Method and control device for warning a vehicle driver of a risk of the vehicle overturning

Abstract

In a method for warning a vehicle driver of a risk of the vehicle overturning about its longitudinal axis, a control device detects the current transverse acceleration of the vehicle and emits a warning signal based thereon when a risk of overturning is presented. The warning signal is dependent upon at least one transverse acceleration value, which is critical for overturning, detected by the control device while the vehicle is being driven, and a measurement of the transverse acceleration of the vehicle at which the vehicle would actually overturn about its longitudinal axis. The transverse acceleration value that is critical for overturning is determined automatically based on the vehicle behavior exhibited during driving on a curve.

Claims

1. A method for warning the driver of a vehicle of a risk of the vehicle overturning about its longitudinal axis, the method comprising: using a control device, detecting a current lateral acceleration of the vehicle, determining a rollover-critical lateral acceleration value for the vehicle based on the lateral acceleration of the vehicle at which the vehicle would overturn about its longitudinal axis, subjecting a wheel of the vehicle on the inside of a turn to a low brake force relative to a maximum possible brake force, adaptively adjusting the rollover-critical lateral acceleration value based on wheel revolution rate behavior of the wheel subjected to the low brake force, based on a subsequent lateral acceleration of the vehicle relative to the adjusted rollover-critical lateral acceleration value, outputting a warning signal when a risk of the vehicle overturning is presented, wherein the warning signal is prompted in response to the subsequent lateral acceleration of the vehicle relative to the adjusted rollover-critical lateral acceleration value exceeding a predetermined risk limit value, such the warning signal corresponds to the subsequent lateral acceleration being at least a predetermined percentage, less than one hundred percent, of the adjusted rollover-critical lateral acceleration value, and displaying the adjusted rollover-critical lateral acceleration value as a stationary warning marker and displaying the subsequent lateral acceleration of the vehicle as an artificial horizon that is rotatable relative to the stationary warning marker, wherein the warning signal causes a further visual warning or audible warning for the driver.

2. The method as claimed in claim 1, further comprising adaptively adjusting the rollover-critical lateral acceleration value using the control device starting from an initial value during at least one traversal of a turn by the vehicle by analyzing at least one other input variable detected by the control device.

3. The method as claimed in claim 2, further comprising increasing the rollover-critical lateral acceleration value during the at least one traversal of a turn by the vehicle.

4. The method as claimed in claim 1, wherein adaptively adjusting the rollover-critical lateral acceleration value includes increasing the rollover-critical lateral acceleration value by a step value when test braking does not cause a characteristic reduction in speed of rotation of the wheel subjected to test braking.

5. A control device configured to effect the method as claimed in claim 1.

6. The method as claimed in claim 1, wherein the rollover-critical lateral acceleration value is determined based on an extent of load relief on at least one wheel of the vehicle on the inside of the turn.

7. The method as claimed in claim 1, further comprising using the control device to determine a first rollover-critical lateral acceleration value that measures the lateral acceleration of the vehicle at which the vehicle would overturn about its longitudinal axis in left turns, and a second rollover-critical lateral acceleration value that measures the lateral acceleration of the vehicle at which the vehicle would overturn about its longitudinal axis in right turns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in greater detail below using exemplary embodiments with reference to the accompanying drawing figures, in which;

(2) FIG. 1 is a plan view of a vehicle making a left turn in accordance with an embodiment of the present invention;

(3) FIGS. 2, 3 and 4 illustrate process steps for warning the driver of a vehicle of a risk of the vehicle overturning about its longitudinal axis according to embodiments of the present invention;

(4) FIG. 5 is a visual representation of lateral acceleration values according to one embodiment of the present invention; and

(5) FIG. 6 is a visual representation of lateral acceleration values according to another embodiment of the present invention.

(6) In the figures, the same reference characters are used for corresponding elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) FIG. 1 is a plan view of a vehicle 2, 3, in this case consisting of tractor unit 2 and a trailer 3, making a left turn on a road 1. The invention is, however, not limited to such type of vehicle. The trailer 3 comprises a brake system of a pneumatic type, which can be subjected to brake pressure from the tractor unit 2 as a result of brake pedal operation by the driver or as a result of certain control and regulation functions in the vehicle. For this purpose, the tractor unit 2 is connected to the trailer 3 by electrical and pneumatic lines 11.

(8) The tractor unit 2 and the trailer 3 are rotatably connected to each other at a point of rotation 10.

(9) The brake system of the trailer 3 comprises, e.g., electrically operated components such as, e.g., ABS brake pressure modulators or even purely electrically operated brake actuators. The brake modulators or brake actuators are controlled by a control device 13 in the form of an electronic controller. The controller 13 and the brake modulators or brake actuators are supplied with electrical energy and the pressure medium or the braking energy via electrical and pneumatic lines 12. The electronic controller 13 is also supplied with speeds of rotation v.sub.4, v.sub.5, v.sub.7, v.sub.8 of the wheels 4, 5, 7, 8 in a manner that is known within anti-lock brake systems.

(10) In the present case, the wheels 4, 5, 6 are thus the wheels of the trailer on the outside of the turn, and the wheels 7, 8, 9 are wheels on the inside of the turn.

(11) The electronic controller 13 performs a series of control and regulation tasks in the trailer 3. These tasks include detecting the risk of the vehicle 2, 3 overturning about its longitudinal axis and preventing the same by controlled brake application, as illustrated by way of example in FIG. 2.

(12) The method illustrated in FIG. 2 starts with a block 20. In a following block 21, the speeds of rotation v.sub.4, v.sub.5, v.sub.7, v.sub.8 of the wheels 4, 5, 7, 8 are read in. Then, in an allocation block 22, a first lateral acceleration signal a.sub.q,1 is determined from the speeds of rotation v.sub.4, v.sub.7 and a second lateral acceleration signal a.sub.q,2 is determined from the speeds of rotation v.sub.5, v.sub.8 according to the following relationships:

(13) $\begin{array}{cc}{a}_{q,1}=\frac{1}{2.Math.S}.Math.v_4-v_7.Math.v_4+v_7& \left[1\right]\\ a_{q,2}=\frac{1}{2.Math.S}.Math.v_5-v_8.Math.v_5+v_8& \left[2\right]\end{array}$

(14) The variable S represents the track width of the vehicle. The lateral acceleration signals a.sub.q,1, a.sub.q,2 are, respectively, measures of the current lateral accelerations of the vehicle 2, 3. The lateral acceleration signals a.sub.q,1, a.sub.q,2 are both used in the following procedure instead of a single lateral acceleration signal, e.g., determined from the speeds of rotation v.sub.4, v.sub.5, v.sub.7, v.sub.8. In this way, the method is less susceptible to signal noise, different tire diameters and the like, so that an incorrect response can be avoided.

(15) In a decision block 23, a determination is made as to whether the brake system has already been subjected to a brake force F.sub.2 for prevention of overturning in an earlier performance of the process illustrated in FIGS. 2, 3 and 4. If this is the case, by by-passing the downstream subprogram block 26 (explained in more detail hereinafter using FIG. 3), which is used, among other things, to detect the risk of overturning, the process branches directly to block 24, in which a determination is made as to whether there is no longer a risk of overturning.

(16) Otherwise, the process continues with the subprogram block 26 illustrated in FIG. 3, which starts with a block 30. In a downstream decision block 31, a determination is made as to whether both the first lateral acceleration signal a.sub.q,1 and also the second lateral acceleration signal a.sub.q,2 exceed a lateral acceleration threshold a.sub.q,Krit specified for a response of the process. The lateral acceleration threshold a.sub.q Krit corresponds to the rollover-critical lateral acceleration value. If this is the case, in a block 32, the wheels 4, 5, 6, 7, 8, 9 of the trailer 3 are subjected to a relatively low brake force F.sub.1. The brake force F.sub.1 is specified such that only a relatively small braking effect occurs that is hardly noticeable by the driver and that does not cause locking of wheels, even on road surfaces with a relatively high coefficient of friction, if there is no risk of overturning. In typical pneumatic brake systems, a brake pressure of approximately 1 to 2 bar is controlled to apply the brake force F.sub.1.

(17) Moreover, in block 32, the ABS slip signals for the wheels 7, 8 are blocked in order to prevent execution of the anti-lock function as a result of high slip. Execution as a result of acceleration signals continues to be possible so that possible damage to the tires can be avoided.

(18) In a subsequent decision block 33, following the expiry of an adequate settling time of the brake pressure build-up or of the brake force F.sub.1 build-up, a determination is made as to whether the speeds of rotation v.sub.7, v.sub.8 of the wheels 7, 8 on the inside of the turn are lower in a characteristic manner than the speeds of rotation v.sub.4, v.sub.5 of the wheels 4, 5 on the outside of the turn, while the speeds of rotation of the wheels on the outside of the turn essentially remain unchanged. The former is checked by comparing the sum of the speeds of rotation v.sub.7, v.sub.5 of the wheels on the outside of the turn with the sum of the speeds of rotation v.sub.4, v.sub.5 of the wheels on the inside of the turn amended by a factor K.sub.1. The latter is checked using the sum of the decelerations of the wheels 4, 5, i.e., the first time derivative of the associated speeds of rotation v.sub.4, v.sub.5. The check on the wheels 4, 5 on the outside of the curve for continuing relatively high speeds of rotation is used to prevent incorrect responses of the process at relatively low coefficients of friction, e.g., on ice. Here, not only the speeds of rotation of the wheels on the inside of the turn can reduce as a result of the brake force F.sub.1 applied as a test braking, but also the speeds of rotation v.sub.4, v.sub.5 of the more highly loaded wheels 4, 5 on the outside of the turn. In this case, the speed reduction of the wheels 7, 8 on the inside of the turn is not an indication that the vehicle 2, 3 is about to overturn.

(19) If both of the previously mentioned conditions are fulfilled, an immediate risk of overturning is assumed. Therefore, in a subsequent block 34, the wheels 4, 5, 6 on the outside of the turn having the better adhesion between the road surface and the tires are subjected to a high brake force F.sub.2 compared to the brake force F.sub.1. The brake force F.sub.2 is dimensioned such that the lateral acceleration, and, hence, also the risk of overturning, is immediately reduced by a reduction of the speed of the vehicle. The physical relationship between the lateral acceleration a.sub.q of the vehicle and the speed of the vehicle v is determined by the relationship below, wherein the variable R represents the radius of the turn:

(20) $\begin{array}{cc}{a}_q=\frac{v^2}{R}& \left[3\right]\end{array}$

(21) Locking of the wheels subjected to the brake force F.sub.2 is prevented by the anti-lock brake system. The wheels 7, 8, 9 on the inside of the turn are further subjected to the low brake force F.sub.1. A pressure of about 4 to 8 bar is preferably controlled to generate the brake force F.sub.2 with a conventional pneumatically controlled brake system.

(22) The subprogram then terminates with a block 36.

(23) If the condition checked in decision block 23 in FIG. 2 is in the affirmative, a determination is made in a subsequent decision block 24 as to whether both the first lateral acceleration signal a.sub.q,1 and also the second lateral acceleration signal a.sub.q,2 are below the lateral acceleration threshold a.sub.q,Krit. If this is the case, there is no longer a risk of overturning and the brake forces F.sub.1, F.sub.2 can be removed in a subsequent block 25, and the ABS slip signals blocked in block 32 are enabled again. Otherwise, by by-passing the block 25, the process branches directly to a block 27, and the process terminates.

(24) The wheels 7, 8, 9 on the inside of the turn that are subjected to low wheel load when there is a risk of overturning tend towards a reduction in the speed of rotation as a result of the brake force F.sub.1 of the test braking. This, in turn, causes a relatively large difference in speed of rotation between the wheels on the inside of the turn and the wheels on the outside of the turn. Using equations [1] and [2], this causes a rapid rise of the first and the second lateral acceleration signals a.sub.q,1, a.sub.q,2. Conversely, reinstating contact of the wheels 7, 8, 9 on the inside of the turn, e.g., as a result of braking with the brake force F.sub.2 in block 34, causes the calculated lateral acceleration signals a.sub.q,1, a.sub.q,2 to reduce rapidly. Because of the rapid change in the lateral acceleration signals, the test braking, which brings the wheels subjected to low wheel load or raised from the ground to rest if there is a risk of overturning, is used for reliable detection of the reinstatement of contact of the wheels or the termination of the risk of overturning, because the wheels on the inside of the turn start turning again as a result of the increasing wheel load despite the braking effect caused by the brake force F.sub.1, which causes a characteristic rise in the speeds of rotation v.sub.7, v.sub.8 of the wheels.

(25) Referring to FIG. 3, if one or both of the conditions checked in the decision block 33 is/are not fulfilled, then, by performing the allocation block 35, in which the lateral acceleration threshold a.sub.q,Krit is increased by the value K.sub.3, the process branches to block 36, and the process terminates.

(26) If one or both of the conditions checked in the decision block 31 is/are not fulfilled, the process branches to block 36, and the process terminates.

(27) It should be understood that the inventive method is also suitable for vehicles with only one axle or with only one axle fitted with speed of rotation sensors.

(28) FIG. 4 illustrates an embodiment of a method for warning the driver of the vehicle 2, 3 using the current lateral acceleration of the vehicle and the rollover-critical lateral acceleration value. The method starts at block 40. In a subsequent block 41, a risk value H is determined as the quotient of the current lateral acceleration a.sub.q and the rollover-critical lateral acceleration value a.sub.q,Krit, for which the lateral acceleration threshold determined in block 35 according to FIG. 3 can be used. As the current lateral acceleration a.sub.q, e.g., the average value of a.sub.q,1 and a.sub.q,2 can be used. In a subsequent block 42, a visual output of the risk value H is carried out as an artificial horizon, as explained below. The risk value H can, e.g., thereby be converted directly proportionally into an inclination of the artificial horizon relative to the horizontal.

(29) In a subsequent decision block 43, a determination is made as to whether the risk value H exceeds a risk limit value H.sub.Grenz. If this is the case, the process branches to an output block 44, in which the output of a warning tone is initiated. The process then terminates at block 45.

(30) The output of the warning can, e.g., then take place if the magnitude of the current lateral acceleration of the vehicle reaches or exceeds 95% of the rollover-critical lateral acceleration value.

(31) The driver is hereby not unnecessarily warned of an impending risk of the vehicle overturning. Especially for unladen vehicles, there is no risk of overturning, so, unnecessary warnings are avoided.

(32) FIG. 5 schematically depicts a visual representation of the current lateral acceleration of the vehicle in relation to the rollover-critical lateral acceleration value as an artificial horizon according to one embodiment of the present invention. An animation of an artificial horizon with a display area 60 can be illustrated, e.g., on a graphics-capable display of the vehicle. Within the display area 60, a horizontal bar arrangement 61 represents the horizontal. A line 62 that can vary in respect of its inclination indicates an artificial horizon, as it would correspond to the perception of the driver of the vehicle in the event of a corresponding tilting of the vehicle. FIG. 5 is an exemplary representation during a left turn. The angle between the line 62 and the bar arrangement 61 is a measure of the current lateral acceleration of the vehicle, wherein, optionally, the current lateral acceleration can be used directly for this or in relation to a roll-over-critical lateral acceleration value. Warning markers 63, 64 indicate the position of the rollover-critical value for the lateral acceleration. If the line 62 reaches one of the warning markers 63, 64, then the vehicle is in a hazardous state in which there is a risk of overturning about the longitudinal axis.

(33) The warning markers 63, 64 can be merged into a visual output of the artificial horizon 60 by the control device at a desired position that corresponds to the rollover-critical lateral acceleration value, i.e., it is calculated numerically from this. The line 62 is shown directly according to the current lateral acceleration, wherein, based on the visual output, the relationship to the rollover-critical lateral acceleration value is given using the warning markers 63, 64. In this case, the generation of the quotient or of the difference of the current lateral acceleration and the rollover-critical lateral acceleration value is not necessary. The warning markers 63, 64 can also be merged at fixed positions. In this case, it is advantageous to determine the line 62 in relation to its inclined position using a calculated relationship between the current lateral acceleration and the rollover-critical lateral acceleration value, e.g., by means of the quotient generation or the difference generation.

(34) FIG. 6 shows another embodiment of the visual representation of the current lateral acceleration in relation to the rollover-critical lateral acceleration value in the form of an artificial horizon. At the bottom left of FIG. 6, an output display is shown in a block 70, which consists of three bar displays 71, 72, 73 disposed adjacent to each other, e.g., formed by light emitting diodes. Each of the bar displays 71, 72, 73 can be formed by blocks of differently colored light emitting diodes, e.g., in the lower area with a block 76 of green light emitting diodes, in the center with a block 75 of yellow light emitting diodes, and in the upper area with a block 74 of red light emitting diodes. The safety or the risk of the vehicle state can be signaled by the colors, where, for example, green stands for a low risk and red for a high risk.

(35) In the right area of FIG. 6, the type of the display is illustrated by way of example using a left turn of the vehicle (block 77), straight-ahead travel (block 78), and a right turn (block 79). Illuminating light emitting diodes are thereby characterized by hatching. The arrows shown beneath the blocks are only used for the illustration and are not part of the visual representation of the output display. For the left turn, it can be seen from the left bar display 71 that two of the green light emitting diodes are illuminating, from the central bar display 72, the topmost green light emitting diode is illuminating, and from the right bar display 73, the topmost green light emitting diode is illuminating, as well as all yellow light emitting diodes. This signals traversing of a left turn with a risk of overturning that is already somewhat increased but not yet critical. For straight-ahead travel, block 78, in which the topmost green light emitting diode of each bar display 71, 72, 73 is illuminating, illustrates a safe driving state without significant lateral acceleration. The illustration for a right turn in block 79 corresponds analogously to the illustration for the left turn, but with a correspondingly reversed sequence of the representation of the bar displays 71, 72, 73.

(36) It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

(37) It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.