Abstract:
A method and apparatus for controlling a temperature in a combustion cylinder in an internal combustion engine. The cylinder is fluidly connected to an intake manifold and an exhaust manifold. The method and apparatus includes increasing a back pressure associated with the exhaust manifold to a level sufficient to maintain a desired quantity of residual exhaust gas in the cylinder, and varying operation of an intake valve located between the intake manifold and the cylinder to an open duration sufficient to maintain a desired quantity of fresh air from the intake manifold to the cylinder, wherein controlling the quantities of residual exhaust gas and fresh air are performed to maintain the temperature in the cylinder at a desired level.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates generally to a method and apparatus for controlling a temperature in a cylinder in an internal combustion engine and, more particularly, to a method and apparatus for controlling levels of internal exhaust residual and fresh air in a cylinder to control the temperature in the cylinder.  
       BACKGROUND  
       [0002]     Internal combustion engines often experience different problems associated with varying operating conditions. For example, compression ignition engines, in particular those operating in homogeneous charge compression ignition (HCCI) mode, tend to be susceptible to incomplete combustion at low loads due to low in-cylinder temperatures. It is thus often desired to increase in-cylinder temperatures under these operating conditions by, for example, adding a quantity of internal exhaust residual into the cylinders.  
         [0003]     The methods employed to add internal exhaust residual often create additional problems, however. For example, it is common to modify exhaust cams to change the duration in which exhaust valves remain open. This technique may be successful in providing internal exhaust residual at low loads, but it also may be detrimental to the engine during high load operation. Another possible method is to use an engine turbocharger to increase engine back pressure at low loads. For example, a variable geometry turbine (VGT) may be used. The use of a VGT for this purpose, however, also results in additional airflow being created, which in turn reduces the effect of any additional internal exhaust residual.  
         [0004]     The present invention is directed to overcoming one or more of the problems as set forth above.  
       SUMMARY OF THE INVENTION  
       [0005]     In one aspect of the present invention a method for controlling a temperature in a combustion cylinder in an internal combustion engine is disclosed. The cylinder is fluidly connected to an intake manifold and an exhaust manifold. The method includes the steps of increasing a back pressure associated with the exhaust manifold to a level sufficient to maintain a desired quantity of residual exhaust gas in the cylinder, and varying operation of an intake valve located between the intake manifold and the cylinder to an open duration sufficient to maintain a desired quantity of fresh air from the intake manifold to the cylinder, wherein controlling the quantities of residual exhaust gas and fresh air are performed to maintain the temperature in the cylinder at a desired level.  
         [0006]     In another aspect of the present invention a method for controlling a temperature in a cylinder of an internal combustion engine is disclosed. The method includes the steps of determining a load condition of the engine, determining a cylinder temperature as a function of the load condition, determining a desired cylinder temperature, increasing a back pressure associated with an exhaust manifold located on the engine and fluidly connected to the cylinder to a level sufficient to maintain a desired quantity of residual exhaust gas in the cylinder, and extending an open duration of an intake valve located between the cylinder and an intake manifold fluidly connected to the cylinder to a duration sufficient to maintain a quantity of fresh air from the intake manifold to a level below a desired threshold, wherein the increased back pressure and extended open duration of the intake valve are controlled to maintain the desired cylinder temperature.  
         [0007]     In yet another aspect of the present invention an apparatus for controlling a temperature in a combustion cylinder in an internal combustion engine is disclosed. The apparatus includes an intake manifold fluidly connected to the cylinder, an intake valve located between the intake manifold and the cylinder, an exhaust manifold fluidly connected to the cylinder, means for increasing a back pressure associated with the exhaust manifold to a level sufficient to maintain a desired quantity of residual exhaust gas in the cylinder, and means for varying operation of the intake valve to an open duration sufficient to maintain a desired quantity of fresh air from the intake manifold to the cylinder, wherein controlling the quantities of residual exhaust gas and fresh air are performed to maintain the temperature in the cylinder at a desired level.  
         [0008]     In still another aspect of the present invention an apparatus for controlling a temperature in a combustion cylinder in an internal combustion engine is disclosed. The apparatus includes an intake manifold fluidly connected to the cylinder, an intake valve located between the intake manifold and the cylinder, an exhaust manifold fluidly connected to the cylinder, a turbocharger system connected between the intake and exhaust manifolds, a variable intake valve system controllably connected to the intake valve, and a controller electrically connected to the turbocharger and variable intake valve systems for controlling the turbocharger system to increase a back pressure associated with the exhaust manifold, and for controlling the variable intake valve system to vary an open duration of the intake valve, wherein the back pressure and the open duration of the intake valve are controlled to respectively maintain a desired increased quantity of residual exhaust gas and a desired decreased quantity of fresh air in the cylinder, such that the temperature in the cylinder is maintained at a desired level. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a block diagram illustrating a preferred embodiment of the present invention;  
         [0010]      FIG. 2  is a diagrammatic illustration of a variable valve system suited for use with the present invention;  
         [0011]      FIG. 3  is a diagrammatic illustration of an engine having a turbocharger system suited for use with the present invention; and  
         [0012]      FIG. 4  is a flow diagram illustrating a preferred method of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]     Referring to the drawings, a method and apparatus  100  for controlling a temperature in a combustion cylinder  202  (hereinafter referred to as a cylinder  202 ) in an internal combustion engine  102  is shown.  
         [0014]     Referring particularly to  FIG. 1 , a block diagram illustrating principle components suited for use with the present invention are shown. An engine  102  may be of a compression ignition type, for example a compression ignition diesel engine. However, other types of engines, for example a spark ignition engine such as a gasoline engine may also be used. The present invention finds particular use with homogeneous charge compression ignition engines, commonly referred to as HCCI engines. In particular, the present invention may be suited for use in an HCCI engine under conditions such as low load, in which a temperature in the cylinder  202  may be lower than desired.  
         [0015]     A means  103  for varying operation of an intake valve  226  may be found on the engine  102 . The means  103  may be a variable intake valve system  104 , described in more detail below with respect to  FIG. 2 .  
         [0016]     A means  105  for increasing a back pressure may also be found on the engine  102 . The means  105  may be a turbocharger system  106 , described in more detail below with respect to  FIG. 3 .  
         [0017]     Back pressure, as is well known in the art, is the resultant pressure acting on an exhaust system of an engine from the creation of a pressure, i.e., a boost pressure, intended for an intake system of the engine. Back pressure may impede the flow of exhaust gas from the cylinder of the engine.  
         [0018]     A controller  108  may be electrically connected to the variable intake valve system  104  and the turbocharger system  106  for control in accord with the present invention, as is described in more detail below. The controller  108  may be microprocessor-based and may be either dedicated to the purpose herein described or may be used for additional purposes, such as engine control, diagnostics, and the like.  
         [0019]     Referring to  FIG. 2 , a variable intake valve system  104  suited for use with the present invention is shown in detail. Cylinder  202  includes a piston  204  therein, configured to move within the cylinder  202  as is well understood in the art.  
         [0020]     A rocker arm assembly  206  includes a rocker arm  208  located to move about a pivot  210 . A push rod  212  provides a mechanical force against the rocker arm  208  and may include a cup  214  at one end. A lash adjustment screw  216  mounted to the rocker arm  208  may, in cooperation with the cup  214 , provide an adjustable coupling between the push rod  212  and the rocker arm  208 .  
         [0021]     The push rod  212  may be driven by a lifter assembly  218 , which in turn may be driven by a cam  220 .  
         [0022]     An electro-hydraulic assist actuator  222  may include a plunger assembly  224  for providing a hydraulic force used to vary the open duration of an intake valve  226 . More particularly, the rocker arm assembly  206 , as enabled by the cam  220 , may be used to open the intake valve  226  and the electro-hydraulic assist actuator  222  may be used to hold the intake valve  226  open for a period of time longer than the cam  220  is designed to do.  
         [0023]     The intake valve  226  includes a valve member  228  controllably movable to provide a fluid opening from an intake manifold  232  to the cylinder  202  by way of an intake passage  230 .  
         [0024]     It is noted that the above description of a variable intake valve system  104  is indicative of a hydraulically enhanced mechanical valve system. Other types of valve systems may be used as well, such as fully hydraulic valve control systems, electric valve control systems, and mechanical valve control systems having some type of technique for mechanically varying the open duration of the intake valve  226 .  
         [0025]     Referring to  FIG. 3 , a diagrammatic illustration of an exemplary turbocharger system  106  as it may be configured with an engine  102  is shown.  
         [0026]     The engine  102  includes an engine block  302 , which houses at least one cylinder  202 , for example six cylinders  202  as shown. It is noted that any number of cylinders may be used, such as four, six, eight, ten, twelve, or any other number. Hereinafter, reference to a cylinder  202  refers to one or more cylinders  202 .  
         [0027]     An exhaust manifold  304 , located on the engine  102 , is configured to receive exhaust gas from the cylinder  202  during normal engine operation.  
         [0028]     The exhaust gas is delivered to the turbocharger system  106  which, in the embodiment shown, includes a first turbocharger  306  having a first turbine  308  and a first compressor  310 , followed by a second turbocharger  312  having a second turbine  314  and a second compressor  316 .  
         [0029]     In operation, the exhaust gas passes through and drives the first turbine  308 , then the second turbine  314 , which in turn drive, respectively, the first compressor  310  and the second compressor  316 . Compressed air from the first and second compressors  310 ,  316  is then delivered to the intake manifold  232 , e.g., through an air cooler  318 , for controlled delivery to the cylinder  202 .  
         [0030]     After passing through the turbocharger system  106 , the exhaust gas may then be delivered to an exhaust system  320 .  
         [0031]     The exhaust system  320  may include an exhaust gas recirculation (EGR) system  322 , which in turn may include a particulate matter (PM) filter  324  and an oxidation catalyst  326  in a downstream path, and an EGR cooler  328  and an EGR valve  330  in a return path. The EGR valve  330  may be configured to controllably introduce a quantity of exhaust gas with the fresh air being supplied to the first and second compressors  310 ,  316 .  
         [0032]     Preferably, at least one turbocharger  306 ,  312  is configured as a variable geometry turbocharger, i.e., having a variable geometry turbine (VGT).  
         [0033]     For example, each of the first and second turbines  308 ,  314  may be variable geometry turbines. As such, each turbine  308 ,  314  would be controlled by VGT vane actuators  332 ,  334 , as is well known in the art. The controller  308  would be electrically connected to the VGT vane actuators  332 ,  334  to control each VGT  308 ,  314  in accord with the present invention. For example, to increase back pressure, the VGT vane actuators  332 ,  334  may be actuated to close the vanes of the turbines  308 ,  314 .  
         [0034]     Other configurations of the turbocharger system  106  may be used as well. For example, two VGTs may be connected in series as shown in  FIG. 3 , or may be connected in parallel. Alternatively, the turbocharger system  106  may have one large VGT and one back pressure valve (not shown), or one VGT large enough to provide the needed back pressure for the present invention.  
         [0000]     Industrial Applicability  
         [0035]     Referring to  FIG. 4 , a flow diagram illustrating a preferred method of the present invention is shown.  
         [0036]     In a first control block  402 , a load condition of the engine  102  may be determined. For example, it may be determined that the engine  102  is in a low load condition. The load condition may be determined in a number of ways, for example as a function of engine speed, fuel demand, torque, and the like. In a particular example, a low load condition may be an indication that the engine  102  is operating such that the temperature in the cylinder  202  is lower than desired, thus resulting in increased emissions. This may be a particular problem with HCCI mode engines.  
         [0037]     In a second control block  404 , the engine cylinder temperature may be determined as a function of the load condition. The temperature may be determined as an absolute value or as a trigger that low load correlates with low temperature. Determination of the cylinder temperature may be based on reference to a load-temperature map or may be derived.  
         [0038]     As an alternative to first and second control blocks  402 ,  404 , the temperature in the cylinder may be monitored directly, either by sensed means or derived from other factors. Thus, a low temperature determination may be used to trigger use of the present invention, rather that a low load determination.  
         [0039]     In a third control block  406 , a desired cylinder temperature may be determined. The desired temperature may either be an absolute value or a desired minimum temperature threshold. Other factors, such as the operating state of the engine  102 , may be considered as well.  
         [0040]     Determination that the cylinder temperature has fallen below the desired value or threshold may then trigger actuation of fourth and fifth control blocks  408 ,  410 .  
         [0041]     In the fourth control block  408 , the back pressure at the exhaust manifold  304  is increased, preferably by actuating at least one VGT  308 ,  314 .  
         [0042]     More specifically, at least one VGT  308 ,  314  is actuated by closing the vanes of the turbine  308 ,  314  to increase boost pressure at the intake manifold  232  and subsequently increase back pressure at the exhaust manifold  304 . The increased back pressure has the effect of preventing a quantity of exhaust gas from exiting the cylinder  202 , which in turn increases the temperature in the cylinder  202 .  
         [0043]     Unfortunately, the increased boost pressure at the intake manifold  232  also has the effect of forcing more fresh air into the cylinder  202 , which tends to decrease the temperature. In the fifth control block  410 , however, the open duration of the intake valve  226  is extended, for example up to about one half of the compression stroke, to allow the compression within the cylinder  202  to prevent some of the excess fresh air from entering and perhaps even pushing a quantity of the fresh air back out of the cylinder  202  into the intake manifold  232 .  
         [0044]     Thus, the excess fresh air from the increased boost pressure is not allowed into the cylinder  202 , and the temperature remains increased due to the residual exhaust gas.  
         [0045]     Other aspects can be obtained from a study of the drawings, the disclosure, and the appended claims.