METHOD FOR CORRECTING A HEIGHT VALUE, MEASURED USING A HEIGHT SENSOR, OF A MOTOR VEHICLE BY A CORRECTION VALUE

Abstract

Method for correcting a height value, measured using a height sensor, of a spring-damper unit of a motor vehicle, wherein the measured height value is corrected by a correction value that is dependent on an acceleration value if the motor vehicle is accelerated in a longitudinal and/or lateral direction, the correction value being adjusted while the motor vehicle is moving.

Claims

1. A method for correcting a height value, measured using a height sensor, of a spring-damper unit of a motor vehicle, wherein the measured height value is corrected by a correction value that is dependent on an acceleration value if the motor vehicle is accelerated in a longitudinal and/or lateral direction, wherein the correction value is adjusted while the motor vehicle is moving.

2. The method as claimed in claim 1, wherein the correction value is adjusted on the basis of a height change of the spring-damper unit, the height change being caused by a longitudinal or lateral acceleration of the motor vehicle.

3. The method as claimed in claim 2, wherein the height change of the spring-damper unit is ascertained from a reference height value and an acceleration-dependent height value.

4. The method as claimed in claim 3, wherein the acceleration-dependent height value is read off on the basis of a predetermined acceleration interpolation point value.

5. The method as claimed in claim 3, wherein the reference height value is stipulated when at least the following conditions exist: a vehicle speed of the motor vehicle is above a predetermined speed threshold value, and the longitudinal and lateral acceleration of the motor vehicle are below a respective predetermined acceleration threshold value, and a steering angle of the motor vehicle is below a predetermined steering angle threshold value, and a gradient of the height value measured using the height sensor is below a predetermined gradient threshold value or the height value measured using the height sensor is within a height value threshold value range, and if these conditions are met, no ride height control process for the motor vehicle must have taken place within a predetermined period of time beforehand.

6. The method as claimed in claim 3, wherein the ascertained height change of the spring-damper unit is supplied iteratively to an averaging section, resulting in an average height change value that is used to adjust the correction value.

7. The method as claimed in claim 6, wherein the average height change value represents the adjusted correction value.

8. The method as claimed in claim 3, wherein the ascertained height change of the spring-damper unit is supplied iteratively to a weighted averaging section, in which the ascertained height change is multiplied by a weighting factor, resulting in a weighted-average height change value that is used to adjust the correction value.

9. The method as claimed in claim 8, wherein the weighted-average height change value represents the adjusted correction value.

10. The method as claimed in claim 1, wherein the adjusted correction value is stored in an adaptive acceleration value/correction value characteristic curve.

11. The method as claimed in one of claim 1, wherein the method is carried out using an electronic open-loop and closed-loop control device of the motor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Other advantages of the disclosed subject matter will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0032] FIG. 1 shows a motor vehicle on a roadway,

[0033] FIG. 2 shows an illustrative acceleration value/height value graph, and

[0034] FIG. 3 shows an illustrative acceleration value/correction value graph.

DETAILED DESCRIPTION

[0035] FIG. 1 schematically shows a motor vehicle 1 whose wheels 4 are moving along a roadway 8. The motor vehicle 1 comprises a vehicle body 2, which is spring-mounted as a sprung mass in relation to the respective wheels 4 as unsprung masses by a multiplicity of spring-damper units 3. The spring-damper units 3 of the front and rear axles have respective associated height sensors 5. It goes without saying that two spring-damper units 3 with respective height sensors 5 are provided on each axle of the motor vehicle 1.

[0036] Height sensors 5 are used to measure a height 7 of the vehicle body 2 in relation to the wheel 4 as a component part of the vehicle chassis. The height 7 is the distance between the upper attachment of the spring-damper unit 3 to the vehicle body 2 and the lower attachment of the spring-damper unit 3 to the wheel support, or wheel 4. As a result, the height sensor 5 is used to measure the relative distance between the vehicle body 2 as a sprung mass and the wheel 4 as an unsprung mass. The measurement signals from the height sensors 5 are supplied continuously to an electronic open-loop and closed-loop control device 6 of the motor vehicle 1, where they are processed. There, the measurement signals generally undergo filtering in order to be processed further as smoothed height values, or for the purpose of target/actual control of the ride height position of the motor vehicle 1. The measurement signals from the height sensors 5 thus provide information about the current ride height position of the motor vehicle 1.

[0037] According to the prior art, the electronic open-loop and closed-loop control device 6 of the motor vehicle 1 stores correction values, or a family of characteristic curves containing correction values, that are dependent on an acceleration of the motor vehicle 1. The acceleration is generally a longitudinal and/or lateral acceleration of the motor vehicle 1. The correction values are linked to specific acceleration values and are read in an appropriate manner as soon as the motor vehicle 1 undergoes an acceleration in the longitudinal and/or lateral direction, with the result that correction of the height values is necessary. If the motor vehicle 1 undergoes a longitudinal acceleration, for example, the front axle is raised. That is to say that the spring-damper units 5 of the front axle are expanded and a height change occurs that is caused by the acceleration. The actual height value measured using the height sensor 5 differs from a target height value, with the result that a ride height control process would actually need to be triggered. However, this is prevented by setting the height value measured using the height sensor 5 against a correction value that is dependent on the acceleration that occurs. This correction value may be incorrect during vehicle operation, however, on account of the facts cited in the introduction. That is to say that if, e.g., the stored correction value differs too greatly from the height change caused by the acceleration, an undesirable ride height control process could be carried out. This means that the acceleration-dependent correction value stored in the system is no longer correct for the acceleration that has occurred. Accordingly, the actual height value is corrected by an incorrect correction value, and during the subsequent target/actual comparison a difference is ascertained that results in ride height compensation that is actually unwanted. Acceleration-dependent correction values that are no longer correct are therefore safety-critical.

[0038] FIGS. 2 and 3 that follow are intended to be used to explain the illustrative method for correcting a height value measured using a height sensor in more detail, said method ensuring that the correction value used is selected as precisely as possible.

[0039] The graph in FIG. 2 is intended to be used to explain the adaptive selection of a correction value during vehicle operation. The graph shows the acceleration a and time T on the x-axis. The height H is plotted on the y-axis. The solid line is used to illustrate the response of the height value H of a spring-damper unit as acceleration a increases by way of example. To be able to select or adjust a correction value, a height change ha; ha at a spring-damper unit is ascertained that was caused by an acceleration of the motor vehicle, for example in a longitudinal direction.

[0040] So that the height change ha; ha can be calculated, there is first a need for a reference height value hr. The reference height h.sub.r represents the zero position around which the height of the spring-damper unit changes positively or negatively when the motor vehicle undergoes an acceleration. To be able to determine the reference height h.sub.r, the motor vehicle must not be subject to driving dynamics influences. As such, at least the following conditions must exist together in order for the reference height h.sub.r to be able to be stipulated: The motor vehicle must be moving; it must not be stationary. The vehicle speed must thus be above a predetermined speed threshold value. The longitudinal and lateral acceleration must also be below respective predetermined acceleration threshold values. In addition, a steering angle must be below a predetermined steering angle threshold value. Furthermore, it is necessary for the height value H of the spring-damper unit not to vary too greatly. As such, the gradient of the height value H measured using the height sensor is meant to be below a predetermined gradient threshold value or the height value H measured using the height sensor must be within a height value threshold value range. If these conditions exist, no ride height control process must have taken place within a certain period of time beforehand in order for the reference height value h.sub.r to be able to be stipulated. In the graph, the stipulation is made by way of example at a reference time to, at which the cited conditions are met.

[0041] If the motor vehicle is then accelerated in the longitudinal direction, for example, at another time, and a lateral acceleration is then below a predetermined lateral acceleration threshold value, it is possible to ascertain acceleration-dependent height values H.sub.a1; H.sub.a2, from which the height change h.sub.d1; h.sub.d2 is calculated. As such, there is provision for a first acceleration interpolation point value a1 and a second acceleration interpolation point value a.sub.2, for example, on the basis of which the acceleration-dependent height values H.sub.a1; H.sub.a2 are read off. If the motor vehicle undergoes only a longitudinal acceleration at a first time t.sub.1, for example, and said acceleration is at the first acceleration interpolation point value a.sub.1 (for example 1 m/s.sup.2), then a first acceleration-dependent height value ha1 is read off that was present at the spring-damper unit at this time, or was caused by this acceleration value. It is therefore possible to use the first acceleration-dependent height value ha1 (for example 6 mm) and the reference height value h.sub.r (for example 0) to calculate a first height change h.sub.d1 (for example 6 mm). This ascertained first height change hd1 is then used to adjust the correction value assigned to the first acceleration interpolation point value a.sub.1. This ascertainment can also be performed for an acceleration of the motor vehicle in the lateral direction if a longitudinal acceleration is below a predetermined longitudinal acceleration threshold value.

[0042] If, over the course of time, the motor vehicle undergoes a further longitudinal acceleration to a second acceleration interpolation point value a.sub.2 (for example 2 m/s.sup.2) at a second time t.sub.2, said second acceleration interpolation point value can be taken as a basis for reading off a second acceleration-dependent height value h.sub.a2. Accordingly, the second acceleration-dependent height value h.sub.a2 (for example 14 mm) and the reference height value h.sub.r (for example 0) are used to calculate a second height change h.sub.d2 (for example 14 mm). This second height change h.sub.d2 is then taken as a basis for adjusting the correction value for the second acceleration interpolation point value az.

[0043] This illustrative method is carried out repeatedly if the aforementioned necessary constraints exist. As such, the correction value is preferably not adjusted on the basis of the most recently measured height change h.sub.d1; h.sub.d2, but rather the ascertained height changes are averaged over the repeating measurement processes. For example, the ascertained height change h.sub.d1; h.sub.d2 of the current calculation is added to the height changes of the previous calculations and divided by the total number of calculations performed. Furthermore, the height change h.sub.d1; h.sub.d2 of the current calculation is preferably weighted by multiplying it by a weighting factor. The weighting factor is dependent on the number of calculations already iteratively performed, with the result that the height change h.sub.d1; h.sub.d2 of the current calculation is included in the averaging to an ever smaller extent. The weighting factor=1/n, n being the total number of iterative calculations of the height change h.sub.d1; h.sub.d2.

[0044] The method is not limited to the adjustment of a correction value from an acceleration-induced height value, but rather a correction value characteristic curve is formed that results from consideration of the acceleration-induced height change. The correction value characteristic curve contains a multiplicity of acceleration interpolation point values linked to respective correction values, the correction values being adaptively defined on the basis of the height change h.sub.d1; h.sub.d2.

[0045] The graph in FIG. 3, then, is thus intended to be used to explain the adaptive selection of a correction value K in more detail. The acceleration a is plotted on the x-axis and the correction K is plotted on the y-axis. The solid line is used to show an initial correction value characteristic curve K.sub.i by way of example and the dashed line is used to show an adaptive correction value characteristic curve K.sub.a by way of example.

[0046] First, the electronic open-loop and closed-loop control device of the motor vehicle values used for correcting the height values are not established for the life of the motor vehicle, however, but rather are adaptive by way of illustration. That is to say that if it was must initially store an acceleration-dependent correction value characteristic curve K.sub.i. The acceleration-dependent correction possible to determine a height change of the spring-damper unit under the conditions described above, then these values can be used to convert the initial correction value characteristic curve K.sub.i into an adaptive correction value characteristic curve K.sub.a. The method for correcting a height value, measured using a height sensor, of a spring-damper unit of a motor vehicle, which corrects the measured height value by a correction value K that is dependent on an acceleration value, then no longer uses the initial correction value characteristic curve K.sub.i, but rather obtains the acceleration-dependent correction values K from the adaptive correction value characteristic curve K.sub.a.

[0047] That is to say that after the height change has been calculated for the first time, a first initial correction value K.sub.i1 for the first acceleration interpolation point value a.sub.1 is replaced by a first adaptive correction value K.sub.a1 and a second initial correction value K.sub.i2 for the second acceleration interpolation point value a.sub.2 is replaced by the second adaptive correction value K.sub.a2. From then on, the constantly adapting correction value characteristic curve K.sub.a is used for correcting the height value.

[0048] Producing the adaptive correction value characteristic curve K.sub.a also has the advantage that changes to the spring-damper units or the chassis over the life of the motor vehicle can be observed and identified. Comparing the initial correction value characteristic curve K.sub.i with the adaptive correction value characteristic curve K.sub.a reveals differences caused for example by wear. It is also possible to continually check whether the adaptive correction value characteristic curve K.sub.a is within a predefined tolerance, and if this is not the case, a service report can be sent.

[0049] The present invention has been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.