Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-06-22
2001-03-06
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S456000
Reexamination Certificate
active
06196191
ABSTRACT:
PRIOR ART
The invention is based on a fuel injection system for internal combustion engines as. In one such fuel injection system for internal combustion engines, known from the professional journal “mot”, No. 13 (1997), Jun. 7, 1997, page 62, a high-pressure pump fills a high-pressure collection chamber (common rail) with fuel at high pressure from a tank. From this high-pressure collection chamber, which is preferably formed by a distributor strip, all the injection lines lead away to the individual injection valves. The high-pressure fuel pump is supplied with fuel from a fuel tank by means of a prefeed pump, which via a low-pressure line system pumps into a work chamber of the high-pressure pump. In the known fuel injection system, a control valve is inserted into the low-pressure line system to control the high-pressure pumping quantity of the high-pressure pump. This control valve controls the flow from a low-pressure feed line into the work chamber of the high-pressure pump, and a high-pressure line leads away from the pump side of this feed line to the high-pressure collection chamber. Adjusting the high-pressure pumping quantity at the high-pressure feed pump is now done by closing the overflow cross section between the part of the line leading away from the pump work chamber into the low-pressure line system during the pumping stroke phase of the high-pressure feed pump. The prefeed pump uninterruptedly supplies the pump work chamber with fuel, and the fuel first passes through the control valve in the low-pressure line system. At the onset of the pumping stroke motion of the high-pressure feed pump, the control valve remains open, so that initially some of the fuel located in the pump work chamber is forced back into the low-pressure line system. If high-pressure pumping is to be done at the high-pressure pump, the control valve closes the overflow cross section into the low-pressure line system, so that in the further course of the pumping stroke motion of the high-pressure pump, a high fuel pressure is then built up in the pump work chamber and is carried on into the high-pressure collection chamber via the pressure line. The control of the high-pressure pumping quantity is effected via the instant of closure of the overflow cross section from the pump work chamber into the low-pressure operating system by means of the control valve; the high-pressure pumping quantity decreases, the later the control valve closes this overflow cross section, and vice versa.
The known fuel injection system for internal combustion engines has the disadvantage, however, that the entire fuel quantity pumped by the prefeed pump first flows into the work chamber of the high-pressure pump, and then at least some of it is positively displaced back into the low-pressure line system. In this initial expulsion of the fuel from the work chamber of the high-pressure pump, an unnecessary mass motion of fuel takes place, which unnecessarily lessens the efficiency of the high-pressure feed pump.
ADVANTAGES OF THE INVENTION
The fuel injection system for internal combustion engines according to the invention has the advantage over the prior art that the prefeed pump actually fills the pump work chamber of the high-pressure feed pump with only the fuel quantity needed at that moment, so that an unnecessary additional positive displacement work on the part of the pump pistons of the high-pressure feed pump can be avoided. This pumping flow filling control of the pump work chamber of the high-pressure feed pump as needed is achieved in a structurally simple way via control means in the low-pressure circuit filled by the prefeed pump. The low-pressure circuit is advantageously divided, in a first exemplary embodiment, into three branches which are jointly filled with fuel by the prefeed pump, preferably embodied as an electric fuel feed pump. A first branch is formed by a feed line to the pump work chamber of the high-pressure feed pump, into which line a constant pressure regulating valve is inserted. A second branch forms a lubricant oil line, which flows through a driving gear chamber of the pump drive of the high-pressure feed pump and in the process lubricates and cools the pump. This lubricant oil line preferably has a return flow throttle restriction downstream of the pump driving gear and discharges into the tank via a return line that forms the third branch. An electric pressure control valve, preferably a magnet valve, is intended into this return line into the tank. This electric pressure control valve in cooperation with the constant pressure valve in the feed line to the high-pressure pump forms the control means by way of which the degree of filling of the pump work chamber of the high-pressure pump can be adjusted. The holding pressure or minimum opening pressure of the electric pressure control valve in the return line is embodied as less than the opening pressure of the constant pressure valve in the feed line to the high-pressure pump and at the same time is greater than the flow resistance in the lubricant oil line. In this way, a reliable flow through the lubricant oil line and thus reliable cooling and lubrication of the pump driving gear are assured. In
FIG. 2
, a further advantageous exemplary embodiment is shown, in which the low-pressure circuit has only two branches. Here part of the feed line into the pump work chamber of the high-pressure feed pump forms the lubricant oil line through the pump driving gear. The electric pressure control valve is inserted into the feed line between the pump driving gear and the pump work chamber. The mechanical constant pressure valve required to set a certain standard pressure is inserted into the return line into the tank. A further advantage is attained by the additional provision of a bypass line between the feed side of the prefeed pump and the high-pressure collection chamber, into which line a check valve opening in the direction of the high-pressure collection chamber is inserted. In this way, when the engine to be supplied is started, a rapid pressure buildup in the high-pressure collection chamber is attained, and the injection pressure in the high-pressure collection chamber can be set to the maximum available value from the prefeed pump. In order to prevent flow losses via the lubricant oil line, it is advantageous to dispose a so-called flow limiter in series with the throttle restriction in the lubricant oil line; beyond a certain maximum flow, the flow limiter breaks the connection with the tank. For rapid pressure relief of the fuel injection system after the engine is turned off, it is furthermore advantageous to provide a 2/2-way magnet control valve in a relief line of the high-pressure collection chamber that discharges into the tank. Via a throttle upstream of this valve, the pressure can also be rapidly decreased when the control valve is open. In systems with variable injection pressure, a rapid adaptation to a lower pressure level is also possible. In order to avert the risk of overheating of the high-pressure pump, which exists because of the low pumping flow at high ambient temperatures and low injection quantities or high-pressure pumping quantities, the control valve in the relief line of the high-pressure collection chamber is opened purposefully during the pauses between injections if the ambient or fuel temperature exceeds a predetermined value. The resultant increase in the pumping flow into the pump work chamber of the high-pressure pump then assures sufficient cooling of the high-pressure pump.
Further advantages and advantageous features of the subject of the invention can be learned from the description, drawing and claims.
REFERENCES:
patent: 5441026 (1995-08-01), Akimoto
patent: 5537980 (1996-07-01), Yamamoto
patent: 5558068 (1996-09-01), Kunishima et al.
patent: 5626114 (1997-05-01), Kushida et al.
patent: 5758622 (1998-06-01), Rembold et al.
Kellner Andreas
Rembold Helmut
Gimie Mahmond M
Greigg Edwin E.
Greigg Ronald E.
Kamen Noah P.
Robert & Bosch GmbH
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