GB2551338A

GB2551338A - High pressure fuel pump circuit

Info

Publication number: GB2551338A
Application number: GB1610249.3A
Authority: GB
Inventors: Serenas Karolis
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2016-06-13
Filing date: 2016-06-13
Publication date: 2017-12-20
Also published as: GB201610249D0

Abstract

A fuel pump system suitable for a vehicle engine includes a cam driven piston pump (figure 1, 4) which comprises a pump housing/cambox 9, a flow path provided to allow flow from the cambox directly to a return circuit 17 which incorporates a conduit portion 19 having an aspect ratio of more than 70. The conduit portion may be located within the return circuit and may be part of or integral with the pump and / or be provided as a drilling or bore. The conduit portion preferable is an insert element and may be press fitted to the pump, pump housing or return circuit. The insert element is preferably adapted with means to locate or insert via a sealing means, which may be o rings. The aims is to reduce the effects of cold conditions whereby high viscosity of fuels produce a large amount of flow across the pump and increased fuel filter waxing.

Description

HIGH PRESSURE FUEL PUMP CIRCUIT Field of the Invention

This disclosure relates to high pressure fuel pumps and systems and has particular application to high pressure fuel (e.g. Diesel) pumps comprising a cam driven piston (plunger) adapted to pressurise fuel, said pumps including an internal pump housing (cambox).

Background to the Invention

In general high pressure fuel pumps (e.g. those used in Diesel passenger cars) are driven by the engine. In the fuel pump, a driveshaft with a cam profile is normally used to convert the rotational motion to a reciprocating motion. A reciprocating pumping element (plunger) within a cylinder bore then compresses the fuel to pressurise fuel in a fuel chamber which is then pumped out e.g. to a common rail via an outlet valve. The pumping chamber is re-filled with fuel through an inlet valve on the downward stroke of the pumping element.

There are different types of hydraulic circuits used to deliver and meter fuel from the inlet of the pump to the pumping chamber. The drivetrain housing (cambox) normally contains fuel at inlet pressure and any undelivered (unmetered) fuel is evacuated across the bearings to provide lubrication. To meet the lubrication needs of both the bearings and the drivetrain, an orifice or a regulator is used to increase the permeability of the pump. This is of high advantage at elevated fuel temperatures as hot fuel gets evacuated faster due to the increased flow. To meet the flow budgets of the vehicle electric lift pumps (ELP), the orifice can be of different diameters and the regulator can have different opening pressures or dimensions.

However during cold conditions and high viscosity of fuels, both of these devices are insensitive to viscosity and produce a large amount of flow across the pump. What is more, fuel filter waxing is a known issue. It can cause problems starting the engine or problems regarding being able to maintain engine idling.

It is an object of the invention to overcome such problems.

Statement of the Invention

In one aspect is provided a fuel pump system for a vehicle engine including a cam driven piston pump, said pump including a pump housing/cambox, said system including flow path provided to allow flow from said cambox directly to a return circuit, said flow path including a conduit portion, said conduit portion having an aspect ratio of more than 70.

Said conduit portion may be located in the return circuit

Said conduit portion may be provided as part of, or integral with, the pump.

Said conduit portion may be provided as a drilling or bore.

Said conduit portion may be provided as an insert element adapted to be inserted or located into the pump, pump housing, or return circuit.

Said insert element may be press-fitted to said pump, pump housing or return circuit.

Said insert element may be adapted with means to locate or insert said element into said pump, pump housing or return circuit via sealing means.

Said sealing means may include O rings or means to locate O rings.

Brief Description of Drawings

Figure 1 shows a schematic diagram of a fuel supply system for an engine such as a vehicle Diesel engine;

Figures 2 and 3 shows schematic diagrams of a flow circuits of prior art high pressure pumping systems;

Figure 4 shows a schematic diagram of a flow circuits of a according to one example;

Figure 5a and b show designs of the viscous drilling or conduit element;

Figures 6 and 7 show and compare simulated results for prior art design and an example of the invention.

Prior Art

Figure 1 shows a schematic diagram of a fuel supply system for an engine such as a vehicle Diesel engine. Fuel is provided from a fuel tank 1 by a low pressure (e g. electric lift) pump 2 via filter 3 to a high pressure pump 4 e.g. as described above. The high pressure pump pressurises fuel to supply one or more fuel injectors 5 via a common rail 6. Typically the common rail includes a high pressure valve 7.

Figure 2 shows schematic diagram of a flow circuit of a prior art high pressure fuel pump system for a vehicle engine. The cambox (pump housing) of a high pressure pump is shown by reference numeral 9. The lift pump feed flow is shown by reference numeral 10. Flow from the cam box space enters an inlet metering valve 11 where it is pressurised by the pumping element (plunger in a pumping chamber, represented schematically by block 12) where pressurised fuel exits to the fuel rail or directly to fuel injectors; so a high pressure outlet. Reference numerals 13 and 14 represent the front and rear bearings of the pump respectively; thus flow is provided and exits via return flow paths 15 to provide lubrication of the bearings. An orifice represented as 16 is shown where flow is from the cambox volume to the tank via return circuit 17.

Figure 3 shows another design of prior art flow circuit which is identical to figure 2 except rather than an orifice 16, a low pressure regulator 18 is provided.

Description of the Invention

Some vehicle Low Pressure (LP) systems can divert pressurised fuel from the rail into the tank fuel filter. High Pressure Valve (HPV) (see figure 1) leakage is used for controlled temperature rise in order to prevent or reverse filer waxing .

The problem of cold start and engine stalling is solved in one example of the invention by a the use of a high aspect ratio conduit element (e.g. viscous drilling) positioned in the low pressure circuit of the high pressure fuel pump. Thus the prior art orifice / low pressure regulator is replaced with a drilling or conduit element 19 shown schematically in figure 4. Again the figure is otherwise identical to figures 2 and 3. Preferably the drilling or conduit element has a high aspect ratio ; greater than 35, preferably greater than 50 and preferably greater than 70.

The flow through the drilling (conduit element) will have a relationship with fuel viscosity and at cold temperatures will limit the pump return flow (compared to an orifice or a regulator). As a consequence more fuel will be delivered to the high pressure circuit. This fuel will then be injected to the engine cylinders providing the necessary amount to maintain combustion without engine stall. If the vehicle system uses HPV leakage to heat and de-wax the fuel filter -this type of low pressure circuit in the pump will have the highest benefit on vehicle.

Figure 5a and b show designs of the viscous drilling or conduit element. In figure 5a is shown an element suitable for press fitting (to the cambox/integral with the high pressure pump), and figure 5b shows an element suitable for appropriate insertion (e.g. into the cambox housing ) via sealing via e,g. O rings, /internal diameter). This is preferably greater than 35, preferably greater than 50, preferably greater than 70, and preferably at least 100.

Figures 6 and 7 show and compare simulated results for a conduit (e.g. drilling) having an aspect ratio of 100 compared to a low pressure regulator and an 00.6mm orifice.

Figure 6a b and c compares results and shows total return flow as a function of inlet pressure at different temperatures, and figure 7a,b,c, and d shows inlet pressure against return flow on an HP pump at different temperatures.

The conduit element may be manufactured form injection moulded plastic - with a pin in place to manufacture the high aspect ratio ‘drilling’. The bore can then be polished to achieve a required surface finish; the provision of such a drilling or conduit element from plastic provides cheaper manufacture.

Examples provide a number of advantages over the prior art. The invention provides for minimising number of components (compared to regulator). No filter is required, preferably for this the -the drilling diameter provided is > 0 0.6 mm.

Examples provide also cold start benefits. Higher pressure retention in the HP pump allowing more HP flow, resulting in faster filter de-wax and less risk of stalling. Aspects provide enhanced durability (drivetrain) and minimise minimum cambox pressure. There are no disadvantages at high temperature compared to an orifice - bearing cooling flow not compromised. The invention also allows reverse flushing.

Claims

1. A fuel pump system for a vehicle engine including a cam driven piston pump (6), said pump including a pump housing/cambox (9) , said system including flow path provided to allow flow from said cambox directly to a return circuit (17), said flow path including a conduit portion (19), said conduit portion having an aspect ratio of more than 70.

2. A system as claimed in claim 1 wherein said conduit portion (19) is located in the return circuit (17).

3. A system as claimed in claim 1 wherein said conduit portion(19) is provided as part of, or integral with, the pump (6).

4. A system as claimed in claims 1 to 3 where said a conduit portion (19) is provided as a drilling or bore.

5. A system as claim in claims 1 to 4 wherein said conduit portion (19) is provided as an insert element adapted to be inserted or located into the pump, pump housing, or return circuit.

6. A system as claimed in claims 1 to 5 wherein said insert element is press-fitted to said pump, pump housing or return circuit.

7. A system as claimed in claims 1 to 6 wherein said insert element is adapted with means to locate or insert said element into said pump, pump housing or return circuit via sealing means.

8. A system as claimed in claim 7 wherein said sealing means includes O rings or means to locate O rings.