Patent Publication Number: US-2004055283-A1

Title: Control system for internal combustion engine with catalyst for purifying exhaust gas

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to a control system for an internal combustion engine, which incorporates catalyst for purifying exhaust gas, and in particular to a technology of fast activation of catalyst for purification of exhaust gas from an internal combustion engine, by controlling an engine cooling system or the like.  
       RELATED ART  
       [0002] As disclosed in, for example, JP-A-2000-34584 or JP-A-2000-45843, there have been well-known many technologies of inhibiting radiation of heat from an engine to cooling water during a cold start in order to shorten the time of warm-up of the engine.  
       [0003] For example, the JP-A-2000-34584 discloses such a technology that the supply of cooling water is controlled in accordance with a temperature of a combustion chamber during operation of an engine so as to promote warm-up of the engine while the temperature of the wall surface of a combustion chamber, which correlates to a quantity of emergence of unburned HC components during a cold start is raised along an optimum temperature rising characteristic. Specifically, the cooling water is held in a reservoir tank when the wall temperature T of the combustion chamber during engine operation is lower than a first reference wall temperature T1, but the cooling water is displaced into a cooling water jacket of the engine when it is higher than T1. After the above-mentioned displacement of the cooling water is completed, the circulation of the cooling water is started.  
       [0004] Further, the JP-A-2000-45843 discloses a technology of retarding the ignition timing in an unwarmed-up condition so as to abruptly increase the exhaust temperature, exceeding a temperature of activation of catalyst for purification of exhaust gas so as to aim at promoting warm-up of catalyst for purification of exhaust gas in order to allow the catalyst to exhibit its purification characteristic in a short period.  
       [0005] Neither such a control technology that the warm-up of an engine and the warm-up of catalyst for purification of exhaust gas are associated with each other so as to carry out rational control, nor such a technology of short-time warm-up of an internal combustion engine that the control of a cooling water system and the control of combustion are combined with each other has not yet been built up in success.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006] An object of the present invention is to provide a control system for an internal combustion engine, which can rationally control the warm-up of the internal combustion engine and the warm-up of catalyst in the order of priority during a cold start.  
       [0007] To the end, according to the first aspect of the present invention, there is provided a control system for an internal combustion engine incorporating catalyst for purifying exhaust gas therefrom, which controls, during a cold start, a heat (cooling loss) transmitted from combustion gas to an engine block and a heat (heat radiation for cooling) transmitted from the engine block to engine cooling water, in order to aim for early warm-up of the catalyst. Further, there is provided a system for controlling the cooling loss and the heat radiation for cooling, so that the warm-up of the catalyst is preferential to the warm-up of the internal combustion engine while the engine and the catalyst are warmed up in a short time.  
       [0008] The control of the cooling loss is made by controlling, for example, the ignition timing while the control of the heat radiation for cooling is made by controlling the flow rate of cooling water through the intermediary of a water pump. That is, in such a case that the temperature of the catalyst has not yet risen up to its activation temperature, retardation control of the ignition timing is made so as to decrease the cooling loss, and as well, control is made such that the flow rate of cooling water is decreased to zero or a value smaller than a normal value so as to decrease the heat radiation for cooling.  
       [0009] The above-mentioned control is carried out being based at least upon a temperature of engine cooling water or a temperature of the catalyst. These temperatures are detected by a water temperature sensor and a catalyst temperature sensor. Further, the temperature of the catalyst can be estimated or computed from an engine speed, a load, an ignition timing, an EGR quantity, an intake air quantity and an intake air temperature, a distance from the engine to the catalyst, the thermal capacity (a number of cells or a volume) of the catalyst and the like.  
       [0010] Further, according to the first aspect of the invention, there is proposed a control system for controlling the engine in such a way that the heat radiation for cooling is minimized during activation control of catalyst until the catalyst is activated while the cooling loss is maximized during control of warm-up of the engine until the engine is warmed up after the activation of the catalyst.  
       [0011] With the above-mentioned control, the engine and the catalyst can be warmed up in a short time, thereby it is possible to restrain the environmental contamination caused by exhaust gas and to enhance the fuel economy.  
       [0012] Further, according to the first aspect of the present invention, the ignition timing is retarded from the normal timing if the catalyst temperature is lower than its activation temperature while the ignition timing is advanced from the normal timing until the temperature of cooling water rises up to a temperature at which the warm-up of the engine is completed, after the catalyst temperature rises up to its activation temperature.  
       [0013] With the configuration as stated above, not only the activation of the catalyst but also the warm-up of the engine can be promoted. Further, the provision of a knock sensor for detecting knocking of the internal combustion engine is desirable so that the ignition timing is retarded when the knock sensor detects a knock during ignition timing control, and further, the flow rate of the cooling water by the water pump is increased in order to promote the warm-up of the internal combustion engine in a sure and safe manner.  
       [0014] According to a second aspect of the present invention, there is provided a control system for an internal combustion engine having a turbocharger for supercharging intake air in the internal combustion engine and a cooling passage for cooling the turbocharger, incorporating a valve for controlling a flow rate of cooling water flowing through the cooling passage, in order to control the valve so as to reduce the flow rate of the cooling water flowing through the cooling passage if the temperature of catalyst is not greater than an activation temperature thereof, thereby it is possible to promote the activation of the catalyst.  
       [0015] Further, according to a third aspect of the present invention, there is provided a control system for an internal combustion engine including a transmission for transmitting a power from the internal combustion engine, an oil cooler for cooling oil lubricating the transmission and a cooling passage for cooling the oil cooler, comprising a shut-off valve for shutting off the cooling passage, wherein the shut-off valve is controlled so as to stop the flow of the cooling water in the cooling passage if a temperature of catalyst is not greater than its activation temperature, thereby it is possible to promote the activation of the catalyst.  
       [0016] Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.  
       [0017] The present invention will be hereinbelow detailed in the form of preferred embodiments with reference to the accompanying drawings in which: 
     
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING  
     [0018]FIG. 1 is a block diagram of the present invention:  
     [0019]FIG. 2 is a conceptual diagram for explaining a cooling loss and a heat radiation for cooling in the present invention;  
     [0020]FIG. 3 is a diagram showing a relationship between an EGR quantity and a cooling loss;  
     [0021]FIG. 4 is a diagram showing a relationship between an ignition timing during combustion by spark ignition, and cooling loss;  
     [0022]FIG. 5 is a diagram showing a relationship between a fuel injection timing and a cooling loss during combustion by compression ignition;  
     [0023]FIG. 6 is a diagram showing a relationship between a flow rate of cooling water in an engine, and a heat radiation for cooling;  
     [0024]FIG. 7 is a diagram showing a relationship between a water temperature of cooling water in an engine and a heat radiation for cooling;  
     [0025]FIG. 8 is a control flow-chart for a temperature controller;  
     [0026]FIG. 9 is a view illustrating an engine system in a first embodiment of the present invention;  
     [0027]FIG. 10 is a diagram illustrating a control flow-chart in the embodiment shown in FIG. 9;  
     [0028]FIG. 11 is a view illustrating an example of a time-chart in an application of the present invention;  
     [0029]FIG. 12 is a diagram showing a relationship between a desired value of the flow rate of cooling water, and a heat radiation for cooling;  
     [0030]FIG. 13 is a diagram showing a relationship between a desired value of the ignition timing, and a cooling loss;  
     [0031]FIG. 14 is a view illustrating an engine system in a second embodiment of the present invention;  
     [0032]FIG. 15 is a control flow-chart in the embodiment shown in FIG. 14;  
     [0033]FIG. 16 is a time-chart during execuation of the control shown in FIG. 15;  
     [0034]FIG. 17 is a view illustrating an engine system in a third embodiment of the present invention;  
     [0035]FIG. 18 is a control-flow chart in part in the embodiment shown in FIG. 17; and  
     [0036]FIG. 19 is a time-chart during execution of the control shown in FIG. 15. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION  
     [0037] The present invention will be hereinbelow made of embodiments of the present invention with reference to the accompanying drawings.  
     [0038] Referring to FIG. 1 which is a block diagram illustrating a control system for an intern combustion engine, in accordance with an embodiment of the present invention, a temperature controller  101  carries out temperature control of the engine and catalyst (which is aim at purifying exhaust gas from the engine) so as to aim for early warm-up of both engine and catalyst during a cold start of the engine.  
     [0039] Signals indicating a temperature of the catalyst, a temperature of cooling water and knocking, which are detected by sensors, are received by the temperature controller  101  which therefore computes a desired heat radiation for cooling, and a desired cooling loss in order to control an engine cooling system. The cooling loss and the heat radiation for cooling will be detailed after the configuration shown in FIG. 1 is briefly explained.  
     [0040] The desired heat radiation for cooling is delivered to a cooling system controller  102  while the desired cooling loss is delivered to an engine controller  103  for controlling the combustion of the engine.  
     [0041] Further, the cooling system controller  102  controls a water pump in the engine cooling water passage, a flow passage control valve, a radiator and the like in accordance with the desired heat radiation for cooling so as to control the value of heat radiation for cooling. Meanwhile, the engine controller  103  controls intake and exhaust valves, a fuel injection valve an ignition unit, an EGR valve and the like in accordance with the desired cooling loss so as to control the cooling loss.  
     [0042] The temperature controller  101 , the cooling system controller  102  and the engine controller  103  may be constituted by, for example, a control unit C.  
     [0043] The essential feature of the present invention is the provision of the control of the cooling loss and the heat radiation for cooling in accordance with at least either one of a temperature of the catalyst and a temperature of cooling water, and an object of the present invention is to materialize both early activation of the catalyst and early warm-up of the internal combustion engine.  
     [0044] Explanation will be hereinbelow made of the cooling loss and the heat radiation for cooling in detail with reference to FIG. 2 which shows the transmission of heat which is generated from a combustion chamber  1  in the engine and which is then transmitted to cooling water  2 .  
     [0045] The cooling loss in the present invention is a heat value with which a heat generated from the combustion gas in the combustion chamber (cylinder)  1  of the engine is transmitted to an engine block  3 . The cooling loss relates to an averaged temperature Ta and a temperature to the engine block  2  during engine cycles (intake cycle, compression cycle, expansion cycle and exhaust cycle) carried by a piston  4 , and in particular to those during a period from the compression cycle to the exhaust cycle. Thus, it is understood that the cooling loss significantly relates to the combustion. As shown in FIG. 3 which shows, as an example, the relationship between an EGR (exhaust gas recirculation) value and the cooling loss, an increase in the EGR value causes the averaged temperature Ta to lower since a possible maximum combustion temperature is lowered. Thus, the cooling loss can be controlled by adjusting the EGR value through the control of the EGR valve and the intake and exhaust valves.  
     [0046] Further, the averaged temperature also relates to an ignition timing, and accordingly, the cooling loss can be controlled by the ignition timing during combustion by spark ignition, as shown in FIG. 4, and it can be controlled by an injection timing during combustion by compression ignition (Diesel combustion or combustion by premix self-ignition), as shown in FIG. 5.  
     [0047] Meanwhile, the heat radiation for cooling, concerned in the present invention, is a heat value transmitted from the engine block  3  to the cooling water  2 . The heat radiation for cooling mainly relates to a flow rate and a temperature of the cooling water  2 .  
     [0048] Referring to FIG. 6 which shows an example of the relationship between the flow rate of the cooling water and the heat radiation for cooling, the relationship between the flow rate and the heat radiation for cooling, as shown in FIG. 6, exhibits, the higher the flow rate, the greater the heat radiation for cooling. Further, referring to FIG. 7 which shows a relationship between the temperature of the cooling water and the heat radiation for cooling, if the temperature of the engine block is constant, the lower the temperature of the cooling water, the greater the heat radiation for cooling. Thus, the heat radiation for cooling can be controlled by a discharge quantity of the water pump or by a radiator for radiating a heat from the cooling water into the atmospheric air.  
     [0049] Further, another feature of the present invention, is the provision of the control for the heat radiation for cooling and the cooling loss in accordance with a temperature of the catalyst and a temperature of the cooling water.  
     [0050]FIG. 8 shows a flow-chart as to the temperature controller  101 .  
     [0051] Referring to FIG. 8, at step  801 , outputs from a catalyst temperature sensor, a water temperature sensor and the like are transmitted to the controller  101 .  
     [0052] At step  802 , the catalyst temperature is compared with a catalyst activation temperature at which the catalyst can purify exhaust gas, and if the catalyst temperature is not less than the catalyst activation temperature, step  804  is carried out, but if it is false, step  803  is carried out.  
     [0053] At step  803 , a desired heat radiation for cooling is minimized. It is noted here that the minimum desired heat radiation for cooling corresponds to a minimum value in a controllable range. Due to this minimum control of the heat radiation for cooling, the heat value transmitted to the cooling water is decreased while the temperature of exhaust gas is increased so as to enable early warm-up of the catalyst, that is, it is possible to fast raise the temperature of the catalyst up to the activation temperature in comparison with the conventional one. A specific example of the minimum control of the heat radiation for cooling will be described later.  
     [0054] At step  804 , whether the temperature of engine cooling water comes up to a warm-up temperature at which the engine can be efficiently operated as usual or not is determined, and if it is true, step  806  is carried out, but if it is false, step  805  is carried out.  
     [0055] At step  805 , the desired cooling loss is set to be maximum. As a result, the heat value transmitted to the engine block is increased, and further, since the heat radiation for cooling is minimized, the engine can be warmed up fast in comparison with a conventional one. The maximum control of the heat radiation for cooling will be described later. It is noted here that the maximum of the cooling loss corresponds to a maximum value in a controllable range.  
     [0056] At step  806 , whether the water temperature is not lower than an overheat temperature at which there would be a risk of occurrence of seizure of the engine, or not is determined, and if it is true, step  805  is carried out, but if it is false, step  807  is carried out. At step  807 , optimum fuel consumption control is carried out and the desired cooling loss is minimized.  
     [0057] It is noted that the desired cooling loss is in a controllable range, and it indicates a position of optimum spark advance (optimum spark ignition timing) as shown in FIG. 4 if the cooling loss is controlled only by the spark ignition timing. This optimum spark ignition timing enables the engine to operate with a high degree of efficiency.  
     [0058] At step  808  at which control is made for an abnormal operation, that is, the desired heat radiation for cooling is maximized so as to carry out cooling of the engine block by the cooling water at a maximum degree in order to prevent occurrence of seizure of the engine.  
     [0059] Referring to FIGS.  9  to  12 , a specific control example in this embodiment will be explained.  
     [0060]FIG. 9 is a view which shows a configuration of the engine in this embodiment.  
     [0061] In this example, a cooling system for an engine  5  is composed of a cooling water circulation passage  6 , a water pump  7  for controlling heat radiation for cooling in the cooling system, a water temperature sensor  8  for measuring a temperature of cooling water, a radiator  9  for radiating heat from the cooling water into the atmospheric air, a radiator fan (which is not shown) for controlling the radiation of heat from the radiator into the atmospheric air, and a flow passage change-over valve (thermostat)  10  for introducing cooling water.  
     [0062] Further, catalyst  12  ( 3  way catalyst) for purifying exhaust gas and a catalyst sensor  13  for detecting a temperature of the catalyst are incorporated in an exhaust pipe  11  of the engine. Further, there is provided a knocking sensor  14  for detecting knocking of the engine.  
     [0063] Referring to a flow-chart shown in FIG. 10, explanation will be hereinbelow made of control for early warm-up of both catalyst  12  and engine  5 .  
     [0064] At step  1001 , outputs from the catalyst temperature sensor  13 , the water temperature sensor  8  and the knocking sensor  14  are read.  
     [0065] At step  1002 , whether a value detected by the catalyst temperature sensor  13  is not less than the activation temperature of the catalyst or not is determined, and if it is true, step  1004  is carried out, if it is false, step  1003  is carried out.  
     [0066] At step  1003 , the water pump  7  is stopped while the ignition timing is retarded in order to fast warm up the catalyst  12 . As the water pump  7  is stopped, the heat radiation for cooling to cooling water becomes minimum so as to aim at raising the temperature of the engine  5 , and further, the temperature of exhaust gas from the engine is raised through the control of retardation of the ignition timing. As a result, it is possible to aim for early warm-up of the catalyst. It is noted that the retardation of the ignition timing may decrease the cooling loss, as shown in FIG. 4, but may not minimize the cooling loss. Although the cooling loss is minimized at a position where the ignition timing is optimum, but in-this case, since efficient combustion is carried out, the temperature of exhaust gas may not be raised as is made through the control of retardation.  
     [0067] At step  1004 , whether a value of engine cooling water detected by the water sensor  8  reaches the warm-up temperature of the engine  5  or not is determined, and if it is true, step  1006  is carried out, but if it is false step  1005  is carried out.  
     [0068] At step  1005 , in order to warm up the engine  5 , the ignition timing is advanced so as to raise the temperature of the engine cylinder. At this time, through the control of the cooling system, the stop and the operation of the water pump  7  are repeated or the discharge rate of the pump  7  is controlled to be minimum although it is operated.  
     [0069] Through the circulation of cooling water at a small rate as mentioned above, it is possible to prevent occurrence of thermal stress in the engine block and knocking due to a hot spot in the engine cylinder.  
     [0070] At step  1006 , it is determined that whether a value detected by the water temperature sensor or an estimated value of the temperature of the engine is not less than an overheat temperature at which the seizure of the engine is expected, or not. If it is true, step  1008  is carried out, but if it is false, step  1007  is carried out. At step  1007 , control for minimizing the fuel consumption is carried out. Thus, the ignition is controlled at an ignition timing with which the cooling loss is minimized, and the pump is controlled so that the temperature of cooling water becomes not less than the warm-up temperature but not greater than the overheat temperature at which the seizure of the engine occurs.  
     [0071] It is noted that a temperature of the engine is estimated from the cooling loss and the heat radiation for cooling, and if the history of temperature of the engine exhibits an increase while the engine load is high, foreseeing control through which the flow rate of cooling water increases in advance may be carried out. In this foreseeing control, if the history of temperature of the engine exhibits a decrease while the engine load is low, the flow rate of cooling water is decreased in advance, or the circulation of cooling water into the radiator may be stopped.  
     [0072] At step  1008 , control upon overheating is carried out, that is, the flow rate of cooling water from the pump  7  and the output of the radiator are maximized so as to increase the heat radiation for cooling in order to prevent occurrence of seizure of the engine. Further, if the temperature is not lowered within a predetermined time after the above-mentioned controlled is carried out, the ignition timing is retarded so as to also decrease the cooling loss. Further, since the overheating is caused by any abnormality in the cooling system including the radiator and the pump, a warning lamp is turned on for indication of requirement for a fault diagnosis.  
     [0073] As to the fault diagnosis, if, for example, a water temperature is higher than an overheat temperature while the engine is operated at an idle speed, the radiator fan is operated being alternately changed over between a highest speed and a lowest speed (including a stop), every predetermined time. At this time, a fault diagnosis for the radiator can be made in accordance with a speed of the radiator fan and a variation in the output of the water temperature sensor. Specifically, a correlation between the speed of the radiator fan and a variation in the output of the water temperature sensor is calculated, and if the thus calculated correlation is small, it can be determined that the radiator or the thermostat fails.  
     [0074] Similarly, by changing over the output of the pump every predetermined time between a high output power and a low output power, it is possible to carry out a fault diagnosis of the pump in accordance with a correlation between a variation in temperature of cooling water and a control input to the pump. Specifically, a correlation between a control input of the pump and a variation in the output of the water temperature sensor is calculated, and if this correlation is small, it can be determined that the pump fails.  
     [0075] Referring to FIG. 11 which shows an example of a time-chart in the case of execution of the warm-up control for both catalyst and engine, according to the present invention, during warm-up of the catalyst until the temperature of the catalyst comes up to its activation temperature, the ignition timing is retarded, and the pump is stopped so as to set the flow rate to zero. During warm-up of the engine after activation of the catalyst, the ignition timing is advanced, and if knocking is detected, the ignition timing is retarded while the flow rate of the pump is increased in order to prevent occurrence of abnormal combustion.  
     [0076] After completion of the warm-up of the engine, the pump is operated in a steady-state, and also the ignition timing is reset to a normal position.  
     [0077] Referring to FIG. 12 which shows control objectives of the flow rate in the control according to the present invention, cooling water is blocked until the warm-up of the catalyst is completed so as to minimize the heat-radiation for cooling, and after completion of the warm-up of the catalyst, the flow rate of cooling water is controlled so as to be low as possible as it can until the warm-up of the engine is completed. After the completion of the warm-up of the engine, the flow rate is controlled in accordance with a value of the heat radiation for cooling, thereby it is possible to optimumly materialize early warm-up of the catalyst and the engine.  
     [0078] Further, referring to FIG. 13 which shows control objectives of the ignition timing in the control according to the present invention, optimum early warm-up can be materialized by retarding the ignition timing at one and the same engine speed during warm-up of the catalyst but by advancing the ignition timing up to a knocking critical value during warm-up of the engine after completion of the warm-up of the catalyst, with respect to a normal ignition timing after completion of the warm-up. That is, if the ignition timing is retarded, after-burning is caused in exhaust gas discharged from the cylinder of the engine, and accordingly, the temperature of the exhaust gas becomes higher, thereby it is possible to aim for early warm-up. At this time, although the cooling loss is small, it is, more or less, greater than that with the normal ignition timing (efficiency drive) after completion of the warm-up.  
     [0079] Referring to FIGS.  14  to  16 , explanation will be hereinbelow made of a second embodiment of the present invention.  
     [0080] Referring to FIG. 14 which shows the configuration of an engine in the second embodiment, this configuration is the same as that shown in FIG. 9, except that there are provided a turbocharger  15  for supercharging the intake air in an exhaust pipe  11 , a cooling passage  6   a  for cooling the turbocharger  15 , a bypass passage  6   b  bypassing the cooling passage  6   a,  and a bypass valve  16  for blocking the flow in the bypass flow passage  6   a.    
     [0081] The cooling passage  6   a  and the bypass passage  6   b  are alternately connected to the engine cooling passage  6  through switching control of the bypass valve  16 .  
     [0082] Referring to FIG. 15 which is a control flow-chart of the bypass valve  16  in this embodiment, at step  1501 , a value from the catalyst temperature sensor  13  is read, and at step  1502 , whether the temperature of the catalyst is greater than an activation temperature thereof or not is determined. If it is true, step  1504 , the bypass valve  16  is closed (default). Meanwhile, it is false, at step  1503 , the bypass valve  16  is opened so as to bypass cooling water flowing through the turbocharger  15  during warm-up of the catalyst.  
     [0083] Referring to FIG. 16 which shows a time-chart in the case of execution of the control according to the present invention, during warm-up of the catalyst, by opening the bypass valve  16 , the lowering of the temperature of exhaust gas, which is caused when the exhaust gas passes through the turbocharger, can be minimized, thereby it is possible to fast warm-up the catalyst. It is noted that even during warm-up of the engine, if a relief valve for bypassing the flow of exhaust gas flowing into a turbo-turbine is closed, no cooling is required for the turbocharger, and accordingly, the bypass valve  16  may be opened.  
     [0084] Referring to FIG. 17 which shows a third embodiment of the present invention, the configuration of this embodiment is the same as that shown in FIG. 9, except that there are provided an oil cooler  18  for cooling a transmission  17 , a cooling passage  6   c  for cooling the oil cooler  18  and a shut-of valve  19  for blocking the cooling passage  6   c.    
     [0085] Referring to FIG. 18 which shows an control flow-chart of the shut-off valve  19  in this embodiment, at step  1801 , a value from the catalyst temperature sensor  13  is read, and at step  1802 , whether the catalyst temperature is not less than its activation temperature or not is determined. If it is true, at step  1804 , the shut-off valve  19  is opened, but if it is false, at step  1803 , the shut-off valve  19  is closed.  
     [0086] Referring to FIG. 19 which shows a time-chart in the case of execution of the control according to the present invention, during warm-up of the catalyst, the shut-off valve  19  is closed so as to shut-off the flow of cooling water flowing through the oil cooler  18  in order to decrease the heat radiation for cooling, and as a result, the exhaust temperature rises up, thereby it is possible to fast warm up the catalyst.  
     [0087] According to the present invention, by controlling the cooling system in accordance with a catalyst temperature, the catalyst can be fast activated. Further, in combination of the control of the cooling system for the engine or the like with the control of the engine, the warm-up of the catalyst can be made prior to the warm-up of the engine while aiming at warming up both the catalyst and the engine. Thus, with the application of the present invention, it is possible to reduce emission of exhaust gas due to early activation of the catalyst, and to improve the fuel consumption due to early warm-up of the internal combustion engine.  
     [0088] It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.