GB2266934A

GB2266934A - Cold-starting devices for fuel injection pumps.

Info

Publication number: GB2266934A
Application number: GB9309763A
Authority: GB
Inventors: T G Nagender; Chandra Prakash Mathur; Neeli Venkanna
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-05-13
Filing date: 1993-05-12
Publication date: 1993-11-17
Anticipated expiration: 2013-05-12
Also published as: CZ283945B6; GB9309763D0; GB2266934B; JPH0650240A; CZ82293A3; DE4215721A1

Abstract

A cold-starting device for a fuel-injection pump comprises a hydraulic tappet (1) connected to a feed pump (14) via a fluid line (13) having a non-return valve (17), a fluid pressure accumulator (18) and a control valve (19) connected in series. The fluid pressure accumulator (18) has a latch mechanism (45) which, with the actuating means (20) of the control valve (19), is connected to an ignition switch (33), At start-up of the associated engine the ignition switch is moved to position (332) and on to position (333). Such action causes opening of the valve (19) and release of the accumulator's latch mechanism (45). Hydraulic fluid is thus expelled from the accumulator (18) to move the tappet to the start position (a) for advanced injection. Expansion of a unit (35) occurs during engine warm up and this changes over the valve (19) and causes re-charging and latching of <IMAGE>

Description

2266934

DESCRIPTION COLD-STARTING DEVICES FOR FUEL INJECTION PUMPS

The invention relates to cold-starting devices for fuel injection pumps and in particular, but not exclusively, to devices for single or multicylinder internal combustion engines in, for example, motor vehicles.

It is known from DE-OS 29 32 672 to provide, for a cold-starting device, a non-return valve and a control valve downstream of a pressure supply pump and to provide between the non-return valve and the control valve a pressure accumulator which, upon the opening of the relatively large flowthrough cross section in the control valve, increases the quantity of fluid which may be introduced into the hydraulic tappet. Quite apart from the fact that the pressure accumulator is disposed laterally of the actual line and therefore requires connection means to connect it into this line, the pressure ratios are not adequately defined when introducing the fluid. In a coldstarting device of this type, it is important that, upon starting, a maximum fluid gap with a required fluid pressure, that is, a sufficiently high fluid pressure, becomes effective in the hydraulic tappet over a specific period time in order to produce a defined advance of the injection operation, and that -2this fluid gap disappears again, that is, becomes zero, when a specific temperature is reached.

In accordance with the present invention there is provided a coldstarting device for a fuel injection pump, in which a hydraulic tappet is connected to a feed pump by way of a fluid line in which a non-return valve, a fluid pressure accumulator and a control valve are located one after the other, wherein the control valve has an actuating means and the fluid pressure accumulator has a latch mechanism which latch mechanism and actuating means are connected to an ignition switch.

This renders it possible to maintain defined pressure ratios during the entire discharge of the fluid into the hydraulic tappet and to store a maximum adapted quantity of fluid in the fluid pressure accumulator. The latch mechanism renders it possible to shut off the fluid pressure accumulator entirely when the engine of a motor vehicle is sufficiently hot. A magnet associated with the control valve ensures rapid and reliable operation.

A simple means of actuation is rendered possible by coupling the coldstarting device to the ignition switch which is at the same time the ignition switch of the motor vehicle. Advantageously, the coupling is undertaken in such a way that in addition to the "off" -3position of the ignition switch. the first position of the switch opens the solenoid valve and the second position of the switch releases the fluid pressure in the accumulator.

When the conditions of the cold start no longer exist, that is. the engine has attained an adequate temperature, an expansion unit. such as an expansion sensor operating in dependence upon temperature, acts upon a switch which limits the efficacy of the coldstarting device. restores the control valve by means of the magnet. and locks the piston which has been forced back into its initial position.

In the same way as on the control valve, a solenoid may be provided on the latch mechanism for the purpose of actuating it. The latch mechanism may at the same time be secured to a rod which is secured to the piston and extends out of the pressure accumulator which is in the form of a cylinder, or may act directly upon the piston through the cylinder.

By way of example only. specific embodiments of the invention will now be described. with reference to the accompanying drawings. in which:- Fig. 1 is a schematic view of a first embodiment of the cold-starting device constructed in accordance with the invention; Fig. 2 is a schematic illustration of the fluid -4pressure accumulator of a second embodiment; and Fig. 3 is a schematic view of the fluid pressure accumulator of Fig. 2 in a different switching position.

Fig. 1 shows a hydraulic tappet 1 having a roller 3 rolling on a cam 2, a tappet body 5 which slides in a housing 4, a tappet plunger 6 displaceable in the tappet body 5, a hood-shaped cover part 7 which is partially counter-sunk into the tappet body 5 and loaded by a compression spring 10, and a foot 81 of a piston 8 which abuts against the tappet plunger 6 by way of spring abutment plate 44. A compression spring 9 abuts at one end against the cover plate 7 and at its other end against the spring abutment plate 44 which fixes the piston foot 81 in its axial position. A pin 11 serves to secure the tappet plunger 6 against rotation. A fluid passage 12 in the housing 4 and in the tappet body 5 serves to feed a fluid which can widen a gap 43, acting as a pressure chamber, which already partially exists between the tappet body 5 and the tappet plunger 6, in such a way that. corresponding to a stroke of the tappet plunger 6, the adjacent front faces of the tappet body 5 and the tappet plunger 6 can move away from one another up to a specific amount designated a. All the parts of the hydraulic tappet 1 are disposed coaxially to a -5longitudinal axis X-X of the pump piston 8.

The hydraulic tappet 1 is connected by way of a fluid line 13 to a feed pump 14 which is part of an internal combustion engine (otherwise not show) and which has an associated reservoir 15. The fluid line 13 extending downstream from the feed pump 14 contains a branch 16 leading to other systems. and, one behind the other, a non-return valve 17, a fluid pressure accumulator 18, and a three-port two-position control valve 19 which is actuated by a solenoid 20. Thus, the control valve 19 is a solenoid valve having three ports and two positions.

The fluid pressure accumulator 18 comprises a cylinder 21 in which a piston 23, cooperating with a compression spring 22, is movable in the direction of arrow 24. A rod 25 is secured to the piston 23 and extends out of the cylinder 21 and into a housing 26 (only partially shown) in which is located a rod 29 which is actuated by a solenoid 27 and a spring 28 and which co-operates with a latch recess 30 in the piston rod 25. The components 26 to 30 form a latch mechanism 45.

An electrical lead 32 leads from a d.c. source 31 (vehicle battery of, for example, 12 volts) to an ignition switch 33 which may assume three switching positions 331, 332r 333, of which the switching -6position 331 signifies "OFF". Leads 321 and 322 lead from the other two switching positions 332 and 333 respectively to the solenoid valve 19 and to the solenoid 27 by way of a limit switch 34 and render it possible to actuate the solenoid valve 19 and the latch mechanism 45. The switch 34 is connected to an expansion unit 35 which, for example, is in the form of an expansion sensor and expands when the engine is hot and effects corresponding switching of the switch 34.

The cold-starting device in accordance with the invention is located in the position shown in Fig. 1. BefEore starting, the ignition switch 33 is in the "OFF" position 331, the control valve 19 is closed, and the cylinder 21 is filled with fluid or oil which cannot escape to the feed pump 14 through the nonreturn valve 17 or to the hydraulic tappet 1 through the control valve 19. If, as is customary upon cold starting, the ignition switch 33 is now switched from switching position 331 into switching position 332 and immediately thereafter into switching position 333, the solenoid valve 19 is opened and the latch mechanism 26 to 30 is released, so that oil may flow in an unobstructed manner from the line 13 and into the hydraulic tappet 1 through the control valve 19 and the passage 12. The oil emerges from the line 13 -7and flows into the hydraulic tappet 1 at a pressure of from three to four bar and includes the oil which is forced out of the fluid pressure accumulator 18 by the piston 23 in the cylinder 21 urged to the left, as viewed in the drawing, by the spring 22. Since the oil cannot escape from the hydraulic tappet 1, the gap 43 fills with pressurised oil and forms between the tappet plunger 6 and the tappet body 5 a gap sufficient to obtain an earlier injection of fuel corresponding to the cold-starting conditions. Upon forcing the oil into the hydraulic tappet 1, the front face of the tappet plunger 6 is removed from the adjacent face of the tappet body 5 by the amount a against the initial stress of the compression spring 9. The tappet body 5 and the tappet plunger 6 remain in this mutual position until, as a result of the heating of the internal combustion engine (otherwise not shown). the unit 35 has expanded to the extent that it actuates the switch 34 and thus the magnet 20 and renders the latch mechanism 45 inoperative. The control valve 19 is switched over in this manner, so that the oil can escape from the gap (not shown) between the tappet body 5 and the tappet plunger 6 into the reservoir 15 by way of a portion of the line 13. Furthermore, the piston 23 in the cylinder 21 is urged to the right, as viewed in the drawing, against -8the force of the compression spring 22 by the oil pressure generated by the feed pump 14 and is finally arrested by the interlocking of the tip of the rod 29 in the latch recess 30. In this manner, the oil or fluid pressure required for the next cold start is built up in the cylinder 21.

A fluid pressure accumulator 36, having a cylinder 37 and a piston 39 under the pressure of a spiral spring 38, is shown in Figs. 2 and 3. The fluid line 40 for the inflow and outflow of the fluid leads from the feed pump 14 to the control valve 19 (Fig. 1) through the cylinder 37. A latch mechanism 41 is mounted directly on the cylinder 37. The rod 42 extends into the cylinder 37 when in its locking position (Fig. 2) and prevents the piston 39 from moving to the left as viewed in the drawing. When the rod has been pulled in by the solenoid 46, it is possible for the piston 39 to move to the left as viewed in the drawing and travel across the end of rod 42 (Fig. 3).

The mode of operation is otherwise similar to that described with reference to Fig. 1.

Claims

1. A cold-starting device for a fuel injection pump, in which a hydraulic tappet is connected to a feed pump by way of a fluid line in which a nonreturn valve, a fluid pressure accumulator and a control valve are located one after the other, wherein the control valve has an actuating means and the fluid pressure accumulator has a latch mechanism which latch mechanism and actuating means are connected to an ignition switch.

2. A cold-starting device as claimed in claim 1, wherein the fluid pressure accumulator has a piston which is held against the fluid pressure in the fluid line by a spring whose force is less than the fluid pressure during operation of the hot internal combustion engine.

3. A cold-starting device as claimed in claim 1 or 2, wherein the control valve is a solenoid valve.

4. A cold-starting device as claimed in at least one of claims 1 to 3, wherein the ignition switch has at least three switching positions, one of which connects to the control valve and another of which connects to the fluid pressure accumulator.

5. A cold-starting device as claimed in claim 4, wherein a limit switch is disposed in the connection between the ignition switch and the control valve and/or between the ignition switch and the fluid -10accumulator, the limit switch being actuable by an expansion unit.

6. A cold-starting device as claimed in claim 1 or 2, wherein the latch mechanism is electromagnetic.

7. A cold-starting device as claimed in any one of claims 2 to 6, wherein the latch mechanism acts upon a piston rod of the piston of the fluid pressure accumulator.

8. A cold-starting device as claimed in any one of claims 2 to 6, wherein the latch mechanism is disposed on the cylinder of the fluid pressure accumulator and acts directly upon the piston.

9. A cold-starting device constructed, arranged and adapted to operate substantially as described herein, with reference to, and as illustrated in, the accompanying drawings.