Soft Start Clutch Controller Using PWM Current Monitoring
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Solution Overview
Problem
Existing electromagnetic clutch controllers fail to provide a soft start mechanism effectively, leading to abrupt engagement, increased wear, and undesirable operating characteristics, especially in small engine applications, due to complexity and high costs of mechanical solutions and suboptimal performance of simple electrical switches.
Innovation Solution
A pulse width modulated controller that adjusts current to the clutch coil based on inductance changes, using a normalization factor to adapt to different clutch sizes and detecting pull-in through current signature analysis, allowing for a controlled and adaptive soft start.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple electrical switch is used to control clutch engagement, then the device complexity and cost are reduced, but the clutch engagement remains abrupt and causes increased wear and undesirable operating characteristics
Solution Approach 1:
The patent applies pulse width modulation (PWM) to deliver periodic pulses to the clutch coil instead of continuous DC power. By controlling the duty cycle of these periodic pulses, the system achieves progressive clutch engagement where the clutch plates gradually come together over multiple pulses, reducing abrupt mechanical stress and wear while maintaining simple electrical control components
Solution Approach 2:
The system dynamically changes the electrical parameters (pulse width, frequency, duty cycle) delivered to the clutch coil based on detected clutch engagement state. By monitoring coil current and detecting the characteristic current drop when clutch plates contact, the controller adapts the PWM parameters to provide smooth progressive engagement, transforming the engagement process from abrupt to controlled
2Object-affected harmful factors
If mechanical arrangements are used to reduce clutch engagement abruptness, then the clutch wear and mechanical stress are reduced, but the device complexity and cost increase significantly
Solution Approach 1:
The patent replaces complex mechanical progressive engagement mechanisms with an electrical control system that uses PWM pulse sequences and current monitoring. The electrical system detects clutch engagement through characteristic current signatures and controls the engagement process electronically, eliminating the need for complex mechanical arrangements while achieving the same wear-reduction benefit
Solution Approach 2:
The clutch engagement control system uses the clutch coil's own electrical characteristics (inductance changes, current drop patterns) as feedback to automatically detect engagement state and adjust pulse parameters. This self-sensing capability eliminates the need for external sensors or complex control mechanisms, allowing the system to self-regulate the engagement process for smooth progressive coupling
3Reliability
If the duty cycle is increased to ensure full clutch engagement, then the reliability of clutch engagement is improved, but the time required for clutch engagement increases
Solution Approach 1:
The system continuously monitors the clutch coil current and detects the characteristic current drop that occurs when clutch plates make contact. This feedback signal triggers the controller to switch from progressive PWM pulses to continuous DC power delivery, ensuring reliable full engagement while minimizing the time spent in the gradual engagement phase. The feedback mechanism allows the system to adapt the engagement duration to actual clutch response
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 enables a smooth and adaptive clutch engagement, reducing wear and mechanical stresses, while being cost-effective and suitable for various clutch sizes, by monitoring inductance changes and current signatures to manage clutch engagement.
Implementation Method 1
an electromagnetic clutch includes a coil or solenoid through which a current is passed to actuate the clutch, an at least partially ferrous core is arranged to be drawn into the magnetic circuit when current is supplied to the coil
Implementation Method 2
the magnetic field of the coil builds as the drum is magnetized to the point where the output disk (armature core) is pulled across the air-gap and contacts the drum face
Implementation Method 3
the inductance of the coil increases significantly... the present invention permits the position of the clutch to be determined from the increase in the inductance of the coil that occurs as the core is drawn into the magnetic circuit
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3C
AI summary
A clutch actuator for an electromechanical clutch having a solenoid actuating coil initially provides power to the solenoid at a high rate by using a high duty cycle pulse with a modulated controller. When the initial engagement of the clutch elements is sensed by a decrease in current, the duty cycle of the pulse width modulator is reduced and thereafter increased in a controlled fashion to accomplish a soft start.