GB2588752A

GB2588752A - Fuel pump assembly

Info

Publication number: GB2588752A
Application number: GB1915185.1A
Authority: GB
Inventors: J Maclane Stephen; J Hutchins Stephen
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2019-10-21
Filing date: 2019-10-21
Publication date: 2021-05-12
Anticipated expiration: 2039-10-21
Also published as: GB2588752B; GB201915185D0

Abstract

A fuel pump assembly, for an i.c. engine, comprises a pump housing 8, 10, 42, a high pressure (HP) pump 4, and a low pressure (LP) pump 6 including a fuel gallery 60 which provides fuel to the HP pump 4. The HP pump 4 comprises a pumping plunger 18 which is driven by a drive arrangement mounted on a pump drive shaft 62, eg a camshaft. The LP pump 6 comprises an input gear 50, eg an outer gear, mounted on an input drive shaft 44 which meshes with an output gear 52, eg an inner (idler) gear, mounted on the HP pump drive shaft 62, so that a gear ratio between the input gear 50 and the output gear 52 determines the ratio between rotation of the input drive shaft 44 and the pumping frequency of the HP pump. A pressurising component 54 may be located between the inner and outer gears 50, 52. The input and output gears 50, 52 may be located within a fuel gallery 60.

Description

FUEL PUMP ASSEMBLY

FIELD OF INVENTION

The invention relates to the field of fuel pump assemblies for internal combustion engines. In particular, the invention relates to a fuel pump assembly and a method of making a fuel pump assembly.

BACKGROUND

Fuel pump assemblies are used in the field of internal combustion engines to pressurise fuel before it is injected into the cylinders of the engine. The fuel is typically pressurised in two stages, with a low pressure pump performing an initial pressurisation of the fuel, before a high pressure pump pressurises the fuel to the pressure required at a common rail, where the fuel is stored before injection. The fuel stored within the common rail is typically stored at a pressure of around 2000 bar, although this value may be higher or lower depending on the requirement of individual engines.

The high pressure pump is often driven by a pumping plunger and it is therefore common for the flow from the low pressure pump to lubricate the high pressure pump whilst also feeding it with fuel to be pressurised. Current high pressure pumps need to be supplied with a constant inlet pressure from the low pressure pump. The inlet pressure is commonly provided by an electrical lift pump in the fuel tank or by a mechanical transfer pump encapsulated within the packaging of the high pressure pump.

In the current state of the art, it is common practice to use a mechanical connection to mount the high pressure pump from either the crank or the camshaft of the engine. In certain situations, there is a benefit to driving the high pressure pump from the crank shaft to achieve a 1:1 pump to engine ratio. For a single plunger pump with two pumping events per revolution, there will be one pumping event for every injection event into a 4 cylinder engine. This ensures that the injector delivers a good pressure and quantity of fuel.

However, in some applications, it is not possible to drive the high pressure pump in such a way. This limits the overall efficiency of the fuel injection system. An alternative pumping configuration that would allow a 1:1 pump to engine ratio would therefore be a desirable advancement in the field.

It is against this background that the invention has been devised.

STATEMENTS OF INVENTION

According to an aspect of the invention, there is provided a fuel pump assembly for an internal combustion engine comprising a low pressure pump including a fuel gallery which provides fuel to a high pressure pump. The high pressure pump comprises a pumping plunger which is driven by a drive arrangement mounted on a pump drive shaft. The low pressure pump comprises an input gear mounted on an input drive shaft and an output gear mounted on the pump drive shaft, the input gear and the output gear defining a gear ratio between them and, wherein the gear ratio determines a ratio between rotation of the input drive shaft and a pumping frequency of the high pressure pump.

The gear ratio between the input gear and the output gear determines the ratio between rotation of the drive shaft and the pumping frequency of the high pressure pump. Therefore, if the pump is employed to supply fuel to a common rail, tailoring the gear ratio of the input and output gears allows tailoring of the rate at which fuel is pumped into the common rail, relative to the speed of rotation of the drive shaft. This tailoring of the rotation speed of the camshaft and the pumping of fuel into the common rail can allow for a 1:1 pump to engine injection ratio, where the pumping of fuel into the common rail occurs at the same time as fuel is injected into the cylinders of the engine. When considering a single plunger pump, with two pumping events per revolution, this gives 1 pumping event for every injection evening on a four cylinder engine, which has benefits for the efficiency of performance.

Depending on the number of cylinders in the engine, and the form of the cam, different input/output gear ratios will be required to enable a 1:1 pump to engine injection ratio. For example, an idler gear/rotor gear ratio of 2:1 or 1:2 may be most suitable to achieve this aim, depending on the number of cylinders in the engine. This allows the invention to be utilised with a variety of engine types without the desired end effect being compromised.

The input gear may form an outer gear which is radially outward of the output gear which may form an inner gear. A pressurising component may be located between the input and output gears. The input and output gears may be located, at least in part, within a fuel gallery. The fuel gallery may communicate with an inlet drilling provided in a closure plate of the pump housing to allow fuel to flow into the fuel gallery.

The fuel pump assembly may comprise a first bearing for mounting the input drive shaft within the low pressure pump housing. In addition, or alternatively a bearing (a second bearing) is provided for mounting a front end of the pump drive shaft within the low pressure pump housing. In addition, or alternatively, a third bearing is located at a rear end of the pump drive shaft for mounting the rear end of the pump drive shaft within the low pressure pump housing.

The second bearing may be provided with an annular groove for receiving fuel from the fuel gallery.

The first bearing may support the drive shaft within a closure plate of the pump housing.

The fuel pump assembly may comprise the high pressure pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which; Figure 1 is a cross-sectional view of a pump assembly according to an embodiment of the invention; Figure 2 shows an embodiment of a low pressure pump; Figure 3 is a perspective view of the low pressure pump of Figure 2, and Figure 4 is an alternative perspective view of the low pressure pump of Figures 2 and 3.

SPECIFIC DESCRIPTION

Figure 1 shows an embodiment of a fuel pump assembly 2. The fuel pump assembly 2 comprises a high pressure pump, referred to general as 4 and comprising a main pump housing 8, and a low pressure pump, referred to generally as 6 The high pressure pump 4 comprises a pump head 10, mounted on the main pump housing 8, which includes a substantially tubular turret 12. The turret 12 extends downwardly (in the orientation shown) from the pump head 10, the pump head 10 being provided with a cylindrical plunger bore 16, which extends through the turret 12 and beyond into the main pump housing 8. The plunger bore 16 is configured to receive a plunger 18, the lower end of which extends beyond the open end of the plunger bore in from the turret 12.

The plunger 18 is moveable between a bottom-dead-centre positon (hereinafter, "BDC position") and a top-dead-centre position (hereinafter, "TDC position"), defining a pump stroke, and between the TDC position and the BDC positon, defining a return stroke. A pump stroke followed by a return stroke defines a pumping cycle for the plunger 18 and pump.

It should be understood that references to top and bottom, and other such directional or relative references, including references to upper and lower portions of components, are made in relation to the orientations of the components shown in Figure 1 and are not intended to be limiting.

A spring plate 20 forms a collar around the plunger 18 in a lower region of the plunger 18 and is affixed to the plunger 18 such that their respective motions are coupled together. The spring plate 20 defines an abutment surface for one end of a plunger return spring 22 ("return spring" hereinafter). The other end of the return spring 22 engages an under surface of the pump head 10.

A pump chamber 24 is defined by a combination of the upper end of the plunger 18 and the plunger bore 16; its volume decreases and increases during the pump and return strokes respectively. The pump chamber 24 communicates with inlet and outlet valve assemblies 26, 28 via internal inlet and outlet passages respectively 30, 32. The inlet valve assembly 26 is used to control flow of the fuel from a high pressure pump inlet 34 through to the pump chamber 24 and the outlet valve assembly is used to control the flow of fuel from the pump chamber 24 through to a high pressure pump outlet 36 and to a common rail (not shown). Each valve assembly 26, 28 includes a spring, which acts to close the valve assembly to prevent the passage of fuel therethrough.

Figure 1 also shows a cross sectional view of the low pressure pump 6, which takes the form of a geared pump. The low pressure pump 6 comprises a low pressure pump housing part (housing' hereinafter) in the form of a closure plate 42 through which an input drive shaft 44 ("drive shaft" hereinafter) extends. The main pump housing 8, the pump head 10 and the closure plate 42 therefore together form the pump housing for the assembly. The drive shaft 44 is mounted on the closure plate 42 via a first bearing 46 located towards a front end 48 of the fuel pump assembly. The low pressure pump 6 further comprises an outer (rotor) gear 50, coupled to, and driven by, the drive shaft 44, an inner (idler) gear 52 and a pressurising component 54, which together define a gear system. The outer gear therefore forms the 'input' gear and the inner gear forms the 'output' gear. The inner (idler) gear 52 is coupled to a camshaft 62.

Referring also to Figures 2, 3 and 4, the low pressure pump 6 includes a fuel inlet 56, defined by an inlet drilling 58 which is provided in the closure plate 42. The fuel inlet 56 opens into a fuel gallery 60, within which the rotor gear 50, idler gear 52 and the pressurising component 54 are housed. The idler gear 52 in the embodiment shown in the Figures is of smaller diameter than the rotor gear 50 and has fewer teeth. The idler gear 52 and pressurising component 54 are both positioned radially within the outer rotor gear 50, the idler gear 52 being positioned such that it's radially outwardly extending teeth mesh with the radially inwardly extending teeth of the rotor gear 50. The pressurising component 54 is broadly kidney-shaped and is positioned between the rotor and idler gears 50, 52 such that there are small clearances between each side of the pressurising component 54 and the rotor gear 50 and idler gear 52 respectively. In examples, the pressurising component is fixed to the closure plate, for example via a face of the pressurising component, and may either be machined as part of the closure plate or bolted or otherwise attached thereto.

The idler gear 52 is coupled to a pump drive shaft 62 in the form of a camshaft to which is mounted a double-lobed cam 64. The camshaft 62 and cam 64 are housed within a cam box 66 defined within the main pump housing 8. A shoe 68 and engages with the surface of the cam 64 and is driven by the cam 64 as it rotates with the camshaft 62, in use. The camshaft 62 is co-axial with the idler gear 52 and consequently is parallel with, but displaced from, the axis of the drive shaft 44 and the rotor gear 50, as best seen in Figure 4.

The camshaft 62 is mounted on a second (middle) bearing 70, positioned at a front end 72 of the camshaft 62 (identified in Figure 1) and located axially between the idler gear 52 and the cam box 66, as can be seen in Figures 1 and 3. A third bearing 74 is also provided to mount a rear end 76 of the camshaft 62 within the main pump housing 8.

On a face of the middle bearing 70 facing toward the rotor and idler gears 50, 52 is defined a first groove 71a that allows fluidic communication of fuel, in use, between the fuel gallery and a first region 80 of space between the rotor gear 50 and idler gear 52 nearest a first end 82 of the pressurising component 54. On the same face of the middle bearing 70 is also defined a second groove 71b that is in fluidic communication with a second region 84 of space between the rotor gear 50 and idler gear 52 nearest a second end 86 of the pressurising component 54.

The second groove 71b is also in fluidic communication, in use, with a bearing drilling (not shown) that passes through the middle bearing 70. The middle bearing 70 also includes a third groove 78 that is in fluidic communication with both the bearing drilling and the cam box 66, in use. To ensure that the middle bearing 70 and third bearing 74 are co-axial, they must be machined in the same operation with the same tool as each other. The first and second grooves 71a, 71b, are both shown schematically in Figure 1, although their exact location around the middle bearing may differ from that shown in Figure 1 depending on the exact configuration of the low pressure pump 6.

It should be noted that to effectively mount the middle bearing 70, a portion of the main pump housing 8 must be removed when compared to configurations common to the state of the art. Removal of material from the main pump housing 8 must be done carefully to ensure adequate structure, rigidity and support is provided for the pump components housed within.

In use, rotation of the drive shaft 44 drives rotation of the rotor gear 50, which in turn drives rotation of the idler gear 52 and, hence, the camshaft 62. The rotation of the camshaft 62 results in rotation of the cam 64 and roller, which causes the shoe 68 to ride over the surface of the cam 64. The shoe 68 drives the footplate at the base of the plunger 18, driving the plunger 18 to reciprocate within the plunger bore 16. It should be noted that the positioning of the idler gear 52 radially within the rotor gear 50 leads to the camshaft 62 rotating in the same direction as the drive shaft 44.

Fuel enters the low pressure pump 6 at the fuel inlet 56 and subsequently enters the fuel gallery 60. Referring specifically to Figure 3, the fuel enters the gear system in the first region 80 of space between the rotor gear 50 and idler gear 52 nearest a first end 82 of the pressurising component 54 via the first groove 71a of the second bearing 70. The rotating action of the rotor and idler gears 50, 52 forces the fuel past the pressurising component 54 through two channels 55, thereby slightly raising the pressure of the fuel in the channels. In the embodiment shown in the Figures, the positioning of the pressurising component 54 would necessitate the drive shaft 44 (and therefore the camshaft 62) to rotate anti-clockwise with respect to the view seen in Figures 2 to 4.

From the channels, the fuel flows into a second region 84 of space between the rotor gear 50 and idler gear 52 nearest a second end 86 of the pressurising component 54 and subsequently into the second groove 71b, bearing drilling and third groove 78 of the second bearing 70. The fuel then flows out of the third groove 78 into the cam box 66. Fuel then flows through a vent (not shown) drilled at the back of the cam box 66 to the high pressure pump inlet 34, as is known in the art.

Fuel is then supplied to the high pressure pump 4 through the high pressure pump inlet 34. With the plunger 18 at the TDC position fuel is prevented from reaching the internal inlet passage 30 by the closed inlet valve assembly 26. The fuel is supplied at a pressure of around 3 bar (300 kPa), having been pressurised slightly by the low pressure pump 6. The return spring 22 provides a return force that acts on the spring plate 20, and hence on the plunger 18, to effect the return stroke and move the plunger 18 from the TDC position towards the BDC position.

This increases the volume of the pump chamber 24, decreasing the pressure within it and establishing a pressure drop across the inlet valve assembly 26. This pressure drop allows the inlet valve assembly 26 to open against the force of the inlet valve spring and fuel enters the pump chamber 24 until the pressure across the inlet valve assembly 26 equalises, causing it to close. This typically occurs just after the plunger 18 reaches the BDC position.

Once the plunger 18 reaches the BDC position, it begins the pump stroke under the influence of the cam 64 and shoe 68 to pressurise the fuel in the pump chamber 24. The rotation of the camshaft 62, in combination with the force provided by the return spring 22, therefore drives the reciprocating motion of the plunger 18.

During the pump stroke, the fuel in the pump chamber 24 is compressed to a pressure exceeding the pressure of the fuel held in the internal outlet passage 32, which substantially equals the pressure in the common rail. This pressure is in the region of at least 200 bar (20 MPa) and can be as high as 3000 bar (300 MPa). A pressure drop is created across the outlet valve assembly 28, allowing it to open against the force of the outlet valve spring and fuel to exit the pump chamber 24 and flow into the common rail fuel volume via the high pressure pump outlet 36. As the plunger 18 reaches the TDC position, the pressure across the outlet valve assembly 28 equalises, causing it to close.

In the embodiment shown in the Figures, the idler gear 52 is positioned radially within the rotor gear 50, the rotor gear 50 having sixteen teeth and the idler gear 52 having ten teeth. The idler gear 52 and camshaft 62 are therefore driven at a faster speed of rotation than the rotor gear 50 and the drive shaft 44. Crucially, this gear ratio may be altered to determine the ratio of speeds of rotation of the drive shaft 44 and the camshaft 62. In certain embodiments, the idler gear 52 may even have more teeth than the rotor gear 50, causing the camshaft 62 to be driven at a slower speed of rotation than the drive shaft 44. This would require the rotor gear 50 to be positioned within the idler gear 52 within the fuel gallery 60, in contrast to the arrangement shown in the Figures.

Since rotation of the camshaft 62 results in the plunger 18 being driven to reciprocate within the plunger bore, and therefore the pumping of fuel through the outlet 36 into the common rail, the gear ratio between the rotor and idler gears 50, 52 determines the ratio between rotation of the drive shaft 44 and the pumping frequency of the high pressure pump 4. Therefore, tailoring the gear ratio of the rotor and idler gears 50, 52 allows tailoring of the rate at which fuel is pumped into the common rail, relative to the speed of rotation of the drive shaft 44.

This tailoring of the rotation speed of the camshaft 62 and the pumping of fuel into the common rail can allow for a 1:1 pump to engine injection ratio, where the pumping of fuel into the common rail occurs at the same time as fuel is injected into the cylinders of the engine. When considering a single plunger pump (such as that shown in Figure 1), with two pumping events per revolution, this gives 1 pumping event for every injection evening on a four cylinder engine, which has benefits for the efficiency of performance.

Depending on the number of cylinders in the engine, and the form of the cam 64, different idler/rotor gear ratios will be required to enable a 1:1 pump to engine injection ratio. For example, an idler gear/rotor gear ratio of 2:1 or 1:2 may be most suitable to achieve this aim, depending on the number of cylinders in the engine. This allows the invention to be utilised with a variety of engine types without the desired end effect being compromised.

It should be noted that, although achieving a 1:1 pump to engine injection ratio is an aim of the embodiments shown and discussed herein, the ability to tailor the ratio of the speeds of rotation of the drive shaft 44 and camshaft 62 means that the invention would be suitable to achieve any desired ratio of the two speeds of rotation, depending on the number of cylinders in the engine.

It should also be noted that it would be appreciated by the skilled person that the invention may take several forms that differ from the embodiments shown in the Figures and still fall within the scope of the appended claims. For example, the drive arrangement on the camshaft 62 may differ from that shown in the Figures, incorporating rollers, shoes, tappets for example, to drive the plunger, and the cam arrangement may also have a different number of lobes. The exact configuration of the high pressure pump 4 may also take a different form. It should also be noted that alternative configurations and positions of the pressurising component 54 to that shown in the Figures may necessitate the drive shaft 44 to rotate clockwise, as opposed to anti-clockwise.

References used: 2 -fuel pump assembly 4 -high pressure pump 6 -low pressure pump 8 -main housing 10-high pressure pump housing 12-turret 16-plunger bore 18-plunger 20-spring plate 22-plunger return spring 24-pump chamber 26-inlet valve assembly 28-outlet valve assembly 30-inlet passage 32 -outlet passage 34-high pressure pump inlet 36-high pressure pump outlet 42 -closure plate 44-input drive shaft 46-first bearing 48-front end of the fuel pump assembly 50-rotor gear 52-idler gear 54-pressurising component 55-channels 56-fuel inlet 58-inlet drilling 60-fuel gallery 62 -pump drive shaft/camshaft 64 -cam 66 -cam box 68 -shoe 70-second bearing 71a -first groove 71b -second groove 72-front end of the pump drive shaft 74-third bearing 76-rear end of the pump drive shaft 78-third groove 80-first region 82-first end of the pressurising component 84-second end of the pressurising component

Claims

CLAIMS1. A fuel pump assembly (2) for an internal combustion engine, the fuel pump assembly (2) comprising; a low pressure pump (6) including a fuel gallery (60) which provides fuel to a high pressure pump (4) comprising a pumping plunger (18) which is driven by a drive arrangement mounted on a pump drive shaft (62), and wherein the low pressure pump (6) comprises an input gear (50) mounted on an input drive shaft (44) and an output gear (52) mounted on the pump drive shaft (62), the input gear (50) and the output gear (52) defining a gear ratio between them and, wherein the gear ratio determines a ratio between rotation of the input drive shaft (44) and a pumping frequency of the high pressure pump (4).
2. The fuel pump assembly (2) of Claim 1, wherein the input gear (50) forms an outer gear which is radially outward of the output gear (52) which forms an inner gear.
3. The fuel pump assembly (2) of Claim 1 or Claim 2, wherein a pressurising component (54) is located between the input gear (50) and output gear (52).
4. The fuel pump assembly (2) of any of Claims 1 to 3, wherein the input gear (50) and the output gear (52) are located, at least in part, within a fuel gallery (60).
5. The fuel pump assembly (2) as claimed in Claim 4, wherein the fuel gallery (60) communicates with an inlet drilling (58) provided in a closure plate (42) of the pump housing (40) to allow fuel to flow into the fuel gallery (60).
6. The fuel pump assembly (2) as claimed in any of Claims 1 to 5, comprising a first bearing (46) for mounting the input drive shaft (44) within the pump housing (40), a second bearing (70) for mounting a front end (72) of the pump drive shaft (62) within the low pressure pump housing (40), and a third bearing (76) located at a rear end (76) of the pump drive shaft (62) for mounting the rear end (76) of the pump drive shaft (62) within the low pressure pump housing (40).
7. The fuel pump assembly (2) as claimed in Claim 6, wherein the second bearing (70) is provided with an annular groove (78) for receiving fuel from the fuel gallery (60).
8. The fuel pump assembly as claimed in Claim 6 or Claim 7, wherein the first bearing (46) supports the drive shaft (44) within a closure plate (42) of the pump housing
9. The fuel pump assembly as claimed in any preceding claim, comprising the high pressure pump (4).