performs control to give a rear wheel turning angle to the same phase according to the front wheel steering amount, traceability of a corner line is improved.

That is, when the front wheel deceleration slip occurs due to the accelerator OFF operation when the front wheel acceleration slip occurs at the time of turning acceleration of a corner or when entering a corner on a low friction coefficient road such as an icy road, acceleration / deceleration slip causes the front wheel to slip. In order to reduce the cornering force, an operation of turning the steering wheel more is performed. However, in the case of the rear-wheel in-phase control, when the front wheel steering amount is increased, the steering angle is corrected to the in-phase side, so that the understeer tendency becomes stronger, so that the line cannot be turned as intended.

On the other hand, in the present control, when the acceleration / deceleration slip amount is large, the rear wheels are largely corrected to the opposite phase side, so that the desired line can be turned by the over-moment due to the opposite phase correction.

In (fast when slipping turn) at high slip turning, as shown in the offset setting value characteristic of FIG. 6, the value of N _OFF is of a large value of N ₁ or -N _3, a large front and rear wheels to exceed this value The fact that the rotation speed difference ΔN does not occur means that the rear wheels 3, 3 are not corrected to the opposite phase, so the rear wheel in-phase during high-speed grip turning based on the above equation until the value exceeds N _OFF Control is maintained, and stability during high-speed turning is ensured.

That is, in a general front heavy front-wheel drive vehicle, the front tire diameter of the above-described tire dynamic radius becomes smaller due to the wheel load, and the detection value of the drive slip amount is erroneously detected as a larger value than the true drive slip amount. Can be considered. At that time,
If the corrected rear wheel steering angle on the opposite phase based on the detected value of the drive slip amount becomes larger than the basic rear wheel steering angle on the same phase during high-speed turning, acceleration / deceleration slip accompanying turning In addition to this, the cornering force of the front wheels is reduced, and in addition, an over-moment acts on the vehicle, leading to vehicle spin, but the offset value N _OFF
Unless a front-rear wheel rotation speed difference ΔN exceeding ΔN occurs, the correction of the rear wheels to the opposite phase is stopped, so that the vehicle spin due to the correction can be prevented.

In addition, a large front and rear wheel rotational speed difference ΔN exceeding the value of N _OFF
Occurs, the rear wheel steering angle target value δ is calculated based on the above equation.
_By giving _r ^*, a reverse phase correction of the rear wheels 3, 3 is added, and occurrence of excessive drift out is prevented.

That is, despite the fact that a large amount of slip occurs on the front wheels and the cornering force of the front wheels has been greatly reduced, if the same-phase rear wheel steering angle is given,
Excessive drift out will occur,
Excessive drift-out is prevented by correcting the rear wheels in reverse phase only at that time.

That is, at the time of high-speed turning, by setting a large steering angle correction dead zone for the front and rear wheel rotation speed difference ΔN, control is performed to prevent both excessive drift out and ensure stability.

Also, by setting the steering angle correction dead zone, most of the detection error of the front and rear wheel rotation speed difference ΔN is absorbed, and the influence on the steering angle control is suppressed to a very small value. Does not need to be subjected to a calculation process or the like that corrects the turning angle based on the turning radius, the tire diameter, and the like.

Although the embodiments have been described with reference to the drawings, the specific configuration is not limited to the embodiments.

For example, in the embodiment, the example of the rear wheel steering angle control system in which only the rear wheels are subjected to the reverse phase correction at the time of the driving slip has been described.
The present invention can also be applied to a system in which only the front wheels are turned. still,
In the case where the front wheels are steered, the front wheels are in-phase corrected so as to increase the over-moment during a drive slip.

(Effects of the Invention) As described above, according to the present invention, in a front-wheel drive vehicle auxiliary steering angle control device that performs auxiliary steering of at least one of a front wheel and a rear wheel during front-wheel steering, a front-rear wheel rotational speed difference is provided. The offset value is set to a small value at which the steering is easily corrected to the oversteer side at low speed, and is set to a value that gradually increases as the vehicle speed increases, and is set to a large value at which the steering angle is hardly corrected to the oversteer side at high speed. Means for performing auxiliary steering angle control for drift prevention based on the difference between the drive slip amount detected from the front and rear wheel rotational speed difference and the vehicle speed corresponding offset setting value. In this case, it is possible to achieve the effect of ensuring the small turning performance and the stability during high-speed turning.

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram showing an auxiliary steering angle control device for a front wheel drive vehicle of the present invention, FIG. 2 is an overall view showing a front wheel drive vehicle to which a rear wheel steering angle control system according to an embodiment is applied, FIG. Is a flowchart showing a flow of a rear wheel steering angle calculation processing operation in a rear wheel steering angle controller of the embodiment system, FIG. 4 is a gain characteristic diagram of a front wheel steering angle corresponding to a vehicle speed, and FIG. 5 is a vehicle speed corresponding gain of a front wheel steering angular velocity. FIG. 6 is a characteristic diagram of the offset set value corresponding to the vehicle speed, and FIG. 7 is a characteristic diagram of the corrected wheel steering angle. a front wheel steering mechanism b auxiliary steering mechanism c front wheel steering amount detection means d basic auxiliary steering angle control amount determination means e front and rear wheel rotational speed difference detection means f vehicle speed detection means g ... Offset value setting means h ... Correction auxiliary steering angle control amount determination means i ... Auxiliary steering angle control amount determination means j ... Output means

Claims (1)

(57) [Claims] 1. A front wheel drive vehicle having front wheels as drive wheels,
A front wheel steering mechanism that steers the front wheels according to the steering wheel operation by the driver, an auxiliary steering mechanism that applies an auxiliary steering angle control amount to at least one of the front wheels or the rear wheels in response to an external drive command, and detects the front wheel steering amount Front wheel steering amount detecting means, basic auxiliary steering angle control amount determining means for determining a basic auxiliary steering angle control amount to be given according to the front wheel steering amount, and front and rear wheels for detecting a difference between the front wheel rotation speed and the rear wheel rotation speed. The rotational speed difference detecting means, the vehicle speed detecting means for detecting the vehicle speed, and the offset value of the front and rear wheel rotational speed difference is set to a small value at which the steering angle is easily corrected to the oversteer side at low speed, and gradually increases as the vehicle speed increases. Offset value setting means that sets a large value that is difficult to correct the steering angle to the oversteer side at high speed, and a front and rear wheel rotational speed difference detection value and a vehicle speed corresponding offset setting value. Correction auxiliary steering angle control amount determining means for determining a correction auxiliary steering angle control amount to be corrected to the oversteer side as the difference in the steering angle increases, and assist steering by a sum of the basic auxiliary steering angle control amount and the correction auxiliary steering angle control amount. Front wheel, comprising: an auxiliary steering angle control amount determining unit that determines an angle control amount; and an output unit that outputs a drive command for obtaining the determined auxiliary steering angle control amount to the auxiliary steering mechanism. Auxiliary steering angle control device for driving vehicles.