Internal-combustion engines – Engine speed regulator – Engine speed reduction by fuel cutoff
Reexamination Certificate
2001-04-18
2004-02-10
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Engine speed regulator
Engine speed reduction by fuel cutoff
C123S335000, C123S436000, C701S110000
Reexamination Certificate
active
06688281
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to internal combustion engines, and in particular a method and control system for use in such engines to control the revolutionary speed thereof. The invention will in the main be described in relation to a direct injection two-stroke spark ignition engine, although it is to be appreciated that use of the method and control system in relation to other engine applications is also envisaged.
Internal combustion engines are used in a wide variety of applications, such as in motor vehicles (cars, all terrain vehicles and two-wheeled vehicles) and watercraft including personal watercraft (PWC's) and outboard engines for boats. In many of these applications, it may be important in the operation of the engine to be able to control the rotational speed of the engine.
For example, a requirement to limit engine speed may arise in order to protect an engine from damage which could be sustained during overly high speed operation, or to limit the overall speed of the vehicle being powered by the engine. Such speed limiting may be desirable in instances where the operator of the vehicle is inexperienced or if maximum speed limits are provided for a given situation.
PWC's are particularly susceptible to overspeed conditions as these craft are often operated at or near their maximum engine speed. During wave jumping for example, a popular activity of PWC enthusiasts, and during rough water conditions, the driving mechanism of the PWC is liable to rise above the water level, thereby creating a sudden drop in load on the engine, and hence an associated increase in engine speed. In this regard and since it is common for PWC's to be operating at or close to maximum engine speed when wave jumping or in rough water, it is important to avoid any “over-revving” of the PWC engine as this may result in damage to the engine.
In the past most engines simply had no maximum speed control except for the engine's natural maximum limit, leaving the engine particularly susceptible to damage from operation at overly high speed. More recently, mechanical devices such as governors have been used, and developments in the electronic control of engines have resulted in a greater ability to control or restrict the maximum speed of internal combustion engines.
For example, in one such development, it has been proposed to prevent further increases in engine speed once the engine reaches a preset upper speed limit by skipping combustion events. In one possible scenario, the ignition event is simply not enabled, and the combustion event does not occur. This method however has the disadvantage that fuel is still delivered into the combustion chamber, and passes out through the engine exhaust system into the environment, in an unburnt state. This is both a significant waste of fuel and can be harmful to the environment. Additionally, residual unburnt fuel can remain in the combustion chamber and adversely affect a subsequent combustion event by reducing the predictability and certainty with regard to the amount of fuel in the combustion chamber.
Another known option is to reduce the fuelling level to the engine so that reduced power is produced thereby and engine speed is reduced. However, whilst this appears to be a reasonable option, bulk air flow through the combustion chamber is not affected by simply reducing the fuelling levels, and the overall result, particularly in the case of wide open throttle operation, may be enleanment of the air fuel ratio of the combustion mixture in the combustion chamber. Such enleanment can result in lean misfire and the overheating of the engine, particularly at high operating loads.
The present Applicant has developed a two-fluid fuel injection system as disclosed in, for example, the Applicant's U.S. Pat. No. 4,693,224, the contents of which are incorporated herein by reference. The method of operation of such a two-fluid fuel injection system typically involves the delivery of a metered quantity of fuel to each combustion chamber of an engine by way of a compressed gas, generally air, which entrains the fuel and delivers it from a delivery injector nozzle. Typically, a separate fuel metering injector, as shown for example in the Applicants U.S. Pat. No. 4,934,329, delivers, or begins to deliver, a metered quantity of fuel into a holding chamber within, or associated with, the delivery injector prior to the opening of the delivery injector to enable direct communication with a combustion chamber. When the delivery injector opens, the pressurised gas, or in a typical embodiment, air, flows through the holding chamber to entrain and deliver the fuel previously metered thereinto to the engine combustion chamber.
In an engine operated in accordance with such a two-fluid fuel injection strategy, there are therefore distinct events in the combustion process, including a fuel metering or fuel event, an air delivery or injection event (as opposed to the bulk air delivery into the combustion chamber which occurs separately), and an ignition event. The engine management system typically required to implement such a strategy includes an electronic control unit which is able to independently control each of the fuel, air, and ignition events to effectively control the operation of the engine on the basis of operator input. Accordingly, the use of such a two-fluid fuel injection system allows combustion events to be partially or completely cancelled, producing a non-combustion event in a selected cylinder.
In the context of this specification, unless otherwise indicated, an “event” is either a combustion event, or a non-combustion event which occurs where the combustion event would have occurred if it had been scheduled.
Hence, in a two-fluid fuel injection system, it is possible for the electronic control unit to simply cut one or more cylinders of the engine by simply providing no fuel for an event, the event then simply consisting of compressing air which is substantially free of fuel, and allowing it to expand again, thus not contributing to any additional engine speed and avoiding the negative consequences of other forms of engine speed control. However, simply cutting a fuel event may result in a certain degree of “drying” of the delivery injector nozzle which would still have a quantity of air being delivered therethrough. This may result in the next combustion event upon reinstatement of the cut cylinder being less than satisfactory.
In a similar manner, it is possible for the electronic control unit to bypass or cut one or more cylinders of the engine by simply not initiating an air event. Thus, any fuel which is metered into the delivery injector nozzle is simply not delivered thereby, hence not contributing to any additional engine speed. However, such a strategy may also have associated problems in that upon reinstatement of the previously bypassed cylinder, the next combustion event may result in twice as much fuel being delivered to a cylinder. That is, the previous undelivered fuel quantity together with a subsequent metered quantity of fuel are delivered in the one injection event upon reinstatement of the previously bypassed cylinder.
It should be understood that cutting the ignition event as alluded to hereinbefore is still an option for producing a non-combustion event in such a two-fluid injection system, but this option still possesses the associated disadvantages as described hereinbefore.
Accordingly, in such a two-fluid injection system, it may be more beneficial to ensure that neither the fuel event nor the air event occur when seeking to cut a cylinder and hence produce a non-combustion event. In this regard, in order to effectively produce a non-combustion event in such a manner, it is obviously better to determine whether a particular combustion event should be skipped, and then arrange the cancellation of the fuel and air events prior to the start of the actual fuel metering for the combustion event.
However, in the above-mentioned two-fluid fuel injection system, the start of the fuel event,
Epskamp Troy Bradley
Woolford Richard Albert
Hoang Johnny H.
Orbital Engine Company (Australia) Pty. Limited
Rothwell Figg Ernst & Manbeck
Wolfe Willis R.
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