Maneuvering assistance

Abstract

The invention relates to a maneuver assistance device for exiting a parallel parking space for a vehicle (A) comprising a front steering axle (F) having a forward steering angle (δf) and a rear steering axle (R) having a rear steering angle (δr) defined by a control law determining the rear steering angle (δr) at least as a function of the front steering angle (δf), wherein the device further comprises a limiter capable of saturating the rear steering angle (δr) resulting from the control law by a lower threshold Si and an upper threshold Ss, before its application to the rear axle (R). Abstract figure: Figure 1

Description

Title of the invention: Assistance with maneuvering Technical field

[0001] The invention relates to a vehicle with four steering wheels or more precisely with two steering axles. The invention proposes to take advantage of the presence of a rear steering axle to offer the driver assistance in maneuvering allowing him to leave parallel parking more quickly. Prior art

[0002] Most current motor vehicles have two steering wheels or more precisely a steering axle, generally the front axle. The front steering angle of this front axle is controlled by the steering wheel angle set by the driver via the steering wheel.

[0003] In order to extend the kinematic performance, certain motor vehicles include four steering wheels or more precisely a second steering gear, at the rear. Such a rear steering gear is not controlled directly by the driver, but is controlled in a known manner, generally, in particular as a function of the front steering angle.

[0004] Thus, in the case of an application for assisting with maneuvering to leave parallel parking, where the vehicle is initially parked along a sidewalk, such a rear steering axle can be used to increase the rotation speed of the vehicle and thus accelerate the exit maneuver.

[0005] The rear steering angle is preferably determined so as to obtain antagonistic behavior relative to the front axle. In order to increase the exit speed from parking, the rear steering angle is maximized.

[0006] This can lead to a damaging collision with the sidewalk.

[0007] Also, an approach is sought that guarantees the absence of collision with the sidewalk. Summary of the invention

[0008] The subject of the invention is a device for assisting the maneuver of exiting a parallel parking space for a vehicle comprising a front steering axle having a front steering angle and a rear steering axle having a rear steering angle defined by a control law determining the rear steering angle at least as a function of the front steering angle, where the device also comprises a limiter capable of saturating the rear steering angle resulting from the control law by a lower threshold Si and an upper threshold Ss, before its application to the rear axle.

[0009] Particular characteristics or embodiments, usable alone or in combination, are: - the upper threshold Ss is equal to the absolute value of the yaw angle relative to the pavement and the lower threshold Si is equal to the opposite of the upper threshold Ss, - the control law further determines the rear steering angle as a function of possible kinematic parameters of the vehicle chosen from: the yaw rate, the yaw angle, the speed of the front axle, the speed of the rear axle, and possible dimensional parameters of the vehicle chosen from: the wheelbase, - the control law determines the rear steering angle according to the formula: ôr = - k * ôf, where ôr is the rear steering angle, ôf is the front steering angle and k is a gain, - the gain k is equal to 0.006, - the yaw angle is calculated by integrating the yaw speed, with an initial yaw angle, at the start of the maneuver, equal to 0, - the yaw rate is calculated according to the formula . V^sinffy+S,.) where ôf is the angle of & — ; ç Lcos]oJ front steering angle, ôr is the rear steering angle, VR is the rear axle speed and L is the vehicle wheelbase, - the maneuvering assistance is inhibited if the speed of the rear axle is lower than a minimum speed or higher than a maximum speed, - inhibition is obtained by a zero gain k.

[0010] According to a second aspect of the invention, a method for assisting the maneuver of exiting a parallel parking space for a vehicle comprising a front steering axle having a front steering angle and a rear steering axle having a rear steering angle defined by a control law determining the rear steering angle at least as a function of the front steering angle, where the method comprises a step of saturating the rear steering angle resulting from the control law by a lower threshold Si and an upper threshold Ss, before its application to the rear axle. Brief description of the drawings

[0011] The invention will be better understood on reading the following description, given solely by way of example, and with reference to the appended figures in which:

[0012] [Fig-1] shows a kinematic model of the vehicle,

[0013] [Fig.2] shows a block diagram of the assistance device,

[0014] [Fig.3] shows a speed versus time diagram,

[0015] [Fig.4] shows a diagram of the front steering angle as a function of time,

[0016] [Fig.5] shows a diagram of the rear steering angle as a function of time,

[0017] [Fig.6] shows a yaw angle versus time diagram. Description of the embodiments

[0018] With reference to [Fig.2], the invention relates to a device for assisting the maneuver of exiting from parallel parking. As illustrated in [Fig.l], parallel parking is parking where the vehicle A is parked along a sidewalk P.

[0019] Vehicle A has a front axle F that is steered. It has a front steering angle ôf. The rear axle R of vehicle A is also steered. It has a rear steering angle ôr.

[0020] The front steering angle ôf of the front axle F is controlled by the steering wheel angle defined by the driver via the steering wheel. The rear axle R is not controlled directly by the driver. On the contrary, it is controlled by an actuator. This actuator receives a rear steering angle setpoint ôr.

[0021] This rear steering angle ôr is defined by a control law 4. The control law 4 determines the rear steering angle ôr according to a function which can take many forms. In general, the control law determines the rear steering angle ôr at least as a function of the front steering angle ôf. Thus, the driver's steering wheel control directly conditions the front steering angle ôf and indirectly the rear steering angle ôr.

[0022] According to one characteristic, the assistance device also comprises a limiter 5. This limiter 5 saturates the rear steering angle ôr, previously calculated by the control law 4 by a lower threshold Si and an upper threshold Ss, before its application 6 to the rear axle R, or more precisely to the actuator which controls the steering of the rear axle R.

[0023] In other words, the rear steering angle ôr, determined by the control law 4, is replaced by a limited rear steering angle ôr b. It is this limited rear steering angle ôri which is transmitted as a command to the actuator which controls the steering of the rear axle R.

[0024] Formulated mathematically, this saturation or limitation carries out the following operations: if ôr < Si, then ôri = Si, if ôr > Ss, then ôri = Ss and if Si <= ôr <= Ss, then ôri = ôr.

[0025] According to another characteristic, the upper threshold Ss is taken equal to the absolute value I d I of the yaw angle d. The yaw angle d is the angle between the longitudinal axis of the vehicle A and the sidewalk P. By definition of the problem treated, the initial yaw angle d, at t = 0, when the assistance is started, is zero, the longitudinal axis being parallel to the sidewalk P at that moment. Correlatively, the lower threshold Si is taken equal to the opposite of the upper threshold Ss. It can also be said that the lower threshold Si is equal to the opposite of the absolute value -I d I of the yaw angle d.

[0026] The yaw angle d is permanently equal to the angle between the vehicle A and the sidewalk P, because the initial yaw angle, at t=0, is zero.

[0027] According to another characteristic, the control law 4 determines the rear steering angle ôr as a function of possible kinematic parameters of the vehicle chosen from: the yaw rate 3, the yaw angle d, the speed of the front axle VF, the speed of the rear axle VR, and possible dimensional parameters of the vehicle chosen from: the wheelbase L.

[0028] According to a known, simple form, the control law 5 determines the rear steering angle ôr according to the formula: ôr = - k * ôf. In this formula ôr is the rear steering angle, ôf is the front steering angle and k is a gain.

[0029] In order to adapt the control law to the particular need, the gain k can be calculated by any suitable law or formula.

[0030] A positive gain k produces antagonistic steering. In this case, the rear axle is steered in the opposite direction to the steering of the front axle. The steerability of the rear axle is then used to produce maximum steering, increasing the parking exit speed.

[0031] A negative gain k produces parallel steering. In this case, the rear axle is steered in the same direction as the front axle. This does not produce maximum steering but can be useful in some cases.

[0032] The control law proposed by the present invention is applicable to any gain k, positive or negative.

[0033] A zero gain k produces no steering. In this case the rear axle remains centered and is not influenced by the front steering. This reproduces a situation without rear steering or without rear steering assistance.

[0034] According to another characteristic, the gain k is chosen to be constant. Satisfactory tests have been carried out with such a constant gain, equal to 0.006.

[0035] According to another characteristic, the yaw angle d, which is used to calculate the thresholds Si and Ss, is calculated by integrating the yaw speed 3. For the calculation of this integration, it is necessary to know the initial conditions. The initial yaw angle, at the start of the maneuver, at time t = 0, is taken as zero.

[0036] According to another characteristic, the yaw speed 3 is calculated according to the following formula: V^sin^j+S,.) In this formula, ôf is the front steering angle, ôr is the angle of rear steering, VR is the speed of the rear axle and L is the wheelbase of the vehicle, i.e. the distance between the front axle F and the rear axle R.

[0037] It should be noted here that the rear axle VR speed can be measured directly. Alternatively, the vehicle speed as measured by the tachometer can be used as an approximation of the rear axle VR speed. The raw reading obtained from the tachometer must be improved as it is very erratic particularly at low speeds.

[0038] The preceding formula can be deduced from the kinematic model of vehicle A, as illustrated in [Fig.l]. An assumption of this kinematic model is that the speed of the vehicle or the speed VF, VR of one of its trains is sufficiently low so that the equations of the dynamics of the vehicle are not representative. Also, a purely kinematic model is valid.

[0039] According to another characteristic, the assistance with the maneuver is inhibited if the speed of the rear axle VR is too low or too high, or if the speed of the rear axle VR is lower than a minimum speed Vmin or is higher than a maximum speed Vmax.

[0040] As an indication, the minimum speed Vmin is taken as equal to 0 km / h and the maximum speed Vmax is taken as equal to 20 km / h.

[0041] To achieve the inhibition, a zero gain k is used. If the gain k is zero, the rear steering angle ôr is zero regardless of the front steering angle ôf. This amounts to simulating a vehicle whose rear axle R is not steered.

[0042] The curves in Figures 3-6 illustrate assistance in the maneuver of exiting a parallel parking space. The four curves are as a function of time.

[0043] [Fig. 3] shows, as a function of time, the speed of the rear axle VR. Two curves are shown comparatively. Curve VR0 shows the evolution of the speed of the rear axle without the invention, or with a non-directional rear axle. Curve VR shows the evolution of the speed of the rear axle with the invention, or by controlling the rear steering angle according to the invention.

[0044] [Fig. 4] shows, as a function of time, the front steering angle ôf. The latter reproduces the steering wheel instruction given by the driver using the steering wheel.

[0045] [Fig. 5] shows, as a function of time, the rear steering angle ôr. Three curves are shown comparatively. Curve ôro shows the evolution of the rear steering angle without the invention, i.e. with a non-directional rear axle. Curve ôr shows the evolution of the rear steering angle as determined by the law of command 4. Finally, the curve ôri shows the evolution of the rear steering angle after limitation by limiter 5.

[0046] [Fig.6] shows, as a function of time, the yaw angle d. In other words, the value of the threshold for limiting the rear steering angle ôr.

[0047] The invention also relates to a method for assisting the maneuver of exiting a parallel parking space for a vehicle A comprising a front steering axle F having a front steering angle ôf and a rear steering axle R having a rear steering angle ôr defined by a control law 4 determining the rear steering angle ôr at least as a function of the front steering angle ôf. According to one characteristic, this method comprises a step 5 of saturating the rear steering angle ôr resulting from the control law 4 by a lower threshold Si and an upper threshold Ss, before its application 6 to the rear axle R.

[0048] This process is more particularly illustrated by the block diagram of [Fig.2].

[0049] This method comprises a first step 1 in which all the necessary data are collected. Here, these data are the front steering angle ôf and the speed of the rear axle VR.

[0050] During a second step 2, the speed of the rear axle VR is compared with the speeds Vmin and Vmax, in order, in the case where VR is outside the interval Vmin, Vmax, to inhibit the assistance by canceling the gain k.

[0051] During a third step 3, the kinematic model is updated. It is calculated pF, the distance from the front axle F to the instantaneous center of rotation CIR, pR, the distance from the front axle R to the instantaneous center of rotation CIR, by the formulas: rÿt ^Sf) % = [* PR “LF

[0052] The yaw speed Ü is then recalculated using the formula: p ~ p r - pf - L co ^

[0053] This yaw rate is then integrated to obtain the yaw angle d.

[0054] In parallel, during a step 4, the control law is implemented to calculate the rear steering angle ôr according to the formula: Ôr = - k* Ôf

[0055] Then, during a fifth step 5, the rear steering angle ôr is limited to obtain the limited rear steering angle ôr b This limitation is carried out by comparing with the thresholds Si, Ss, respectively equal to the opposite of the absolute value of the yaw angle - I d I and to the absolute value of the yaw angle I d I. This yaw angle has just been determined in step 3.

[0056] The limited rear steering angle ôr i thus calculated is then applied to the rear axle R during the sixth and final step 6.

[0057] The invention has been illustrated and described in detail in the drawings and the preceding description. This should be considered as illustrative and given by way of example and not as limiting the invention to this description alone. Numerous alternative embodiments are possible. List of reference signs

[0058] 1: entry step, 2: speed verification step, 3: step of updating the kinematic model, 4: step of calculating the rear steering angle by the control law, 5: limitation step, 6: step of applying the limited steering angle to the rear axle, A: vehicle, CIR: instantaneous center of rotation, ôf: front steering angle, ôr: rear steering angle, from 4, ôr o: rear steering angle without the invention, ôr i: limited rear steering angle, from 5 and applied in 6, d: yaw angle, d; yaw rate, H: projection of the CIR on the median axis of the vehicle, k: gain of the control law, L: wheelbase, F: center of the front axle, R: center of the rear axle, pF: distance from F to the CIR, pR: distance from R to the CIR, P: sidewalk, Si: lower saturation threshold, Ss: upper saturation threshold, VF: speed of F, VR: speed of R, VR o: speed of R without the invention, xR: abscissa of R, yR: ordinate of R, Vmin: minimum speed for activating assistance, Vmax: maximum speed for activating assistance.

Claims

Claims

1. Device for assisting the maneuver of exiting a parallel parking space for a vehicle (A) comprising a front steering axle (F) having a front steering angle (ôf) and a rear steering axle (R) having a rear steering angle (ôr) defined by a control law (4) determining the rear steering angle (ôr) at least as a function of the front steering angle (ôf), characterized in that it further comprises a limiter (5) capable of saturating the rear steering angle (ôr) resulting from the control law (4) by a lower threshold Si and an upper threshold Ss, before its application (6) to the rear axle (R).

2. Device according to the preceding claim, where the upper threshold Ss is equal to the absolute value of the yaw angle (d) relative to a sidewalk (P) and the lower threshold Si is equal to the opposite of the upper threshold Ss.

3. Device according to any one of the preceding claims where the control law (4) further determines the rear steering angle (ôr) as a function of kinematic parameters of the vehicle chosen from: the yaw rate (d), the yaw angle (d), the speed of the front axle (VF), the speed of the rear axle (VR), and dimensional parameter(s) of the vehicle including the wheelbase (L).

4. Device according to any one of the preceding claims, wherein the control law determines the rear steering angle (ôr) according to the formula: ôr = - k * ôf, where ôr is the rear steering angle, ôf is the front steering angle and k is a gain.

5. Device according to the preceding claim, where the gain k is equal to 0.

006.

6. A device according to claim 2 or any one of claims 3 to 5 as dependent on claim 2, wherein the yaw angle (d) is calculated by integrating the yaw rate (#), with an initial yaw angle, at the start of the maneuver, equal to 0.

7. Device according to the preceding claim, wherein the yaw rate (d) is calculated according to the formula

8.

9.

10. V^sin^-rA-) °ù $fest the front steering angle, ôr is the angle L.cos(ô^ rear steering, VR is the rear axle speed and L is the vehicle wheelbase. Device according to any one of the preceding claims, wherein the assistance with the maneuver is inhibited if the speed of the rear axle (VR) is lower than a minimum speed (Vmin) or is higher than a maximum speed (Vmax). Device according to the preceding claim where the inhibition is obtained by a zero gain k. Method for assisting the maneuver of exiting a parallel parking space for a vehicle (A) comprising a front steering axle (F) having a front steering angle (ôf) and a rear steering axle (R) having a rear steering angle (ôr) defined by a control law (4) determining the rear steering angle (ôr) at least as a function of the front steering angle (ôf), characterized in that it comprises a step of saturation (5) of the rear steering angle (ôr) resulting from the control law (4) by a lower threshold Si and an upper threshold Ss, before its application (6) to the rear steering axle (R).

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