Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-12-28
2001-08-14
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S514000
Reexamination Certificate
active
06273067
ABSTRACT:
This invention relates to a control method for use in controlling the operation of a fuel system of the common rail or accumulator type for a compression ignition internal combustion engine. In particular, the invention relates to a control method for use in controlling the fuel pressure within the common rail, in use.
In a known common rail fuel system, a high pressure fuel pump is used to charge a common rail or accumulator with fuel. The fuel pressure within the common rail is controlled by controlling the rate at which fuel is supplied to the high pressure fuel pump using an appropriate metering valve. A pressure limiting valve may be used to prevent the rail pressure exceeding a predetermined threshold for safety purposes.
Such a fuel system operates satisfactorily where the engine is operating at a substantially constant speed against a constant load as the fuel demand is uniform and the metering valve simply needs to be adjusted to supply fuel to the fuel pump at substantially the same rate as fuel is being delivered by the injectors. However, when the engine is not operating in this manner, the metering valve may not be adjusted sufficiently quickly to compensate for changes in the rate of fuel delivery by the injectors thus there may be occasions when the rail pressure exceeds a desired fuel pressure by a significant amount, and it may take a relatively long time for the fuel pressure to fall if the only action taken to correct the fuel pressure is to reduce the rate at which fuel is supplied to the common rail by the fuel pump.
U.S. Pat. No. 5,711,274 describes a method whereby the rail pressure can be relieved, after the engine has been switched off, by supplying control pulses to the control valves of the injectors to permit fuel to be returned to the fuel reservoir without causing the injection of fuel into the cylinders or combustion spaces of the engine. As a result, the provision of a separate pressure relief valve can be avoided.
EP 0896144 describes an arrangement whereby the rail pressure can be relieved, whilst an associated engine is operating, by energising a control valve of one of the injectors, at a time when injection through that injector is not desired, for a period of time sufficient to allow fuel from the rail to escape to a low pressure reservoir through control valve but insufficient to allow injection to commence.
It is an object of the invention to provide a control method whereby, during use of an engine, the fuel pressure within a common rail or accumulator of a fuel system can be controlled.
According to the present invention there is provided a control method for controlling the fuel pressure within the common rail or accumulator of a fuel system whilst an associated engine is operating, the fuel system including a plurality of individually actuable fuel injectors arranged to receive fuel from the common rail, each injector including a control valve operable to control the fuel pressure within a control chamber, fuel escaping from the control chamber being returned to a fuel reservoir, the method comprising:
monitoring the fuel pressure within the common rail;
controlling the rate of fuel supply to the common rail; and
relieving the common rail fuel pressure in the event that the common rail fuel pressure exceeds a predetermined threshold by actuating the control valve of at least one of the injectors to allow fuel to flow from the common rail, through the control chamber of the injector to the fuel reservoir, the control valve(s) being arranged to control the fuel pressure within the control chamber(s) of the said at least one of the injectors in such a manner as to ensure that injection of fuel through that or those injectors does not commence.
It will be understood that such an arrangement is advantageous in that if the rail pressure is significantly greater than a desired pressure, the rail pressure can be relieved quickly rather than having to wait for the rail pressure to fall simply by restricting the quantity of fuel supplied to the common rail and waiting for natural leakage of the system to reduce the pressure.
The control method is preferably preceded by a calibration operation during which the duration of maximum control pulse which can be applied to each injector without causing fuel injection is determined. The calibration operation may include the use of an engine mounted accelerometer, the output signal of which can be filtered in such a manner as to permit detection of movement of a needle of each injector. If desired, the calibration operation may be repeated from time to time.
The common rail may be provided with a separate pressure limiting valve for use in the event that the fuel pressure becomes dangerously high.
Preferably, where the control valve(s) are actuated to relieve the rail pressure, the actuation of the control valves is achieved using a relatively low voltage, for example battery voltage. As a result, the valves can be actuated repeatedly in a short space of time, thus permitting a relatively large quantity of fuel to return to the fuel reservoir. A further advantage of using a low voltage source is that the current applied to the control valve(s) is relatively low resulting in the generation of less heat. Although the use of a low voltage is advantageous in that repeated actuation can be achieved within a short period of time without generating excessive heat, it may be possible to achieve repeated actuation of the control valve(s) using higher voltages.
Where a plurality of the control valves are actuated to relieve the common rail fuel pressure, the control valves are conveniently actuated in sequence.
The rate of fuel supply to the common rail may be controlled using a metering valve to control the fuel supply rate to a high pressure pump. Alternatively, a variable displacement fuel pump could be used to charge the common rail.
REFERENCES:
patent: 5765537 (2000-01-01), Coleman et al.
patent: 5983869 (1999-11-01), Cooke et al.
patent: 6024064 (2000-02-01), Kato
patent: 6102010 (2000-08-01), Yano
patent: 6131549 (2000-01-01), Onishi
Delphi Technologies Incorporated
Moulis Thomas N.
Wells, St. John, Roberts Gregory & Matkin P.S.
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