I. Field of the Invention
The present invention relates generally to fuel delivery systems and, more particularly, fuel delivery systems for a direct injection internal combustion engine.
II. Description of Related Art
In a direct injection internal combustion engine of the type used in automotive vehicles, at least one fuel injector is associated with each combustion chamber in the engine. Furthermore, the fuel injectors are mounted such that the fuel injector injects fuel directly into the combustion chamber rather than upstream from the intake valves as in the previously known multipoint fuel injectors. This direct injection of the fuel into the combustion chamber results in increased engine performance and enhanced fuel economy.
In a conventional direct injection engine, a fuel pump provides pressurized fuel to a fuel rail. Two or more fuel injectors are fluidly connected with the fuel rail. Furthermore, when the engine has cylinders mounted in banks, conventionally a separate fuel rail is provided for each bank of engine combustion chambers.
One of the main advantages of a direct injection fuel delivery system is that it offers better atomization and thereby complete combustion of the fuel since it is injected directly into the combustion chamber at a high pressure. These pressures are on a magnitude of 10-20 times the pressurization required for fuel rails in the previously known multipoint fuel delivery systems.
In order to provide the high pressure fuel to the fuel rail or fuel rails, it has been the previous practice to pressurize the fuel rails with a piston pump that is reciprocally driven by a cam which, in turn, is rotatably driven by the engine. One disadvantage of these previously known piston pumps, however, is that they produce pressure pulsations within the fuel delivery system. In addition, the opening and closing of the injector nozzle (during fuel delivery into the combustion chamber) also result in pressure pulsation. These pressure pulsations result in excessive noise from the fuel delivery system. This noise is particularly noticeable to occupants of the vehicle at low engine speeds.
A still further disadvantage of the previously known direct injection internal combustion engines is that it has oftentimes been necessary to provide two fuel injectors for each combustion chamber. One fuel injector is used during low engine speed when a relatively low amount of fuel is required. Conversely, the second injector is designed to inject larger quantities of fuel into its associated internal combustion chamber at higher engine speeds. Both injectors are controlled by the engine control unit for the vehicle. Typically, pulse width modulation (PWM) is used to activate the proper fuel injector valve between an open and a closed position.
The requirement for two separate fuel injectors disadvantageously increases the overall cost of the fuel injection system.
The present invention provides a fuel delivery system which overcomes the above mentioned disadvantages of the previously known systems.
In one embodiment of the present invention, a first and second fuel rail are provided with each fuel rail associated with one bank of engine combustion chambers. Each fuel rail includes an elongated passageway which is fluidly connected to a plurality of fuel injectors for each fuel rail.
A first fuel pump having a first pumping cycle has an inlet connected to a fuel source, such as the fuel tank, and an outlet fluidly connected to the fuel passageway in the first fuel rail. Similarly, a single fuel pump having a second pumping cycle is provided in which the inlet of the second fuel pump is fluidly connected to the fuel source while the outlet from the second fuel pump is fluidly connected to the fuel passageway in the second fuel rail.
A crossover pipe fluidly connects the outlets of the first and second pumps together. Furthermore, a pressure relief valve is preferably provided between a midpoint of the crossover pipe and the inlet for at least one and preferably both of the fuel pumps.
Each pumping cycle of the first and second pumps has an intake stroke and a pumping stroke. The intake stroke of the first pump coincides with the pumping stroke of the second pump and vice versa. In doing so, pressure pulsations, together with the resultant noise, in the fuel delivery system are reduced.
Noise from the fuel system caused by pressure pulsations is alternatively reduced by providing a plurality of fluid reservoirs so that one fluid reservoir is associated with each of the fuel injectors. The fluid reservoir may be positioned either fluidly in series between the fuel rail and each fuel injector. Alternatively, a fluid reservoir is open to the fuel passageway in the fuel rail at a position aligned with its associated fuel injector, but on the side of the fuel rail opposite from the fuel injector.
A fuel reservoir may also be provided in series in the associated fuel rail.
An improved fuel injector is also provided having an elongated body with an inlet end and an outlet end. A fluid passageway extends between and interconnects the inlet end with its outlet end.
A valve seat is disposed across the outlet end of the body. The valve seat has both a first and second set of fluid passageways wherein each set includes at least one fluid passageway.
A first valve provides fuel for high speed operation and is movably mounted between an open and a closed position in the body. In its closed position, the first valve engages the valve seat and closes the first set of passages. Conversely, in the open position the first valve separates from the valve seat and opens the first set of passages so that fuel flows from the inlet end and to the outlet end of the body and out through the first set of passages.
A second valve provides fuel at low engine speed and is also movably mounted in the body and preferably movably mounted within the first valve between an open and a closed position. In the closed position, the second valve engages the valve seat and closes the second set of orifices. Conversely, in its open position, the second valve separates from the valve seat and opens the second set of orifices to allow fuel flow from the inlet, through the body passageway, and out through the second set of orifices.
An actuator, such as an electromagnet, is contained within the body and selectively energized in a pulse width modulation mode by the engine control unit. Upon the application of a first current, the electromagnet moves the first valve against the force of a compression spring to move the valve from its closed and to its open position. Conversely, the application of a second current value to the electromagnet opens only the second valve while leaving the first valve in a closed position. The second current value is less than the first current value.
A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawing, wherein like reference characters refer to like elements throughout the several views, and in which:
With reference first to
As best shown in
Referring now primarily to
Similarly, a second high pressure pump 42 has its inlet 44 fluidly connected to the fuel source 36 and an outlet 46 fluidly connected by a fuel line 48 to the inlet end 29 of the second fuel rail 23.
With reference now to
In the simplified diagram of
A one-way valve 58 is fluidly connected in series between the pump chamber 52 and the outlet 38. Consequently, during the pump stroke of the pump cycle, the piston 54 moves upwardly as viewed in
A one-way valve 60 is connected in series with the inlet 34 for the pump 32. The valve 60 thus allows fuel flow only through the inlet and into the pump chamber 52. Consequently, during an intake stroke, i.e. when the piston 54 moves downwardly within the pump chamber 52, the piston 54 inducts fuel through the one-way valve 60 and into the pump chamber 52. Each pump cycle, furthermore, consists of a single pump stroke and intake stroke.
As mentioned above, the second fuel pump 42 is substantially identical to the first fuel pump 32. However, the cam associated with the second fuel pump 42 is angularly displaced relative to the cam 56 so that the intake stroke of the first pump 32 coincides with the pump stroke of the second pump 42 and, likewise, the pump stroke of the first pump 32 coincides with the intake stroke of the second pump 42.
The pressure pulsations in the overall fuel delivery system 20 caused by using the two pumps shown in
With reference now to
With reference now to
Unlike the previously described fuel rail 22 or 23, however, a fuel reservoir 106 is associated with each fuel injector 24. Each fuel reservoir 106 has a cross-sectional area, i.e. as viewed along the length of the fuel rail 100, greater than the cross-sectional area of the fuel passageway 102. Each reservoir 106 also is preferably annular in shape and extends around substantially the entire fuel rail 100. As such, the reservoir 106 is fluidly positioned in part in series between the fuel passageway 102 and the fuel injectors 24 and in part on the side of the fuel rail 100 opposite from the fuel injector 24.
In practice, the reservoirs 106 serve to dampen pressure pulsations from the fuel injector. In doing so, the reservoirs 106 reduce the noise of the fuel delivery system, especially at low engine speeds.
With reference now to
With reference now to
The dimensions and volume of the reservoirs in
In practice, the reservoir 106 effectively dampens fuel pressure pulsations that otherwise occur in the fuel rail 100. This is particularly true for low engine speeds. For example, the pressure profile corresponding to
Similarly,
Similarly,
With reference now to
A longitudinally or axially extending fuel passageway 150 fluidly connects the inlet end 144 to the outlet end 146 of the body 142. The outlet end 146 of the body 142, furthermore, is covered by a valve seat 152 best shown in
Although the valve seat 152 extends across and closes the outlet end 146 of the body 142, two sets of orifices are provided through the valve seat 152 to allow fuel to pass from the fuel passageway 150 out through the valve seat 152. As best shown in
Referring again to
A valve guide 162 within the body 142 guides the movement of the first valve 160 between its open and closed positions. Openings 163 through the valve guide 162 establish the fluid communication through the fluid passageway 150. In addition, a spring 164 (
With reference now to
The second valve 170 is movable between a closed position, illustrated in
The second valve 170 is normally urged towards its closed position thus closing the second set 156 of orifices in the valve seat 152. Although any conventional mechanism may be used to urge the second valve 170 towards its closed position, in the preferred embodiment of the invention, an enlarged diameter plunger 180 (
Alternatively, a spring may be used to urge the second valve 170 to its closed position.
With reference now to
Energization of the electromagnet 184 with a relatively low current using pulse width modulation (PWM) to control the amount of opening time of a fuel injector will only be sufficient to move the second valve 170 against the force of the fuel flow from its closed to its open position thus allowing fuel flow out through the second set 156 of orifices in the valve seat 152. However, such low current will not be sufficient to overcome the force of the spring 164 so that the first valve 160 remains in a closed position.
Since only a single orifice 156 in the valve seat 152 is open during a low current condition of the electromagnet 184, the amount of fuel delivered to the engine may be accurately controlled even for very small amounts of fuel by using PWM.
Conversely, during a higher engine speed, a higher current is provided to the electromagnet 184, again using PWM to control the on/off time for the fuel injector. This high current, however, is sufficient to move the first valve 160 against the force of the spring 164 thus uncovering the first set 154 of multiple through orifices in the valve seat 146 thus allowing for increased fuel flow through the valve seat and thus increased fuel flow to the engine combustion chamber. During such high fuel flows, the first valve 160 also preferably moves the second valve 170 to its open position against the force of the incoming fuel flow. As such, both the first set 154 as well as second set 156 of orifices will be open.
From the foregoing, it can be seen that the present invention provides not only an improved fuel delivery system for a direct injection engine, but also an improved fuel injector that can be used for such engines.
Having described our invention, however, many modifications thereto will become apparent to those skilled in the art to which it pertains without deviation from the spirit of the invention as defined by the scope of the appended claims.