Roller Screw Brake Actuation to Prevent Piston Back-Driving
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Solution Overview
Problem
Existing vehicle brake systems, particularly parking brake systems, face challenges in preventing back-driving of the piston mechanism, which can lead to unintended brake engagement or disengagement, due to the use of worm gears or lead screws that are not effectively prevented from reversing motion.
Innovation Solution
A roller screw system is introduced, comprising a spindle with a helically threaded portion, a nut with a helical thread, and non-helically grooved rollers interposed between the spindle and nut, supported by a cage that maintains the rollers' position, allowing for longitudinal motion in both directions through rotational motion transmission, and is integrated into an electromechanical brake apparatus to control the brake pad's position effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a worm gear or lead screw is used to prevent back-driving, then the piston is protected from unintended motion, but the system complexity increases and reliability decreases due to inherent back-driving vulnerabilities
Solution Approach 1:
The patent replaces the traditional worm gear or lead screw mechanical system with a roller screw mechanism. The roller screw uses rollers that engage with the threaded spindle, converting rotational motion to linear motion while inherently preventing back-driving through the roller contact geometry. This substitution eliminates the back-driving vulnerability of worm gears while reducing mechanical complexity compared to traditional lead screw systems with additional locking mechanisms.
2Reliability
If a worm gear is used to prevent back-driving, then piston protection is achieved, but energy loss increases due to friction in the worm gear mechanism
Solution Approach 1:
The roller screw mechanism replaces the high-friction worm gear system. The rollers in the roller screw mechanism roll along the threaded spindle, converting sliding friction into rolling friction, which significantly reduces energy loss. This substitution maintains the back-driving prevention function while dramatically improving energy efficiency by eliminating the inherent friction losses of worm gear mechanisms.
3Ease of operation
If a lead screw is used for motion control, then the piston can be moved, but back-driving can occur leading to unintended brake engagement or disengagement
Solution Approach 1:
The patent substitutes the lead screw mechanism with a roller screw system. The roller screw maintains the ease of operation for piston motion control through smooth rolling contact, while simultaneously providing inherent back-driving prevention. The roller geometry and engagement with the threaded spindle create a mechanical advantage that prevents reverse motion, eliminating the reliability issue of unintended brake engagement or disengagement associated with lead screws.
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 roller screw system ensures reliable and controlled motion of the brake pad in both service and parking brake modes by preventing back-driving and maintaining a constant longitudinal position of the rollers, enhancing the stability and efficiency of the brake system.
Implementation Method 1
At least one non-helically grooved roller is interposed radially between the spindle and the nut. A cage maintains the at least one roller in position radially between the spindle and the nut. The cage supports the at least one roller for rotational motion about a longitudinal axis of the at least one roller.
Implementation Method 2
A spindle includes a helically threaded portion and defines a longitudinal axis about which the spindle rotates. A nut at least partially radially surrounds the helically threaded portion of the spindle. The nut includes a helical thread on an interior lumen wall thereof.
Data Source
AI summary
A roller screw system includes a spindle defining a longitudinal axis about which the spindle rotates. A nut at least partially radially surrounds the spindle. The nut is configured for longitudinal motion with respect to the spindle. At least one non-helically grooved roller is interposed radially between the spindle and the nut. A cage maintains the at least one roller in position radially between the spindle and the nut and supports the at least one roller for rotational motion. The nut is moved in longitudinally in a duty cycle responsive to transmission of rotational motion from the spindle to the at least one roller, and transformation of rotational motion of the at least one roller to longitudinal motion of the nut. A home position of the nut and a home position of the cage both move longitudinally after a predetermined number of duty cycles.