Electric Parking Brake Torque Drop Detection via PWM-ON/OFF Control

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Solution Overview

Problem

Existing electric parking brake systems using PWM control struggle to detect torque drop in the rotation-linear motion conversion mechanism, leading to potential rear wheel dragging issues during brake release.

Innovation Solution

Implementing a drive control strategy that initiates PWM control for the electric motor during brake release and transitions to ON/OFF control after a predetermined time, allowing for detection of torque drop and preventing rear wheel dragging.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If PWM control is used to reduce motor rotations and operating noise, then operating noise is reduced, but torque drop detection becomes impossible leading to rear wheel dragging

Engineering Contradiction:

Improveoperating noiseVSAvoidbrake release reliability

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The brake release process is divided into two distinct phases: an initial PWM control phase for noise reduction, followed by an ON/OFF control phase for reliable torque drop detection. This segmentation allows each control method to be optimized for its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

PWM control is applied first as a preliminary action to reduce operating noise during the early stage of brake release. After a predetermined time elapsed, the control method is switched to ON/OFF control to enable torque drop detection, ensuring both noise reduction and reliable brake release.

Inventive Principle:

Principle #10Preliminary action

2Speed

If PWM control is used with short time interval current control, then target torque is reached quickly, but torque drop cannot be detected due to smooth current transitions

Engineering Contradiction:

Improvetorque response speedVSAvoidtorque drop detection precision

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The control system dynamically switches between PWM control and ON/OFF control based on the operational stage. PWM control provides smooth torque response during the initial phase, while ON/OFF control enables discrete current changes necessary for torque drop detection in the subsequent phase.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control method employs periodic switching between PWM and ON/OFF modes. The PWM control operates during an initial period, then the system transitions to ON/OFF control with periodic current switching that creates detectable torque drops when the brake is fully released.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS9631686B2Electric parking brake device and release method therefor

Publication Date: 2017.04.25 ASTEMO LTD

AI summary

An electric parking brake device holds a parking brake in a braking state by a rotation-linear motion conversion mechanism that converts rotation of an electric motor into a motion in a linear direction, and releases the parking brake by the rotation-linear motion conversion mechanism. In a case of releasing the parking brake, the electric motor is controlled by combining PWM control and ON/OFF control with each other. When the electric motor is driven according to the PWM control, and a predetermined time has elapsed after start of the PWM control, then the electric motor is changed to drive according to the ON/OFF control. In the ON/OFF control, a change in which a drive current of the electric motor is decreased stepwise is detected, whereby a torque drop of the rotation-linear motion conversion mechanism is detected.