Internal-combustion engines – Charge forming device – With fuel pump
Reexamination Certificate
1999-06-10
2001-05-15
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
With fuel pump
C123S1960CP, C417S372000
Reexamination Certificate
active
06230688
ABSTRACT:
PRIOR ART
The invention relates to a process for generating and delivering high-pressure fuel to a high-pressure storage chamber of a fuel injection system, in particular a common rail injection system, of an internal combustion engine, wherein by means of a low-pressure pump as a pre-feed pump, fuel is supplied from a tank and is delivered to the intake side of a high-pressure pump and wherein a part of the fuel delivered by the low-pressure pump is used to lubricate the high-pressure pump.
The delivery volume or the delivery capacity of the low-pressure pump and high-pressure pump must be designed so that a sufficient quantity of high-pressure fuel is always available. However, since the high-pressure pump is usually driven as a function of the motor speed, the available fuel quantity is usually too high in comparison with the required fuel quantity, for example when the driver of a vehicle “lets up on the gas” at a high speed and the vehicle is coasting. The fuel quantity delivered by the high-pressure pump is still very high, but it is not required by the injection system of the internal combustion engine. When a threshold pressure is reached under such circumstances, a pressure regulating valve provided on the high-pressure side is normally opened and a connection to the tank is produced. The fuel is therefore fed in the circuit and is very intensely heated with this high-pressure-side, so-called rail pressure regulation, which is accompanied by dangers. In addition, the use of return lines made of plastic is critical and the overall motor efficiency decreases with high power consumption by the high-pressure pump.
Based on this, the object of an invention is to improve the process of the type mentioned at the beginning so that the above-mentioned disadvantages do not occur, that is in particular a reduction of the high temperature level in the return and in the tank as well as an improvement of the overall motor efficiency is therefore achieved. Furthermore, however, a sufficient and dependable lubrication of the high-pressure pump with fuel should be assured in all operating states and speeds.
BRIEF SUMMARY OF THE INVENTION
This object is attained according to the invention with a process of the type mentioned above by virtue of the fact that the delivery quantity of the low-pressure pump or the delivery pressure on the delivery side of the low-pressure pump is controlled as a function of the currently required fuel quantity determined by sensors and a control device and that a constant lubrication flow quantity, which is essentially independent of the pressure on the delivery side, is branched off from the delivery flow of the low-pressure pump and a residual remainder flow is delivered to the intake side of the high-pressure pump.
This kind of a suction throttle regulation of the high-pressure pump achieves:the fact that the fuel quantity delivered by the high-pressure pump always corresponds to the required fuel quantity of the internal combustion engine so that in the ideal case, no fuel is delivered into the circuit. The actuating variables, for example the position of the gas pedal, are detected by sensors, the currently required fuel quantity is determined in an evaluation and control device, and the delivery quantity of the low-pressure pump (volume flow control) or the delivery pressure on the delivery side of the low-pressure pump (delivery pressure control) is correspondingly predetermined. In a particularly preferred manner, these preset values are also regulated. Since a constant lubrication flow quantity that is essentially independent of the pressure on the delivery side is branched off from the delivery flow of the low-pressure pump, for example on an order of magnitude of 30 l/h, it is achieved according to the invention that even with the above-described low-pressure-side demand regulation of the fuel delivery, a dependable lubrication of the high-pressure pump is assured. The lubricant quantity supplied to the high-pressure pump is independent of the speed of the high-pressure pump and is branched off by means of a flow regulating valve which is embodied so that a constant lubricant quantity that is essentially independent of the inflow pressure is “allowed to pass through”. With changes of the inflow pressure between 0 and 6 bar, the lubricant quantity supplied changes by less than 100%.
According to the first embodiment of the invention, if the delivery quantity of the low-pressure pump is controlled and is regulated in a preferred manner (volume flow regulation), then this can be achieved by means of controlling or regulating the speed of the low-pressure pump. In a particularly advantageous manner, the speed of the low-pressure pump is detected by means of a speed sensor and the signal of the speed sensor is sent back to the control device so that the speed which is to be set in accordance with the volume required is set in a regulated manner.
According to the second embodiment of the invention, if the delivery pressure on the delivery side of the low-pressure pump is adjusted or regulated as a function of the required fuel quantity (delivery pressure regulation), then with the use of a low-pressure pump that can be pressure regulated, this can be achieved because the pump is controlled directly by the control device. The delivery pressure on the delivery side of the low-pressure pump, however, can also be realized by controlling a variable throttle device provided at the outlet of the low-pressure pump, for example by moving a throttle slide valve. However, a synchronized solenoid valve in a pressure relief line, which connects the delivery side of the low-pressure pump to the tank, can also be controlled in order to keep the pressure on the delivery side of the low-pressure pump at the desired value determined by the control device. In such an instance, fuel would be fed in a circular fashion in the low-pressure circuit, which does not lead to a disadvantageous power consumption by the low-pressure pump or to a disadvantageous heating of the fuel.
Another object of the present invention is to supply a system for generating high fuel pressure, with which the process according to the invention can be carried out.
This object is attained by means of a system with the features set forth herein for carrying out the volume flow control or regulation and with other features set forth for carrying out the delivery pressure control or regulation.
Through the use of a low-pressure pump that can preferably be speed controlled and in a very particularly preferable manner, can be speed regulated, a volume flow in the low-pressure pump can be set that corresponds to the currently required fuel quantity and the flow regulating valve provided on the delivery side of the low-pressure pump assures a constant lubricant supply of the high-pressure pump.
To preset the delivery pressure on the delivery side of the low-pressure pump, a low-pressure pump can be used that can be pressure regulated. However, it also turns out to be advantageous if, for example, a gear pump is provided, with a variable throttle device connected after it, which can then be controlled by the control device. In such a case, pressure sensors are advantageously provided, which cooperate with the control device to form a pressure regulation circuit.
It would also be conceivable for a branch line to lead from the delivery side of the low-pressure pump back to the tank, which line has a synchronized solenoid valve that can be controlled by the control device.
With the above-explained use of a variable throttle device or a returning branch line with a controllable valve, a non-regulatable low-pressure pump can be used, wherein the pressure regulation occurs at a subsequent location by means of the throttle device or by controlling the solenoid valve.
Other features, details, and advantages of the invention ensue from the claims, the graphic depiction, and the subsequent description of the system according to the invention and the process according to the invention for generating high fuel pressure
Faix Erhard
Westphal Marc
Greigg Edwin E.
Greigg Ronald E.
Miller Carl S.
Robert & Bosch GmbH
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