Internal-combustion engines – Charge forming device – With fuel pump
Patent
1990-02-09
1991-07-23
Miller, Carl Stuart
Internal-combustion engines
Charge forming device
With fuel pump
123179L, F02M 3704
Patent
active
050334417
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a fuel-injection pump comprising a feed pump synchronously driven with the fuel injection pump and connected with the plunger chambers of a pressure control valve and a timer. A fuel-injection pump is known from German Offenlegungsschrift No. 3,148,214, in which the normally speed-proportional control pressure changing the start of injection, can be varied by a delivery valve in dependence on pressure and temperature. During cold starting, the delivery valve advances the start of injection so far that consequently sufficient time remains for the preparation of the fuel and correspondingly better ignition or combustion takes place.
A disadvantage is that, with an unfavourable configuration of the pressure-control valve, even when the injection pump is at a standstill a small gap in the shut-off orifice can be opened, and when the fuel injection pump is being started up, the delivery of the feed pump is then insufficient to build up the necessary pressure at low speeds in the return chamber, with the delivery valve closed, for the cold-start advance of the start of injection during the cold starting of the internal-combustion engine (cold-start function).
SUMMARY OF THE INVENTION
The object of the invention is a fuel-injection pump in which the cold-start function can be guaranteed by providing a counterpressure in the exhaust line. The object of the invention is achieved by providing an adjustable pressure valve in the exhaust line.
The counterpressure generated in the exhaust line by the pressure valve can be obtained by various valve designs, so that a pressure increase correction is also possible during normal functioning, without the cold-start function.
The present invention both as to its construction so to its mode of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of the preferred embodiments when read with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows schematically a fuel supply system with a pressure valve of a fuel-injection pump according to the invention;
FIG. 2 shows a diagram of pressure variations with the cold-start function in comparison with normal functioning, and FIGS. 3, 4 and 5 show different constructions of the pressure valve.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a distributor injection pump with a feed pump 1 which runs at the speed of the internal-combustion engine. The feed pump 1 sucks fuel from a fuel tank 49 via the feed-pump suction line 48 and conveys it via a delivery line 2, a distributor 6 and a connecting line 5 into a suction gallery 14 of the fuel-injection pump, from which the actual fuel-injection pump is supplied with fuel in a known manner. The suction gallery 14 is connected, via a bore 15 in an adjusting piston 11, to a working chamber 12 limited by the latter in a cylinder of a injection start adjusting device 9. A connecting line 3 also branches off from the distributor 6 and leads to a pressure chamber 18 of a pressure-control valve 7. The pressure-control valve 7 controls the fuel pressure prevailing downstream of the feed pump 1, that is also the pressure in the suction gallery 14, as a control pressure in dependence on the engine speed, the control pressure rising proportionally with an increasing speed. The adjusting piston 11 is displaced against a bias of a return spring 13 according to the control pressure and thereby engages with a pin 10 a cam drive, not shown, of the fuel-injection pump for adjusting the start of injection. Thus, during the normal operation of the internal-combustion engine or when the internal-combustion engine is running hot, the start of injection is "advanced" with an increasing speed. Because of the poor ignition quality of the fuel when the engine is cold, in order to ensure perfect starting, that is to say a rapid run-up of the engine with as little emission of blue smoke as possible, the start of injection must be set
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Miller Carl Stuart
Robert & Bosch GmbH
Striker Michael J.
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