The present invention relates to a driveshaft assembly, and more specifically to a cam and shaft for a driveshaft assembly.

BACKGROUND OF THE INVENTION

Fuel pumping and pressurising plungers of Electronic Unit Injectors (EUI), Unit Injectors (UI) and Electronic Unit Pumps (EUP), are operated in a reciprocating manner. In a known driveshaft arrangement or assembly 1, as illustrated in Figures la and lb, reciprocating motion of a plunger 90, as indicated by arrow P, is caused by a rotating cam 2 located on a shaft 12. The cam 2 is formed of a base cylinder section 8, and an integral further section 10, protruding from part of the circumference of the base cylinder section 8. The cam 2 therefore has an outer surface 4 defined partly by the outer surface 4a of the base cylinder 8, and partly by the outer surface 4b of the further section 10.

The cam 2 operates on a plunger 90, either directly (as illustrated in the Figures la and lb), or indirectly via a pivoting rocker arm (not shown). Lift is transferred to the plunger 90 or rocker arm in the direction of arrow L, via a lift point 6 on the outer surface 4 of the cam 2, where the outer surface 4 of the cam contacts with the plunger 90 (or rocker arm). In the orientation of Figures la and lb, point 6 is the uppermost point of the outer surface 4 cam 2. The cam 2 rotates about a centre of rotation, defined by a longitudinal central axis 14 of the shaft 12, which is coincident with a central axis 70 of the base cylinder section 8. As the cam 2 rotates with the shaft 12, the contact point between the cam 2 and the plunger 90, moves around the outer surface 4 of the cam, i.e. lift point 6 moves relatively around the outer surface 4 of the cam 2. As illustrated in Figures la and lb, the instantaneous lift L of the cam 2 is calculated as below:

L = A - B; where A is the distance from a central axis 14 of the shaft 12 to the lift point 6, and B is the distance from the central axis 14 of the shaft 12 to the external surface 4a of the base cylinder section 8, i.e. a radius of the base cylinder section 8.

During part of the rotation cycle, when the lift point 6 occurs on the external surface 4b of the further section 10, the distance A will vary in accordance with the external profile 4b of the further section 10. During the part of the rotation cycle when the lift point 6 occurs on the external surface 4a of the base cylinder section 8, distance A will be constant and will be equal to distance B.

Figure la illustrates a rotational position of the cam 2 which provides maximum lift, Lmax, i.e. lift point 6 is at a maximum distance from the centre 14 of the shaft 12, and distance A is therefore maximised.

Figure lb illustrates a rotational position of the cam 2 providing minimum lift, i.e. lift point 6 is at a minimum distance from the centre 14 of the shaft 12, and distance A is therefore minimised. In this position, A and B are equal, therefore the minimum lift Lmin is zero.

Typically, the prior art embodiment of Figures la and lb also provides a constant plunger rate period. A known disadvantage of the prior art embodiment such as that illustrated in Figures la and lb is that the maximum lift Lmax of the driveshaft assembly 1, and therefore the travel of the plunger 90, is predetermined and fixed, as each driveshaft assembly has a set value of B and set maximum value of A. To obtain a different value for the travel of the plunger 90, it is necessary to disassemble the driveshaft assembly 1 by removing the cam 2 from the shaft 12, and replacing it with an alternative cam having a different external profile, i.e. a different value of B and/or maximum A, and/or by replacing the rocker arm or changing the pivot point of the rocker arm. Accordingly, in prior art embodiments, it is difficult to accommodate the differing plunger travel requirements. For example, it is difficult to accommodate the specific lift range requirements of different EUI, UI and EUP families, which could typically range from 9mm to 19mm.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved driveshaft assembly which at least mitigates the above mentioned problems.

Accordingly the present invention comprises, in a first aspect, a driveshaft assembly in accordance with claim 1. The present invention enables different values of maximum lift to be achieved using a single cam and shaft combination, i.e. a variable plunger lift is enabled for a single cam and shaft combination. Accordingly, a required value of maximum lift can be selected by use of the same cam and shaft, avoiding the need to use a multiple cam and/or rocker arm combinations to achieve different values of maximum lift.

The offset value may vary between zero and a maximum offset value.

The indexing means may comprises splines. In one embodiment, the splines comprise a first annular set of splines provided on an internal surface of the through bore of the cam, which correspond with a second annular set of splines provided on a section of the shaft, wherein a centre of a circumference of the splines is offset from the central axis of the shaft, and wherein the cam is a push fit onto the shaft, and wherein the plurality of rotational positions comprise a plurality of discreet rotational positions.

The driveshaft assembly may further comprise a position indicator, to indicate a relative position at which the cam has been assembled onto the shaft.

In a further aspect, the present invention comprises a driveshaft and plunger assembly, comprising a driveshaft assembly in accordance with the first aspect of the present invention, and a plunger arranged for reciprocating movement caused by lift imparted by the cam during rotation of the shaft.

The driveshaft and plunger assembly may further comprise a rocker arm, wherein lift is imparted to the plunger by the cam to the plunger via the rocker arm.

In a further aspect, the present invention comprises a machine for testing a fuel injectors or pump, such as an UI, EUI or EUP, comprising a driveshaft assembly in accordance with the first aspect of the present invention, wherein the driveshaft assembly causes reciprocating movement of a plunger of the fuel inj ector or pump .

The present invention provides a simpler and cheaper solution than prior art driveshaft assemblies.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 2 is an exploded view of a driveshaft assembly in accordance with the present invention; Figures 3a and 3b are end views of the driveshaft assembly of Figure 2 wherein the cam is located on the shaft in a first, a minimum Lmax lift position; Figure 4 is a graphical representation of a lift profile of the driveshaft assembly at the minimum lift position of Figures 3 a and 3b;

Figures 5a and 5b are end views of the driveshaft assembly of Figure 2, in which the cam is located on the shaft in a second, maximum Lmax lift position;

Figures 6 is a graphical representation of a lift profile of the driveshaft assembly at the maximum lift position of Figures 5 a and 5b;

Figures 7a and 7b are end views of the driveshaft assembly of Figure 2, in which the cam is positioned on the shaft at a third, mid-Lmax position;

Figure 8 is a graphical representation of a lift profile of the driveshaft assembly at the mid-Lmax position of Figures 7a and 7b; and

Figure 9 is an isometric view of a testing machine in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to Figure 2, the present invention comprises a driveshaft assembly 100 comprising a cam 102 and a shaft 112. The cam 102 comprises a base cylinder section 108, having a longitudinal central axis 170, and an integral further section 110, protruding from part of the circumference of the base cylinder section 108. An outer surface 104 of the cam 102 is defined by an outer surface 104a of the base cylinder section 108, and an outer surface 104b of the further section 110.

In the illustrated embodiment, the driveshaft assembly 100 is arranged to act upon a reciprocating component comprising a plunger 190 (shown in Figures 3a, 3b, 5a, 5b, 7a and 7b).

A longitudinally extending bore 116 is provided through the base cylinder section 108.

The bore 116 is provided with a first set of splines, comprising a plurality of internal splines 118 defined by a plurality of troughs and peaks.

An annular section 150 of the shaft 112 is provided a second set of splines, comprising a plurality of external splines 152, defined by a plurality of peaks and troughs. The annular section 150 is eccentric with the shaft 112, i.e. the central axis of the splines 152 is offset from a central axis 114 of the shaft 112.

On assembly of the driveshaft assembly 100, the cam 102 is pushed onto the shaft 112, until the splines 118 of the cam 102 are located over the external splines 152 of the shaft 112.

The external splines 152 of the shaft 112 cooperate with the internal splines 118 provided on the cam bore 116, such that the cam 102 is a push fit onto shaft 112.

An annular section 180 of the shaft 112 (shown on Figure 2), which is of greater diameter that of the bore 116 of the cam 102, provides a stop, ensuring that the cam 102 and shaft 112 are located correctly with one another after the cam 102 has been pushed onto the shaft 112.

On operation of the driveshaft, rotation of the shaft 112 causes rotation of the cam 102, which acts upon the plunger 190 (Figures 3a, 3b, 5a, 5b, 7a and 7b) at a lift point 106, thereby imparting lift to the plunger 190 and causing the plunger 190 to move in a reciprocating movement, in the directions of arrow P (shown on Figure 3 a). The splines 118 of the cam 102, together with the splines 152 of the shaft 112, form a splined section 162, which forms an indexing means. In this embodiment illustrated in the Figures, the indexing means is annular and cylindrical. Due to the eccentricity of the annular section 150 with the shaft 112, a central axis 154 of the splined section 162 of the assembled driveshaft assembly 100 is offset from the central axis 114 of the shaft 112, by a distance C, as indicated in the Figures. In other words, a circumference of the indexing means is eccentric with the shaft 112.

The indexing means allow the cam 102 to be located on the shaft 112 at a number of discreet positions, each of which provides a different maximum value of lift, Lmax. (The calculation and variation of Lmax is described in greater detail below).

Three central axes are defined above (as illustrated in Figures 3, 3b, 5a, 5b, 7a and 7b):

a central axis 170 of the base cylinder section 108;

a central axis 114 of the shaft 112;

a central axis 154 of the splined section 162. As above, the central axis 154 of the splined section 162 is offset from the central axis 114 of the shaft 112, by distance C, in all arrangements of the cam 102 and shaft 112, i.e. at all indexed positions. However, the central axis 170 of the base cylinder section 108 from the central axis 114 of the shaft 112 can be varied between zero and D (D is illustrated in Figures 5a and 7a), in either or both of the X and Y axes (indicated in the Figures). Each discreet position at which the cam 102 can be located on the shaft 112 provides a different offset value D, which determines the maximum value of lift, Lmax. A position indicator 156 (shown in Figures 3a, 3b, 5a, 5b, 7a and 7b), is provided to indicate the relative position of the cam 102 on the shaft 112. In the illustrated embodiment, eleven positions of the cam 102 relative to the shaft 112 are indicated by numerals 1 to 11; each of these positions provides a known value of Lmax and therefore a known value of travel of the plunger 190.

As illustrated in Figures 3a, 3b, 5a, 5b, 7a and 7b, the instantaneous lift L of the cam 102 is calculated as below:

L = A - B; where A is the distance from the central axis 114 of the shaft 112 to the lift point 106, and B is the distance from the central axis 114 of the shaft 112 to the external surface 104a of the base cylinder section 108. As the cam 102 rotates and the lift point 106 moves around the outer surface 104 of the cam 102, due to the external profile of the outer surface 104 of the cam 102, distance A will vary in accordance with the rotational orientation of the cam 102 with respect to the centre 114 of the shaft 112.

The lift, L, of the driveshaft assembly 100 varies between a maximum value, Lmax, and a minimum value of zero. As illustrated in Figures 3a, 5a and 7a, Lmax occurs when distance A is maximised and distance B is minimised. The minimum, zero value of lift occurs when distance A is equal to distance B, as illustrated in Figures 3b, 5b and 7b. A maximum value of A is equal to the maximum distance between the central axis 114 of the shaft 112 and the outer surface 4b of the further section 110 of the cam 102. The cam 102 assembled onto the shaft 112 at three of the eleven positions will be described below in greater detail.

In Figures 3a and 3b, the cam 102 has been assembled onto the shaft 1 12 at position 11, providing a minimum value of Lmax, and therefore a minimum value of travel of the plunger 190.

In this position, the offset D of the central axis 170 of the base cylinder section 108, from the central axis 1 14 of the shaft 112, is zero, i.e. the central axes 170 and 114 are coincident.

Figure 3a illustrates the driveshaft assembly 100 at the maximum lift position, i.e. wherein the value of distance A is maximised. Figure 3b illustrates the driveshaft assembly 100 further around the rotational cycle, wherein distance A is at a minimum and is equal to distance B thereby providing an instantaneous lift value L of zero.

Figure 4 provides an example of a lift profile during rotation, of the driveshaft assembly 100 when the cam 102 is located on the shaft in position 11, and wherein the offset C, (of the central axis 154 of the splined section 162 and the central axis 114 of the shaft 112), is 1.5mm. (The maximum value of offset D for this arrangement is also 1.5mm). The lift L varies between zero and an Lmax value of 12mm.

In Figures 5 a and 5b, the cam 102 has been assembled onto the shaft 112 in position 1, wherein the cam 102 has been rotated 180° with respect to the position of Figures 3a and 3b. In this position, the driveshaft assembly 100 provides a maximum value of Lmax, and therefore a maximum travel of a plunger.

In the arrangement of Figures 5 a and 5b, the central axis 170 of the base cylinder section 108 is offset from the central axis 114 of the shaft 112, by distance D, in the X axis.

Relative to the arrangement of Figures 3a and 3b, the maximum value of distance A (which occurs at the rotational position illustrated in Figure 5 a), has increased by both the offset values C and D, and maximum value of distance B, has decreased by both the offset values C and D. Accordingly, Lmax, which occurs at the rotational position of Figure 5 a, is maximised.

Figure 5b illustrates the driveshaft assembly 100 in position 1, further around the cycle, when distance A is equal to distance B, and instantaneous lift L is therefore zero.

Figure 6 corresponds to Figure 4, and illustrates the lift profile of the same embodiment of driveshaft assembly 100 when the cam 102 has been assembled onto the shaft 112 in position 1. As illustrated, the maximum value of lift, Lmax, is now 18mm, an increase of 6mm relative to the arrangement of Figures 3a and 3b.

In Figures 7a and 7b, the cam 102 has been assembled onto the shaft 1 12 in position 6, wherein the cam 102 has been rotated 90° with respect to the position of Figures 3a and 3b. In this position, the driveshaft assembly 100 provides a mid- value of Lmax and therefore a mid-value of travel of the plunger 190.

In the position of Figures 7a and 7b, the central axis 170 of the base cylinder portion 108 is offset by distance D from the centre of rotation 114 of the shaft 112, in both the X and Y axes. Figure 8 corresponds to Figures 4 and 6, and illustrates the lift profile of the same embodiment of driveshaft assembly 100, when the cam 102 has been assembled onto the shaft 112 in position 6. As illustrated, the maximum value of lift Lmax is now 15.5mm, i.e. between the Lmax values of Figures 4 and 6.

Examples of the values of A, B and L for a driveshaft 100 in accordance with the present invention, in the three positions described above, are provided in the table below, wherein the offsets C and D are each 1.5mm. The values of L are instantaneous values at the rotational position illustrated in each Figure.

In the embodiments described above, the cam 102 acts directly on the plunger 190. Alternatively, the cam 102 could act indirectly on the plunger 190, via a rocker arm.

The present invention can replace any driveshaft embodiment. One particular use could be for a testing machine for a fuel injector or pump such as an UI, EUI or EUP. An example of a machine 200 for testing an injector 300 is illustrated Figure 9, and comprises a driveshaft assembly 101 in accordance with the present invention. The cam 102 is housed in a cambox 210 comprising a cambox cover 208. The cambox 210 is mounted on a bedplate adapter 21 1 via an adapter plate 209. The machine 200 further comprises a pressure plate 213 and injector support plate 212 into which the injector 300 is clamped and held in position by a locknut 203. A rotary drive is connected to the camshaft 112 and rotates the shaft 112 and cam 102, for example at speeds of 30 to 4000rpm, which causes a cam follower 205 and hence a pressurising plunger (not shown) of the injector 300 to move in a reciprocating motion. The plunger generates an increasing fuel pressure within the injector 300 when an electronically operated spill valve (not shown) is closed. A nozzle (not shown) of the injector 300 is caused to open when fuel pressure within the injector 300 reaches a predetermined threshold.

During operation, the machine 200 measures parameters of the injector 300 such as injected fuel quantity.

The machine 200 may be used to test different types of injector or pump which have plungers requiring different values of maximum lift Lmax. The driveshaft assembly 101 of the present invention enables the machine to test different injector/pump types having different Lmax requirements, without requiring the fitting of different cams / cam follower combinations to the machine.

In the above embodiments, the indexing means comprises cooperating splines provided on the shaft and on the bore of the cam. In alternative embodiments of the present invention, alternative indexing means could be used. Furthermore, alternative embodiments could enable a different number of discreet indexed positions, and therefore a different number of possible values of Lmax. For example, a different number of splines would enable a different number of discreet positional arrangements of the cam onto the shaft. REFERENCES driveshaft assembly 100

cam 102

cam outer surface 104

base cylinder section outer surface 104a

further section outer surface 104b

lift point 106

base cylinder section 108

cam further section 1 10

shaft 112

shaft central axis 114

bore 116

internal splines 1 18

shaft annular section 150

external splines 152

splined section central axis 154

position indicator 156

splined section 162

base cylinder longitudinal central axis 170

increased diameter shaft annular section 180

plunger 190

offset C

maximum value of lift Lmax

plunger movement P

variation of base cylinder central axis D

axes X, Y

offset Y

cam shaft relative positions 1 - 11

distance central axis of shaft to lift point A

distance central axis of shaft to external surface base cylinder section B machine 200

locknut 203

cam follower 205 cambox cover 208 adapter plate 209 cambox 210

bedplate adapter 21 1 pressure plate 213 injector support plate 212 injector 300