Internal-combustion engines – Engine speed regulator – Idle speed control
Reexamination Certificate
2002-04-22
2003-12-09
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Engine speed regulator
Idle speed control
C123S339190
Reexamination Certificate
active
06659079
ABSTRACT:
The present invention is generally directed to control strategies for internal combustion engines, and in particular to the control of the engine idle speed. Although the present invention will in the main be described in relation to engines having direct injected fuel injection systems, it is to be appreciated that the invention is also applicable on engines using alternative fuelling systems.
The Applicant has developed dual fluid direct injected fuel injection systems for use on both two and four stroke internal combustion engines. An example of such a dual fluid fuel injection system is described in the Applicant's U.S. Pat. No. 4,693,224, the contents of which are incorporated herein by reference. These fuel systems can be used in a wide variety of recreational, marine, automotive and aeronautical engine applications.
Such directed injected engines are typically controlled by varying the fuelling rate to the engine as a function of engine load and speed. When the engine is operating at idle, an idle controller including a Proportional Integral Differential (PID) system is typically used to return or maintain the operation of the engine at a predetermined base idle speed. The idle controller generally provides closed loop engine idle speed control by varying the fuelling rate to the engine so that the engine speed is maintained and returned to the base idle speed. When initially coming out of an off-idle mode of operation and into idle, the idle controller may achieve this by setting engine speed set-points which progressively ramp the engine speed down to the final base idle speed.
Operation of the idle controller is normally initiated when the engine speed drops below a predetermined level as it approaches idle. This predetermined level is known as the “idle entry set-point”. Once the engine speed falls below this idle entry set-point speed, the idle controller then acts to reduce the engine speed by varying the fuelling rate to the engine to progressively bring the engine speed to the final base idle speed. The idle controller then maintains the engine speed at this steady state base idle speed while the engine is in its idle or no load state. Hence, the idle controller is typically initialised at a certain offset above the base idle speed and this is primarily done to ensure that a smooth transition from off-idle engine speeds to idle is possible.
It has been found for certain engine applications that it may not always be practical to use an idle speed control strategy wherein only a single idle entry set-point has been defined. This may particularly be the case in respect of vehicles having low inertia engines and/or a continuously variable transmission (CVT) such as, for example, scooters and all-terrain-vehicles (ATVs). In such vehicles, the CVT may not de-clutch from the engine at the same speed at which the clutch engages. Therefore, situations can arise whereby the engine can enter the idle control process with either the CVT engaged or disengaged. Hence, in one possible scenario, while the engine may be in an unloaded or “zero demand” state, the engine may still continue to be driven through the CVT. The result of this is that the rate of engine speed deceleration is lower than would normally be the case if the engine had been de-clutched. As a result, the engine speed may, for an extended period of time, be maintained at a significantly higher level than the set-point or final base idle speed.
If the engine is not de-clutched from the vehicle drive-train, the idle controller cannot satisfactorily control the engine speed down to the set-point base idle speed. The idle controller, in trying to control the engine speed down to the base idle speed, will typically react to the large error between the actual idle speed and the base idle speed by significantly reducing the engine fuelling rate. However, once the engine is finally de-clutched from the drive-train of the vehicle, with little to no fuel present in the fuel system due to the previous efforts of the idle controller, it is difficult to prevent the engine speed from dropping well below the base idle speed. This can result in significantly reduced torque backup and typically stalling of the engine.
This is generally the case if a relatively high idle entry set-point is defined in the idle speed control strategy. Whilst this problem may be partially addressed by instead adopting a relatively low idle entry set-point (ie: such that the error between the actual engine speed and the set-point or base idle speed is comparatively small when there exists no demand on the engine and it is being driven through the CVT), this then introduces other problems. In particular, where the engine is de-clutched from the vehicle drive-train and the rate of engine speed deceleration is quite high, the adoption of a low idle entry set-point will typically not give the idle controller enough of an opportunity to ensure that undershoot of the set-point engine speed and/or stalling does not occur.
Accordingly, certain applications exist where it may be beneficial to have two or more idle entry set-points such that satisfactory idle speed control can be effected by the idle controller in response to a number of different scenarios.
It is therefore an object of the present invention to provide an improved method of controlling the engine idle speed which ameliorates at least some of the above noted problems.
With this in mind, according to one aspect of the present invention, there is provided a method of controlling the idle speed of an internal combustion engine including, in response to the engine speed being below a predetermined level: determining the rate of change of the speed of the engine; selecting an idle entry set-point as a function of said rate; and initiating idle speed control of the engine on the basis of said idle entry set-point to thereby control the engine speed to a base idle speed.
Preferably, the rate of change of the speed of the engine is determined after it has been established that the engine speed is decelerating. Preferably, the rate of change of speed is determined following a reduction in the engine speed to a point below the predetermined level. Conveniently, the rate of change of engine speed is determined once it has been established that an off-idle to idle transition is occurring in the operation of the engine. In this way, it is ensured that the rate of change of engine speed is only determined when it is apparent that the engine will soon be seeking to enter an idle mode of operation.
Preferably, idle speed control of the engine speed is performed in a closed loop manner. In this regard, any suitable idle speed controller may be adapted for use with the method of the present invention.
Conveniently, during closed loop idle speed control of the engine, engine speed set-point curves may be set and the engine speed controlled to follow the set-point curves so as to progressively reduce the engine speed down to the base idle speed. The idle speed controller is typically embodied in an electronic control unit (ECU) which manages the operation of the engine. Such ECU's are well known in the field of engine management and as such will not be elaborated on further herein. Conveniently, the idle speed controller will comprise a “PID” system which serves to determine the error between the actual engine speed and the set-point speed to facilitate close loop idle speed control for the engine. The idle speed controller may however incorporate or use any other appropriate system including, for example, a “PI” or “P” system.
Conveniently, the rate of change of the engine speed may be determined as an idle entry gradient, the gradient increasing with increasing rate of change of engine speed. Hence, where a rapid deceleration in engine speed were to occur due to, for example, a short sharp burst of the vehicle throttle whilst at standstill, the gradient would typically be quite sharp (ie: large). In contrast, where a lower rate of deceleration of the engine speed were to occur, for example, where the
Argenbright Tony M.
Orbital Engine Company (Australia) Pty Limited
Rothwell Figg Ernst & Manbeck
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