Electromechanical Brake Force Estimation via Piston Travel Sensing
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Solution Overview
Problem
Conventional electromechanical vehicle brakes require complex and costly force sensors to determine braking pressure, which is not discernible by motor movement due to wear-related changes in actuation travel.
Innovation Solution
An electromechanical vehicle brake system that includes a ball screw drive, a spring element with a known characteristic curve, and a travel sensor to determine braking force without a dedicated force sensor, using the travel sensor's signal and motor parameters to calculate the applied braking force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional force sensors are used to determine braking pressure, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical force sensor system with an electromechanical measurement system. The ball screw drive converts the actuation force into rotational torque on the spindle, which is measured by an encoder or resolver. This substitution eliminates the need for direct force sensors while maintaining measurement capability through the relationship F = T / (π * d * lead), where T is torque and d is spindle diameter.
Solution Approach 2:
The ball screw mechanism acts as an intermediary between the actuation piston and the braking assembly. Instead of measuring force directly at the brake caliper, the system measures the equivalent torque on the spindle through the ball screw transmission. The ball screw converts linear force into rotational motion, providing an indirect but accurate measurement path that avoids complex force sensing.
2Reliability
If force sensors are installed to measure braking pressure, then reliability is improved, but ease of manufacture deteriorates
Solution Approach 1:
The ball screw spindle serves multiple functions: it acts as both the actuation mechanism to move the brake caliper and as the measurement element to determine braking force. The encoder or resolver on the spindle provides positional feedback for control while simultaneously enabling force calculation. This multi-functionality eliminates the need for separate force sensing components, simplifying manufacturing.
Solution Approach 2:
The ball screw drive system is self-measuring in the sense that its own operational parameters (spindle torque and rotation) directly provide the braking force information. The system uses its actuation mechanism's inherent mechanical properties to generate measurement data, eliminating the need for external sensing infrastructure and reducing manufacturing complexity.
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
Enables the determination of braking force in an electromechanical vehicle brake without the need for a force sensor, using a travel sensor and characteristic curve of the spring element to measure linear displacement and calculate the applied force, reducing complexity and cost.
Implementation Method 1
a ball screw drive which has a spindle rotatable by the electric motor as well as a ball screw nut displaceable on the spindle
Implementation Method 2
a spring element, which is arranged in the actuation piston between the stop and the ball screw nut
Implementation Method 3
a Hall sensor or a capacitive sensor, that is to say a robust and economical sensor, can be used as travel sensor
Implementation Method 4
a Hall sensor or a capacitive sensor, that is to say a robust and economical sensor, can be used as travel sensor
Implementation Method 5
an electric motor and an actuation piston which acts on a braking assembly... the spindle rotatable by the electric motor
Data Source
AI summary
An electromechanical vehicle brake has an electric motor and an actuation piston, which acts on a braking assembly, as well as a ball screw drive. The ball screw drive comprises a spindle rotatable by the electric motor and a ball screw nut displaceable on the spindle. The ball screw nut is received in the actuation piston and cooperates with a stop on an inner axial end of the actuation piston to displace the actuation piston in an actuation direction. A spring element is arranged in the actuation piston between the stop and the ball screw nut. A travel sensor measures a linear displacement of the actuation piston. With the aid of the signal of the travel sensor, which indicates a displacement position of the actuation piston, a braking force currently applied by the actuation piston to the braking assembly is determined under consideration of the characteristic curve of the spring element.