Electromechanical Brake Booster Plunger Rod Return Control
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Solution Overview
Problem
The return of the brake pedal lever in electromechanical brake boosters is hindered by friction and hysteresis effects, leading to slower return motion and high Bernoulli forces at the end stop, which can result in undesirable pedal feel and noise.
Innovation Solution
A control device is used to determine a setpoint return velocity for the plunger rod based on pedal force and motion variables, generating an activation signal for the gear motor to actively control the return motion, thereby reducing Bernoulli forces and allowing for individual adaptation of the return behavior without complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If hydraulic pressure is used to return the brake pedal lever, then the system structure is simple, but the return motion is slower due to friction and hysteresis effects
Solution Approach 1:
The patent replaces the traditional mechanical/hydraulic return mechanism with an electromechanical system. A gear motor is coupled to the plunger rod, and a control device actively controls the return motion based on input variables including pedal force and plunger rod motion. This substitution enables faster and more controllable return motion while eliminating the limitations of friction and hysteresis inherent in purely mechanical systems.
Solution Approach 2:
The control device utilizes the existing pedal force variable and plunger rod motion variable as input signals to automatically determine the setpoint return velocity and generate the activation signal for the gear motor. The system serves itself by using its own operational parameters as control inputs, eliminating the need for additional sensors or complex external control signals.
2Ease of operation
If return springs are used to provide response force, then the pedal feel is improved with brand-typical setting, but high Bernoulli forces occur at the end stop due to high plunger rod velocity
Solution Approach 1:
The patent implements dynamic control of the plunger rod return velocity through the control device. Instead of relying on fixed mechanical springs that cause high velocity at the end stop, the control device continuously adjusts the gear motor activation signal based on the plunger rod motion variable and pedal force variable. This enables the system to maintain appropriate response force for good pedal feel while dynamically reducing velocity near the end stop to minimize Bernoulli forces.
Solution Approach 2:
The control device uses feedback from the plunger rod motion variable and pedal force variable to regulate the return velocity. The feedback loop allows the system to sense the current state and adjust the gear motor activation accordingly, ensuring that the plunger rod velocity is reduced before reaching the end stop, thereby eliminating high Bernoulli forces while maintaining proper pedal feel throughout the travel.
3Reliability
If active control of plunger rod return velocity is implemented, then brake release behavior is improved and Bernoulli forces are reduced, but control system complexity increases
Solution Approach 1:
The control device performs multiple functions using a unified control approach: it determines the setpoint return velocity, generates the gear motor activation signal, and adapts to different braking conditions. By using the same control structure for various operating scenarios (normal braking, emergency braking, different pedal forces), the system achieves high reliability without proportionally increasing complexity. The control device serves as a multi-functional unit that handles all return control scenarios.
Solution Approach 2:
The control device improves reliability by dynamically changing the setpoint return velocity parameter based on input variables such as pedal force and plunger rod motion. Rather than using a fixed velocity profile, the system adapts the return velocity parameter in real-time to match actual operating conditions, ensuring optimal brake release behavior across different scenarios while maintaining a relatively simple control structure.
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 solution improves brake release behavior, reduces high Bernoulli forces, and ensures a smooth, noise-free return of the brake pedal lever to its starting position, adaptable to different vehicle and brand-specific settings.
Implementation Method 1
a gear motor (22), which is coupled with the plunger rod (21)
Implementation Method 2
the return of the brake pedal lever using hydraulic pressure in the brake master cylinder
Implementation Method 3
Due to friction and hysteresis effects, the return of the brake pedal lever
Implementation Method 4
Due to friction and hysteresis effects, the return of the brake pedal lever
Implementation Method 5
return springs situated in the system, which provide a defined response force
Implementation Method 6
return springs situated in the system
Implementation Method 7
the plunger rod velocity is too high toward the end of the return motion, so that high Bernoulli forces may occur at the end stop
Data Source
AI summary
An electromechanical brake booster having a plunger rod for connecting a brake pedal lever to a brake master cylinder, a gear motor, which is coupled with the plunger rod, and a control device for driving the gear motor. A pedal force variable representing the pedal force and a plunger rod motion variable representing the motion of the plunger rod are supplied to the control device as input variables. The control device is configured to determine a setpoint return velocity for the plunger rod with the aid of the plunger rod motion variable and an actual return velocity for the plunger rod and the pedal force variable from the setpoint return velocity and to generate an activation signal for the gear motor. This makes it possible to improve the brake release behavior and to reduce high Bernoulli forces at the end stop for the starting position of the brake pedal lever.