Abstract:
A heated fuel injector system and controller that includes a temperature sensing means to provide closed-loop control of a heating element heating fuel dispensed by a heated fuel injector. Closed-loop control provides more accurate temperature control of the heating element so that fuel heating is provided as quickly as possible while also protecting the fuel from being boiled and protecting the heated fuel injector from being damaged by excessive temperature. By monitoring how the signal from the temperature sensing means varies over time, fault conditions such as a lack of fuel flow, and fuel ethanol percentage may be detected.

Description:
TECHNICAL FIELD OF INVENTION 
     The invention generally relates to heated fuel injectors, and more particularly relates to a system providing a temperature sensing means to enable closed loop temperature control of fuel dispensed by a heated fuel injector. 
     BACKGROUND OF INVENTION 
     It is known that heating fuel consumed by an internal combustion engine during a cold start, particularly fuel comprising alcohol, reduced hydrocarbon (HC) and carbon monoxide (CO) emissions. The Society of Automotive Engineers publications entitled Heated Injectors for Ethanol Cold Starts (SAE 2009-01-0615) by Daniel Kabasin et al. and Emission Reduction with Heated Injectors (SAE 2010-01-1265) by Daniel Kabasin et al. document the benefits of using heated fuel injectors to reduce engine emissions, the entire contents of which are hereby incorporated by reference herein. The temperature control of such heated injectors typically uses an open loop approach that regulates power to a heater element based on extensive empirical testing of output fuel temperatures for various fuel flow rates, ambient temperatures, coolant temperatures, elapsed time from initiation of crank, and estimated fuel flow rates. The open-loop temperature control is supposed to keep the heater element temperature below a maximum failure temperature of the heater element, below a melting temperature of a protective plastic covering the heater element, and below the boiling temperature of the fuel resident in the injector. This open-loop control also considers manufacturing variation of heater resistances and so requires a safety margin in the power applied to the heaters in order to avoid vapor lock or damage due to excessive heating. Consequently, the open-loop approach may result in less than optimal heating of the fuel and/or failed cold starts. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of this invention, a heated fuel injector system for heating fuel dispensed by a heated fuel injector is provided. The system includes a heated fuel injector, a heater element, and a temperature sensing means. The heated fuel injector is operable to controllably dispense a fuel. The heater element is arranged to heat the fuel dispensed by the heated fuel injector. The temperature sensing means is configured to output a temperature signal indicative of a fuel temperature of the fuel dispensed by the heated fuel injector. 
     In another embodiment of the present invention, a controller for operating a heated fuel injector is provided. The controller includes a temperature signal input and an electric power regulator. The temperature signal input is configured to receive a signal indicative of a fuel temperature of a fuel dispensed by the heated fuel injector. The electric power regulator means is configured to regulate electric power to a heater element based on the temperature signal. 
     Further features and advantages of the invention will appear more clearly on a reading of the following detail description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a heated fuel injector in accordance with one embodiment; 
         FIG. 2  is a cut-away view of part of the heated fuel injector in  FIG. 1  in accordance with one embodiment; 
         FIG. 3  is a circuit diagram of a heated fuel injector system for operating the heated fuel injector in  FIG. 1  in accordance with one embodiment; 
         FIG. 4  is a circuit diagram of a heater control circuit for operating the heated fuel injector in  FIG. 1  in accordance with one embodiment; 
         FIG. 5  is a graph of temperature signals within the heated fuel injector in  FIG. 1  in accordance with one embodiment; 
         FIG. 6  is a graph of temperature signals within the heated fuel injector in  FIG. 1  in accordance with one embodiment; 
         FIGS. 7A-C  are schematic diagrams of temperature indicator circuits suitable for use in  FIG. 3  in accordance with one embodiment; 
         FIGS. 8A-B  are schematic diagrams the heated fuel injector in  FIG. 1  in accordance with two embodiments; and 
         FIG. 9  is a circuit diagram of a heater control circuit for operating the heated fuel injector in  FIG. 1  in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     In accordance with an embodiment of a heated fuel injector system,  FIG. 1  illustrates an exemplary heated fuel injector  10  having five connector pins  12   a - 12   e , a fuel inlet end  14 , a fuel dispensing end  16 , and a shell  18  overlying a fuel injector body  20 . Typically, the heated fuel injector  10  would be attached to an internal combustion engine, the fuel inlet end  14  would be coupled to a source of pressurized fuel, and the fuel dispensing end  16  would be positioned so fuel passing through the body  20  would be dispensed by the heated fuel injector  10  to be utilized by the engine to operate the engine. By way of a non-limiting example, connector pins  12   a  and  12   b  may be coupled to an actuation coil (not shown) within the body  20  of the heated fuel injector  10  that operates a valve (not shown) also within the body  20  and generally located at the fuel dispensing end  16 . Continuing with the example, if a voltage is applied across connector pins  12   a  and  12   b , the valve may open to allow fuel to flow from the fuel inlet end  14 , through the body  20 , and out of the fuel dispensing end  16 . When the voltage is removed or actively forced to zero volts, the valve may close and stop or obstruct the flow of fuel. By alternating the voltage applied to the connector pins  12   a  and  12   b , the heated fuel injector  10  may be operated to controllably dispense the fuel. 
       FIG. 2  illustrates cut-away view of the shell  18  with the body  20  removed. A heater element  22  formed of electrically conductive material is arranged to heat the fuel within the body  20  so that heated fuel may be dispensed by the heated fuel injector  10 . The heater element  22  exhibits a heater resistance so that as electric current flows through the heater element  22  heat is generated that increases a heater temperature and thereby heats the heater element  22  and increases a fuel temperature. An exemplary non-limiting value of the resistance of the heater element  22  is nominally 0.3 Ohms at 20° C. When the heated fuel injector  10  is assembled, the heater element  22  is suitably thermally coupled to the body  20  to be effective to heat fuel passing through the body  20 . The heater element  22  may be formed, for example, of thick-film resistive material that may be applied to the exterior of the body  20 , or applied to the interior of the shell  18 . Alternately, the heater element  22  may be formed of metal foil or wire that is suitably arranged to heat the fuel injector body  20  and thereby heat the fuel passing through the heated fuel injector  10 . The heater element  22  may be connected to the connector pins  12   c  and  12   d  by soldering or other known methods. 
     The heated fuel injector system also includes a temperature sensing means configured to output a temperature signal or exhibit an electrical characteristic indicative of a fuel temperature of the fuel within the body  20  and/or the fuel dispensed by the heated fuel injector  10 .  FIG. 2  illustrates one embodiment of the temperature sensing means as a thermistor  24 . The thermistor  24  generally exhibits a resistance value that corresponds to a thermistor temperature of the thermistor  24 . The thermistor  24  may also be formed of thick film material applied using methods similar to those used to apply thick film material to form the heater element  22 . The thermistor  24  may also be a discrete electrical component such as a positive temperature coefficient (PTC) or negative temperature coefficient (NTC) device attached using solder or the like. Unless stated otherwise and for the purposes of discussion, it should be assumed that the thermistor  24  has a positive temperature coefficient. It would be apparent to those skilled in the art how to adapt any of the exemplary embodiments to a negative temperature coefficient thermistor. The location of this sensor  24  shown in  FIG. 2  is a non-limiting example of suitable locations. For example, the thermistor  24  when formed of thick film material may overlay the heater element  22 , separated from the heater element  22  by a layer of electrically insulating material, and be sized to sense temperature over a substantial area of the heater element  24 . Alternately, the temperature sensing means may be a temperature indicator circuit, several examples of which are illustrated in  FIG. 7  and described in more detail below. 
     In one embodiment, the thermistor  24  is coupled to a connector pin also used by the heater element  22 ,  12   b  for example, so that only three terminals ( 12   c ,  12   d , and  12   e ) are needed to make an electrical connection to a heater contact  26 , a thermistor contact  28 , and a common contact  30  illustrated in  FIG. 2 . By arranging the thermistor  24  to be thermally coupled to the fuel passing through the injector body, or to the surface of the heater element  24 , the thermistor  24  will exhibit a thermistor resistance indicative of the fuel temperature and/or the heater temperature, respectively. By arranging the thermistor or other temperature sensing means to be thermally coupled to the fuel being dispended by the heated fuel injector, the temperature signal may directly correspond to the fuel temperature of the fuel dispensed by the heated fuel injector. The thermistor  24  may be electrically coupled to any of a number of known electrical networks, such as a voltage divider network, adapted to output a temperature signal that is based on the thermistor resistance and is thereby indicative of the fuel temperature of the fuel dispensed by the heated fuel injector, or the fuel temperature of fuel in the body  20 , or the heater temperature. 
     In another embodiment, the heated fuel injector  10  may have four connector terminals ( 12   a ,  12   b ,  12   c ,  12   d ) instead of five connector terminals ( 12   a ,  12   b ,  12   c ,  12   d ,  12   e ) as illustrated in  FIG. 1 . For this embodiment, the actuator coil, heater element  22 , and thermistor  24  may all have one connection in common, and the remaining three connector terminals are coupled to the other ends of each of the actuator coil, heater element  22 , and thermistor  24 . Such an arrangement may reduce the cost of the heated fuel injector  10 . By way of a non-limiting example, electrical power supplied to the heater element  22  may be pulse-width-modulated (PWM) waveform, modulated to regulate the average power supplied. In this case, the voltage applied to the heater element  22  may be periodically interrupted, and during this interrupted time a thermistor resistance may be determined. 
       FIG. 3  illustrates a circuit diagram useful for describing the operation of an embodiment of the heated fuel injector system. The system may include a controller  32  configured to receive a temperature signal  34 , and regulate electric power to the heater element  24  based on the temperature signal  34 . The controller  32  may output a power switch control signal  36  that is effective to open and close a power switch  38  and thereby modulate power to the heater element  22 . The power switch  38  is illustrated as a mechanical switch. However, it is understood that the power switch  38  may suitably be a relay or a solid state switch such as a transistor. In one embodiment the controller  32  may pulse width modulate or frequency modulate the power switch control signal  36  to regulate the heating power supplied to the heater element  22  and thereby control the temperature of the heater element  22 . Alternately, the power switch may be a transistor that is operated in a linear mode by the switch control signal  36 . 
     The controller  32  may include a microprocessor or other control circuitry as would be evident to those skilled in the art. The controller  32  may include memory, including non-volatile memory, such as electrically erasable programmable read-only memory (EEPROM) for storing one or more routines, thresholds and captured data. The one or more routines may be executed by the microprocessor to generate the switch control signal  36 . The controller  32  and other components shown in  FIG. 3  may be integrated within the heated fuel injector  10  so the heated fuel injector  10  may operate in an autonomous manner, independent of the engine control system. The controller  32  may provide a time-out function can give this heated fuel injector  10  additional stand-alone capability whereby the controller  32  determines to connect the heater element  22  to electrical power based on the temperature signal  34 . For example, the controller  32  may only supply electrical power to the heater element  22  if the temperature signal  34  indicates that the temperature is below 30° C. The controller  32  may also include programming to disconnect the heater element  22  after a pre-determined time following either being initially energized or following the energizing of an injector actuator coil  42 . 
       FIG. 9  illustrates a non-limiting example of a portion of the controller  32  that includes a comparator means in the form of a comparator  46  arranged to receive the temperature signal  34  and a reference signal  44 , and output a switch control signal  36  based on a comparison of the temperature signal  34  and the reference signal  44 . Alternately, the comparator means may be provided by an amplifier such as an LM2904, or may be provide by a microprocessor executing a program that inputs the temperature signal  34  and the reference signal  44 , and outputs the switch control signal  36  in accordance with the program. A reference voltage V+ may be supplied by an adjustable voltage reference (not shown) or the reference voltage V+ may be derived from a vehicle supply voltage B+. A reference resistor RR is arranged with the thermistor  24  to form a voltage divider network that generates the temperature signal  34  corresponding to a fraction of the reference voltage V+. A second voltage divider network is formed by a series combination of resistors RA and RB to generate the reference signal  44  corresponding to a fraction of the supply voltage V+. An exemplary value for RA, RB, and RR is 10 kOhm, and thermistor  24  may be selected to have a resistance of about 10 kOhm at a desired control temperature, such as 150 C. The controller  32  may also include a hysteresis feedback resistor RF having a non-limiting exemplary value of 10 Mega Ohm. Including the resistor RF in the circuit reduces the risk of electrical noise causing rapid switching of the comparator  46 . In this example, a transistor T 1  serves as the power switch  38  and is operated by the switch control signal  36  to modulate power to the heater element  22 . The transistor T 1  is selected based on the voltage of the supply voltage B+, the expected current through heater element  22 , and the ambient operating temperature experienced by transistor T 1 . By this exemplary arrangement, if the voltage of the temperature signal  24  is less than the voltage of the reference signal  34  by an amount sufficient to overcome the hysteresis provided by hysteresis resistor RF, the transistor T 1  is turned on by the comparator  46  so that electric power is supplied to the heater element  22  to heat the heated fuel injector  10 . When the temperature signal  24  is greater than the voltage of the reference signal  34  by an amount sufficient to overcome the hysteresis provided by hysteresis resistor RF, the transistor T 1  is turned off by the comparator  46  so that electric power to the heater element  22  is blocked. 
     In  FIG. 3  the thermistor and the heater element are distinct electrical devices.  FIG. 4  illustrates another embodiment of a temperature control circuit where the temperature sensing means may be provided by using the resistance of the heater element  22  to monitor heater temperature and provide an indicator of fuel temperature. For such an embodiment, the heater element  22  is suitably formed of a material having a non-zero temperature coefficient of resistance so that the heater element  22  exhibits a heater resistance corresponding to the heater temperature. As such, the heater resistance may be indicative of the fuel temperature. In this embodiment, the heater element  22  may form part of a Wheatstone bridge network configured to control the temperature of the heater element  22  by using the heater resistance to influence the balance of the Wheatstone bridge. As suggested by the illustration, one or more of the other three resistors completing the Wheatstone bridge may be adjusted to calibrate the Wheatstone bridge and thereby compensate for part to part variation of the heater resistance. Alternately, the temperature sensing means of the heated fuel injector system may include a current measuring means configured to measure the current passing through the heater element  22 , and a voltage measuring means configured to measure the voltage drop across the heater element  22 . It follows then that the heater resistance may be calculated based on the current through the heater element  22  and the voltage across the heater element, and so the heater temperature may be determined. 
     It has been discovered that a time-rate-change characteristic of the temperature signal  34  may be useful to diagnose the heated injector system or determine an operating condition such as, but not limited to, an empty injector condition, a low fuel pressure condition, a lack of fuel flow condition, or an onset of fuel boiling condition.  FIG. 5  shows time-rate-change characteristics of the temperature signal  34  for several exemplary operation conditions. Curve A on  FIG. 5  corresponds to the empty injector condition. If there is no fuel or other liquid in the heated fuel injector  10 , then the thermal mass of the heated fuel injector  10  is relatively low and so the time-rate-change characteristic has a relatively high slope. Curve B corresponds to the low fuel pressure condition where the pressure of fuel in the heated fuel injector is lower than normal. Here the temperature initially rises at a rate slower than Curve A because the thermal mass has increased due the presence of fuel, but the fuel present begins to boil as indicated by the increase in the slope of the time-rate-change characteristic. Curve C corresponds to the lack of fuel flow condition. Here, the fuel is pressurized at a pressure higher that for curve B and so the onset of boiling is delayed. However, once boiling begins, the slope increases to a value comparable to the slope of curve B after the onset of fuel boiling. Curve D corresponds to and normally pressurized fuel flowing at some typical rate so the temperature rises at a lower rate than the previously described curves. However, the plateau where the slope of the curve is about zero is at a temperature provides an indication that fuel is beginning to boil. The plateau effect is due to the rapid heat transfer of heat away from the heater element caused by the continuous vaporization of flowing fuel. 
     It has also been discovered that the time-rate-change characteristic of the temperature signal  34  may be useful to estimate an ethanol percentage of the fuel.  FIG. 6  shows time-rate-change characteristics of the temperature signal  34  for three different ethanol percentages. By analyzing the slope of heater temperature rise and/or plateau temperature and taking into account the fuel flow the ethanol percentage of the fuel may be determined. Knowing the ethanol percentage based on the time-rate-change characteristic may be used by an engine control system to confirm a reading from a separate ethanol sensor or may allow the ethanol sensor to be eliminated from the engine control system and thereby save cost. 
     Furthermore, the time-rate-change characteristic of the temperature signal  34  may be useful to provide an indication of water being present in the heated fuel injector.  FIG. 6  shows a time-rate-change characteristics of the temperature signal  34  for water. Detecting the presence of water in the fuel may be particularly useful for fuel with high ethanol concentration levels since ethanol and water form a liquid solution. 
     In another embodiment, the temperature sensing means may be a temperature indicator circuit. As used herein, a temperature indicator circuit is generally a network of electrical components that exhibits an electrical characteristic indicative of temperature. In one non-limiting example, the electrical characteristic may be a voltage exhibited by the temperature indicator circuit that generally corresponds to a Zener voltage that varies with temperature. In another non-limiting example, the electrical characteristic may be generally characterized as switching between an open circuit and a resistive value based on the temperature about the temperature indicator circuit.  FIG. 7  illustrates exemplary temperature indicator circuits  710 ,  720 , and  730  that form two-terminal networks that may be used in place of the thermistor  24  described above. For example, temperature indicator circuit  710  includes a negative temperatures coefficient (NTC) thermistor coupled to a resistor/transistor network as shown. When the temperature is relatively low, transistors Q 1  and Q 2  are biased off and so the resistance value of the network is relatively high and may be characterized as an open circuit. As the temperature increases, the resistance value of the NTC decreases until transistors Q 1  and Q 2  are turned on whereby the electrical characteristic of the network is a voltage drop having a voltage value dependent on temperature. A BCR35 from Infineon includes the resistors and transistors illustrated in the integrated circuit  710 . Another exemplary temperature indicator circuits may use an LM431 Zener Shunt Regulator as illustrated in temperature indicator circuit  720 , or a TN1215 Thyristor Silicon Controlled Rectifier as illustrated in temperature indicator circuit  730 . Other suitable networks may also afford a temperature characteristic that switches between an open circuit and a short circuit based on the temperature about the temperature indicator circuit. 
     In another embodiment, the heated fuel injector  10  may have four connector terminals ( 12   a ,  12   b ,  12   c ,  12   d ) instead of five connector terminals ( 12   a ,  12   b ,  12   c ,  12   d ,  12   e ) illustrated in  FIG. 1 . For this embodiment a temperature indicator circuit such as one of those illustrated in  FIG. 7  may be electrically coupled to the heater element  22  and the actuator coil  42  to form exemplary networks  810  or  820  as illustrated in  FIG. 8 . The network  810  has a temperature indicator circuit  710 ,  720 , or  730  arranged to couple the injector actuator coil  43  to the heater element  22 . By this arrangement, when no voltage is being applied to the injector actuator coil  42  or the heater element  22 , then the corresponding pin  12   b  or  12   c  may be monitored to detect if the temperature indicator circuit exhibits an open circuit or a closed circuit. Alternately, the temperature indicator circuit may be coupled to the injector actuator coil as illustrated for network  810 . For this arrangement, if the temperature indicator circuit is exhibiting a short circuit, then the current drawn when the injector actuator coil is energized may be monitored, or the back EMF voltage that occurs when the injector actuator coil is de-energized may be monitored. 
       FIG. 9  shows an embodiment where a temperature signal  34  may be output for the purpose of diagnosing an operating condition of the heated fuel injector  10 . By way of a non-limiting example, an Engine Control Module (ECM)  48  may receive the temperature signal  34  for the purpose of diagnosing the operating condition of the heated fuel injector  10 . The ECM  48  may be a general purpose engine controller that inputs signals from a variety of engine sensors (not shown) such as a crank sensor or an engine intake airflow sensor, an outputs signals to a variety of engine devices (not show) such as an electronically controlled throttle body or an exhaust recirculation control valve. An operating condition of the heated fuel injector  10  may be indicated by the temperature signal  34  if the temperature signal  34  is substantially equal to the reference voltage V+, whereby an open circuit connection to ground (GND) may be indicated. If the temperature signal  34  is substantially equal to GND, then an open circuit connection to reference voltage V+ and/or battery supply voltage B+ may be indicated. Those skilled in the art will appreciate that other operating conditions such as those suggested above regarding  FIG. 5  and  FIG. 6  may be indicated by analyzing the temperature signal  34 . It should be appreciated that the heater control circuit shown in  FIG. 9  may be adapted to either the 5-pin heated fuel injector  10  illustrated in  FIG. 1 , or may be adapted to a 4-pin version by integrating the electronics within the heated fuel injector and coupling V+ and B+ to the positive supply voltage B+ for the injector coil  43  as shown in  FIG. 3 . 
     The ECM  48  may be further configured to output a signal onto the connection with the temperature signal  34  to influence the heater control circuit shown in  FIG. 9 . For example, if the temperature signal  34  were shorted to the reference voltage V+, then the switch control signal  36  would be held low such that the power switch  38  would not turn on to supply electrical power to the heater element  22 . By this, the temperature sensing means may be further configured to receive a heater circuit disable signal from the ECM  48 , or receive a signal to influence the fuel temperature of the fuel dispensed by the heated fuel injector  10 . In another exemplary embodiment, the ECM  48  may connect one end an additional resistor to the temperature signal  34  connection and the other end of the additional resistor to either the reference voltage V+ or ground GND to change the value of the temperature signal  34  and thereby change the target control temperature of the heated fuel injector  10 . 
     Accordingly, a heat fuel injector system, a heated fuel injector  10 , and a controller  32  are provided. The inclusion of a temperature sensing means in the heated fuel injector  10  provides for closed-loop heater element control that avoids under-heating of the fuel, thereby more effectively reducing engine emissions, and avoids over-heating the heated fuel injector, thereby avoiding vapor lock and damage to the injector. The fuel temperature can be more accurately controlled and less influenced by variations in fuel flow rate, fuel formulations&#39;, and ambient temperatures. Furthermore, the time-rate-change characteristic of the temperature can be analyzed to detect various operational fault conditions and provide an indication of the fuel formulation, especially when combined with other information available to typical engine control systems. By integrating the electronics necessary for controlling electrical power to the heater element into the heated fuel injector, a heated fuel injector is provided that is easily adapted for use by engine control system that already use open-loop heater control strategies. By providing a connection to the temperature signal within the heated fuel injector, the heater control circuit may be turned on or off, or the target control temperature for heating fuel may be adjusted. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.