Title of Invention

A METHOD AND SYSTEM FOR GENERATING FUEL WHICH IS HIGH PRESSURE

Abstract

A process and system for generating and delivering high-pressure fuel to a high-pressure storage chamber of a fuel injection system of an internal combustion engine. The system includes a low-pressure pump as a pre-feed pump by which fuel is supplied from a tank and is delivered to the intake side of a high-pressure pump and - a part of the fuel delivered by the low-pressure pump is used to lubricate he high- pressure pump. In order to reduce the temperature level in the return and to increase the overall efficiency of the motor, the system is embodied so 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. 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 is residual remainder flow is delivered to the intake side of the high-pressure pump.

Full Text

Method for generating fuel, which is under high pressure and system for generating fuel high pressure Prior art The invention relates to a method for generating fuel which is under high pressure and for feeding it to a high-pressure storage space of a fuel injection system, in particular of a common-rail injection system, of an internal combustion engine, fuel being conveyed out of a tank by means of a low-pressure pump functioning as a fore-pump and being fed to the suction side of a high-pressure pump, and part of the fuel conveyed by the low-pressure pump being used for lubricating the high-pressure pump. The delivery volume or delivery capacity of the low-pressure pump and high-pressure pump must be designed in such a way that a sufficient fuel quantity which is under high pressure is always available* However, since the high-pressure pump is usually driven as a function of the engine speed, the fuel quantity available is mostly too high, as compared with the fuel quantity demanded or required, for example when the driver of a motor vehicle throttles back" at a high engine speed and the vehicle is in the coasting mode. The fuel quantity conveyed by the high-pressure pump is still very high, but is not required by the injection system of the internal combustion engine. In such a case, when a threshold pressure is reached, normally a pressure-regulating valve provided on the high-pressure side is opened and a connection to the tank is made. The fuel is therefore recalculated and heats up to a very great extent during this so-called rail pressure regulation on the high-pressure side, thus entailing risks. Moreover, the use of plastic return lines is critical and the overall engine efficiency is impaired ' during the high consumption of power by the high-pressure pump. Proceeding from this, the object on which the invention is based is to improve the method of the type described in the introduction in such a way that the abovementioned disadvantages do not arise, that is to say, in particular, a lowering of the high temperature level in the return and the tank and an improvement in overall engine efficiency are achieved. Furthermore, however, sufficient and reliable lubrication of the high-pressure pump with fuel is to be ensured in all operating states and at all engine speeds. Invention In a method of the type mentioned, this object is achieved, according to the invention, in 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 instantaneously required fuel quantity determined by measurement transducers and a control device, and in that a constant lubricating stream quantity, essentially independent of the pressure on the delivery side, is branched off from the delivery stream of the low-pressure pump, and a remaining residual stream is fed to the suction side of the high-pressure pump. Such suasion-throttle regulation of the high-pressure pump ensures that the fuel quantity conveyed by the high-pressure pump always corresponds to the fuel quantity demanded or required by the internal combustion engine, so that, ideally, no fuel is recalculated. By means of measurement transducers which record control variables, such as, for example, the position of the accelerator pedal, the instantaneously required fuel quantity is determined in an evaluation and control device and the delivery quantity of the low-pressure pump (volumetric flow control) or the delivery pressure on the delivery side of the low-pressure pump (delivery pressure control) is preset accordingly. These preset tings are also regulated in a particularly preferred way. Since a constant lubricating stream quantity, for example of the order of magnitude of 30 1/h, which is essentially independent of the pressure on the delivery side, is branched off from the delivery stream of the low-pressure pump, this ensures, according to the invention, that reliable lubrication of the high-pressure pump is ensured even when fuel conveyance is regulated on demand on the low-pressure side, as described. In this case, the lubricant quantity fed to the high-pressure pump is independent of the rotational speed of-the high-pressure pump and is branched off by means of a flow-regulating valve which is designed in such a way that a constant lubricant quantity is ^^passed through" essentially independently of the inflow pressure. If there are changes in the inflow pressure of between 0 and 6 bar the lubricant quantity conveyed changes by less than 10%. If, according to the first variant of the invention, the delivery quantity of the low-pressure pump is controlled and is regulated in a preferred way (volumetric flow regulation), this can be achieved by controlling or regulating the rotational speed of the low-pressure pump. In a particularly advantageous way, the rotational speed of the low-pressure pump is recorded by means of a rotational-speed transducer and the signal from the latter is fed back to the control device, so that the rotational speed to be set according to the volume demand is set in a regulated manner. If, according to the second variant of the invention, the delivery pressure on the delivery side of the low-pressure pump is set or regulated as a function of the fuel quantity required (delivery pressure regulation), this can be achieved, when a pressure-regulatable low-pressure pump is used, by activating the latter directly by the control device. However, the delivery pressure on the delivery side of the low-pressure pump may also be regulated by activating a variable throttle device provided at the outlet of the low-pressure pump, for example by the displacement of a throttle slide. However, a timed solenoid valve in a pressure relief line connecting the delivery side of the low-pressure pump to the tank could also be activated, in order to maintain the pressure on the delivery side of the low-pressure pump at the desired value determined by the control device. In such a case, fuel would be recalculated in the low-pressure circuit, but this would not lead to an adverse power consumption of the low-pressure pump or heating-up of the fuel. The object on which the present invention is based is, furthermore, to provide a system for generating fuel high pressure, by means of which the method according to the invention can be carried out. This object is achieved by means of a system having the features of Claim 2, for carrying out volumetric flow control or regulation, and having the features of Claim 5, for carrying out delivery pressure control or regulation. By the use of a low-pressure pump, of which the rotational speed can preferably be controlled and the rotational speed can in a particularly preferred way be regulated (Claim 3), a volumetric flow corresponding to the instantaneously required fuel quantity can be set on the low-pressure pump, and the flow-regulating valve provided on the delivery side of the low-pressure pump ensures a constant supply of lubricant to the high-pressure pump. In order to preset the delivery pressure on the delivery side of the low-pressure pump, a pressure-regulatable low-pressure pump may be used (Claim 6). However, it also proves advantageous if, for example, a gear pump having a following variable throttle device is provided, the latter then being capable of being activated by the control device (Claim 7) . In such a case, pressure sensors are advantageously provided, which cooperate with the control device in order to form a pressure-regulating circuit. It would also be conceivable for a branch line to lead back from the delivery side of the low-pressure pump to the tank, the said branch line having a timed solenoid valve which can be activated by the control device (Claim 9). In the above-explained use of a variable throttle device or of a branch line leading back and having an activatable valve, a non-regulatable low-pressure delivery pump may be employed, pressure regulation taking place at the following point by means of the throttle device or by the activation of the solenoid valve. Further features, details and advantages of the invention may be gathered from the claims and from the diagrammatic illustration and following description of the system according to the invention and method according to the invention for generating fuel high pressure- In the drawing: Figure 1 shows a diagrammatic illustration of the low-pressure circuit of the system according to the invention for generating fuel high pressure, in the case of volumetric flow control; Figure 2 shows the delivery quantity of the high-pressure pump in the case of volumetric flow control at different degrees of throttling; Figure 3 shows the conveyed lubricant quantity as a function of the rotational speed of the high-pressure pump at different degrees of throttling; Figure 4 shows a diagrammatic illustration of the low-pressure circuit of the system according to the invention for generating fuel high pressure^ in the case of delivery pressure control; Figure 5 shows the delivery quantity of the high-pressure pump as a function of the inflow pressure on the suction side during various revolutions of the high-pressure pump; Figure 6 shows the delivery quantity of the high-pressure pump as a function of the rotational speed at various inflow pressures; and Figure 7 shows the conveyed lubricant quantity as a function of the rotational speed of the high-pressure pump at a differing inflow pressure. Figure 1 shows schematically the low-pressure circuit of a system for generating fuel high pressure, with regulation on demand, implemented in the low-pressure circuit, for metering fuel to the high-pressure pump. A line 4 leads from a fuel tank 2 to the suction side of a low-pressure pump 6. The delivery side 8 of the low-pressure pump 6 is connected to a flow-regulating valve 10 and, in parallel with this, to the suction side 12 of a high-pressure pump, indicated as a whole by the reference symbol 14, the high-pressure side 16 of which leads to the high-pressure storage space (rail) of a fuel injection system (not illustrated). The flow-regulating valve leads to the lubricating circuit 17 of the high-pressure pump 14. Furthermore, there is provided a control device 20 which cooperates with a number of measurement transducers 18 and in which the instantaneous fuel demand of the internal combustion engine is determined and a control signal is generated accordingly- The control signal is fed to the low-pressure pump 6, Figure 4 shows a diagrammatic illustration of the low-pressure circuit of the system according to the invention for generating fuel high pressure, in the case of delivery pressure control; Figure 5 shows the delivery quantity of the high-pressure pump as a function of the inflow pressure on the suction side during various revolutions of the high-pressure pump; Figure 6 shows the delivery quantity of the high-pressure pump as a function of the rotational speed at various inflow pressures; and Figure 7 shows the conveyed lubricant quantity as a function of the rotational speed of the high-pressure pump at a differing inflow pressure. Figure 1 shows schematically the low-pressure circuit of a system for generating fuel high pressure, with regulation on demand, implemented in the low-pressure circuit, for metering fuel to the high-pressure pump. A line 4 leads from a fuel tank 2 to the suction side of a low-pressure pump 6. The delivery side 8 of the low-pressure pump 6 is connected to a flow-regulating valve 10 and, in parallel with this, to the suction side 12 of a high-pressure pump, indicated as a whole by the reference symbol 14, the high-pressure side 16 of which leads to the high-pressure storage space (rail) of a fuel injection system (not illustrated). The flow-regulating valve leads to the lubricating circuit 17 of the high-pressure pump 14. Furthermore, there is provided a control device 20 which cooperates with a number of measurement transducers 18 and in which the instantaneous fuel demand of the internal combustion engine is determined and a control signal is generated accordingly. The control signal is fed to the low-pressure pump 6, designed as an electric fuel pump, as a control signal for the rotational speed of the latter. A rotational-speed transducer 22 supplies to the control device 20 a measurement value which is processed there in order to regulate the rotational speed and, consequently, the volumetric flow of the low-pressure pump 6. A lubricant stream, essentially independent of the inflow pressure and rotational speed of the high-pressure pump, is branched off, via the flow-regulating valve 10, from the fuel quantity conveyed by the low-pressure pump 6 and is led via the lubricating circuit 17 into the pump inner casing 24 of the high-pressure pump 14. The residual quantity is conveyed via the suction side 12 into the suction space 25 of the high-pressure' pump 14 and from there into the rail. The volumetric flow of the low-pressure pump 6, the said flow being calculated by the control device 20 according to the demanded or required fuel quantity, is conveyed by the electric fuel pump having a regulatable rotational speed. Furthermore, a safety valve 26 is illustrated, which interrupts the feed of fuel to the high-pressure pump 14 if the pressure falls below a predetermined value of about 1 bar, so that the engine is switched off in the event of leakage or the like. Figures 2 and 3 show the fuel quantity conveyed by the high-pressure pump 14, as a function of the rotational speed of the high-pressure pump 14, at various degrees of throttling, the degree of throttling being obtained from the quotient of the excess quantity Qz provided by the electric fuel pump and the geometric delivery volume of the high-pressure pump QH (degree of throttling = QZ/QH X 100%), where the excess quantity Qz is to be understood as signifying the fuel quantity conveyed by the low-pressure pump minus the lubricant quantity. Figure 4 shows a further embodiment of a low-pressure circuit having controlled delivery pressure, in which the low-pressure pump 6' is formed by a gear pump having following pressure regulation. In order to regulate the pressure on the delivery side of the gear pump, a-branch line 30 is provided, which leads back to the tank 2, a timed solenoid valve 32 being provided in the branch line 30. Furthermore, a pressure sensor 34, which cooperates with the control device 20, is provided. In this case, the output signal from the control device 20 is a control signal for the solenoid valve 32 which, as a function of the measurement value of the pressure sensor 34, controls or regulates a predetermined pressure on the delivery side of the low-pressure pump 6' as a function of the fuel quantity demanded. Figures 5 and 6 illustrate the delivery quantity of the high-pressure pump in the case of delivery pressure regulation in the low-pressure circuit according to Figure 4 as a function of the inflow pressure at various rotational speeds and as a function of the rotational speed in the case of various inflow pressures respectively. Figure 7 shows the lubricant quantity as a function of the rotational speed at various inflow pressures; the lubricant quantity is essentially independent of the rotational speed of the high-pressure pump and of the inflow pressure. It is pointed out that the illustrations of the delivery quantities and lubricant quantities relate to calculated magnitudes. 09.08,1997 Robert Bosch GmbH, 70469 Stuttgart 1. Method for generating fuel which is under high pressure and for feeding it to a high-pressure storage space of a fuel injection system of an internal combustion engine, fuel being conveyed out of a tank by means of a low-pressure pump functioning as a fore-pump and being fed to the suction side of a high-pressure pump, and part of the fuel conveyed by the low-pressure pump being used for lubricating the high-pressure pump, characterized in 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 instantaneously required fuel quantity determined by measurement transducers and a control device, and in that a constant lubricating stream quantity, essentially independent of the pressure on the delivery side, is branched off from the delivery stream of the low-pressure pump, and a remaining residual stream is fed to the suction side of the high-pressure pump. 2. System for generating fuel high pressure in a fuel injection system, in particular in a common-rail injection system, of an internal combustion engine, with a low-pressure pump (6) sucking in from a tank (2) , with a high-pressure pump (14) fed from the low-pressure pump (6) and conveying into a high-pressure storage space, and with a lubricating circuit for lubricating the high-pressure pump (14), the said lubricating circuit using as a lubricant the fuel which is to be conveyed, characterized in that the low-pressure pump (6) has a controllable volumetric flow and is activated by a control device (20), by means of which a volumetric flow corresponding to the instantaneously required fuel quantity can be set on the low-pressure pump (6) , and in that the delivery side (8) of the low-pressure pump (6) communicates with a flow-regulating valve (10) leading to the lubricating circuit of the high-pressure pump and, in parallel with the said valve, with the suction side (12) of the high-pressure pump (14) . 3. System according to Claim 2, characterized in that the low-pressure pump (6) is an electric fuel pump having a controllable rotational speed. 4. System according to Claim 3, characterized by a rotational-speed transducer (22) which is assigned to the electric fuel pump having a controllable rotational speed and which cooperates with the control device (20) as feedback, so as to bring about a regulation of the rotational speed of the electric fuel pump. 5. System for generating fuel high pressure in a fuel injection system, in particular in a common-rail injection system, of an internal combustion engine, with a low-pressure pump (6) sucking in from a tank (2) , with a high-pressure pump (14) fed from the low-pressure pump (6) and conveying into a high-pressure storage space, and with a lubricating circuit for lubricating the high-pressure pump (14), the said lubricating circuit using as a lubricant the fuel which is to be conveyed, characterized in that the delivery pressure on the delivery side of the low-pressure pump (6') can be controlled as a function of the instantaneously required fuel quantity by means of a control device (20) , and in that the delivery side of the low-pressure pump (6') communicates with a flow-regulating valve (10) leading to the lubricating circuit of the high-pressure pump (14) and, in parallel with the said valve, with the suction side (12) of the high-pressure pump (14). 6. System according to Claim 5, characterized in that the low-pressure pump (6') is pressure-regulatable and can be activated by the control device (20), 7. System according to Claim 5/ characterized in that the low-pressure primp (6') is formed by a gear pump having a following variable throttle device which can be activated by the control device (20). 8. System according to Claim 7, characterized in that the following variable throttle device is a throttle slide. 9. System according to Claim 1, characterized in that the following variable throttle device is a timed solenoid valve (32) which can be activated by the control device (20) and which is provided in a branch line (30.) leading back to the tank (2). 10. System according to one of Claims 2 to 8, characterized by a safety valve (26) on the delivery side of a low-pressure pump (6, 6' ) and which interrupts the feed of fuel to the high-pressure pump (14) if the pressure falls below a predetermined value. ii. Method for generating fuel which is under high pressure and for feeding it to a high-pressure storage space of a fuel injection system. substantially as herein described with reference to the accompanying drawings,

Documents:

2222-mas-1998-abstract.pdf

2222-mas-1998-claims filed.pdf

2222-mas-1998-claims granted.pdf

2222-mas-1998-correspondnece-others.pdf

2222-mas-1998-correspondnece-po.pdf

2222-mas-1998-description(complete)filed.pdf

2222-mas-1998-description(complete)granted.pdf

2222-mas-1998-drawings.pdf

2222-mas-1998-form 1.pdf

2222-mas-1998-form 26.pdf

2222-mas-1998-form 3.pdf

2222-mas-1998-priority document.pdf