Device and Method for Influencing the Spring Force Characteristic of an Active Chassis of a Motor Vehicle

Abstract

A device and a method for influencing the spring force characteristic of an active chassis of a motor vehicle are provided. A wheel spring device is arranged between a vehicle body and a wheel carrier of the motor vehicle. The spring force characteristic of the wheel spring device can be modified by controlling an actuating device. A sensor detects a prediction variable representing the vertical profile of a route ahead in the direction of travel of the motor vehicle. A control device controls the actuating device as a function of the detected prediction variable in such a way that the spring force characteristic of the wheel spring device is adapted in a predictive fashion to the course of the sensed vertical profile of the route ahead in the direction of travel of the motor vehicle.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT International Application No. PCT/EP2007/006843, filed Aug. 2, 2007, which claims priority under 35 U.S.C. § 119 to German Patent Application No. 10 2006 039 353.8, filed Aug. 22, 2006, the entire disclosures of which are herein expressly incorporated by reference.

This application is related to U.S. patent application Ser. No. ______ “Influencing Device Comprising a Diagnosis Unit for Influencing an Active Suspension System of a Vehicle” and U.S. patent application Ser. No. ______ “Influencing Device for Influencing an Active Chassis System of a Vehicle” both of which are filed on even date herewith and the entire disclosure of which is herein expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a device and a method for influencing the spring force characteristic of an active chassis of a motor vehicle. In addition, the invention relates to a motor vehicle which is equipped with such a device.

Active chassis can run up against physical limits in the conflict between driving dynamics and driving comfort. This is due to, inter alia, the fact that conventional active chassis only react comparatively late to travel-related roadway excitations that occur, for example, when traveling uneven ground or the like. The information is of course not available at the sensors of the active chassis—which sensors serve, for example, to sense vertical acceleration of the vehicle body and/or the spring travel occurring at the wheel spring devices of the motor vehicle—until the roadway excitations are already acting on the motor vehicle or the vehicle body. Consequently, the remaining time for compensating the travel-induced roadway excitations is correspondingly short and is primarily restricted to damping its effects subsequently.

These disadvantages can be avoided, or at least considerably reduced, by using a predictively acting active chassis as set forth by the present invention.

For this purpose, three-dimensional information about the expected vertical profile of the roadway in the direction of travel of the motor vehicle is used. The detection of an obstacle ahead by evaluating the vertical profile of the roadway makes it possible to adapt the spring force characteristic of the active chassis in a predictive fashion to the respective type of obstacle in order to ensure that the obstacle is traveled over with the smallest possible degree of transmission of disruption to the motor vehicle and to the vehicle body.

The procedure of such an active chassis can be divided into a plurality of successive steps. In a first step, an obstacle ahead is sensed as early as possible. In a second step, the type of obstacle is then analyzed and an appropriate travel-over strategy for the type of obstacle is selected. Finally, in a third step suitable measures for traveling over the obstacle are initiated by adapting the spring force characteristic of the active chassis.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.

BRIEF SUMMARY OF THE DRAWING FIGURES

The device according to the invention and the method according to the invention will be explained in more detail below with reference to the appended drawings, in which:

FIG. 1 is a schematically illustrated travel situation when an obstacle is being traveled over by a motor vehicle which is equipped with the device according to the invention,

FIG. 2 is an embodiment of the device according to the invention which is illustrated by way of example, and

FIG. 3 is a schematically illustrated travel situation when an obstacle is traveled over on the basis of a long-term strategy carried out by the device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematically illustrated travel situation when an obstacle is being traveled over by a motor vehicle 10 equipped with the device according to the invention.

The obstacle is, according to FIG. 1a), a step-shaped ridge 11 which has, for example, a height of approximately 10 centimeters and is assumed to be at a distance of approximately 10 meters in front of the motor vehicle 10 in the direction of travel. The maximum available spring travel of the motor vehicle 10 is less than the height of the ridge 11 so that it is not possible to travel over the ridge 11 without a perceptible transmission of disruption. The vehicle body 12 is therefore raised, according to FIG. 1b), in the direction of the arrow 13 before the ridge 11 is used for the purpose of increasing the maximum available spring travel so that, according to FIG. 1c), it is possible to travel over the ridge 11 comfortably.

FIG. 2 shows, with reference to FIG. 1, an embodiment of the device according to the invention for carrying out the method according to the invention which is illustrated by way of example. The device 14 comprises a plurality of wheel spring devices 15i which are assigned to the individual vehicle wheels and which are arranged between the vehicle body 12 and the wheel carriers of the motor vehicle 10. The wheel spring devices 15i can be adjusted using associated actuating devices 16i in order to adapt the maximum available spring travel with respect to the spring force characteristic. The wheel spring devices 15i are, like the actuating devices 16i, a component of an active chassis of the motor vehicle 10 here. The present case involves a four-wheel motor vehicle 10 so that i=1, . . . , 4.

More specifically, the actuating devices 16i permit adaptation of the spring force or of the spring force characteristic of the wheel spring devices 15i and thus ultimately of the position of the vehicle body 12 relative to the surface of the roadway. This also permits, in addition to raising or lowering of the vehicle body 12 before an obstacle is traveled over, compensation of relatively small roadway excitations owing to unevenness of the roadway or the like.

The device 14 also has a plurality of chassis sensors 20 for sensing spring travel values z_i occurring at the wheel spring devices 15i, and for sensing vertical acceleration values a_i acting on the vehicle body 12 due to travel in the region of the wheel spring devices 15i. In addition, predictive sensors 21 for three-dimensional sensing of the vertical profile of the roadway are also present in the direction of travel of the motor vehicle 10. The sensor raw data which are made available by the chassis sensors 20 and the predictive sensors 21 are fed to a control device 22 which, on the basis of a predefined control strategy, controls the actuating devices 16i in the sense of comfort-oriented adaptation of the spring force characteristic of the wheel spring devices 15i to the vertical profile of the roadway ahead.

Through suitable control of the actuating devices 16i, both the vertical acceleration values a_i which act on the vehicle body 12 and the spring travel values {circumflex over (z)}_i which are to be made available at the individual wheel spring devices 15i are minimized by predefining set point values a_i,setp=0 and {circumflex over (z)}_i,setp=0 which are to be complied with.

For this purpose, in a subtraction element 23, a difference-forming process a_{i,setp, −ai} and {circumflex over (z)}_i,setp, −{circumflex over (z)}_i is carried out during which the set point values a_i,setp and {circumflex over (z)}_i,setp are compared with the corresponding actual values a_i and {circumflex over (z)}_i which are detected using the chassis sensors 20. The differences which are formed in this way are subsequently fed to a controller 24 which controls the actuating devices 16i in the sense of reducing travel-induced roadway excitations which are expressed as corresponding forces F_disr occurring in the region of the wheel spring devices 15i on the vehicle body 12 and/or corresponding spring travel values z_disr occurring at the wheel spring devices 15i. The influence of the transmitted disruption F_disr and z_disr, acting from the outside due to travel, on the control circuit is illustrated here by an adder element 25.

The motor vehicle 10 is equipped in the present case with a total of two of the predictive sensors 21, each of which sense the lane in the region in front of the front wheels of the motor vehicle 10 in order to acquire three-dimensional information about the vertical profile of the roadway in front of the motor vehicle 10. For example, the two predictive sensors 21 are laser scanners, but it is also conceivable to use image-producing radar systems and/or CCD cameras. The laser scanners operate with pulsed infrared light and scan the route in front of the left-hand front wheel and the right-hand front wheel of the motor vehicle 10 in a punctiform fashion. The sensor raw data are transmitted via an interface to the control device 22 and evaluated there in order to detect a prediction variable h_i within the scope of real-time conditioning 30 carried out by the control device 22.

The prediction variable h_i provides a three-dimensional representation of the vertical profile of the route ahead in the direction of travel of the motor vehicle 10 and is used to control the actuating devices 16i by acquiring a corresponding pilot control variable s_i within the scope of a pilot control process 31.

The pilot control variable s_i is subsequently input using an adder element 32, which is arranged between the controller 24 and the actuating devices 16i.

Owing to travel-induced movements of the vehicle body 12, which are expressed as corresponding pitching movements, rolling movements and/or reciprocating movements, the data which are made available by the predictive sensors 21 are corrected within the scope of the real-time conditioning 30 in that the data are reconciled with the data of the chassis sensors 20. The latter therefore provide direct information about pitching, rolling and/or reciprocating movements of the vehicle body 12 which occur relative to the surface of the roadway.

More specifically, the control device 22 calculates the prediction variable h_i as a function of a state variable ζ_i which represents the current state of movement of the vehicle body 12 relative to the surface of the roadway being traveled on. The state variable ζ_i is a function of a pitch angle variable representing a pitching movement of the vehicle body 12 with respect to a longitudinal axis of the body, a rolling angle variable representing a rolling movement of the vehicle body 12 with respect to a transverse axis of the vehicle body, and/or a reciprocating movement variable representing a reciprocating movement of the vehicle body 12 with respect to a vertical axis of the vehicle body.

In order to improve the quality of data, during the calculation of the state variable ζ_i during the real-time conditioning 30 a plurality of vertical profiles of the roadway which are sensed successively and stored are superimposed. In this case, statistical averaging of the sensor raw data which is made available by the predictive sensors 21 can also be carried out so that the quality of the prediction variable h_i can be improved.

As a result of the use of the predictive sensors 21, the three-dimensional information relating to the expected vertical profile of the roadway is already available at a distance of several meters in front of the motor vehicle 10. Accordingly, immediately after an obstacle has been detected on the roadway it is possible to initiate suitable countermeasures by controlling the actuating devices 16i. The mechanical inertia of the actuating devices 16i and the possible delays owing to the conditioning or processing of the sensor raw data no longer play any role. The compensation strategy which is implemented in this way requires only a comparatively small prediction horizon of a few meters.

With knowledge of the vertical profile of the roadway at a relatively large distance in front of the motor vehicle 10, it is additionally possible to provide a long-term strategy which permits early pre-conditioning of the active chassis to be performed.

The implementation of such a long-term strategy is illustrated in FIG. 3, and according to FIG. 3a) after the ridge 11 has been sensed an ideal movement sequence of the vehicle body 12 is detected here with the aim of minimizing the transmission of disruption which is to be expected when the ridge 11 is traveled over. In this context, the respective vehicle wheels are, according to FIG. 3b), raised just before the ridge 11 is reached, by suitably controlling the actuating devices 16i in the direction of the arrow 33 so that according to FIG. 3c) it is subsequently made possible for the ridge 11 to be traveled over with significantly reduced transmission of disruption.

Which of the two strategies is used depends ultimately on the roadway conditions and the resulting prediction horizon of the detected prediction variable h_i.

The presence of the pilot controller 31 can lead to conflicts with the controller 24. Specifically, since the pilot controller 31 and the controller 24 know nothing about one another, the controller 24 incorrectly interprets the intervention of the pilot controller 31 in the actuating devices 16i to be transmission of disruption from the outside due to travel and attempts to compensate for it by correspondingly controlling the actuating devices 16i.

In order to avoid such conflicts, the pilot controller 31 takes into account information which is supplied by means of a feedback loop 34 and which relates to the present or expected activities of the controller 24 and therefore ultimately the current and/or expected state of movement of the vehicle body 12 by evaluating the state variable ζ_i and/or its change ζ_i and ζ_i over time.

If the pilot controller 31 detects an error, for example due to implausible information relating to the sensed vertical profile of the roadway due to a failure of one or more of the sensors 20 or 21, the pilot control variable hi which is made available by the pilot controller 31 is ignored. In this case, the active chassis operates without prediction and ensures that a minimum travel comfort which is familiar from conventional active chassis is maintained.

For this purpose, a quality factor g_i, which results from evaluation of the quality of the data on which the sensed vertical profile of the roadway is based, is logically combined with the pilot control variable h_i by means of a multiplier element 35. If the diagnostic quality is adversely affected owing to failure of one or more of the sensors 20 or 21, the quality factor g_i is set equal to 0. If, on the other hand, the quality of the data is not adversely affected, the quality factor g_i is set equal to 1. In particular, the quality factor g_i can also have a value in the range from 0 to 1 which increases with the quality of the data.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

Claims

1-19. (canceled)

20. A device that influences a spring force characteristic of an active chassis of a motor vehicle, the device comprising:

a wheel spring device arranged between a vehicle body and a wheel carrier of the motor vehicle, wherein the spring force characteristic of the wheel spring device is modifiable by controlling an actuating device;

a sensor that detects a prediction variable representing a vertical profile of a route ahead in a direction of travel of the motor vehicle; and

a control device that controls the actuating device as a function of the detected prediction variable such that the spring force characteristic of the wheel spring device is adapted in a predictive fashion to the sensed vertical profile of the route ahead in the direction of travel of the motor vehicle.

21. The device as claimed in claim 20, wherein a spring travel available at the wheel spring device is modified in accordance with the sensed vertical profile by adapting the spring force characteristic.

22. The device as claimed in claim 20, wherein the sensor is a laser scanner that senses the vertical profile.

23. The device as claimed in claim 22, wherein precisely two laser scanners are arranged in a front region of the motor vehicle.

24. The device as claimed in claim 20, wherein the sensor is an image-producing radar system and/or a CCD camera.

25. The device as claimed in claim 20, wherein the detected prediction variable provides a three-dimensional representation of the sensed vertical profile.

26. The device as claimed in claim 20, wherein the control device detects the prediction variable by superimposing chronologically successively sensed vertical profiles.

27. The device as claimed in claim 20, wherein the control device selects, as a function of the detected prediction variable, a strategy for controlling the actuating device that is adapted to the sensed vertical profile.

28. The device as claimed in claim 27, wherein the strategy is selected as a function of a prediction horizon on which the prediction variable is based.

29. The device as claimed in claim 20, wherein the control device detects the prediction variable as a function of a calculated state variable representing a current state of movement of the vehicle body relative to the surface of the roadway being traveled on.

30. The device as claimed in claim 29, wherein the control device calculates the state variable based on a comparison of chronologically successively sensed vertical profiles.

31. The device as claimed in claim 29, wherein the state variable is a function of a pitch angle variable representing a pitching movement of the vehicle body with respect to a longitudinal axis of the body, a rolling angle variable representing a rolling movement of the vehicle body with respect to a transverse axis of the vehicle body, or a reciprocating movement variable representing a reciprocating movement of the vehicle body with respect to a vertical axis of the vehicle body.

32. The device as claimed in claim 20, wherein the control device detects a pilot control variable that is dependent on the prediction variable in order to control the actuating device.

33. The device as claimed in claim 32, wherein the control device modifies the pilot control variable as a function of the quality of the data of the prediction variable.

34. The device as claimed in claim 33, wherein the control device multiplies the pilot control variable by a quality factor that is dependent on the quality of the data of the prediction variable.

35. The device as claimed in claim 34, wherein the quality factor has a value in the range of 0 to 1 which increases with the quality of the data.

36. The device as claimed in claim 32, further comprising:

a controller that interacts with the control device and that adjusts the pilot control variable at the actuating device taking into account the current or expected state of movement of the vehicle body.

37. A method for influencing the spring force characteristic of an active chassis of a motor vehicle, comprising:

detecting a prediction variable corresponding to a vertical profile of a route ahead in a direction of travel of the motor vehicle; and

adapting the spring force characteristic of a wheel spring device, arranged between a vehicle body and a wheel carrier of the motor vehicle, of the active chassis in a predictive fashion to a course of the sensed vertical profile of the route ahead in the direction of travel of the motor vehicle as a function of the detected prediction variable.

38. A motor vehicle, comprising:

a device that influences a spring force characteristic of an active chassis of the motor vehicle, the device comprising a wheel spring device arranged between a vehicle body and a wheel carrier of the motor vehicle, wherein the spring force characteristic of the wheel spring device is modifiable by controlling an actuating device; a sensor that detects a prediction variable representing a vertical profile of a route ahead in a direction of travel of the motor vehicle; and a control device that controls the actuating device as a function of the detected prediction variable such that the spring force characteristic of the wheel spring device is adapted in a predictive fashion to the sensed vertical profile of the route ahead in the direction of travel of the motor vehicle.