Reverse-Acting Centrifugal Clutch for Smoother EV Gear Shifts
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Solution Overview
Problem
The challenge in electric vehicles is matching the rotational speed of electric motors to transmission inputs during shift events, leading to sudden spikes in vehicle wheel speed and decreased traction due to the lack of slipping in traditional friction clutches.
Innovation Solution
A centrifugal clutch system with a biasing member and counterweight assembly that allows slipping between friction plates in response to torque disturbances during gear shifts, coupled with a control module for active torque control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional friction clutch is used to couple the electric motor to the transmission, then the clutch can transmit torque, but it does not slip during quick shift events causing sudden spikes in wheel rotational speed and decreased traction
Solution Approach 1:
The clutch system dynamically adjusts its torque transmission characteristics by allowing controlled slipping during shift events. The friction clutch is designed to slip when torque disturbances occur during gear shifts, thereby smoothing out sudden speed spikes and maintaining wheel traction through dynamic speed modulation.
2Productivity
If the electric motor rotational speed is quickly matched to transmission input speed, then shift events occur rapidly, but this causes sudden spikes in wheel speed and loss of traction
Solution Approach 1:
The friction clutch acts as an intermediary element between the electric motor and transmission. During shift events, it mediates the speed mismatch by allowing controlled slipping, which smooths the transmission of torque and prevents direct coupling of speed spikes to the wheels, thereby maintaining traction during rapid shifts.
3Power
If a centrifugal friction clutch is used to increase torque holding capacity at high RPM, then power transmission is improved for ICE vehicles, but this is not suitable for electric motors with constant torque characteristics
Solution Approach 1:
The clutch system changes its operational parameters based on the electric motor's constant torque characteristics. Instead of increasing torque holding capacity with RPM like ICE applications, the friction clutch is configured to maintain appropriate slip characteristics across the electric motor's operational range, allowing controlled slipping during shift events while transmitting full torque during normal operation.
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
This system smooths transmission shifts, maintaining traction and reducing wheel speed disturbances, enhancing overall vehicle performance and efficiency.
Implementation Method 1
The counterweight assembly is coupled to the second friction plate and configured to apply a counterweight force on the second friction plate in a second axial direction that is away from the first friction plate in response to a rotational speed of the second friction plate exceeding a predetermined rotational speed
Implementation Method 2
The second friction plate is configured to frictionally engage the first friction plate to transmit torque therebetween
Data Source
AI summary
An electric vehicle includes an electric drive motor, transmission, and centrifugal clutch. The centrifugal clutch is drivingly coupled in a torque transmission path between the electric drive motor and the transmission. The centrifugal clutch includes a first friction plate, second friction plate, biasing member, and counterweight. The first friction plate is rotatable about an axis. The second friction plate is rotatable about the axis and axially movable relative to the first friction plate. The second friction plate is configured to frictionally engage the first friction plate to transmit torque therebetween. The biasing member biases the second friction plate toward the first friction plate. The counterweight assembly is coupled to the second friction plate and configured to apply a counterweight force on the second friction plate away from the first friction plate in response to a rotational speed of the second friction plate exceeding a predetermined rotational speed.