Patent Application
20130261875
The present invention generally relates to a control module and method for controlling or regulating a vehicle system.
Vehicle dynamics control systems enable vehicle instabilities to be identified and corrected. In particular, rolling tendencies of the vehicle and oversteer or understeer tendencies may be determined. The vehicle stability systems sometimes have lateral acceleration sensors and yaw rate sensors for this purpose. With the aid of the determined yaw rate of the vehicle, i.e., the rotational frequency around the vertical axis of the vehicle, and the lateral acceleration in the lateral direction as well as the known vehicle velocity, vehicle stability can be improved by targeted wheel brake interventions or corrective behavior can be indicated for the driver.
In general, a control module, to which a central control unit and, e.g., the yaw rate sensor and lateral acceleration sensor are attached, is used for the vehicle dynamics control system or vehicle stability control system. The installation location is in general the center of gravity of the vehicle, since the relevant vehicle dynamics variables can be directly measured there. DE 198 56 303 A, DE 10 2005 033 237 B4, DE 10 2005 059 229 A1, and EP 1351843 B1 describe corresponding sensor systems and vehicle dynamics control systems.
In some vehicles, however, placement of the sensor module in the vehicle center of gravity or very close to the vehicle center of gravity is not possible. Thus, e.g., in tour buses, the vehicle center of gravity can be in or about the passenger compartment or occupied by other vehicle components. The yaw rate of a vehicle is generally equal in all points of the vehicle and therefore can also be determined by means of a sensor outside the center of gravity; however, the measurement of the vehicle lateral acceleration outside the center of gravity results in incorrect values, since contributions arise through the dynamic rotation of the vehicle, i.e., the yaw rate.
US 20070106444 A1 describes a system in which the lateral acceleration is measured by means of a sensor outside the vehicle center of gravity. Subsequently, the lateral acceleration in the vehicle center of gravity is determined from this measured lateral acceleration, a yaw rate change, and the lever arm, which is formed as the sensor distance between the center of gravity and the sensor installation location. For this purpose, the yaw rate change is determined from two successive measuring signals of the yaw rate sensor. The sensor distance of the lateral acceleration sensor in relation to the vehicle center of gravity is assumed to be given.
However, such a measuring system is subject to the disadvantage that because of the signal noise during successive measured values, a yaw rate change thus determined can be relatively large, and in combination with incorrect specifications of the sensor distance of the lateral acceleration sensor in relation to the center of gravity, compensation values may occur, which are greater than the lateral acceleration measuring signal. A vehicle lateral acceleration of the vehicle center of gravity thus determined is therefore generally not sufficiently precise for vehicle control systems.
Generally speaking, it is an object of the present invention to provide a sensor module for a vehicle system and a method for controlling or regulating a vehicle, that enable sufficiently precise determination of the vehicle lateral acceleration even when at least the lateral acceleration sensor is installed outside the vehicle's center of gravity.
According to embodiments of the present invention, calculating the vehicle lateral acceleration in the vehicle center of gravity while measuring the vehicle lateral acceleration outside the center of gravity is salutary if appropriate corrections are performed in the case of some of the employed variables. A light low-pass filtering of the yaw rate measuring signal even before the formation of a time derivative is advantageous. In particular, a Tschebyscheff filter is quite suitable for performing low-pass filtering before the formation of the time derivative. The use of a limiting frequency in the range of about 7 to 10 Hz, in particular, about 7.5 to 8.5 Hz is advantageous in this case.
In accordance with embodiments of the present invention, through the use of a Tschebyscheff filter (which is not excessively complex with regard to computation) for the recorded yaw rate measuring signals, a significant improvement of the correction or compensation, i.e., of the determination of the vehicle lateral acceleration in the vehicle center of gravity, is possible. A particular advantage of the Tschebyscheff filter is its flank steepness. The filtering by the Tschebyscheff filter should be sufficiently low to eliminate noise; however, an excessively low limiting frequency could cause the correction of the lateral acceleration to occur excessively slowly in the event of a rapid change of the yaw rate and thus cause overshoots to arise on the corrected signals, i.e., the dynamic response or consideration of the time change of the yaw rate could become excessively small, in order to be able to operate a safety-relevant vehicle control system in this way.
According to embodiments of the present invention, using a Tschebyscheff filter and simultaneously incorporating calculated values of the sensor distance is particularly advantageous. In the event of incorrect sensor distance values in the formula for determining the vehicle lateral acceleration from the yaw rate change and the distance, use of a Tschebyscheff filter can rapidly result in incorrect values, which can be greater than with other low-pass filters.
An instantaneous determination of the sensor distance can be performed in this case in particular by determining the vehicle center of gravity. Determining the vehicle center of gravity is possible in the vehicle X direction by applying a torque equilibrium, in which the wheel loads or axle loads, i.e., weight distributions acting on the wheel axles in the vehicle longitudinal direction, are used, or the vehicle is divided into modules and the effect of the module weights on the wheel axles is determined.
Therefore, through these two calculations, on the one hand, the Tschebyscheff filtering before determining the yaw rate change and, on the other hand, the determination of the vehicle center of gravity relative to the lateral acceleration sensor, precise determination of the vehicle lateral acceleration in the vehicle center of gravity is possible.
Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.
The present invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and embodies features of construction, combinations of elements, and arrangement of parts adapted to effect such steps, all as exemplified in the detailed disclosure hereinafter set forth, and the scope of the invention will be indicated in the claims.
The invention will be explained in greater detail hereafter on the basis of the appended drawings of exemplary embodiments, in which:
A utility vehicle 1 has three axles A1, A2, and A3, wherein A1 is the front axle. The vehicle 1 travels in the longitudinal direction or X direction. The transverse direction or Y direction and vertical direction or Z direction are shown accordingly in
The control module 2 has a central control unit 6, a yaw rate sensor 7 for measuring a yaw rate φ, and a lateral acceleration sensor 8 for measuring a sensor lateral acceleration a_s. The yaw rate sensor 7 outputs a yaw rate measuring signal S2 to the central control unit 6; the lateral acceleration sensor 8 accordingly outputs a lateral acceleration measuring signal S3 to the central control unit 6. The central control unit 6 also records other signals, in particular wheel speed signals of wheel speed sensors or ABS sensors (not shown) on the wheels of the axles A1, A2, and A3, as is known per se to a person skilled in the art. In the schematic illustration of
The control module 2 including the sensors 7, 8 is spaced apart in the X direction by a distance d from the center of gravity S of the vehicle 1. In the center of gravity S, the center of gravity lateral acceleration aq occurs, which can in general be different from the sensor lateral acceleration a_s. The yaw rate φ, in contrast, is independent of the longitudinal position in the X direction.
The measured sensor lateral acceleration a_s is compensated or corrected in order to ascertain the center of gravity lateral acceleration aq therefrom. This is performed based on the sensor lateral acceleration a_s, the yaw rate φ, and the distance d according to the formula:
aq=φ′d+a
—
s,
where φ′ is the yaw rate change, i.e., the time derivative dφ/dt of the yaw rate φ.
The distance d therefore represents the lever arm, with which the yaw rate change φ′ provides a contribution to the sensor lateral acceleration signal a_s.
According to an embodiment of the present invention, the distance d and the yaw rate change φ′ are therefore to be determined. The installation position of the lateral acceleration sensor 8 or of the entire control module 2 is known, wherein the sensors 7 and/or 8 can also be installed outside the control module 2. The center of gravity S or its longitudinal position is therefore to be determined. This can preferably be accomplished by:
Furthermore, according to an embodiment of the invention, the yaw rate change φ′ is determined, in that the yaw rate measuring signal S2 is first subjected to low-pass filtering, and subsequently the time derivative is formed, as described hereafter.
A control method according to an embodiment of the invention is illustrated in greater detail in the schematic flow chart of
According to an embodiment of the invention, Tschebyscheff low-pass filtering is employed in order to filter the yaw rate measuring signals to form the time derivative. The high flank steepness is advantageous in this case of Tschebyscheff filtering.
A limiting frequency fg of about 7 to 10 Hz, preferably 7 to 9 Hz or 7.5 to 8.5 Hz, i.e., around about 8 Hz, is advantageous for the Tschebyscheff filter. Filtering using fg above 10 Hz is not recommended. The yaw rate measuring signals S2 per se are themselves still sufficient for ascertaining a yaw rate if necessary; however, they can scatter too much for the formation of a time derivative, so that a time differential formation or formation of the time derivative as a difference quotient of two successive measurements does not result in sufficient accuracy. An excessively strong low-pass filtering in turn can worsen the dynamics and response time of the vehicle control system or of the vehicle stability program.
At excessively low limiting frequencies, variations in the measuring signal are remedied again; however, a potential disadvantageous effect is that in the event of rapid change of the yaw rate, the correction of the signal and therefore also the correction of the calculated lateral acceleration occurs too slowly and, in this way, overshoots may arise on the corrected signals.
The time derivative dφ/dt can already be produced by forming a simple differential quotient, which is formed as the quotient Δφ/Δt from the difference between two successive values and the difference of the points in time of the measurements. However, a time derivative is advantageously formed while incorporating multiple measured values, i.e., as a tangent formation on the previously determined function of the filtered signal S4, since a smoother function is formed by the Tschebyscheff filtering; this subsequent derivation by tangent formation is advantageous, since it takes the curve profile as a whole into consideration.
In step St4, the vehicle center of gravity S is determined substantially instantaneously. Because of different loads and load states of the vehicle 1, previously set vehicle data may not be sufficiently precise; therefore, the respective instantaneous determination of the distance d is made possible in that the installation location of the module 2 or of the lateral acceleration sensor 8, respectively, is known and the center of gravity S is determined from current measuring signals or measuring data, optionally with incorporation of external signals or measuring signals.
The determination of the center of gravity S can be performed by different variants. According to an embodiment shown in
where the summation is respectively performed via the index i, e.g., in the case of three modules with i=1, 2, 3, whereby the following results:
According to an embodiment shown in
According to an embodiment shown in
According to the embodiment described with reference to
The vehicle length Lges may be determined from this data and from the wheel base known per se, i.e., R1 and R2. Under the assumption that the structure is homogeneously distributed, the vehicle center of gravity S and the weight of the structure can be calculated. The reference point for the determination of the center of gravity of the entire vehicle can be fixed in this case on the vehicle rear. This is schematically shown in
Since the structure of the individual vehicles 1 can differ in height, it is reasonable to keep the mass distribution of the middle module AB4 variable. In this case, the following values for AB4 can be applied for the following vehicle types:
low-floor bus 450 kg/m,
high-decker bus 500 kg/m,
double-decker bus 650 kg/m.
This constant is used as GB in the following system of equations:
The center of gravity S can therefore be determined accordingly.
In this case, supplementary data about the size and position of the luggage compartment, also the size and position of the diesel tank, and the size and position of the battery can also be incorporated, which are initially used in generalized form in the above applied modules.
According to another embodiment, the vehicle center of gravity S can also be determined by external systems or their data signals, wherein, e.g., values for the wheel loads F1, F2, and F3 can be used by a level control system, in particular an electronically regulated ECAS of the vehicle 1. With incorporation of the known wheel bases R1 and R2, the center of gravity S of the vehicle may be determined in
A compensation to determine the center of gravity lateral acceleration aq can therefore subsequently be performed.
In the embodiments discussed above, the compensation in the X direction was determined first. A corresponding compensation or correction can accordingly also be performed in the Z direction, i.e., the vertical axis, wherein the roll angle change is used instead of the yaw rate change φ′. If a triangle quadrant yaw rate sensor is used as the yaw rate sensor 7, which therefore also detects this dynamic change variable of the roll angle, the installation location is therefore absolutely variable.
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 in the above processes and constructions 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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102010050635.4 | Nov 2010 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/004139 | 8/17/2011 | WO | 00 | 5/3/2013 |
