Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-07-29
2001-02-13
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S456000, C123S514000
Reexamination Certificate
active
06186120
ABSTRACT:
PRIOR ART
The invention relates to a high-pressure pump for fuel a supply in fuel injection systems of internal combustion engines, in particular in a common rail injection system, in which the fuel injection system includes a low-pressure part that contains a fuel tank and a prefeed pump and a high-pressure part that contains a high-pressure pump and a common distributor strip, or common rail, into which a fuel flow is fed from the high-pressure pump through a common conduit.
In conventional fuel injection systems of this type, normally a constant fuel flow is pumped by the prefeed pump into individual elements of the high-pressure pump, regardless of demand. The individual elements of the high-pressure pump may for instance be a plurality of cylinders, in each of which one piston can reciprocate in order to aspirate the fuel and impose high pressure on the fuel. If a constant rpm-dependent fuel supply is pumped by the high-pressure pump into the common rail regardless of demand, this means that the power consumption of the high-pressure pump is constant even if the demand is dropping. This has an unfavorable effect on the overall efficiency of the engine. The excess fuel quantity, compressed to high pressure, must moreover be diverted from the high-pressure pump again, which leads to temperature changes in the fuel.
To improve the overall efficiency of the engine, it has already been proposed that a regulated electric low-pressure feed pump be used for controlling the fuel flow to the individual elements of the high-pressure pump. This has the disadvantage, however, that damage from cavitation can occur in the intake stroke of the high-pressure pump.
It has also been proposed, in European Patent 0 481 964, to control the filling of each of the individual elements of the high-pressure pump with a respective magnet valve. This is very complicated, however, and entails high costs, since one magnet valve is needed for each element of the high-pressure pump.
An object of the invention is therefore to furnish a high-pressure pump which overcomes the above disadvantages. In particular, damage to the individual elements of the high-pressure pump during operation is to be avoided. Furthermore, a high-pressure pump of simple design, which meets stringent safety requirements and can nevertheless be produced economically, is to be created.
This object is attained by the high-pressure pump set forth hereinafter. Particular types of embodiment of the invention are disclosed hereinafter.
In a high-pressure pump for fuel supply in fuel injection systems of internal combustion engines, in particular in a common rail injection system, in which the fuel injection system includes a low-pressure part that contains a fuel tank and a prefeed pump and a high-pressure part that contains a high-pressure pump and a common rail into which a fuel flow is fed from the high-pressure pump through a common conduit, the object of the invention is attained in that an integrated demand-based quantity control for the fuel flow pumped by the high-pressure pump is integrated with the pump. The demand-based quantity control integrated with the high-pressure pump contributes to improving the overall engine efficiency, because the power consumption of the high-pressure pump drops as a result. The demand-based quantity control of the fuel flow pumped by the high-pressure pump offers the advantage that incomplete filling of the individual elements of the high-pressure pump is averted. This lessens the risk of cavitation.
One particular type of embodiment of the invention is characterized in that the demand-based quantity control includes a multi-way valve, which furnishes the fuel flow pumped by the high-pressure pump either to the common rail or to the low-pressure part of the fuel injection system, as needed. This makes it possible to regulate to a desired set-point value, by means of a suitable regulation strategy. The high-pressure pump then acts as an adjuster in the pressure regulation circuit. The demand-based quantity control of the fuel flow pumped by the high-pressure pump is advantageously accomplished with only a single multi-way valve. This saves on the cost of producing the high-pressure pump. It advantageously reduces the installation space required by the high-pressure pump as well.
Another particular type of embodiment of the invention is characterized in that the multi-way valve is a 3/2-way valve, which is mounted in the common conduit and which connects the common conduit in a first valve position, to the common rail and, in a second valve position, to the low-pressure part of the fuel injection system. In the second valve position, the fuel flow returns, pressureless, to the low-pressure part of the fuel injection system without being subjected to high pressure. The fuel flow can be returned either to the fuel tank or to the connecting line between the prefeed pump and the high-pressure pump. Because the entire fuel flow is pumped by the high-pressure pump, dividing it into a feed flow and a lubricating flow in the low-pressure part can be dispensed with.
Another particular type of embodiment of the invention is characterized in that a check valve is disposed between the multi-way valve and the common rail. In the first valve position, the common conduit communicates with the common rail. By means of the check valve disposed between the multi-way valve and the common rail, it is attained that the fuel is compressed by the individual elements of the high-pressure pump until such time as a desired pressure is reached. Once the desired pressure is attained, the check valve opens, and the fuel flows into the common rail. Thus the fuel is aspirated at high pressure in the high-pressure pump only when the multi-way valve is in the first valve position.
Another particular type of embodiment of the invention is characterized in that the multi-way valve is magnetically actuatable. By means of the magnetic actuation, short switching times can be attained.
Another particular type of embodiment of the invention is characterized in that the high-pressure pump is a radial piston pump that includes a drive shaft, which is supported in a pump housing and is embodied eccentrically or having camlike protrusions in the circumferential direction, and preferably a plurality of pistons, disposed radially relative to the drive shaft in a respective cylinder chamber, which are movable radially back and forth in the respective cylinder chamber by rotation of the drive shaft. Such radial piston pumps are especially well suited to common rail injection systems. As the pistons reciprocate, fuel is first aspirated and then compressed.
The present invention has the advantage in general that it can be made simply and economically. The fundamental concept of the present invention can moreover be employed in a simple way in conventional high-pressure pumps, because known components of conventional high-pressure pumps can be used. This keeps both development effort and costs low.
Further advantages, characteristics and details of the invention will become apparent from the ensuing description, in which one exemplary embodiment is described in detail with reference to the drawings. Characteristics recited in the claims and mentioned in the description may be essential to the invention either individually or in arbitrary combination with one another. One way of realizing the claimed invention is explained below in detail in conjunction with the drawings.
REFERENCES:
patent: 4838232 (1989-06-01), Wich
patent: 5085193 (1992-02-01), Morikawa
patent: 5718207 (1998-02-01), Ito
patent: 5785025 (1998-07-01), Yoshiume et al.
patent: 5884606 (1999-03-01), Kellner et al.
patent: 5915361 (1999-06-01), Heinz et al.
patent: 1 97 01 392 A1 (1997-07-01), None
patent: 0 481 964 A2 (1989-11-01), None
patent: 0 735 268 A2 (1996-03-01), None
Aktuell, Pumpen-Pionier, p. 62, 1997.
Guentert Josef
Hammer Juergen
Greigg Edwin E.
Greigg Ronald E.
Moulis Thomas N.
Robert & Bosch GmbH
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