JPH02189277A - Rear-wheel steering system for vehicle - Google Patents

Abstract

PURPOSE:To secure safety at time of something wrong in a car speed sensor or the like by performing rear-wheel steering on the basis of a target steering angle only when this target steering angle is within the specified range before steering rear wheels on the basis of this target steering angle at the time of steering the rear wheels in accordance with the target steering angle being operated on the basis of a specific formula. CONSTITUTION:When a front-wheel steering angle being detected by a front- wheel steering angle sensor 35 is set to thetaF, a car speed being detected by a car speed sensor 31 to V, a yaw rate being detected by lateral G sensors 33, 34 to psi, and factors dependent upon a car characteristic to KF and KR, respectively, each target steering angle TGthetaR of rear wheels is calculated on the basis of a numerical formula of TGthetaR=-KF.thetaF+KR.V.psi. Then, a servomotor 20 is controlled on the basis of this target steering angle TGthetaR. In this case, whether there is TGthetaR within the range of allowable value being set on the basis of the car speed V or not is judged before steering the rear wheels on the basis of the operated value of TGthetaR, and only when it exists there, the rear wheels are steered on the basis of TGthetaR.

Description

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

(Prior Art) Conventionally, as a four-wheel steering device for a vehicle, one that steers the rear wheels according to the vehicle speed and steering angle is known. At low speeds, they are controlled in opposite phases depending on the steering angle, and at high speeds, they are controlled in the same phase depending on the steering angle.

However, with this type of control, at the beginning of a turn,
When turning the steering wheel slowly while turning a corner, the amount of steering angle between the front and rear wheels is different, so the necessary yaw rate will occur and no problem will occur, but if you turn the steering wheel suddenly At high speed, the rear wheels are in the same phase, so the vehicle moves diagonally, the yaw rate is suppressed, and the slip angle β between the vehicle's direction and the direction of travel is not 0, and the request to change direction is satisfied. Not done.

That is, at the time of initial steering, it is desirable to first change the direction and then become in phase and stabilize, so that the slip angle β-0 is always achieved.

Therefore, in order to satisfy the above requirements, TGθR−−I(P−θp+KI?−V−necessaryTGθR:
Target steering angle θF of the rear wheels: Steering angle V of the front wheels: Vehicle speed φ: Yaw rate KPSKR: It has been proposed to steer the rear wheels based on a constant determined by the characteristics of the vehicle. Note that the coefficients I(P, I(1?) are determined by the following equation.

I (P = C+ /C: KR = WV/g (C21: -CI 1+ )
/V'; W/ C2g CI, C2: Cornering power W: Weight 11: Distance between the center of gravity of the vehicle and the front wheel axle 12: Distance between the center of gravity of the vehicle and the rear wheel axle, that is, at low speeds, V is small and the second term The effect is small and the phase is reversed, but at high speeds, the vehicle speed V.

Both yaw rates increase, the influence of the second term increases, and they become in phase. However, at the beginning of the turn, the yaw rate is still small, so the influence of the second term is not so large, and the phase is opposite.

By the way, as described in, for example, Japanese Unexamined Patent Publication No. 57-44568, a vehicle is known in which the rear wheels are steered in accordance with the output of a yaw rate sensor in order to correct the influence of external disturbances such as crosswinds.

(Problem to be Solved by the Invention) However, when such a device is actually applied to a rear wheel steering device of a vehicle, there is a possibility that the yaw rate sensor that detects the yaw rate, the vehicle speed sensor that detects the vehicle speed, etc. break down. It becomes a problem. For example, if the yaw rate sensor or vehicle speed sensor is malfunctioning and the output becomes 0, the second term becomes O,
At high speeds, the phase becomes reversed, resulting in an unstable state.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a rear wheel steering device for a vehicle that can ensure safety even when a yaw rate sensor, a vehicle speed sensor, etc. are out of order.

(Means for Solving the Problem) In order to achieve the above object, the invention of claim (1) uses the formula % formula % TGθR; target steering angle of rear wheels θF: steering angle of front wheels; Yaw rate I (F 5I (R: Yaw rate I) In a vehicle having a steering control means for steering the rear wheels based on a coefficient determined by the characteristics of the vehicle, the control means is linked to the steering means and rotates the rear wheels based on the calculated value of TGθR. Before steering, determining means determines whether TGθR exists within a range of allowable values determined based on the vehicle speed, and only when it exists, the steering control means steers the rear wheels based on TGθR. The patent 8 value range, which is characterized by having , refers to a certain range in which the rear wheels must move in order to achieve the slip angle β-0.

Claim ('2J invention is based on the formula % formula % TGθR: target steering angle θF of rear wheels; steering angle V of front wheels; vehicle speed required: yaw rate KPSKI?1, IR2: coefficient determined by vehicle characteristics (KI?2> 0) It is characterized by having a steering control means for steering the rear wheels based on the following.

That is, by providing kR2.-, an in-phase component is generated even when -0.

The invention of claim (3) is based on the mathematical formula % TGθR: target steering angle of rear wheels θF=steering angle of front wheels V; vehicle speed φ: yaw rate; >0) It is characterized by having a steering control means for steering the rear wheels based on the following.

That is, by adding the third term, stability becomes a problem when the steering wheel is turned, so the in-phase component is increased in that case.

(Operation) According to the invention of claim (1), before steering the rear wheels based on the calculated value of TGθR, it is determined whether TGθR is within the range of an allowable value determined based on the vehicle speed. judge,
Only when the rear wheels are present, the rear wheels are steered based on TGθR1;

According to the invention of claim ('2J), V-
Even with O, the in-phase component does not become zero, and the direction is more stable than in the case using formula (2).

According to the invention of claim (3), even if the yaw rate is small, when the steering angle of the front wheels is large, the vehicle is in a stable direction due to IR2・necessary・θF.

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

In FIG. 1 showing the overall configuration of a rear wheel steering device of a vehicle,
IL and IR are the left and right front wheels, respectively, and 2L.

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

The front wheel steering mechanism A includes a pair of left and right knuckle arms 3L, 3R and a tie rod 4L, respectively.

4R, and a relay rod 5 that connects the pair of left and right tie rods 4L and 4R. A steering mechanism C is linked to this front wheel steering device +:+SA, and the steering mechanism C is of a rack-and-binion type, and its component pinion 6 is connected to a handle 8 via a shaft 7. has been done.

As a result, when the handlebar 8 is turned to the right for shore harvesting, the relay rod 5 is displaced to the left in FIG. The steering wheel is steered clockwise in the same figure by the amount of time. Similarly, when the steering wheel 8 is turned to the left, the left and right front wheels IL and IR are
will be steered to the left.

Similarly to the front wheel steering mechanism B, the rear wheel steering mechanism A also has a pair of left and right knuckle arms IOL, IOR, and a tie rod I.
LL, IIR, and the pair of left and right tie rods IIL, I
It has a relay rod 12 that connects the IRs, and a neutral holding means 13 is attached to this relay rod 12.

As shown in detail in FIG. 2, the neutral holding means 13 has a casing fixed to the vehicle body 14, and a pair of spring receivers 16a, 16b are loosely fitted into the casing 15. A compression spring 17 is arranged between the springs 16b and 16b. The relay rod 12 extends through the casing 15, and a pair of flanges 12a and 12b are formed on the relay rod 12 at an interval, and the flange portions 12a and 12b hold the spring receivers 16a and 16b. The relay rod 12 is connected to the compression spring 1.
7, it is always biased in the neutral direction. compression spring 1
7 is said to have enough spring force to overcome side forces during cornering.

The rear wheel steering mechanism B is linked to a servo motor 20 as a drive source for steering the rear wheels 2L and 2R. In the linkage mechanism between the relay rod 12 and the servo motor 20,
A clutch 22 is interposed. This allows the clutch 22 to mechanically disconnect the servo motor 20 and the rear wheel steering mechanism B as appropriate.

With the above configuration, when the clutch 22 is in the connected state, the servo motor 20 rotates in the forward or reverse direction.
The relay rod 12 is displaced to the left or right in FIG. 1, and the knuckle arm 10L.

10R rotates the servo motor 2 around its rotation center.
The steering wheel is steered clockwise or counterclockwise in the figure by an amount corresponding to the amount of rotation at zero. On the other hand, when the clutch 22 is in the connected state, the neutral holding means 13 controls the rear wheel 2L.

2R is forcibly returned to the neutral position and held at this neutral position. In other words, when the clutch 22 is disengaged, only the front wheels IL and IR are steered, resulting in a so-called 2WS vehicle.

Rear wheel steering control is performed based on the following equation.

Formula % Formula % TG θR Target steering angle θF = Front wheel steering angle V 2 Vehicle speed Required: Yaw rate Note that the coefficients I (P, I (R are constants determined by the characteristics of the vehicle, but change based on the vehicle speed) It may also be a variable.

In order to perform the above control, the control small roll unit U has a steering control means 101 that steers the rear wheels based on the above mathematical formula, and further has a TG steering control means 101 linked to the above steering control means 101.
Before steering the rear wheels based on the calculated value of oR, the functions f1 (V), fz (V) [f+ (V
) > fz (V)] to determine whether or not TGoR exists within the tolerance range Sl (see Figure 3);
Only when the rear wheels are present, the steering control means 101 causes the rear wheels to TGo.
It has determination means 1.02 for steering based on R (sixth
(see figure). The range S1 of the above-mentioned allowable value is adapted to shift in the in-phase direction as the vehicle speed increases.

In addition, the range of allowable values determined based on vehicle speed does not take into account only vehicle speed V, but also vehicle speed V and steering ratio θS-
It may be determined by considering θR/θF.

That is, in FIG. 4, the functions g+(V), g2
(V) The range S2 may be defined by [g+ (V)>gz (V)].

Specifically, as shown in FIG. 1, signals from a steering wheel angle sensor 30, a vehicle speed sensor 31, an encoder 32 that detects the rotational position of the servo motor 20, a front structure G sensor 33, and a rear structure G sensor 34 are transmitted. The steering wheel angle θF (front wheel steering angle) is input to the control unit U.
Based on and vehicle speed ■, the target rear wheel steering angle TGθR is calculated using the above formula (■) in consideration of the yaw rate φ, and a control signal corresponding to the required rear wheel steering amount is output to the servo motor 20. The encoder 32 constantly monitors whether or not the servo motor 20 is operating properly, that is, under feedback control, the rear wheels 2L,
2R steering is performed.

The control system described above has a two-phase configuration for fail-safe purposes.

In other words, as shown in FIG.
A front wheel steering angle sensor 35 is added to the vehicle speed sensor 3.
A vehicle speed sensor 36 is added to the encoder 32, and a rear wheel steering angle sensor 37 is added to the encoder 32 to detect the mechanical displacement of a member closer to the relay rod 12 than the clutch 22. In .35, 36.37, rear wheel steering is performed only when both corresponding sensors detect the same value. That is,
In the sensors 30 to 32, 35 to 37, for example, when the vehicle speed detected by the vehicle speed sensor 31 and the vehicle speed detected by another vehicle speed sensor 36 are different, it is assumed that a failure has occurred, and the rear wheels 2L, 2R are controlled in the fail mode. is designed to hold it in a neutral position.

The above-mentioned both lateral G sensors 33 and 34 are respectively disposed on the center axis of the vehicle body in front and behind the center of gravity to detect the magnitude of lateral G and are used to detect the yaw rate φ. , 34, the current yaw rate (j
/n is calculated.

in-φn-+ 10 (GF-GR) t/Ωφn-1=
Previous yaw rate GF: Output GR of the front lateral G sensor 33: Output t of the rear lateral G sensor 34: Measurement interval g: Interval in the longitudinal direction of both lateral G sensors Note that the yaw rate ψ is directly detected instead of the lateral G sensor. It is also possible to add a yaw rate sensor.

In addition, for various controls, the control unit U includes a vehicle height sensor 39, a raindrop sensor 40, a brake switch 41, a reverse switch 42, and an accelerator switch 4.
Although not shown, a signal representing the presence or absence of power generation is input from the L terminal of the alternator.

The vehicle height sensor 39 detects the vehicle height, and thereby indirectly detects the loaded weight. The raindrop sensor 40 detects raindrops, thereby indirectly detecting the friction coefficient μ of the road surface. The brake switch 41 outputs an on signal when the brake pedal is depressed, the reverse switch 42 outputs an on signal when the shift lever is in the reverse position, and the accelerator switch 43 outputs an on signal when the shift lever is in the reverse position. It outputs an on signal when the rate of change exceeds a predetermined value.

Control is carried out by the main controller and troller 50A, which are interconnected.
and sub-controller 50B,
Each controller 5OA, 50B has various sensors 30.3
7, 39, 40 and the alternator's terminal are inputted to the sensors 31, 35, 3 through the analog buffer 51 and the A/D converter 52, respectively.
6 and switches 41, 42, 43 are input to each via a digital buffer 53, and signals from both TFJG sensors 33, 34 are input to the main via another analog buffer 54 and A/D converter 55. It is input to the controller 50A.

On the other hand, the signal generated in the main controller 50A is output to the servo motor 20 via the servo amplifier 61 and the servo driver 62, and is set as the target rear wheel steering angle. The rotation amount of the servo motor 20 is determined by the encoder 32.
A signal from the encoder 32 is input to the main controller 50A via the servo amplifier 61, and the servo motor 20 is feedback-controlled.

Furthermore, signals from both controllers 50A and 50B are compared in an AND circuit 71, 72, and only when they match, clutches 73, 74 are connected to enable steering of the rear wheels. Further, the OR circuit 75 also compares the signals, and when the two signals do not match, a warning lamp 76 is turned on.

Note that this rear wheel steering control is performed using alternator r=b2.
It is started on the condition that the signal from the child becomes high (Hi).

In addition, in the figure, 77 is a voltage control circuit that has a 5V regulator and resets the main controller 50A in the event of an abnormality, 78 is a battery, 79 is an ignition switch, and 80 is a fuse. Therefore, with the above configuration, 9, steering control means 10
If the target steering angle TGθR of the rear wheels calculated in step 1 is within the range of allowable values shown in FIGS. 3 and 4, the determination means 102 determines that there is no abnormality, and the steering control is performed. The means 101 steers the rear wheels based on the target steering angle TGeR.

On the other hand, if the value is not within the allowable range, the system immediately shifts to fail-safe mode and performs two-wheel steering. Therefore, if the yaw rate detecting means or the vehicle speed detecting means is out of order, the second term in the above formula becomes zero, prohibiting anti-phase control, and ensuring safety.

In the embodiment described above, fail-safe is performed immediately, but alternatively, fail-safe may be performed when n times (for example, 5 times) of determinations are outside the range of allowable values. In that case, until the nth determination is made, either stop the 4-wheel steering and continue the 2-wheel steering until it becomes normal, or use the calculated value (target turning angle TGθR of the rear wheels) within the range of the above tolerance. ) may be used.

Further, in the case of the above embodiment, the front wheel steering angle 1θF1 is, for example, 1
At the time of a small steering angle of 5 degrees or less, if the allowable value range S2 shown in FIG. 4 is used, θS becomes too large and accurate control cannot be performed, so it is necessary to use the range S1 shown in FIG. 3. Further, during a predetermined period of time (for example, 100 m5) when the sign of the front wheel steering angle θF is reversed, there is a delay in the steering control of the rear wheels by the 7-wheel motor 20, so it is preferable not to perform the above determination.

In the above embodiment, it is determined whether or not the calculation result of the steering control means is within the allowable value range. Good too. In that case, the rear wheels will be controlled based on the following formula 〇.

Formula % Formula % TGeR: Rear wheel target steering angle θF: Front wheel steering angle ■Second vehicle speed required: Yaw rate KP, I (R1, KP2: Coefficient determined by vehicle characteristics (I (R2>0)) Control using this formula ■ According to The direction is stable.

Further, the steering control of the rear wheels may be performed using the following formula (2).

Formula % Formula % TGθR: Rear wheel target steering angle θF: Front wheel steering angle ■2nd vehicle speed φ: Yaw rate KP, KJ? I, KP3: Coefficient determined by vehicle characteristics (KP3>O) According to the control using this formula (■), Kl? 3.phi..theta.F not only makes the in-phase component positive when the vehicle speed is V-0, but also provides a stable direction when the steering angle of the front wheels is large even if the yaw rate is small.

(Effect of the Invention) The invention of claim (1) provides that, before the rear wheels are steered based on the calculated value of the target steering angle TGθR by the steering control means, the steering angle is within the range of the allowable value determined based on the vehicle speed. determines whether TGθR exists in the
Since the rear wheels are steered based on R, safety is ensured even if the yaw rate detection means and vehicle speed detection means are out of order.

In the invention of claim 21, since the in-phase component tends to increase due to I(R2·φ, the control is always performed in a stable direction, and safety is ensured even when the vehicle speed detection means etc. are malfunctioning. be done.

According to the invention of claim (3), Kl? Due to 2, φ, and θF, even if the yaw rate is small, the in-phase component increases and becomes stable when the steering angle of the front wheels is large, which poses a problem for stability, and safety is maintained even when the vehicle speed detection means etc. are malfunctioning. gender is ensured.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which FIG. 1 shows a rear wheel steering system of a vehicle, FIG. 2 shows an enlarged sectional view of a neutral holding means, and FIGS. 3 and 4 are explanatory diagrams showing a range of permissible values. FIG. 5 is a block diagram of the control system, and FIG. 6 is a block diagram of the control unit. U...Control unit 30...Handle steering angle sensor 31.36...Vehicle speed sensor 33.34...Lateral G sensor 35... Front wheel steering angle sensor 101 ... Steering angle control means 102 ... Judgment means U ... Control unit 102 ... Judgment means " Fig. 6

Claims (3)

[Claims] (1) Formula TGθR = -KF・θF+KR・V・■ TGθR: Rear wheel target steering angle θF: Front wheel steering angle V: Vehicle speed ■: Yaw rate KF, KR: Rear wheel rotation based on coefficients determined by vehicle characteristics. In a vehicle having a steering control means for steering, before steering the rear wheels based on the calculated value of TGθR in conjunction with the steering control means, the TGθR is within a range of an allowable value determined based on the vehicle speed. It is determined whether or not the vehicle is present, and only if it is present, the steering control means is used to set the rear wheels to TGθ.
A rear wheel steering device for a vehicle, characterized in that it has a determining means for steering based on R. (2) Formula TGθR = -KF・θF + (KR1・V+KR2)・■ TGθR: Rear wheel target steering angle θF: Front wheel steering angle V: Vehicle speed ■: Yaw rate KF, KR1, KR2: Coefficient determined by vehicle characteristics (KR2>0) A rear wheel steering device for a vehicle, comprising a steering control means for steering a rear wheel based on (KR2>0). (3) Formula TGθR=-KF・θF+KR1・V・■ +KR3・■・θF TGθR: Rear wheel target steering angle θF: Front wheel steering angle V: Vehicle speed ■: Yaw rate KF, KR1, KR3: Determined by vehicle characteristics A rear wheel steering device for a vehicle, comprising a steering control means for steering rear wheels based on a coefficient (KR3>0).