Abstract:
This invention relates to an engine torque controller for spark ignition internal combustion engines and more specifically for direct injection engines. The invention provides a torque controller and a method of controlling torque for an engine in which torque is controlled in dependence upon a filtered difference signal where the filtered difference signal is the difference between a desired torque signal and a signal representing an estimate of the current torque.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to an engine torque controller for spark ignition internal combustion engines and more specifically for direct injection engines.  
         BACKGROUND  
         [0002]    An engine torque controller is comprised of a torque demand controller and a torque producer. The torque demand controller determines a required target torque, in accordance with an accelerator pedal position, current engine speed, external loads and other factors. This determined torque is then used by the torque producer to produce the desired torque by controlling the spark angle and the air/fuel ratio.  
           [0003]    Direct Injection Spark Ignition (DISI) engines inject fuel directly into cylinders where it is ignited by a spark from a spark plug. DISI engines operate in a stratified mode or a homogenous mode. When a DISI engine is in the stratified mode, the combustion chambers contain stratified layers having different air/fuel mixtures. The strata closest to the spark plug contains a stoichiometric mixture, which is a mixture in which the exact amount of air to combust the amount of fuel is present, i.e. when the combustion leaves no excess oxygen or unburned fuel. Subsequent strata contain progressively leaner mixtures. Operation in a stratified mode occurs at lower speeds and lower load conditions.  
           [0004]    When the engine is in a homogenous mode, a homogenous mixture of air and fuel is introduced into the combustion chamber. Homogenous operation may be either lean of stoichiometry (i.e. higher air/fuel ratio), at stoichiometry, or rich of stoichiometry (i.e. lower air fuel ratio).  
           [0005]    In engine torque controllers for DISI engines, when the engine is operating in stratified mode, spark angle has little influence on the torque produced. The torque producer modifies the air/fuel in order to control the torque produced. Conversely, when the engine is operating in homogenous mode, the air/fuel ratio is controlled tightly in order to maintain correct operation of the catalytic converter to reduce noxious emission. The torque producer modifies the timing of the spark ignition in order to control the torque produced.  
           [0006]    A problem occurs in either of these modes of operation when there is a steady state error between the torque demanded and the estimate of the torque produced. In the stratified mode if a fuel adjustment occurs due to such a steady state error then the air/fuel ratio will not be ideal and fuel economy will suffer and performance of the catalytic converter will deteriorate. In the homogenous mode, if the timing of the spark ignition is altered due to such a steady state torque error then the fuel economy will once again suffer and the engine is more likely to stall when a load is imposed. Therefore, there is a need for a method of correction for a steady state error between the torque demanded and an estimate of the torque produced.  
         SUMMARY  
         [0007]    In a preferred embodiment, the engine is a direct injection spark ignition engine and the transient torque controller is arranged to receive a combustion mode signal indicating whether the engine is operating in a stratified mode or a homogeneous mode. If the signal indicates that the engine is operating in the stratified mode then the fuel and spark controller is arranged to control the fuel adjustment signal. If the signal indicates that the engine is operating in the homogeneous mode then the fuel and spark controller is arranged to control the spark adjustment signal.  
           [0008]    Preferably, the controller also has an air charge controller arranged to receive an air charge demand signal, a throttle position signal, an engine speed signal, a manifold pressure signal and an air charge temperature signal and arranged to output the estimated air charge signal. Preferably, there is also an air charge demand controller arranged to receive the desired torque signal, a desired spark angle signal and a desired air/fuel ratio signal and to output the air charge demand signal.  
           [0009]    According to another aspect of the invention, there is provided a method of controlling torque for an engine. The method includes estimating a current torque signal in dependence upon a received current spark angle signal, a received current air/fuel ratio signal and a received estimated air charge signal, comparing the estimated current torque signal with a desired torque signal to provide a difference signal, and filtering low frequency components from the difference signal. Finally, controlling a fuel adjustment signal and a spark adjustment signal in dependence upon the filtered difference signal.  
           [0010]    These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description of the invention in combination with the accompanying figures. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0011]    [0011]FIG. 1 is a block diagram illustrating part of an engine and an engine controller, in accordance with the present invention;  
         [0012]    [0012]FIG. 2 is a block diagram of a torque demand controller, in accordance with the present invention; and  
         [0013]    [0013]FIG. 3 is a block diagram of a torque producer, in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]    [0014]FIG. 1 illustrates an embodiment of a direct injection spark ignition engine  100  which has an engine controller  1 . The engine controller  1  receives signals from an accelerator pedal and sensor assembly  2 , an engine speed sensor  3 , an engine temperature sensor  4 , an air charge temperature sensor  5 , a manifold absolute pressure sensor  110  and a throttle position indicator  6 .  
         [0015]    A fuel injector  130  injects fuel directly into a combustion chamber  108 . The injected fuel mixes with an air charge which enters through an air intake valve  102  via an air intake manifold  152 . The air charge is controlled by a throttle  9  and the fuel injected is controlled by a fuel pump  8 . A spark control unit  7  controls a spark plug  106 , to generate a spark for ignition of the air/fuel mixture. Exhaust gases from the resulting combustion exit via an exhaust valve  104  into an exhaust manifold  154 . The exhaust manifold  154  has a three way catalytic converter  142  and a Nox trap/catalyst  144 .  
         [0016]    [0016]FIG. 2 illustrates an embodiment of a torque demand controller  11  that is part of the engine controller  1 . The torque demand controller  11  calculates a required output torque signal  13 , based on an accelerator pedal position signal received from the accelerator pedal and sensor assembly  2 , an engine speed signal received from the engine speed sensor  3  and an engine temperature signal received from the engine temperature sensor  4 . A loss load torque signal  12 , which represents losses due to losses in the engine and powertrain system, is added to the required output torque signal  13  by an adder  14  to generate a torque demand signal  15 .  
         [0017]    Referring now to FIG. 3, an adder  17  receives as inputs the torque demand signal  15  and a pumping losses signal  16 , which represents losses due to the inherent losses in the engine cycle (i.e. due to the energy required to draw air in and to push out exhaust gases). The adder  17  outputs a desired torque signal.  
         [0018]    An air charge demand controller  27  receives as inputs the desired torque signal, a desired spark angle signal  25  and a desired air fuel ratio signal  26 . The desired spark angle signal  25  and the desired air fuel ratio signal  26  are calculated elsewhere in the engine controller  1  and depend upon signals such as engine speed, engine load and engine temperature.  
         [0019]    The air charge demand controller  27  generates an air charge demand signal that is received by an air charge controller  29 . The air charge controller  29  also receives as inputs a signal indicating throttle position that is received from the throttle position indicator  6  (FIG. 1), the engine speed sensor  3 , the manifold absolute pressure sensor  110  and the air charge temperature meter  5 . The air charge controller  29  generates a signal indicating desired throttle position that is sent to throttle  9  (FIG. 1) and a signal representing an estimate of the air charge.  
         [0020]    The estimated air charge may be different from the air charge demanded by the air charge demand controller  27  due to delays in the engine  100 , such as the time taken for the throttle  9  to move, the time taken for the pressure in the air intake manifold  152  to rise or fall, or any errors in position of the throttle. The air charge estimate signal is sent to a current torque estimator  22 .  
         [0021]    The current torque estimator  22  uses the air charge estimate signal, together with a signal representing the current spark angle and a signal representing the current air/fuel ratio to generate a signal representing an estimate of the current torque.  
         [0022]    The estimate of the current torque is compared to the desired torque signal by a comparator  18  to generate an error signal which is then filtered by a high pass filter  20 . The resulting filtered error signal is used by a transient torque controller  21  to generate signals for temporarily adjusting the torque produced by the engine  100 .  
         [0023]    A combustion mode signal  19 , which is produced elsewhere in the engine controller  1 , indicates whether the engine  100  is operating in a stratified mode or in a homogenous mode. If the engine  100  is operating in the stratified mode then a fuel adjustment signal is generated and sent to the fuel pump  8  in order to adjust the amount of fuel which is injected into the combustion chamber  108  by the fuel injector  130 . If the engine  100  is operating in the homogenous mode then a spark adjustment signal is generated and sent to the spark control unit  7  to adjust the timing of the ignition spark generated by the spark plug  106 .  
         [0024]    The signal representing the current spark angle is calculated by a calculator  23  using the desired spark angle and any spark adjustment signal received from the transient torque controller  21 . The signal representing the current air fuel ratio is calculated by a calculator  24  using the desired air fuel ratio and any fuel adjustment signal received from the transient torque controller  21 . When the engine  100  is operating in stratified mode the current spark angle will be equal to the desired spark angle  25 . When the engine  100  is operating in homogenous mode the current air/fuel ratio will be equal to the desired air fuel ratio  26 .  
         [0025]    As any person skilled in the art of systems and methods of controlling the torque output of an engine will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.