GB2375845A

GB2375845A - A vehicle engine management system for reducing vehicle mass oscillations by controlling the engine torque

Info

Publication number: GB2375845A
Application number: GB0112597A
Authority: GB
Inventors: Andy Wicks
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2001-05-24
Filing date: 2001-05-24
Publication date: 2002-11-27
Anticipated expiration: 2021-05-24
Also published as: GB2375845B; GB0112597D0

Abstract

A vehicle engine management system comprises means for estimating vehicle deceleration caused by dynamic and frictional losses, means for estimating, the reaction torque acting on the engine as a result of the deceleration, and means for computing, the torque reduction necessary to counteract vehicle mass oscillations. The torque reduction necessary to counteract the mass oscillations takes into account the engine reaction torque caused by the dynamic and frictional deceleration forces acting on the vehicle.

Description

VEHICLE ENGINE MANAGEMENT SYSTEM Field of the invention The present invention relates to a vehicle engine management system which controls engine parameters such as throttle position, fuel quantity, spark advance and valve timing in order to achieve a desired torque output.

Background of the invention For some time, it has been recognised that changes in engine net torque are responsible for vehicle shunting, during which the vehicle mass oscillates at certain frequencies, dependent on vehicle line and set-up. Such shunting can occur during tip-in- (where the demand pedal is depressed abruptly), tip-out (where the demand pedal is released abruptly), gear changes (both in automatic and manual transmissions), traction control events, engagements and disengagements of an air conditioning system, locking and unlocking of a torque converter and on exiting from fuel shut off during deceleration.

Engine management system (EMS) software has been produced to try and eliminate this fore-aft shunting by smoothing and damping engine net torque by various means which vary with the software manufacturer and vehicle type.

The control strategies implemented in known software use the engine positive/negative torque point as a reference point when calculating torque reduction in order to avoid shunt.

Summary of the invention With a view to achieving more accurate control of torque reduction to avoid vehicle shunting, the present invention provides a vehicle engine management system which comprises means for estimating vehicle deceleration caused

by dynamic and frictional losses, means for estimating the reaction torque acting on the engine as a result of the latter deceleration, and means for computing the torque reduction necessary to counteract vehicle shunting, wherein the means for computing the torque reduction take into account the engine reaction torque caused by the dynamic and frictional deceleration forces acting on the vehicle, the latter torque being taken as the reference engine torque that results in no vehicle acceleration.

In known engine management systems, torque reduction to avoid shunt is estimated without allowing for vehicles drag factors (aerodynamic and frictional) that affect the shunting characteristics. Consequently, a compromise is always necessary at different vehicle speeds. By contrast, in the present invention, these dynamic and frictional losses are estimated and the estimate is used when calculating the torque reduction required from the engine to smooth the shunting.

The invention improves the torque control strategy, particularly at higher vehicles speeds, because whereas current strategies make the erroneous assumption that when the engine produces'zero torque'the vehicle will travel with constant velocity, the present invention uses as the reference point the torque reaction caused by the dynamic and frictional forces acting on the vehicle, that is to say the torque necessary to maintain constant vehicle velocity.

The invention will now be described further, by way of example, with reference to the accompanying drawing, which is a schematic diagram showing the variation of engine output torque with time. In the drawing, trace A shows the engine output torque and the B represents the constant vehicle deceleration torque. The dotted line C represents the reference line when the engine generates zero output torque.

Trace A shows a typical situation in a modem vehicle where the driver performs a tip-out and then a tip-in of the accelerator pedal. During the tip-out, the engine output torque drop suddenly from a positive value to a negative value, i. e. the engine acts as a brake. In the later tipin, the driver suddenly accelerates and the engine switches rapidly from a braking torque to a high driving torque.

Drivability problems arise when there is a sudden change in engine net torque, causes the vehicle to surge forwards and then oscillate due to several factors including driveline compliance, engine mounting and suspension characteristics.

In the prior art, such oscillations were reduced by performing torque control, (for example by altering the airflow, fuel flow or ignition timing to the engine) as the engine changed from producing negative net torque to positive net torque. More particularly, when sensors detected a sudden forward body surge the engine output torque was reduced while a sensed rearward surge would be used to increase the engine output torque. The output torque would thus oscillate about the zero net engine torque point in anti-phase with the shunt oscillations in order to damp the oscillation.

The present invention is based on the realisation that this is not ideal as the major shunt and oscillation is caused when the engine net torque approaches and exceeds a torque equivalent to a torque produced by the vehicles deceleration forces. Therefore, the focal point of torque reduction/smoothing should be at the aforementioned point, and should take into account the rate of desired torque increase through that point. The invention may thus use any feedback system as found in the prior art to damp the shunt oscillations by and requires only that the torque error signal of the feedback loop be referenced to an engine positive torque sufficient to overcome the vehicle deceleration torque rather than zero engine output torque.

Claims

1. A vehicle engine management system which comprises means for estimating vehicle deceleration caused by dynamic and frictional losses, means for estimating the reaction torque acting on the engine as a result of the latter deceleration, and means for computing the torque reduction necessary to counteract vehicle shunting which take into account the engine reaction torque caused by the dynamic and frictional deceleration forces acting on the vehicle.