GB2548832A

GB2548832A - High pressure fuel pump arrangement

Info

Publication number: GB2548832A
Application number: GB1605171.6A
Authority: GB
Inventors: Fuller Trevor; James Lloyd
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2016-03-29
Filing date: 2016-03-29
Publication date: 2017-10-04
Also published as: GB201605171D0

Abstract

A fuel injection system including a high pressure fuel pump featuring a cam driven plunger 10 adapted to pressurize fuel in a pumping chamber 11. The pumping chamber includes a fuel inlet fluidly connected to a fuel supply line, and the cam is located in a cambox. A first flow path fluidly connects said fuel supply line to said cambox, and includes a first regulator valve 20. A second flow path connects the fuel supply line to the pumping chamber. The first regulator valve allows the system to maintain a constant pressure within the cambox. The system may also include a second regulator valve and a metering valve 13 in the second flow path.

Description

High pressure Fuel Pump Arrangement

Field of the Invention

This disclosure relates to fuel systems for engines and has particular application, but not exclusively, to high pressure fuel pump systems which utilise cam driven piston pumps.

Background to the Invention,

In order to supply fuel under high pressure to a number of injectors, typically a high pressure pump is used in modem vehicle engines to supply high pressure fuel such as Diesel to a common rail which supplies the fuel injectors individually with high pressure fuel.

In a typical fuel system, fuel is drawn from a fuel tank by a low pressure pump, supplying fuel to a high pressure pump. Typically these high pressure (e g. Diesel) pumps are piston (plunger type) pumps driven by a cam. So a cam mechanism (such as an eccentric cam follower system) is used to drive a reciprocating plunger or piston to supply fuel to a pump head (e.g. head cap portion) and then to the common rail/injectors.

Typically the cam is housed in a space referred to commonly as the “cambox” which is pressurized. An inlet metering valve is located between the cambox/plunger pump arrangement and the hydraulic head and high pressure supply to the common rail.

Inlet valve instability results in significant variation in high pressure flow between pumping events. This manifests as a (common) rail pressure error. The cause of inlet valve instability is non-periodic head cap pressure due to high pressure amplitudes in the high pressure pump cambox including periods of negative pressure.

It is an object of the invention to overcome these problems and to provide an arrangement to improve head cap pressure stability.

Statement of the Invention

In one aspect is provided a system adapted to provide high pressure fuel to one or more fuel injectors, said system including a high pressure fuel pump comprising a cam driven plunger adapted to pressurize fuel in a pumping chamber, said pumping chamber including a fuel inlet fluidly connected to a fuel supply line, and wherein said cam is located in a cambox volume, wherein said system includes a first flow path fluidly connecting said fuel supply line to said cambox volume, said first flow path including a first regulator valve, and a second flow path connecting said fuel supply line to said pumping chamber.

Said second flow path may include an inlet metering valve adapted to regulate flow from said fuel supply line to said pumping chamber.

Said second flow path may include a second regulator valve located between fuel supply line/ inlet metering valve and said pumping chamber.

Said first regulator valve may be adapted to open so as to allow flow of fuel into said cambox at a certain pressure.

Said first regulator valve is integral with said cambox or cambox housing.

Said fuel supply line may include a pump, adapted to pump fuel from a fuel tank.

Brief Description of the Drawings

The invention will now be described by way of example and with reference to the following figures of which :

Figure 1 shows a schematic diagram of components and flow circuitry in a prior art system used to supply high pressure fuel.

Figure 2 shows a partial section of the head cap and inlet valve arrangement of a high pressure pump.

Figure 3 a shows volumetric efficiency against cam speed for different inlet pipe length at 4 bar inlet pressure.

Figure 3b shows rail pressure against cam speed at different loads.

Figure 4 shows a schematic diagram of components and flow circuitry used to supply high pressure fuel according to one example.

Figure 5 shows a plot of cambox speed and pressure plots of the prior art with annotations on the right to explaining the effects of arrangement according to examples.

Detailed Description

Figure 1 shows a prior art system 1 used to supply (e.g. Diesel) fuel to appropriate engine components such as a common rail or fuel accumulator volume 2, for supplying fuel to fuel injectors 3. Fuel is pumped from a tank 4 by a low pressure pump 5 such as vane pump to a high pressure pump/pump system 6. Typically the high pressure pump/pump system comprises a cam driven piston/plunger type pump. The cam may be driven by belt or chain means form the engine camshaft/crankshaft. Front and rear bearings with respect to the pump camshaft are show as reference numerals 8 and 9 respectively. The cam mechanism is usually located in a volume referred to as a cambox 7. This cambox is supplied with low pressure fuel at typically 4 bar from the low pressure pump. The cam acts to drive a piston 10 to pressurise the fuel in a pumping/pressure chamber 11 to provide high pressure fuel to the common rail/injectors. The cam is driven by shaft means with front and rear bearings. There is provided lubrication flow paths 12 for these bearings. Low pressure fuel is supplied to the pumping chamber from the cambox via an inlet metering valve 13 and a head cap inlet valve 14. A backflow/retum path 15 is provided from the injectors and the common rail to the tank as shown.

Figure 2 shows a schematic showing a portion of the high pressure pump system showing the pumping chamber, inlet head (cap) valve 14, head cap volume 15 and head cap inlet valve spring 16. The head cap volume is fed with fuel the rate of which is controlled by the IMV. Outlet valve assembly is shown by reference numeral 17. The inlet valve opening and movement is controlled by the pressure difference across the valve - (the head cap volume to pumping chamber) inlet valve spring preload and rate. In a steady state operating condition, both the inlet valve movement and head cap pressure should be periodic with little variation in pumping event.

However there are issues of (head cap) inlet valve/head cap pressure instability which causes rail pressure instability due to variable delivered quantities of fuel from pumping event to pumping event. In other there are oscillations in pressure due to cambox pressure fluctuations which include periods of negative pressure under specific operating conditions.

Figure 3a shows volumetric efficiency against cam speed for different inlet pipe length at 4 bar inlet pressure. Figure 3b shows rail pressure against cam speed at different loads. As can be seen there are pressure spikes.

Figure 4 shows a diagram of a fuel supply system for an engine according to one example. Specifically the figure shows flow circuitry similar to figure 1; like components have the same reference numerals. In the system, a regulator valve 20 is located between the low pressure supply and the cambox volume.

There is also a connection from the low side pressure side of this inlet connector valve to the inlet metering valve i.e. from a point in the low pressure supply to the high pressure pump and the IMV. So effectively there is a first flow path 21 fluidly connecting said fuel supply line to said cambox volume said first flow path including the regulator valve 20, and a second flow path 22 connecting fuel supply line to said pumping chamber. The valve 20 is a pressure control (i.e. regulator) valve and may be formed in adjacent or integral with the cambox and in this case would be considered an inlet connector integrated valve. The valve prevents high pressure in the head cap side.

Figure 5 shows plots of speed of the cam-drive and pressure in the cambox of the prior art (e.g. figure 1) and the boxes on the right hand side of the figure indicate how the invention reduces the problems of such pressure spikes. The mean cambox pressure is about 4 bar. When the cambox pressure is greater than a nominal or set level e.g. 4 bar the inlet connector integrated valve closes. When the cambox pressure is less than the nominal or set level e.g. 4 bar, the inlet connector integrated valve closes. In this way the (inlet connector integrated valve) shields the head cap from high amplitude pressure oscillations which can result in inlet valve instability and also, shielding of the inlet line form pressure spikes which can result in e.g. filter leakage.

Claims

1. A system adapted to provide high pressure fuel to one or more fuel injectors, said system including a high pressure fuel pump comprising a cam driven plunger adapted to pressurize fuel in a pumping chamber, said pumping chamber including a fuel inlet fluidly connected to a fuel supply line, and wherein said cam is located in a cambox volume, wherein said system includes a first flow path fluidly connecting said fuel supply line to said cambox volume, said first flow path including a first regulator valve, and a second flow path connecting said fuel supply line to said pumping chamber.

2. A system as claimed in claim 1 wherein said second flow path includes an inlet metering valve adapted to regulate flow from said fuel supply line to said pumping chamber.

3. A system as claimed in claim 1 wherein said second flow path includes a second regulator valve located between fuel supply line/ inlet metering valve and said pumping chamber.

4. A system as claimed in claims 1 to 3 wherein said first regulator valve is adapted to open so as to allow flow of fuel into said cambox at a certain pressure.

5. A system as claimed in claims 1 to 4 wherein first regulator valve is integral with said cambox or cambox housing.

6. A system as claimed in any previous claim wherein said fuel supply line includes a pump, adapted to pump fuel from a fuel tank.