Pumps – Expansible chamber type – Moving cylinder
Patent
1996-03-15
1997-12-23
Thorpe, Timothy
Pumps
Expansible chamber type
Moving cylinder
123450, 123506, 25112915, 417505, F04B 3700, F02M 4100
Patent
active
057001391
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 continuation of PCT/DE94/00695, filed Jun. 18, 1994.
BACKGROUND OF THE INVENTION
The invention is based on a fuel injection pump of the distributor type.
Fuel injection pumps of this kind with inward-opening switching valves (I-valves), or in other words with a valve member that upon valve opening is to be displaced counter to the fuel flow, have the advantage of operating stability over fuel injection pumps with outward-opening switching valves (A-valves). In such I-valves the operating direction of the valve member and the flow direction of the fuel flow that begins when the valve opens are in the same direction, since unlike the A-valve, the hydraulic pulse forces occurring in the opening operation and oriented oppositely of the fuel flow direction act to reinforce opening, so that brief closing phases in the opening operation and an attendant instability of the switching valve are fundamentally precluded.
Nevertheless, an unstable performance has been found during the injection phase in the opening and closing operation of such I-valves. This instability has the following causes: Before the onset of the injection event, the pump piston pumps fuel from the pump work chamber to the first valve chamber, via the valve opening uncovered by the valve member to the second valve chamber located in the low-pressure region. This pumping is continuous, so that one can say that there is a moving column of fuel. To initiate the injection event, the switching valve is closed, which tears the fuel column apart. Since this fuel column has its own dynamics, it remains in motion and is later braked by the pressure prevailing in the low-pressure region. Before that, however, it creates a void in the second valve chamber below the closed valve member. Subsequently, the braked fuel column is accelerated in the opposite direction in the low-pressure region, or in other words into the previously created void, and the void is then again filled. This creates a filling surge that strikes the end face of the valve member. If the valve member is still in motion at the time, then the motion of the valve member becomes uncontrollable, which leads to an unstable injection event. In a similar way, instabilities arise from opening of the valve member during termination, if at that time pressure pulsations are occurring in the fuel.
British Patent 2 261 035 discloses a distributor fuel injection pump, which has a pumping and distributor piston that is driven to both reciprocate and at the same time rotate in a pump cylinder and that in the pump cylinder on one side defines a pump work chamber that is closed off on the other side by a solenoid valve housing inserted in the housing of the fuel injection pump. Filling and relief of the pump work chamber are done by means of the solenoid valve, which with its valve member makes and breaks the transition from a first valve chamber, acted upon by high pressure and communicating with the pump work chamber, to a second valve chamber communicating with a relief chamber, and thus controls the phase in which the pump piston brings the fuel-filled pump work chamber to a high pressure that is effective for injection. The valve member has a low-pressure-side relief piston and is urged in the opening direction by a valve spring counter to the fuel outflow direction from the pump work chamber and in the closing direction by an electromagnet.
This known embodiment has the disadvantage that because of the solenoid valve adjacent to the pump cylinder, considerable space is needed for the fuel injection pump, and there is also a large idle volume because of the solenoid valve housing and the valve chambers and incoming lines that it contains; this idle volume must be prestressed to injection pressure by the pump piston upon each feed stroke of the pump piston yet is not available actively for injection. Moreover, the entire solenoid valve housing must close off the pump work chamber in a high-pressure-proof manner, which makes for further complication and expense in production
REFERENCES:
patent: 5228844 (1993-07-01), Klopfer et al.
patent: 5345916 (1994-09-01), Amann et al.
patent: 5582153 (1996-12-01), Dutt et al.
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
Thorpe Timothy
Tyler Cheryl J.
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