Internal-combustion engines – Charge forming device – Fuel flow regulation between the pump and the charge-forming...
Reexamination Certificate
1999-06-23
2001-03-27
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel flow regulation between the pump and the charge-forming...
C123S456000
Reexamination Certificate
active
06205981
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates in general to fuel systems in internal combustion engines and in particular to high-pressure direct injection fuel systems.
The present invention is an improvement to the invention disclosed in U.S. Pat. No. 5,832,900 issued Nov. 10, 1998, entitled “Fuel Recirculation Arrangement and Method for Direct Fuel Injection Systems” and having the same inventor as the present application. The aforementioned U.S. patent is hereby expressly incorporated by reference.
Fuel injection systems have in recent years been equipped with injector valves which protrude from pressurized fuel rails, with fuel sprayed out of the injector valves when each is opened at timed intervals by the engine controls. The injectors typically have been arranged to spray the fuel into the intake manifold adjacent the intake valves of the engine cylinders such that the fuel in the fuel rail need only be pressurized to moderate levels, i.e., 3-4 bars.
In “direct injection” systems the injectors spray fuel directly into the engine cylinders. This requires a much higher fuel pressure, on the order of 20-140 bars at the injector tip. The fuel pressure is developed by a high-pressure pump. Fuel is supplied from the fuel tank to the inlet of the high-pressure pump by a conventional lower pressure supply pump.
As engine load varies, fuel demand is varied. To meet changing fuel demand, the pressure in the fuel rail is controlled by a regulator allowing a controlled outflow of fuel from the fuel rail to a lower pressure region. The high operating pressures in the fuel rail create the possibility that the fuel will be changed to a gaseous state when discharged by the regulator. Lighter dissolved components of the fuel, such as butane, methane, or even air, have a tendency to separate and form bubbles, which are very difficult to recombine with the liquid fuel. The presence of bubbles in the liquid fuel recirculated back to the high-pressure pump inlet could damage the high-pressure pump.
The work performed by the high pressure pump in raising the fuel to these high pressures also adds to the internal heat of the fuel, increasing the tendency for gaseous formation of bubbles to occur.
U.S. Pat. No. 5,832,900 (the '900 patent), referenced above, provides a fuel recirculation arrangement and method for minimizing the tendency for fuel to gasify in such high-pressure direct injection systems. In the '900 patent, the high-pressure return fuel flows through a fixed size orifice. The fixed size orifice limits the operating range of the recirculation system. At low flow rates of the high-pressure return fuel, most of the high-pressure pump output is being used by the flow to the injectors. Thus, at low flow rates of the high-pressure return fuel, it is difficult to maintain a minimum backpressure in the supply line to the high-pressure pump.
SUMMARY OF THE INVENTION
It is an object of the invention to increase the fuel pressure at the inlet of the high-pressure pump.
It is another object of the invention to reduce the energy required by the high-pressure pump to pressurize the fuel, thereby reducing the tendency for vaporization of the fuel.
It is a further object of the invention to provide a high-pressure venturi pump with a variable orifice to compensate for varying flow rates in the high-pressure return line.
It is still another object of the invention to provide a high-pressure venturi pump with a variable orifice to maintain a minimum backpressure in the supply line to the high-pressure pump.
These and other objects of the invention are achieved by a high pressure direct injection fuel system comprising a low pressure fuel supply; a venturi pump including a variable orifice, first and second inlets and an outlet, the low pressure fuel supply connected to the first inlet of the venturi pump; a high pressure pump connected to the outlet of the venturi pump; a fuel rail connected to an outlet of the high pressure pump, the fuel rail including at least one fuel injector and a pressure sensor; a high pressure regulator connected to the fuel rail; a return flow line connected between the fuel rail and the second inlet of the venturi pump; and an electronic control unit connected to the pressure sensor and the high pressure regulator.
The venturi pump comprises a housing defining a passageway therethrough for flow of return fuel, a chamber downstream of the passageway for mixing of the return fuel and low pressure supply fuel, and a spring loaded valve disposed in the passageway. The spring-loaded valve includes a downstream end having a diverging portion and a converging portion.
The variable orifice connects the passageway to the chamber and a size of the variable orifice is variable depending on the position of the downstream end of the spring-loaded valve.
Preferably, the first inlet of the venturi pump includes an annular region fluidly connected to the chamber downstream of the variable orifice.
In one embodiment, the downstream end of the passageway includes a converging section.
Another aspect of the present invention is a method of recirculating fuel in a high pressure direct injection system comprising controllably releasing high pressure fuel from a fuel rail into a venturi pump; varying the size of a variable orifice in the venturi pump depending on a pressure of the high pressure fuel released from the fuel rail; mixing the high pressure fuel with low pressure fuel to create an intermediate pressure fuel with a pressure between a pressure of the high pressure fuel and a pressure of the low pressure fuel; and supplying the intermediate pressure fuel to a high pressure pump.
The high-pressure fuel is controllably released from the fuel rail depending on the pressure sensed in the fuel rail.
In a preferred embodiment, the size of the variable orifice in the venturi pump is varied by movement of a spring-loaded valve having a downstream end with diverging and converging portions.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the following drawing.
REFERENCES:
patent: 5133324 (1992-07-01), Michiaki
patent: 5139000 (1992-08-01), Sawert
patent: 5285759 (1994-02-01), Terada et al.
patent: 5832900 (1998-11-01), Lorraine
patent: 5983869 (1999-11-01), Cooke et al.
Castro Arnold
Siemens Automotive Corporation
Yuen Henry C.
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