Abstract:
The present invention provides a diesel engine capable of preventing a PM accumulation amount from increasing excessively. If DOC inlet exhaust gas temperature (“IEGT”) does not reach a predetermined value T0, a control unit carries out air intake amount feedback control (“AIAFC”), and a target value of intake throttling is set to a predetermined air intake amount. If the DPF regenerating processing is not started even if elapsed time reaches a predetermined value t after AIAFC is started in a state where the DOC IEGT does not reach the predetermined value T0, the control unit changes AIAFC to exhaust gas temperature feedback control (“EGTFC”). In EGTFC, the control unit changes a target value of intake throttling to a predetermined DOC IEGT T0. If application of a load exceeding a predetermined amount is detected before the DOC IEGT reaches the predetermined value T0, the control unit returns EGTFC to AIAFC.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a diesel engine, and more particularly, to a diesel engine capable of preventing a PM accumulation amount of a DPF from increasing excessively. 
     (2) Description of Related Art 
     As conventional diesel engines, there is a diesel engine including a DOC, a DPF, a PM accumulation amount estimating device of the DPF, a control unit, a DPF regenerating device, a DOC inlet temperature detector, an intake throttle device and an air intake amount detector (see Japanese Patent Application No. 2007-321705 (FIG. 1) for example). 
     The engine of this kind has a merit that even if the PM is accumulated on the DPF, DPF can be regenerated by the DPF regenerating device and the DPF can be reused. 
     However, the conventional diesel engine has such a problem that an intake throttling target value for regenerating the DPF to increase exhaust gas temperature to activation temperature of the DOC is only an air intake amount. 
     BRIEF SUMMARY OF THE INVENTION 
     Problem 
     There is concern that a PM accumulation amount of the DPF increases excessively. 
     According to the conventional diesel engine, since the intake throttling target value for regenerating the DPF is only the air intake amount, an intake throttling amount in air intake amount feedback control is limited, and in an operating state where a load is light and exhaust gas temperature is low, DOC inlet exhaust gas temperature does not rise up to DOC activation temperature, regeneration of the DPF is postponed for long periods, and there is concern that the PM accumulation amount of the DPF increases excessively. In this case, the DPF can not be used and exchange thereof is required in some cases. 
     It is an object of the present invention to provide a diesel engine capable of preventing a PM accumulation amount from increasing excessively. 
     Means for Solving the Problem 
     A matter to define the invention is as follows. 
     As illustrated in  FIG. 1 , a diesel engine includes a DOC  1 , a DPF  2 , a PM accumulation amount estimating device  3  of the DPF  2 , a control unit  4 , a DPF regenerating device  5 , a DOC inlet exhaust gas temperature detector  6 , an intake throttle device  7 , an air intake amount detector  8  and a load detector  9 , when a PM accumulation estimate value of the DPF  2  reaches a predetermined value P and DOC inlet exhaust gas temperature reaches a predetermined value T0, DPF regenerating processing is started, unburned fuel is mixed into exhaust gas  10  in the DPF regenerating processing by the DPF regenerating device  5  under control of the control unit  4  as illustrated in  FIG. 1 , temperature of exhaust gas  10  rises by catalytic combustion at the DOC  1  of the unburned fuel, PM accumulated on the DPF  2  is burned and removed and the DPF  2  is regenerated as shown in  FIG. 2 , when the DOC inlet exhaust gas temperature does not reach the predetermined value T0, air intake amount feedback control is carried out by the control unit  4 , in the air intake amount feedback control, a target value of DPF regenerating intake throttling S 8  is set S 5  to a predetermined air intake amount V, and when the DOC inlet exhaust gas temperature reaches the predetermined value T0 by the DPF regenerating intake throttling S 8 , the DPF regenerating processing is started, and when the DPF regenerating processing is not started even when elapsed time reaches a predetermined value t after the air intake amount feedback control is started in a state where the DOC inlet exhaust gas temperature does not reach the predetermined value T0, the air intake amount feedback control is changed to exhaust gas temperature feedback control by the control unit  4  as shown in  FIG. 2 , in the exhaust gas temperature feedback control, a target value of DPF regenerating intake throttling S 15  is changed to S 13  predetermined DOC inlet exhaust gas temperature T0 by the control unit  4 , when the DOC inlet exhaust gas temperature reaches the predetermined value T0 by the DPF regenerating intake throttling S 15 , the DPF regenerating processing is started, and when application of a load exceeding a predetermined amount is detected before the DOC inlet exhaust gas temperature reaches the predetermined value T0, the exhaust gas temperature feedback control is returned to the air intake amount feedback control by the control unit  4  as shown in  FIG. 2 . 
     Effect of the Invention 
     It is possible to prevent a PM accumulation amount of a DPF from increasing excessively. 
     As illustrated in  FIG. 2 , when the DPF regenerating processing is not started even when elapsed time reaches a predetermined value t after the air intake amount feedback control is started in a state where the DOC inlet exhaust gas temperature does not reach the predetermined value T0, the air intake amount feedback control is changed to exhaust gas temperature feedback control by the control unit  4  as illustrated in  FIG. 2 . Therefore, limitation of the intake throttling of the air intake amount feedback control for regenerating the DPF is released, and air intake is further throttled. According to this, even in the operating state where a load is light and exhaust gas temperature is low, it is possible to raise DOC inlet exhaust gas temperature up to activation temperature of a DOC  1  in a short time, DPF regenerating processing is carried out early, and it is possible to prevent the PM accumulation amount of the DPF from increasing excessively. 
     Effects 
     Even if a load is applied, it is possible to stabilize rotation of an engine. 
     As illustrated in  FIG. 2 , when application of a load exceeding a predetermined amount is detected before the DOC inlet exhaust gas temperature reaches the predetermined value T0, the exhaust gas temperature feedback control is returned to the air intake amount feedback control by the control unit  4 . Therefore, an air intake amount suitable for main injection which is increased by an applied load is secured, and it is possible to stabilize rotation of an engine. 
     It is possible to stabilize rotation of an engine. 
     As illustrated in  FIG. 2 , in the exhaust gas temperature feedback control, before the DPF regenerating intake throttling S 15  in which the target value is set to a predetermined DOC inlet exhaust gas temperature T0, exhaust gas preliminary temperature rising processing S 14  is carried out by the control unit  4 , after-injection S 14 - 3  by the common rail device  11  is included in the exhaust gas preliminary temperature rising processing S 14 , and the after-injection S 14 - 3  is carried out at injection timing which is earlier than that of the post-injection S 3 . Therefore, it is possible to preliminary raise temperature of exhaust gas  10  before the DPF regenerating intake throttling S 15  by the after-injection S 14 - 3 , and it is possible to correspondingly make the intake throttling gentle and to correspondingly increase the air intake amount, and it is possible to stabilize the rotation of the engine by increase in output. 
     Effects 
     It is possible to swiftly start the DPF regenerating processing. 
     As illustrated in  FIG. 2 , before the DPF regenerating intake throttling S 15 , after-injection S 14 - 3  preliminary raises temperature of exhaust gas  10 , temperature of the DOC  1  is brought close to activation temperature. Therefore, it is possible to swiftly start the DPF regenerating processing. 
     It is possible to swiftly start the DPF regenerating processing. 
     As illustrated in  FIG. 2 , in the air intake amount feedback control, before the DPF regenerating intake throttling S 8 , the after-injection S 7 - 3  preliminary raises temperature of exhaust gas  10  and temperature of DOC  1  is brought close to activation temperature. Therefore, it is possible to swiftly start the DPF regenerating processing. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
       In the drawings: 
         FIG. 1  is a schematic diagram of a diesel engine according to an embodiment of the present invention; 
         FIG. 2  is a main flowchart of control of the engine shown in  FIG. 1 ; 
         FIG. 3  is a sub-flowchart showing details of after-injection under air intake amount feedback control in  FIG. 2 ; and 
         FIG. 4  is a sub-flowchart showing details of after-injection under exhaust gas temperature feedback control in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 to 4  are diagrams for describing a diesel engine according to an embodiment of the present invention. In this embodiment, a vertical type straight four-cylinder diesel engine will be described. This engine is used for an engine generator. 
     A general outline of this engine is as follows. 
     A cylinder head  13  is assembled into a cylinder block  12 , an engine cooling fan  14  is placed on a front portion of the cylinder block  12 , and a flywheel  15  is placed on a rear portion of the cylinder block  12 . 
     An intake manifold (not shown) is assembled into one of lateral sides of the cylinder head  13 , and an exhaust manifold  16  is assembled into the other lateral side. 
     A supercharger  17  is mounted on the exhaust manifold  16 , an exhaust path  18  extends from an exhaust turbine  17   a  of the supercharger  17 , and an air suction path  38  extends from an air compressor  17   b  of the supercharger  17 . 
     As shown in  FIG. 1 , this engine includes a DOC  1 , a DPF  2 , a PM accumulation amount estimating device  3  of the DPF  2 , a control unit  4 , a DPF regenerating device  5 , a DOC inlet exhaust gas temperature detector  6 , an intake throttle device  7 , an air intake amount detector  8  and a load detector  9 . 
     As shown in  FIG. 1 , the DOC  1  is placed on an upstream side in a DPF case  36  of an exhaust path  18 , and the DPF  2  is placed on a downstream side in the DPF case  36 . 
     The DOC  1  is an oxidation catalyst, and an oxidation catalyst component of the DOC  1  is supported by a honeycomb-shaped ceramic carrier. The DOC  1  is a flow-through monolith having cells  1   a , both ends of the cells  1   a  are opened, and exhaust gas  10  passes through an inside of the cells  1   a.    
     The DPF  2  is a diesel particulate filter, an oxidation catalyst component of the DPF  2  is supported by a honeycomb-shaped ceramic carrier, the DPF  2  is a wall-flow monolith having adjacent cells  2   a  and  2   a , ends of the cells  2   a  and  2   a  are alternately closed, exhaust gas  10  passes through a wall  2   b  between the adjacent cells  2   a  and  2   a , and PM included in the exhaust gas  10  becomes trapped. The PM is an abbreviation of particulate material. 
     The PM accumulation amount estimating device  3  of the DPF  2  is a computation unit of an engine ECU which is the control unit  4 . The PM accumulation amount estimating device  3  estimates a PM accumulation amount of the DPF  2  from map data which is previously obtained experimentally based on the engine target rotation number, the engine actual rotation number, DPF inlet exhaust gas temperature, DPF inlet exhaust gas pressure, exhaust gas differential pressure at an inlet and an outlet of the DPF  2 , DPF outlet exhaust gas temperature and fuel injection amount which are respectively detected by an engine target rotation number setting device  19 , an engine actual rotation number detector  20 , a DPF inlet exhaust gas temperature detector  21 , a DPF inlet exhaust gas pressure detector  22 , a differential pressure detector  23  and a DPF outlet exhaust gas temperature detector  37 . 
     The engine ECU is an engine electronic control unit and is a microcomputer. 
     As shown in  FIG. 1 , the DPF regenerating device  5  includes the DOC  1  and a common rail device  11 . 
     The common rail device  11  includes injectors  24 , a common rail  25 , a fuel supply pump  26  and a fuel tank  27 . The injector  24  is mounted on the cylinder head  13  for each of the cylinders, and the injectors  24  are connected to the common rail  25  through high pressure pipes. Fuel  28  is supplied, under pressure, from the fuel tank  27  to the common rail  25  by the fuel supply pump  26 . A solenoid valve  24   a  of the injector  24  is electrically connected to the control unit  4 , the solenoid valve  24   a  is opened for predetermined time at predetermined timing, and a predetermined amount of fuel is injected at predetermined timing. 
     As shown in  FIGS. 2 to 4 , as injections of the common rail device  11 , there are main injection which is injected near a top dead center of a compression stroke, after-injections S 7 - 3  and S 14 - 3  and a post-injection S 3  which are injected in an exhaust stroke. Injection timing of the after-injections S 7 - 3  and S 14 - 3  is earlier than the post-injection S- 3 . The main injection is injection for obtaining engine output. The after-injections S 7 - 3  and S 14 - 3  are injections for preliminary raising temperature of exhaust gas  10  before intake throttling S 8  and S 15  for regenerating the DPF. The post-injection S 3  is injection for mixing unburned fuel into exhaust gas  10 , for catalytic burning the fuel by the DOC  1 , for raising temperature of exhaust gas  10 , and for regenerating the DPF  2 . 
     As shown in  FIG. 1 , injection timing and injection time of the injectors  24  are controlled by the control unit  4  based on the engine actual rotation number and a crank angle respectively detected by the engine actual rotation number detector  20  and a crank angle detector  29 , and phases of combustion cycles of the cylinders detected by a cylinder discriminating device  30 . The engine actual rotation number detector  20  and the crank angle detector  29  are pickup coils which face an outer periphery of a rotor plate  31  of the flywheel  15 . The engine actual rotation number detector  20  and the crank angle detector  29  detect the number of teeth which are provided in quantity on an outer periphery of the rotor plate  31  at constant intervals from one another. The cylinder discriminating device  30  is also a pickup coil which faces an outer periphery of a sensor plate  32  which is mounted on a camshaft. The cylinder discriminating device  30  discriminates phases of combustion cycles of the cylinders by detecting projections provided on the outer periphery of the sensor plate  32 . The cylinder discriminating device  30  and the pickup coils configuring the engine actual rotation number detector  20  and the crank angle detector  29  are electrically connected to the control unit  4 . 
     As the DPF regenerating device  5 , it is possible to use a combination of the DOC  1  and an exhaust gas pipe fuel injection device in addition to a combination of the DOC  1  and the common rail device  11 , and it is also possible to use an electric heater as the DPF regenerating device  5 . 
     As shown in  FIGS. 1 and 2 , the intake throttle device  7  is an intake throttle valve. When DOC inlet exhaust gas temperature is less than activation temperature T0 of the DOC  1 , intake throttling S 8  and S 15  for gradually reducing an opening degree of the intake throttle valve is carried out by the control unit  4 , the air intake amount is reduced, and DOC inlet exhaust gas temperature rises. 
     The intake throttle device  7  is placed between the intake manifold and an intercooler  33  provided downstream of the air compressor  17   b  of the supercharger  17 . 
     The air intake amount detector  8  is an air flow sensor, and is placed between an air cleaner  34  and the air compressor  17   b  of the supercharger  17 . The intake throttle device  7  and the air intake amount detector  8  are electrically connected to the control unit  4 . 
     The load detector  9  is a computation processing unit of the engine ECU, and detects a load based on increase in an injection amount of the main injection. 
     When a mechanical cam-type fuel injection pump is used instead of the common rail device  11 , it is possible to use a rack position sensor which detects a fuel amount adjusting rack position of a fuel injection pump as the load detector  9 . 
     As shown in  FIG. 2 , if the PM accumulation estimate value of the DPF  2  reaches a predetermined value P and the DOC inlet exhaust gas temperature reaches the predetermined value T0, the regenerating processing of the DPF  2  is started. As shown in  FIG. 1 , in the DPF regenerating processing, unburned fuel is mixed into the exhaust gas  10  by the DPF regenerating device  5  under control of the control unit  4 , temperature of the exhaust gas  10  rises by catalytic combustion at the DOC  1  of the unburned fuel, PM accumulated on the DPF  2  is burned and removed, and the DPF  2  is regenerated. 
     As shown in  FIG. 2 , when the DOC inlet exhaust gas temperature does not reach the predetermined value T0, the air intake amount feedback control is carried out by the control unit  4 . In the air intake amount feedback control, a target value of DPF regenerating intake throttling S 8  is set S 5  to a predetermined air intake amount V, and if the DOC inlet exhaust gas temperature reaches the predetermined value T0 by the DPF regenerating intake throttling S 8 , the DPF regenerating processing is started, and even if predetermined time value t is elapsed after the air intake amount feedback control is started in a state where the DOC inlet exhaust gas temperature does not reach the predetermined value T0, if the DPF regenerating processing is not started, the air intake amount feedback control is changed to exhaust gas temperature feedback control by the control unit  4 . 
     As shown in  FIG. 2 , in the exhaust gas temperature feedback control, a target value of the DPF regenerating intake throttling S 15  is changed to predetermined DOC inlet exhaust gas temperature T0 S 13  by the control unit  4 , and if the DOC inlet exhaust gas temperature reaches the predetermined value T0 by the DPF regenerating intake throttling S 15 , the DPF regenerating processing is started, and if a load exceeding a predetermined amount is detected before the DOC inlet exhaust gas temperature reaches the predetermined value T0, the exhaust gas temperature feedback control is returned to the air intake amount feedback control by the control unit  4 . 
     As shown in  FIGS. 2 and 4 , in the exhaust gas temperature feedback control, before the DPF regenerating intake throttling S 15  in which the target value is the predetermined DOC inlet exhaust gas temperature T0 is carried out, the exhaust gas preliminary temperature rising processing S 14  is carried out by the control unit  4 , the after-injection S 14 - 3  by the common rail device  11  is included in the exhaust gas preliminary temperature rising processing S 14 , and the after-injection S 14 - 3  is carried out at injection timing which is earlier than the post-injection S 3 . 
     As shown in  FIGS. 2 and 3 , in the air intake amount feedback control, before the DPF regenerating intake throttling S 8  in which the target value is the predetermined air intake amount V is carried out, exhaust gas preliminary temperature rising processing S 7  is carried out by the control unit  4 , the after-injection S 7 - 3  by the common rail device  11  is included in the exhaust gas preliminary temperature rising processing S 7 , and the after-injection S 7 - 3  is carried out at injection timing which is earlier than the post-injection S- 3 . 
     A flow of processing carried out by the control unit  4  is as follows. 
     As shown in  FIG. 2 , it is determined in step S 1  whether an accumulation estimate value of PM which is accumulated on the DPF  2  reaches a predetermined value P. The value P is a determination reference value of DPF regeneration. If the decision in step S 1  is NO, determination in step S 1  is repeated, and the decision becomes YES, the procedure is shifted to step S 2 . 
     It is determined in step S 2  whether the DOC inlet exhaust gas temperature reaches the value T0, and if the decision is YES, the procedure is shifted to step S 3 . The value T0 is activation temperature of the DOC  1 . 
     The post-injection is carried out in step S 3 , and it is determined in step S 4  whether a regeneration completion condition of the DPF  2  is satisfied. The regeneration completion condition is that accumulated time of a DPF inlet exhaust gas temperature more than a predetermined value reaches predetermined time. If the decision in step S 4  is YES, the DPF regenerating processing is completed. If the decision in step S 4  is NO, the procedure is returned to step S 3 . 
     If the decision in step S 2  is NO, the air intake amount feedback control of the intake throttling is carried out. 
     In the air intake amount feedback control, the intake throttling target value is set to the air intake amount V in step S 5 . The air intake amount V is such an air intake amount that even if a certain level of load is applied to the engine, the engine rotation can stably be maintained, and the intake throttling is more limited as compared with the exhaust gas temperature feedback control in which the exhaust gas temperature is used as a target value. 
     Time keeping is started in step S 6 . The time keeping is carried out by a time keeping unit  35  of the control unit  4 . 
     The exhaust gas preliminary temperature rising processing is carried out in step S 7 . Details of the exhaust gas preliminary temperature rising processing will be described later. 
     The DPF regenerating intake throttling is carried out in step S 8 , the intake throttle valve is gradually closed and an opening thereof degree becomes small. 
     It is determined in step S 9  whether the air intake amount reaches the target value V, and if the decision is YES, the procedure is shifted to step S 10 , and if decision is NO, the procedure is returned to step S 8 . 
     It is determined in step S 10  whether the DOC inlet exhaust gas temperature reaches the value T0. If the decision is YES, the procedure is shifted to step S 3 , and if the decision is NO, the procedure is shifted to step S 11 . 
     It is determined in step S 11  whether the counted elapsed time reaches a predetermined value t. The value t is set to such a time value that postponement of regeneration of the DPF  2  can not further be permitted. If the decision in step S 11  is YES, the time keeping is completed in step S 12 , and control of the intake throttling is switched to the exhaust gas temperature feedback control. If the decision in step S 11  is NO, the procedure is returned to step S 10 . 
     In the exhaust gas temperature feedback control, the target value of the DPF regenerating intake throttling S 15  is changed from the air intake amount V to the DOC inlet exhaust gas temperature T0 in step S 13 . 
     The exhaust gas preliminary temperature rising processing is carried out in step S 14 . Details of the exhaust gas preliminary temperature rising processing will be described later. 
     The DPF regenerating intake throttling is carried out in step S 15 , the intake throttle valve is gradually closed and its opening degree becomes small. 
     It is determined in step S 16  whether the DOC inlet exhaust gas temperature reaches the value T0. If the decision is YES, the procedure is shifted to step S 3 , and if the decision is NO, the procedure is shifted to step S 17 . 
     It is determined in step S 17  whether application of a load exceeding a predetermined amount is detected. If the decision is YES, the procedure is returned to step S 5 , and the exhaust gas temperature feedback control of the intake throttling is returned to the air intake amount feedback control. 
     Details of the exhaust gas preliminary temperature rising processing by the air intake amount feedback control are as follows. 
     As shown in  FIG. 3 , in step S 7  where the exhaust gas preliminary temperature rising processing is carried out, intake throttling for after-injection is first carried out in step S 7 - 1 . The intake throttle target value for the after-injection is DOC exhaust gas inlet temperature T0′. The value T0′ is temperature of the exhaust gas  10  at which after-injection is burned, and is lower than the value T0 which is the DOC activation temperature. 
     It is determined in step S 7 - 2  whether the DOC inlet exhaust gas temperature reaches the target value T0′. If the decision is YES, procedure is shifted to step S 7 - 3 , and if the decision is NO, procedure is returned to step S 7 - 1 . 
     The after-injection is carried out in step S 7 - 3 . 
     It is determined in step S 7 - 4  whether the DOC inlet exhaust gas temperature reaches the value T0. If the decision is YES, the procedure is shifted to step S 7 - 8 , and if the decision is NO, the procedure is shifted to step S 7 - 5 . 
     In step S 7 - 8 , the after-injection is continued even after that, and the procedure is shifted to step S 3 . 
     It is determined in step S 7 - 5  whether an amount of after-injection reaches an upper limit. If the decision is YES, the procedure is shifted to step S 7 - 6 , and if the decision is NO, the procedure is shifted to step S 7 - 7 . 
     In step S 7 - 6 , the injection amount is fixed, the after-injection is continued even after that, and the procedure is shifted to step S 8 . 
     In step S 7 - 7 , the after-injection amount is increased and the procedure is returned to step S 7 - 3 . 
     The exhaust gas preliminary temperature rising processing in the exhaust gas temperature feedback control is the same as the exhaust gas preliminary temperature rising processing in the air intake amount feedback control, and details thereof are as follows. 
     As shown in  FIG. 4 , in step S 14  where the exhaust gas preliminary temperature rising processing is carried out, intake throttling for after-injection is first carried out in step S 14 - 1 . The intake throttling target value for the after-injection is DOC exhaust gas inlet temperature T0′. The value T0′ is temperature of the exhaust gas  10  at which after-injection is burned, and is lower than the value T0 which is the DOC activation temperature. 
     It is determined in step S 14 - 2  whether the DOC inlet exhaust gas temperature reaches the target value T0′. If the decision is YES, the procedure is shifted to step S 14 - 3 , and if the decision is NO, the procedure is returned to step S 14 - 1 . 
     The after-injection is carried out in step S 14 - 3 . 
     It is determined in step S 14 - 4  whether the DOC inlet exhaust gas temperature reaches the value T0. If the decision is YES, the procedure is shifted to step S 14 - 8 , and if the decision is NO, the procedure is shifted to step S 14 - 5 . 
     In step S 14 - 8 , the after-injection is continued even after that, and procedure is shifted to step S 3 . 
     It is determined in step S 14 - 5  whether an amount of after-injection reaches an upper limit. If the decision is YES, procedure is shifted to step S 14 - 6 , and if the decision is NO, the procedure is shifted to step S 14 - 7 . 
     In step S 14 - 6 , the injection amount is fixed, the after-injection is continued even after that, and the procedure is shifted to step S 15 . 
     In step S 14 - 7 , the after-injection amount is increased and the procedure is returned to step S 14 - 3 . 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.