Friction Clutch Pressure Control With Unambiguous Actuation Path

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Solution Overview

Problem

Friction clutches in motor vehicle drive trains face ambiguity in actuation pressure assignment due to non-linear characteristic curves, making clear control of the clutch impossible in automatically actuated systems.

Innovation Solution

A method to control a friction clutch by recording and analyzing the time profile of actuation processes, using an electrically actuated directional control valve to determine the actuation path and apply corresponding pressures, ensuring unambiguous assignment of actuation pressure to the path, and incorporating a pressure sensor to monitor and adjust pressures for precise control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Extent of automation

If a pressure supply device is used to automatically actuate the friction clutch, then automation is improved, but the assignment of actuation pressure to actuation path becomes ambiguous due to non-linear characteristic curves

Engineering Contradiction:

Improveautomatic actuationVSAvoidambiguous pressure-path assignment

Core Design Contradiction:

Extent of automationVSLoss of information

Solution Approach 1:

A sensor is integrated into the actuation system to detect the actual actuation path of the clutch. This sensor feedback is transmitted to the control device, which uses the information to determine the current position on the non-linear characteristic curve and adjust the actuation pressure accordingly, resolving the ambiguity between pressure and path

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The mechanical system with ambiguous non-linear characteristics is supplemented with an electronic control system that includes a control device and sensor. This electronic system replaces the need for a purely mechanical linear relationship by computationally determining the correct actuation path based on sensor feedback and control algorithms

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If an additional sensor cylinder with linear pressure/displacement ratio is added to compensate for ambiguous characteristic curves, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improveactuation path detectionVSAvoidadditional sensor cylinder

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The actuation system uses the existing actuation pressure and a sensor detecting the actual actuation path to self-determine the position on the characteristic curve. The control device processes this information to control the friction clutch, allowing the system to self-compensate for non-linearities without requiring an additional linear sensor cylinder

Inventive Principle:

Principle #25Self-service

3Ease of operation

If the actuation pressure is reduced to disengage the friction clutch, then the clutch opening function is achieved, but leakage causes unintended closing due to pressure loss

Engineering Contradiction:

Improveclutch disengagementVSAvoidpressure maintenance

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The sensor continuously monitors the actuation path and provides feedback to the control device. When leakage causes pressure loss and unintended closing, the sensor detects the path change and the control device compensates by adjusting the actuation pressure, maintaining reliable clutch engagement despite leakage

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The control device continuously monitors the actuation path via the sensor and continuously adjusts the actuation pressure to maintain the desired clutch state. This continuous action compensates for leakage and ensures the clutch remains in the intended position without interruption

Inventive Principle:

Principle #20Continuity of useful action

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 method allows for clear and precise control of the friction clutch, enabling reliable opening and closing operations, even in the presence of leakage, and provides a limp-home function in hybrid drive trains, ensuring drivability from zero speed.

Implementation Method 1

an actuation pressure applied along an actuation path

Methodology Applied

Scientific EffectPressure: Pressure Increase

Implementation Method 2

frictional engagement with the friction linings is gradually eliminated

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS11873870B2Method for controlling a friction clutch, and torque transmission device comprising same

Publication Date: 2024.01.16 SCHAEFFLER TECHNOLOGIES AG & CO KG

AI summary

A method for controlling a friction clutch actuated by an actuation system using an actuation pressure ambiguously applied along an actuation path includes providing the friction clutch and the actuation system, detecting a time curve of an actuation processes of the friction clutch, and comparing the time curve with the actuation pressure to ascertain an unambiguous friction clutch actuation path. The method may also include using the time curve to determine whether the friction clutch is in an opening state or a closing state and whether the actuation pressure is applied to an opened friction clutch actuation path or a closed friction clutch actuation path, and starting from a set actuation pressure, carrying out a directional control of the friction clutch by specifying the actuation pressure.