Brake-by-Wire Pressure Balanced Piston for Torque Management
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Solution Overview
Problem
Existing brake-by-wire systems face challenges in replicating the feel of traditional brake systems and efficiently managing the difference between driver-requested braking torque and regenerative braking torque, leading to inconsistencies in battery life and braking performance in electric and hybrid vehicles.
Innovation Solution
An electro-hydraulic brake system with a pressure supply unit (PSU) assembly that includes an electric motor, ball screw actuator, and a PSU piston, which divides the piston bore into two chambers to provide a balanced pressure supply, simulating the feel of a conventional brake system and efficiently managing the difference between driver-requested and regenerative braking torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If regenerative braking is used to recharge batteries, then energy efficiency is improved, but braking torque consistency with driver input deteriorates
Solution Approach 1:
The patent introduces a pressure supply unit (PSU) as an intermediary device between the driver's brake pedal input and the regenerative braking system. The PSU contains a pressure-balanced piston that receives hydraulic fluid from the master cylinder and generates supplemental braking pressure. This mediator allows the system to maintain driver-requested braking torque while the regenerative system handles energy recovery, resolving the contradiction between energy efficiency and braking torque consistency.
Solution Approach 2:
The braking system is segmented into two independent but coordinated functions: the master cylinder handles driver input and pedal feel, while the pressure supply unit handles supplemental braking pressure generation. The pressure-balanced piston within the PSU further segments the hydraulic system into separate chambers that independently manage pressure balance and fluid flow, allowing each component to optimize its specific function without compromising overall system performance.
2Reliability
If brake pedal is isolated from master cylinder in brake-by-wire system, then braking performance is improved, but pedal feel simulation becomes more complex
Solution Approach 1:
The pressure-balanced piston acts as a mechanical intermediary that maintains the hydraulic connection between the master cylinder and brake system. By using this passive mechanical element rather than an active electronic actuator, the system achieves brake-by-wire isolation while keeping pedal feel simulation relatively simple. The piston automatically responds to pressure differential without requiring complex sensors or control algorithms.
Solution Approach 2:
The pressure-balanced piston design creates equipotential conditions by exposing both sides of the piston to equal hydraulic pressure when no braking is applied. This eliminates the need for complex spring mechanisms or electronic actuators to maintain pedal position, simplifying the pedal feel simulation while still allowing full isolation between the brake pedal and master cylinder during brake-by-wire operation.
3Reliability
If ball bearings are submerged in hydraulic fluid, then lubrication is improved, but contamination risk increases
Solution Approach 1:
The patent converts the potential harm of hydraulic fluid contamination into a benefit by deliberately submerging the ball bearings in the hydraulic fluid. The same fluid that could contaminate the bearings also provides continuous lubrication to the pressure-balanced piston and ball screw mechanism. The system accepts the contamination risk as a trade-off for the superior lubrication and cooling provided by the hydraulic fluid environment.
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
The system effectively replicates the feel of a traditional brake system while optimizing battery life by efficiently managing the difference between driver-requested and regenerative braking torque, enhancing the overall braking performance and longevity of electric and hybrid vehicles.
Implementation Method 1
an electric motor coupled to a ball screw actuator... a ball screw actuator including a spindle coupled to the electric motor and configured to transfer rotary motion to linear motion
Implementation Method 2
The ball screw actuator includes an actuator nut assembly having a plurality of ball bearings each disposed within the piston bore and submerged in the hydraulic fluid
Implementation Method 3
a first MC fluid passageway configured to receive pressurized fluid from a single-circuit master cylinder... each of the first chamber and the second chamber containing a hydraulic fluid
Data Source
AI summary
An electro-hydraulic brake system comprises a single-circuit master cylinder (MC) fluidly coupled to a first MC fluid passageway and configured to supply fluid into the first MC fluid passageway in response to pressing force on a brake pedal coupled thereto. The electro-hydraulic brake system also comprises a pressure supply unit (PSU) assembly including an electric motor coupled to a ball screw actuator, a PSU housing defining a piston bore having a terminal end opposite the electric motor, and a PSU piston disposed within the piston bore and movable by the ball screw actuator through the piston bore and dividing the piston bore into a first chamber and a second chamber, with each of the first chamber and the second chamber containing a hydraulic fluid. The ball screw actuator includes an actuator nut assembly having a plurality of ball bearings each disposed within the piston bore and submerged in the hydraulic fluid.