GB1599769A

GB1599769A - Arm and linkage for converting rectilinear movement into angular movement a pump element including such an arm and a fuel pump incorporating such a linkage

Info

Publication number: GB1599769A
Application number: GB2542777A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1977-06-17
Filing date: 1977-06-17
Publication date: 1981-10-07
Also published as: ES261127Y; FR2394723A1; ES261127U

Description

(54) ARM AND LINKAGE FOR CONVERTING RECTILINEAR MOVEMENT INTO ANGULAR MOVEMENT, A PUMP ELEMENT INCLUDING SUCH AN ARM AND A FUEL PUMP INCORPORATING SUCH A LINKAGE (71) We, LUCAS INDUSTRIES LI MITED, a British Company, of Great King Street, Birmingham B19 2XF England, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an arm for use in a linkage for converting rectilinear movement into angular movement, to a linkage and a pump element including such an arm, and to a fuel pump incorporating such a linkage.

According to one aspect of the present invention, there is provided an arm for use in a linkage for converting rectilinear movement into angular movement, which linkage includes a rectilinearly movable element, comprising a configurated end which includes two main curved portions which can engage respective opposed parts of said rectilinearly movable element in use, each of the main curved portions having a profile which is defined substantially by the curve traced by one of the ends of a straight line of fixed length when that line is rotated about a first point thereof from a first position to a second position, and by the other end when the line is further rotated in the same rotational direction about a second point thereon from said second position to a third position, the second point being spaced from the first point, one of said main curved portions engaging one of said parts when the arm is moved in one direction about an axis remote from said end and the other of said main curved portions engaging the other of said parts when the arm is moved in the other direction.

According to another aspect of the present invention, there is provided a pump element comprising a cylinder, a piston reciprocable within the cylinder, and an arm as defined in any of the last preceding paragraph operably connected to the piston for angular movement therewith about the piston axis.

According to a further aspect of the present invention, there is provided a linkage for converting rectilinear movement into angulular movement, comprising a rectilinearly movable element having a pair of opposed parts, and an angularly movable arm having a configurated end including two main curved portions which can slidingly engage said opposed parts of the rectilinearly movable element respectively, each of the main curved portions having a profile which is defined substantially by the curve traced by the ends of a straight line of fixed length when that line is rotated about a first point thereon from a first position to a second position, and by the other end when the line is further rotated in the same rotational direction about a second point thereon from said second position to a third position, the second point being spaced from the first point, one of said main curved portions engaging one of said parts when the arm is moved in one direction about an axis remote from said end and the other of said main curved portions engaging the other of said parts when the arm is moved in the other direction.

According to a still further aspect of the present invention, there is provided a fuel pump comprising a casing including a plurality of cylinders, a piston axially reciprocable within each cylinder so as to deliver fuel at pressure to a respective outlet, the quantity of fuel delivered by each piston in each stroke being adjustable by moving the piston angularly about its axis, and a rectilinearly movable control rod, each piston being connected to the control rod by means of a linkage as defined in the last preceding paragraph, the arm of each linkage being operatively connected to the respective piston for angular movement therewith about the piston axis and the rectilinarly movable element of each linkage being carried out by the control member, such that rectilinear movement of the control rod causes simultaneous angular movement of the pistons.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure I is a sectional end view of part of a fuel pump according to the present invention; Figure 2 is a plan view of a linkage according to the present invention which forms part of the fuel pump in Figure 1; Figure 3 is a schematic plan view of an end of an arm according to the present invention which forms part of the linkage of Figure 2; Figure 4 is a schematic plan view of an end of a modified arm; Figures 5A and 5B are diagrams illustrating the geometry of the arm of Figure 4; Figure 6 is a diagram comparing the performance of the linkage of Figure 2 with a conventional linkage; and Figure 7 is a graph of the fuelling characteristics of a pump according to the present invention and two conventional pumps.

Referring first to Figure 1, the fuel pump shown therein is an in-line pump for a compression ignition engine, and comprises a casing 10 which includes a plurality of cylinders or barrels 11 arranged in a line.

Only one of the cylinders 11 is shown in Figure 1, and this will now be described in detail, it being understood that the other cylinders are identical thereto.

A piston or plunger 12 is axially reciprocable within the cylinder 11 to deliver fuel at high pressure to an outlet 13. Opening onto the internal side wall of the cylinder 11 are an inlet port 14, by means of which fuel is supplied to the space above the piston 12, and a spill port 15. The spill port 15 is arranged to communicate with a helical groove 16 in the external wall of the piston 12 at a certain point in the piston's stroke.

The groove 16 communicates with the space above the piston 12 by means of an axial bore in the piston, so that fuel can be spilled from said space through the spill port 15 when the latter communicates with the groove 16. The point during the piston's stroke at which fuel is spilled, and consequently the quantity of fuel delivered to the outlet 13 in each stroke of the piston, is determined by the angular position of the groove 16 relative to the spill port 15. This angular position, and therefore the quantity of fuel delivered per stroke, can be adjusted by moving the piston 12 angularly about its axis relative to the cylinder 11. Such angular movement is effected by means of an elongate control rod 17 which extends along the line of cylinders 11, and a linkage 18 connecting each piston 12 to the control rod 17. Each linkage 18 includes an arm 19 operably connected to the respective piston 12 for angular movement about the latter's axis.

The arrangement of the control rod 17 and the linkage 18 is shown in detail in Figure 2. Each linkage 18 also includes a bifurcated element 20 mounted on the control rod 17, between the forks of which is engaged an end of the respective arm 19.

The control rod 17 is rectilinearly movable in its longitudinal direction under the action of a governor (not shown), such that its longitudinal position relative to the cylinders 11 can be varied inter alia in dependence upon the speed of the engine. Each linkage 18 converts such rectilinar movement of the control rod 17 into angular movement of the respective arm 19 about the axis of the respective piston 12 whereby the quantity of fuel delivered by that piston in each stroke is adjusted. It will be manifest that all of the pistons 12 are adjusted simultaneously and by the same amount.

Each arm 19 comprises a circular portion 21 having a central aperture 22 therein which receives part of the respective piston 12, and a stem portion 23 extending radially from the circular portion 21. The end 24 of the arm which engages the respective bifurcated element 20 is configurated, as is shown in detail in Figure 3, and includes two main curved portions 25 and 26 which slidingly engage the forks of the bifurcated element 20, respectively.

Portion 25 has a profile which is defined by the curve traced by one end of a straight line of fixed length when that line is rotated anticlockwise about its other end from a first position, indicated by a line 27, to a second position, indicated by a line 28. Portion 26 has a profile which is defined by the curve traced by said other end of the aforementioned straight line and that line is rotated anticlockwise about its said one end from said second position to a third position, indicated by a line 29. The geometry of the curved portions 25 and 26 is so arranged that the lines 27, 28 and 29 form an equilateral triangle, with the curved portions 25 and 26 meeting at the point of intersection P of lines 27 and 29. In addition, the line 28 is perpendicularly bisected by a radial line R from the respective piston axis.

The main curved portions 25 and 26 are connected to the stem portion 23 by means of respective further curved portions 30 and 31. Each of the portions 30 and 31 has a profile which is defined by part of an arc centred on the aforementioned point P, a further part of this arc being indicated in dot-dash line. Portions 25 and 30 meet at the point of intersection of lines 28 and 29, and portions 26 and 31 meet at the point of intersection of lines 27 and 28.

When the arm 19 is disposed in a central position, in which the line 28 is parallel to the direction of movement of the control rod 17, the configurated end 24 contacts the forks of the respective bifurcated element 20 at points X and Y respectively, point X being located at the junction between portions 25 and 30 and point Y being located at the junction between portions 26 and 31.

When the control rod 17 is moved to the right so as to move the arm 19 clockwise, as viewed in Figure 2, the contact point X remains at the junction between portions 25 and 30 but contact point Y moves along the profile of portion 26 towards the point P, for example to a position Y'. Similarly, when the control rod 17 is moved to the left so as to rotate the arm 19 anticlockwise from its central position, the contact point Y remains at the junction between the portions 26 and 31 whereas the contact point X moves along the profile of curved portion 25 towards point P, for example to a position X'. It will be manifest that, during angular movement of the arm 19, the distance between the contact points X and Y remains constant and equal to the length of the aforementioned straight line.

The configurated end of a modified form of arm is shown in Figure 4, and its geometry will now be described with particular reference to Figures 5A and SB. The modified arm end includes two curved portions 32 and 33 which respectively slidingly engage the forks of the respective bifurcated element 20. Portion 32 consists of two mutually adjoining sections including a main section 34 and a minor section 35 and portion 33 consists of two mutually adjoining sections including a main section 36 and a minor section 37.

As can be seen to advantage in Figure 5A, the sections 34 and 37 have profiles which are defined respectively by the curves traced by the ends of a straight line of fixed length when that line is rotated clockwise about a first point 38 thereon from a first position, indicated by a line 39, to a second position, indicated by a line 40. As can be seen to advantage in Figure SB, the sections 35 and 36 have profiles which are defined respectively by the curves traced by the ends of said straight line when that line is rotated clockwise about a second point 41 thereon from said second position to a third position, indicated by a line 42.

The first and second points 38 and 41 are equidistantly spaced from the mid-point of said straight line and on opposite sides of the mid-point. The geometry of the curved portions 32 and 33 is such that the lines 39, 40 and 42 define an equilateral triangle, and the line 40 is perpendicularly bisected by a radius R' from the axis of the respective piston. The lines 30 and 42 intersect at a point P'.

The main sections 34 and 36 of the curved portions 32 and 33 respectively are interconnected by a curved portion 43 having a profile which is defined by an arc centred on the point P'. The minor sections 35 and 37 of the curved portions 32 and 33 respectively are connected to the stem portion of the arm by respective further curved portions 44 and 45, the profiles of the portions 44 and 45 being defined by parts of a further arc centred on the point P'.

When the arm is disposed in a central position, such that the line 40 is parallel to the direction of movement of the control rod 17, the configurated end of the arm contacts the forks of the associated bifurcated element at points X and Y respectively, point X lying at the junction between the sections 34 and 35 of the curved portion 32 (i.e. at one end of the line 40), point Y lying at the junction between the sections 36 and 37 of the curved portion 33 (i.e. at the other end of the line 40). When the control rod is moved so as to rotate the arm in a clockwise direction, contact point X moves along the profile of section 34 and contact point Y moves along the profile of section 37, for example to positions X' and Y' respectively.

It will be manifest that. due to the particular geometry of the configurated arm end, a line joining the contact points at positions X' and Y' will pass through the point of intersection of the lines 39 and 40. Similarly, when the control rod is moved so as to rotate the arm anticlockwise from its central position, contact point X moves along the profile of section 35 and contact point Y moves along the profile of section 36, for example, to positions X" and Y" respectively. Due to the geometry of the arm end, a line joining the contact points at positions X" and Y" will pass through the point of intersection of the lines 40 and 42.

It will be apparent from the above that the distance between the contact points X and Y as the arm is moved angularly remains constant and equal to the length of the aforesaid straight line. Typically, this line is 1.0 cm long and the points 38 and 41 are each spaced 0.1 cm from the respective end thereof, so that the profiles of sections 34, 36 and portions. 44, 45 have a radius of 0.9 cm, and the profiles of the sections 35, 37 and portion 43 have a radius of 0.1 cm.

The performance of a linkage according to the present invention will now be compared with that of a conventional linkage with reference to Figure 6. On the left-hand side of this Figure is shown a linkage 18 according to the present invention at a point wherein the arm 19 thereof is at a central position. When the bifurcated element 20 of the linkage is moved rectilinearly so as to rotate the arm 19 out of its central position, the arm 19 can move through an angle 6 before the configurated end 24 thereof disengages from the element '(). The linkage 18 is shown on the right-hand side of the Figure at a point just before such disengages ment occurs. the bifurcated clement having moved a distance M from its central position.

A conventional linkage for effecting angular adjustment of the pistons of an in-line fuel pump for a compression ignition engine is generally similar to that described above. except that the end of the arm which slidingly engages the bifurcated element is of circular form. as is indicated in broken lines at 50 in Figure 6. On the left-hand side of this Figure, the arm of the conventional linkage is shown schematically in its central position. When the bifurcated element of the conventional linkage is moved rectilinearly. the conventional arm can rotate through an angle 62 from its central position before the end 50 thereof disengages from the bifurcated element.

As can be seen from Figure 6, for a conventional linkage and a linkage according to the present invention having similar dimensions and wherein the distance moved by the bifurcated element is the same, (3, > 62. In other words, for a given movement of the control rod on which the bifurcated element is mounted, the angular displacement of the arm is greater in the linkage according to the present invention than in the conventional linkage. Therefore, a greater control over the angular adjustment of the respective fuel pump piston is possible using the linkage of the present invention.

Typically, about 10% extra angular adjustment of the fuel pump piston can be obtained for the same control rod movement.

In certain fuel pump applications, it is necessary for the helix angle of the groove 16 (see Figure 1) in each fuel pump piston to be comparatively large, for example to ensure an adequate range in the quantity of fuel which can be delivered by the piston in each stroke whilst keeping the angular extent of the groove 16 within the maximum angle by which the piston can be rotated.

This can lead to inferior fuel spillage characteristics. Using the linkage of the present.

invention, the maximum angle by which the piston can be moved (i.e. before the end of the arm 19 disengages from the respective bifurcated element 20) is increased, which enables the helix angle of the groove 16 to be reduced whilst maintaining an adequate fuelling range, thereby improving the fuel spillage characteristics.

Figure 7 illustrates the fuelling characteristics of a pump in which (A) a conventional linkage is used for angularly displacing each piston and the helix angle of each groove 16 is 45 , (B) a conventional linkage is used and the helix angle of groove 16 is increased to 50 , and (c) a linkage according to the present invention is used for angularly displacing each piston and the helix angle of each groove 16 is 45 .

WHAT WE CLAIM IS: 1. An arm for use in a linkage for converting rectilinear movement into angular movement, which linkage includes a rectilinearly movable element, comprises a configurated end which includes two main curved portions which can engage respective opposed parts of said rectilinearly movable element in use, each of the main curved portions having a profile which is defined substantially by the curve traced by one of the ends of a straight line of fixed length when that line is rotated about a first point thereon from a first position to a second position, and by the other end when the line is further rotated in the same rotational direction about a second point thereon from said second position to a third position, the second point being spaced from the first point, one of said main curved portions engaging one of said parts when the arm is moved in one direction about an axis remote from said end and the other of said main curved portions engaging the other of said parts when the arm is moved in the other direction.

2. An arm according to Claim 1 in which the first and second points are equidistantly spaced from the mid-point of said line.

3. An arm according to Claim 2 in which said points are positioned at the ends of said line.

4. An arm according to Claim 3 in which said line when in its first, second and third positions defines first, second and third sides of a triangle, respectively, and said main curved portions are interconnected by a further curved portion having a profile which is defined substantially by an arc centred on the apex of said triangle based on said second side thereof.

5. An arm according to Claim 2 in which said points are spaced from the ends of said line, whereby the configurated end has minor curved portions defined by the portions of the line lying on the sides of said points remote from the portions of the line which defines said major curved portions.

6. An arm according to Claim 4 in which said triangle is an equilateral triangle.

7. A pump element comprising a cylinder, a piston reciprocable within said cylinder and an arm as defined in any one of Claims 1, 2, 3, 4, 5 or 6 operably connected to the piston, said axis being the axis of the piston.

8. A pump element according to Claim 6 in which the line when in its second

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. rotate the arm 19 out of its central position, the arm 19 can move through an angle 6 before the configurated end 24 thereof disengages from the element '(). The linkage 18 is shown on the right-hand side of the Figure at a point just before such disengages ment occurs. the bifurcated clement having moved a distance M from its central position. A conventional linkage for effecting angular adjustment of the pistons of an in-line fuel pump for a compression ignition engine is generally similar to that described above. except that the end of the arm which slidingly engages the bifurcated element is of circular form. as is indicated in broken lines at 50 in Figure 6. On the left-hand side of this Figure, the arm of the conventional linkage is shown schematically in its central position. When the bifurcated element of the conventional linkage is moved rectilinearly. the conventional arm can rotate through an angle 62 from its central position before the end 50 thereof disengages from the bifurcated element. As can be seen from Figure 6, for a conventional linkage and a linkage according to the present invention having similar dimensions and wherein the distance moved by the bifurcated element is the same, (3, > 62. In other words, for a given movement of the control rod on which the bifurcated element is mounted, the angular displacement of the arm is greater in the linkage according to the present invention than in the conventional linkage. Therefore, a greater control over the angular adjustment of the respective fuel pump piston is possible using the linkage of the present invention. Typically, about 10% extra angular adjustment of the fuel pump piston can be obtained for the same control rod movement. In certain fuel pump applications, it is necessary for the helix angle of the groove 16 (see Figure 1) in each fuel pump piston to be comparatively large, for example to ensure an adequate range in the quantity of fuel which can be delivered by the piston in each stroke whilst keeping the angular extent of the groove 16 within the maximum angle by which the piston can be rotated. This can lead to inferior fuel spillage characteristics. Using the linkage of the present. invention, the maximum angle by which the piston can be moved (i.e. before the end of the arm 19 disengages from the respective bifurcated element 20) is increased, which enables the helix angle of the groove 16 to be reduced whilst maintaining an adequate fuelling range, thereby improving the fuel spillage characteristics. Figure 7 illustrates the fuelling characteristics of a pump in which (A) a conventional linkage is used for angularly displacing each piston and the helix angle of each groove 16 is 45 , (B) a conventional linkage is used and the helix angle of groove 16 is increased to 50 , and (c) a linkage according to the present invention is used for angularly displacing each piston and the helix angle of each groove 16 is 45 . WHAT WE CLAIM IS:

1. An arm for use in a linkage for converting rectilinear movement into angular movement, which linkage includes a rectilinearly movable element, comprises a configurated end which includes two main curved portions which can engage respective opposed parts of said rectilinearly movable element in use, each of the main curved portions having a profile which is defined substantially by the curve traced by one of the ends of a straight line of fixed length when that line is rotated about a first point thereon from a first position to a second position, and by the other end when the line is further rotated in the same rotational direction about a second point thereon from said second position to a third position, the second point being spaced from the first point, one of said main curved portions engaging one of said parts when the arm is moved in one direction about an axis remote from said end and the other of said main curved portions engaging the other of said parts when the arm is moved in the other direction.

8. A pump element according to Claim 6 in which the line when in its second

position is bisected by a radial line from the piston axis.

9. A linkage for converting rectilinear movement into angular movement comprising a rectilinearly movable element having a pair of opposed parts, and an angularly movable arm having a configurated end including two main curved portions which can slidingly engage said opposed parts of the rectilinearly movable element respectively, each of the main curved portions having a profile which is defined substantially by the curve traced by the ends of a straight line of fixed length when that is rotated about a first point thereon from a first position to a second position, and by the other end when the line is further rotated in the same rotational direction about a second point thereon from said second position to a third position the second point being spaced from the first point, one of said main curved portions engaging one of said parts when the arm is moved in one direction about an axis remote from said end and the other of said main curved portions engaging the other of said parts when the arm is moved in the other direction.

10. A fuel pump comprising a casing including a plurality of cylinders, a piston axially reciprocable within each cylinder so as to deliver fuel at pressure to a respective outlet, the quantity of fuel delivered by each piston in each stroke being adjustable by moving the piston angularly about its axis, and a rectilinearly movable control rod, each piston being connected to the control rod by means of a linkage as claimed in Claim 9. the arm of each linkage being operatively connected to the respective piston for angular movement therewith about the piston axis and the rectilinearly movable element of each linkage being carried by the control member, such that rectilinear movement of the control rod causes simultaneous angular movement of the pistons.

11. A fuel pump for supplying fuel to an internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.