The present invention relates to high pressure fuel supply pumps for gasoline common rail injection systems.
Single piston, cam driven high pressure fuel pumps have become a common solution for generating high pressure fuel in common rail direct injection gasoline engines. It is known in the industry that the pump must incorporate an outlet check valve to prevent pressure bleed back from the rail while the pump is in the intake stroke cycle. It has become an industry requirement to incorporate a pressure relief valve within the pump to protect the entire high pressure system from an unexpected excess pressure caused by a system malfunction. In order to protect the rail and injectors, the pressure relief valve must be in hydraulic communication with the rail, i.e., in parallel with the pump flow. In order to make the parallel hydraulic communication, typical executions have located the outlet check valve and pressure relief valve as separate devices within the pump housing.
The conventional configuration of separate outlet check valve and pressure relief valve within the housing suffers from several disadvantages including high cost, difficulty in pre-testing the sub-assembly, and restrictions on the radial location of the outlet fitting. These disadvantages are overcome with the present invention.
According to an aspect of the present invention, the outlet check valve and the pressure relief valve are contained within a single fitting of the high pressure fuel pump. The advantages include lower system cost, ability to pre-test the function of the outlet check and pressure relief valve prior to assembly into the pump housing, and improved flexibility of outlet fitting radial location.
The disclosed embodiment is directed to a high pressure single piston fuel pump in which a fitting at the housing has flow passages at opposite ends, wherein a first end flow passage is in fluid communication with the pumping chamber and provides an inlet to the discharge check valve and an outlet from the pressure relief valve, and a second end flow passage is in fluid communication with the fuel reservoir and provides an outlet for the discharge check valve and an inlet for the pressure relief valve. Preferably, the fitting assembly is bounded by a cylindrical body having a central bore and a valve seat member is fixed within the bore such the corresponding two valve seats area coaxially aligned.
The seat member has a first internal flow path for discharge flow between the first and second end passages and a distinct second internal flow path for pressure relief flow between the second and the first end passages. A first valve and first valve spring are operatively associated with the first internal flow path and a second valve and second valve spring are operatively associated with the second internal flow path. The first valve is biased with a force corresponding to the fuel discharge opening pressure and the second valve is biased with a force corresponding to the overpressure relief opening pressure.
In one embodiment the valve seat member is substantially centrally fixed within the fitting, having a first flow path obliquely oriented from the bore diameter to a first seat at the axis for discharge flow between the first and second end passages and a second flow path obliquely oriented from the bore diameter to a second seat at the axis for pressure relief flow between the second and the first end passages.
In another embodiment, the first flow path through the seat member is substantially parallel to the bore axis and the second flow path through the seat member is substantially radial.
In another aspect, the invention is directed to the fitting assembly itself, comprising a cylindrical body having a through bore with first and second ends, a valve seat member fixed in the bore and having a first internal flow path operatively associated with a first check valve for controlling flow from the first end to the second end and a second internal flow path operatively associated with a second, coaxially aligned check valve for controlling flow from the second end to the first end.
All flow in each direction is contained within the body, and passes through the same flow passages at both ends of the body.
As represented in
During normal pump operation, the fuel flow follows the arrow path P1 during the pumping phase of the operational cycle. During the charging phase, the outlet check valve 19 closes, preventing any backflow through the fitting into the pumping chamber 10. If a pressure above the set point of the pressure relief ball 22 is reached during the charging phase, the ball will open, allowing backflow to follow the arrow path P2, and into the pumping chamber 10.
It can thus be appreciated that in both embodiments the first, discharge check valve 19 and the second, pressure relief valve 22 are contained within the through bore of a single fitting assembly 17 on (
The unitary valve seat member 18 is substantially centrally fixed within the fitting assembly 17, having a first internal flow path P1′, P1″ to a first seat facing the second end 29, for discharge flow between the first and second end passages 28, 29 and a second internal flow path P2′, P2″ to a second seat facing the first end 28, for pressure relief flow between the second and the first end passages 29, 28. A first valve element 19 is biased against the first seat with a force corresponding to the fuel discharge opening pressure and a second valve element 22 is biased against the second seat with a force corresponding to the overpressure relief opening pressure.
In the embodiment of
The first flow path P1′ enlarges at the axis to a cylinder 31 and the first valve element 19 is a flat plate with a sealing face biased by the spring 20 against the cylinder. The second flow path P2′ enlarges with a taper at the axis and the second valve element 22 is a ball biased against the tapered surface.
Preferably, the first valve element 19 is biased by a coil spring 20 interposed between the first valve element 19 and a first stopper 21 fixed in the bore adjacent the second end 29 of the flow passage, and the second valve element 22 is biased by a second coil spring 24 interposed between the second valve element and a second stopper 25 fixed in the bore adjacent the first end 28 of the flow passage. The first coil spring 20 seats in the first valve element 19 on a side of the plate opposite the sealing face and the second coil spring 24 seats over an axially slidable spring seat 23 having a nose 34 bearing on the ball valve element 22.
As in the embodiment of
In general function, the combination valve assembly could be mounted anywhere between the pumping chamber and common rail, but as a practical matter it should be close enough to the pumping chamber to avoid pumping chamber dead volume, which results in poor efficiency. To achieve many of the advantages discussed in the Summary, the pump embodiment has the valve arrangement within the fitting, and the fitting assembly is preferably affixed at the pump housing. In this context, “affixed at the housing” should be understood as encompassing “affixed to” and “affixed on” the housing. The fitting assembly and check valves can protrude into the confines of the pump housing.
It can be appreciated that in the preferred embodiments, (1) all the flow paths and valves for both functions are entirely within a single bore in a solid body, (2) all the flow in each direction passes through the same unitary valve seat member, which is substantially centrally located in the bore and has distinct coaxial valve seats, and (3) all the flow in each direction passes through the same coaxial, substantially cylindrical flow passages on either axial side of the valve seat member. This combination of features facilities simple testing of both valves before installation at the pump, with only two test connections (i.e., one at each end of the body).