CLIAMS:We Claim:
1. A driving mechanism (10) for a high pressure pump, said driving mechanism (10) driving a rollet tappet (24) of said high pressure pump, said driving mechanism (10) comprising:
a variable geometry cam (14), said variable geometry cam (14) extending axially from a first end (15) to a second end (17), wherein said first end (15) has a radial length that is larger than said second end (17);
an actuator (20) coupled to said first end (15) by means of a shaft (18), and wherein said actuator (20) actuates said variable geometry cam (14) against a biasing force of a spring member (22); and
said second end (17) coupled to an engine crank shaft (16), wherein said engine crank shaft (16) transmits rotational motion to said variable geometry cam (14) of said high pressure pump.
2. The driving mechanism (10) in accordance with Claim 1, wherein said actuator (20) actuates said variable geometry cam (14) in a manner such that movement of said variable geometry cam (14) causes said roller tappet (24) to contact with said variable geometry cam (14) at any location between said first end (15) and said second end (17) of said variable geometry cam (14).
3. The driving mechanism (10) in accordance with Claim 2 wherein movement of said variable geometry cam (14) causes said roller tappet (24) to contact with said variable geometry cam (14) at any location between said first end (15) and said second end (17) of said variable geometry cam (14) to facilitate varying a pressure and quantity of fuel delivered from said high pressure pump.
4. A high pressure pump, said high pressure pump comprising:
a fuel outlet supply path coupled to a pump housing of said high pressure pump; characterized in that
a variable geometry cam (14), said variable geometry cam (14) extending axially from a first end (15) to a second end (17), wherein said first end (15) has a radial length that is larger than said second end (17);
an actuator (20) coupled to said first end (15) by means of a shaft (18), and wherein said actuator (20) actuates said variable geometry cam (14) against a biasing force of a spring member (22); and
said second end (17) coupled to an engine crank shaft (16), wherein said engine crank shaft (16) transmits rotational motion to said variable geometry cam (14) of said high pressure pump.
5. The high pressure pump in accordance with Claim 4 wherein said actuator (20) actuates said variable geometry cam (14) in a manner such that movement of said variable geometry cam (14) causes a roller tappet (24) to contact with said variable geometry cam (14) at any location between said first end (15) and said second end (17) of said variable geometry cam (14).
6. The high pressure pump in accordance with Claim 5 wherein movement of said variable geometry cam (14) causes said roller tappet (24) to contact with said variable geometry cam (14) at any location between said first end (15) and said second end (17) of said variable geometry cam (14) to facilitate varying a pressure and quantity of fuel delivered from said high pressure pump. ,TagSPECI:The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention:
[001] This invention relates to a driving mechanism for a high pressure pump and a high pressure pump thereof.

Background of the invention:
[002] Fuel is channelled to a high pressure pump where it is pressurized and delivered to a fuel injector. A cam lobe that is formed on a cam of the high pressure pump facilitates pressurizing and delivering fuel from an outlet of the high pressure pump. Specifically, the cam facilitates pressurizing and delivering fuel during a single stroke of a plunger of the high pressure pump. Since a stroke length of the roller tappet is constant for every pumping stroke of the plunger, the pressure and quantity of fuel delivered at an outlet of the high pressure pump cannot be varied. In order to vary the pressure and quantity of fuel delivered at the outlet of the high pressure pump, it is required to redesign the cam in such a manner that the cam profile is that of a variable geometry. The variable geometry cam may be actuated by means of a linear actuator.

[003] GB Patent Number 1385052-A: For reduced exhaust emissions from spark-ignition reciprocating piston engines as in motor vehicles, conventional vacuum and centrifugal advance controls are replaced by a three-dimensional cam mechanism. This includes a cam follower for angular adjustment of the distributor contact breaker assembly, as through a cable. The adjustment depends on the engine speed and the throttle setting. Conveniently the cam is rotatable by another cable connected to the accelerator, while a hydraulic diaphragm capsule axially adjusts the cam in response to a pump output pressure related to the engine speed.

Brief description of the accompanying drawings:
[004] An exemplifying embodiment of the invention is explained in principle below with reference to the drawing. The drawing is:
[005] Figure 1 shows a schematic view of a variable geometry cam that may be coupled to a high pressure pump.

Detailed Description of the invention:
[006] As shown in Figure 1, a driving mechanism 10 for a high pressure pump is described. The driving mechanism 10 drives a rollet tappet 24 of the high pressure pump. The driving mechanism 10 comprises a variable geometry cam 14, the variable geometry cam 14 extending axially from a first end 15 to a second end 17, wherein the first end 15 has a radial length that is larger than the second end 17. An actuator 20 is coupled to the first end 15 by means of a shaft 18, and wherein the actuator 20 actuates the variable geometry cam 14 against a biasing force of a spring member 22. The second end 17 is coupled to an engine crank shaft 16, wherein the engine crank shaft 16 transmits rotational motion to the variable geometry cam 14 of the high pressure pump.

[007] In addition, a high pressure pump is described. The high pressure pump comprises a fuel outlet supply path coupled to a pump housing of the high pressure pump. A variable geometry cam 14, the variable geometry cam 14 extending axially from a first end 15 to a second end 17, wherein the first end 15 has a radial length that is larger than the second end 17. An actuator 20 is coupled to the first end 15 by means of a shaft 18, and wherein the actuator 20 actuates the variable geometry cam 14 against a biasing force of a spring member 22. The second end 17 is coupled to an engine crank shaft 16, wherein the engine crank shaft 16 transmits rotational motion to the variable geometry cam 14 of the high pressure pump.

[008] The high pressure pump includes a pump housing. A fuel injector is coupled to the high pressure pump via a fuel outlet supply path. The fuel outlet supply path facilitates channeling pressurized fuel from an outlet of the high pressure pump to the fuel injector. The pressurized fuel is discharged from an outlet of the fuel injector to an engine cylinder.

[009] The driving mechanism 10 for the high pressure pump includes a housing 12. A variable geometry cam 14 is positioned within the housing 12. The variable geometry cam 14 is driven by means of an engine crank shaft 16. Specifically, the engine crank shaft 16 is coupled to the second end 17 of the variable geometry cam 14 by means of a coupling mechanism and imparts rotary motion to the variable geometry cam 14. The first end 15 of the variable geometry cam 14 is coupled to a shaft 18 by means of a coupling mechanism. The shaft 18 is translated in an axial direction by means of a actuator 20. The actuator 20 facilitates actuating the variable geometry cam 14 in an axial direction between the first end 15 and the second end 17 of the variable geometry cam 14.

[0010] A roller tappet 24 is in contact with the variable geometry cam 14. Specifically, an end portion of the roller tappet 24 is in contact with the variable geometry cam 14 and is actuated by the variable geometry cam 14. When the roller tappet 24 is in contact with the first end 15 of the variable geometry cam 14, the roller tappet 24 is lifted to a greater extent during the rotational movement of the variable geometry cam 14. When the roller tappet 24 is in contact with the second end 17 of the variable geometry cam 14, the roller tappet 24 is lifted to a lesser extent during the rotational movement of the variable geometry cam 14. The degree of lift of the roller tappet 24 is directly proportional to the pressure and flow rate of fuel delivered by the high pressure pump.

[0011] A spring member 22 is coupled between the actuator 20 and the first end 15 of the variable geometry cam 14. The spring member 22 applies a biasing force against the variable geometry cam 14. The biasing force applied by the spring member 22 on the variable geometry cam 14 facilitates axially translating the roller tappet 24 to the second position 17 when the actuation force by the actuator 20 has been withdrawn and the actuator shaft 18 returns to its original unextended position. In an alternate embodiment, the actuator 20 translates the actuator shaft 18 axially to facilitate translating the roller tappet 24 to the second position 17, wherein the variable geometry cam 14 is guided by the retention force of the spring member 22.

[0012] An operation of the driving mechanism 10 for the high pressure pump is described as an example. When it is desired to supply a reduced quantity of fuel from the high pressure pump at a low operating pressure, the roller tappet 24 is at the second end 17 of the variable geometry cam 14. In this position, the variable geometry cam 14 is rotated by means of the crank shaft 16. Due to the lesser lift afforded by the variable geometry cam 14, the roller tappet 24 is lifted to a lesser extent. Therefore, owing to the lesser lift of the roller tappet 24, the output pressure and quantity of fuel delivered by the high pressure pump is lower.

[0013] When it is desired to supply an increased quantity of fuel from the high pressure pump, the actuator 20 actuates the variable geometry cam 14 by means of the linear actuator shaft 18. Therein, the roller tappet 24 slides axially towards the first portion 15 of the variable geometry cam 14 against a biasing force of the spring member 22. Due to the greater lift afforded by the variable geometry cam 14 on any portion axial to the first portion 17 of the variable geometry cam 14, the roller tappet 24 is lifted to a greater extent. Therefore, owing to the greater lift of the roller tappet 24, the output pressure and quantity of fuel delivered by the high pressure pump currospondingly increases. Any value of fuel pressure and fuel quantity between the higher and lower operating points may be selected by translating the variable geometry cam 14 axially to the desired location between the first portion 15 and the second portion 17.

[0014] The above described driving mechanism 10 for the high pressure pump is cost effective and highly reliable. The first end 15 of the variable geometry cam 14 facilitates pressurizing and delivering fuel from the high pressure pump at a lower pressure and flow rate, while the second end 17 of the variable geometry cam 14 facilitates pressurizing and delivering fuel from the high pressure pump at a higher pressure and flow rate to the fuel outlet supply path. Any value between the higher pressure and flow rate and the lower pressure and flow rate of fuel delivered may be selected by translating the roller tappet 24 axially between the first end 15 and second end 17 of the variable geometry cam 14. Moreover, the modular nature of each sub-system of the high pressure pump facilitates easy disassembly and replacement of individual system components as required.

[0015] It must be understood that the embodiments explained in the above detailed description is only illustrative and does not limit the scope of this invention. The scope of this invention is limited only by the scope of the claims. Many modification and changes in the embodiments aforementioned are envisaged and are within the scope of this invention.