DE19925249B4 - Method for controlling a brake system to support a starting process in a motor vehicle - Google Patents

Abstract

Method for controlling a brake system to assist a starting process in a motor vehicle, with a externally controllable, meterable parking brake device and a externally controllable service brake device, wherein the motor vehicle is held in the idle state by means of the parking brake device before the start of the starting process with the steps:
Detection of data controlled by the vehicle operator, which clearly signal the start-up process,
Determination of a time interval dt within a control device on the basis of the data set by the vehicle operator for the starting process,
Operating the service brake device with an intensity sufficient to hold the motor vehicle at rest,
Arbitrarily fast release of the parking brake device,
- Dosed release of the service brake device during the starting process, within the time period dt, wherein the metered release of the braking force F _brake over the time t of the starting operation for a continuous, functional relationship F _brake (t / dt) is performed, the brake intervention after the period dt is completely finished.

Description

The present invention relates to a control method and the use of this control method for a brake system to assist the starting process in a motor vehicle, in particular on an inclined road.

It is known that especially when starting on an inclined surface problems can occur. For example, the vehicle operator usually has to release the service brake via a foot pedal in order to actuate the accelerator pedal and thus be able to provide an engine torque which is necessary for the starting process. The complementary use of a mechanical parking brake device allows only experienced and skilled vehicle operators trouble-free starting. At the same time, the steeper the road, the more difficult it is to start off.

From the EP 0 822 129 A1 In this context, a method for assisting the starting process is known, according to which the resting state of the vehicle is ensured by brake intervention via external force or external power means in the event that the braking force exerted by the vehicle operator is not sufficient for the safe holding of the vehicle. Furthermore, it is necessary to detect the engine torque delivered by the drive motor of the vehicle and to end the brake intervention from a specific, present engine torque. Overall, a combined control or regulating device is necessary for the coordinated support of the starting process, which assumes the control or regulation of the starting process on the basis of input data relating to the motion and engine condition of the vehicle. Due to the large amount of data that has to be processed within the control device, this is very complex. Despite such a high system complexity, a comfortable sequence of the starting process, in particular with regard to a low-jerk vehicle movement during startup, is not necessarily ensured.

From the DE 42 18 717 A1 an actuator for a parking brake device is known which comprises an electric motor and a controller and allows to release the parking brake device upon detection of a starting situation with an adjustable, adapted to the driving situation, positioning speed. Thus, the motor vehicle is held by the parking brake device in the idle state before the start of the starting process. If the vehicle operator signals a start-up process, the parking brake device is released in doses with the adjusted actuating speed.

Proceeding from this, the object of the invention is to provide a method for controlling a brake system to support a start-up process, which facilitates a comfortable start, in particular with an inclined roadway with reduced control or regulation effort.

The object is achieved by a control method for a brake system with the features of claim 1. Thereafter, the first engaged brake or applied to the brake braking force F _brake during the startup over a period of time dt away according to a predetermined continuous time function F _Brake (t / dt) solved. However, the release of the brake is only when it has been clearly established that the vehicle operator really wants to start. For this purpose, appropriate operator actions of the vehicle operator, such. B. deactivation of the parking brake, engaging a transmission gear or an automatic transmission, actuation of the accelerator pedal, etc., as well as the periods between these operations mentioned, detected and fed corresponding data to a control device. From these data can be clearly identified by the control device of the desire of the vehicle operator with respect to the starting process. Furthermore, the period of time dt determined from the data set by the vehicle operator data for the starting process, in particular from the data on the operating amplitude and the operating speed of the accelerator pedal, which determines the time period in which a complete release of the brakes during the starting process. In practice, the length of the period of time dt should typically be a maximum of 1-3 seconds. Depending on the specifications of the vehicle operator this time span dt z. B. when detecting a driver's request for a quick start - ie with faster and / or intensive operation of the accelerator pedal (high speed operation or large actuation amplitude) - be shortened accordingly. For this purpose, either the accelerator pedal position can be sensed directly or an engine management system provides a corresponding signal, such. As the requested or actual engine torque available. By such a metered release of the braking force according to a time function taking into account the driver's request F _brake (t / dt) can be saved compared to known methods to support a start-up a significant control and control effort.

bzw. dem Verlauf der Splinefunktion: $$F_{Brems}\left(t/dt\right)=1-3\cdot {\left(t/dt\right)}^2+2\cdot {\left(t/dt\right)}^3$$

According to advantageous embodiments, the metered release of the braking force follows F _brake for example, the trigonometric function context: $$F_{Brems}\left(t/dt\right)=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\cdot \left(1+\text{cos}\left(\pi \cdot t/dt\right)\right)$$

or the course of the spline function: $$F_{Brems}\left(t/dt\right)=1-3\cdot {\left(t/dt\right)}^2+2\cdot {\left(t/dt\right)}^3$$

Both continuous functional relationships allow the implementation of a particularly comfortable starting process, which in particular allows a low-jerk movement of the motor vehicle. Of course, other suitable functional relationships are applicable, which ensure the desired goal of a comfortable start-up.

According to the invention, a control method is provided in which a metered release of a service brake device takes place during the starting process. In this case, the brake system includes both a Festellbremseinrichtung as well as an active service brake device, both of which are designed externally controllable. Before the start of the starting process, the motor vehicle is kept in the idle state by means of the activated parking brake device. After submission of appropriate specifications of the vehicle operator, which signal the startup process, the service brake device is actuated with an intensity sufficient to hold the motor vehicle at rest. Thereafter, an arbitrarily fast and possibly undosed release of the parking brake device takes place, whereby to a certain extent a transfer from the parking brake device to the service brake device takes place with regard to the braking force. In this state, the motor vehicle is thus no longer held by the parking brake device but rather by the active service brake device. Subsequently, the service brake device is released dosed during the startup according to the above functional context within the time span dt. Such a method can also be used in parking brake devices that allow only a sudden release in external control.

In an alternative variant, a parking brake device which is in engagement before the start of the starting process is released in a metered manner directly during the startup. This requires within the brake system a externally controllable, active parking brake device, which must also be designed to be finely dosed. For example, an electrically actuated parking brake can be activated in this manner.

Particularly advantageous is the control method described to support a start-up on an inclined roadway, thus apply on inclines and declines. In particular, inadequate control of the brake intervention could result in the vehicle initially moving backwards against the intent of the vehicle operator when starting uphill and starting off when driving downhill, the vehicle may start to move faster than the vehicle operator desires. In order to avoid this, the instructions of the vehicle operator signaling the starting process are first of all clearly detected before the brake is released over the time span dt with a specially selected time function. This time function ensures a smooth, low-jerk transition from the vehicle operating state "standing" to the state "driving". The vehicle operator can, as described, in particular over the period of time from the deactivation of the parking brake to the operation of the accelerator pedal, as well as the operating speed of the accelerator pedal influence on the length of the period dt take and so quickly or leisurely start as desired. In the latter case, the vehicle operator can allow comfortable times between the individual operations without the risk of a spontaneous rolling away of the motor vehicle.

When starting on a level road, a rapid release of the brake can cause no unwanted rolling away of the vehicle. Nevertheless, in this case also results from the release of the brake according to the invention with the specially selected time function an advantage in the event that the parking brake is not disabled before, but during the starting process, characterized in that the starting operation is quiet.

Within the single drawing, the functional relationship of the metered release process of the brake during the startup process is shown.

1 shows a diagram in which the braking force F _brake is plotted as a function of a related time variable t / dt. In this case, t determines the time during the start-up process and the time span dt indicates the period until the complete release (F _brake (t / dt) = 0) of the brake.

In 1 is the braking force F _brake plotted in percent [%], wherein a braking of 100%, ie F _brake = 100%, within the diagram corresponds to a braking force sufficient to hold the motor vehicle. Within the figure, several function graphs are shown, which represent the reduction of the braking force during startup for different starting operations. In this case, the steep course of the function graph means 'fast start-up' and, correspondingly, the flat course of the function graph means 'slow start-up'. As already described, the exact sequence of the starting process is determined in detail by the vehicle operator in addition to the given functional context. On the basis of these driver specifications, the length of the time span dt is ultimately determined and thus determines the dynamics of the startup process.

Overall, it can be seen from the steady course of the different function graphs that the braking force reduction during the starting process takes place smoothly evenly and thus a substantially smooth start-off is guaranteed.

Claims (5)

Method for controlling a brake system for supporting a starting process in a motor vehicle, with a externally controllable, meterable parking brake device and a externally controllable service brake device, wherein the motor vehicle is kept in the idle state by means of the parking brake device before the start of the starting process with the steps: - detection of data controlled by the vehicle operator, clearly signal the start-up process, - determination of a time span dt within a control device based on the data from the vehicle operator data for starting, - pressing the service brake device with an intensity sufficient to hold the motor vehicle at rest, - arbitrarily fast release the parking brake device, - dosed Releasing the service brake device during the starting process, within the time span dt, wherein the metered release of the braking force F _brake over the time t of the starting process it is performed after a steady, functional relationship F _brake (t / dt), wherein the brake intervention after the time period dt is completely completed. Method for controlling a brake system after Claim 1 , characterized in that the time span dt is determined as a function of the actuation amplitude and the actuation speed of an accelerator pedal. Method for controlling a brake system according to one of the preceding claims, characterized in that the metered release of the braking force F _brake the functional relationship $$F_{Brems}\left(t/dt\right)=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\cdot \left(1+\text{cos}\left(\pi \cdot t/dt\right)\right)$$

follows. Method for controlling a brake system according to one of Claims 1 - 2 , characterized in that the metered release of the braking force F _brake the functional relationship $$F_{Brems}\left(t/dt\right)=1-3\cdot {\left(t/dt\right)}^2+2\cdot {\left(t/dt\right)}^3$$

follows. Use of a method for controlling a brake system according to any one of the preceding claims to support a starting process on inclines and / or slopes.

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