Abstract:
An engine output control method for a vehicle having a throttleless internal combustion engine system responsive to a desired engine speed signal. The method includes generating a driver demanded engine speed value corresponding to an operator input and generating a speed control system engine speed value corresponding to a predetermined speed value to permit vehicle operation at a constant speed by a speed control system. The method arbitrates between the driver demanded engine speed value and the speed control system engine speed value to derive a first desired engine speed value. This value is limited by a vehicle speed limit value, engine speed limit value, and transmission speed limit value to generate a second desired engine speed value. The engine is then controlled as a function of the second desired engine speed value and an actual engine speed value. Engine control is accomplished by way of variable valve timing, fueling rate and/or fuel flow, and spark advance.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a Continuation-In-Part of U.S. application Ser. No. 09/657,877 filed on Sept. 8, 2000 entitled “Engine Output Controller.” 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates generally to control systems for internal combustion engines, and more particularly, concerns a powertrain controller for a throttleless engine.  
           [0003]    Conventional internal combustion engines generally fall into two categories: spark ignited (SI) engines and compression ignition (CI) engines. In general, an SI engine&#39;s power is controlled through a process called throttling. Throttling controls the density of air that enters an engine&#39;s combustion chambers. The throttle system is typically comprised of one or more throttle blades which are within the intake air stream. During engine idle or a closed throttle condition, the throttle blade closes off the air inlet creating a large pressure drop and density decrease. When the throttle is wide open, the throttle blade is generally parallel to the air stream and presents a minimal air restriction to inducted airflow. Under most engine operating conditions, the throttle blade is somewhere between fully open and fully closed thus presenting a controlled restriction of the intake airflow.  
           [0004]    Fuel in an SI engine is generally introduced into the inlet air stream to provide a combustible air fuel mixture. Fuel injectors are often located in a common plenum feeding all of the cylinders on a multi-cylinder engine. When injected at this location, the engine is said to be throttle-body injected. Injectors can alternatively be located in the intake runners feeding the individual cylinder intake ports. This type of injection is referred to as port injection. Alternatively, fuel injectors can be located directly within each cylinder. This type of injection is referred to as a direct injection engine.  
           [0005]    Power output of an internal combustion engine can also be controlled entirely by the amount of fuel introduced into the combustion chamber just prior to ignition. In CI engines such as diesel engines, the engine typically does not have a throttle. Air entering the engine is restricted only by the intake manifold design. Fuel is injected directly into the cylinder of the CI engine just prior to ignition, and ignition is caused by the high temperature generated during the piston compression stroke.  
           [0006]    Also, alternative fuel systems have become an ever-greater concern in the search to conserve energy. Alternative energy power plants under consideration must provide the required power necessary to operate the vehicle, and at the same time be energy efficient, reduce emissions, and be cost effective. One such alternative energy power plant under consideration is a hydrogen-fueled internal combustion engine. Natural gas has also long been a potential gaseous alternate fuel for internal combustion engines.  
           [0007]    For throttleless engine-equipped vehicles such as a variable valve timing-equipped vehicle, it is also necessary to interpret driver demand and convert it to an appropriate engine control command to deliver the desired engine/vehicle response. Prior engine control arbitration schemes typically use throttle angle as a common control variable to control airflow and, hence, engine output. See, for example, U.S. Pat. No. 5,400,865.  
           [0008]    Interpreting driver demand and generating an appropriate engine command, however, is complicated by the existence of other sub-systems including vehicle, engine or transmission constraints such as vehicle speed limits, engine speed limits and transmission speed or torque limits. Further, in an throttleless engine, engine output must be controlled by a mechanism other than the throttle plate. Accordingly, there is a need for an arbitration scheme which selects the most appropriate engine control parameter from the various requesters. Arbitration schemes that rely upon a common control variable such as airflow by way of a throttle position may not be suitable for some vehicle and engine systems. Accordingly, there is a need for an improved engine output controller for use in throttleless engines.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides an engine output control method and system for a vehicle having a throttleless engine system responsive to a desired engine speed signal. An engine output control method for a vehicle having a throttleless internal combustion engine system responsive to a desired engine speed signal. The method includes generating a driver demanded engine speed value corresponding to an operator input and generating a speed control system engine speed value corresponding to a predetermined speed value to permit vehicle operation at a constant speed by a speed control system. The method arbitrates between the driver demanded engine speed value and the speed control system engine speed value to derive a first desired engine speed value. This value is limited by a vehicle speed limit value, engine speed limit value, and transmission speed limit value to generate a second desired engine speed value. The engine is then controlled as a function of the second desired engine speed value and an actual engine speed value. Control of the engine output is accomplished by way of variable valve timing, fueling rate and/or fuel flow, and spark advance. In another aspect of the invention, a traction control value and transmission limiting value are generated in the torque domain and arbitrated against the speed domain-based second desired engine speed value to control the engine output.  
           [0010]    In another embodiment of the present invention, values are generated in the acceleration domain to control the engine output. Specifically, values are generated for a driver demanded vehicle acceleration value corresponding to an accelerator pedal position; a speed control system vehicle acceleration value corresponding to a predetermined speed value to permit vehicle operation at a constant speed by a speed control system; a vehicle speed limit acceleration value corresponding to a maximum vehicle acceleration value to achieve a predetermined vehicle speed limit; and a traction control vehicle acceleration value corresponding to a maximum vehicle acceleration value to prevent wheel slip. These values are then arbitrated to derive a first desired vehicle acceleration value. The first desired vehicle acceleration value is limited by an engine speed limit value and transmission speed limit value to generate a second desired vehicle acceleration value. The resulting value can be used to control the engine output directly or converted to a desired engine acceleration value to control the engine output. Again, engine output is controlled by way of variable valve timing, fueling rate and/or fuel flow, and spark advance.  
           [0011]    Other advantages of the invention will become apparent upon reading the following detailed description and appended claims and upon reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    For a more complete understanding of this invention, reference should now be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of example to the invention.  
         [0013]    In the drawings:  
         [0014]    [0014]FIG. 1 is a schematic diagram of an internal combustion engine and associated control system according to one embodiment of the present invention.  
         [0015]    [0015]FIG. 2 is a block diagram of one embodiment of the controller of FIG. 1.  
         [0016]    [0016]FIG. 3 is a block diagram of another embodiment of the controller of FIG. 1.  
         [0017]    [0017]FIG. 4 is a block diagram of another embodiment of the controller of FIG. 1.  
         [0018]    [0018]FIG. 5 is a block diagram of another embodiment of the controller of FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    Turning first to FIG. 1, there is shown a schematic diagram of an internal combustion engine  10  and associated engine controller  12  in accordance with one embodiment of the present invention. The engine  10  includes a plurality of combustion chambers  14 , one of which is shown. Each combustion chamber  14  has an associated intake  16  and exhaust  18  operated by a respective valves  20 ,  22 . Valves  20 ,  22  allow variable valve timing and are controlled electronically using electromagnetic actuators rather than a conventional cam arrangement. Combustion occurs as a result of the intake of air and fuel from the intake manifold  24  and fuel injector  26  respectively, compression by the piston  28  and ignition by the spark plug  30 . Engine  10  may also operate in a compression ignition mode wherein combustion occurs as a result of the intake of air and fuel and compression by the piston  28  without ignition by the spark plug  30 . Combustion gases travel through the exhaust manifold  18  to the downstream catalytic converter (not shown) and are emitted out of the tailpipe. A portion of the exhaust gases may also be recirculated back through the intake manifold  24  to the engine cylinders  14  by way of an EGR valve (not shown).  
         [0020]    The engine  10  is preferably a gaseous-fueled engine wherein gaseous fuel such as hydrogen is supplied to the engine  10  from a fuel supply  35  by way of the fuel injector  26 . It should be understood that although one injector  26  is illustrated per cylinder  14 , two or more injectors could be provided for each cylinder or for each intake port of the engine  10 . Also, the injector  26  may be located adjacent the spark plug  30  for direct injection of fuel into the cylinder. Direct injection may also be preferable in the case of liquid fuels such as in a direct-injected diesel engine.  
         [0021]    The engine  10  is a throttleless engine, thus, the airflow through the intake manifold  24  is controlled by valve timing. A mass airflow (MAF) sensor  36  measures the amount of air flowing into the engine  10 . An engine speed sensor  37  provides a value indicative of the rotational speed of the engine  10 . Further, additional sensors are represented by block  40  which provide feedback to the engine controller  12  relating to the status of the engine  10  transmission  42  and wheels  44 ,  46 . Controller  12  receives various signals such as a first measurement of vehicle speed of wheel  44  from sensor  48 , a second measurement of vehicle speed of wheel  46  from sensor  50 , measurement of vehicle acceleration from an accelerometer (not shown) as well as various other signals from sensors such as engine coolant temperature (ECT), barometric pressure (BP), air charge temperature (ACT), and manifold pressure (MAP).  
         [0022]    In the throttleless engine  10 , output in the form of torque, speed or acceleration is controlled by airflow via valves  20 ,  22 , fuel via injector  26 , and spark timing via spark plug  30 .  
         [0023]    Transmission  42  is coupled to the crankshaft  52  of engine  10  and a first set of drive wheels  46 . In addition, to provide all wheel drive, transmission  42  can also be coupled to a second set of drive wheels  44 . Transmission  42  can be a combined gear set and torque converter, a manual transmission, automatic transmission, a continuously variable transmission, or any other power transfer unit known to those skilled in the art and suggested by this disclosure.  
         [0024]    Continuing with FIG. 1, in addition to receiving various signals from sensors, controller  12  also receives inputs from the driver demand system  60 , speed control system  62  and the traction control system  64 . Controller  12  is a conventional microcomputer including a microprocessor unit  70  in communication with various computer readable storage media. The computer readable storage media preferably includes read-only memory (ROM)  74 , random access memory (RAM)  76 , and keep-alive memory. The computer readable storage media may be implemented using any of a number of known memory devices such as PROMs, EPROMs, EEPROMs, flash memory, or any other electric, magnetic, optical, or combination-memory device capable of storing data, some of which represents executable instructions, used by microprocessor  70  in controlling the engine. Microprocessor  70  communicates with the various sensors and actuators via an input/output (I/O) interface  72 .  
         [0025]    The driver demand system  60  interprets the operator&#39;s requested engine output by monitoring the position of the accelerator  80  by pedal position sensor  82 . The pedal position value as measured by the sensor  82  is communicated to the controller  12  wherein a desired engine output is determined by known methods. The driver demand could also be determined from operator inputs other than the accelerator pedal such as push button. The speed control system  62  communicates a desired speed set by the vehicle operator to the controller  12  to maintain the vehicle speed at that desired by the operator. Traction control system  64  monitors wheel slip and/or vehicle acceleration to limit the engine output power accordingly.  
         [0026]    [0026]FIG. 2 shows a block diagram of one embodiment of the controller  12  of FIG. 1. FIG. 2 shows a manual transmission application wherein arbitration takes place between at least two different control variables. Specifically, driver demand and speed control are arbitrated in the engine speed domain, and the resulting desired engine speed is then arbitrated with traction control requirements in either the torque, acceleration, or speed domain.  
         [0027]    Referring to FIG. 2, in block  100 , the driver demanded engine acceleration is determined by known methods such as the pedal position input. The conversion from driver demand to engine acceleration will typically be a function of engine speed and inferred or measured driveline ratio in addition to the pedal position. In block  102 , the desired engine acceleration is integrated with respect to time to generate a desired engine speed value. A desired engine idle speed is also determined in block  104  which represents a minimum engine speed for the engine operating conditions. By way of the selection mechanism  106 , a new target engine speed is determined based on the idle speed request from block  104  and the driver demand from block  100 . Typically, selection mechanism  106  will select the maximum engine speed as between the desired idle speed and the driver demand. Preferably, the selection mechanism is formed such that no “dead pedal” feel exists and any driver demand from an idle condition results in an increase in scheduled engine speed and resulting change in actual engine speed.  
         [0028]    If active, a desired vehicle speed from the speed control system  108  will also be generated. A desired vehicle speed is translated into a desired engine speed in block  110  by way of the measured or inferred transmission gear ratio. The resulting engine speed is then arbitrated with the engine speed in the selection arbitration block  112  with the engine speed resulting from the selection mechanism  106 . Preferably, the greater of the engine speed requests from the driver demand and speed control system will be selected in block  112 .  
         [0029]    The resulting engine speed value from arbitration block  112  is then constrained by vehicle engine and transmission speed limits. Vehicle speed limiting is determined in block  114  and is again converted to an engine speed limit associated therewith in block  110 . This value is then passed along to the arbitration block  116 . Similarly, an engine speed limit value from block  118  is also used to constrain the desired engine speed value resulting from the driver demand or speed control systems. Optionally, the system may also include integrated transmission speed protection in block  120 , in which case, the transmission speed limit is applied as a clip to the engine speed limit request  118 .  
         [0030]    The desired engine speed as derived from the speed domain  121  is then communicated to the engine speed controller  122 . Engine speed controller  122  can be PID controller which receives as an input a measured engine speed and outputs a desired airflow, fueling rate, valve timing and spark timing in the case of a gasoline engine to achieve the desired engine speed. In the case of gaseous-fueled engine, fuel flow and timing can also be controlled to modify the engine output. The controller  122  also accommodates other system constraints as received from the torque domain  124 . The controller  122  determines the valve timing, fuel and spark control target values which result in the desired engine output speed. These values are generated by known methods during engine mapping and calibration for the particular engine configuration under consideration. For example, given the desired engine output torque or speed and measured engine speed (RPM) the desired spark advance (SA) can be determined. The corresponding valve timing command is determined as a function of the relative fuel-air ratio (AFR), the manifold absolute pressure (MAP), and intake mass airflow (MAF). Similarly, a fuel command is generated to achieve the desired engine output torque or speed as a function of the fuel rail temperature and pressure. The determined valve, fuel and spark control target values are arbitrated to optimize the engine operation for the current running conditions. Thus, for example, under low load conditions, the desired engine output speed or torque may be realized by operating the engine as a CI engine with throttleless airflow whereby the engine torque is regulated with only the fuel command and spark angle. In such a case, the wide flammability range of hydrogen fuel can be more fully utilized allowing the engine to run extremely lean during low torque demand situations. The throttleless airflow compression in a CI engine operation has the advantages of improved fuel economy, minimized engine output emissions and minimized engine pumping losses.  
         [0031]    Torque domain restraints on the engine speed include a maximum torque value to prevent wheel slip as determined by the traction control system  126 , and any torque-based transmission requirements in control block  128 . These torque-based constraints are then clipped in block  130  and communicated to the engine speed controller  122 . The engine speed controller  122 , in turn, limits the engine output according to the torque-based constraints. Alternatively, the traction control system and transmission limiting can be derived in terms of an engine speed or engine acceleration and the resulting constraint arbitrated against the desired engine speed to control the engine accordingly.  
         [0032]    [0032]FIG. 3 shows a block diagram of another embodiment of the controller  12  of FIG. 1. FIG. 3 shows an automatic transmission application wherein arbitration takes place between at least two different control variables. Specifically, driver demand and speed control are arbitrated in the engine speed domain, and the resulting desired engine speed is then arbitrated with traction control requirements in either the torque, acceleration, or speed domain.  
         [0033]    Referring to FIG. 3, in block  150 , the driver demanded vehicle acceleration is determined by known methods such as a pedal position input. This is applicable when the transmission is engaged in gear. The conversion from driver demand to vehicle acceleration will typically be a function of vehicle speed and inferred or measured driveline ratio in addition to the accelerator pedal position. In block  152 , the desired vehicle acceleration is integrated with respect to time to generate a desired road speed value. If active, a desired vehicle speed from the speed control system  154  will also be generated. Preferably, the system also includes vehicle speed limiting in block  156  which acts as a clip to ensure that the requested vehicle speed does not exceed a maximum allowable value. These values are arbitrated in block  158  and a selection is made of the most appropriate value of desired road speed from among the in-gear driver demand, speed control system, and speed limiting system.  
         [0034]    For transmission shift scheduling purposes, the desired road speed or acceleration can be used as a measure of driver demand as shown in block  160 .  
         [0035]    The desired vehicle speed is then converted in block  162  to an equivalent engine speed based on the measured or inferred transmission ratio. A corresponding in-neutral driver demand engine speed acceleration is determined in block  164  and is translated in block  166  to an equivalent in neutral engine speed demand. The selection mechanism  168  selects a new value of target engine speed based upon the idle engine speed request from block  170 , the converted vehicle speed request from block  162 , and the in-neutral driver request from block  166 . Preferably, the selection mechanism  168  is formed such that no “dead pedal” feel exists in any driver demand from an idle condition results in an increase in scheduled engine speed and resulting change in actual engine speed.  
         [0036]    The resulting engine speed value from arbitration block  168  is then constrained by an engine speed limit value from block  172 . Optionally, the system may also include integrated transmission speed protection in block  174 , in which case, the transmission speed limit value is also applied as a clip to the engine speed limit request  172 . Arbitration block  176  acts to constrain the desired engine speed value from the driver demand and speed control systems by the engine speed limit and transmission speed limit values.  
         [0037]    The desired engine speed as derived from the speed domain  180  is then communicated to the engine speed controller  182 . Engine speed controller  182  can be PID controller which receives as an input in measured engine speed and outputs a desired valve timing, fueling rate, and spark timing in the case of a gasoline engine to achieve the desired engine speed. Fuel flow in the case of a gaseous-fueled engine may also be controlled to modify the engine output. The controller  122  determines the valve timing, fuel and spark control target values which result in the desired engine output speed. These values are generated by known methods during engine mapping and calibration for the particular engine configuration under consideration. The controller  182  also accommodates other system constraints as received from the torque domain  184 .  
         [0038]    Torque domain restraints on the engine speed include a maximum torque value to prevent wheel slip as determined by the traction control system  186 , and any torque-based transmission requirements in control block  188 . These torque-based constraints are then clipped in block  190  and communicated to the engine speed controller  182 . The engine speed controller  182 , in turn, limits the engine output according to the torque-based constraints. Alternatively, the traction control system and transmission limiting can be derived in terms of an engine speed or engine acceleration, and the resulting constraint arbitrated against the desired engine speed to control the engine accordingly.  
         [0039]    [0039]FIG. 4 shows a block diagram of another embodiment of the controller  12  of FIG. 1. FIG. 4 shows a manual transmission application wherein arbitration takes place between the driver demand, speed control, and traction control systems in the engine acceleration domain. In block  200 , the driver demanded engine speed acceleration is determined by, for example, the pedal position input. The conversion from pedal position input to desired engine speed acceleration will typically be a function of engine speed and inferred or measured driveline ratio in addition to the pedal position input. A desired engine acceleration request to maintain the engine idle at its predetermined value is also determined in block  202 . By way of the selection mechanism  204 , a new target engine speed acceleration is determined based upon the idle engine speed acceleration request from block  202  and the driver demanded engine speed acceleration request from block  200 . Typically, the selection mechanism  204  will select the maximum engine speed acceleration as between the idle speed request and driver demand. Preferably, the selection mechanism  204  is formed such that no “dead pedal” feel exists and any driver demand from an idle condition results in an increase in scheduled engine speed acceleration and resulting change in actual engine speed.  
         [0040]    If active, a desired vehicle speed acceleration from the speed control system  206  will also be generated. The desired vehicle speed acceleration is translated to a desired engine speed acceleration in block  208  by way of the measured or inferred transmission gear ratio. The resulting desired engine acceleration is then arbitrated in block  210  with the engine acceleration request from selection block  204 .  
         [0041]    This system also includes vehicle speed limiting in block  212  and traction control system  214  both of which generate vehicle speed acceleration limits, the lowest one of which is selected in block  216 . The resulting value is again converted from a vehicle acceleration value to an engine acceleration value in block  208  and communicated to arbitration block  218 .  
         [0042]    Preferably, the system also includes engine acceleration speed limiting  220 , and integrated transmission speed protection  222  as well as acceleration-based transmission torque truncation  224 . All of these values which act to limit the engine acceleration are also communicated to the arbitration block  218 , wherein the received values are arbitrated with the driver demand and speed control resulting engine acceleration value to produce a final desired engine acceleration value.  
         [0043]    The desired engine acceleration value as derived from the acceleration domain  226  is then communicated to the engine acceleration controller  228 . The engine acceleration controller  228  is preferably a PID controller which receives as an input a measured engine acceleration value and outputs a desired airflow, fueling rate, and spark timing in the case of a gasoline engine to achieve the desired acceleration value.  
         [0044]    [0044]FIG. 5 shows a block diagram of another embodiment of the controller  12  of FIG. 1. FIG. 5 shows an automatic transmission application wherein arbitration takes place in the acceleration domain  240 . In block  242 , the driver demanded vehicle acceleration is determined when the transmission is engaged. The conversion from the driver demand to a desired vehicle acceleration will typically be a function of vehicle speed and the inferred or measured driveline ratio in addition to the accelerator pedal position. If active, a desired vehicle speed acceleration from the speed control system  244  will also be generated. Preferably, this system also includes vehicle speed limiting  246  and traction control system  248  which each generate vehicle acceleration limit values. The resulting vehicle acceleration values are arbitrated in block  250 . For transmission shift scheduling purposes, the desired vehicle acceleration from arbitration block  250  can be used as a measure of driver demand in block  252 .  
         [0045]    The desired vehicle acceleration value from arbitration block  250  is then converted to an equivalent engine acceleration value in block  254  based on the measured or inferred transmission ratio. If the transmission is not in gear, an in-neutral driver demand engine acceleration request is determined in block  256 . By way of the selection mechanism  258 , a new value of target engine acceleration is determined based upon the idle engine acceleration request  260 , the converted vehicle acceleration request  254 , and the in-neutral driver demand  256 . Preferably, the selection mechanism  258  is formed such that no “dead pedal” feel exists and any driver demand from an idle condition results in an increase in scheduled engine speed acceleration and a resulting change in actual engine speed.  
         [0046]    As in the manual transmission application of FIG. 4, the system of FIG. 5 also includes engine speed limiting  262 , transmission speed limiting  264 , and acceleration-based transmission torque truncation  266 . These clips are then applied in arbitration block  268  so as to ensure that the requested engine acceleration does not exceed any maximum allowable values. The resulting desired engine acceleration is communicated to the engine acceleration controller  270 . Engine acceleration controller  270  can be PID controller which receives as an input a measured engine acceleration and outputs a desired valve timing, fueling rate, and spark timing in the case of a gasoline engine to achieve the desired engine acceleration. Fuel flow and timing in the case of a gaseous-fueled engine can also be controlled to modify the engine output. The final desired engine acceleration value can also be integrated to be put in the speed domain and a controller  270  can use feedback on the measured engine speed to achieve the desired engine speed.  
         [0047]    From the foregoing, it can be seen that there has been brought to the art a new and improved engine control system for an throttleless engine-equipped vehicle. While the invention has been described with reference to one or more embodiments, it should be understood that it is not limited to these embodiments. On the contrary, the invention covers all alternatives, modifications, and equivalents as may be included with the spirit and scope of the appended claims.