Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Reexamination Certificate
1998-01-20
2001-02-06
Thorpe, Timothy S. (Department: 3746)
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
C417S199100, C123S502000
Reexamination Certificate
active
06183209
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an advance arrangement for use in adjusting the timing of fuel delivery of a high pressure fuel pump.
BACKGROUND OF THE INVENTION
In a known high pressure fuel pump, a rotor is provided with one or more bores, pumping plungers being reciprocable within the bores. The outer end of each pumping plunger has a shoe and roller arrangement associated therewith, the rollers being engageable with the cam surface of a cam ring. As the rollers ride over cam lobes forming part of the cam surface during rotary motion of the rotor with respect to the cam ring, the plungers are pushed inwardly into the respective bores, pressurizing and displacing fuel from the bores to permit fuel to be supplied under pressure to the cylinders of an associated engine.
It will be appreciated that the timing of fuel delivery by the pump is dependent upon the position of the cam lobes, and hence upon the angular position of the cam ring. The timing of fuel delivery can therefore be advanced or retarded by moving the cam ring. One way of moving the cam ring is to provide the cam ring with an outwardly extending peg which is received within a recess or opening provided in an advance piston. The piston is slidable within a bore, and is spring biased towards one end of the bore. Fuel under pressure is supplied to the bore, the fuel pressure acting on a surface of the piston to apply a force to the piston acting against the spring. In such an arrangement, variations in the fuel pressure applied to the bore result in the advance piston occupying different axial positions, the engagement between the piston and the peg transmitting axial movement of the piston to the cam ring, adjusting the angular position of the cam ring.
The fuel supplied to the advance piston is conveniently drawn from a low pressure feed pump which is used to supply fuel to the high pressure pump. The output pressure of the feed pump is conveniently controlled so as to be related to engine speed, and in such an arrangement, the timing of fuel delivery by the high pressure pump is related to engine speed. It is known to provide a valve arrangement between the feed pump and the advance piston whereby the fuel pressure applied to the advance piston, and hence the timing of fuel delivery, can be controlled independently of engine speed.
It is advantageous to minimize the quantity of fuel drawn from the feed pump for purposes other than supplying the high pressure pump with fuel in order to reduce the maximum capacity of the feed pump.
BRIEF SUMMARY OF THE INVENTION
According to the present invention there is provided an advance arrangement for use with a high pressure pump which is arranged to be supplied with fuel by a feed pump, the advance arrangement comprising an advance piston slidable within a bore, the advance piston being cooperable with the cam arrangement of the high pressure pump to transmit axial movement of the advance piston to the cam arrangement to adjust the timing of fuel delivery by the high pressure pump, a face of the advance piston defining, with the bore, a control chamber, and pump means independent of the feed pump for supplying fluid to the control chamber.
The pump means conveniently comprises a reciprocating electromagnetically operated axial piston pump. The pump is preferably operated under the control of a control system whereby the speed of reciprocation of the pump is adjusted to control the fluid volume within the control chamber.
It will be appreciated that as the pump means is independent of the feed pump, the operation of the advance arrangement does not draw fuel from the feed pump, thus the maximum capacity of the feed pump can be reduced.
REFERENCES:
patent: 4393846 (1983-07-01), Mowbray et al.
patent: 4407250 (1983-10-01), Eheim et al.
patent: 4733640 (1988-03-01), Laufer et al.
patent: 4743179 (1988-05-01), Waas et al.
patent: 5059096 (1991-10-01), Harris
patent: 1932600 (1971-01-01), None
patent: 3516456A1 (1986-11-01), None
patent: 58-59320 (1983-04-01), None
patent: 58-59319 (1983-04-01), None
Lucas Industries Limited
Michael & Best & Friedrich LLP
Thorpe Timothy S.
Tyler Cheryl J.
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