METHOD FOR OPERATING A VEHICLE BRAKE SYSTEM, AND BRAKE SYSTEM

Abstract

A method for operating a vehicle brake system, wherein the brake system has at least one friction brake and at least one regenerative brake. A defined switching pattern is specified for switching between a self-cleaning operating mode for cleaning the friction brake and a normal operating mode of the brake system. The method includes determining information describing the state of the at least one friction brake, determining the state of the at least one friction brake from the information, determining whether the state satisfies a specific switching criterion, and, if the self-cleaning operating mode is to be activated according to the switching pattern and the state of the friction brake does not satisfy the switching criterion, suppressing activation of the self-cleaning operating mode and maintaining the normal operating mode.

Claims

1. A method of operating a vehicle brake system comprising at least one friction brake and at least one regenerative brake, the method comprising: determining a state of at least one friction brake; determining that the state satisfies a specific switching criterion for switching between a self-cleaning operating mode for cleaning the at least one friction brake and a normal operating mode of the vehicle brake system; determining that a self-cleaning operating mode is to be activated according to a switching pattern for switching between the self-cleaning operating mode for cleaning that at least one friction brake and the normal operating mode of the brake system and the state of the at least one friction brake does not satisfy the switching criterion; and suppressing activation of the self-cleaning operating mode and maintaining the normal operating mode in response to determining that the self-cleaning operating mode is to be activated according to the switching pattern and the state of the at least one friction brake does not satisfy the switching criterion.

2. The method as claimed in claim 1, wherein the self-cleaning operating mode specifies a fixed relationship between a deceleration torque applied by the at least one friction brake and a deceleration torque applied by the at least one regenerative brake for the purpose of decelerating the vehicle.

3. The method as claimed in claim 2, wherein the switching pattern defines a time interval or a number of braking operations between successive activations of the self-cleaning operating mode.

4. The method as claimed in claim 3, wherein only the at least one friction brake is used to decelerate the vehicle in the self-cleaning operating mode.

5. The method as claimed in claim 3, wherein the switching pattern depends on environmental conditions in the region of the vehicle.

6. The method as claimed in claim 1, wherein determining the state of the friction brake comprises determining the state of the friction brake based on weather information in the region of the vehicle.

7. The method as claimed in claim 6, wherein the weather information is determined by at least one sensor of the vehicle.

8. The method as claimed in claim 6, wherein the weather information is determined from information sources outside the vehicle.

9. The method as claimed in claim 1, wherein the information describing the state of the at least one friction brake is an energy input over a defined time period into at least one of the friction partners of the friction brake.

10. The method as claimed in claim 9, wherein t the defined time period comprises a time period since the last activation of the self-cleaning operating mode.

11. The method as claimed in claim 1, wherein the information describing the state of the at least one friction brake is a vehicle speed or a vehicle deceleration or a slope of a roadway in the region of the vehicle or a time period since the last activation of the self-cleaning operating mode.

12. The method as claimed in claim 1, wherein the state of the friction brake is determined individually for the at least one individual friction brakes or axle-wise.

13. The method as claimed in claim 1, wherein determining that the self-cleaning operating mode is to be activated according to the switching pattern comprises determining individually for each friction brake among the at least one friction brake or jointly for the at least one friction brake on a vehicle axle whether the self-cleaning operating mode is to be activated according to the switching pattern.

14. The method as claimed in claim 1, wherein the suppressing comprises suppression of the activation of the self-cleaning operating mode in a wheel-specific manner.

15. The method as claimed in claim 1, wherein the suppressing comprises suppression of the activation of the self-cleaning operating mode axle-wise.

16. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Preferred embodiments of the present application are explained in more detail below on the basis of the drawings. In the drawings:

[0042] FIG. 1 shows a flow diagram of a method according to the example, and

[0043] FIG. 2 shows a schematic illustration of the time characteristic of a switching pattern.

DETAILED DESCRIPTION

[0044] In the text which follows, features that are similar or identical are denoted by the same reference signs.

[0045] FIG. 1 shows a flow diagram of a method 100 according to the example for operating a vehicle brake system. Here, the vehicle brake system is used in a vehicle with four wheels, for example, wherein each wheel of the vehicle has a friction brake and a regenerative brake, for example. Alternatively, it is also possible to make provision for only some of the wheels to be equipped with friction brakes or regenerative brakes. The method described below remains substantially unaffected by this.

[0046] A friction brake is, for example, a disk brake in which friction pads arranged in a brake caliper are pressed on to the brake disk with a defined application force in the case of deceleration, with the result that a deceleration torque acts on the brake disk and hence on the corresponding vehicle wheel. Here, the application force can be made available either hydraulically or electromechanically.

[0047] The regenerative brake of a wheel can be implemented, for example, by connecting an electric-motor drive to the wheel, wherein the drive is designed to convert kinetic rotational energy of the wheel into electrical or thermal energy in a generator mode and, in the process, to exert a deceleration torque on the wheel.

[0048] Based on this infrastructure, an illustrative embodiment of the method according to the present application is explained below.

[0049] In this case, information which describes the state of at least one friction brake of the vehicle is initially determined in a first method step 102. This can be, for example, environmental data, such as an ambient temperature, information from a light or rain sensor, or weather data from external sources (internet). Furthermore, it is also possible to take account of information which relates to the previous actuations of the friction brake. It is possible here, for example, to include an elapsed time since the last actuation of the friction brake, an energy input into the friction brake during previous braking maneuvers, a brake pressure applied during previous braking maneuvers or a corresponding braking duration, a vehicle speed measured during braking, or a vehicle deceleration achieved by means of the braking maneuver.

[0050] Based on this information, the state of at least one friction brake of the vehicle is determined in a subsequent step 104. The state of the friction brake can, for example, indicate a remaining deceleration effect of the friction brake, assuming that in the meantime a certain quantity of contaminants or rust have accumulated on the surface of the brake disk.

[0051] Here, steps 102 and 104 can preferably be repeated continuously, ensuring that the state of the friction brake is known at all times.

[0052] After the state of the friction brake has been determined in step 104, a check is then made in step 106 to determine whether the state of the friction brake satisfies a defined switching criterion, which is specified by a corresponding switching pattern for switching between a self-cleaning operating mode for cleaning the friction brake and a normal operating mode of the brake system. The switching criterion can, for example, consist in that the self-cleaning operating mode is to be activated according to the switching pattern if the deceleration effect of the friction brake has fallen below a defined threshold.

[0053] Here, the check according to step 106 can be performed continuously or only as required, e.g. as soon as an activation of the self-cleaning operating mode is envisaged according to the switching pattern.

[0054] If, according to the switching pattern, an activation of the self-cleaning operating mode is, and it has been detected in step 106 that the state of the friction brake satisfies the switching criterion, the self-cleaning operating mode of the brake system is then activated in step 108 and taken into account in carrying out a subsequent braking demand. For example, it may be envisaged here that, in a subsequent implementation of a braking demand in the self-cleaning operating mode, only the friction brake is to be used to produce the deceleration torque demanded. As an alternative, provision may be made for a fixed proportion of the necessary deceleration torque to be produced by the friction brake. Thus, provision may be made, for example, for the braking force to be divided evenly between the friction brake and the regenerative brake in the self-cleaning operating mode.

[0055] If, on the other hand, it is established in step 106 that the state of the friction brake does not satisfy the switching criterion and that, furthermore, according to the switching pattern, an activation of the self-cleaning operating mode is provided, the envisaged activation of the self-cleaning operating mode is suppressed in step 110 until a subsequent activation provided in the switching pattern is pending. Instead, the friction brake and the regenerative brake continue to be operated in the normal operating mode and are controlled by a corresponding control unit in such a way that as high a proportion as possible of the kinetic energy that is released during a deceleration of the vehicle is converted into electrical energy and fed into the energy source of the vehicle.

[0056] In carrying out step 108, i.e. the activation of the self-cleaning operating mode for cleaning the friction brake, it is possible here for the self-cleaning operating mode to specify a number of criteria and/or parameters from which actuation of the friction brake due to a braking demand is sufficient for the brake to count as cleaned and consequently for it to be possible to switch back into the normal operating mode of the brake system. It is possible here, for example, to specify a minimum amount of energy to be produced and input into the brake disk that must be met for the friction brake to count as cleaned due to its use.

[0057] The time characteristic of a switchover between a self-cleaning operating mode and a normal operating mode with a corresponding switching pattern, together with corresponding braking demands, is described by way of example below with reference to FIG. 2. Here, a time scale is indicated on the horizontal axis of the diagram. The solid line 200 indicates whether there is a braking demand, while the chain-dotted line 300 indicates whether the brake system and consequently the friction brake is operating in the normal operating mode or whether the friction brake is operating in a self-cleaning operating mode.

[0058] Here, at a first time t.sub.0, the brake system switches into the normal operating mode, with the result that incoming braking demands are preferably implemented by activation of the regenerative brake. In this case, the friction brake is normally used only for a small proportion of the deceleration of the vehicle, thus making it possible to achieve operation of the vehicle in a manner which is as energy-efficient as possible. Here, the state of the friction brake is monitored continuously by means of corresponding state information.

[0059] According to the switching pattern, a time window within which activation of the self-cleaning operating mode is provided according to the switching pattern begins at time t.sub.1. Between time t.sub.1 and t.sub.2, however, there is no braking demand, and therefore the system remains in a standby state, and the operating state initially does not change.

[0060] Only at time t.sub.2 is a braking demand received, triggering the method according to the present application. Since, according to the switching pattern, the self-cleaning operating mode is to be activated and the friction brake satisfies the switching criterion, the brake system switches into the self-cleaning operating mode. Consequently, the braking demand is then implemented according to the self-cleaning operating mode with defined parameters by the friction brake, and therefore self-cleaning of the friction brake takes place. Here, in the example illustrated, the first braking demand received after time t.sub.2 is not sufficient for self-cleaning of the friction brake. The self-cleaning operating mode is therefore maintained at least until a further braking demand is received. In this case, the subsequent braking demand is sufficient in terms of its duration and the deceleration produced, and therefore it can be assumed that the friction brake has been sufficiently cleaned after its actuation to implement the braking demand. Consequently, the brake system switches back into the normal operating mode at time t.sub.3.

[0061] In this case, it is possible, in particular, to envisage that, in the event of a braking demand, a predefined proportion of the vehicle deceleration specified by the braking demand or of the corresponding braking torque must be produced by the friction brake in the time between t.sub.2 and t.sub.3.