Brake control system for motor vehicles

Abstract

Brake control system for motor vehicles with an electronic control unit by means of which an automatic parking brake function can be activated when the motor vehicle is stationary, the deactivation of which is carried out depending on the current drive torque, wherein, when the parking brake function is activated, deactivation of the parking brake function can be suppressed if, due to a function carried out when the motor vehicle is stationary, an automatic increase in the drive torque is required which does not result from a driver's desire to start off, characterized in that, depending on the change in state of a consumer, a corresponding absolute value and / or relative value and / or a corresponding gradient value of the drive torque increase is inferred,wherein, depending on this absolute value and / or this relative value and / or depending on this gradient value of the drive torque increase, a basic drive torque condition is corrected to deactivate the automatic parking brake function.

Description

[0001] The invention relates to a brake control system for motor vehicles according to the preamble of patent claim 1.

[0002] Methods and devices are known from various patent applications and patent specifications, such as DE 199 50 034 A1, DE 196 11 359 C1; DE 199 50 162 B4; DE 198 48 448 C2; DE 101 51 846 B4; DE 199 41 482 A1; US ​​2005 / 0 109 550 A1 and others, which are intended to prevent vehicles from rolling away - in particular, but not necessarily, on inclines. In most cases, in at least one operating state when the brake pedal is actuated or by another actuating element, braking force is maintained or actively built up on at least one wheel of a vehicle depending on or independently of the extent of pedal actuation or another actuating element. Different entry and / or triggering conditions are provided jointly or alternatively for the activation or deactivation of the function.

[0003] These methods and devices are known, for example, under the names start-off assistant, hill assist, hill hold(er) or automatic hold. These methods are collectively referred to below as automatic parking brake functions. What all these automatic parking brake functions have in common, for example, a hydraulic, mechanical, electro-hydraulic, electromechanical or pneumatic, electronically controlled braking system, by means of which the vehicle is held in place and prevented from rolling. Methods are also known in which the vehicle is prevented from rolling via the transmission (particularly automatic transmission). In all of these functions, for example, the brake pedal or the handbrake or via associated switching elements or other actuating elements (e.g. switches, buttons, etc.) is operated.) the function is activated; deactivation is carried out using the same or other means (such as accelerator pedal position, clutch signal, engine torque signals, etc., or even after a defined holding time has elapsed).

[0004] Other important aids, control signals or switching devices required for displaying the functions are, for example, one or more speed signals for detecting when the vehicle is stationary, mechanical, pneumatic or hydraulic actuators (electro-hydraulic, electro-pneumatic or electric actuators are also conceivable in principle) in the wheel brakes or in the supply lines to the wheel brakes, via which the braking effect can be built up and released or at least temporarily maintained (e.g. control / regulating valves integrated in the form of an existing control or regulating device, for example ABS, ASC / ASR, DSC / ESP / EHB system), if necessary also longitudinal acceleration or inclination sensors, by means of which the longitudinal inclination of the road can be determined and from this the required braking force for safely bringing the vehicle to a standstill and the starting torque required for the road inclination can be determined and one or moreseveral pressure sensors with the help of which the brake pressure or the applied braking torque on the wheel brake(s) can be determined.

[0005] The object of the invention is to release the braking torque as needed and precisely at a sufficiently high starting torque so that, on the one hand, the vehicle cannot unintentionally roll prematurely against the desired direction of travel and thereby possibly cause accident situations, and, on the other hand, the vehicle does not have to start moving against the braking holding force and thus cause a loss of comfort due to the braking force being held for too long (due to an excessively high required starting torque).

[0006] This object is achieved according to the invention by the features of patent claim 1. Advantageous developments of the invention are the subject matter of the dependent claims.

[0007] The invention is based on the following findings: With the known methods and devices, under certain conditions during the activated parking brake function (holding phase, for example, of a hillholder function), the problem can arise that due to an "automatic" (i.e., not directly specified by the driver via accelerator pedal) increase in engine torque, or more generally in drive torque, a premature start-up request is detected, and the braking torque (or braking force or brake pressure) is then automatically reduced by the system. As a result, the vehicle is no longer sufficiently held on the incline and may unintentionally start rolling too early, which can at the very least lead to impaired comfort.

[0008] Reasons or triggers for an “automatic” or automatic – usually only temporarily effective – increase in drive torque can be, for example, the following: In particular, by actuating the steering (steering movements) by the driver, possibly also by a steering system (e.g., AFS, EPS), but also, for example, by the air conditioning system (activation / deactivation of the air conditioning compressor), the starting of the engine (electric) fan, the activation and deactivation of other mechanical, electromechanical, electrical, pneumatic, or hydraulic consumers in the vehicle (e.g., transmission torque changes due to the activation / deactivation of torque converter lock-up clutches, etc.), i.e., generally by internal vehicle consumers and systems or components that require the drive engine to generate a consumption torque (e.g., friction torque, drag torque) that must first be corrected by the engine control / regulation system or its idle speed controller. The correction process of the engine control / regulation system usually results in brief fluctuations or excesses in the delivered drive torque, which can ultimately lead to incorrect detection of a move-off request.

[0009] Now, by appropriately adapting / applying the automatic parking brake function, the required target drive torque (as a basic drive torque condition), which already varies at least depending on the gradient, could generally be set higher and / or fluctuations could be dampened by temporally filtering the drive torque signal, so that automatic drive torque changes as described above during the stopping phase do not lead to the described false detection of the start-up request. However, this would have the disadvantage that, in the case of a "real" start-up request via the accelerator pedal, the automatic parking brake function would release the braking torque significantly too late. This would always create the impression of at least briefly hitting the brakes when starting off, which would be associated with considerable disadvantages in terms of comfort and quality.

[0010] A general distinction in the case of an automatic parking brake function between the above-mentioned unwanted increases in drive torque and the increase in drive torque as a result of a "start request via the accelerator pedal" is generally not permitted, since the automatic parking brake function is often defined in such a way that a comfortable start (i.e. the timely release of the braking torque) without rolling against the desired direction of travel must also be possible simply by applying the idling torque (or creeping torque), without the driver having to press the accelerator pedal.

[0011] In order to suppress any disruptive influence caused by drive torque fluctuations during the holding phase of the system, it is necessary to record these influences individually or collectively and to correct the drive torque considered for the automatic parking brake function (e.g. hillholder function) accordingly.

[0012] According to the invention, a brake control system for motor vehicles with an electronic control unit, by means of which an automatic parking brake function can be activated when the motor vehicle is stationary (holding phase), the deactivation of which is carried out as a function of the instantaneous drive torque, is designed in such a way that when the parking brake function is activated, deactivation of the parking brake function can be suppressed if, due to a function carried out when the motor vehicle is stationary, an automatic increase in the drive torque is required which does not result from a driver's desire to start off.

[0013] Via information available on a data bus connected to the control unit (e.g., CAN bus), the value or gradient of this automatic drive torque increase can be made available to the control unit itself. Additionally or alternatively, changes in the status of internal vehicle consumers that could cause an increase in drive torque can be monitored to detect an automatic increase in drive torque.

[0014] Depending on a change in the state of a consumer, a corresponding absolute value and / or relative value and / or gradient value of the drive torque increase is determined. Depending on this absolute value and / or relative value and / or gradient value of the drive torque increase, a basic drive torque condition that must be met to deactivate the automatic parking brake function is corrected. The basic drive torque condition can be the exceeding of a first absolute and / or relative threshold value and / or a first gradient threshold value.

[0015] The braking torque required to activate the automatic parking brake function during the stop phase can be compared with the drive torque. The braking torque can be increased if the automatic increase in the drive torque exceeds a defined second absolute and / or relative threshold and / or a defined second gradient threshold, to the extent that safe stopping of the vehicle at a standstill cannot be guaranteed.

[0016] Example of a correction of the basic drive torque condition during activated parking brake function (e.g. “hillholder holding phase”) during steering operations: During steering movements (= changes in the state of the steering system consumer) when the vehicle is stationary (e.g. during parking maneuvers) in situations in which the hillholder function is active - i.e. the vehicle is held at least temporarily by the applied braking torque at at least one or more vehicle brakes -, changes in the drive torque are directly induced by changes in the steering torque, especially in hydraulic steering systems.

[0017] An adaptation of the basic drive torque condition can, for example, take place in the form that continuously during the hillholder holding phase 1. depending on the steering angle speed (steering angle gradient) or steering wheel angle speed or when a defined threshold is exceeded and / or 2. depending on the steering angle or steering wheel angle or under- / overshooting of a defined threshold and / or 3. depending on an available signal that describes the steering movement or a steering torque sufficiently accurately in another way (e.g. steering pump pressure or pressure in the hydraulic steering lines; steering torque that is output by signal transmission (e.g. CAN) from a steering control unit (e.g. AFS, EPS) and is available to the hillholder functionality) or when a defined threshold is exceeded or undershot and / or 4. Depending on an activation / deactivation signal (e.g. CAN activation message, activation bit, switching signal, etc.) that signals a steering movement, a correction is carried out that depends on the aforementioned variables.

[0018] A correction can be made, for example, using the aforementioned variables, such as steering angle or steering angle velocity, or steering pressure level, by adding or subtracting a constant (torque) offset derived from them as a fixed value and / or a variable value from a mathematically functional dependency (e.g., a proportional relationship via a linear or curved characteristic curve) to or from the drive torque value relevant for the hillholder function. Alternatively, a multiplicative correction or correction according to another defined functional dependency would also be conceivable.

[0019] In the case of a torque signal already available (e.g. steering torque request via CAN from a steering control unit), this can also be used to correct the drive torque evaluated in the hillholder.

[0020] Corrections of the hillholder drive torque corresponding to the embodiment example can also be made in an analogous manner for other possible influencing variables.

Claims

[1] Brake control system for motor vehicles with an electronic control unit by means of which an automatic parking brake function can be activated when the motor vehicle is stationary, the deactivation of which is carried out as a function of the current drive torque, whereby when the parking brake function is activated, deactivation of the parking brake function can be suppressed if, due to a function carried out when the motor vehicle is stationary, an automatic increase in the drive torque is required which does not result from a driver's desire to start off, characterized bythat, depending on the change in state of a consumer, a corresponding absolute value and / or relative value and / or a corresponding gradient value of the drive torque increase is inferred, wherein, depending on this absolute value and / or this relative value and / or depending on this gradient value of the drive torque increase, a basic drive torque condition for deactivating the automatic parking brake function is corrected. [2] Brake control system according to claim 1, characterized by that, in order to detect an automatic increase in the drive torque, changes in the state of internal vehicle consumers that can cause an increase in the drive torque are monitored. [3] Brake control system according to one of the preceding claims, characterized bythat the braking torque required to activate the automatic parking brake function for the stopping phase is compared with the drive torque and that the braking torque is increased if the automatic increase in the drive torque exceeds a defined absolute threshold value and / or a relative threshold value and / or a defined gradient threshold value, in such a way that safe stopping of the motor vehicle when stationary cannot be guaranteed.