Fuel feed pump for internal combustion engines

A fuel feed pump is provided that has a fuel flow-rate regulating valve, on the inlet side. The fuel flow-rate regulating valve includes a housing with a fuel inlet port and a fuel outlet port, a valve mechanism for controlling the flow rate of the fuel from the inlet port to the outlet port, and a regulating mechanism for regulating a backpressure to control the position of a needle valve of the valve mechanism in response to a system pressure, to thereby control the flow rate by controlling the fuel flow through an opening provided in a valve chamber. This arrangement makes it difficult for contamination to accumulate, and also enables a low-cost implementation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a fuel feed pump for internal combustion engines.

2. Background Art

Various types of feed pump are used as fuel supply pumps of vehicles. Conventionally, such pumps use a configuration that allows the maximum flow rate to be changed in order to make the pumps adaptable to a broad range of specifications. Japanese Public Disclosure No. Hei 8-210210, for example, discloses a feed pump used as the supply pump in a common-rail type fuel-injection pump. In the case of the disclosure, a pressure valve is provided in the bypass passage to make it possible to control the amount of fuel being moved. In accordance with this configuration, during normal operation a large quantity of fuel is fed to a high-pressure pump and fuel movement is suppressed at non-injection times. This makes it possible to prevent a large amount of fuel being wastefully circulated between the fuel pump and the fuel tank.

However, this conventional technology uses a check valve that is opened/closed in response to pressure, making it possible for contamination to occur by foreign matter being drawn onto the valve seat during valve operation, so that when the value is open the flow rate tends to be altered by the contamination. For this reason, control of the flow rate has not been very precise. Another problem has been that of the noise and vibration produced by the seating impact each time the valve opens and closes.

SUMMARY OF THE INVENTION

An object of this invention is therefore to provide a fuel feed pump for internal combustion engines that overcomes the aforesaid shortcomings of the prior art.

Another object of the invention is to provide a fuel feed pump for internal combustion engines in which it is difficult for contaminants to accumulate.

Another object of the invention is to provide a fuel feed pump for internal combustion engines that enables the cost to be reduced.

Another object of the invention is to provide a fuel feed pump for internal combustion engines that is highly reliable.

For achieving these objects, the invention provides a fuel feed pump for internal combustion engines having a fuel flow-rate regulating valve on an inlet side, wherein the fuel flow-rate regulating valve comprises a housing having a fuel inlet port and a fuel outlet port, a valve mechanism for controlling a flow rate of fuel from the fuel inlet port to the fuel outlet port, said valve mechanism being equipped in the housing, and a regulating mechanism for regulating a backpressure to regulate a position of a valve element of the valve mechanism in response to a system pressure. The valve element can be a needle valve. The valve mechanism can have a configuration comprising a chamber that operably accommodates the valve element and an opening provided in the chamber that communicates with the fuel inlet port, in which the valve element controls the fuel flow rate by controlling the flow rate of fuel in the opening.

If a needle valve is used as the valve element, the valve mechanism can have a configuration comprising a chamber that operably accommodates the valve element and an opening provided in the chamber that communicates with the fuel inlet port, in which a valve seat formed on an edge portion of the opening and the valve element cooperate to control the flow rate of the fuel.

The regulating mechanism can have a configuration in which means are provided that resiliently urges the valve element in a valve-open direction, and a fuel discharge acts on the valve element to restrain the valve element in the valve-open direction.

The invention will be better understood and other objects and advantages thereof will be more apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Details of an embodiment of the invention will now be described with reference to the drawings.

FIG. 1is a general schematic diagram of an embodiment of the invention.

With reference toFIG. 1, a fuel injection apparatus1is configured as a common rail type fuel injection apparatus in which high-pressure fuel stored in a common rail2is injected into the cylinders (not shown) of an internal combustion engine by injectors3-1to3-N. The common rail2is provided with a pressure regulation valve21for regulating the pressure of the fuel in the common rail2to a prescribed pressure. The injectors3-1to3-N are each provided for a corresponding cylinder, and are operated under the control of an injection control unit (not shown) configured using a microcomputer.

In, theFIG. 1, reference numeral4denotes a reservoir and6a high-pressure pump. Reference numeral7denotes a fuel feed pump7according to this invention, provided as a low-pressure feed pump on the low-pressure side of the high-pressure pump6. Fuel5in the reservoir4is drawn up, via fuel pipe8, by the fuel feed pump7, and delivered as low-pressure fuel from outlet port7A of the fuel feed pump7. The low-pressure fuel is delivered to the high-pressure pump6, via a fuel feed pipe10that is provided with a fuel flow rate control valve9for regulating the flow of fuel to the high-pressure pump6, via suction valves11and12.

In this embodiment, the high-pressure pump6has two high-pressure plungers,61and62, which are driven by cams64and65affixed to a camshaft63that is rotated by a rotational force from an internal combustion engine that is not shown.

The high-pressure plunger61comprises a piston61B housed in a cylinder61A, with the piston61B able to move reciprocally along the axis of the cylinder61A. The reciprocating movement of the piston61B is driven by the rotation of the cam64against tappet61C. Via the suction valve11, low-pressure fuel is supplied to a plunger chamber61D, where it is pressurized by the piston61B. The high-pressure fuel thus obtained is fed into the common rail2via an injection line14that has a check valve13that opens in the direction of the common rail2.

The high-pressure plunger62has the same configuration as the high-pressure plunger61. That is, the high-pressure plunger62comprises a piston62B housed in a cylinder62A, with the piston62B able to move reciprocally along the axis of the cylinder62A, with the reciprocating movement of the piston62B being driven by the rotation of the cam65against tappet62C. Via the suction valve12, low-pressure fuel is supplied to a plunger chamber62D, where it is pressurized by the piston62B, and the high-pressure fuel thus obtained is fed into the common rail2via an injection line16that has a check valve15that opens in the direction of the common rail2.

In order to return to the reservoir4fuel backflow produced by the operation of the fuel flow rate control valve9, a return channel17is provided between the outlet port7A of the fuel feed pump7and the reservoir4. The return channel17has a check valve18that opens in the direction of the reservoir4. The portion of the low-pressure fuel discharged from the feed pump7that does not go to the high-pressure pump6, due to the fuel flow rate control valve9, is returned to the reservoir4via the return channel17.

To improve the non-injection control characteristics of the high-pressure pump6of the fuel injection apparatus1, a return channel19is also provided on the outlet side of the fuel flow rate control valve9. As a result, any fuel leakage from the fuel flow rate control valve9that may occur when the fuel flow rate control valve9is closed during non-injection control of the high-pressure pump6is returned to the reservoir4via a zero delivery orifice20provided in the return channel19.

The feed pump7has a pump body70, and a fuel flow-rate regulating valve80provided on the fuel outlet side of the pump body70.

FIG. 2is a detailed cross-sectional view of the flow-rate regulating valve80. The flow-rate regulating valve80has a housing81, which has an inlet port82through which fuel5from the reservoir4is received via the fuel pipe8, and an outlet port83via which flow-rate-regulated fuel is delivered to the pump body70. The housing81also has a chamber85formed therein that operably accommodates a needle valve84.

A stepped guide rod86is affixed to the rear end of the needle valve84, to be coaxial therewith. A guide-hole87is formed in a chamber85. The guide rod86is movably supported in the guide-hole87by a large-diameter portion86A, so that the guide rod86can move freely along the axis thereof.

The chamber85communicates with the outlet port83via a channel88formed in the housing81. One end of a channel89that extends from the inlet port82opens into the chamber85. In this embodiment, the channel89is formed concentrically with the needle valve84. The opening90of the channel89is formed into a valve seat91.

The needle valve84has a conical tip that tapers down towards the tip, forming a valve mechanism100in which the flow rate of fuel flowing into the inlet port82and out of the outlet port83can be regulated according to the degree by which the tip of the needle valve84is inserted into the opening90.

The needle valve84is urged away from the valve seat91by a compressed coil spring93disposed in a spring chamber92provided behind the guide-hole87.

The housing81has a pressure introduction port94in communication with the spring chamber92. The system pressure of the fuel injection apparatus acts on the pressure introduction port94via a pipe95. In this embodiment, pressure generated in the return line to the reservoir, on the downstream side of the common-rail pressure regulation valve21, is utilized as the system pressure (seeFIG. 1). In this way, the system pressure of the fuel injection apparatus1is introduced into the pressure introduction port94and applied as backpressure to the needle valve84, so that the needle valve84is positioned at a point at which the forces of the system pressure and the compressed coil spring93are in balance. As a result, the degree of opening of the valve mechanism100is set according to the delivery pressure of the fuel.

With the flow-rate regulating valve80thus configured, when a large quantity of fuel is flowing through the flow rate control valve9to the system because not enough fuel is being discharged from the pump body70, the opening of the valve mechanism100increases, increasing the amount of fuel delivered to the pump body70. On the other hand, if a small quantity of fuel is flowing through the flow rate control valve9because there is an overflow of fuel from the pump body70, the opening of the valve mechanism100decreases, reducing the amount of fuel delivered to the pump body70.

As a result, in response to the system pressure, just the required amount of fuel is supplied to the feed pump7, effectively preventing wasteful circulation of fuel between the feed pump7and the reservoir4.

The flow-rate regulating valve80has a regulating mechanism110disposed concentrically with the valve mechanism100. The regulating mechanism110includes the spring chamber92, compressed coil spring93and pressure introduction port94, and is for regulating the backpressure to adjust the position of the needle valve84of the valve mechanism100in accordance with the system pressure. Since the holes are all disposed concentrically, processing is simple, and both processing and assembly can be accomplished at low cost.

Also, since the needle valve84is used to regulate the fuel flow rate, the state of the spacing between the needle valve84and the valve seat91is constantly changing, making it difficult for dirt and other such contaminants to accumulate. There is therefore almost no risk of flow rate control being hindered by contaminants or the like, so the flow rate can be controlled with very high reliability.

Moreover, in accordance with the valve mechanism100shown inFIG. 2, any fuel that might leak after the needle valve84is seated on the valve seat91will always leak towards the fuel inlet.

Thus, the flow-rate regulating valve80is configured so that the fuel flow area can be continuously changed by moving the tapered tip portion of the needle valve84. Since there is no sliding between the needle valve84and the valve seat91, such as in the case of a spool valve, contamination-resistance is improved. As a result, in high-pressure pumps used for high flow-rate Amplified Piston Common Rail System (APCRS) applications, it is possible to use the feed pump7with a variable-throttle function without worrying about contaminants accumulating.

Moreover, ideal opening characteristics can be readily set by changing the shape of the tapered tip of the needle valve84, making the invention superior to the prior art in terms of function and processing.

The above explanation of the invention has been made with respect to its application to the fuel feed pump of a fuel injection apparatus. However, the invention is not limited to the embodiment shown, but may be similarly applied to fuel feed pumps for other purposes, with the same effect.

In accordance with this invention, a fuel feed pump for internal combustion engines is provided that has high reliability with excellent contamination-resistance.