Hydraulic Brake Pressure Control for Hybrid Vehicle Energy Recovery
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Solution Overview
Problem
Hydraulic vehicle brake systems in electric and hybrid vehicles face challenges in maintaining consistent braking performance when the electric drive motor operates in generator mode, leading to variable braking effects that can cause 'blinding' for the driver, where the contribution of the electric motor to braking is not transparent, and the hydraulic system must compensate fully or partially to avoid lengthening the braking distance.
Innovation Solution
A method that involves using an electromechanical brake booster and a hydraulic accumulator with a controllable valve to adjust brake pressure, allowing the hydraulic brake system to compensate for the electric drive motor's braking effect by feeding brake fluid into the accumulator and reducing wheel brake pressure, while maintaining consistent pedal feel by opposing the actuation of the master brake cylinder when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the electric drive motor operates in generator mode to provide braking effect, then energy recovery is improved, but the braking effect becomes variable and causes blinding for the driver
Solution Approach 1:
The control unit acts as an intermediary that manages the blending between electric motor braking and hydraulic brake braking. It continuously monitors the electric motor's braking effect and adjusts the hydraulic brake pressure accordingly to maintain total braking force, preventing blinding while allowing energy recovery through generator mode operation.
2Use of energy by moving object
If the electric drive motor provides braking effect in generator mode, then energy recovery is improved, but the braking distance may be lengthened due to variable braking effect
Solution Approach 1:
The control unit proactively compensates for the variable braking effect of the electric motor by pre-adjusting the hydraulic brake pressure. When the electric motor's braking effect decreases (e.g., at low speeds or when accumulator is full), the control unit increases hydraulic brake pressure in advance to maintain sufficient total braking force and ensure braking distance requirements are met.
Solution Approach 2:
The control unit continuously monitors the electric motor's braking effect parameters (speed, torque, accumulator charge state) and uses this feedback to dynamically adjust the hydraulic brake pressure. This closed-loop control ensures that the total braking force remains sufficient to meet braking distance requirements while maximizing energy recovery.
3Ease of operation
If the hydraulic brake system compensates fully for the electric motor braking effect, then consistent pedal feel is maintained, but the complexity of the control system increases
Solution Approach 1:
The control unit dynamically changes the hydraulic brake pressure parameter based on the electric motor's operating state. By monitoring parameters such as motor speed, torque, and accumulator charge level, the control unit adjusts brake pressure to maintain consistent pedal feel while accounting for the variable braking contribution of the electric motor across different operating conditions.
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 solution ensures that the driver experiences consistent pedal feel and behavior during braking, regardless of the electric drive motor's generator mode contribution, without noticing the fluctuation in braking effect, thereby preventing 'blinding' and maintaining the same braking performance as without the electric drive motor's assistance.
Implementation Method 1
a hydraulic accumulator (11) which is connected to the vehicle brake system (1; 2; 4; 6; 8) via a controllable valve (8)
Implementation Method 2
the electric drive motor can be operated as a generator for braking. A drive torque for driving the electric drive motor as a generator decelerates the motor vehicle as a braking torque. The electric power generated by the generator operation is stored in an accumulator
Implementation Method 3
an electromechanical brake booster which increases the actuating force of the master brake cylinder (2)
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a method for controlling the activation of a hydraulic vehicle brake system (1) of a hybrid vehicle which can be braked by generator operation of an electric drive motor (12). In order to compensate for the braking effect of the electric drive motor (12), the invention proposes reducing a wheel brake pressure in the wheel brakes (4) of the vehicle wheels by opening brake pressure-reducing valves (8) which are braked with the electric drive motor (12).