CA1047337A

CA1047337A - Method and an apparatus to control the temperature of an engine exhaust gas purifying device

Info

Publication number: CA1047337A
Application number: CA252,575A
Authority: CA
Inventors: Yukio Miyamori; Kenji Masaki
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1975-05-16
Filing date: 1976-05-14
Publication date: 1979-01-30
Also published as: GB1500882A; FR2311180B1; FR2311180A1; JPS51136039A; AU1373076A; DE2621609A1

Abstract

Abstract of the Disclosure The temperature of an exhaust gas purifying device is maintained within an optimum range by enriching an air-fuel mixture for the engine, retarding the ignition timing of the engine, supplying secondary air into engine exhaust gases fed to the purifying device and producing a spark therein when the temperature of the purifying device is below the minimum of the optimum range and by diluting the air-fuel mixture, advancing the engine ignition timing to a normal value, stopping supply of the secondary air and production of the spark when the temperature of the purifying device is higher than the maximum of the optimum range.

Description

~0~337 The present invention relates generally to a method of and an apparatus for controlling the per-formance of an exhaust gas purifying device of an engine to a desired value and particularly to a method of and an apparatus for maintaining the temperature of the exhaust gas purifying device within a desired or optimum temperature range in which the exhaust gas purifying device perform~ most satisfactorily to purify exhaust gases of the engine.
As is well known in the art, internal combustion engines are now provided with an exhaust gas purifying device such as a thermal or catalytic reactor which oxidi~es burnable noxious components such as hydro-carbons (HC) and carbon monoxide ~C0) contained in exhau~t gases emitted from the engine and renders the burnable components into water (H20) and carbon dioxides (C02). The production of nitrogen oxides (N0x) contained in the engine exhaust gases can be reduced by employing a rich or lean air-fuel mixture having an air-fuel ratio lower or higher than a stoichiometric air-fuel ratio.
In this instance, the rich air-fuel mixture is usually cmployed becau~e the lean air-fuel mixture is difficult to ignite and burn in engine combustion chambers.
Howe~er, by use of the rich air-fuel mixture, the content of the burnable components in the engine exhaust

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gases is increased to promote the combustion of the engine exhaust gases in the reactor to increa~e the temperature of the reactor to, for example, above l,O00C. As a result, there has been a danger that the reactor is heated above its heat resistance limit and is damaged by heat and/or the reactor body is burned and discharged to the atmosphere to cause secondary public nuisance. Furthermore, the use of the rich air-fuel mixture results in lncrease in the rate of fuel consumption. :`' . On the other hand, it is necessary for combustion of the burnable components in the reactor to maintain the temperature in the reactor above a predetermi11ed level such as, for example,~~~,OOO ~-. When the temperature ~ 15 f the reactor is below the predetermined level the ; reactor cannot satisfactorily function to purify the engine exhaust gases and allows discharge of engine exhaust gaseS containing large quantities of burnable noxious components into the atmosphere. Accordingly, when the temperature in the reactor is below the prede-termined level as during starting operation of the engine, it is necessary to increase the temperature of the reactor above the predetermined level as quickly as possible.
It is, therefore, an obJect of the invention to ,~

33~7 provide a method of and an apparatus for maintaining the temperature in an exhaust gas purifying device of an engine within a desired or optimum temperature range in which the purifying device most satisfactorily purifies exhaust gases from the engine by controlling the air-fuel ratio ofan air-fuel mixture to be burned in a combustion chamber of the engine, the ignition timing of the engine, the amount of secondary air fed into the engine exhaust gaces and the ignition of gases in the exhaust gas purifying device so that the exhaust gas purifying device is prevented from being ; undesirably or excessively heated and from being burned to prevent occurrence of secondary public nuisance, the rate of f~el consumption i~ reduced, and the temperature ln the exhaust gas purify.ing device is increased in a minimum time to a predetermined level necessary to purify the engine exhaust gases.
This and other objects and advantages of the ~:
lnvention will become.more apparent from the following d~tailed description taken in connection with the ~ccompanying drawing which is a schematic view of a preferred embodiment of a combination of an engine and Rn apparatus for carrying out a method according to the . 1nvetltion.

~ Referring to the drawing, there is shown an internal ' ~' 33~

combustion engine 10 and an apparatus 11 for carrying out a method according to the invention and which is combined with the engine 10. The engine 10 comprises intake and exhaust system~ 12 and 14. The intake system 12 includes an induction passage or conduit 16 communi-cating with the atmosphere through an air cleaner 18 and with a combustion chamber (not shown) of the engine 10 for feeding air and an air-fuel mixture into the combustion chamber, and a carburetor ?0 including a part of the induction passage 16.
The carburetor 20 include.~ a throttle valve 21 rotatably mounted in the induction passage 16, a fuel bowl or float chamber 22 containing liquid fuel 24, a main fuel passage 26 communicating with the fuel bowl 22, a main nozzle 28 which communicates with the main fuel passage 26 and which opens into a choke or venturi 30 formed in th0 induction passage 16, a main air bleed 3Z ~ented to the atmosphere and communicating with the main fuel passage 26 to feed thereinto air for emulsi- :
fication of fuel fed to the main nozzle 28, a qlow running fuel passage 34 branching from the main fuel passage 26 and communicating with a slow running nozzle or port ~6 opening into the induction passage 16 at a position immediately downstream of the throttle valve 21 in its fully closed position, and a slow running air : :' ~7337 bleed ~8 vented to the atmosphere and communic~ting with the slow running fuel passage ~ to feed thereinto air for emulsification of fuel fed to the slow running port 36. The emulsified fuel is drawn into the induction passage 16 through the main nozzle 28 and/or the slow :~ running port ~6 by air passing in the induction passage 16 and is mixed with the air to form an air-fuel mixture fed into and burned in the combustion chamber. An intake mani~old 40 for~ing part of the induction passage 16 opens into the combustion cha~ber~
The exhaust system 14 includes an exhaust gas passage or conduit 42 communicating with an exhaust port (not shown) of the combustion chamber and vented ~:
to the ambient atmosphere, an exhaust'manifold 44 extending from the exhaust port and forming part of the exhaust gas pas~age 42, and an exhaust gas treating device 46 such as a thermal reactor or a catalytic con~erter or reactor which is disposed in the exhaust gas passage 42 at a position adjacent to the exhaust port. The exhaust gas purifying device 46 serves to effect oxidation of burnable components such as hydro-carbons (HC? and carbon monoxide (C0) contained in exhaust gases emitted from the engine 10 and to render the burnabl0 components into water (H20) and carbon : :
dioxides (C02). The exhaust gas reburning device 46 is : :

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7~37 as~umed to be a thermal reactor in this embodiment.
The engine 10 is provided with an exhaust gas . recirculation (EGR) syst~m 48 for recirculating or ~eeding engine exhaust gases into the combustion chamber through the induction passage 16 to lower the temperature of combustion in the combustion chamber to reduce the amount of nitrogen oxides (N0x) produced by combustion of an air-fuel mixture therein. The EGR system ~8 includes an EGR passage or conduit 50 branching from the exhaust gas pas~age 42 at a position upstream of or downstream of the thermal reactor 46 and terminating in the induction passage 16 at a position downstream of the throttle valve 21, and a flow control valve 52 disposed in the EGR passage 50 and operable to control or meter the flow rate of en~ine exhaust gases fed into the induction passage 16 to a predetermined ratio to the flow rate of air drawn into the combustion chamberO
The flow control valve 52 includes an actuator 54 having ~ flex.tble diaphragm 56 which is operatiYely connected to the flow control valve 52 and is operated or deformed ln response to the vacuum in the induction passage 16 at n position downstream of the throttle valve 21 which vacuum is fed through a passage or conduit 58 to the dinphragm 56. Th~ a¢tuator 51~ operate9 the flow control valve 52 with the diaphragm 56 in such a manner as to .
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3~7 increase and reduce the degree of opening of the valve 52 in accordance with decrease and increase in the induction passage vacuum, respectively.
The apparatus 11 serves to maintain the temperature of the combustion temperature in the exhaust gas treat-ing device 46 within a desired or optimum temperature range within which the device 46 treats or purifies the r~sf engine exhaust gases ~satisfactorily or efficiently :~ :
to maximi~e the amount of the burnable components rendered harmless and is simultaneously prevented from being damaged by undesirably high temperatureS~*nre~
The optimum temperature range is assumed as, for example, oO0 to 900 C in this embodiment. The minimum and maximum -~
(800C and 900 C) of the predetermined temperature range i are hereinafter referred respectively to as first and ~ocond desired temperatures or levels. The apparatus 11 comprises an air-fuel ratio control device 60 or a combination of the device 60 and one or more of an ignition timing control device 62, a secondary air supply control device 6~, and an exhaust gas ignition control device 66.
Th~ air-fuel ratio control device 60 comprises sensin~ means 68 such as a thermistor or thermocouple . which is located in the reactor 46 or on an external wall surface thereof or in the exhaust gas passage 42 ' .

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'733~7 at a position adjacent to and downstream of the reactor l~6. The sensor 68 senses the temperature or combustion temperature in the reactor 46 or a te~perature corres-ponding to or representing the temperature or reaction temperature thereof and generates an electric output sisnal having a value representing the sensed temperature and is electrically connected to a control circuit 70 to apply the temperature ~ignal thereto. The comparator circuit 70 compares the value of the temperAtUre signal with first and second reference values corresponding respectively to the first and second desired temperatures and generates first and second electric error signals when the value of the temperature signal is smaller ~nd larger than the first and second reference values, respectively. The air-fuel ratio control device 60 also comprises first and second auxiliary air bleeds 72 and 74 for feeding respectively in*o the main and slow running fuel passages 26 and ~4 additional air for mixing with or emulsifying fuel therein. The auxiliary air bleeds 72 and 74 open into the atmosphere through inlet ports 76 and 78 and include therein control valves 80 and 82 for closing and opening the auxiliary air bleeds ~-~h~ 72 and 74 to separate the main and slow running fuel passages 26 and 34 from the inlet ports ~6 and 78, respectively. The control valves 80 and 82 .
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~ a'7~37 are provided respectively with solenoids 84 and 86 ~or operating same and which are electrically connected to the comparator circuit 70 to receive therefxom the first and second error signalsO The solenoids 84 and 86 cause the con-trol valves 80 and 82 to close the auxiliary air bleeds 72 and 74 in response to the first error signal and to open the auxiliary air bleeds 72 and 74 in response to the second error signal.
The combination of the engine 10 and the air-fuel ratio control device 60 thus far described is operated as follows:
The emulsified fuel is drawn from the main and/or slow running nozzle 28 and/or 36 into the induction passage 16 and is mixed with air therein to form an air fuel mixture which is drawn into and burned in the combustion chamber. When the sensor 68 senses the reaction temperature in the reactor 46 being less than the first desired temperature, the control valves 80 and 82 close the auxiliary air bleeds 72 and 74 in response to the first error signal of the comparator circuit 70 so that the amount of fuel fed from the main and slow running fuel passages 26 and 34 into the induction passage 16 is increased by the amount of air not fed from the auxiliary air bleeds 72 and`74 to form an enriched air-fuel mixture. This causes an increase in the content of burnable components , .

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-10- , 7~337 in the engine exhaust gases to intensi~y the cor~ustion of the - engine exhaust ~ases in the reactor 46 in increase the com-_ bustion temperature therein. When the sensor 68 senses the combustion temperature in the reactor 46 being increased above the second desired temperature, the control circuit 70 generates the second error signal in response to which the control valves J 80 and 82 open the auxiliary air bleeds 72 and 74 to reduce the amount of fuel fed from the main and slow running fuel passages ! 26 ancl 34 into the induction passage 16 by the amount of air fed from the auxiliary air bleeds 72 and 74 to form a diluted or ;~ lean air-fuel mixture. As a result, the content of the burnable components in the engine exhaust gases is reduced to reduce the intensity of combustion of the engine exhaust gases in the reactor 45 to reduce the reaction temperature therein. By repetition of the above-mentioned operation, the reaction temp-erature in the thermal reactor 46 is maintained at the optimum temperature range.
, The ignition timing control device 62 comprises a primary circuit 88 including an electric power source 90, an ignition switch 92, an ignition coil 94 and a usual or normal ~ ignition timing breaker contact 96 of an ignition distributor i~ 98, a secondary circuit 100 including the ignition coil 94 and a high voltage , _ 30 :, : . ; -~ V~ d .~ 3 7 current distributor 102 of the ignition distributor 98, th0 sensor 68~ the comparison circuit 70, and an i~nition timing retarding circuit 104 including a relay switch 106 and a retarding breaker contact lOo connected in ~eries to each other. The ignition timing retarding ; . circuit 104 is connected to the comparison circuit 70 r~fe~ rc~
and ln parallel to the primary circuit 88. The ~i~g J
breaker contact 108 is set to be opened later than the usual ignition timing breaker contact 96 at every cycle of the engine 10. When the relay switch 106 is opened, the engine 10 is ignited at a normal timing by the u~ual breaker contact 96 at e~ery cycle. ~ :
The combination of the engine 10 and the ignition timing control device 62 thus far described is operated as follows:
When the sensor 68 senses the reaction temperature in the reactor 46 being lower than the first desired lcvel, the relay switch 106 is supplied with the first error signal from the control circuit 70 and is closed to complete the ignition timing retarding circuit 104.
Since the retarding breaker contact 108 is connected : in parallel with the normal breaker contact 96 due to the completion of the circuit 104, a high voltage is not yet generated in the secondary circuit 100 so as not to produce a spark in the combustion chamber when ' .

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the normal ignition timing breaker sontact 96 is opened and the retarding breaker contact 108 is still closed.
The high voltage is generated in the secondary circuit 100 to produce the spark in the combustion chamber when the retarding breaker contact lOo is opened with a time lag after the usual breaker contact 96 has been opened.
Accordingly, when the ignition timing retarding circuit 104 is completed, the ignition timing of the engine 10 is retarded by the time lag as compared with when the engine ignition i8 effected at the normal timing by the usual breaker contact 96. The delay in the ignition timing causes lengthening of combustion time in the engine combustion chamber to increase the temperature of the engine exhaust gases and accordingly the reaction lS temperature in the reactor 46. As a result, when the ~ensor 68 senses the combustion temperature in the reactor 46 being increased aboYe the second desired level, the relay switch 106 is supplied with the second error ~ignal from the comparator circuit 70 so that it i9 opened to open the ignition timing retarding circuit 10l~ to restore the ignition timing into a normal con-dition. This causes shortening of the combustion time in the engine combustion chamber to reduce the tem-perature of the engine exhaust ga~es. By repetition f the above-mentioned operation, the reaction temperature .
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~, in the r~ 46 is maintained at the optimum tem-perature range.
The secondary air supply control device 64 com-prises an air pump 110 to discharge ~econdary air under presqure, passage means 112 communicating at one end with a discharge port of the air pump 110 and opening at the other end into the exhaust gas passage ~2 at a position upstream of the exhaust gas treating de~ice 46 through an injecting no2zle 114, a flow path control valve 116 for alternatively communicating the upstream i part 112a of the passage means 112 with the downstream part 112b of the passage means 112 and with the atmos-phere in accordance with the error signals, and branch passage means 118 communicating at one end with the up~tream part 112a through the control valve 116 and opening at the other end into the air cleaner 18. The control valve 116 includes an actuator such as a solenoid (not shownj electrically connected to the control circuit 70 to receive the error signals therefrom and operates th~ control valve 116 to communicate the upstream part 112a with only the downstream part 112b in response to the fir~t error signal and with only the branch passage means 118 in response to the second error signal.
Th2 combination of the engine 10 and the secondary air s-~ppIy control device 64 thus far described is .
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When the sensor 68 sen~es the combustion temperature in the reactor 46 being lower than the firs-t desired levell the control valve 116 is operated in response to the first error signal from the control circuit 70 to communicate the air pump 110 with the exhaust gas passase 42 to supply secondary air thereinto so that the combustion of the burnable components in the engine exhaust gases in the reactor 46 is promoted to cause increase in the combustion temperature in the reactor 46. As a result, when the sensor 68 senses the com-bu~tion temperature in the reàctor 46 being increased hi~her than the second desired level, the control valve 116 is operated in response to the second error signal from the control circuit 70 to switch over connection o~ the upstream part 112a from the downstream part 112b to the branch passage means 118 ko stop supply of second~ry air into the exhaust gas passage 42 and to divert secondary air to the air cleaner 18. Aq a result, the intensity o~ the combustion in the reactor 46 is reduced to bring the reaction temperature in the ~-eactor 46 into the desired temperature range. ~y repetltion of the above-mentioned operation, the reaction temperature in the reactor 46 is maintained within the desired temperature range.

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The exhau~t ga~ ignition control device 66 comprises a spark plug 120 located in the reactor ~6, and a high voltage generator 122 electrically connected to the spark plug and to the control circuit 70 to receive : 5 the error signals therefrom The combination of the engine 10 and the exhaust gas ignition control device 66 thus constructed is operated as follows:
When the sensor 68 senses the combustion temperature in the reactor 46 being less than the ~irst desired vAl~e, the high ~oltage generator 122 generates a high voltage in response $o the first error ~ignal from the control circuit 70 so that the spark plug 120 provides a spark in the reactor 46 to facilitate igni-tion of and promote combustion of the engine exhaust gases in the reactor 46 to cause increase in the combus-tion temperature in the reactor 46. In this instance, the spark plug 120 makes possible ignition of engi.ne exhaust gases resulting from an air-fuel mixture which is so lean that ignition of the exhaust gases is impossible unless a spark is provided by a spark plug. When the sensor 68 senses the combustion temperature in the reactor 46 being increased higher than the second desired value, the high voltage generator 122 stops generation of the high voltage in response to the second ' ' ' - 16 - ~

error signal from the control circuit 70so that the ; spark plug 120 ceases production of the spark to lighten combustion in the reactor 46 to reduce the combustion temperature in the reactor 46. By repetition of the above-~entioned operation, the combustion temperature in the reactor 46 is maintained within the desired : temperature range.
Aq the result of the temperature in the reactor 46 being maintained at the desired range by providing the engine 10 with the device 60 or the combination of the device 60 and one or more of th~ devices 62, 64 and 66, the reactor 46 satisfactorily performs its furlcti.on of purifying the engine exhaust gases to reduce the content of the burnable noxious components therein to a sati5factory ~r minimum value. It is also preYented : from being undesirably heated and damaged or from being burned to eliminate the occurrence of secondary public nui~ance, and is heated or warmed up in a reduced or minimum time to a temperature necessary to purify the engine exhaust gases as during starting operation of the engine lOo Thus the engine 10 is supplied with a minimum of fuel to reduce the rate of fuel consumption.
It will be appreciated that the invention provides ~a method of maintaining the temperature in an exhaust gas purifying de~ice of an engine at a desired range .:
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which comprises the first step of enriching or diluting an air-fuel mixture for the engine when the temperature of the purifying d~vice is above or below the minimum or maximum of the desired range, or, the first step and one or more of the following, which includes: the second step of retarding or advancing the ignition timing of thè engine from or to a normal value, the third step of effecting or stopping supply of secondary air into the engine exhaust gases fed to the purifying device, and the fourth step of producing a spark in the purifying device or stopping production of the spark, when the temperature of the purifying device is above :
or below the minimum and maximum of the desired ra~ge, : -80 tha-t the purifying device most satisfactorily performs it~ function of purifying engine exhaust gases to reduce the contents of the burnable components therein to a satisfactory or minimum value. Thus the purifying device i9 prevented from being undesirably heated and from being burned to eliminate the occurrence of secondary -.
public nuisance and is heated in a reduced or minimum tlme to a temperature necessary to purify the engine exhaust gases, and the engine is supplied with a minimum of fuel to reduce the rate of fuel consumption, and .
that the invention provides an apparatus for carrying out rhe method, - la -:

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~7~7 With the secondary air supply control device 64, secondary air can be fed or drawn into the exhaust gas passage 42 by a vacuurn produced in the exhaust gas passage 42 or in a venturi formed therein in place of the air pump 110.
The exhaust gas treating device 46 rnay be merely an exhaust manifold which is provided therein with a port liner and serves to purify engine exhaust gases, in place of the thermal or catalytic reactor.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE

PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of maintaining the combustion temperature in an exhaust gas purifying device of an engine within a predetermined temperature range, comprising the steps of sensing a temperature representing said combustion temperature, generating a temperature signal having a value representing the sensed temperature, comparing said value of said signal with first and second reference values representing the minimum and maximum of said predetermined temperature range, respectively, generating a first error signal when said value of said temperature signal is less than said first reference value and a second error signal when said value of said temperature signal is greater than said second reference value, reducing the air-fuel ratio of an air-fuel mixture to be burned in a combustion chamber of said engine when said first error signal is generated to cause increase in the contents of burnable components in exhaust gases of said engine to intensify combustion of the engine exhaust gases in said exhaust gas purifying device to thereby increase said combustion temperature, and increasing said air-fuel ratio when said second error signal is generated to cause decrease in the content of said burnable components to reduce the intensity of said combustion of said engine exhaust gases to thereby reduce said combustion temperature.

2. A method as claimed in Claim 1, in which said step of increasing said air-fuel ratio is performed by supplying additional air for emulsifying fuel for forming said air-fuel mixture and said step of reducing said air-fuel ratio is performed by stopping supply of said additional air.

3. A method as claimed in Claim 1, further com-prising the steps of retarding the ignition timing of said engine when said first error signal is generated to cause lengthening of combustion time of said air-fuel mixture in said combustion chamber to increase the temperature of said engine exhaust gases to thereby increase said combustion temperature, and advancing the engine ignition timing to a normal value when said second error signal is generated to cause shortening of said combustion time to reduce the temperature of said engine exhaust gases to thereby reduce said com-bustion temperature.

4. A method as claimed in Claim 3, further com-prising the steps of supplying secondary air into said engine exhaust gases to be fed into said exhaust gas purifying device when said first error signal is generated to increase the intensity of combustion of said engine exhaust gases in said exhaust gas purifying device to thereby increase said combustion temperature, and stopping supply of secondary air into said engine exhaust gases when said second error signal is generated to reduce the intensity of combustion of said engine exhaust gases in said exhaust gas purifying device to thereby reduce said combustion temperature.

5. A method as claimed in Claim 4, further comprising the steps of producing a spark in said exhaust gas purifying device when said first error signal is generated, and stopping the production of said spark when said second error signal is generated.

6. An apparatus for maintaining the combustion temperature in an exhaust gas purifying device of an engine at a predetermined temperature range, comprising sensing means for sensing a temperature representing said combustion temperature and for generating a temperature signal having a value repre-senting the sensed temperature, control means connected to said sensing means for comparing said value of said signal with first and second reference values representing the mimumum and maximum of said predetermined range, respectively and for generating a first error signal when said value of said temperature signal is less than said first reference value and a second error signal when said value of said temperature signal is greater than said second reference value, and air-fuel ratio adjusting means connected to said control means for reducing in response to said first error signal, the air-fuel ratio of an air-fuel mixture to be burned in a combustion chamber of said engine to cause an increase in the content of burnable components in exhaust gases of said engine to intensify combustion of the engine exhaust gases in said exhaust gas purifying device to thereby increase said combustion temperature and for increasing in response to said second error signal, said air-fuel ratio to cause a decrease in the content of said burnable components to reduce the intensity of said combustion of said engine exhaust gases to thereby reduce said combustion temperature,

7. An apparatus as claimed in Claim 6, in which said air-fuel ratio adjusting means comprises passage means for supplying into fuel for forming said air-fuel mixture additional air for emulsifying said fuel, valve means disposed in said passage means for closing in response to said first error signal, said passage means to stop supply of said additional air to reduce said air-fuel ratio and for opening, in response to said second error signal, said passage means to supply said additional air into said fuel to increase said air-fuel ratio.

8. An apparatus as claimed in Claim 6, further com-prising an ignition timing control device comprising switch means connected to said control means so as to be closed in response to said first error signal and to be opened in response to said second error signal, and means connected to said switch means for retarding the ingition timing of said engine in response to closing of said switch means to lengthen combustion time of said air-fuel mixture in said combustion chamber to increase the temperature of said engine exhaust gases to thereby increase said combustion temperature and for advancing the engine ignition timing into a normal condition in response to opening of said switch means to shorten said combustion time to reduce the temperature of said engine exhaust gases to thereby reduce said combustion temperature.

9. An apparatus as claimed in claim 8, in which said means to retard and advance said engine ignition timing compri-ses an ignition distributor, a normal ignition timing breaker contact forming part of said ignition distributor, and a retarding breaker contact connected to said switch means to form a series circuit, said series circuit being connected in parallel with said normal breaker contact, said normal breaker contact causing said ignition distributor to produce a spark for said engine at a normal timing when said switch means is opened, said retarding breaker contact being opened later than said normal breaker contact and causing said ignition distributor to produce said spark at a retarded timing when said switch means is closed.

10. An apparatus as claimed in Claim 8, further comprising a secondary air supply control device com-prising a source of secondary air, passage means communicating with said source for supplying secondary air from said source to an exhaust gas passage at a position upstream of said exhaust gas purifying device, and a flow path control valve disposed in said passage means to divide it into upstream and downstream sections and including actuating means which is connected to said control means to receive said error signals therefrom and operates said flow path control valve in response to said first error signal to communicate said upstream section with said downstream section to supply secondary air to said exhaust gas passage to increase the intensity of said combustion of said engine exhaust gases to thereby increase said combustion temperature and in response to said second error signal to isolate said upstream section from said downstream section and to communicate said upstream section with the atmosphere to divert secondary air thereto to reduce the intensity of said combustion of said engine exhaust gases to thereby reduce said combustion temperature.

11. An apparatus as claimed in Claim 10, further comprising an exhaust gas ignition control device comprising a high voltage generator connected to said control means to receive said error signals therefrom for generating a high voltage in response to said first error signal and for stopping generation of said high voltage in response to said second error signal, and a spark plug connected to said high voltage generator to receive said high voltage therefrom and located in said exhaust gas purifying device for producing a spark therein in response to said high voltage.

12. A combination of an engine including an exhaust gas passage and an exhaust gas purifying device located therein with an apparatus for maintaining the combustion temperature in said exhaust gas purifying device at a predetermined range, said apparatus comprising sensing means for sensing a temperature representing said combustion temperature and for generating a temperature signal having a valve representing the sensed temp-erature, control means connected to said sensing means for com-paring said value of said signal with first and second reference values representing the minimum and maximum of said predeter-mined range, respectively and for generating a first error signal when said value of said temperature signals in less than said first reference value and a second error signal when said value of said temperature signal is greater than said second reference value, and air-fuel ratio adjusting means connected to said control means for reducing, in response to said first error signal, the air-fuel ratio of an air-fuel mixture to be burned in a combustion chamber of said engine to cause increase in the content of burnable components in exhaust gases of said engine to intensify combustion of the engine exhaust gases in said exhaust gas purifying device to thereby increase said combustion temperature and for increasing, in response to said second error signal, said air-fuel ratio to cause a decrease in the content of said burnable components to reduce the intensity of said combustion of said engine exhaust gases to thereby reduce said combustion temperature.

13. A combination as claimed in Claim 12, in which said engine includes an induction passage having a throttle valve rotatably mounted therein, and an exhaust gas recircul-ation device including an exhaust gas recirculation conduit interconnecting said exhaust gas passage and said induction passage at a position downstream of said throttle valve for recirculating said engine exhaust gases into said induction passage, and an exhaust gas recirculation control valve disposed in said recirculation conduit for metering the flow of said engine exhaust gases recirculated into said induction passage in accordance with a vacuum in said induction passage at said position.