Electric Parking Brake Motor Control for Lever Return Accuracy
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Solution Overview
Problem
The existing electric parking brake devices face issues with incomplete or excessive return of the parking lever during brake release, leading to brake drag or delayed response in subsequent operations, due to the assistance of return springs and varying no-load current timings.
Innovation Solution
An electric parking brake device with a motor control unit that calculates a rotational load determination value to control the electric motor's operation, ensuring the parking lever is accurately returned to its predetermined position by applying a set rotational load, thereby preventing incomplete or excessive returns through a conversion mechanism and load applying mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric motor is stopped when a predetermined current flows during forward rotation, then a predetermined parking brake force is always obtained, but the brake shoe may be incompletely returned or excessively returned during release due to return spring assistance
Solution Approach 1:
The motor control unit continuously monitors the current flowing in the electric motor during reverse rotation and uses this feedback to determine the precise stop timing. By detecting when the current becomes the no-load current (indicating the parking lever has reached the return position), the system accurately controls the release operation without requiring additional sensors, thereby resolving the contradiction between reliable brake force and precise return position control.
2Ease of operation
If the electric motor is reversely rotated to release the parking brake, then the parking lever returns to the return position, but the timing when no-load current is achieved differs from when the parking lever actually returns due to return spring assistance
Solution Approach 1:
The patent replaces mechanical sensor-based detection systems with an electrical current-based detection method. By monitoring the electrical characteristics (no-load current) of the electric motor during reverse rotation, the system determines the exact moment the parking lever reaches the return position, eliminating the time loss associated with mechanical detection and ensuring timely response for subsequent operations.
3Device complexity
If no sensor is used to detect parking lever state, then the device complexity is reduced and cost is lowered, but the control precision of the parking lever position may be insufficient
Solution Approach 1:
The electric motor serves a dual function: it both actuates the parking brake mechanism and provides its own position feedback through the current characteristics during rotation. The motor control unit utilizes the no-load current signature inherent to the motor's operation to detect when the parking lever has reached the return position, allowing the system to self-monitor without requiring separate sensors, thus maintaining both simplicity and precision.
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 ensures precise control of the electric motor's operation, preventing brake drag and response delays by accurately determining the rotational load, allowing for reliable and consistent parking brake operation without the need for sensors, and enabling cost-effective miniaturization of the load applying mechanism.
Implementation Method 1
an electric motor (motor) included in the electric actuator is rotated forward to make it possible to drive the electric actuator forward
Implementation Method 2
the brake shoe of the drum brake generally includes a return spring biasing the brake shoe toward the return position
Data Source
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AI summary
Electric parking brake devices are configured such that a parking lever (17) is driven by an electric actuator (20). The electric actuator (20) according to the present invention is provided with: an electric motor (21) which can be driven in a forward/reverse direction and of which operation is controlled by a motor control unit (ECU) according to rotational loads; a conversion mechanism (22) capable of converting a rotational motion into a linear motion, moving the parking lever (17) from a return position toward an operating position through the forward rotation of the electric motor (21), and moving the parking lever (17) from the operating position toward the return position through the reverse rotation of the electric motor (21); and a load applying mechanism (a stopper (27) and a disc spring assembly (28)) for applying a predetermined rotational load to the electric motor (21) by driving a constituent member of the conversion mechanism (22) after the parking lever (17) is moved from the operating position to the return position through the reverse rotation of the electric motor (21).