Hydraulic Shifting Element Draining Control for Transmission Comfort

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Solution Overview

Problem

Existing methods for determining the draining behavior of hydraulically actuated shifting elements in transmissions are inadequate, particularly in continuously variable power-branched transmissions, leading to suboptimal shifting comfort due to incomplete drainage between rapid engagement and disengagement cycles, which affects the transmission capacity and shifting quality.

Innovation Solution

A method that determines the draining behavior by changing the shifting element from a completely drained to a completely filled condition using actuating pressure, monitoring rotational speed, and adjusting pressure levels to assess and adapt the filling and draining times, allowing for precise actuation and improved shifting comfort.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If rapid succession engagements of the same clutch are performed, then productivity is improved, but the clutch cannot drain completely between engagements resulting in degraded shifting quality

Engineering Contradiction:

Improveengagement speedVSAvoidshifting quality

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The control system performs preliminary drainage of the clutch before re-engagement by maintaining a drainage pressure phase after disengagement. This preliminary action ensures the clutch is sufficiently drained even during rapid succession engagements, preventing incomplete drainage and maintaining shifting quality without sacrificing engagement speed.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention dynamically adjusts the actuating pressure profile based on the operational state. During rapid succession engagements, the system extends the drainage phase and adjusts pressure levels to ensure complete drainage, while adapting the filling phase duration and pressure to achieve optimal engagement. This dynamic adaptation allows maintaining both high productivity and reliable shifting quality.

Inventive Principle:

Principle #15Dynamics

2Ease of operation

If iterative calibration with increasing rapid filling time is performed, then shifting comfort is improved, but measurement time and complexity increase

Engineering Contradiction:

Improveshifting comfortVSAvoidcalibration time

Core Design Contradiction:

Ease of operationVSLoss of time

Solution Approach 1:

The calibration method uses feedback from rotational speed monitoring to automatically determine optimal filling parameters. The system monitors the rotational speed of the shifting element half connected to the transmission output and uses this feedback to identify when the shifting element reaches its closed operating condition, eliminating the need for extensive iterative testing and reducing calibration time while maintaining shifting comfort.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The invention replaces extensive mechanical iterative testing with an automated electronic calibration process. By using electronic sensors to monitor rotational speed and automated control to adjust filling parameters, the system reduces calibration time from multiple manual iterations to a single automated process that quickly determines optimal parameters.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enables better shifting behavior and comfort by accurately determining the draining behavior of shifting elements, reducing measurement errors, and accounting for manufacturing tolerances, thereby enhancing the quality of gearshifts, especially during rapid succession engagements.

Implementation Method 1

The piston chamber of a shifting element is acted upon by a defined rapid filling pressure for the rapid filling time

Methodology Applied

Scientific EffectHydraulic pressure: Pressure Gradient

Implementation Method 2

the rotational speed is monitored by a suitable recognition function. In each case the calibration process is based on the assumption that the shifting element whose rapid filling time is currently being calibrated changes to a completely drained operating condition between the individual iteration steps for determining the rapid filling times

Methodology Applied

Scientific EffectRotational speed monitoring:

Data Source

PatentUS9695890B2Method for determining the drainage control of a hydraulic switching element of a transmission

Publication Date: 2017.07.04 ZF FRIEDRICHSHAFEN AG

AI summary

A method for determining a draining behavior of a hydraulically actuated transmission shifting element. By applying actuating pressure, the shifting element is changed from a completely drained, open operating condition to a completely filled closed operating condition, and the reference filling time, until the closed condition has been reached, is determined. Upon recognition of the closed condition, then by adjusting the actuating pressure for a predefined draining time, the shifting element is changed to its open condition and, thereafter, again completely filled and closed. Upon recognition of the closed condition, the shifting element is actuated direction toward the open condition by reducing the actuating pressure. Then, before completely opening, the shifting element is again returned to its closed operating condition and the filling time, until the partially drained shifting element has reached the completely filled and closed operating condition, is determined.