Actuator with Non-Reversible Screw-Nut System
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional drum brake actuators, particularly those using a screw-nut system, face inefficiencies in transmitting braking torque due to high energy absorption in the transmission means, limiting their effectiveness in performing parking and emergency braking functions.
Innovation Solution
A linear actuator with a screw-nut system optimized for efficiency, featuring a helix angle less than the angle of friction by up to 3%, combined with a trapezoidal thread profile and an elastically deformable element, ensures irreversible force transmission and reduced energy consumption, allowing for enhanced torque application without continuous motorization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a screw-nut system with conventional helix angle is used in the actuator, then the transmission ratio is sufficient to provide braking torque, but a significant part of the energy supplied by the motor is absorbed by the transmission means
Solution Approach 1:
The patent applies parameter changes by optimizing the helix angle of the screw threads to be less than the angle of friction. This specific parameter modification reduces the energy absorption in the transmission means while maintaining sufficient braking torque through the optimized mechanical advantage of the screw-nut system
2Loss of energy
If the helix angle is made very small to reduce energy absorption, then energy efficiency improves, but the efficiency of the screw-nut system itself deteriorates
Solution Approach 1:
The patent resolves this contradiction by precisely optimizing the helix angle parameter to be less than the angle of friction. This specific parameter value achieves the dual benefit of reducing overall energy absorption in the transmission while maintaining high efficiency in the screw-nut system itself, avoiding the pitfalls of both very small and conventional helix angles
3Weight of moving object
If a high gear ratio is used with high rotational speed motorization, then the motor size and weight are reduced for a given power, but the energy absorption in transmission means increases
Solution Approach 1:
The patent applies parameter changes to the screw thread geometry (helix angle less than friction angle) to create a more efficient transmission system. This allows the use of lighter, high-speed motors with lower gear ratios, achieving both weight reduction and reduced energy absorption in the transmission means simultaneously
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 the efficiency of the screw-nut system and the entire actuator, providing a more effective braking torque with reduced energy consumption, enabling better performance in both parking and emergency braking modes.
Implementation Method 1
a linear actuation assembly by screw-nut system... comprising a rotating element and a second element cooperating together via respective male and female threads to form a screw-nut system
Implementation Method 2
the helix angle β of the threads of the system screw-nut is less than the angle of friction φ... to guarantee the irreversibility of the actuator and that a force coming from the segments does not risk causing the rotating element to rotate
Implementation Method 3
The actuator also comprises an elastically deformable element, at least along the direction of actuation
Data Source
AI summary
The invention relates to an actuator with a screw-and-nut system, in particular for actuating the brake shoes of a drum brake of a motor vehicle. The invention also relates to a drum brake and a braking device provided with such an actuator. The linear actuator includes a transmission sub-assembly driven by a rotary motor and driving a linear actuator assembly. Said assembly includes a rotary element and a second element engaging with one another by means of respective male and female threads in order to form a screw-and-nut system. The actuator is arranged such as to press the brake shoes selectively against the drum of the brake, separating the first ends of the brake shoes from one another when the rotary element is rotated via the transmission sub-assembly. The helix angle β of the threads of the screw-and-nut system is smaller than the angle of friction φ, with a deviation of no more than 3% of the value of the angle of friction, for example β = 0.98 x φ.