Abstract:
Methods and apparatus for controlling fuel injection pressure for fuel through a nozzle for combustion in an engine are disclosed. These include methods and apparatus for injecting the fuel at an injection pressure by means of an injector, maintaining the pressure during injection by closing a primary control valve for the fuel, and releasing a portion of the pressure during a predetermined portion of the fuel injection.

Description:
TECHNICAL FIELD 
     The present invention relates to a method and arrangement for controlling the pressure when injecting fuel, such as diesel oil, in an engine, whereby the pressure in a conventional way is obtained by a piston which is driven by a cam shaft and which presses oil out through a nozzle connected to a cylinder cavity in which the piston works. The spray nozzle is provided with small narrow holes through which the liquid fuel is atomized. 
     PRIOR ART 
     Many different arrangements for injecting diesel oil are known hitherto. They differ substantially from each other but have in common that a high pressure must be obtained so that the liquid is atomized and that the injection must occur quickly and start as a predetermined moment and be completed at a predetermined limited moment. Most arrangement are therefore based on the principle that a piston presses the fuel against a nozzle having holes at such high speed that a pressure of in the order of amount 300 Bar is created, whereby the injection of the fuel starts. This can occur by making the injection holes so small that they cannot allow all fuel which is pressed against them to pass. The pressure continues to rise even though fuel is flowing out from the nozzle. To release the pressure a connection between the pressure chamber and a valve is arranged, which valve opens when the injection is to be completed so that the pressure instantaneously drops to a zero value. The oil which flows through this regulating valve when it is opened flows via a drainage pipe back to the oil store. 
     The regulating valve is usually actuated by an electromagnet. It is of great importance that this valve works instantaneously since the whole injection cycle takes only time of in the order of 3 ms (milliseconds) having a highest pressure of about 1500 Bar. 
     The pressure-creating device, usually a piston in a cylinder, has usually a simple construction and the variations of the fuel injection arrangements which are present relate mostly to the controlling or steering valve which is connected to the fuel pressure. Examples of such arrangements are described in the German patent specification 3741526, the international patent application WO 89/00242, the European patent specification 0193788 and the American patent specification 5517973. All these patent descriptions describe quite different arrangements and it is therefore difficult to compare them with each other and with other prior art. 
     THE TECHNICAL PROBLEM 
     In the known arrangements having only one controlling valve the fuel pressure is built up quickly to a value of in the order of 300 Bar and it increase thereafter to about 1500 Bar until the pressure is released by means of the control valve. The injection through the injection holes starts at about 300 Bar. At the beginning of the injection cycle the fuel is combusted with relatively large formation of nitrogen oxide (NO x ), which from an environmental view is a disadvantage. Since the content of nitrogen oxides is limited by law, which law is continually made more stringent the moment of injection and thus the combustion must normally be postponed to reduce the contamination. This postponement has a negative influence on the efficiency of the engine. A further disadvantage with known arrangements is that at high speeds the pressure can be built up too quickly and become too high above the limit which the injection construction allows. It is therefore a requirement to be able to influence the pressure or to relieve it somewhat during the injection cycle at chosen moments, such as at the beginning, in order to decrease the NO x  emission and at the end to avoid too high pressures. 
     THE SOLUTION 
     According to the present invention, the above problem has been solved by a control valve which only closes and opens and an arrangement and a way of regulating the injection pressure of liquid fuel, such as diesel oil, by a nozzle having narrowed injection openings has been brought about, the pressure being created by a quick action from, for example, a piston in a cylinder and a main control valve in connection with the liquid fuel before the nozzle, which main control valve is kept closed during the injection, which method is characterized in that the pressure is relieved at a suitable moment during the injection cycle through a secondary valve. 
     According to the invention, it is suitable that the injection pressure is relieved at the beginning of the injection cycle for decreasing developed nitrous gases (NO x ) during combustion. 
     According to the invention, it may also be suitable that the injection pressure is relieved at the end of the injection cycle to allow higher speeds of the pressure-creating piston or the like. 
     The invention also comprises an arrangement for regulating the injection pressure of liquid fuel such as diesel oil by a nozzle having narrowed injection openings, whereby the pressure is created by a quick action from, for example, a piston in a cylinder and control valve in connection with the liquid fuel before the nozzle, which main control valve is kept closed during the injection, which arrangement is characterized in that a secondary valve within the main control cylinder for relieving the injection pressure. 
     According to the invention, the main control valve comprises a moveable valve body, which through an electromagnet, can be moved up and down against a first spring force having an enlargement at its lower part which is intended to co-operate with a surrounding housing to create a valve which can be closed or opened for the flow of liquid between the housing and the valve body, which liquid-flow is connected to the liquid before the liquid injection nozzle, which arrangement is characterized by a moveable rod within the valve body which is attached to the up and down moveable part of the electromagnet and which at its other end carries a second spring abutting against the lower part of the valve body, which second spring is stiffer than the first spring acting on the valve body, wherein radial holes have been made in the valve body inwardly against the rod and in that the rod co-operate with the valve body to make a valve. 
     According to the invention it is suitable that the radial holes in the valve body are located somewhat above the edge where a narrowing in the rod starts so that passage of liquid through the holes is prevented when the rod is located in its lower position with the stiffer second spring expanded. 
     It is also possible according to the invention that the radial holes in the valve body end in a ring-shaped part in the valve body around the rod and that the lower part of the ring-shaped part and a circular edge delimiting a narrowing of the rod make a valve. 
     According to the invention, it is suitable that the outlet side for the flow in both the main valve and the secondary valve drain into the fuel store. 
     According to the invention, it is suitable that the first spring acting on the valve body abuts with its other end via a support against the upper side of the body and with its second end against a part of the housing. 
     According to the invention, both springs are suitably co-axial and the electromagnet is arranged to be activated in at least two steps, whereby in the first step the main control valve is closed and in the second step when the main control valve is closed the secondary control valve is opened. 
    
    
     FIGURE DESCRIPTION 
     The invention will in the following be described more in detail in connection with the enclosed drawings where 
     FIG. 1 schematically shows an injection arrangement for fuel with a control valve of known kind, where 
     FIG. 2 shows the same arrangement with the control valve in another position, where 
     FIG. 3 shows the control arrangement according to the present invention having an open main control valve and a closed secondary valve, where 
     FIG. 4 shows the same arrangement as according to FIG. 3 but with a closed main valve and an open secondary valve and where 
     FIG. 5 shows another embodiment of the control valve according to the present invention having an open main control valve and a closed secondary valve. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows schematically a fuel injection device according to the prior art having a piston  1  which is forced down into a cylinder  2  in which the liquid fuel is present. The approximate piston stroke can be in the region of 15-17 mm. It is accordingly a question of very small and quick movements of the piston  1  which usually are activated from the cam shaft. From the cylinder cavity a conduit  3  leads to the injection nozzle. This comprises usually a wart-like device having for, example, eight injection holes with a diameter of 0.2 mm. 
     From the injection conduit  3  a branch conduit  4  leads to a control valve which is denoted throughout with the reference numeral  5 . This is influenced by an electromagnet  6  having an upper stationary part and an under part being moveable upwards and downwards. From this lower moveable part a rod  7  extends downwardly and a valve body  8  is connected to this rod  7 . Around the valve body  8  a housing  9  is arranged and this housing  9  is shaped with a valve seat  10  which, together with the body  8 , forms a valve. The valve body  8  is kept in the downwardly pressed position by means of a first spring  11 . However, when the electromagnet is activated the valve body  8  is lifted and the valve is closed. 
     When the fuel shall be injected into the engine through the nozzle from the fuel conduit  3 , this control valve must be closed. If not, no pressure in the conduit  3  can be built up and the fuel takes the route through the control valve and out through the drainage conduit  12 . 
     Below the schematic construction drawing of the injection arrangement the force influence from the electromagnet is shown first in FIG.  1 B. The influence is as appears from the start  0 , but at the point A the electromagnet is activated and it is kept activated by an even force until the point B when it again is deactivated. 
     In FIG. 1C the resulting injection pressure is shown. As appears from the figure, this pressure is practically  0  at the beginning, but it first builds up to the point C when it obtains a value of about 300 Bar when the injection starts through the holes in the nozzle, as a result of which the curve is given a push downward to thereafter continue up to the point D where the pressure can receive a value of about 1500 Bar. At the point D the electromagnet is deactivated and the pressure sinks quickly down to a very small value. When the pressure has come down, the injection will accordingly cease through the nozzle and the remaining pressure brings about only a flow through the open valve and the drainage conduit  12  to the fuel storage. 
     FIG. 2 shows the same arrangement as the one according to FIG. 1, but in this case the control valve is open and the fuel flow will then go, as appears from the figure, via the connecting conduit  4  and the open valve  8 ,  10  through the drainage conduit  12 . No injection will occur in this case. 
     FIG. 3 shows a control valve according to the present invention where the denotations  4 - 12  relate to the same elements as in FIGS. 1 and 2. What distinguishes this figure from FIGS. 1 and 2 is that radial holes  13  are made in the valve body  8 , which holes face towards the cylindrical rod  7 . Additionally, the cylindric rod  7  has been made narrowing at the part  14  below the level for the radial holes  13  and the lowest part  15  of the rod  7  has been provided with plane surfaces so that liquid can flow between this lower part of the rod  7  and the hollow valve body  8 . The lowermost part  16  of the rod  7 , which is a plate, carries a second spring  17  which at its other end abuts against a plane underside of the valve body  8 . This second spring  17  is stiffer than the first spring  11  between the valve body  8  and the housing  9 . The valve body  8  is provided at its lower part with a pressed in plate  19  which preloads the spring  17  and determines the basic position for the rod  7 . 
     The housing  9  is provided below the valve with an abutment  20  which makes a stop for the valve and which, through its position, determines the basic position of the valve in its opened position. 
     In the position which the figure shows, the secondary valve, i.e. the valve which consists of the rod  7  against the valve body  8 , is closed whereas the main valve is open and the fuel liquid can therefore flow past the main valve and out through the drainage opening  12 . 
     When the electromagnet  6  is activated, the lower part thereof will be pulled against the upper stationary part which means that it, together with the rod  7 , will be pulled upwardly. Since the first spring  11  is weaker than the second spring  17 , the spring  11  will thereby be compressed until the valve body  8  has abutted against the valve seat  10  on the housing  9  and accordingly closed the main control valve. On further stronger activation of the electromagnet, the rod  7  will move further upward whereupon the second spring  17  will be compressed and the radial holes  13  in the valve body  8  will be uncovered towards the part  14  on the rod  7 . This position is shown in FIG.  4 . Liquid can then flow from the connection conduit  4  in through the radial holes  13  downward past the second spring  17  and out through the drainage conduit  12 . The dimension and the number of holes  13  and the flow resistance in the secondary valve must be such that the pressure does not reach zero but is only somewhat decreased when the main control valve is closed. 
     It is important that the rod  7  seals with a tight gliding fit against the cavity of the valve body  8  so that when the holes  13  are located against the rod  17  no passage exists for the liquid. That part of the rod  7  which is located immediately above the part  14  must therefore have a smallest length of 1-2 mm so that a sealing can occur, but this part of the rod should not be too long since it should mean a too long lifting of the rod  7  to uncover the holes  13 . 
     The lower part  15  of the rod  7  has partly plane polished surfaces, so that passage for the flowing fuel between this part and the valve body  8  exists. 
     FIG. 5 shows another embodiment of the invention. The reference numerals  4 - 17  in this figure relate to the same element as in the earlier figures. The difference between this embodiment and the one according to FIGS. 3 and 4 is that the holes  13  face towards a ring-shaped chamber  18  on the inner side of the valve body  8  and around the rod  7 . The lower part of the ring-shaped chamber  13  is shaped as a valve seat and the rod  7  is shaped with an edge against this valve seat so that when the rod  7  is in its lower position the chamber  18  is closed at its bottom. To open the chamber  18  so that liquid may flow out therethrough, the rod  7  must be slightly lifted. In FIG. 5 the secondary valve is shown in its closed position and the main control valve in its open position, i.e. the electromagnet is not activated. 
     By the method and the arrangements according to the present invention it has become possible to regulate the pressure of the liquid fuel and the amount of injection thereof in a more accurate way than earlier. The means for bringing about this great advantage is the provision of the secondary valve and the possibility to be able to influence both the valves by two different levels of the electric current to the electromagnet. This switching on of the electric current occurs automatically and it is easy to regulate it by means of the trigger unit of the engine. 
     No substantial reconstruction of earlier known constructions without secondary valves is necessary with the construction according to the present invention. The valve body in the main control valve is substantially the same as with earlier constructions, but a central hole has to be made to allow the rod to be moved in the cavity. It is very important that the rod has a tight sliding fit compared to the valve body so that the secondary valve seals properly in its closed position. It is also important that the two springs are co-axial so that no side forces arise which could lock the secondary valve when the electromagnet is activated in two steps. 
     The invention is not limited to the embodiment shown but can be varied in different ways within the scope of the claims. Thus, the radial holes  13  may for example consist of elongated slots or non-round holes instead of drilled round holes.