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Electric Park Brake: Drive Away Release Strategy for vehicles with manual transmission®

IP.com Disclosure Number: IPCOM000129301D
Publication Date: 2005-Oct-05
Document File: 3 page(s) / 24K

Publishing Venue

The IP.com Prior Art Database

Abstract

The Air Pressure Compensation aspect of a Drive Away Release (DAR) software strategy aims to modify the release behaviour of the system to take into account the difference in engine performance resulting from variation in ambient air pressure. The environmental parameter actually affecting engine performance is ambient air density, however, this data is not available to the EPB system without the addition of extra sensing apparatus. Instead, the ambient air pressure value is considered by this strategy as this data is available on the vehicle network in the form of an existing data message. For the purposes of this simple compensation strategy the two parameters can be considered the same in terms of effect on engine performance.

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Electric

Park

Brake:  Drive Away Release Strategy for vehicles with manual transmission;

Air Pressure Compensation Algorithm

The Air Pressure Compensation aspect of a Drive Away Release (DAR) software strategy aims to modify the release behaviour of the system to take into account the difference in engine performance resulting from variation in ambient air pressure.

The environmental parameter actually affecting engine performance is ambient air density, however, this data is not available to the EPB system without the addition of extra sensing apparatus.  Instead, the ambient air pressure value is considered by this strategy as this data is available on the vehicle network in the form of an existing data message.  For the purposes of this simple compensation strategy the two parameters can be considered the same in terms of effect on engine performance.

Throughout this document the term pedal % refers to the accelerator pedal position, where 0% is released and 100% is fully depressed.

The ambient air pressure can be said to reduce with increasing air temperature and / or increasing altitude.  This can be summarised as follows:-

> air temperature = < air pressure

> altitude above sea level = < air pressure

The effect of air pressure changes on engine output can be generalised as:-

< air pressure = < engine torque output

Therefore:-

> air temperature = < engine torque output

> altitude above sea level = < engine torque output

It follows that the "hot and high" condition can be considered a worst case in terms of available engine torque to move the vehicle away from stationary.

From investigation of atmospheric characteristics it is appropriate to generalise that the effect of air temperature increase on air pressure is markedly less than the effect of increase in altitude.

The Air Pressure compensation algorithm fits into the overall DAR strategy between the Pedal % determination stage and the Pedal % wait stage.  The algorithm takes the calculated pedal % value from the initial stage of the DAR strategy and modifies this value to result in an increased pedal % requirement.  The DAR strategy then continues to the Pedal % wait stage where the pedal % value is monitored until the required % is seen.

The strategy can be summarised as follows:-

Air Pressure Compensation Strategy

 
Pedal % Value                                                               Modified Pedal %

From interpolated        ...