Internal-combustion engines – Charge forming device – Fuel flow regulation between the pump and the charge-forming...
Reexamination Certificate
1999-06-07
2001-08-28
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel flow regulation between the pump and the charge-forming...
C123S497000, C123S458000
Reexamination Certificate
active
06279544
ABSTRACT:
BACKGROUND
1. Field of the Invention
Pressure-maintaining device The invention relates to a pressure-maintaining device for a fuel supply system of an internal combustion engine of a motor vehicle, having a pressure reservoir which is intended to be connected to a supply line between a fuel pump and the internal combustion engine, has a pressure chamber, has a pretensioned, movable wall in order to bound a volume of fuel in the pressure chamber and has means for registering the position of the movable wall, it being possible for the fuel pump to be regulated by means of a regulating device as a function of the position of the movable wall.
2. Related Art
It is well know to insert pressure regulators into fuel supply systems wherein the regulators regulate a fuel pump as a function of the position of the diaphragm of the pressure regulator (See, for example, U.S. Pat. No. 3,824,974; U.S. Pat. No. 1,837,504; U.S. Pat. No. 4,728,264). The disadvantage of these arrangements is that, in spite of the fuel pump being regulated, pressure fluctuations in the fuel supply system occur because of internal and external influences.
Such fuel supply systems are already used experimentally in motor vehicles and are therefore known. The pressure reservoir is used for the intermediate storage of fuel and permits cyclic operation of the fuel pump. The pressure reservoir has two limit switches which limit the reciprocating travel of the movable wall. As soon as the pressure chamber has been filled, the regulating device switches off the fuel pump. The internal combustion engine is then supplied with fuel by the pressure reservoir. After the pressure chamber has been virtually completely emptied, the fuel pump is switched on again and supplies the internal combustion engine with fuel. The pressure-maintaining device is used in particular instead of a return line, which is provided to return excess fuel from the internal combustion engine into a fuel tank. By comparison with a fuel supply system having a return line, the pressure-maintaining device has the advantage that the power demand of the fuel pump may be reduced up to 95%. This leads, in particular in city traffic, to a reduction in the fuel consumption of the motor vehicle.
A disadvantage in the case of the known pressure-maintaining device is that, while the fuel pump is operating, a higher pressure prevails in the fuel supply system than when the internal combustion engine is being supplied from the pressure reservoir with the fuel pump switched off. These pressure differences have their origin in the pretensioning forces, which are variable over the reciprocating travel of the movable wall, and in the influence of frictional forces on the movement of the movable wall. Pressure fluctuations in the fuel supply system are produced in this way, and have to be compensated for by a pressure-regulating valve. However, this pressure-regulating valve is a component which is susceptible to faults and very costly.
SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS
The invention is based on the problem of configuring a pressure-maintaining device of the type mentioned at the beginning such that it is as cost-effective as possible to produce and, by using it, pressure fluctuations in the fuel supply system can largely be avoided.
According to the invention, this problem is solved by the regulating device being designed to produce a central position of the movable wall.
As a result of this configuration, pressure fluctuations in the fuel supply system are largely avoided without using a pressure-regulating valve, since the pressure chamber initially serves briefly as a buffer for insufficiently or excessively delivered fuel. The movable wall serves as a sensor for the regulating device for regulating the fuel pump to meet the demand. The pressure-maintaining device comprises few components, as a result of omitting the pressure-regulating valve, so that it is particularly cost-effective to produce. The fuel supply system according to the invention is suitable for use in a fuel supply system having an injection system or having a carburetor.
As in the case of the known pressure-maintaining device, the fuel pump could be switched on and of f by switches. For this purpose, these switches would have to be arranged close to the central position of the movable wall. However, this leads to frequent switching of the fuel pump. However, according to an advantageous development of the invention, the pressure-maintaining device does not require frequent switching of the fuel pump, if the position of the movable wall can be ascertained by an electrical displacement transducer, which is connected to the regulating device, and if the delivery of the fuel pump can be regulated by the regulating device. By this means, the fuel supply system according to the invention has a system which regulates the fuel pump as a function of the demand, while the pressure reservoir is used to compensate for pressure fluctuations, caused, for example, by load changes in the internal combustion engine.
According to another advantageous development of the invention, the delivery of the fuel pump may be regulated simply if the rotational speed of the fuel pump can be varied by the regulating device. In this case, it is advantageous if the fuel pump has a flat pump characteristic (Q=f
(u)
at p= const.).
The pressure chamber of the pressure reservoir could be connected, for example via a spur line, to a supply line arranged between the fuel pump and the internal combustion engine. As a result, however, the fuel supply system reacts very sluggishly to pressure fluctuations in the fuel supply system, because of the fuel in the spur line. The pressure-maintaining device reacts particularly rapidly to pressure fluctuations if the pressure chamber has an inlet to connect it to the fuel pump and an outlet to connect it to the internal combustion engine. By this means, the pressure chamber always has fuel flowing through it during operation of the fuel pump. Even in the case of cyclic operation of the fuel pump, this leads only to insignificant pressure fluctuations in the fuel supply system. In addition, the omission of the spur line further simplifies the installation of the pressure-maintaining device.
The movable wall could, for example, bound the upper region of the pressure chamber and, by way of its weight, produce the envisaged pressure in the pressure chamber. As an alternative to this, the movable wall could also be constructed as a float. The pressure provided in the fuel supply system would then be produced by the fuel column. However, this leads to vibration having a great influence on the actuating device. One could also consider producing the envisaged pressure by means of an air pad located in the pressure reservoir. However, such an air pad has the disadvantage of being temperature-dependent and requiring to have the pressure reservoir large dimensions. However, according to another advantageous development of the invention, the pressure-maintaining device has a particularly compact configuration if the movable wall is pretensioned by a spring element. Since, in this case, vibration has only a slight influence on the movable wall, a particularly constant pressure is produced by the spring element in the central position of the movable wall. For the most constant possible pressure over the reciprocating travel of the movable wall in the pressure chamber, it is advantageous, according to another advantageous development of the invention, if the spring element has a particularly flat spring characteristic.
According to another advantageous development of the invention, a fuel column in the pressure chamber counteracts the spring force if the movable wall is arranged in the bottom region of the pressure chamber.
According to another advantageous development of the invention, a fuel column in the pressure chamber has no influence on the pressure produced in the fuel supply system if the movable wall is arranged in a side region of the pressure chamber.
According to another
Mannesmann VDO AG
Mayer Brown & Platt
Moulis Thomas N.
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