METHOD FOR OPERATING A BRAKE CONTROL SYSTEM, BRAKE CONTROL SYSTEM, COMPUTER PROGRAM, AND COMPUTER-READABLE STORAGE MEDIUM

Abstract

In an example method for operating a brake control system for a vehicle having a first axle and a second axle that follows the first axle in the direction of travel of the vehicle, the brake control system is provided with a thrust signal representative of a coasting mode; depending on the thrust signal, the recuperation brakes are activated; the brake control system is provided with a brake signal representative of a vehicle brake actuation; depending on the brake signal, the brake is triggered; the brake control system is provided with a lock signal representative of an active anti-lock braking control of the brake; and depending on the lock signal, while maintaining the activation of the recuperation brake associated with the second axle, the recuperation brake associated with the first axle is deactivated. Further provided are a corresponding brake control system, computer program and computer-readable storage medium.

Claims

1. A method for operating a brake control system for a vehicle having a first axle and a second axle that follows the first axle in a direction of travel of the vehicle, whereinthe first and second axles are each associated with a recuperation brake for decelerating the vehicle while feeding energy back into an energy storage of the vehicle, andthe first axle is associated with a brake with anti-lock braking control, and wherein the method comprises: providing the brake control system with a thrust signal, which is representative of a coasting mode of the vehicle; depending on the thrust signal, activating the recuperation brakes associated with the first and second axle; providing the brake control system with a brake signal, which is representative of a vehicle brake actuation; depending on the brake signal, trigger the brake associated with the first axle; providing the brake control system with a lock signal, which is representative of an active anti-lock braking control of the brake associated with the first axle; and depending on the lock signal, while maintaining the activation of the recuperation brake associated with the second axle, deactivating the recuperation brake associated with the first axle.

2. The method according to claim 1, wherein in activating the recuperation brakes, the recuperation brakes associated with the first and second axle are each set to a thrust recuperation state.

3. The method according to claim 1, wherein in triggering the brake, the recuperation brakes associated with the first and second axle are each set to a brake recuperation state.

4. The method according to claim 1, wherein the second axle is associated with a further brake with anti-lock braking control, and wherein in triggering the brake, depending on the brake signal, the further brake associated with the second axle is triggered.

5. The method according to claim 4, wherein the method further comprises: providing the brake control system with a further lock signal, which is representative for an active anti-lock braking control of the further brake associated with the second axle; and depending on the further lock signal, deactivating the recuperation brake associated with the second axle.

6. The brake control system for the vehicle having the first axle and the second axle that follows the first axle in the direction of travel of the vehicle, wherein the brake control system is configured to perform the method of claim 1.

7. A computer program for operating the brake control system, comprising instructions, which, when executed on a computer, cause the computer to perform the method according to claim 1.

8. A computer-readable storage medium, having stored thereon the computer program according to claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Example embodiments of the invention are detailed along the schematic drawings in that:

[0043] FIGS. 1 to 5 illustrate example measured parameters when operating a vehicle;

[0044] FIG. 6 illustrates an example comparison of state sequences when operating a vehicle;

[0045] FIG. 7 illustrates example input and output parameters of a brake control system for a vehicle; and

[0046] FIG. 8 illustrates an example flow diagram of a method for operating a brake control system for a vehicle.

DETAILED DESCRIPTION

[0047] Elements of the same design or function are labelled with the same reference symbols across all figures.

[0048] At low friction, a motor vehicle decelerates worse in the partially braked range, i.e. in the event that the braking effect is generated exclusively by the mechanical or hydraulic brake system, with active anti-lock braking control of the brake system of one axle (two wheels) than with recuperation on all four wheels. In the following, an improvement in the overall deceleration of electrified vehicles in the partially braked range and only one axle (preferably the front axle) in ABS control is proposed through simultaneous recuperation on the non-ABS braked (rear) axle, and thus an increase in the overall vehicle deceleration to the identical level as during recuperation on all four wheels.

[0049] If the front axle, especially at a low coefficient of friction, is in ABS control and the rear axle is not, braking may be interrupted because the rear axle does not utilise its full braking potential (see M* in FIG. 3 and RHA* and V* in FIG. 6 right)the ABS attempts to enable maximum deceleration at the given coefficient of friction.

[0050] The wheels of the underbraked axle then run at the ABS reference speed ABSRef (see GHA in FIG. 2 below), while a slip pattern (usual for an ABS control system) can be recognised on the front axle (see GVA in FIG. 2 above).

[0051] The pressure BHA applied to the rear axle corresponds to the driver's brake pressure BF (see FIG. 5). If ABS braking is detected, regardless of the wheel, the recuperation can be cancelled/deactivated and the ABS takes over the task of decelerating the vehicle. If, as described, only one axle is in ABS control, then the full potential of the available coefficient of friction cannot be utilised (see M* in FIG. 3 and RHA* and V* in FIG. 6 right).

[0052] In the brake control system and method of operation proposed here, recuperation is maintained on the non-ABS braked until it is also in ABS control. This can help to avoid dips in the deceleration (see E1 in FIG. 1) and thus barely resolve the transition from recuperation to ABS. In an advantageous way, maximum deceleration without deceleration fluctuations is achieved or contributed to.

[0053] During the transition from recuperation braking, i.e. the vehicle decelerates purely via recuperation to partially braked driver braking, it can happen that the front axle runs into ABS control at low u, i.e. low friction, but the rear axle, e.g. due to the higher axle load at the rear, which is common in electric or hybrid vehicles (battery electric vehicle, BEV or plug-in hybrid electric vehicle, PHEV), and the fact that the driver's pre-pressure BF on the brake is still too low, the rear axle may not enter ABS control (see FIG. 5), as the necessary thresholds are not met. This leads to a noticeable reduction in vehicle deceleration (see E1 in FIG. 1), as recuperation is reduced when ABS braking is recognised. To prevent this, a recuperation function (actuator-related wheel slip limitation) on the non-ABS braked axle would have to maintain recuperation until the axle is also brought into ABS control. The transition from recuperation and driver braking to ABS is preferably applicable in a ramped manner in order to make deceleration changes as comfortable as possible. By way of example, the situation without using the brake control system according to the invention or the method for operating it is described using a measurement (see FIGS. 1 to 5).

[0054] FIG. 1 shows a measured curve of the (total) deceleration V of the vehicle. The vertical dashed line indicates the starting point S of the recuperation, after which the deceleration V is largely reduced to an average value M (horizontal dash-dot line, while recuperation here is approx. 0.2 g). The dashed outline shows an area E1, E2 where the ABS control starts and the deceleration drops accordingly (left, E1) as well as where the ABS control stops and the deceleration increases accordingly (right, E2).

[0055] FIG. 2 shows a measured curve of the vehicle's wheel speeds. The speed GVA of the left and right front wheels and an ABS reference speed ABSRef are shown at the top, while the speed GHA of the left and right rear wheels and an ABS reference speed ABSRef are shown at the bottom. During recuperation (to the right of the starting point S of recuperation), the curve of the speed GVA, GHA shows a slip on both the front and rear axles; after entering ABS control (see E1 in FIG. 1 and FIG. 4), only the front axle continues to slip, while the progression of the speed GHA of the rear axle runs at the ABS reference speed ABSRef.

[0056] FIG. 3 shows a measured curve of the actual braking torque MI of the electric machine and a target braking torque MS. The second vertical dashed line indicates a starting point B for driver braking. After entering the ABS control (see E1 in FIG. 1 and FIG. 4), a clear deviation between the target and actual braking torque MS, MI can be recognised. Also shown in bold is a possible improvement potential M* compared to the measured actual braking torque MI as a result of recuperation in accordance with the proposed brake control system or method of operating it.

[0057] FIGS. 4 and 5 show a measured curve of the brake pressure. FIG. 4 shows the brake pressure BVA of the left and right front wheels as well as a driver's pre-pressure BF, while FIG. 5 shows the brake pressure BHA of the left and right rear wheels as well as the driver's pre-pressure BF.

[0058] In deviation from the proposed brake control system or method of operating it, recuperation is completely cancelled at the front axle when entering E1 ABS control.

[0059] There is no ABS control on the rear axle; as can be seen in FIG. 5, the brake pressure BHA on the wheel corresponds to the driver's brake pressure BF.

[0060] FIG. 6 shows an exemplary comparison of state sequences during operation of a vehicle over time t, whereby situation 1 with the above measurements is shown on the left and situation 2 according to the method proposed here is shown on the right. The values 0 and 1 assigned to the state sequences are merely exemplary and can indicate activation or deactivation or normalisation.

[0061] Initially in situations 1 (t1) and 2, the recuperation RVA on the front axle and the recuperation RHA on the rear axle are both active, while the ABS control ABSVA on the front axle and the ABS control ABSHA on the rear axle are inactive, so that a normalised deceleration V=1 is achieved.

[0062] Then (t2), the ABS control ABSVA on the front axle is activated and the recuperation RVA on the front axle is deactivated accordingly, while the ABS control ABSHA on the rear axle remains inactive. In situation 1, the recuperation RHA on the rear axle is also deactivated, whereas in situation 2, the recuperation RHA on the rear axle is maintained despite the active ABS control ABSVA on the front axle (see hatching RHA*), thus achieving increased deceleration (see hatching V*).

[0063] FIG. 7 shows exemplary input and output parameters of the proposed brake control system 10.

[0064] For example, the brake control system 10 is provided with a first signal 11 that is representative of thrust recuperation. In addition, the brake control system 10 can be provided with a second signal 12 that is representative of a brake pressure >0.

[0065] The brake control system 10 controls, for example, the mechanical or hydraulic brakes associated with the front axle 13 and rear axle 14 as well as the recuperation brakes. For example, if the front axle 13 switches to ABS control 15, a comparison 16 of the predetermined brake pressure is made with a predetermined threshold value up to which the rear axle is kept in a brake recuperation state 17 in order to achieve a deceleration V of the vehicle.

[0066] A data and program memory is assigned to the brake control system 10, for example, on which a program for executing the proposed method is stored, which is explained in more detail below with reference to the flow diagram in FIG. 8. The program is started in a step SO, for example variables are initialised here. In a step S1, a thrust signal is provided that is representative of a coasting mode of the vehicle. The recuperation brakes associated with the front and rear axles are then activated (step S2). Steps S1 and S2 exemplify the situation when a driver releases the accelerator pedal and the vehicle recuperates.

[0067] In a step S3, a brake signal is provided that is representative of a vehicle brake actuation. The recuperation brakes remain activated. In a step S4, the mechanical or hydraulic brake associated with the front axle is activated depending on the brake signal. The recuperation brakes remain activated. Steps S3 and S4 are examples of the situation when the driver decides to actuate the operating brake and recuperation is maintained (blending).

[0068] In a step S5, a lock signal is provided that is representative of active ABS control of the front axle. In a step S6, the recuperation brake of the front axle is deactivated depending on the lock signal while the recuperation brake of the rear axle is still active. As an example, the process is then ended (step S7) or restarted. Alternatively, it is also conceivable to wait for any further lock signal representative of active ABS control of the rear axle, then also deactivate the recuperation brake of the rear axle and only then terminate the procedure. Steps S5 ff. exemplify the situation when the front axle is guided into ABS control due to the friction value conditions and the driver's pre-pressure is not sufficient to guide the rear axle into ABS control. With the potential M* possible for one axle (see FIG. 3), the recuperation remains at the axle not braked by ABS, while the ABS controls the front axle and no recuperation takes place.

[0069] The invention is not limited to the description based on the embodiments. Rather, the invention includes any new feature as well as any combination of features, which includes in particular any combination of features in the patent claims, even if this feature or combination itself is not explicitly stated in the patent claims or embodiments.