Electrically Actuated Friction Brake with Cam Transmission
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Solution Overview
Problem
Electrically actuated friction brakes face challenges in achieving short actuation times while maintaining cost-effectiveness and ensuring consistent braking performance over the service life, due to high energy requirements and oversized electric actuators, which are inefficient and costly.
Innovation Solution
A second transmission element with an elevation curve and a coupling element is introduced, allowing the electric actuator to apply input torque that follows an envelope curve over torsion angles, reducing the load on the electric actuator and enabling smaller gear ratios, thus reducing costs and actuation time, while maintaining consistent braking performance across varying brake lining wear states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a linear transmission element is used with a constant transmission ratio, then the brake can generate the required maximum pad pressure force, but the electric actuator is oversized and cannot be optimally utilized for partial braking maneuvers
Solution Approach 1:
The patent applies a nonlinear transmission element (cam or eccentric mechanism) that dynamically changes the transmission ratio during actuation. The transmission ratio is highest at the beginning of the stroke and decreases as the brake pad approaches the friction surface, allowing the electric actuator to operate at optimal power levels throughout the entire braking range while still achieving the required maximum pad pressure force.
2Loss of time
If a high transmission ratio is used to achieve short actuation times, then the actuation speed increases, but the electric actuator requires correspondingly high electrical power
Solution Approach 1:
The nonlinear transmission element creates a dynamic transmission ratio that is highest when the actuator travels the longest distance (at the beginning of the stroke) and decreases as the stroke progresses. This allows the system to achieve short actuation times without requiring proportionally high electrical power, as the high transmission ratio is only needed when the actuator has the most distance to travel.
3Force
If the transmission ratio is optimized for full braking, then maximum pad pressure force is achieved, but partial braking maneuvers cannot be performed optimally
Solution Approach 1:
The nonlinear transmission characteristic inherently provides adaptability for different braking maneuvers. The continuously varying transmission ratio allows the electric actuator to operate efficiently whether performing full braking, partial braking, or light braking maneuvers, as the transmission ratio automatically adjusts to the current stroke position rather than being fixed for a single operating point.
4Power
If a nonlinear transmission element is used to improve actuator utilization, then the transmission ratio varies during actuation, but the force curve over the actuation path becomes complex to design
Solution Approach 1:
The patent implements a nonlinear transmission element where the transmission ratio varies as a function of the actuator's travel position. By designing the cam or eccentric mechanism with a specific profile, the transmission ratio changes continuously during actuation, allowing the electric actuator to operate at optimal power levels throughout the stroke while maintaining a relatively simple mechanical structure.
Data Source
Figure 1~6
Figure 2
Figure 3~4
AI summary
To reduce the attainable actuation times of an electrically actuated friction brake and simultaneously keep the friction brake inexpensive, a second transmission element (8) with an elevation curve (17) is proposed, wherein a coupling element (15) is provided on a first transmission element (5), and on the coupling element (15) there is arranged a follower element (14) which follows the elevation curve (17) under the action of the electric actuator (12) for the actuation of the first transmission element (5), and a release spring (21) is provided which acts on the actuating device (10), wherein, in the event of actuation of the friction brake (1), the rotation of the actuating shaft (6) stresses the release spring (21) in a first rotational angle range and, in a second rotational angle range, for assistance of the actuation of the friction brake, relieves the release spring of stress.