Brake System Fallback for Electrical Failure
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Solution Overview
Problem
In existing brake systems, a failure of the electric drive of the electrohydraulic pressure generating device during braking leads to a significant lengthening of the brake pedal travel, causing confusion for the vehicle driver, as perceived as a brake failure.
Innovation Solution
The brake system incorporates a hydraulic piston-cylinder arrangement with two series pistons, a travel simulation device, an electrohydraulically controllable pressure generating device, and an electronic control unit, which includes electrically actuable valves and pressure sensors to maintain brake system pressure and simulate pedal feel, ensuring operation even in the event of electrical system failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric drive of the electrohydraulic pressure generating device fails during braking, then the brake system cannot maintain pressure, but the brake pedal travel lengthens significantly causing driver confusion
Solution Approach 1:
The patent implements a fallback operating mode that is prepared in advance through specific valve configurations. The first cut-off valve is designed to automatically close when electrical power fails, redirecting hydraulic flow through alternative paths before the failure fully manifests. This preliminary action prevents the harmful effect of excessive pedal travel by establishing an emergency hydraulic circuit proactively.
Solution Approach 2:
The patent introduces intermediary components including the first and second cut-off valves, and the third valve that mediate between the electrohydraulic pressure generating device and the pressure modulation unit. These intermediaries can redirect hydraulic flow around the failed electric drive through alternative pathways, maintaining brake function while preventing driver confusion by keeping pedal travel within normal ranges.
2Productivity
If the electrohydraulic pressure generating device is used to improve braking efficiency, then brake performance increases, but electrical system failure causes brake pedal travel lengthening
Solution Approach 1:
The patent segments the brake system into distinct functional zones controlled by separate valves. The first cut-off valve separates the electrohydraulic pressure generating device from the pressure modulation unit, while the second cut-off valve and third valve create additional segmentation. This allows the electrically assisted braking path to be isolated from the mechanical fallback path, enabling high-performance electric braking when available while ensuring reliable mechanical operation when electrical systems fail.
Solution Approach 2:
The patent changes the operational parameters of the hydraulic system based on electrical system status. When electrical power is available, the system operates in high-performance mode with electrically controlled pressure generation. When electrical power fails, the cut-off valves redirect hydraulic flow to change the system parameter from electrically-assisted to purely mechanical operation, maintaining adequate braking function without excessive pedal travel.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration prevents driver confusion by maintaining brake system functionality and pedal feel even when the on-board electrical system fails, ensuring safe braking operations.
Implementation Method 1
two pistons which are arranged in series and which, in the housing, delimit two pressure chambers, which pistons are subjected to an actuating force (pedal force) when the brake system is actuated by the driver, and which pistons are positioned in an initial position by restoring springs when the brake pedal is not actuated
Implementation Method 2
a travel simulator with a simulator enable valve which, in the 'brake by wire' operating mode, imparts the familiar brake pedal feel to the vehicle driver, the travel simulator being hydraulically connected to one of the pressure chambers
Implementation Method 3
an electrohydraulic pressure generating device which outputs a brake system pressure
Implementation Method 4
a pressure medium reservoir which is assigned to the pressure chambers and which is at atmospheric pressure
Data Source
AI summary
A brake system for motor vehicles, which brake system can be actuated both by the vehicle driver and also independently of the vehicle driver in a “brake by wire” operating mode, is preferentially operated in the “brake by wire” operating mode, and can be operated in at least one fall-back operating mode in which only operation by the vehicle driver is possible. The brake system has inter alia an electrohydraulic pressure generating device (5) which outputs a brake system pressure, and a pressure modulation unit which has one inlet valve (6a-6d) and one outlet valve (7a-7d) per wheel brake (8, 9, 10, 11) for setting wheel-specific brake pressures derived from the brake system pressure, wherein the inlet and outlet valves (6a-6d, 7a-7d) output or transmit the brake system pressure when in the non-actuated state.