Vehicle Brake Clamping Force Control Without Pressure Sensors
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Solution Overview
Problem
Existing vehicle brake systems with electrohydraulic and electromotive parking brake devices face inefficiencies in controlling brake fluid volume to achieve target clamping forces, particularly on inclined surfaces, due to the use of expensive and slow-responding pressure sensors, leading to increased component wear and residual friction torque.
Innovation Solution
A method utilizing signal oscillations from the electric motor to determine piston position and speed, allowing precise calculation of additional brake fluid volume needed to exceed target clamping forces, thereby improving control quality and reducing the need for expensive pressure sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pressure sensors are used to detect brake fluid pressure and control additional volume delivery, then the target clamping force can be achieved, but the system becomes expensive and the response behavior becomes slow
Solution Approach 1:
The patent replaces the mechanical pressure sensor-based control system with an electromechanical control system. The control unit calculates the additional brake fluid volume based on electrical signals from the parking brake device's electric motor, spindle drive parameters, and pre-stored calibration data, eliminating the need for physical pressure sensors and achieving faster response times.
Solution Approach 2:
The patent creates a virtual model of the brake system's mechanical properties by storing calibration data in the control unit that represents the relationship between electric motor parameters and brake fluid volume requirements. This virtual model allows the system to predict and control brake fluid delivery without direct mechanical sensing.
2Device complexity
If the parking brake device is used alone to provide clamping force, then the system is simpler, but it cannot reliably ensure sufficient clamping force on inclined road surfaces
Solution Approach 1:
The patent merges the parking brake device and service brake device into a coordinated system. The control unit calculates and controls the service brake device to deliver additional brake fluid volume that supplements the parking brake device's clamping force, ensuring sufficient total clamping force on inclined surfaces while maintaining system simplicity.
Solution Approach 2:
The patent performs preliminary calculation of the required additional brake fluid volume before actual brake application. The control unit determines the exact volume needed based on the parking brake device's intended clamping force and delivers it proactively via the service brake device, ensuring optimal clamping force is achieved from the start rather than requiring iterative adjustment.
3Reliability
If the service brake device delivers excessive brake fluid volume to ensure target clamping force, then sufficient clamping force is achieved, but component wear increases due to excessive piston movement
Solution Approach 1:
The patent applies partial action by calculating and delivering only the precise additional brake fluid volume needed to achieve the target clamping force, rather than delivering excessive volume. The control unit uses the formula V_add = f(M_soll, F_ZP, V_P) to determine the exact volume required, minimizing unnecessary piston movement and reducing component wear while ensuring sufficient clamping force.
4Reliability
If larger actuators are used in the service brake device to ensure sufficient brake fluid delivery, then reliable braking is achieved, but the system size and energy consumption increase
Solution Approach 1:
The patent applies partial action by delivering only the precise additional brake fluid volume needed rather than using large actuators capable of excessive delivery. The control unit calculates V_add based on actual requirements from parking brake parameters, allowing the use of smaller, more energy-efficient actuators in the service brake device while maintaining reliable braking performance.
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 approach enhances control precision, reduces component wear, and minimizes residual friction torque, enabling smaller actuators and lower energy consumption while ensuring reliable parking brake performance.
Implementation Method 1
the pressure in the piston chamber of the brake piston that is provided for the brake fluid are influenced
Implementation Method 2
an electrohydraulic service brake device which fulfils the normal brake functionality
Implementation Method 3
an electromotive parking brake device having a spindle drive which is driven by an electric motor
Implementation Method 4
spindle drives of electromotive parking brake devices, in a self-locking state, are able to maintain higher clamping forces
Implementation Method 5
the required target clamping force, combined with a safety margin, taking account of the force component of the parking brake device
Data Source
AI summary
The present relates to a method for operating a vehicle brake system which comprises a vehicle brake having a brake piston, an electrohydraulic service brake device, and an electromotive parking brake device having a spindle drive driven by an electric motor, wherein the electrohydraulic service brake device and/or the electromotive parking brake device act on the brake piston. The method determines an additional brake fluid volume to be delivered by the electrohydraulic service brake device in order to ensure a target clamping force (Fz-Soll) for a brake pad of the parking brake on application of the parking brake device.