Patent Publication Number: US-8116962-B2

Title: Method of fuel injection

Description:
CROSS-REFERENCE-TO-RELATED-APPLICATION 
     This is a continuation-in-part of U.S. application Ser. No. 12/038,915 filed Feb. 28, 2008, and entitled A METHOD OF FUEL INJECTION, (Allowed), which claims priority to United Kingdom Application No. GB0703880.5, filed Feb. 28, 2007, and entitled A METHOD OF FUEL INJECTION, (issued as patent GB 2 447 045), each incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This invention relates to a method of fuel injection for an internal combustion engine and to a fuel injection system or a fuel injection unit for implementing the method. 
     BACKGROUND 
     Most internal combustion engines in automobiles currently use fuel injection systems to supply fuel to the combustion chambers of the engine. Fuel injection systems have replaced the earlier technology of carburetors because they give better control of the delivery of fuel and enable the engine to meet emission legislation targets as well as improving overall efficiency. 
     It is important that the fuel injection system delivers an appropriate amount of fuel at an appropriate time. Inappropriate delivery of the fuel may lead to a reduction in the output power of the engine and a wastage of fuel. 
     Whilst the sophisticated and highly developed fuel injection systems currently available (as described above) are ideal for use in internal combustion engines in automobiles, there are many other applications for internal combustion engines where such a level of sophistication is not appropriate and too costly. For instance, small single cylinder engines as used for a variety of engine powered gardening devices (such as lawn mowers, hedge trimmers, chain saws, rotovators, lawn aerators, scarifiers and shredders), small generators, mopeds, scooters, etc. are built to very tight cost targets and therefore cannot afford the cost of a sophisticated fuel injection system. To date, such small engines have used traditional cheaper carburetor technology. However, small engines of this type will soon face the same kind of exhaust gas emission legislation as automobile engines and so must be modified to meet the emission targets. Therefore, a cheap and simple system of fuel injection is required for such small engines. 
     In GB 2425188 the applicant described a fuel injection unit suitable for a small engine. The injector described injects in each operation a set amount of fuel into the charge air; the controller of the unit decided in each engine cycle how much fuel was needed and then operated the injector a number of times to come closest to the ideal amount of fuel. Since the amount of fuel can only be controlled in steps equivalent to the volume dispensed by the injector, the control was quite coarse. The engine could be over-fuelled or under-fuelled. 
     SUMMARY 
     According to a first aspect of the invention, there is provided a method of operating an internal combustion engine. In a preferred embodiment, the method includes the steps of supplying fuel to charge air using an injector which in each operation delivers a set amount of fuel; controlling how much fuel is supplied to the charge air in each engine cycle by controlling how many times the injector operates in each engine cycle; determining from engine speed and load a desired fuel demand as a number of operations of the injector calculated to at least one decimal place; rounding the desired fuel demand to a near integer to provide an output fuel demand for the injector as a number of operations of the injector for the next operating cycle; and calculating an aggregated fuel demand for a plurality of engine cycles and when the calculation aggregated fuel demand is not equal to an aggregated number of operations of the injector if for each cycle of the plurality of cycles the output fuel demand is calculated independently then controlling the output fuel demands sent to the injector over the plurality of cycles to operate the injector an aggregate number of operations closer to the calculated aggregated desired fuel demand for the plurality of cycles than if for each cycle of the plurality of output cycles the output fuel demand is calculated independently. 
     According to a second aspect of the invention, there is provided a method of operating an internal combustion engine including the steps of: supplying fuel to charge air using an injector which in each operation delivers a set amount of fuel; controlling how much fuel is supplied to the charge air in each engine cycle by controlling how many times the injector operates in each engine cycle; the method having first and second fuel demand calculation routines including: a first fuel demand calculation routine in which a desired fuel demand is determined with reference to engine speed and load for each engine cycle individually as a number of operations of the injector calculated to at least one decimal place and the desired fuel demand is rounded to a near integer to provide an output fuel demand as a number of operations of the injector for the next engine cycle; and a second fuel calculation routine in which a desired fuel demand is determined with reference to engine speed and load for a plurality of engine cycles as an aggregate number of operations of the injector over the plurality of the operating cycles and the injector is controlled over the plurality of engine cycles to achieve the desired fuel demand with the number of operations in at least one engine cycle of the plurality differing from the number of operations in other engine cycles of the plurality. 
     According to a third aspect of the invention, there is provided a method of operating an internal combustion engine including the steps of: supplying fuel to charge air using an injector which in each operation delivers a set amount of fuel; varying fuel supply by varying the number of operations of the injector in each engine cycle; calculating a desired aggregate number of operations of the injector over a set of engine cycles of a chosen number; and for at least some engine cycles determining a number of operations to be implemented by the injector in each of the engine cycles by: calculating how many engine cycles are left remaining in the set of cycles; by subtracting the number of operations already performed by the injector in engine cycles of the set from the calculated desired aggregate number of operations; and by dividing the result of the subtraction by the number of remaining cycles and rounding the result to a near integer. 
     Without increasing the complexity or cost of the injection apparatus itself the applicant has devised a way to achieve finer control of the amount of fuel delivered to a combustion chamber in each cycle to improve the efficiency of the engine, its fuel consumption and its emissions. 
     Internal combustion engines that make use of embodiments of the invention can do away with complicated, heavy and expensive fuel injection timing systems. Instead, they may make use of a cheaper and simpler system. 
     Further respective aspects and features of the invention are defined in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  schematically illustrates a first embodiment of an internal combustion engine having a fuel injection system according to the present invention; 
         FIG. 2  schematically illustrates a second embodiment of an internal combustion engine having a fuel injection unit according to the present invention; 
         FIG. 3  schematically illustrates the electronic controller used in the fuel injection unit of  FIG. 2 ; 
         FIG. 4  schematically illustrates a fuel injector for use in the fuel injection system of  FIG. 1  or the fuel injection unit of  FIG. 2 ; 
         FIG. 5  is a flowchart of a first method of operation of the engine control unit illustrated in  FIGS. 1 and 2 ; and 
         FIG. 6  is a flowchart of a second method of operation of the engine control unit illustrated in  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an internal combustion engine  100  comprising a cylinder  102  in which reciprocates a piston  104  with the piston  104  and the cylinder  102  defining between them a combustion chamber  106 . The piston  104  is connected by a connecting rod  108  to a crankshaft  110 . The crankshaft  110  drives a camshaft (not shown) which in turn drives an inlet valve  112  and an exhaust valve  114 . The inlet valve  112  and the exhaust value  114  are driven in timed relationship to the movement of the piston  104  in the cylinder  102 , with return springs (not shown) biasing the valves  112 ,  114  back into their valve seats. 
     The fuel injection system of the engine  100  comprises a fuel injector  116  arranged to deliver fuel  118  into an inlet passage  120  upstream of the inlet valve  112 . A throttle valve  122  is placed in the inlet passage  120  to control the flow of charge air into the inlet passage  120  and the combustion chamber  106 . 
     An engine control unit  124  controls the time at which the fuel  118  is injected into the charge air present in the inlet passage  120  and also controls the quantity of fuel  118  that is injected. The engine control unit  124  receives a signal from the throttle valve  122  via a control line  126 , the signal indicating the rotational position of the throttle valve  122  and hence the engine load. Additionally, the engine control unit  124  receives a timing signal from a crankshaft sensor  128  (which could be replaced by a camshaft sensor) via a control line  130 . The crankshaft sensor  128  is responsive to teeth  132  on the crankshaft  110  and to a gap  134  in the teeth  132 . The engine control unit  124  can determine, from the timing signal received from the crankshaft sensor  128 , the speed of the engine  100  and the position of the piston  104  within the cylinder  102 , this being used to determine the timing of opening and closing of the inlet valve  112 . Having regard to the timing signal produced by the crankshaft sensor  128  and the load signal produced by the sensor attached to the throttle valve  122 , the engine control unit  124  generates a control signal which is relayed to the injector  116  via a line  136  and controls the operation of the injector  116 . 
       FIG. 2  schematically illustrates an internal combustion engine  600  having a fuel injection unit  602 . The internal combustion engine  600  is similar to the internal combustion engine  100  shown in  FIG. 1 . Components of the engine  600  that are the same as components of the engine  100  are given the same reference numeral and, for conciseness, a description of them will not be repeated. 
     The engine  600  has a crankshaft  202 , which is similar to the crankshaft  110  shown in  FIG. 1 , except that the crankshaft  202  does not have the teeth  132  and hence does not have the gap  134 . 
     The engine  600  also has a pressure sensor  204  for detecting the pressure of the air within the inlet passage  120 . The pressure sensor  204  supplies an electronic controller  206  with a pressure signal via a control line  208 . 
     The electronic controller  206  determines, from the pressure signal received from the pressure sensor  204 : (i) the engine load; (ii) the engine speed; and (iii) the timing of the opening and/or closing of the inlet valve  112 . This will be described in more detail later. In addition, as before, the electronic controller  206  generates a control signal which is relayed to the injector  116  via the line  136  and controls operation of the injector  116 . 
     In the engine  100  shown in  FIG. 1 , the engine control unit  124  uses the signal from the crankshaft sensor  128  to determine the engine speed and the timing of the opening and closing of the inlet valve  112 . The electronic controller  206  determines both the engine speed and the timing of the opening and closing of the inlet valve  112  from the pressure signal received from the pressure sensor  204  and the engine  200  does not require the crankshaft sensor  128  of the engine  100  (nor the control line  130 ). Thus the crankshaft  202  of the engine  200  is more simply formed than the crankshaft  110  of the engine  100 , i.e. the crankshaft  200  does not need to be provided with the teeth  132  and the gap  134 . 
     In the engine  100  shown in  FIG. 1 , the engine control unit  128  uses the load signal from the sensor attached to the throttle valve  122  to determine the engine load. The electronic controller  206  determines the engine load from the pressure signal received from the pressure sensor  204  and the engine  600  does not require the sensor attached to the throttle valve  122  (nor the control line  126 ). 
       FIG. 3  schematically illustrates the electronic controller  206 . The pressure signal from the pressure sensor  204  representing the pressure of the air in the inlet passage  120  is received by the engine control unit  206  via the control line  208 . The pressure signal is then supplied to a low pass filter  400  and a high pass filter  402 . The outputs of the low pass filter  400  and the high pass filter  402  are supplied separately to a processor  404 . The processor  404  has access to a look-up-table  406  stored in a memory  408 . The processor  404  uses the output of the low pass filter  402 , the output of the high pass filter  404  and the look-up-table  406  to generate a control signal to be supplied to the injector  116  via the control line  136 . 
     The processor unit  404  uses the low pass filtered pressure signal to determine the load of the engine  200 . The processor unit  404  also uses the high pass filtered pressure signal to determine the speed of the engine  200  and the timing of the opening and closing of the inlet valve  112 . 
       FIG. 4  shows an embodiment of an injector  116 . It comprises a piston  1000  slideable in a housing  1001 . The piston  1000  is acted upon by a solenoid  1002  and by a biasing valve spring  1003 . The piston is moveable to draw fuel into and dispense fuel from a fuel chamber  1004 . A one-way inlet valve  1005  allows fuel to flow into the fuel chamber  1004  from a fuel inlet  1006 , while preventing flow of fuel out of the fuel chamber  1004  to the fuel inlet  1006 . A one-way sprung-loaded outlet valve  1007  allows fuel to be dispensed from the fuel chamber  1004  to a fuel outlet  1008 , but prevents fuel being drawn back into the fuel chamber  1004  from the fuel outlet  1008 . 
     In the operation of the fuel injector  116  the activation of the solenoid  1002  moves the piston  1000  against the biasing force of the spring  1003  to displace from the fuel chamber  1004  fuel via the outlet valve  1007  to the fuel outlet  1008 . Then, when the solenoid  1002  is de-energised the biasing spring  1003  forces the piston  1000  to move to draw fuel into the fuel chamber  1004  via the inlet valve  1005 . The piston  1000  has a defined piston stroke X p  This piston stroke is defined by setting the travel of the piston between two end stops. By setting a definite piston travel the amount of fuel dispensed in each dispensing operation of the fuel injector  116  can be set at a set value. Thus, whenever the solenoid  1002  is operated then the fuel injector  116  dispenses a set amount of fuel, i.e. a volume of fuel identical (or substantially so) in and constant for all operations of the injector, preset and not variable by the injector or the controller of the injector. This means that in each engine cycle the amount of fuel dispensed by the fuel injector  116  can be controlled by controlling the number of times that the solenoid  1002  is activated during the engine cycle. Unlike pulse width modulated injectors, the amount of fuel delivered by the fuel injector is insensitive to pressure variations in the intake passage  1006 . 
     Previously it has been proposed for each engine cycle to take measured engine speed and load and then use a look-up table to determine how many times in the engine cycle the injector  116  should be operated. This was determined separately for each engine cycle, independently of all other engine cycles. However, this gives only a coarse control of the amount of fuel going into the engine for combustion. 
     The applicant has realized that not all fuel dispensed by the injector  116  prior to a combustion cycle reaches the combustion chamber and is combusted. Instead a significant amount of fuel hangs on the walls of the intake passage  120 . This is usually considered undesirable and so the injector  116  is usually situated as near as possible to the back of the valve head of valve  112  to minimize the length of the passage  120  in whose walls fuel can hang. 
     The applicant has realized that the fact that fuel hangs on walls, normally felt undesirable, can be used to advantage in the use of an injector as described above with reference to  FIG. 4 . The applicant has designed new control strategies to be used by the electronic controllers  124  of  FIGS. 1 and 206  of  FIGS. 2 and 3 . The strategies are illustrated by the flow charts of  FIGS. 5 and 6 . 
     Turning first to  FIG. 5 , as described in the previous patent GB 2425188, the controller  124  or  206  will use measured engine load and speed to address a look-up table at step  2000 . This will give an idealized amount of fuel to be delivered by the injector  116  for a single engine cycle. This figure can be modified at  2001  to take account of factors such as changing engine temperature, fuel temperature, atmospheric pressure, etc, although this step is optional. 
     The innovation of the first fuelling strategy of the present invention is to move away from looking at a single engine cycle and to consider instead 8 consecutive cycles. This happens at  2002 , where the ideal amount for one cycle is multiplied to give the total needed over 8 operating cycles of the engine. Then a fuel demand (d) as a number of operations of the injector  116  is calculated at  2003  and this is fed on to a fuel count calculator  2004 , which will be described later. 
     The fuel demand (d) is calculated for every cycle of the engine. At  2005  it is determined (by comparing the new fuel demand with the previous fuel demand) whether the fuel demand is constant or increasing or decreasing. This result is communicated to the fuel count calculator  2004 . Also if the demand is not constant, but is increasing or decreasing then this information is fed to a reset function  2006 . 
     A sensor  2007  either measures the rate of revolution of the engine (rpm) or in some other way notes the beginning of each new engine cycle (in the  FIG. 1  embodiment the sensor  2001  can be provided by sensor  128  and in the  FIG. 2  embodiment the sensor can be provided by the sensor  204 ). This information is fed to a cycle counter  2008 . In the illustrated embodiment the cycle counter counts sets of 8 cycles. However, this only happens if the fuel demand is constant and the counter is reset to start again at zero if the reset function  2006  dictates this. This reset function could be varied so that reset occurs only when the fuelling is increasing or decreasing by more than a threshold amount. Also it may be determined to dispense with this reset function altogether, e.g. if it is known that the engine will be operating within acceptable variation limits. 
     The cycle number (i.e. 1 to 8) is output at  2009  and at  2010  the number of cycles remaining of a set of 8 is determined. If it is determined that no cycles are left then the reset function  2011  is alerted and this then resets the counter  2008  to zero. 
     The number of cycles remaining (n) is fed to the fuel count calculator  2004 . This calculates the fuel demand for the next engine cycle as a number of operations of the injector  116  during the cycle. This is output at  2011 . 
     The number of injector operations for 8 cycles has already been calculated at (d) at  2003 . In a steady state condition the calculator calculates the number of injector operations by dividing the number of operations left in an 8 cycle sequence (r) by the number of cycles remaining (n) calculated at  2010 . The result is rounded to the nearest integer. The number of remaining operations (r) is calculated at  2012 . Initially it will be (d) at the start of a set of 8 cycles, but it will be decreased each cycle by the fuel demand output at  2011  by the calculator  2004 . This is why the flowchart has an arrow leading from the calculator  2004  to the fuel count remaining calculator  2012 . 
     The above operation will lead to the number of operations in a cycle varying from cycle to cycle despite a constant fuel demand in all cases other than when the total fuel demand for the cycle is exactly divisible by 8. For instance if the number of operations over 8 cycles is 70 then: 
     1. For the first cycle the number of operations will be determined as 70/8=8.75, therefore the number of operations output at  2011  will be 9. 
     2. For a second cycle the number of operations will be determined as (70−9)/7=61/7=8.71, therefore again the number of operations output at  2011  will be 9. 
     3. For a third cycle the number of operations will be determined as (70−18)/6=52/6=8.67, therefore again the number of operations output at  2011  will be 9. 
     4. For a fourth cycle the number of operations will be determined as (70−27)/5=43/5=8.6, therefore again the number of operations output at  2011  will be 9. 
     5. For a fifth cycle the number of operations will be determined as (70−36)/4=34/4=8.5, therefore again the number of operations output at  2011  will be 9. 
     6. For a sixth cycle the number of operations will be determined as (70−45)/3=25/3=8.33, therefore the number of operations output at  2011  will be 8. 
     7. For a seventh cycle the number of operations will be determined as (70−53)/2=17/2=8.5, therefore again the number of operations output at  2011  will be 9. 
     8. For the eighth and final cycle the number of operations will be determined as (70−62)/1=8/1=8, therefore again the number of operations output at  2011  will be 8. 
     By varying the number of operations stroke to stroke, the controller achieves a finer degree of control—in effect giving steps equal to ⅛ th  of the volume of fuel dispensed by the injector. There will be no noticeable unevenness in the running of the engine because the effect of the fuel ‘hanging’ on the walls serves to average the fuel delivered to the combustion chamber in any event. 
     If the fuel demand increases or decreases then the set of 8 cycles can be broken and a new set calculated; during changing demand the calculator  2004  can suspend its normal rounding operation and always round up to the nearest integer in the case of increasing demand or always round down to the nearest integer in the case of decreasing demand. However, this is not necessary and instead the engine could always look at a set of e.g. 8 cycles, regardless of varying fuel demand 
     Whilst the example above discusses averaging over 8 cycles, the method could be applied over any number of cycles from 2 to 16. Indeed, the number of cycles in the set considered for averaging purposes could itself be varied with engine speed and/or load. When the engine operation is very stable then the number of cycles for averaging could be 12-16 to achieve best refined performance, whilst if the operating conditions are more variable then the number of cycles in the set could be 2 or 3. Selecting a low number of cycles in a set, e.g. 2 or 3, makes it easier to round the calculation of aggregated fuel demand, as described above, continuously, without a need for different mode of operation. 
       FIG. 6  illustrates a second method of operation according to the present invention. As with the first method there is an initial step taken (at  3000  in the Figure) at the beginning of each engine cycle in which a desired fuel demand is calculated based upon the measured engine speed and load at the beginning of the engine cycle. The desired amount is determined as a number of operations of the fuel injector, such number be calculated to one or two decimal places. For instance, a desired fuel demand might be 3.6 operations of the fuel injector. Obviously the injector itself can only operate 3 times a cycle or 4 times a cycle and cannot itself operate 3.6 times a cycle. 
     At  3001  the fuel demand is rounded to a near decimal. For instance, a 3.6 fuel demand may be rounded to 4. This is an output as a demand D. The difference between the output demand D and the input demand calculated at  3000  is determined, in this case −0.4. This difference is output to 3002. 
     The output demand D is relayed to 3003. At  3003  the final output to the injector is determined. 
     At  3004  the demand D is monitored to see whether it is constant (i.e. within predefined limits, e.g. not varying by plus or minus 2 cycles) for 3 or more cycles. If a demand has been constant for 3 or more cycles then a signal is sent to the box  3002  to start accumulating the difference signals sent from box  3001 . If the output is varying or has not been constant for at least 3 cycles then a reset signal is sent to the box  3002  to clear the box  3002  back to zero. It may be decided to dispense with step  3004  and to continuously accumulate a difference at  3002 , regardless of varying demand D. 
     The difference calculated at  3001  is accumulated at  3002 . Then, at  3005  it is determined whether the accumulated difference is greater than 1. If the accumulated difference is greater than 1 then one is added to the number D at box  3003  so that the output from  3003  is D+1. 
     At  3006 , it is determined whether the accumulated difference at  3002  is less than −1. If the accumulated difference is less than −1 then 1 is subtracted from D at  3003  and the output to the injector is D−1. 
     During times of decreasing or increasing demand the rounding operation at  3001  can be varied. At  3007  it is determined whether the output D is less than, equal to or more than the immediately preceding output D. If the current output is less than the preceding output D then at  3001  the rounding operation is always downwards. For instance, 3.8 would be rounded down to 3. If the demand D is constant then at  3001  there will be rounding to the nearest integer. If the demand D is increasing then at  3001  the demand is always rounded up to the nearest integer, e.g. 3.2 would be rounded up to 4. This adds in an anticipation of a need for a fuelling increase or a fuelling decrease in the next cycle. 
     The method in  FIG. 6  allows an averaging to take place over a number of engine cycles to give a total fuel delivery to the combustion chamber which is closer to that determined at the step  3000  than if no differences are accumulated in the process. 
     The  FIG. 6  embodiment is particularly suited to operate continuously, in varying and steady state conditions. 
     The foregoing description of preferred embodiments for this disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the disclosure and its practical application, and to thereby enable one of ordinary skill in the art to utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the disclosure as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.