Abstract:
In an injection system with pressure intensification with a simple and space-saving design, control means are provided permitting a large range fuel injection pressure control, which also permits rapid adaptation of the fuel injection pressure to the various engine operating conditions.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a fuel injection system with fuel pressure intensification, in which there is arranged, at the transition from a pressure source, which is formed in particular by a pressure accumulator, to a fuel injection injector, a pressure intensifier having a control space whose pressure level determines the degree of intensification and, consequently, the pressure increase over the initial pressure in the pressure accumulator and the operating pressure for the injector. The nozzle needle is loaded in the closing direction by the fuel pressure in a pressure chamber formed at the rear side of the nozzle needle. 
     In a known system of this type, the control space and also the pressure chamber are connected to a fuel return independently of one another, in each case by way of a control valve so that, by control of the pressure intensifier, a particular shape for the pressure curve can be established. By controlling the injector independently a range of the pressure curve suitable for injection can be selected. A mutually independent control of the pressure intensifier and of the injector is provided by magnetically actuated 2/2-way valves. This requires in addition to space and costs, a highly accurate coordination in the activation of the injectors and the valves since even small tolerances result in marked differences in the injection behavior. 
     In order to reduce the space requirement and the costs, and also to simplify the control so as to be able to sufficiently affect the engine combustion, in a first solution according to the invention, the connection of the control space and of the actuation space to the fuel return is controlled in a combined manner via a common valve connection. As a result, although the breadth of variation is restricted, the expenses are considerably reduced and space is saved, still wide-ranging possibilities for exerting influence are afforded. That is the combustion behavior of the internal combustion engine can be sufficiently influenced particularly with regard to obtaining favorable exhaust gas values. 
     A further solution according of the invention utilizes the fuel injector itself as a control element or control valve in that a part, which is involved in actuating the nozzle needle and moveable together with the nozzle needle, is a spool valve, which, by the design of the control cross-section thereof, particular the rising flank of the pressure profile can be varied in relation to the pressure prevailing at the nozzle needle seat. 
     Finally, in a further solution according to the invention the connection of the control space or of the action space to the return is influenced by a control valve in the form of a pressure balance with connections which branch off, on one hand, from the inlet and, on the other hand, from a connection between the inlet and the connection of the actuator space or of the control space to the return. In this solution, a separate valve control is implemented for connecting the control space and the actuation space to the return, but the control outlay is substantially reduced depending on the hydraulic conditions. The other valve control, which is disposed in the connection of the actuation space or of the control space to the return and which is established via the directional valve, affords the possibility of influencing the hydraulic conditions and consequently the control behavior of the pressure balance by a corresponding timing of the directional valve. 
     In a preferred design, one of the connections is branched off from the inlet and the other is branched off from a throttled connection between the inlet and the connection of the actuation space to a downstream control valve. 
     In such a design, the injector and the pressure intensifier are activated virtually simultaneously. A rising pressure profile during injection is thereby ensured. 
     This, in turn, makes it possible to provide for a process sequence which makes it possible, in particular, to affect the rising ramp of the pressure profile at the nozzle seat and which leads to a virtually rectangular pressure profile, in particular in the region of the rising ramp. 
     For this process sequence, it is assumed that the closing position of the magnetically activated control valve corresponds to a closing position of the nozzle needle due to the high pressure prevailing in the actuation space and due to the blocking of the control space to the return as determined by the pressure balance. When the magnetically activated control valve, which is in particular a 2/2-way valve, is briefly opened, the pressure drops in the actuation space and, with some delay, also in the control space. As a result, the pressure on the control piston of the pressure balance in the direction of its closing position is reduced. In this intermediate phase, however, the nozzle needle is still closed, so that, in the event of a correspondingly brief opening of the control valve, the pressure in the actuation space is reduced, but not the pressure prevailing at the inflow side, assuming corresponding dimensioning of the throttle cross-sections in the inlet and in the outlet to the actuation space. If, then, the control valve is once again opened, initially the pressure in the action space is reduced along with the high pressure at the inlet side, so that, during the opening of the nozzle needle, a correspondingly steep pressure rise at the nozzle-needle seat, and consequently, a steep pressure ramp, is obtained. This occurs especially since the previous lowering of pressure as a result of the preceding brief opening of the control valve also causes a reduction of the pressure acting on the control spool of the pressure balance in a closing direction. Consequently, when the control valve is once again opened in order to initiate fuel injection, there is a rapid displacement of the control spool of the pressure balance to the opening position connecting the control space to the return line. 
     In a further design, in which the pressure balance is branched off, on the one hand, from the inflow and, on the other hand, from a throttled connection between the inflow and the connection of the control space to the following control valve, when injection is initiated by opening of the control valve, the pressure intensifier is cut in before the injector is released. The result of this is a high pressure prevailing at the injector when the latter responds, this, in turn, entailing a steep, virtually rectangular pressure profile during injection. 
     Overall, therefore, in the solutions according to the invention, with only one magnetically activated control valve, an operating behavior is achieved, in which tolerances in the operation of the valve are avoided and the space requirements and also the control requirements are reduced overall, and in which, irrespective of these simplifications, both, fuel preinjection and fuel post injection are possible and the injection pressure is freely selectable. 
    
    
     Further details and features of the invention will become apparent from the following description of the invention with reference to the accompanying drawings: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows diagrammatically an injection system with pressure intensification, in which the communication between the control space of the pressure intensifier and of the actuation space of the injector is controlled via a control valve, 
     FIG. 2 is a diagrammatic illustration of the pressure profile at the nozzle-needle seat over time, 
     FIG. 3 shows an embodiment of an injection system with pressure intensification wherein the stroke movement of the nozzle needle of the fuel injector is utilized for controlling communication between the control space of the pressure intensifier and the fuel return, and 
     FIGS. 4 and 5 show other embodiments of an injection system with pressure intensification according to the invention, in which communication between the control space of the pressure intensifier or the communication between the actuator space of the fuel injector and the return are controlled via a pressure balance. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the figures,  1  designates an injection system which comprises a pressure source  2  in the form of a pressure accumulator, as is customary, particularly in common rail systems, and a fuel injector  3 . The fuel injector  3  is illustrated merely diagrammatically and has a nozzle-needle bore which extends to a nozzle seat  4  which is provided with injection holes and in which a nozzle needle  5  is supported. The nozzle needle  5  is spring-loaded towards it closing position as indicated diagrammatically at  6 . At the rear side, an actuation space  7  is provided which is connected in a throttled manner, indicated by a diaphragm or throttle  8 , to a fuel supply line  9  and which also has a connection  10  to the fuel return  11 . A throttle  12 , which may also be in the formal a diaphragm, is provided at the transition between the actuation space  7  and the connection  10 . 
     A pressure intensifier  13  is connected to the fuel supply line  9  from the pressure source  2  to the fuel injector  3 , specifically in the portion  14  of the fuel supply line  9  and a non-return valve  15  is disposed in the line portion  14 . 
     The pressure intensifier  13  comprises a stepped piston arrangement including a pressure receiver  16  and a pressure transmitter  17 . The pressure receiver  16  has a larger action surface  18  than the pressure transmitter  17 , the action surface of which is designated by  19 . 
     Opposite the action surface  18 , the pressure receiver  16  includes a control space  20  in which a spring  47  is disposed. The control space  20  is connected in a throttled manner, illustrated symbolically by the throttle  21 , to the inflow line  22  between the pressure source  2  and the working space  23  over the action surface  18  of the pressure receiver  16 . 
     The control space  20  is in communication by a line  24  to the fuel return  11 . The communication line  24  from the control space  20  to the return  11  extends to the return  11  by way of a control valve  25  which is a magnetically controlled 2/2-way valve. Also, the fuel injector  3  is connected to the line  24  so that the control space  20  and the fuel injector, that is the actuation space  7  thereof, can be in communication with the return line  11  under the control of the valve  25 . 
     In the illustrated initial position of the control valve  25 , the lines  10  and  24  which lead to the return  11  are blocked with the result that the pressure intensifier  13  is not activated and the nozzle needle  5  is held in its closed position by the pressure maintained in the actuation space  7 . 
     When the control valve  25  is opened, the control space  20  and also the actuation space  7  are simultaneously connected to the return  11  and are consequently relieved of pressure. As a result, the pressure intensifier  13  is activated and the nozzle needle  5  is raised into the opening position via the injection medium, which is present under high pressure. With the pressure intensifier  13  interposed, the pressure prevailing on the inlet side via the pressure source  2  is increased so that, depending on the degree of intensification, very high injection pressures are available. The pressure intensification however is restricted to that part of the injection medium, which flows to the fuel injector  3 . The response times in the connection between the control space  20  and the return  11  or respectively, between the actuation space  7  and the return  11  can be influenced via the respective flow cross sections, as illustrated for the line  10  by the throttle  12 . 
     FIG. 2 illustrates the profile of the pressure P at the nozzle-needle seat  4  over time, t, P 1  designating the pressure provided by the pressure source and P 2  designating the pressure which prevails at the inlet side during activation of the pressure intensifier  13 . t 1  designates the point in time of the opening of the control valve  25  and t 2  its subsequent closing point of time. The opening-side ramp of the pressure-profile curve is designated by  26  and the ramp occurring during closing is designated by  27 . A steeper or flatter profile of the ramps  26 ,  27  is obtained as a function of the pressure reduction in the actuation space  7  and of the level of the high pressure prevailing on the inlet side. It is the aim to have a steep, preferably virtually rectangular profile particularly at the opening side. 
     FIG. 3 shows another embodiment, corresponding parts or connections being given the same reference numerals. 
     Contrary to the illustration according to FIG. 1, the connection from the control space  20  to the return  11  designated by  28  extends to a control spool  29 , which is an integral part of the nozzle needle operating mechanism disposed above the actuation space  7  of the nozzle needle  5  and which delimits the actuation space  7  at on the nozzle-needle side. The control spool  29  has a control groove  30  for controlling the fuel flow to the return  11 . 
     Via the control groove  30  and its position in relation to the connection cross sections of the connection  28  to the injector  3 , the control times can be adjusted. The control groove  30  may also form a throttle cross-section. 
     In the embodiment according to FIG. 4, as in the previous versions, the control valve  25  is disposed in the connection line  10  to the return line  11 . The connection line  31  between the control space  20  and the return line  11  extends through a pressure control valve  32  containing a control spool  33 , which has a control groove  34  and which is spring-biased toward one end position by a spring  35 . The pressure control valve  32  is connected, at the end opposite the spring  35 , to the fuel supply line  9 , and a throttled connection  36  extending via the throttle  37  from the inflow  9  to the connection line  10  of the actuation space  7  to the return line  11 . The connection for that end of the control spool  33 , which is acted upon by the spring  35 , is branched off from the connection  36 . Depending on the pressure, the control groove  34  is in alignment with the connection  31  of the control space  20  providing for connection with the return  11  or alternately blocking off this connection. 
     When the control valve  25  is opened, the pressure in the actuation space  7  and also the spring-side action of pressure on the control spool  33  of the pressure control valve  32  drops, so that the pressure intensifier  13  is activated. The corresponding time sequences can be influenced in a more or less throttling manner by means of appropriate connection line cross sections. A corresponding influence is also possible by the timing of the control valve  25 , for example such that the latter is first opened briefly, so that the pressure in the action space  7 , is lowered but the nozzle needle  5  does not lift off the nozzle seat  4 . When the control valve  25  is re-opened after a brief closing phase, an initial period is provided in which there is a lower pressure in the actuation space  7  and therefore the high pressure built up via the pressure intensifier  13  acts upon the nozzle needle  5  against a lower counter-pressure thus leading to a virtually immediate opening of the nozzle needle  5  along with a correspondingly steep pressure rise at the nozzle seat  4 . 
     In the embodiment according to FIG. 5, once again a pressure control valve  38  is used for operation, the valve having a control spool  39  which is biased towards one end position via a spring  40  and which has a control groove  41 . 
     The control space  20  of the pressure intensifier  13  is connected to the return line  11  via the connection line  24  and the control valve  25 . The pressure control valve  38  is disposed between the inlet line  9  and the connection line  24  extending from the control space  20  to the return  11 . The spring-side end of the pressure control valve  38  is connected to a connection line  42 , which extends to the inlet line  9  via a throttle  43  and to the connection line  24  via a throttle  44 . The connection  45  to the spring side of the pressure control valve  38  is branched off between the throttles  43  and  44 . The opposite connection designated by numeral  46  is connected, unthrottled to the inlet line  9 . In this embodiment, during the opening of the valve  25 , the pressure intensifier  13  is first activated and there is a relatively small delay in the response of the injector  3 , so that, at the start of injection, a high pressure is rapidly available at the nozzle needle  5  and an approximately rectangular profile of the pressure curve is obtained.