Friction Clutch Contact Point Control via Ramp Rate Adaptation
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Solution Overview
Problem
Existing methods for determining the contact point of a friction clutch in motor vehicles are imprecise, leading to issues like tip-in strikes and body vibrations, especially during the first 100 km of operation, due to slow contact point changes and reliance on constant driving conditions.
Innovation Solution
A method that adapts the contact point value of a friction clutch at predetermined times, reducing it with a ramp rate that depends on the distance traveled, ensuring the reduction does not exceed a predetermined value, thereby improving precision and preventing engagement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the contact point is determined via momentum balance using Kalman filter, then the determination can be performed during drive operation, but the precision is limited to approximately 1 mm due to errors in engine torque offset, clutch dynamics, and dimensional stability assumptions
Solution Approach 1:
The patent applies preliminary action by performing a reference measurement with an open clutch before normal operation to establish accurate drag moment and inertia values. This preliminary characterization of the inactive shaft allows subsequent momentum-based contact point determinations during drive operation to achieve higher precision without being affected by uncertain parameters.
2Measurement precision
If the contact point is determined via transmission input shaft method, then reference measurement and drag moment determination are achieved, but constant driving operation is necessary which cannot be performed in traffic jams or urban areas
Solution Approach 1:
The reference measurement with open clutch is performed as a preliminary action during initial vehicle operation or service, storing the characterized drag moment and inertia values. This allows the system to later use momentum-based contact point determination during normal drive operation without requiring additional constant driving conditions, resolving the contradiction between measurement precision and operational flexibility.
3Adaptability or versatility
If the contact point changes are not pilot controlled, then the system adapts naturally, but rapid changes cause jerk or flare until the contact point is learned again
Solution Approach 1:
The patent implements feedback by continuously monitoring the contact point position and comparing it with the learned reference values. When deviations exceed a threshold, the system activates pilot control to gradually adjust the contact point back to the reference position, preventing harmful engagement behavior while maintaining natural adaptation capabilities.
Solution Approach 2:
The system applies preliminary anti-action by detecting potential rapid contact point changes before they cause harmful effects. The pilot control activates in advance to counteract the deviation, preventing jerk and flare from occurring in the first place rather than correcting them after they manifest.
4Reliability
If momentum-based determination is used as emergency strategy, then major errors are prevented, but fine adjustment capability is lost
Solution Approach 1:
The patent resolves this contradiction by performing preliminary characterization of the clutch system parameters (drag moment, inertia) during initial operation. This stored reference data enables the momentum-based determination to achieve both reliability for error prevention and fine adjustment capability, as the system can detect small deviations from the reference contact point position with high accuracy.
Data Source
AI summary
In a motor vehicle, a friction clutch is disposed between a drive unit and a transmission. The value of the contact point of the clutch is adapted at predetermined points in time. A method for controlling the friction clutch includes the steps of determining a value of the contact point of the friction clutch, this value having been modified as a result of an adaptation thereof, and of continuously reducing the value of the contact point at a predetermined ramp rate, without letting this value drop below a predefined contact point reduction value.