BRAKE SYSTEM FOR A MOTOR VEHICLE

Abstract

A brake system for a motor vehicle, comprises a hydraulic brake arrangement and an electric brake arrangement which are designed to be at least partially redundant with respect to one another. In particular, in the event of failure of hydraulic components, a braking demand can be electrically assisted.

Claims

1. A brake system for a motor vehicle which has a number of wheels comprising: a hydraulic brake arrangement which acts on a first group of the wheels; an electric brake arrangement which acts on a second group of the wheels; a first control arrangement controllably connected to the hydraulic brake arrangement; a second control arrangement controllably connected to the electric brake arrangement; and an energy supply arrangement connected to the to the first control arrangement and the second control arrangement to supply electrical energy to the first control arrangement and the second control arrangement separately from one another.

2. The brake system as claimed in claim 1, wherein the electric brake arrangement is a parking brake.

3. The brake system as claimed in claim 1, wherein the hydraulic brake arrangement is a service brake.

4. The brake system as claimed in claim 1, wherein the hydraulic brake arrangement has a driver-operated brake cylinder and an electrically operated actuator for the purposes of generating pressure.

5. The brake system as claimed in claim 1, wherein the energy supply arrangement has at least one of an inverter, a battery and a capacitor for at least one of drawing and storing the electrical energy.

6. The brake system as claimed in claim 1, wherein the energy supply arrangement selectively connects at least one of the first control arrangement and the second control arrangement to at least one energy supply arrangement for at least one of drawing and storing the electrical energy.

7. The brake system as claimed in claim 1, wherein the first control arrangement is configured for at least one of: detection and/or processing of a driver braking demand, communication via a CAN bus; communication with a vehicle network; processing of signals from wheel rotational speed sensors; supply of hydraulic energy to the hydraulic brake arrangement; calculation and/or execution of brake control functions, anti-lock brake system, electronic brake force distribution and/or electronic stability program; and ascertainment of a driver demand via a parking brake switch, via a human-machine interface and/or via a vehicle network.

8. The brake system as claimed in claim 1, wherein the second control arrangement is configured for one or more of the following functions: detection and/or processing of a driver braking demand; detection and/or processing of standstill information; generation of substitute signals for standstill detection with information from a vehicle network, from a camera, a radar, a transmission and/or a motor; detection and/or processing of wheel slip information; detection and/or processing of a position of an electric parking brake switch; and supply of electrical energy to the electric brake arrangement.

9. The brake system as claimed in claim 1, wherein the first and the second control arrangements are configured to boost a driver braking demand using one of the hydraulic brake arrangement when the first control arrangement and the hydraulic brake arrangement are functioning correctly, and by the electric brake arrangement in the event of at least partial failure of the first control arrangement and/or of the hydraulic brake arrangement.

10. The brake system as claimed in claim 1, wherein the first control arrangement has at least one of the following components: a power control unit configured to at least one of supply voltage to internal electronics, read in wheel rotational speed information and control valves, and control hydraulic means or an actuator; and an execution unit for software for the closed-loop control of the hydraulic brake arrangement.

11. The brake system as claimed in claim 1, wherein the second control arrangement has at least one of the following components: a microcontroller which to supply voltage to internal electronics and/or to read in wheel rotational speed information; an execution unit for software for the closed-loop control of the electric brake arrangement; a parking brake control unit which is configured to control an H-bridge; and an H-bridge.

12. The brake system as claimed in claim 1, wherein components of the first control arrangement are structurally and/or electrically separate from components of the second control arrangement.

13. The brake system as claimed in claim 1, wherein in the event of at least partial failure of the first control arrangement, output a fault message and/or allow operation of the electric brake arrangement, which occurs in response to an identified failure of the first control arrangement, only for a predetermined period of time or until a predefined event.

14. The brake system as claimed in claim 1, wherein the electric brake arrangement is designed for direct electric braking of the wheels.

15. The brake system as claimed in claim 1, wherein the brake system is for a motor vehicle with four wheels, and wherein the first group comprises all four wheels and the second group comprises the rear wheels.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Further features and advantages will be gathered by a person skilled in the art from the exemplary embodiment described below with reference to the appended drawing, in which:

[0036] FIG. 1 shows a brake system; and

[0037] FIG. 2 shows a circuit diagram of components of a brake system.

DETAILED DESCRIPTION

[0038] FIG. 1 shows a brake system 5 according to an exemplary embodiment in a purely schematic illustration. The brake system 5 has a hydraulic brake arrangement 10 with an associated first control arrangement 12. The brake system 5 has an electric brake arrangement 20 with an associated second control arrangement 22. The first control arrangement 12 is configured to control the hydraulic brake arrangement 10 and to supply energy thereto. The second control arrangement 22 is configured to control the electric brake arrangement 20 and to supply energy thereto.

[0039] An energy supply arrangement 30 is provided for the common energy supply. Said energy supply arrangement has an inverter in the form of an alternator 32, a battery 34 and a capacitor 36.

[0040] The energy supply arrangement 30 is designed to selectively connect the first control arrangement 12 and the second control arrangement 22 to each of the components alternator 32, battery 34 and capacitor 36. As a result, electrical energy can be supplied to the two control arrangements 12, 22 and thus also the two brake arrangements 10, 20 separately from one another.

[0041] When all components, for example those of the first control arrangement 12 and of the hydraulic brake system 10, are functioning normally, a driver braking demand is detected which can be initiated by the driver for example by operation of a brake pedal. The driver braking demand can then be electrically boosted, for example by means of a linear actuator (not illustrated).

[0042] However, if the components required for this fail, then the second control arrangement 22 can use the electric brake system 20 to assist the driver braking demand. Otherwise, the electric brake system 20 serves primarily as a parking brake.

[0043] Typical vehicles are presently configured at least such that, in the event of a fault, that is to say in the event of failure of the entire vehicle electrical system, they can perform a deceleration of 2.44 m/s.sup.2 in the presence of a driver-imparted pressure of 500 N. Typically, however, it is desirable to achieve a deceleration of for example 4 m/s.sup.2 or 4.88 m/s.sup.2 in the presence of a brake force of 200 N.

[0044] In order to increase the deceleration and/or to reduce the driver-imparted brake pressure required for this, electrical detection and boosting of the driver-imparted brake pressure with the aid of an energy source is typically required.

[0045] In normal operation, when the components are functioning normally, a driver braking demand is typically implemented and boosted by means of a hydraulic brake arrangement. In the case of presently used embodiments, however, if this boosting fails, typically only a deceleration of around 2.5 m/s.sup.2 to 4 m/s.sup.2 in the presence of 500 N can be ensured.

[0046] By means of the embodiment of a brake system described herein, redundancy of the driver boosting can be ensured by establishing independence between the generation of a braking torque by means of a hydraulic actuator and an electric actuator (typically a parking brake). This independence is not only found in the actuator itself, but may for example additionally relate to the following aspects: voltage supply; sensor information (sensor arrangement); evaluation (logic arrangement); and execution (actuator arrangement).

[0047] The embodiment of a brake system 5 described herein ensures that a driver braking demand is implemented by means of hydraulic or electrical boosting in the case of a majority of the known individual faults. This boosting may be provided for example at the rear axle.

[0048] The components described in FIG. 1 may communicate with one another in particular by means of a vehicle bus, for example a CAN bus. For the sake of simplicity, such a bus system is not illustrated.

[0049] The first control arrangement 12 and the hydraulic brake arrangement 10 can also be regarded as a first path of the brake system 5. The second control arrangement 22 and the electric brake arrangement 20 can accordingly be regarded as a second path of the brake system 5. Here, the two paths are preferably of redundant design with respect to one another.

[0050] Here, the first path typically has the following tasks: detection of a driver braking demand; establishment of communication with the vehicle network; reading-in of the wheel rotational speed sensor information; supply of hydraulic energy (“brake pressure”) to the brake system; and calculation of the associated brake control functions such as ABS, EBD or ESP (also referred to as AYC).

[0051] The second path typically has the following tasks: detection of the driver braking demand; detection of the vehicle status with regard to a standstill; detection of the vehicle status with regard to wheel slip; reading-in of the parking brake switch, and supply of electrical energy to the parking brake actuators for the purposes of generating a braking torque by means thereof.

[0052] Here, the first path typically represents the capability of an electronic control unit (ECU) to generate a braking torque by means of the hydraulics. The second path typically represents the capability to generate a braking torque by means of a parking brake actuator.

[0053] The boosting of the driver braking demand is implemented by means of in each case one of these paths or else both paths. As long as the first path is available, the boosting is typically performed by means of the hydraulics for reasons of comfort. In the event of failure or unacceptable degradation, this boosting can be performed by the second path. A combination is also possible.

[0054] FIG. 2 shows a circuit diagram with one possible redundancy concept with regard to sensors, processing and actuators.

[0055] Here, the left side as far as the X-bar serves for generation of mutually redundant voltages KL30_1 and KL30_2.

[0056] This may be implemented as follows: safeguarding of the independence between KL30_1 and KL30_2 through clear separation of the input voltages; and switchover capability of the X-bar to switch the input voltage to KL30_1 and/or KL30_2 depending on the state.

[0057] In the present case, the execution paths are composed of the following modules:

First path (“hydraulics”): [0058] PCU 1: voltage supply to the internal electronics, reading-in of the wheel rotational speed information, and control of the valves (“valve”) and the hydraulic actuating means (“LAC”); and [0059] MCU 1: execution unit for the software of the hydraulic brake control system (CPU).
Second path (“parking brake”): [0060] PCU 2: as a voltage supply to the internal electronics, reading-in of the rear wheel rotational speed information; [0061] MCU 2: execution unit for the software of the parking brake control (CPU); [0062] parking brake driver: control of the H-bridge for the operation of the parking brake actuator; and [0063] H-bridge: control of the current on the basis of control commands from the IPEX.

[0064] Alternatively, the components in the respective paths may be combined in a different way, as long as the independence of these from the components in the other path is ensured.

[0065] Below, a description will be given of a function of the illustrated system, which can for example ensure redundancy:

[0066] 1. In the absence of faults, the wheel slip in the first path is ascertained directly from the wheel rotational speed information. If this communication path fails, the rear wheel rotational speed signals are switched over to the second path by means of a switchover within the control unit (MUX). By means of this switchover, the second path can independently control the wheel slip.

[0067] 2. If the source itself fails, driver-boosted operation is possible by means of the first path. The brake force distribution can be set by means of a static EBD with a fixed characteristic curve, such that safe driver boosting is possible without slip occurring prematurely at the rear axle (correct locking sequence).

[0068] 3. The signals of the wheel rotational speed sensors or the signal of the driver demand are transmitted to the second path via the internal bus, such that the parking brake software located there allows the static release or setting of the parking brake only in the safe state.

[0069] 4. In the control unit, there are two independent sensors for establishing the driver braking demand (normally a pressure sensor and a position sensor). Normally, both sensors are connected to the first hydraulic path in order to allow a quick reaction to the driver demand. In the event of a fault, one of the sensors is routed to the second path by means of a switchover mechanism. This can be utilized to read in and evaluate the driver demand and to allow closed-loop control of the braking torque by means of the electric parking brake actuator.

[0070] 5. The system will use monitoring mechanisms to check the functioning of the valves, hydraulic actuating means and the parking brake actuators. If a loss of redundancy has occurred here, the driver must be warned. In addition, the braking demand is boosted by means of the other path.

[0071] 6. If the driver is already performing a hydraulic braking operation and if a loss of the boost capability is detected by means of existing pressure and/or volume monitoring, the driver is informed and the second path is activated.

[0072] 7. In order to ensure that the system is woken up by a parking brake switch, the second path is provided with the facility to wake up the first path via a wake-up line.

[0073] 8. If the capability to identify a standstill state by means of the wheel rotational speed sensors has been lost, both the first path and the second path can establish standstill information from other sensors of the vehicle via CAN communication. This may for example be a camera, a radar or a transmission.

[0074] The components and procedures mentioned are merely exemplary. They may be implemented completely as mentioned or else individually or in any combination.

[0075] Electric boosting of a braking demand can in particular be set such that the deceleration desired by the driver is achieved. At the start of a braking process initiated by the driver, purely hydraulic braking without boosting typically takes place. Above a certain value, the electric parking brake is controlled in closed-loop fashion such that a defined braking torque is generated and thus the vehicle is additionally decelerated.

[0076] After a certain period of time, for example ignition changeover, the electric boosting can be deactivated or reduced. This may be expedient if the boosting by means of the electric parking brake does not lead to such a loss of comfort that the driver or owner of the vehicle initiates a repair because they are also satisfied with the properties of the degraded function. In the case of long-term operation, this would lead to a safety risk and increased wear. The driver should therefore be urged to have the defective components repaired.

[0077] It should further be pointed out that refinements, features and variants of the invention which are described in the various embodiments or exemplary embodiments and/or shown in the figures can be combined with one another in any desired manner. Single or multiple features may be interchanged with one another in any desired manner. Combinations of features arising therefrom are intended to be understood to be covered by the disclosure of this application as well.

[0078] Features which are disclosed only in the description or features which are disclosed in the description or in a claim only in conjunction with other features may fundamentally be of independent significance essential to the invention. They may therefore also be individually included in claims for the purpose of distinction from the prior art.

[0079] The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.