|Title of Invention||
|Abstract||An injection system for an internal combustion engine having a plurality of cylinders to be supplied, the injection system comprising an electronic control unit and for each individual cylinder, the following a fuel pump, an injection nozzle which is provided with a nozzle needle and with an electronically controlled valve which can control the opening of the nozzle needle, a connecting line between the fuel pump and the injection nozzle, both each of the fuel pumps and each of the electronically controlled valves being connected to the electronic control unit and being controlled by the latter, characterized in that each injection nozzle is provided with a storage space which is flow-connected both to the connection line and to the nozzle needle and in which a fluid can be built up by means of the electronically controlled valve, so that the pressure then acting holds the nozzle needle in its closed position.|
The invention relates to a fuel injection system for an internal combustion engine having a fuel pump for each cylinder of the internal combustion engine to be supplied, which is electronically controlled, an injection nozzle, which is provided with a nozzle needle, and a.connecting line between the fuel pump and the injection nozzle.
Such a fuel inj ection system constitutes a single-cylinder system, in which the fuel-injection pump is 'driven by a camshaft, for example. When actuated by a cam the fuel to be injected is pressurized in the fuel pump and delivered to the injection nozzle. The start of delivery and end of delivery by the fuel pump may be *" controlled, for example, by means of a spool-type valve, which in an initial state connects the delivery chamber of the pump to a return line, so that fuel is not delivered, and in a second state closes the connection to the return line so that a build¬up of pressure is possible. In this way the start of injection can be controlled, as can the fuel injection quantity by controlling the length of the injection ■sequence. The injection pressure, however, is a function of the speed of the camshaft driving the pump. Furthermore, the rate of injection and any pilot injection can be influenced only on the pump side. This places limitations on the pilot fuel injection quantity and the shape of the rate of injection curve and leads to
unacceptable variations between the individual cylinders of the internal combustion engine.
The object of the invention, therefore, is to develop the known fuel injection system in such a way that not only the fuel injection quantity and start of injection, but also the injection pressure, rate of injection, pilot injection, after-injection and multi-injection can be influenced in the desired way.
Advantages of the invention
The fuel injection system according to the invention with the features . of claim 1 has the advantage that through suitable actuation of the electronically controlled valve on the injection nozzle the volume of fuel delivered by the fuel pump can be injected in the desired way, additional parameters being provided for controlling the rate of injection that do not vary as a function of the start of delivery and end of delivery of the fuel pump. Unlike conventional systems, in which the nozzle needle opened automatically as soon as a predetermined pressure was exceeded following the start- of- "delivery by the fuel pump, and the nozzle needle likewise automatically closed again as soon as the pressure fell below a certain minimum pressure towards the end of delivery, with the fuel injection system according to the invention injection can now take place essentially irrespective of the rate of delivery of the fuel pump. Furthermore, given the same fuel pump dimensions it is now possible to utilize the entire lift of the pump and thereby to increase the output of the system for the same dimensions. A further advantage is that only minor modifications are necessary compared to conventional systems. It is merely necessary to replace the injection nozzle hitherto used with an electronically controlled injection nozzle.
Compared to so-called "common-rail systems", in which a single fuel pump is used to supply a high-pressure accumulator, from which the fuel is then injected :into the individual cylinders, - the system according to the invention affords greater operating reliability, since the modular construction of the system means that, in the event of any failure of the fuel pump, only the corresponding cylinder of the internal combustion engine is affected. The rate of injection can in this case be variably controlled in the same way as is possible with a common-rail system.
Advantageous embodiments of the invention are set out in the subordinate claims.
The invention will be described below with reference to various embodiments, which are represented in the drawings attached, in which:
- Fig.l in a diagrammatic, partially sectional view shows a fuel injection system according to the invention in a first embodiment of the invention;
- Fig. 2 shows the section II in Fig. 1 on an enlarged scale;
- Fig. 3 in a view corresponding to that in Fig. 1, shows a fuel injection system in a second embodiment of the invention;
- Fig, 4 in a side view shows an injection nozzle, which may be used in a fuel injection system in a third embodiment of the invention;
- Fig. 5 shows the section V. in Fig. 4. on an enlarged scale; and
- Figs 6a to 6d show various diagrams of characteristic values relevant to the rate of injection that can be
achieved with the fuel injection system according to the invention.
Description of exemplary embodiments
Figure 1 represents a fuel injection system according to the invention in a first embodiment. It contains, as the major components, a fuel pump 10, an injection nozzle 12 and a connecting line 14 between the fuel pump and the injection nozzle.
The fuel pump 10 is actuated by a rotating cam 16 and has a pump piston 18/ which moves in a delivery chamber 20, The fuel to be injected is delivered to the fuel pump• 10 through a fuel inlet 22, presented in diagrammatic form. A fuel return 2 4 is provided for returning fuel to a fuel reservoir. The low-pressure system, formed by the fuel inlet 22 and a pre-supply pump for the fuel, together with the return system at zero pressure formed by the fuel return 24 are not represented in the drawing. Also not represented in detail are various leakage returns 2 6., which may be assigned to the fuel return 24.
The fuel pump 10 is provided with a valve spool 2 8, which is actuated by an electronically controlled actuator 30, which is connected to an electronic control unit 32. As a function of instructions from the control unit 32, the valve spool 2 8 can be adjusted by the actuator 3 0 between an open position, in which the delivery chamber 2 0 of the fuel pump is connected to the fuel inlet 22 and to the fuel return 24, so that no fuel is delivered, and a closed position, in which the connection to the fuel inlet and to the fuel return is closed and a displacement of the pump piston 18 in the delivery chamber 20 means that fuel present in the delivery chamber 20 is delivered to the injection nozzle 12 by way of the connecting line 14.
The injection nozzle 12, which is provided with a storage chamber 13, has a nozzle needle 34, which is displaceable between a closed position, in which the fuel provided cannot leave the injection nozzle 12, and an open position, in which the fuel provided is injected into the cylinder of the internal combustion engine. The nozzle needle 3 4 is supported on a spindle 3 6 (see Figure 2) , which closes off a control pressure chamber 38 at one side. The control pressure chamber 38 is provided with an inlet 40, which has an inlet restriction 42 in the form of a hole of small cross section, and with an outlet 44, which likewise has an outlet restriction 46 in the form of a hole of small cross section. The cross section of the outlet restriction 4 6 is larger than the cross section of the inlet restriction 42.
The outlet 44 from the control pressure chamber 3 8 is controlled by a valve element 48, which can be adjusted by an actuator 50, which is likewise connected to the control unit 32, between a position closing off the outlet 44 and a position exposing the outlet 44, When the valve element 48 closes off the outlet 44, a fluid, usually fuel, delivered by way of the inlet 40, is accumulated in the control pressure chamber 38. As a result, the spindle 36 exerts a force on the nozzle needle 34, which keeps the latter in the closed position against an opening force, which is generated by the fuel pressure bearing on the nozzle needle. When, on the other hand, the valve element 4 8 exposes the outlet 44, the fluid accumulated in the control pressure chamber 38 can flow out of the latter, since the outlet restriction 46 has a larger cross section than the inlet restriction 46[sic]. Consequently there is no longer any force opposed to a displacement of the spindle 3 6, and the fuel pressure acting on the nozzle needle 34 lifts it off from its valve seat, so that the fuel can be injected into the cylinder.
The fuel injection system described operates on the following principle: the injection sequence is initiated by activation of the actuator 3 0 - This shifts the valve spool 28 into the position in which the connection between delivery chamber and fuel inlet and fuel return is closed, so that the fuel pump delivers fuel. As a result, the pump piston 18 compresses fuel in the connecting line 14 and in the injection nozzle 12. During this process the nozzle needle 34 remains in its closed position until the required pressure level is reached; the time between closing of the valve spool 2 8 and opening of the nozzle needle 34 thereby defines the available injection pressure. When the injection sequence is to commence, valve element 4 8 opens the outlet 44, so that the nozzle needle 34 can lift off from its valve seat. In this sequence a pilot injection, a main injection with any rate of inj ection and an after-injection can be controlled by actuation of the valve element 4 8 independently of the valve spool 2 8. The various characteristic values relevant to this are shown in the diagram in Figures 6a to 6d.
Figure 6 a shows the flow through the actuator 3 0 as a function of the angle of rotation of the crankshaft of the internal combustion engine to be supplied with fuel. In Figure 6a the flow through the actuator 50 of the injection nozzle is shown as a function of the crankshaft angle of rotation. Figure 6c shows the lift of the valve spool 2 8 as a function of the crankshaft angle of rotation. Finally Figure 6d represents the lift of the valve element 48 as a function of the crankshaft angle of rotation.
It can be clearly seen from the diagrams that the valve element 4 8 can be controlled independently of the control of the valve spool 28, so that the desired rate of inj ection can be freely selected.
Figure 3 shows a fuel injection system according to a second embodiment. This differs from the fuel injection system shown in Figure 1 in that a high-pressure collecting chamber 21 is arranged inside the fuel pump 10 between the pump piston 18 and the valve spool 28. The high-pressure collecting chamber 21 acts as a pressure accumulator, so that an even greater delay is possible between the start of delivery by the fuel pump 10 and the opening of the nozzle needle 34 of the inj ection nozzle 12.
Figures 4 and 5 show an injection nozzle 12 for a fuel injection system according to a third embodiment. Here a. valve spool 52 is used instead of the valve element 48, so that a 3/2-way directional control valve is formed. Here too, an inlet restriction 42 and an outlet restriction 46 are provided, the inlet to the nozzle needle 34 being opened on opening of the valve spool 52. In the closed state of the valve spool 52 the inlet to the nozzle needle 34 and the nozzle chamber as a whole is relieved by the valve spool 52 to the fuel return 2 4. The advantage of this embodiment is that the injection nozzle is only subjected to the fuel pressure during injection.
1. An injection system for an internal combustion engine having a plurality of
cylinders to be supplied, the injection system comprising an electronic control unit
(32) and for each individual cylinder, the following :
a fuel pump (10),
an injection nozzle (12) which is provided with a nozzle needle (34) and with an electronically controlled valve (48, 50; 50, 52) which can control the opening of the nozzle needle (34),
a connecting line (14) between the fuel pump (10) and the injection nozzle
both each of the fuel pumps (10) and each of the electronically controlled valves (48, 50; 50, 52) being connected to the electronic control unit (32) and being controlled by the latter, characterized in that each injection nozzle (12) is provided with a storage space (13) which is flow-connected both to the connecting line (14) and to the nozzle needle (34) and in which a fluid can be built up by means of the electronically controlled valve (48, 50; 50, 52), so that the pressure then acting holds the nozzle needle (34) in its closed position.
2. The injection system as claimed in claim 1, wherein each fuel pump (10) is provided with an electronically controlled control slide (28).
3. The injection system as claimed in any one of claim 1 and 2, wherein each fuel pump (10) is provided with a high-pressure space (21).
4. The injection system as claimed in any one of claims 1 to 3, wherein each electronically controlled valve is a 3/2-way valve is provided with a valve slide (52).
|Indian Patent Application Number||IN/PCT/2001/1432/CHE|
|PG Journal Number||07/2008|
|Date of Filing||17-Oct-2001|
|Name of Patentee||ROBERT BOSCH GMBH|
|Applicant Address||Postfach 30 02 20 D-70442 Stuttgart|
|PCT International Classification Number||F02M 47/02|
|PCT International Application Number||PCT/DE2001/000119|
|PCT International Filing date||2001-01-13|