Internal-combustion engines – Charge forming device – With fuel pump
Patent
1992-12-24
1993-11-23
Argenbright, Tony M.
Internal-combustion engines
Charge forming device
With fuel pump
417292, 123514, F02M 3704
Patent
active
052634566
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a fuel flow arrangement for a combustion engine and in particular to a fuel flow arrangement for a diesel engine. Although the invention is particularly intended for use on a diesel engine, it may also be applied to a petrol engine.
BACKGROUND TO THE INVENTION
There is a continuing need for more accurate control of the combustion process in engines in order to minimise engine emissions. It is desirable to be able to feed fuel at a constant temperature to the engine as this can help to control the operation of the engine
SUMMARY OF THE INVENTION
According to the present invention, there is provided a fuel flow arrangement for a combustion engine, the arrangement comprising a fuel reservoir, a fuel feed line extending from the reservoir to the engine, a fuel return line extending from the engine to the reservoir, and a bypass passage which provides a communication between the feed and return lines, the arrangement also comprising a fuel lift pump which has the characteristic of increasing its pumping performance with increasing temperature and which is located in the feed line between the reservoir and the bypass passage, a fuel pressurization pump located between the engine and the bypass passage and fuel flow restrictions located both in the bypass passage and in the return line between the bypass passage and the reservoir.
Because the lift pump works at different efficiencies at different temperatures, the relative pressures created by the two pumps will vary over a range of ambient temperatures. At low temperatures when the lift pump is working inefficiently there will be a relatively high rate of recirculation flow through the bypass passage so that a large proportion of the fuel which has been presented to the pressurization pump (located close to the engine), and has therefore been warmed, is recirculated to the engine. On the other hand, at high ambient temperatures when the lift pump is working at greater efficiency, there is an opposite flow through the bypass passage and the fuel presented to the engine is drawn entirely from the reservoir which represents cooler fuel than that recirculated from the pressurization pump.
The lift pump is preferably a diaphragm pump in which the diaphragm material becomes stiffer at lower temperatures and this results in the lift pump having the characteristic of increasing its pumping performance with increasing temperature. The relevant temperature is the temperature of the fuel which is passing through the pump. The fuel comes in contact with the pump diaphragm so that the temperature of the diaphragm itself moves towards the fuel temperature. Before the engine is started, the temperature of the fuel is determined by the ambient temperature.
A suitable material for the diaphragm is a nitrile rubber/cotton compound. On a diesel engine, the lift pump will preferably be a mechanical lift pump.
In a diesel engine the fuel is fed by the mechanical lift pump to a fuel pressurization pump in the form of an injection pump. The fuel injection pump passes a proportion of the fuel it receives to the fuel injectors and recirculates the excess fuel along the fuel return line.
The fuel flow restrictions may take the form of orifices, or they may be simple check valves which open at a preset fluid pressure to allow fuel to pass. The restriction in the bypass passage is preferably a simple orifice. It may be desirable to give the flow restriction in the return line a progressive characteristic, for example by using a spring with a variable spring rate to control a check valve, in order to optimise the performance.
The size of the orifice in the bypass passage will depend on the nature of the engine to which it is fitted. However for a 2.5 liter direct injection diesel engine, a suitable orifice size has been found to be 4 mm and tests have shown that the size of this orifice may vary between 1 mm and 8 mm.
In a diesel engine, the fuel feed line includes a filter, and the fuel return line can be arranged so that it passes th
REFERENCES:
patent: 4179245 (1979-12-01), Fuller
patent: 4187813 (1980-02-01), Stumpp
patent: 4502450 (1985-03-01), Duprez
patent: 4730704 (1988-03-01), Ohno
patent: 5070849 (1991-12-01), Rich et al.
patent: 5197443 (1993-03-01), Hodgkins
Argenbright Tony M.
Drouillard Jerome R.
Ford Motor Company
May Roger L.
Moutis Thomas
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