Claims:We claim:
1. A fuel pump (100) comprising:
- a housing (104);
- an inlet (106) in said housing (104) to receive fuel for compression;
- a piston (108) reciprocably and rotatably movable in a bore in said housing (104);
- a cam drive means coupled to said piston through a cam interface (114), said cam interface (114) comprising a rotatable roller ring (120) to adjust the pressure stroke of said piston; said roller ring (120) being in contact with a set of rollers (121) which are in contact with cam interface (114);
said injection pump (100) characterized by:
- an electrical motor (126); shaft (302) of said electrical motor (126) is coupled to said roller ring (120) through a nut (303) and a lever (301); rotary motion of said shaft (302) is converted to linear motion of said nut (303) which rotates said roller ring (120) using said lever (301).
2. A fuel pump (100) according to claim 1 wherein said electrical motor 126 is rotated in a first direction to advance the pressure stroke of said piston (108).
3. A fuel pump according to claim 1 wherein said electrical motor is rotated in a second direction to retard the pressure stroke of said piston (108).
4. A fuel pump according to claim 1 wherein said electrical motor (126) is controlled by an electronic control unit.
5. A fuel pump according to claim 1 wherein said shaft (302) and said nut (303) are coupled using threads.
6. A fuel pump according to claim 1 wherein said nut (303) is coupled to said lever (310) using an eccentric shaft
7. A fuel pump according to claim 1 wherein said roller ring is coupled to said lever using said eccentric shaft
, Description:Field of the invention:
[0001] This invention relates to the field of fuel injection systems. The invention relates to high pressure pumps used in the field of fuel injection systems.

Background of the invention:
[0002] The fuel pumps with mechanically controlled timing devices are known in prior arts. The US patent 4,388,909 discloses one such fuel injection timing control system for a Diesel engine, having a fuel injection pump supplying fuel to the engine according to the rotation of the engine crankshaft. A device is connected to the fuel pump to vary the fuel injection timing in terms of crank angle. A control unit is connected to the device and the arrangement to drive them in such a manner that when the arrangement is operative to effect the exhaust gas recirculation, the fuel injection timing is advanced to facilitate effective exhaust gas re-circulation.

Brief description of the accompanying drawings:
[0003] Shown in fig. 1 is a sectional view of a fuel pump with an electrical motor to control a timing device according to one embodiment of the invention.
[0004] Shown in fig 2 is the timing device available in prior arts
[0005] Shown in fig 3 and fig. 4 is a sectional view of an electrically controlled timing device for the fuelpump

Detailed description of the embodiments:
[0006] Shown in fig. 1 is a cross sectional view of a fuel pump 100. The fuel pump comprises a housing 104; an inlet 106 in the housing 104 to receive fuel for compression; a piston 108 reciprocably and rotatably moves in a bore in the housing 104; a cam shaft 102 coupled to said piston through a cam interface 114, said cam interface 114 comprising a rotatable roller ring 120 to adjust the pressure stroke of said piston; said roller ring 120 being in contact with a set of rollers 121 which are in contact with cam interface 114. The fuel pump 100 additionally comprises an electrical motor 126 for controlling the timing of the compression stroke of the piston; the shaft 302 of the electrical motor 126 is connected to the roller ring 120 through a nut 303 and a lever 301; rotary motion of the shaft 302 is converted to linear motion of the nut 303 which rotates the roller ring 120 using the lever 301.
[0007] The fuel pump is also referred as high pressure pump or just as a pump in this document. The cam interface 114 comprises cam plate. The terms cam interface and cam plate are used interchangeably in this document. The pump in addition comprises a distributor groove 110 to supply pressurized fuel to a set of injectors which are not shown in fig..
[0008] The pump 100 is mainly divided into four parts, a low pressure pumping stage; a high pressure pumping stage; a timing device and a speed governor. The low pressure pumping stage, the high pressure pumping stage, the timing device and the speed governor are located in the same housing 104. The low pressure stage typically comprises a vane pump 112. The low pressure stage is used to ensure the fuel entering the high pressure stage is at a required constant pressure.
[0009] The high pressure stage comprises the piston 108, the cam plate 114 coupled to the piston 108, and the distributor or distributor groove 110. The piston 108 moves reciprocably and also rotates at the same time. During each pressure stroke of the piston 108, fuel is fed from a pump chamber 116 through the distribution groove 110 to one of a plurality of pressure conduits. From these pressure conduits, the fuel goes to fuel injectors. The pump chamber 116 is supplied fuel through a suction chamber 118 in the housing 104.
[0010] The rotary movement of the drive shaft 102 is transferred to the piston 108 via the cam plate 114. The cam plate 114 is forced against a roller ring 120 by a spring 122, and when the roller ring 120 rotates the cam lobes riding on the ring’s rollers 121 convert the purely rotational movement of the drive shaft 102 into a rotating-reciprocating movement of the cam plate 114. The piston is forced to its TDC (Top Dead Centre) position by the cams on the cam plate 114, and the return springs 122 force it back again to its BDC (Bottom Dead Centre) position. These springs 122 also prevent the cam plate jumping off the rollers during harsh acceleration.
[0011] The fuel enters through the inlet 106, passes through the low pressure pumping stage 112, passes through the suction chamber 118, then into the high pressure stage, into the pump chamber 116. The piston 108 pressurizes the fuel in the pump chamber 116 and the pressurized fuel is delivered to the injectors through the distributor groove 110. There will be as many distributor grooves as the number of injectors.
[0012] The speed governor 124 comprises a shaft and a set of flyweights. The shaft is driven by the drive shaft through a gear. As the speed of the engine changes, the flyweights either move towards the shaft or away from the shaft, thereby regulating the amount of fuel entering the high pressure stage.
[0013] The pump 100 comprises a timing device comprising an electrical motor 126 which is coupled to the roller ring 120 through the lever.
[0014] Fig. 2 shows a timing device 200 used in the pump 100 in the prior art pumps. In the prior art pumps, the timing device controls the timing of the injections by altering the timing of the TDC of the piston 108, using mechanical components. The hydraulically controlled timing device 200 is located in the bottom of the pump’s housing, at right angles to the pump’s longitudinal axis. The timing device 200 comprises the ring 120 and the rollers 121.
[0015] The ring 120 has a U-shaped cross section and has an injection adjustment piston 202. The piston 202 is free to move in the pump housing. The housing is closed with a cover on each side. There is a passage in one end of the piston 202 through which the fuel can enter, while at the other end the piston 202 is held by a compression spring 204. The piston 202 is connected to the ring through a sliding block and a pin 206 so that movement of the piston 202 can be converted to rotational movement of the ring 120. The piston 202 is held in its initial position by the spring 204. During operation, the pressure control valve regulates the fuel pressure inside the pump so that it is proportional to engine speed. As a result, the engine speed dependent fuel pressure is applied to the end of the piston 202 opposite to the spring 204.
[0016] When the engine speed increases, the fuel pressure increases in the suction chamber 118. The piston 202 is displaced against the force of the spring 204 and the roller ring 120 undergoes a corresponding turning, whereby the rollers 121 come into contact with the cams of the cam plate 114 somewhat earlier and therefore initiate the start of the compression stroke of the piston 108 resulting in fuel feeding process earlier in time. Therefore, the higher the speed, the earlier is the beginning of delivery of pressurized fuel.
[0017] When the speed of the engine reduces, the piston 202 is displaced away from the spring 204. The roller ring 120 undergoes a corresponding turning, whereby the rollers 121 come into contact with the cams of the cam plate 114 somewhat later and therefore initiate the start of the compression stroke of the piston 108 resulting in fuel feeding process later in time. Therefore, at lower speeds, the later is the beginning of delivery of pressurized fuel.
[0018] The timing device 200 in the above pumps is completely mechanical. The invention proposes an electronically controlled timing device 300.
[0019] Shown in fig. 3 and 4 is the electronically controlled timing device comprising an electrical motor 126 coupled to the roller 120. The electrical motor 126 is controlled by an electronic control unit ECU which is not shown. As nowadays all the fuel injection systems are controlled by an electronic unit, the same ECU can be used to control the electrical motor of the timing device of the pump. In other embodiments, the engine is controlled by an engine control unit and the same engine control unit may be used to control the timing device. The ECU controls the electric motor based on the torque demand by the user. The motor is mounted on a supporting bracket. The motor shaft 302 of the motor 126 is extended and with threads on the other end which mate with threads of the nut 303 which is pivotally secured in the roller ring lever 301. Controlled by the ECU, the motor shaft 302 rotates with specified angle resulting in the linear motion of the nut 303. The nut 303 is coupled to an eccentric shaft 304 which is coupled to roller ring 120.
[0020] The working of the time timing device is explained below
[0021] When the speed of the engine increases, the electrical motor is rotated in a first direction by the ECU. The rotational motion of the shaft of the electrical motor is converted into linear motion of the nut. As the nut is coupled to the lever, the lever moves in a circular direction as lever is pivoted, corresponding to motor rotation. The lever is coupled to the eccentric shaft. The eccentric shaft moves thereby rotating the roller ring 120 in a first direction. This in turn results in earlier compression stroke of the piston as explained earlier for mechanical timing device. When the engine speed decreases the electrical motor is rotated in a second direction by the ECU, leading to rotation of roller ring in a second direction. This in turn results in later compression stroke of the piston as explained earlier for mechanical timing device, resulting in delayed fuel delivery.
[0022] Thus by rotating the electrical motor in a first or second direction, the compression stroke of the piston 108 is either advanced or delayed. The direction of rotation of the electric motor is controlled by the ECU depending upon whether the speed of the engine is increasing or decreasing.
[0023] As the mechanically controlled timing device is replaced by the electronically controlled timing device, the timing can be controlled easily and accurately. As all the associated mechanical components are eliminated, the complexity of the pump is reduced and also the wear and tear of the components is largely reduced. As, typically an ECU will be already available in the vehicle, the same ECU is used to control the electrical motor, making the timing device simple and cost effective.