Abstract:
A fuel injection equipment for an internal combustion engine is piloted by a central electronic unit, the equipment includes a piloted low pressure pump drawing the fuel from a low pressure tank and sending the fuel toward a piloted inlet valve controlling the inlet of a high pressure pump which pressurises the fuel and sends it pressurised toward a manifold to which is connected at least one injector. The equipment also includes a high pressure accumulator, distinct from the manifold, and a piloted high pressure valve in fluid communication between the outlet of the high pressure pump and the manifold so that the high pressure accumulator stores and delivers pressurised fuel to the manifold.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage application under 35 USC 371 of PCT Application No. PCT/EP2014/068161 having an international filing date of Aug. 27, 2014, which is designated in the United States and which claimed the benefit of GB Patent Application No. 1316439.7 filed on Sep. 16, 2013, the entire disclosures each are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a hybrid fuel injection equipment enabling energy recuperation when in foot-off mode. 
       BACKGROUND OF THE INVENTION 
       [0003]    Diesel fuel injection equipment, such as common rail system, equip all modern diesel engines. In these systems, an electric pump sucks the fuel from the fuel tank and sends it to a high pressure pump then, to the common rail that feeds all injectors. The high pressure pump is typically driven by the engine crankshaft and its inlet and outlet are controlled by valves. When the engine is requested to accelerate, in a so-called “foot-on” mode, the pressure inside the common rail is at its highest level and, to the opposite, when the engine decelerates, in “foot-off” mode the fuel is injected at a much lower pressure. Consequently the pressure in the rail raises and decreases quickly and often. The decrease of the pressure is normally done by opening a high pressure valve letting the fuel at high pressure return to the fuel tank. The energy spent to pressurise this fuel is then lost. 
       SUMMARY OF THE INVENTION 
       [0004]    Accordingly, it is an object of the present invention to provide a fuel injection equipment for an internal combustion engine. The equipment is piloted by a central electronic unit and it comprises a piloted low pressure pump drawing the fuel from a low pressure tank and sending the fuel toward a piloted inlet valve. Said piloted inlet valve pilots the inlet of a high pressure pump which pressurises the fuel and sends it pressurised toward a manifold, to which is connected at least one injector. The equipment further comprises a high pressure accumulator means, distinct from the manifold, and a piloted high pressure valve arranged in fluid communication between the outlet of the high pressure pump and the manifold, so that the high pressure accumulator means stores and delivers pressurised fuel to the manifold. 
         [0005]    The low pressure pump is an electric pump only driven when the pressure inside the accumulator falls below a predetermined threshold. 
         [0006]    Alternatively the low pressure pump can be a mechanical pump permanently driven, a bypass channel controlled by a piloted valve being arranged to enable or prevent the fuel to enter said mechanical pump. 
         [0007]    In a further alternative, the mechanical pump may be provided with a switchable means, such as a piloted clutch, enabling to disengage the pump from its driving means. 
         [0008]    According to an embodiment, the manifold is a common rail feeding in parallel a plurality of injectors. The equipment further comprises a second high pressure valve arranged on the rail and provided with a return low pressure line leading to the tank. 
         [0009]    Also, the equipment further comprises a one-way valve arranged between the high pressure pump and the accumulator, said one-way valve forbidding the fuel pressurised in the accumulator to flow back to the high pressure pump when the high pressure pump is stopped. 
         [0010]    The equipment further comprises a bypass channel connecting directly the high pressure pump to the manifold. A control valve normally closed arranged in said bypass channel, said control valve solely opening when the pressure of the fuel needed in the manifold, is superior to the pressure of the fuel in the accumulator means, for instance at cold start. 
         [0011]    The invention is also related to an engine management control process for controlling fuel injection equipment as described in the prior paragraphs. The process comprises the step of entering an energy saving mode by stopping the low pressure pump when the accumulator pressure is superior to a pressure threshold. Then, the accumulator means delivers the necessary fuel at the necessary pressure to the injectors. The threshold can either be constant or fixed and predetermined or, can be variable and constantly adapted as being the pressure at which the fuel must be injected. 
         [0012]    Furthermore, the energy saving mode comprises the step of:
       determining the operation mode of the engine and, if the engine operates on “foot-off” mode and comparing the accumulator pressure to the threshold.       
 
         [0014]    Also, the process exits the energy saving mode by actuating the low pressure pump if the accumulator pressure falls below the threshold. In the particular case of a variable threshold, the low pressure pump could be actuated when the decreasing accumulator pressure approached too closely the pressure at which the fuel must be injected. 
         [0015]    The process further comprises the step of running the low pressure pump so the accumulator means builds-up in pressure if at the determining step the operation mode of the engine is identified as “foot-on” and if the accumulator pressure is inferior to the pressure demanded for the injection. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention is now described by way of example with reference to the accompanying figures. 
           [0017]      FIG. 1  is a first embodiment of the fuel injection equipment as per the invention. 
           [0018]      FIG. 2  is a second embodiment of a fuel injection equipment as per the invention. 
           [0019]      FIG. 3  is a process of operation of the fuel injection equipment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    In the following description, similar elements will be designated with the same numeral reference. 
         [0021]      FIG. 1  is a representation of a first embodiment of a fuel injection equipment (FIE)  10  wherein fuel circulates from a tank  12  to the combustion chambers  14  of an internal combustion engine. Described in following the fuel flow, the FIE  10  comprises the low pressure tank  12  where fuel is sucked by a low pressure electric pump  16  and sent at a low pressure, approximately three to five bars, through a filter  18  then toward a piloted inlet valve  20  that controls the inlet of a high pressure pump unit  22 . In the high pressure pump  22  the fuel is highly pressurised, at several hundred bars, and is then sent to a high pressure accumulator means  24 . Said accumulator means  24  may for instance be a reservoir internally divided by a soft membrane. The pressurized fuel fills one side while a pressurised gas fills the other side of the membrane. Multiple alternatives can be imagined for such accumulator  24 . The pressure of the fuel inside the accumulator means  24  is monitored by a pressure sensor  26 . The outlet of the accumulator means  24  is controlled by a piloted high pressure valve  28  that opens into a manifold  30  distributing the fuel to the injectors  32 . In  FIG. 1  four injectors are sketched but another quantity can of course be arranged. Another pressure sensor  34  monitors the pressure inside the manifold  30 . 
         [0022]    A low pressure return line  36  is arranged between all the injectors  32  and the tank  12 . In said line  36 , the fuel which has not been injected in the combustion chambers  14  returns to the low pressure tank  12 . The low pressure return line  36  comprises also a back leak pressure regulator  38  where arrives a line from the high pressure pump  22 . A fuel line  40  is arranged between the filter  18  and said return line  36  so, for instance at cold start, to quickly heat the fuel at the high pressure pump inlet  22 . 
         [0023]    An electronic control unit  42  receives information signals from all sensors involved in the operation of the engine and, sends command signals to all piloted component for the FIE  10  of the engine. 
         [0024]      FIG. 2  is a representation of a second embodiment of the FIE  10 . The main difference between the second embodiment and the first embodiment is that the manifold  30  is replaced by a well-known common rail  44 . Said another pressure sensor  34  now monitors the pressure inside the rail  44  and, a second high pressure valve  46  arranged on the rail  44  can be open to enable the fuel in overpressure in the rail  44  to flow back to the low pressure tank  12  via another return line. 
         [0025]    A process  100  of operation of the FIE  10  is now described with reference to  FIG. 3 . The process  100  applies to both embodiments here above described. 
         [0026]    After starting the engine in the initial step  100 , the process comprises a first alternative step  110  where the engine condition is determined. In said alternative step  110  is especially determined whether the fuel to be injected is demanded a high pressure, the engine being on “foot-on” mode, or if no injection is required when the engine is in deceleration in “foot-off” mode. Is this description “foot-off” and “foot-on” designate the action of the driver on the throttle pedal and, the engine operation mode implied by this action. When the driver wants to accelerate, he is on “foot-on” and the fuel injected is at high pressure. To the contrary when for instance going downhill on engine brake the driver is “foot-off” and the fuel injected is at a low pressure just to maintain the engine running at idle speed. 
         [0027]    During the first alternative step  110  if the engine condition corresponds to a “foot-off” mode then the process  100  proceeds to a second alternative step  120 . In  FIG. 3  this is symbolised by the numeral “1” written close to the link between alternative steps  110  and  120 . When the engine is on foot-off mode the engine speed decreases to reach the idle speed. To maintain the idle speed and to prevent the engine from stopping and also to be ready for acceleration, fuel at low pressure is injected. 
         [0028]    In the second alternative step  120  the actual engine speed is compared to the idle speed. If the engine speed exceeds the idle speed, link “1” then, no injection is required and the engine continues on foot-off mode and the process continues in a third alternative step  130 . 
         [0029]    In the third alternative step  130  the accumulator pressure Pacc, measured by the pressure sensor  26 , is compared to a predetermined pressure threshold P1 memorised in the control unit  42 . The threshold P1 is chosen to be close, but slightly lower, than the maximum operational pressure Pmax of the FIE  10 . In an alternative, the threshold pressure P1 could be the maximum operational pressure Pmax of the FIE  10 . Distinguishing both pressures P1 and Pmax enables a range within which the accumulator pressure can evolve. If the accumulator pressure Pacc is smaller than the threshold P1 than the process  100  interprets that the accumulator pressure Pacc is insufficient than it proceeds to step  140 , link “1”. In step  140  the control unit  42  sends running command signals to the low pressure pump  16  and to the inlet piloted valve  20  which consequently enable fuel to be sucked from the tank  12  and directed to the high pressure pump  22 , then to the accumulator means  24  and, consequently the accumulator pressure Pacc raises. This running command signal is sent as long as the accumulator pressure Pacc is inferior the threshold P1. In  FIG. 3  this is symbolized by the loop between the steps  130  and  140 . 
         [0030]    As this happens in “foot-off” mode, there is no injection and the first and second high pressure valves  28 ,  46 , and the injectors  32  are closed. 
         [0031]    To the contrary, while still being in “foot-off” mode, if during the third alternative step  130 , the accumulator pressure Pacc is measured equal or superior to the threshold P1, the control unit  42  sends turn off signals to the low pressure pump  16  and to the piloted valve  20  saving the energy normally utilized by the pump  16 . From the third alternative step  130 , the process proceeds, link “0”, back to the first alternative step  110 . 
         [0032]    The mode here above described is an energy saving mode ESM wherein the low pressure pump  26  is stopped when the accumulator pressure Pacc is sufficient. In this case, the process  100  follows a loop between steps  110 ,  120 ,  130 . 
         [0033]    To the contrary, if the accumulator pressure Pacc is insufficient, the low pressure pump  26  is actuated, process  100  adding a loop between the steps  130 - 140 , until the accumulator pressure Pacc reaches the threshold P1 and, at that point process  100  returns to step  110 . 
         [0034]    In the above paragraphs, the threshold P is described fixed, constant and predetermined. It is memorized in the control unit  42 . 
         [0035]    Alternatively, the threshold P can be variable and equal to the pressure demanded Pdem by the injectors. As long as the accumulator pressure Pacc is sufficient to deliver said demanded pressure Pdem, the process remains in the energy saving mode ESM. 
         [0036]    During the first alternative step  110  if the engine condition corresponds to a “foot-on” mode, to the contrary of the preceding paragraphs, then process  100 , step  110 —link “0”, proceeds to a fourth alternative step  150  where the pressure demanded Pdem for injection is compared to the accumulator pressure Pacc. 
         [0037]    In the fourth alternative step  150 , if the pressure demanded Pdem is inferior to the accumulator pressure Pacc then,—link “1”, the process  100  proceeds to a step  170  where an opening signal is send to the high pressure valve  28  that controls the outlet of the accumulator means  24  therefore flowing high pressure fuel toward the injectors  32  and proceeding to an injection event in step  200 . 
         [0038]    If, to the contrary the pressure demanded Pdem is superior to the accumulator pressure Pacc then, link “0”, the process  100  proceeds to a step  160  where the control unit  42  sends running command signals to the low pressure electric pump  16  and to the inlet piloted valve  20  and, consequently, fuel is sucked from the tank  12  and is directed to the high pressure pump  22  then to the injectors  32  via the accumulator means  24 . 
         [0039]    Summarizing the “foot-on” mode, in reference to  FIG. 3 , the process  100  follows the steps  110 ,  150  and, if the accumulator pressure Pacc is sufficient the process stops actuating the low pressure pump  26  entering the energy saving mode ESM. The fuel inside the accumulator means  24  is then released— 170 —toward the injector to proceed to an injection event— 200 . 
         [0040]    To the contrary, if the accumulator pressure Pacc is too low than— 160 —the low pressure pump  26  is actuated and fuel is sucked from the tank and pressurized prior to be sent to the injectors to proceed to an injection— 200 . 
         [0041]    In an alternative embodiment not represented the low pressure pump  16 , which was previously described as an electric pump, can be replaced by a mechanical pump. Furthermore, it can be mechanically integrated with the high pressure pump and directly driven by the engine. 
         [0042]    In this mechanical alternative, the low pressure pump cannot be stopped in foot-off mode, as previously described, but its energy consumption is important only when fuel is sucked. To provide the energy saving mode ESM and similar advantageous results, a fluid bypass controlled by a piloted valve can be arranged around the mechanical low pressure pump. Therefore, when the bypass is closed and the fuel is normally sucked from the tank and sent to the high pressure pump and, in ESM mode, the bypass is open and no fuel is sucked, the mechanical pump rotates in consuming a minimum energy. Instead of a bypass channel, the mechanical pump can be provided with a piloted clutch that would couple or de-couple the pump from its driven means.