WO2016184797A1

WO2016184797A1 - Pump assembly for a fuel injection system

Info

Publication number: WO2016184797A1
Application number: PCT/EP2016/060815
Authority: WO
Inventors: James McHattie
Original assignee: Delphi International Operations Luxembourg S.À R.L.
Priority date: 2015-05-18
Filing date: 2016-05-13
Publication date: 2016-11-24
Also published as: GB201508464D0; EP3298264A1

Abstract

A pump assembly for delivering high pressure fuel to a fuel injection system comprises: at least one pumping unit having an associated pumping element; a housing (12) defining a chamber (20) for a lubricating fluid provided through a fluid inlet (54); and a drive shaft (14) rotatably mounted in the housing, the drive shaft being rotatable about its longitudinal axis to actuate, by a cam section (40) thereof, the pumping element of the at least one pumping unit, the drive shaft comprising a radial flange (50) protruding in said chamber (20). At least one collecting channel (58) is provided in the flange (50), the collecting channel (58) having an outer end (60) opening into the chamber (20) at the outer periphery of the flange and an inner end (62) in fluid communication with a central channel (64) in the drive shaft. The central channel (64) extends longitudinally in the drive shaft (14) and has an outlet (66) in the vicinity of a fluid outlet (56) of the chamber, whereby the collecting channel (58) and central channel (64) form a back-leak flow path in said drive shaft (14).

Description

PUMP ASSEMBLY FOR A FUEL INJECTION SYSTEM

FIELD OF THE INVENTION

The present invention generally relates to a pump assembly, in particular a pump assembly suitable for high pressure fuel supply in a fuel injection system.

BACKGROUND OF THE INVENTION

As it is well known in the art, a fuel injection system of a diesel engine conventionally comprises a high pressure fuel pump that receives a fuel flow from the fuel tank and delivers high pressure fuel to the common rail, which in turn supplies the fuel to the fuel injectors.

So-called radial piston pumps are often used as high pressure fuel pumps. They generally comprise a plurality of pumping units disposed radially about a rotating driveshaft with a cam portion. The cam portion is used to drive the pumping unit components which, together with the driveshaft, are housed in a pump housing. An embodiment of such radial piston pump used in a fuel injection system is for example described in EP 2 093 421 .

In a radial fuel pump, the housing is generally filled with fuel that acts as lubricant. The fuel is fed at low pressure from the vehicle tank through an inlet port. But the housing may also be fed with fuel originating from the fuel injectors' backleak circuit. Another possible source of aerated mix is from the pumping units, leaking in the housing. The fuel is hot and aerated and it is possible that air will collect in the housing, possibly to a point where the driveshaft bearings are not fully submerged and therefore not cooled and lubricated sufficiently.

Furthermore, as the fuel pump contains high speed moving parts, an air and fuel mix tends to be whipped into a foam-like mixture. This is problematic in architectures where the fuel having transited through the housing will be further compressed and fed to the common rail, possibly causing an unstable rail pressure.

A solution to this problem has been to provide an orifice at the top of the housing that allows evacuating the entrapped air that will collect during a key-off cycle. There are two shortcomings to this solution: (1 ) the orifice must be located at the highest point in the housing, which causes an issue when the pump would need to be rotated to fit different engine designs; and (2) the sizing of the orifice must be made carefully to avoid outflow of fuel once air has been evacuated.

OBJECT OF THE INVENTION

The object of the present invention is to provide an improved pump design that allows evacuating air from inside the housing.

This object is achieved by a pump assembly as claimed in claim 1

SUMMARY OF THE INVENTION

Against this background, from a first aspect, the present invention resides in a redesigned pump assembly, where the problem of air and air/fuel mixture accumulation in the cam box chamber is solved by using a redesigned drive shaft, which avoids the need for a dedicated air evacuating orifice at the top of the housing.

Accordingly, the present invention proposes a pump assembly comprising:

at least one pumping unit having an associated pumping element; a housing defining a chamber for a lubricating fluid provided through a fluid inlet; and

a drive shaft rotatably mounted in the housing, the drive shaft being rotatable about its longitudinal axis to actuate the pumping element of the at least one pumping unit, the drive shaft comprising a radial flange protruding in the chamber.

It shall be appreciated that at least one collecting channel is provided in the drive shaft flange, the channel having an outer end opening into the chamber at the outer periphery of the flange and an inner end in fluid communication with a central channel in the drive shaft. The central channel extends longitudinally in the drive shaft and has an outlet in the vicinity of a fluid outlet of the chamber.

Hence, the collecting channel and the central channel form a back-leak flow-path integrated within the drive shaft. Since the collecting channel has its outer aperture at the outer periphery of the flange, it can reach out to most remote regions of the chamber. As it will be understood by those skilled in the art, when the drive shaft is in an angular position such that the outer channel aperture is proximate to the top most region, it will allow air, air-fuel mix and/or foamy mixtures to enter the channel and flow inside the drive shaft towards its outlet, which is close-by the outlet port of the housing.

The benefit of this design is to define a prescribed flow path for air and air/fuel mixtures that form or accumulate in remote cam box chamber areas that does not depend on the orientation of the pump assembly.

Preferably, the one or more collecting channels extend generally radially in the flange. They are preferably sensibly straight, although other shapes could be possible to the extent that they do not hinder the back flow.

In one embodiment, the flange comprises one channel. It has an outer aperture opening into the chamber at the outer periphery of the flange and an inner aperture in fluid communication with the central channel in the drive shaft.

In another embodiment, a set of three or more collecting channels is provided in said flange, each collecting channel having an outer aper- ture opening into the cam box chamber at the outer periphery of the flange and an inner aperture in communication with the central channel, preferably through a common section channel.

Preferably, each collecting channel has a main section, the diameter of which is between 0.3 and 0.7 times, preferably 0.3 to 0.5 times, the diameter of the central channel.

In general, the outer end of each collecting channel may be provided in the outer peripheral edge of the flange.

In order to ensure that the cam or bearing surfaces of the drive shaft are wetted by the lubricant, the flange preferably extends radially beyond the other portions of the drive shaft, namely beyond the front and rear portions, and beyond the cam section. The radial extension of the flange may be at least 75% of the maximum radial extent of the chamber having regard to the drive shaft longitudinal axis, preferably about 80 or 90%.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 : is a longitudinal cross-sectional view through an embodiment of the present pump assembly;

Fig. 2: is a cross-sectional view of the drive shaft of Fig .1 alone;

Fig. 3: is a cross-sectional view of the drive shaft of Fig.1 alone, in perspective;

Fig. 4: is a cross-sectional view the pump assembly of Fig .1 , with the drive shaft rotated by 180°;

Fig. 5: is a longitudinal cross-sectional view through an second embodiment of the present pump assembly, where the drive shaft has three collecting channels;

Fig. 6: is a view of drive shaft of Fig.5, shown in a transversal cross-section through the flange; and

Fig. 7: is a perspective view the drive shaft of Fig.5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a cross section of an embodiment of the present pump assembly 10 suitable for supplying fuel to a fuel injection system in an internal combustion engine. The fuel pump 10 is used, for example, in a common rail injection system for supplying high pressure fuel to the internal combustion engine.

Such a pump typically receives the fuel from the vehicle tank at about 2 to 5 bars and delivers a high pressure of up to 2000 bars and even higher to the common rail of the fuel injection system. The common rail in turn supplies the fuel to the fuel injectors.

The pump assembly 10 comprises a housing 12 that may also be referred to as cam box housing, in which an elongate drive shaft 14 is accommodated. The cam box housing 12 includes a housing body 16 and a front plate 18 that together define an internal volume referred to as chamber 20, which may be of generally cylindrical shape.

The drive shaft 14 extends along a respective drive shaft axis A and is arranged to rotate there around. The drive shaft 14 has a front portion 22 that extends through a bore 24 or aperture in the front plate 18 to protrude out of the housing 12. The front portion 22 has a bearing section 26 that is rotatably supported in the bore 24 in any appropriate way. The front portion 22 ends by a drive section 28 (outside the housing 12), preferably conically tapered, bearing an end gear 30; the drive shaft 14 is rotatably driven by this drive section 28 e.g. by a toothed belt that may be coupled (directly or through a gearbox) to the crankshaft (not shown). The rear portion 32 of the drive shaft 14 is also rotatably supported in a bore 34 in the rear wall 36 of the cam box housing 16, by any appropriate means.

To facilitate rotation of the drive shaft, the bore 24 in the front plate may e.g. be provided with a tubular plain bearing (not shown). Similarly, the rear bore 34 may be provided with tubular plain bearing (not shown) to constrain the lateral movement of the drive shaft whilst allowing rotation thereof. The bearings may be of any known and appropriate type, e.g. using a PTFE multilayer bushing press-fitted into the bores 24 and 34. Other types of bearings may be used.

The middle portion 38 of the drive shaft 14 extends through the chamber 20 and comprises a cam section 40. The cam section 34 may for example be formed as an eccentric cylindrical cam body 42 that is ar- ranged to drive linear reciprocal movement of pumping units (not shown) disposed circumferentially about the drive shaft cam section 40.

Turning now to the pumping units, they may be of a known type, as will be familiar to those skilled in the art. For example, such pumping units may comprise an elongate body section having a blind bore therein, in which a plunger is reciprocally movable. The pumping unit is typically radially disposed and fixed in the housing body 16 at the position of pocket 44. The plunger extends in part in the chamber 20 and has a foot portion maintained in contact with the peripheral surface of cam section 40 by means of a spring. The plunger defines with the respective bore a pumping chamber in the body, and the plunger's reciprocating movement, driven by the cam section, allows reducing the volume of the pressure chamber during a forward or pumping stroke and increasing the volume of the pressure chamber during a return or filling stroke. Each pumping unit has an associated inlet valve that permits fluid (fuel) to flow into the pressure chamber during a filling stroke and an associated outlet valve that allows pressurized fluid/fuel to flow from the pressure chamber to a high pressure supply line and prevents the back-flow of fluid to the pressure chamber.

Reference sign 50 designates a flange that is located in the middle portion, i.e. inside the chamber 20, next to the cam section 40. The flange

50 is axially positioned on the drive shaft 14 to bear against the inner side

51 of the front plate 18 with its outer lateral surface 52 referred to as thrust face, thereby constraining the linear/axial movement of the drive shaft 14.

It may be noted that the flange 50 has a large radial extension and protrudes radially (perpendicularly to axis A) beyond the cam section 42. The drive shaft is also axially constrained against a bottom surface 49 of the housing body 16 by way of a shoulder 53 on the drive shaft 14, formed where the cam section, resp. middle portion, meets the rear portion.

The drive shaft 14 may be made in one piece or from several assembled pieces. Its general outer shape in this first embodiment is similar to that shown in Fig.7.

A lubricant is supplied to the chamber 20. In the case of a fuel pump, the lubricant may be fuel, namely diesel. Reference sign 54 indicates a first drilling that constitutes a lubricant inlet port through which lubricant/fuel flows into the chamber 20. An inlet valve (not shown) is generally arranged to control the inlet flow through drilling 54. Reference sign 56 in turn indicates a second drilling that constitutes a lubricant outlet port, also preferably controlled by a valve (not shown). A circulation of lubricant in the chamber 20 can thus be achieved by supplying fuel through the inlet port 54, and allowing outflow through outlet port 56.

In a vehicle, fuel is supplied to inlet port 54 at low pressure from the vehicle tank. However, depending on the engine design, fuel fed to the chamber 20 may also be fed from the back leak originating from the injectors (fuel returning from the injectors). The fuel is hot and aerated and it is possible that air will collect in the housing, possibly to a point where the driveshaft bearings are not fully submerged and therefore not cooled and lubricated sufficiently. Another possible source of aerated mix is from the pumping units, which may leak in the chamber 20. Furthermore, as the pump 10 contains high speed moving parts, the hot and aerated an air and fuel mix having accumulated in chamber 20 will tend to be whipped into a foam-like mixture. Such air/fuel mix and foamy mixture tend to accumulate, due to their density, in the peripheral region of the chamber located at the top of the housing.

It shall be appreciated that in order to evacuate air/fuel mix and foamy mixtures that may form/accumulate in the chamber, a channel 58 is provided in the flange 50 and has an outer aperture 60 opening into chamber 20 at the outer periphery of the flange 50 and an inner aperture 62 in fluid communication with a central channel 64 in the drive shaft 14. The central channel 64 in turn extends longitudinally in the drive shaft and has an outlet orifice 66 in the vicinity of the outlet port 56.

The channel 58 and central channel 64 form a back-leak path integrated in the drive shaft that provides a return flow from inside the chamber towards the outlet port. Since the channel 58 has its outer aperture 60 at the outer periphery of the flange 50, it can reach out to most remote regions of the chamber. As it will be understood by those skilled in the art, when the drive shaft 14 is in an angular position such that the outer channel aperture 60 is proximate to the top most region, it will allow air, air and fuel mix and/or foamy mixtures to enter the channel 58 and flow inside the drive shaft towards the outlet port 56. Fig.4 for example shows the pump assembly in a configuration where the drive-shaft is rotated by 180° with reference to Fig .1 .

To allow a proper wetting by the lubricant of the required driveshaft contact surfaces, the flange is preferably designed to protrude so as to radially extend beyond the other parts of the driveshaft, namely beyond the cam body outer surface (forming the rider bearing surface of the pumping element) and the bearing surfaces at the front and rear portions of the drive shaft. In other words, the flange diameter is sufficiently large to ensure that the rider bearing and support bearing have a smaller eccenter so that the air collected in the cam box can be evacuated instead of allowing the air to pass over the bearings.

For example, the radial extension of the flange 50 (indicated by radius RF in Fig.1 ) is at least 75% of the maximum radial extent (noted RC) of the chamber 20 having regard to the drive shaft longitudinal axis A, preferably about 80 or 90%.

As can be seen from Figs. 2 and 3, the channel 58 extends radially in the flange and is preferably straight. The outer aperture 60 of channel 58 is positioned in the outer peripheral edge of the flange 50. The central channel 64 may extend along the drive shaft axis (e.g. along and coaxially with axis A) and preferably has its outlet orifice 66 in the end face 68 of the rear portion 34. In this embodiment, the outlet orifice 66 is thus axially aligned with the outlet port 56.

As explained above, as the driveshaft spins the position of the channel 58 follows the flange 50, thus meaning that it is always at some point during a revolution) proximate to the uppermost position, where air will naturally collect.

While debris may be found inside the chamber, it may be noticed that the centrifugal force provides a level of debris protection in hat debris are more likely to rest away from a moving object than near it.

Another noticeable aspect of the present design with a moving channel is that the rotating speed affects the apparent cross-section of the collecting channel 58. Indeed, as the rotating speed increases, the apparent diameter of channel 58 decreases. In other words, the fuel flow rate through the collecting channel 58 is lower at high driveshaft rotating speeds than at lower speeds.

This effect is of advantage in the pump assembly and will be kept in mind when designing the pump. At low drive shaft speeds (low engine RPM), the electric lift pump in the tank is able to easily pressurize the chamber 20 in such a way that also the drive shaft bearings receive their amount of fuel-lubricant. The channel diameter may be broad and allows an important leakage rate back to outlet port 56.

As the drive shaft speed increases, due to an increased fuel de- mand of the injection system, the channel diameter should preferably be comparatively smaller. Centrifugal forces have this effect and act against the pressure in the cam box, reducing the flow through the channel as the rotating speed increases.

Bearing this in mind, a larger drilling diameter may thus be used for the collection channel 58 than one may have expected. The collecting channel 58 will perform its function efficiently yet being unable to block with debris.

Turning now to Figs. 5 to 7, they concern another embodiment of the present pump assembly, which distinguishes over the embodiment of Fig.1 in the internal design of the drive shaft 14'. Accordingly, same or similar parts are designated by same reference signs.

As for the embodiment of Fig .1 , the drive shaft comprises a front portion 22' (with bearing section 26' and drive section 28'), a rear portion 32' and a middle portion 38' with the cam section 40'. The flange 50' is located in the middle portion, inside the chamber 20, next to the cam section 40'; it protrudes radially beyond the cam body 42'.

As can be best seen from Fig.6, the flange 50' contains a plurality (here three) of inner radial channels 58' designed to capture air and air/fuel mixtures in remote areas of the chamber 20. The three channels 58 each have an outer aperture 60' opening into chamber 20 at the outer periphery of the flange and an inner aperture 62' opening into a common/cross channel section 63 in communication with the central channel 64'. In this embodiment, each of the radial channels 58' has a main section with a first cross-section area and the inner aperture 62' is designed as a channel having a narrower, second cross-section area. Two out of the three outer apertures 60', located at the outer periphery of flange 50', can be seen in the drawing of Fig.7. Apart from the inner construction of the channels 58', the general design of drive shaft 14' in Fig.7 is the same as in Fig .1 , especially having regard to the outer shape and dimensions.

This embodiment thus relies on redundancy by using three channels 58' (could be more) in the flange, adding further confidence to prevent possible obturation by debris. The inner aperture 62' of the collecting channels 58' is made narrower to reduce the flow rate of fuel towards the central channel64', given the multiplicity of collecting channels 58'.

In practice, the diameter of the inner aperture 62' may be between ¼ and ½ the diameter of the main section diameter. For example, for a main section diameter of 2 mm, the narrow inner aperture may have a diameter of at least 0.4 mm, for example 0.6 mm.

The diameter of the central channel 64' may be about twice the diameter of the main section channel 58'.

In this embodiment with 3 collecting channels 58', the channels are located in the same half of the flange, spaced by 90°. However other configurations can be devised by those skilled in the art.

Claims

1 . A pump assembly, in particular adapted for delivering high pressure fuel to a fuel injection system, comprising:

at least one pumping unit having an associated pumping element; a housing (12) defining a chamber (20) for a lubricating fluid provided through a fluid inlet (54);

a drive shaft (14) rotatably mounted in the housing, the drive shaft being rotatable about its longitudinal axis to actuate, by a cam section (40) thereof, the pumping element of said at least one pumping unit, the drive shaft comprising a radial flange (50) protruding in said chamber (20);

characterized in that at least one collecting channel (58) is provided in said flange (50), said collecting channel (58) having an outer end (60) opening into the chamber (20) at the outer periphery of said flange and an inner end (62) in fluid communication with a central channel (64) in said drive shaft; and

in that said central channel (64) extends longitudinally in said drive shaft (14) and has an outlet (66) in the vicinity of a fluid outlet (56) of said chamber, whereby said collecting channel (58) and central channel (64) form a back-leak flow path in said drive shaft (14).

The pump assembly according to claim 1 , wherein said at least one collecting channel (58, 58') extends generally radially in said flange (50, 50'), and is preferably substantially straight.

2. The pump assembly according to claim 1 , wherein a set of three or more collecting channels is provided in said flange, each collecting channel having an outer aperture (60') opening into chamber (20) at the outer periphery of said flange (50') and an inner aperture (62') in communication with the central channel (64), preferably through a common section channel (63).

3. The pump assembly according to claim 1 , 2 or 3, wherein said outer end (60, 60') of each collecting channel (58, 58') is provided in the outer peripheral edge of said flange.

4. The pump assembly according to any one of the preceding claims, wherein said collecting channel has a main section, the diameter of which is between 0.3 and 0.7 times the diameter of the central channel.

5. The pump assembly according to any one of the preceding claims, wherein the radial extension of said flange (50, 50') is at least 75% of the maximum radial extent of the chamber having regard to the drive shaft longitudinal axis, preferably about 80 or 90%.

6. The pump assembly according to any one of the preceding claims, wherein said chamber (20) is of substantially cylindrical shape.

7. The pump assembly according to any one of the preceding claims, wherein said drive shaft drive shaft comprises a front portion (22), a middle portion (38) and a rear portion (32), and is rotatably supported in the housing (12) by its front and rear portions.

8. The pump assembly according to any one of the preceding claims, wherein said cam section (40) has an eccentric cam body (42) in contact with the pumping element of said pumping unit.

9. The pump assembly according to claims 8 and 9, wherein the middle portion (38) extends in said chamber (20) and encloses said cam section (40) and said flange (50).

10. The pump assembly according to claim 8, 9 or 10, wherein said flange extends radially beyond the other portions of said driveshaft, in particular beyond said front portion, said rear portion and said middle portion with cam section.

1 1 . The pump assembly according to any one of the preceding claims, wherein said housing comprises a body (16) and a front cover (18), and in that said flange (50, 50') bears against the inner side of said front cover with its outer lateral surface.