EP2708728A2 - Low pressure circuit for a fuel injection system - Google Patents

Abstract

The circuit has a mechanical low pressure-prefeed pump (2) sucking fuel from a fuel tank (4), where the fuel is supplied to a low pressure region of a high pressure pump (1) via a fuel line. A dosing unit (10) is arranged in the region. A zero-delivery line with a zero-delivery throttle (14) is branched downstream of the dosing unit. An overflow line with an overflow valve (6) is branched upstream of the dosing unit. A non-return valve (16) is arranged in the zero-delivery line for selective opening or blocking of the zero-delivery line, and switched between open and closed positions. The mechanical low pressure-prefeed pump is an internal gear pump.

Description

The invention relates to a low pressure circuit for a fuel injection system, in particular a common rail injection system of internal combustion engines, comprising a prefeed pump, by means of which fuel from a fuel tank ansaugbar and a low pressure region of a high-pressure pump can be supplied via a fuel line, wherein in the low pressure region a metering unit is arranged for volume control , Branches downstream of the metering unit, a zero feed line with a zero feed throttle branches off and upstream of the metering unit branches off an overflow with an overflow valve.

A low-pressure circuit for a fuel injection system of the type mentioned above, for example, from the published patent application DE 199 26 308 A1 out. The fuel injection system includes a high pressure pump and an upstream prefeed pump that delivers fuel flow through a fuel line from a fuel tank. The fuel is fed to a metering unit, which is connected upstream of the high-pressure pump for volume control. The metering unit allows the use of a conventional unregulated feed pump. In the high pressure pump, the flow is pressurized and fed to a common rail. The return ensures that excess fuel is not unnecessarily high pressure, but can flow back directly into the tank.

Furthermore, an overflow line is provided with an overflow valve, which branches off from the delivery run in front of the metering unit. The task of the overflow valve is to control the excess quantity of the prefeed pump with respect to the respectively required high-pressure pump delivery rate. In addition, in the published patent application DE 199 26 308 A1 proposed that between the metering unit and the high pressure pump branches off a zero feed line, in which a zero feed throttle is arranged. The zero feed line opens into the fuel line on the suction side of the prefeed pump. The zero delivery line is required because the metering unit is usually not tight even in the fully closed state. During normal operation of the engine, the leakage quantity of the metering unit is thus diverted into the return line via the zero-delivery line and the zero-feed throttle. Without the zero feed throttle it would come in normal operation of the engine in the closed state of the metering unit to promote the amount of leakage in the high pressure circuit, which is undesirable.

From the arrangement of the zero feed line but now there is the problem that at very low engine speeds, i. In particular, when starting the engine, and the associated low flow of Vorförderpumpe a large part of this flow is derived directly via the zero feed throttle back into the non-pressurized return instead of standing for the pressure build-up in the high-pressure system. This can make the engine start much more difficult or even impossible. There is thus a conflict of objectives regarding the realization of a zero promotion on the one hand and the ability to start on the other.

Based on the above-mentioned prior art, the present invention is therefore an object of the invention to provide a low-pressure circuit for a fuel injection system, with which the described conflict of goals can be defused.

To solve this problem, the invention provides in a low-pressure circuit of the type mentioned above, that in the zero-feed line a switchable between an open and a closed state shut-off valve for selectively opening or locking the zero feed line is arranged. This offers the possibility of shutting off the zero-delivery line for the starting process, so that no loss quantities occur in the system. As soon as the regular operation (from idle) starts, the zero feed line should be opened again to realize the zero promotion can. Preferably, the obturator is arranged downstream of the zero-feed throttle, so that the obturator is in the unpressurized region of the low-pressure circuit.

The operation of the obturator can be controlled in different ways. For example, the obturator can be connected to the central engine control or it can be provided sensors for detecting the rotational speed of the internal combustion engine, which open the obturator upon detection of the completion of the starting process. A structurally particularly simple and failsafe design results preferably in that control means are provided for controlling the state of the obturator in dependence on the position of a valve closing member of the overflow valve. In particular, the control means are designed to open the obturator when the overflow valve is opened. The overflow valve opens as soon as a certain pressure has built up in front of the metering unit after engine start. Therefore, the position of the valve closing member of the overflow valve can be used as a control for opening the zero feed line.

Particularly advantageous in this context is a direct mechanical coupling of the valve closing member of the overflow valve with the obturator. The formation is preferably made in this case such that the obturator is formed as a valve with a valve closure member whose movement is coupled with the movement of the valve closing member of the overflow valve, in particular such that the obturator is opened when the overflow valve is opened.

If, as this corresponds to a further preferred embodiment, the valve closing member of the overflow valve is spring-loaded in the closing direction, the overflow valve is opened only after exceeding a lower limit pressure, so that the opening of the obturator is delayed accordingly. Another delay preferably results from the fact that the Movement of the valve closing member of the obturator is coupled to the same after passing through an idle stroke of the valve closing member of the overflow valve.

The overflow valve is advantageously designed as a slide valve whose valve closing member is formed by a displaceable piston.

The obturator may be formed in the context of the invention both as a check valve and as a slide valve.

In order to enable a retrofitting of existing facilities, it is advantageous to structurally combine the obturator with the overflow valve. This is achieved, for example, in that the zero delivery line opens into a spring chamber of the overflow valve and that the obturator is connected to the spring chamber. Another advantageous development provides in this context that the spring chamber is connectable via a slide valve seat with a piston chamber, wherein the piston chamber is connected via a spring space passing through, formed in an insert hole with the fuel return.

Fig. 1

ein Common-Rail-Einspritzsystem mit einem Niederdruckkreislauf nach dem Stand der Technik,

Fig. 2

ein Common-Rail-Einspritzsystem mit einem erfindungsgemäßen Niederdruckkreislauf in einer ersten Ausbildung,

Fig. 3

eine Detailansicht des Niederdruckkreislaufs in einer zweiten Ausbildung,

Fig. 4

eine Detailansicht des Niederdruckkreislaufs in einer dritten Ausbildung,

Fig. 5

ein Common-Rail-Einspritzsystem mit einem erfindungsgemäßen Niederdruckkreislauf in einer vierten Ausbildung und

Fig. 6

eine Detailansicht der Ausbildung gemäß Fig. 5.

The invention will be explained in more detail with reference to embodiments shown schematically in the drawing. In this show

Fig. 1

a common rail injection system with a low pressure circuit according to the prior art,

Fig. 2

a common rail injection system with a low pressure circuit according to the invention in a first embodiment,

Fig. 3

a detailed view of the low-pressure circuit in a second embodiment,

Fig. 4

a detailed view of the low pressure circuit in a third embodiment,

Fig. 5

a common rail injection system with a low pressure circuit according to the invention in a fourth embodiment and

Fig. 6

a detailed view of the training according to Fig. 5 ,

In Fig. 1 a conventional design of a low pressure circuit of a common rail injection system is shown. The high-pressure pump 1 has in the standard version an attached mechanical low-pressure prefeed pump 2, which is designed for example as Außenenzahnrad- or internal gear pump and is driven by the camshaft of the high pressure pump and therefore has the same speed. The prefeed pump 2 sucks the fuel through a pre-filter 3 with integrated water from the tank 4 and promotes this through the main filter 5 to the low pressure region of the high-pressure pump 1. The delivery of the feed pump 2 is usually designed to be larger than the maximum flow of the high-pressure pump 1 to ensure all operating conditions sufficient filling of the high-pressure pump.

In the high-pressure pump 1, an overflow valve 6 is installed, which has the task to control the excess quantity of the feed pump 2 with respect to the respectively required high-pressure pump delivery. Depending on this oversupply, a pre-pressure in front of the high-pressure pump 1 sets in according to a pressure-quantity characteristic of the overflow valve. The overflow valve is designed as a slide valve, that is, depending on the stroke of the valve piston 7, a Absteuerquerschnitt 8 is released. At low Vorförderdrücken such as when starting the engine, the piston 9 of the pressure relief valve 6 is not deflected due to the bias of the spring 9 of the pressure relief valve 6 and thus also not reduced quantity. Only starting from a pressure of approximately 5 bar does a movement take place here and thus an opening of the diversion cross section. In the high pressure pump 1, the delivery rate of the high pressure pump 1 is controlled via a metering unit 10. This metering unit 10 consists for example of a slide valve and a linear magnet. Depending on the activation of the linear magnet is over the Slider valve released a certain flow cross-section and thus adjusted the flow rate of the high-pressure pump 1. Due to the design as a slide valve, the metering unit 10 is not tight even in the fully closed state, ie when concerns the Vorförderdrucks there is a leakage amount in the high pressure pump 1 via the gate gap. Since this leakage would inevitably cause a pressure build-up in the suction chamber 11 of the high-pressure pump 1 and thus would lead to the opening of the suction valves 12 and to promote this leakage in the high-pressure circuit 13, a so-called zero-feed throttle 14 is required for the realization of a flow rate of zero. By the zero feed throttle 14, this leakage quantity is in turn discharged into the non-pressurized return line 15 and thus prevents a rise in pressure in the suction chamber 11.

When starting the engine, the following situation arises: the engine speeds during the engine start process are very low, about 100min ^-1 , accordingly low are the speeds of the high pressure pump 1 and the pre-feed pump 2. The feed pump 2 has at these low speeds due to the games in the conveyor teeth very low conveying efficiencies. The metering unit 10 is fully opened in the start case to achieve a maximum flow rate of the high-pressure pump 1 for the pressure build-up in the high-pressure system. In this state, now a large part of the very small flow rate of the feed pump 2 is derived directly via the zero feed throttle 14 back into the non-pressurized return line 15 and is thus not available for the pressure build-up in the high-pressure system. There is thus a conflict of objectives regarding the realization of a zero promotion on the one hand and the ability to start on the other. In unfavorable circumstances (eg low starting speeds due to low battery voltages, further reduced efficiency of the feed pump due to high temperatures, low ambient pressures due to high altitudes, etc.), this conflict of objectives is further aggravated, so that it can not be resolved without further action, ie either the start of the engine or the zero promotion is not possible.

In the embodiment according to the invention Fig. 2 is now additionally provided a check valve 16 which determines the flow through the zero feed line or the zero feed throttle 14. The check valve 16 is in this case arranged below the overflow valve 6 and is mechanically opened by the movement of the valve piston 7 of the overflow valve 6. The valve closing member of the check valve 16 is mechanically coupled to the valve piston 7 for this purpose. The flowing through the zero feed throttle 14 amount is introduced into the spring chamber 17 of the overflow valve. The outflow of the introduced amount in the direction of the non-pressurized return line 15 is opened and closed via the non-return valve 16 connected to the spring chamber 17. In the start case, the prefeed pressures are smaller than would be necessary for a movement of the valve piston 7. At the same time, the check valve 16 is closed due to the mechanical coupling of the valve piston 7 with the check valve 16 and thus the flow through the zero feed throttle 14 is blocked. From idling operation of the engine is carried by the higher Vorförderdrücke a movement of the valve piston 7 of the overflow valve 6, so that the check valve 16 and thus the flow through the zero feed throttle 14 is opened.

Fig. 3 shows an exemplary structural design of the overflow valve 6 together with check valve 16, in which the check valve 16 is inserted in the bore below the overflow valve 6. The spring 17 of the check valve 16 can be arranged to save space within the spring 9 of the overflow valve 6 or alternatively on the opposite drain side 18. Between the valve piston 7 and the spring 9, a plate 19 is inserted, which the valve closing member of the check valve 16 via a rod 20 after an idle stroke 21 opens. This plate 19 is designed with a bore 22 so that the fuel in the valve piston 7 can freely flow in and out.

In the modified training according to Fig. 4 the spring 9 of the overflow valve 6 is different than in Fig. 3 also used to close the check valve 16: In this embodiment, the valve closing member 23 of the check valve 16 via a rod 20 with a Plate 19 is connected, which is arranged between the valve piston 7 and the spring 9. As a result, the overflow valve 6 and the check valve 16 to a unit with only a single spring 24. In order for this unit is fixed in the pump housing in a pressureless state, an O-ring 25 is disposed in the check valve 16, which also the tightness between the spring chamber 17 and the pressure-free return 15 ensures.

In the training according to Fig. 5 and 6 the flow through the zero feed throttle 14 is controlled via a slide valve. By an additional insert 26 in the spring chamber 17 of the overflow valve 6, a sliding valve seat 27 is realized consisting of the valve piston 7 and the insert 26. The zero flow rate is introduced into the spring chamber 17, via the sliding valve seat, the amount is then passed into the piston interior 28 and via a bore 29 in the insert 26 back into the non-pressurized flow 15. The insert 26 is designed in the Absteuerbereich with longitudinal grooves 30, so that the valve piston 7 is guided clean. In the start case, the valve piston 7 is not deflected and, accordingly, the sliding valve seat 27 is closed and the flow through the zero-feed throttle 14 is blocked. In normal operation, the valve piston 7 is moved and the flow through the zero feed throttle 14 in the non-pressurized return line 15 is released.

Claims (12)

Low-pressure circuit for a fuel injection system, in particular a common rail injection system of internal combustion engines, comprising a prefeed pump, by means of which fuel from a fuel tank and fed via a fuel line to a low pressure region of a high-pressure pump, wherein in the low pressure region a metering unit for volume control is arranged downstream of the metering unit a zero feed line branches off with a zero feed throttle and branches off upstream of the metering unit an overflow with an overflow valve, characterized in that in the zero feed line a switchable between an open and a closed state shut-off valve (16) is arranged for selectively opening or locking the zero feed line. Low-pressure circuit according to claim 1, characterized in that the obturator (16) is arranged downstream of the zero-feed throttle (14). Low-pressure circuit according to claim 1 or 2, characterized in that control means for controlling the state of the obturator (16) in dependence on the position of a valve closing member of the overflow valve (6) are provided. Low pressure circuit according to claim 3, characterized in that the control means are designed to open the obturator (16) when the overflow valve (6) is opened. Low-pressure circuit according to claim 3 or 4, characterized in that the obturator (16) is designed as a valve with a valve closing member (23) whose movement is coupled to the movement of the valve closing member of the overflow valve (6), in particular such that the obturator (16 ) is opened when the overflow valve (6) is opened. Low-pressure circuit of claim 3, 4 or 5, characterized in that the valve closing member of the spill valve (6) is spring-loaded in the closing direction. Low-pressure circuit according to claim 5 or 6, characterized in that the movement of the valve closing member (23) of the obturator (16) is coupled to the same only after passing through an idle stroke of the valve closing member of the overflow valve (6). Low-pressure circuit according to one of claims 1 to 7, characterized in that the overflow valve (6) is designed as a slide valve whose valve closing member is formed by a displaceable piston. Low-pressure circuit according to one of claims 1 to 8, characterized in that the obturator (16) is designed as a check valve. Low-pressure circuit according to one of claims 1 to 8, characterized in that the obturator (16) is designed as a slide valve. Low-pressure circuit according to one of claims 1 to 10, characterized in that the zero-feed line opens into a spring chamber (17) of the overflow valve (6) and that the obturator (16) is connected to the spring chamber (17). Low-pressure circuit according to claim 11, characterized in that the spring chamber (17) via a sliding valve seat (27) is connectable to a piston chamber, wherein the piston chamber via a spring space (17) passing through, in an insert (26) formed bore (29) the fuel return (15) is connected.

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