Brake control system for motor vehicles

Abstract

A brake control system has an electronic control unit such that, when the motor vehicle is at a standstill, an automatic parking brake function can be activated by the control unit. In the presence of an activation condition for the parking brake function, the brake pressure required for this purpose can be determined at least in a manner dependent on the longitudinal inclination and in a manner dependent on an estimated normal force distribution of all of the wheels and/or an estimated capability of all of the wheels to transmit braking and/or drive torque to the underlying surface. Here, the brake pressure can be predefined to be higher the more wheels have a reduced normal force.

Claims

1. A brake control system for a motor vehicle, comprising: an electronic control unit configured such that: an automatic parking brake function is activatable by the control unit in a standstill of the motor vehicle, wherein if an activation condition for the parking brake function is present, brake pressure required for this purpose is determinable at least dependent on a longitudinal inclination and dependent on an estimated contact force distribution and/or torque transmission capability of all wheels of the motor vehicle, and wherein the control unit detects which wheel has a contact force and/or torque transmission capability below a lower limit value, wherein a distribution of the required brake force is predetermined only to the wheels with a contact force and/or torque transmission capability above said lower limit value.

2. The brake control system according to claim 1, wherein the brake pressure is predetermined to be higher, the more wheels have a reduced contact force and/or torque transmission capability.

3. The brake control system according to claim 1, wherein the contact force and/or torque transmission capability of the individual wheels is identified by the control unit on the basis of the wheel suspension height of the individual wheels, a slip of the individual wheels, and/or a transverse inclination of the vehicle.

4. The brake control system according to claim 1, wherein the control unit is further configured such that: a friction coefficient of the road surface is identifiable based on a location of the motor vehicle when the motor vehicle is held in standstill by the parking brake function, at least for the driven wheels, and the brake pressure is also determinable dependent on the friction coefficient of the road below at least one of the driven wheels.

5. A use of the brake control system according to claim 1, in a case of an all-wheel drive motor vehicle.

6. The use of the brake control system according to claim 5, in a case of a defined off-road operation of the motor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of the most important components of the brake control system according to an embodiment of the invention.

(2) FIG. 2 shows two operating situations, for which the brake control system according to the invention can be used in a particularly advantageous manner.

DETAILED DESCRIPTION OF THE DRAWINGS

(3) A brake control system for a preferably all-wheel drive motor vehicle 2 comprising an electronic control unit 1, which can be integrated, for example, into a brake control unit, which is already present, is illustrated schematically in FIG. 1.

(4) The control unit 1 can capture, for example, the following input signals:

(5) The speed of the wheel on the front right n_FR

(6) The speed of the wheel on the front left n_FL

(7) The speed of the wheel on the rear right n_RR

(8) The speed of the wheel on the rear left n_RL

(9) The wheel suspension height of the wheel on the front right h_FR

(10) The wheel suspension height of the wheel on the front left h_FL

(11) The wheel suspension height of the wheel on the rear right h_RR

(12) The wheel suspension height of the wheel on the rear left h_RL

(13) The longitudinal vehicle inclination I_L

(14) The transverse vehicle inclination I_T

(15) The longitudinal acceleration a_L

(16) By evaluating these input signals, at least the relative contact forces on the individual wheels can be estimated (see FIG. 2):

(17) A_FR

(18) A_FL

(19) A_RR

(20) A_RL

(21) The control unit 1 is designed in particular by way of a corresponding input signal evaluation and by way of corresponding program modules, e.g. a situation detection module M1 and a brake pressure determination module M2, such that an automatic parking brake function with the following functional elements is activated in the standstill of the motor vehicle:

(22) if an activation condition is present for the parking brake function, the total brake pressure required for this is determined at least dependent on the longitudinal inclination I_L and dependent on the estimated contact forces of all wheels, the more wheels have a reduced contact force A, the higher the brake pressure p is predetermined.

(23) The invention is only used when at least the longitudinal inclination I_L is greater than a predetermined threshold value.

(24) The following situations in connection with the contact force distribution can be detected in the exemplary embodiment according to FIG. 1:

(25) S1: The contact force A is distributed to three wheels, one wheel hangs in the air, for example.

(26) S2: The contact force A is distributed to two wheels on the same longitudinal side (e.g. μ-split situation).

(27) S3: The contact force A is distributed diagonally to two wheels.

(28) S4: The contact force A acts essentially only on one wheel, e.g. diagonally to the slope in the case of standstill.

(29) Further situations can be identifiable.

(30) According to the invention, a total brake force required for the parking brake function is assigned to each of these situations. The total brake force can be determined by adding a base brake force P with an offset value +ΔP. In the illustrated exemplary embodiment, the offset values +ΔP1 to +ΔP4 are assigned to the situations S1 to S4, wherein ΔP1<ΔP2<ΔP3<ΔP4 applies.

(31) An off-road situation according to S2 is illustrated in FIG. 2, top, and an off-road situation S4 in reality is illustrated in FIG. 2, bottom. In addition to the respective situations S1 and S4, the respective possible estimated contact forces or the contact force distribution, respectively, are shown. The contact force in the plane, e.g., would be dashed, if the brake force were capable of being distributed evenly to all wheels or a lower limit value. The solid circles each show the contact force distributions for S1 and S4 schematically.

(32) In situation S2 of FIG. 2, the contact force C_FR is zero due to the wheel FR, which hangs in the air, and the contact force C_RL is very small, which could be detected, for example, by the wheel height level h_FR and h_RL and/or increased slip FR and RR when driving into the driving situation. The total brake force P+ΔP1 would thus be applied to the remaining three wheels.

(33) In situation S4 of FIG. 2, the contact forces C_FR, C_FL, and C_RR are too small for a sufficient brake force exertion (e.g. smaller than the normal value illustrated by means of dashes as lower limit value), which could be detected, for example, by the wheel height level h_FR and/or the strong transverse vehicle inclination I_T and/or increased slip at FR, FL and RR when driving into the driving situation. The total brake force P+ΔP4 would thus be applied in particular to the wheel RL.

(34) The brake force increase according to the invention can always be used in a particularly preferred manner, when the vehicle is inclined comparatively strongly longitudinally and/or transversely, and optionally when at least one wheel additionally hangs in the air.

(35) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.