Internal-combustion engines – Engine speed regulator – Idle speed control
Patent
1997-07-07
1999-11-09
Wolfe, Willis R.
Internal-combustion engines
Engine speed regulator
Idle speed control
12333919, 123352, F02D 4108, F02D 4116
Patent
active
059794020
DESCRIPTION:
BRIEF SUMMARY
This invention relates generally to the control of an internal combustion engine of a motor vehicle including motorcars, trucks, motorcycles, scooters, snowmobiles and all-terrain-vehicles, and in particular to the control of the idle speed of the engine. The invention is applicable for motor vehicles having either a manual or an automatic transmission, and for both two stroke or four stroke internal combustion engines.
The term "idle speed" refers to the engine speed when there is no operator initiated demand on the engine which may relate to, for example, when the vehicle is stationary or when the vehicle is freewheeling down a hill.
BACKGROUND OF THE INVENTION
It is known to use electronic engine management systems for controlling the operation of an engine within a motor vehicle. It is also known to have a control system for performing "closed loop idle control" to control the idle speed of the engine. This is a control strategy whereby, typically, the actual idle speed of the engine is compared to a desired target value idle speed at regular intervals. The engine idle speed is returned or adjusted to that target value when any deviation from that target value occurs.
In conventional homogeneous charge internal combustion engines, the engine speed and the idle speed in particular are typically controlled by a throttle valve controlling air flow to the engine. In such an engine, the control system will normally define idle as being when the throttle is closed. In contrast, in the case of engines such as the Applicant's stratified charge, air assisted, fuel injected engine, the engine speed is increased or decreased at idle by respectively increasing or decreasing the fuelling rate when under closed loop idle control. Accordingly, in such an engine, the control system may preferably define idle as being when the accelerator pedal of the vehicle is fully disengaged. Typically, the fuelling rate is controlled by varying the opening time, commonly known as the "pulse" time, of the fuel injectors and therefore changing the amount of fuel injected into the cylinders of the engine. The fuel based control system of the Applicant's engine therefore uses the fuelling rate as the primary control parameter and the required air flow is determined as a function of the fuelling rate. Although a throttle valve can and typically will be used to control the air flow to the engine, the throttle valve does not regulate the engine speed as in conventional engines.
In either of these engine applications, idle speed control may occur both when the motor vehicle is stationary and when the motor vehicle is in motion. However, if the control system performs closed loop idle control when the motor vehicle is in motion, significant "driveability problems" associated with the phenomenon commonly referred to as "tip-in/tip-out" can result. This phenomenon can manifest physically as rocking of the engine relative to the motor vehicle chassis during acceleration, such as the throttle opening from idle (tip-in), or deceleration, such as throttle closure to idle (tip-out).
Tip-out problems occur due to the engine being driven through the gearbox during vehicle motion whilst there is no operator demand on the engine, for example, such as when the throttle is closed. In the case of fuelling controlled engines, this tends to maintain the engine speed irrespective of any attempt to control it by fuelling reduction. Accordingly, the closed loop idle control system, sensing this maintained engine speed, typically reduces the fuelling to the engine significantly or totally in an attempt to reduce the engine speed to the target idle speed value. This generally causes a severe vehicle deceleration through the motor vehicle drive-line, which may typically be compounded by induced engine rocking. This is a very undesirable condition which makes the motor vehicle very difficult to drive smoothly.
Tip-in problems in fuelling controlled engines occur partly due to the fuelling rate being significantly reduced (due to closed loop idle) during tip-o
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The Motor Vehicle, Twelfth Edition, Newton et al, 1996, pp. 329-385.
Orbital Engine Company Pty Limited
Vo Hieu T.
Wolfe Willis R.
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