METHOD AND DEVICE FOR DETERMINING THE CROSS SLOPE OF A ROADWAY

Abstract

A method and a device is described for determining the cross slope of a roadway or a negotiated curve for a motor vehicle, an evaluation unit being suppliable with measured values of a yaw rate sensor, of a driving speed sensor and of a lateral acceleration sensor as input signals, and the evaluation unit ascertaining therefrom a cross slope of the presently traveled roadway in that the difference value is formed between a calculated and a measured lateral acceleration, from which the roadway cross slope is derivable. The ascertained value is supplied to an adaptive cruise controller or a system for vehicle dynamics control in order to predefine an acceleration or a deceleration.

Claims

1. A method for determining a maximum permissible curve speed of a motor vehicle, comprising: determining a maximum permissible vehicle speed as a function of a cross slope of a negotiated curve.

2. The method as recited in claim 1, wherein the determining is based on at least one of a yaw rate, a vehicle longitudinal speed, a measured lateral acceleration, and a friction coefficient of a pavement in an area of the negotiated curve.

3. The method as recited in claim 1, further comprising: determining an actual roadway cross slope while the curve is being negotiated.

4. The method as recited in claim 1, wherein the determined actual roadway cross slope is used to determine a maximum curve speed.

5. The method as recited in claim 4, further comprising: regulating one of an acceleration and a deceleration of an adaptive cruise controller as a function of one of the determined actual roadway cross slope and the maximum curve speed.

6. The method as recited in claim 1, further comprising: calculating a first lateral acceleration value from a yaw rate; measuring a second lateral acceleration value via a lateral acceleration sensor; and calculating, for determining the actual roadway cross slope, a difference value from the first lateral acceleration value and the second lateral acceleration value.

7. The method as recited in claim 6, wherein a cross slope angle is ascertained from the difference value.

8. A device for determining a maximum permissible curve speed of a motor vehicle, comprising: an arrangement for determining a maximum permissible vehicle speed as a function of a cross slope of a negotiated curve.

9. The device as recited in claim 8, further comprising: an evaluation unit including a computation arrangement for ascertaining the cross slope of a presently traveled roadway, wherein measured values of a yaw rate sensor, of a driving speed sensor, and of a lateral acceleration sensor are suppliable as input signals to the evaluation unit.

10. The device as recited in claim 8, further comprising: an arrangement for supplying a maximum curve speed value to an adaptive cruise controller, wherein the adaptive cruise controller includes a limiter that limits a speed settable by the adaptive cruise controller.

11. The device as recited in claim 8, further comprising: an arrangement for supplying a maximum curve speed value to a system for vehicle dynamics control, wherein the vehicle dynamics control system decelerates individual wheels of the vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 shows a schematic block diagram of one specific embodiment of the method according to the present invention.

[0021] FIG. 2 shows a schematic block diagram of one specific embodiment of the device according to the present invention.

[0022] FIG. 3 shows a schematic block diagram of a further specific embodiment of the device according to the present invention.

DETAILED DESCRIPTION

[0023] FIG. 1 shows a schematic block diagram in which, on the left-hand side, a first rectangle 1 for yaw rate ω and a second rectangle 2 for vehicle longitudinal speed v are provided as input variables. Yaw rate 1 may be obtained, for example, via a yaw rate sensor, which may be installed in a vehicle usually including a vehicle dynamics control system and thus indicate the rotational speed of the vehicle about its vehicle vertical axis. Vehicle longitudinal speed 2, which is usually also referred to as the vehicle speed, describes the speed of the vehicle in the direction of the vehicle longitudinal axis. This may be ascertained, for example, by averaging the multiple wheel speed sensors, but alternatively or additionally may also be calculated from a GPS signal or determined with the aid of a vehicle surroundings sensor, which, for example, detects reflections on the roadway surface or detects stationary objects on the roadside, and thus is able to ascertain the vehicle's own longitudinal speed via the relative speed of the stationary objects.

[0024] These two input signals yaw rate 1 and vehicle longitudinal speed 2 are supplied to a downstream rectangle 3, which is represented by the two arrows. In this downstream rectangle 3, local lateral acceleration a.sub.y,calc is calculated, which moreover is referred to as calculated lateral acceleration 3. In this block 3, a calculated, local lateral acceleration a.sub.y,calc is calculated from the knowledge of yaw rate 1 and vehicle longitudinal speed 2, for example using the equation a.sub.y,calc =ωXV. Rectangle 4, which represents a global lateral acceleration a.sub.y,meas measured with the aid of a sensor system, is represented also on the left-hand side of FIG. 1 as a further input variable. This measured lateral acceleration may be measured directly, for example with the aid of a lateral acceleration sensor, and is very common, frequently as part of a vehicle dynamics control system or a rollover detection system. This measured lateral acceleration signal a.sub.y,meas may at times be very noisy, so that optionally filtering 5 may be provided, which is optionally represented in FIG. 1 by a dotted rectangle 5. Measured lateral acceleration signal a.sub.y,meas in rectangle 4 is supplied to optional rectangle 5 in which an averaging of measured lateral acceleration signal a.sub.y,meas over time is carried out, which corresponds to a low pass filtering. The output signal of this optional filter stage 5, like the output signal of the calculated, local lateral acceleration in rectangle 3, is supplied to a downstream difference creation device 6, which is again represented by the two arrows from rectangles 3 and 5 to rectangle 6.

[0025] In rectangle 6, a difference creation of the two supplied signals is carried out in that calculated, local lateral acceleration value a.sub.y,calc and optionally filtered, measured, global lateral acceleration value a.sub.y,meas are subtracted from one another. The result of this difference creation 6 is referred to as difference value 7 and forms the output signal of difference creation device 6.

[0026] This difference value 7 is the lateral acceleration difference between the global lateral acceleration, which was measured, and the local lateral acceleration, which was calculated, and represents a measure of the cross slope of the presently traveled roadway. Difference value 7 is supplied to a downstream rectangle 8 in which a conversion of the acceleration difference into an assigned cross slope angle takes place, which may be clearly assigned to difference value 7.

[0027] On the right-hand side of FIG. 1 rectangle 9 is illustrated, which as the result of the described method indicates a cross slope angle alpha α, which may advantageously be used for further settings and parameterizations in driver assistance systems or driver comfort systems.

[0028] FIG. 2 shows a schematic layout of a device with which the method according to the present invention may advantageously be carried out. An evaluation unit 20 is illustrated, for example, to which input signals 11, 12, 13, 24 shown on the left-hand side of FIG. 2 are supplied. An output signal 1 of a yaw rate sensor 11, which represents a yaw rate of the vehicle, is shown as input signals of evaluation unit 20. This yaw rate signal 1 of yaw rate sensor 11 is supplied to an input circuit 14 of evaluation unit 20. Output signal 2 of a longitudinal speed sensor 12, which may be designed as a wheel speed sensor, for example, and represents a vehicle longitudinal speed signal v, is also supplied to input circuit 14. Longitudinal speed sensor 12 may also alternatively or additionally be replaced or supplemented by an evaluation unit of a GPS signal, or replaced or supplemented by a surroundings sensor, which evaluates reflections on stationary objects and indicates the vehicle's own speed with the aid of the ascertained speed relative to stationary objects. As a further input signal, the output signal of a lateral acceleration sensor 13 is supplied to input circuit 14 of evaluation unit 20. This output signal 4 of lateral acceleration sensor 13 is a measured, global lateral acceleration a.sub.y,meas and may optionally be filtered in lateral acceleration sensor 13 in order to eliminate measuring noise. Alternatively, it is also possible to supply measured, global lateral acceleration signal a.sub.y,meas to input circuit 14 and to arithmetically filter an optional filtering in computation means 16 described hereafter. As a further, optional input variable, input circuit 14 of evaluation unit 20 may be supplied with a signal of a further sensor 24 for additional measured variables. Such a further sensor may be a friction coefficient sensor, for example, which indicates the friction coefficient of the presently traveled roadway surface. As a further sensor for additional measured variables 24, it may also be provided within the scope of the present invention that pieces of information are transmitted via a vehicle radio interface, which describe instantaneous, local roadway conditions and are kept available for retrieval on a storage means, for example a data server. For example, such values may have been recorded and made available by vehicles which traveled the presently traveled route at an earlier point in time. It is also possible that the evaluation of a video image is provided as a further sensor 24, in which properties of the roadway are ascertained with the aid of image processing, or that a laser-based sensor is provided, which enables pieces of information with respect to the roadway situated ahead, by scanning with the aid of the laser beam and an evaluation of the ascertained pieces of information.

[0029] The input variables supplied to evaluation unit 20 with the aid of input circuit 14 are supplied by input circuit 14 via an internal data exchange device 15, which may be designed as a bus system, for example, to a computation means 16. Computation means 16 may be designed, for example, as a microprocessor or as a microcontroller or as an application-specific integrated circuit (ASIC) or as free programmable gate array (FPGA). In computation means 16, one or multiple output variables are calculated from the supplied input variables with the aid of a control program and are ascertained according to the described method according to the present invention. The output variables determined by computation means 16 are supplied to an output circuit 17 via internal data exchange device 15. Output circuit 17 outputs the output variables of evaluation unit 20 to downstream actuators or control units for actuators. Such downstream actuators or control units for actuators may be, for example, a conventional cruise controller (CC) 18 or an adaptive cruise controller (ACC) 18, and additionally or alternatively be designed as a vehicle dynamics control system 19. The output variables output with the aid of output circuit 17 are supplied to the particular control units of conventional cruise controller 18 or adaptive cruise controller 18, and additionally or alternatively to the control unit of vehicle dynamics control system 19, where the ascertained cross slope angle alpha a is further processed to increase the driving comfort and the driving safety.

[0030] FIG. 3 shows a further specific embodiment of the system according to the present invention. Yaw rate sensor 11, which makes a yaw rate ω of the vehicle available as an output signal, is shown on the left-hand side of FIG. 3. Beneath, a longitudinal speed sensor 12, which may be designed as a wheel speed sensor, for example, is shown, which makes a vehicle speed signal v available as the output signal. The output signals of yaw rate sensor 11 and of speed sensor 12 are supplied to processing unit 3 in which a calculated, local lateral acceleration a.sub.y,calc is calculated by multiplying the two input variables yaw rate ω and vehicle speed v with one another.

[0031] The output signal of this processing unit 3 is supplied as a first input signal to a difference creation device 6. Unit 4, which ascertains a measured, global lateral acceleration signal a.sub.y,meas and makes it available as the output signal, is also shown on the left-hand side of FIG. 3. This output signal of lateral acceleration sensor 4 is supplied as a second input signal to difference creation device 6.

[0032] The two input signals are subtracted from one another in difference creation device 6, a difference

q=a.sub.y,calc−a.sub.y,meas

being calculated as the output signal. This difference value 7 ascertained in difference creation device 6 is supplied to a threshold value comparator 21, in which a characteristic curve having slope q is stored, which is derived from difference q, i.e., difference value 7. As a result, the slope of the characteristic curve of threshold value comparator 21 changes as a function of how far apart calculated, local lateral acceleration a.sub.y,calc and measured, global lateral acceleration a.sub.y,meas are from one another.

[0033] Due to the minimum/maximum value definition indicated in device 22, which may be stored as values in a control unit, for example, a minimum value and a maximum value are predefined for threshold value comparator 21, which each describe the maximum permitted lateral acceleration in the two lateral directions. Desired lateral acceleration a.sub.y,setpoint is predefined via a further characteristic curve in threshold value comparator 21. From the difference of the two accelerations

aΔ=a.sub.y,setpoint−a.sub.y,actual

it is possible to ascertain a control deviation. If the curve is negotiated too fast, aΔ is negative, and adaptive cruise controller 18 must decelerate. If the curve is negotiated too slowly, aΔ is a positive value, and adaptive cruise controller 18 may continue to accelerate.

[0034] Using a setpoint speed value, which as future lateral acceleration setpoint value a.sub.y,setpoint represents instantaneous lateral acceleration setpoint value a.sub.y,actual plus the product of difference q and a settable factor f, i.e.,

a.sub.y,setpoint=a.sub.y,actual+q*f

this factor f representing the weighting of the influence of the road cross slope, it is possible to create an interface which allows universal execution between output circuit 17 of evaluation unit 20 and the input circuit of the control unit of a conventional or adaptive cruise controller (CC; ACC) 18 and an installation in arbitrarily parameterized and differently configured vehicles without major adaptation measures.