Patent Publication Number: US-6705290-B2

Title: Fuel injection control system and method

Description:
TECHNICAL FIELD 
     The present invention is directed to a fuel injection control system and method. More particularly, the present invention is directed to a system and method for controlling a hydraulically-actuated fuel injector. 
     BACKGROUND 
     Environmental concerns have made the reduction of emission an important factor in the design and control of an internal combustion engine. One method of reducing the emissions generated by an internal combustion engine involves precisely controlling the timing and amount of fuel injected into the combustion chambers of the internal combustion engine. 
     An internal combustion engine may include a fuel injection system that injects fuel to the combustion chambers. The fuel injection system typically includes one fuel injector for each combustion chamber. The fuel injectors may be, for example, hydraulically-actuated electronically-controlled unit injectors. This type of fuel injector dispenses a quantity of fuel into the combustion chamber of the engine based on the controlled introduction of a pressurized fluid, which pressurizes the fuel to injection pressure. 
     The internal combustion engine may also include an electronic control module (“ECM”) that controls each fuel injector to deliver a certain quantity of fuel to each combustion chamber at a certain time in the operating cycle. The ECM may generate and apply an injection signal to each fuel injector to deliver a quantity of fuel to each combustion chamber. In the case of a hydraulically-actuated electronically-controlled fuel injector, the injection signal may be a current applied to a solenoid in the fuel injector. The current energizes the solenoid to open a valve, which allows the pressurized fluid to flow through the fuel injector and pressurize and deliver fuel to the combustion chamber. The magnitude and duration of the current determines the amount of fuel delivery. 
     Because the pressurized fluid is integral to the operation of the fuel injector, the properties of the pressurized fluid may impact the amount of fuel delivered for a given injection signal. For example, if the pressurized fluid has a relatively high viscosity, the amount of fuel delivered for a given injection signal may be different than the amount of fuel delivered when the pressurized fluid has a relatively low viscosity. Accordingly, the ECM may use the properties of the pressurized fluid as an input in determining the magnitude and duration of the injection signal. 
     As described in U.S. Pat. No. 6,102,004, the ECM may use the pressure of the pressurized fluid and the temperature of the engine as inputs when generating the injection signal. Based on these parameters, the ECM accesses a series of “calibration maps” that store data for the fuel injector. These calibration maps provide information on the required duration of the injection signal to achieve the desired fuel delivery amount given the particular operating conditions. Thus, the ECM may generate an appropriate injection signal based on the pressure of the operating fluid and the temperature of the engine. 
     However, generating these calibration maps may be an expensive and time-consuming process. Each fuel injector must be calibrated with each different type of operating fluid that may be used to operate the fuel injection system. This entails testing the fuel injector under a variety of pressure and temperature conditions for each different type of operating fluid. 
     In addition, this type of fuel injection control system does not provide for any feedback on the fuel injection process. The ECM is not able to determine if there is a difference between the desired amount of fuel delivery and the actual amount of fuel delivery. If there is a significant difference, such as, for example, too much fuel is delivered to the combustion chamber, the engine may generate excessive emissions and/or experience “rough” running conditions. The current fuel injection control systems do not provide for the correction of future fuel injections based on fuel delivery discrepancies in past fuel injections. 
     The fuel injection control system of the present invention solves one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is directed to a method of controlling a fuel injector. A first injection signal is applied to a hydraulically actuated fuel injector to inject a quantity of fuel into a combustion chamber of an internal combustion engine. An amount of an operating fluid used by the fuel injector to inject the quantity of fuel into the combustion chamber is calculated. The amount of fuel injected into the combustion chamber is estimated based on the amount of operating fluid used by the fuel injector. A viscosity parameter is determined for the fuel injector based on the duration of the first injection signal and the estimated amount of fuel injected into the combustion chamber. 
     In another aspect, the present invention is directed to a fuel injection system. The fuel injection system includes a fluid supply rail configured to conduct a pressurized fluid. A fuel injector having a valve is configured to introduce an amount of pressurized fluid into the fuel injector from the fluid supply rail. The fuel injector is configured to release an amount of fuel in response to the introduction of the pressurized fluid. An electronic control module is configured to apply a first injection signal to the fuel injector to modulate the valve, to calculate the amount of pressurized fluid used by the fuel injector, to calculate an amount of fuel injected into the combustion chamber based on the calculated amount of pressurized fluid used by the fuel injector, and to determine a viscosity parameter indicating the sensitivity of the fuel injector to the properties of the pressurized fluid. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description, serve to explain the principles of the invention. In the drawings: 
     FIG. 1 is a schematic and diagrammatic illustration of a fuel injection control system in accordance with an exemplary embodiment of the present invention; 
     FIG. 2 is a diagrammatic illustration of a fuel injector in accordance with an exemplary embodiment of the present invention; 
     FIG. 3 is a flowchart illustrating a method of controlling a fuel injector in accordance with an exemplary embodiment of the present invention; 
     FIG. 4 is a graph illustrating an exemplary representation of the pressure of operating fluid in a fluid supply rail during a series of fuel injections; 
     FIG. 5 is an enlarged view of an exemplary fluid supply rail pressure notch experienced during a fuel injection event; and 
     FIG. 6 is a graph illustrating a relationship between temperature and a viscosity parameter for a series of exemplary fluid types. 
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments of the invention, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     An exemplary embodiment of a fuel injection control system is illustrated in FIG.  1  and is designated generally by reference number  10 . The illustrated fuel injection control system  10  is adapted for a direct-injection diesel cycle internal combustion engine  12 . It should be understood, however, that fuel injection control system  10  may be used with other types of internal combustion engines, such as, for example, gasoline or natural gas engines. 
     Fuel injection control system  10  includes an operating fluid supply system  14 . Operating fluid supply system  14  includes a tank  18  configured to hold a supply of operating fluid, which may be, for example, hydraulic oil or fuel. A first source of pressurized fluid  20 , which may be, for example, a pump, draws operating fluid from tank  18  and increases the pressure of the operating fluid. First source of pressurized fluid  20  may direct the pressurized operating fluid through a fluid cooler  22  and one or more fluid filters  24 . 
     As also shown in FIG. 1, operating fluid supply system  14  further includes a second source of pressurized fluid  26 , which may be, for example, a pump. Second source of pressurized fluid  26  receives the filtered operating fluid and further increases the pressure of the operating fluid. Second source of pressurized fluid  26  directs the pressurized operating fluid into a fluid supply line  28 . 
     As further shown in FIG. 1, fluid supply line  28  connects second source of pressurized fluid  26  with an operating fluid manifold  30 . Operating fluid manifold  30  includes a fluid supply rail  31 . A pressure sensor  44  may be disposed in fluid supply rail  31 . Pressure sensor  44  senses the pressure of the operating fluid in fluid supply rail  31  and generates a signal S 1  indicative of the sensed pressure for a given time. Pressure sensor  44  may be any sensor readily apparent to one skilled in the art. 
     Fluid supply rail  31  provides pressurized operating fluid to a series of branch passageways  32 . Each of the series of branch passageways  32  leads to a fuel injector  34 . As described in greater detail below, the pressurized operating fluid is used by each fuel injector  34  to inject an amount of fuel into a combustion chamber of engine  12 . 
     As shown in FIG. 1, a series of waste regulating valves  35  (one of which is illustrated in FIG. 1) are in fluid connection with each fuel injector  34 . 
     Waste regulating valves  35  control the return of operating fluid from fuel injectors  34  to a fluid return line  36 . Under certain circumstances, the fluid released from each fuel injector  34  may be pressurized. 
     As also illustrated in FIG. 1, return line  36  may be connected to a hydraulic motor  38 . Hydraulic motor  38  may be connected to second source of pressurized fluid  26 . Hydraulic motor  38  may use the pressure of the returned hydraulic fluid to generate work, which may be applied to second source of pressurized fluid  26  to assist in the pressurization of operating fluid for use in actuating fuel injectors  34 . 
     As illustrated in FIG. 1, a release line  40  may connect second source of pressurized fluid  26  with tank  18 . A valve  42  may be disposed in release line  40 . Valve  42  regulates the flow of fluid from second source of pressurized fluid  26  to tank  18 . Valve  42  may direct some operating fluid to tank  18  to control the pressure of the operating fluid flowing to fluid manifold  30 . 
     As further shown in FIG. 1, a fuel supply system  16  provides fuel to fuel injectors  34 . Fuel supply system  16  includes a fuel tank  50  and a fuel pump  54 . Fuel pump  54  draws fuel from fuel tank  50  and passes the fuel through one or more fuel filters  56  and into fuel supply line  52 . Fuel supply line  52  directs the fuel into fuel injectors  34 . 
     A fuel return line  62  connects fuel injectors  34  with fuel tank  50 . Return line  62  provides a passageway for fuel to return from fuel injectors  34  to fuel tank  50 . A regulating valve  60  may be disposed in fuel return line  62  to control the flow of fuel from fuel injectors  34  to fuel tank  50 . 
     An exemplary embodiment of a fuel injector  34  is illustrated in FIG.  2 . In the illustrated exemplary embodiment, fuel injector  34  is hydraulically-actuated and electronically-controlled. It should be understood that a variety of alternative embodiments of fuel injector  34  will be readily apparent to one skilled in the art. 
     As shown in FIG. 2, fuel injector  34  includes a fuel inlet  76  that is connected with fuel supply line  52  (referring to FIG.  1 ). Fuel injector  34  includes a fuel passageway  77  that conducts the fuel from fuel inlet  76  to a nozzle  87 . Nozzle  86  may extend through a cylinder head  96  of engine  12 . Nozzle  87  may be configured to inject fuel into a combustion chamber  98  defined by an engine block  94  of engine  12 . 
     As further shown in FIG. 2, an check valve  84  is disposed in nozzle  87  of fuel injector  34 . Check valve  84  may move between a closed position where check valve  84  blocks nozzle  87  and an open position where check valve allows fuel to flow through nozzle  87 . A spring  92  may bias check valve  84  into the closed position. 
     Fuel injector  34  also includes an intensifier piston  82 . Intensifier piston  82  is disposed adjacent a chamber  90  in fuel passageway  77 . In response to a force exerted on the head of the piston, intensifier piston  82  exerts a corresponding force on fuel contained within chamber  90 . This force acts to increase the pressure of the fuel between chamber  90  and nozzle  87 . The pressure of the fuel exerts a force on check valve  84  that opposes the force of spring  92  acting on check valve  84 . When the force exerted by the fuel on check valve  84  exceeds the spring force, check valve  84  will move to the open position and allow the pressurized fuel to flow through nozzle  87  and into combustion chamber  98 . 
     Fuel injector  34  also includes fluid inlet  74  that is configured to receive pressurized operating fluid from branch passage  32  of fluid supply rail  31  (referring to FIG.  1 ). Fuel injector  34  uses the pressurized operating fluid to exert forces on each of the intensifier piston  82  and the check valve  84 . Fuel injector  34  includes a first valve  66  and a second valve  68  that control the flow of the pressurized operating fluid through fuel injector  34 . 
     As shown in FIG. 2, fuel injector  34  includes a first passageway  86  that directs the pressurized operating fluid from fluid inlet  74  to check valve  84 . First passageway  86  includes a low pressure seat  78  and a high pressure seat  80 . When first valve  66  is engaged with low pressure seat  78 , first passageway  86  is connected with fluid inlet  74 . When first valve  66  is engaged with high pressure seat  80 , first passageway  86  is connected with a fluid drain  70 . 
     First valve  66  may include a solenoid  64  that is configured to move first valve  66  between low pressure seat  78  and high pressure seat  80 . A spring  72  may be engaged with first valve  66  to return first valve  66  to low pressure seat  78  when solenoid  64  is de-energized. Thus, energizing solenoid  64  will move first valve  66  to high pressure seat  80  to allow pressurized operating fluid to flow from fluid inlet  74  towards check valve  84 . The pressurized operating will fluid will exert a closing force on check valve  84 . De-energizing solenoid  64  moves first valve to the low pressure seat  78  and allows the pressurized operating fluid to escape from first passageway  86  through fluid drain  70 . This will relieve the closing force exerted on check valve  84 . 
     Fuel injector  34  also includes a second passageway  88  that conducts pressurized operating fluid from fluid inlet  74  to intensifier piston  82 . 
     Second valve  68  is disposed in second passageway  88  and controls the flow of operating fluid through second passageway  88 . Second valve  68  may be, for example, a shuttle valve that is spring biased into a closed position where flow between fluid inlet  74  and second passageway  88  is blocked. In addition, a branch passageway from first passageway  86  may direct pressurized operating fluid from first passageway  86  against second valve  68  to exert an additional closing force on second valve  68 . 
     Second valve  68  may be opened when subject to a pressure differential. As shown in FIG. 2, pressurized fluid from fluid inlet  74  is directed against second valve  68  and exerts an opening force on second valve  68 . When solenoid is energized to move first valve  66  to high pressure seat  80 , the pressurized operating fluid in first passageway  86  will escape through drain  70 , thereby relieving the closing force exerted by the pressurized operating fluid on second valve  68 . The resulting opening force exerted on second valve  68  by the pressurized operating fluid from fluid inlet  74  will overcome the spring bias and open second valve  68 . When second valve  68  is open, pressurized operating fluid may flow through second passageway  88  to intensifier piston  82 . The pressurized operating fluid acts through intensifier piston  82  to increase the pressure of the fuel in chamber  90 , which, in turn, exerts a force on check valve  84 . When the force of the pressurized fluid acting on check valve  84  exceeds the force of spring  92 , check valve  84  moves to an open position and allows fuel to flow through nozzle  87 . 
     The flow of fuel through nozzle  87  may be stopped by de-energizing solenoid  64  and allowing spring  72  to move first valve  66  to low pressure seat  78 . This allows pressurized operating fluid to flow through first passageway  86  to exert a closing force on check valve  84 . The closing force of the pressurized operating fluid will overcome the opening force generated by the pressurized fuel and will move check valve  84  to the closed position. 
     The flow of fuel through nozzle  87  may be restarted by energizing solenoid  64  to move first valve  66  to high pressure seat  80 . This allows the pressurized fluid in first passageway  86  to drain, thereby relieving the closing force on check valve  84 . Thus, the force of the pressurized fuel will again move check valve  84  to the open position and fuel will flow through nozzle  87  into combustion chamber  98 . 
     As illustrated in FIG. 1, fuel injection system  10  includes a computer  46  that generates an injection signal to control the release of fuel from fuel injector  34 . Computer  46  may include an electronic control module  48  that has a microprocessor and memory  49 . As is known to those skilled in the art, the memory is connected to the microprocessor and stores an instruction set and variables. Associated with the microprocessor and part of electronic control module  48  are various other known circuits such as, for example, power supply circuitry, signal conditioning circuitry, and solenoid driver circuitry, among others. 
     Electronic control module  48  may be programmed to control: 1) the fuel injection timing; 2) the total fuel injection quantity during an injection cycle; 3) the fuel injection pressure; 4) the number of separate injections or injection segments during each injection cycle; 5) the time intervals between the injection segments; 6) the fuel quantity of each injection segment during an injection cycle; 7) the operating fluid pressure; 8) the current level of the injection waveform; and/or 9) any combination of the above parameters. Computer  46  may receive a plurality of sensor input signals S 1 -S 8 , which correspond to known sensor inputs relating to engine operating conditions. For example, sensor inputs may include, fluid supply rail  31  pressure, engine temperature, engine load, etc. Electronic control module  48  may use these sensor inputs to determine the precise combination of injection parameters to execute a particular injection event. 
     Electronic control module  48  controls each fuel injection by generating and applying an injection signal, which may be, for example, a current, to solenoid  64  of fuel injector  34 . As will be apparent from the previous discussion, however, the responsiveness of fuel injector  34  to the application of the injection signal will depend, at least in part, on the properties of the operating fluid. For example, a fuel injector using an operating fluid with a high viscosity will experience a different response to a given injection signal than a fuel injector using an operating fluid with a low viscosity. 
     The flowchart of FIG. 3 illustrates an exemplary method of controlling a fuel injector  34  to account for the sensitivity of the fuel injector to the properties of the operating fluid. For the purposes of the present disclosure, the operation of a single fuel injector will be described. It should be understood, however, that multiple fuel injectors may be controlled in the same or a like manner. 
     Electronic control module  48  will generate an initial injection signal. (Step  102 ). The initial injection signal may be based on typical operating parameters and engine performance estimates, such as, for example, engine temperature, engine load, operating fluid pressure, etc. The initial injection signal may be further based on an initial estimate of the oil viscosity derived from engine temperature and operating fluid pressure measurements. The initial injection signal is then applied to fuel injector  34 . 
     The graph of FIG. 4 illustrates an exemplary current waveform  118  applied to a fuel injector  34  through several exemplary injection signals. A first injection signal is designated generally by reference number  120  and a second injection signal is designated generally by reference number  122 . As noted previously, the current waveform of each injection signal is dependent upon the particular operating parameters of the engine. 
     The pressure of the operating fluid (curves  124 ) in fluid supply rail  31  is monitored as injection signals  120  and  122  are applied to fuel injector  34 . (Step  104 ) FIG. 4 also illustrates the change in pressure of the operating fluid in fluid supply line  31  as fuel injector  34  executes injection signals  120  and  122 . The pressure of the operating fluid in fluid supply rail  31  may be sampled periodically, such as, for example, every 6° of crankshaft rotation. Each sampled pressure value may be stored in memory  49 . 
     As shown in FIGS. 4 and 5, a notch  132  may be formed in a plot of the pressure in fluid supply rail  31  as a function of crankshaft rotation. Notch  132  may be defined by a first relative maximum  126  that immediately follows the initiation of first activation signal  120 , a relative minimum  128  following the execution of first activation signal  120 , and a second relative maximum  130  prior to the initiation of second activation signal  122 . 
     Based on the plot of the pressure in fluid supply rail  31 , electronic control module  48  may calculate the dynamic fluid consumption of fuel injector  34  during execution of an injection signal. (Step  106 ). The dynamic fluid consumption is a measure of the amount of operating fluid used by fuel injector  34  to execute the injection signal. The dynamic fluid consumption, ΔV i , may be determined with the following formula:          Δ                   V   i       =       2   ·   A   ·   V       β   ·     (     W   -   DUR     )                         
     where A is a “notch” area, V is the volume of the fluid supply rail, β is the bulk modulus of the operating fluid, W is the time between the first relative pressure maximum and the second relative pressure maximum, and DUR is the time between the first relative pressure maximum and the first relative pressure minimum. 
     FIG. 5 illustrates an exemplary notch  132 . The area (A) of notch  132 , may be determined from the following equation:        A   =         W   2     ·     (       P   0     +     P   1       )       -       ∫     P   0       P   1              P        (   θ   )       ·                   θ                           
     where W is the time between the first relative pressure maximum and the second relative pressure maximum, P 0  is the first relative maximum pressure, P 1  is the second relative maximum pressure, and θ is the rotation angle of the crankshaft. 
     The foregoing equations provide one method of estimating the dynamic fluid consumption of the fuel injector. It should be noted that alternative methods of determining the dynamic oil consumption may be readily apparent to one skilled in the art. 
     Based on the dynamic oil consumption of the fuel injector  34 , electronic control module  48  may estimate the amount of fuel injected into the combustion chamber. (Step  108 ). For a given pressure of fluid supply rail  31 , there is a relationship between the dynamic oil consumption ΔV i  and the amount of fuel injected. This relationship may be determined by testing the fuel injector at a variety of operating fluid pressures and measuring the oil consumption and the fuel delivery amount. The collected data may be stored in a three-dimensional calibration map. Electronic control module  48  may access the calibration map with the fluid supply rail pressure and the dynamic oil consumption to obtain an estimate of the amount of fuel injected into the combustion chamber. 
     The estimated fuel delivery amount may be used to identify potential problems in the fuel injection system. For example, an estimated fuel delivery amount that is above a normal operating range or below a normal operating range may indicate that the fuel injector is not functioning properly. Accordingly, electronic control module  48  may provide an indication that maintenance on the fuel injection system is necessary. 
     The estimated fuel injection amount may also be used to estimate a viscosity parameter for the operating fluid. (Step  110 ). For the purposes of the present disclosure, the viscosity parameter is an indication of the sensitivity of the fuel injector to the properties of the operating fluid. The viscosity parameter is not an absolute measurement of the viscosity of the operating fluid and may take additional properties of the operating fluid into account. In addition, the viscosity parameter may be independent of the actual type of operating fluid used to actuate the fuel injector. 
     As will be recognized by one skilled in the art, a relationship exists between the duration of the injection signal, the amount of fuel delivered, the pressure of the operating fluid in the fluid supply rail, and the viscosity parameter of the operating fluid. This relationship may be defined by obtaining calibration data for the fuel injector under a series of different operating conditions, such as, for example, different injection signal durations, fluid supply rail pressures, and engine temperatures. The calibration data may be stored in memory as one or more calibration maps. 
     Given the known fuel injection signal duration, the estimated fuel delivery amount, and fluid supply rail pressure, electronic control module  48  may access these calibration maps to obtain an estimate of the viscosity parameter. The viscosity parameter provides an indication as to the responsiveness of the fuel injector in the particular operating conditions of the engine. The viscosity parameter may be determined on an injector-by-injector basis. The viscosity parameter may then be used as an input, along with other pertinent engine operating conditions, to generate a future injection signal for the fuel injector. 
     The viscosity parameter may be also be used to determine a fluid type parameter. (Step  112 ). The fluid type parameter provides an indication of the type of fluid used as the operating fluid and is based on a relationship between the viscosity parameter and the engine temperature. The fluid type parameter may be used to predict changes in the viscosity parameter based on predicted changes in the engine temperature. 
     FIG. 6 illustrates. a series of exemplary fluid type parameters  140 ,  142 , and  144 . The fluid type parameters indicate the impact of different types of operating fluid on the viscosity parameter. For example, fluid type parameter  140  may be representative of the relationship of temperature and the viscosity parameter for 10W20 oil, whereas fluid type parameter  142  may be representative of the relationship of temperature and the viscosity parameter for 10W30 oil. Similar relationships may also be defined for other types of operating fluid. 
     The relationship of the fluid type parameter to the viscosity parameter may be stored in memory  49  of electronic control module  48 . Given the estimate of the viscosity parameter and the engine temperature, electronic control module may estimate the fluid type parameter for the particular operating fluid. In other words, electronic control module  48  is able to estimate the type of operating fluid used to actuate the fuel injector without an external input. 
     Electronic control module  48  may use the fluid type parameter to predict a future viscosity parameter of the operating fluid and modify an injection signal accordingly. (Step  114 ). As illustrated in FIG. 6, the viscosity parameter for a given fluid type has an established relationship to the engine temperature. Thus, electronic control module  48  may predict the viscosity parameter of the operating fluid based on the expected engine temperature. For example, when the engine is first starting, the engine temperature will be relatively low. As the engine runs, the engine temperature will gradually increase. Given the operating conditions of the engine, electronic control module  48  may predict the temperature of the engine and, thus, the expected viscosity parameter. 
     Industrial Applicability 
     As will be apparent from the foregoing description, the present invention provides a system and method that allows for improved control over a hydraulically-actuated fuel injector. The present invention provides for the monitoring of engine operating conditions and the monitoring of the actual performance of a fuel injector  34  under the current engine operating conditions. This monitoring allows electronic control module  48  to determine an expected viscosity parameter of the operating fluid. The expected viscosity parameter may allow electronic control module  48  to predict the responsiveness of fuel injector  34  to the characteristics of the operating fluid. Thus, the expected viscosity parameter may be used as an input, along with other pertinent engine operating conditions, when determining the next injection signal. This allows electronic control module  48  to use information gathered during previous fuel injections as feedback in future fuel injections. The present invention, therefore, allows electronic control module  48  to generate injection signals that are tailored to the particular engine operating conditions, which may result in more precision in the control of a fuel injector. 
     An electronic control module monitors the response of a fuel injector to an injection signal by monitoring the pressure of the operating fluid in an operating fluid supply rail. By calculating the amount of operating fluid used by the fuel injector in executing the particular injection signal, the electronic control module may estimate the actual amount of fuel delivered to a combustion chamber. Once an estimate of fuel delivery is obtained, the electronic control module may determine a viscosity parameter based on the pressure in the fluid supply rail, the duration of the injection signal, and the estimated fuel delivery. The viscosity parameter provides an indication of the sensitivity of the fuel injector to the properties of the operating fluid. 
     The current viscosity parameter may be used as an input in generating a future injection signal. However, a change in the temperature of the engine between the determination of the viscosity parameter and the generation of the future injection signal may cause a change in the properties of the operating fluid. Accordingly, the current viscosity parameter may not be a precise indication of the future sensitivity of the fuel injector to the properties of the operating fluid. 
     The electronic control module may, however, estimate a fluid type parameter that defines a relationship between the viscosity parameter and the engine temperature. By identifying the fluid type parameter for the particular operating fluid, the electronic control module may predict the future viscosity parameter based on the expected engine temperature. Thus, the electronic control module may predict the viscosity parameter, or the sensitivity of the fuel injector, with a greater amount of precision. 
     The electronic control module accurately predicts the viscosity parameter for an upcoming fuel injection and the electronic control module alters the shape and/or form of the injection signal to account for the expected viscosity parameter. In addition, the electronic control module may use the expected viscosity parameter in controlling other engine functions, such as, for example, control over the pressure of the fluid in the fluid supply rail, control of the operating fluid pump and high pressure pump, and torque corrections. 
     Thus, the present invention allows for improved control over the fuel injection process. This increased control may allow for a reduction in the generation of emissions. The reduction in emissions may be particularly apparent in cold starts situations where the fuel injectors are particularly sensitive to the properties of the operating fluid. In addition, the increased precision may lead to improved engine performance, elimination of “rough running” symptoms, reduced cold start times, and improved load acceptance. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the fuel injection control system of the present invention without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and their equivalents.