Exhaust gas recirculating apparatus

Abstract

Apparatus associated with an engine on a motor vehicle for either stopping the recirculation of exhaust gas through the engine completely or allowing it at a controlled rate, depending upon the operating condition of the engine, comprising a regulating valve provided with a pair of diaphragms and installed in an exhaust gas recirculating circuit, and a changeover device operationally connected with the regulating valve and the intake side of the engine and adapted to actuate the regulating valve in accordance with the operating condition of the engine.

Parent Case Text

This is a continuation of application Ser. No. 369,002, filed June 11, 1973, now abandoned.

Description

This invention relates to an exhaust gas recirculating apparatus for an engine on a motor vehicle or the like, including a diaphragm type regulating valve and a changeover device for actuating the regulating valve, and moreover, such apparatus further including a solenoid valve operable in response to an electric signal produced by a switch detecting the temperature of engine cooling water, the ambient temperature or the vehicle speed.

It is well known that the content of nitrogen oxide in the exhaust gas from a gasoline engine, which is one of the major causes of air pollution, can be reduced to a large extent by recirculating the exhaust gas through the engine for recombustion. In order to obtain a maximum reduction in the nitrogen oxide content without lowering the engine performance, it is necessary to closely regulate the quantity of the exhaust gas to be recirculated in accordance with the operating condition of the vehicle or the engine.

A valve of the type which is actuated in response to a pressure signal has often been used to regulate the quantity of the exhaust gas to be recirculated, and a diaphragm valve has most commonly been used as it permits application of a relatively large force to actuate the valve rod. But if the opening of the valve is to be controlled in accordance with a slight change in the signal pressure, it is difficult to design the valve for opening with a large pressure, and the force available to keep the valve closed is reduced accordingly. Development of a large negative pressure in the intake side of the engine circuit easily causes the valve to open and allows a considerable amount of exhaust gas to be recirculated into the engine. This causes the engine to lose its operating stability or interrupt combustion during operation at a reduced rate, resulting in undesirable discharge of uncombusted hydrocarbon into the open air.

It is, therefore, an object of this invention to provide an improved exhaust gas recirculating apparatus for use in combination with an engine on a motor vehicle or the like, wherein the recirculation of the exhaust gas can be shut off completely or regulated to best suit the operating condition of the vehicle.

It is another object of this invention to provide an improved exhaust gas recirculating apparatus wherein the recirculation of the exhaust gas from the outlet to the inlet side of an engine on a motor vehicle or the like can be completely shut off when the temperature of engine cooling water, the ambient temperature or the vehicle speed has reached a preset level.

According to a preferred embodiment of this invention, there is provided an exhaust gas recirculating apparatus comprising a diaphragm valve mounted in an exhaust gas recirculating circuit and adapted for either shutting off the recirculation of exhaust gas completely or controllably regulating the flow of the exhaust gas to be recirculated through an engine depending upon the variable operating condition of a vehicle, and a changeover device operationally connected with the diaphragm valve and an intake circuit to the engine and adapted for selectively actuating the diaphragm valve. The diaphragm valve comprises a valve rod, a valve closure member attached to the lower end of the valve rod, a first or upper diaphragm connected to the upper end of the valve rod, a second or lower diaphragm connected to the valve rod and spaced from the first diaphragm, the second diaphragm being sized considerably smaller than the first diaphragm, a first or upper chamber defined between the top of the valve and the first diaphragm and a second or lower chamber defined between the first and the second diaphragms. The changeover device comprises a diaphragm defining a chamber communicating with an intake manifold to the engine through a first inlet port, a second inlet port communicating with both the upper chamber of the diaphragm valve and a Venturi portion of a carburetor, a third inlet port communicating with the intake manifold, an outlet port communicating with the lower chamber of the diaphragm valve and communicatable with the third inlet port, and a fourth inlet port communicating with the open air at one end and selectively communicatable at the other end with the second inlet port or the outlet port. The diaphragm valve operationally combined with the changeover device is designed to operate in such a manner that as the pressure in the lower chamber is raised to nearly the atmospheric pressure with the pressure in the upper chamber falling substantially below the atmospheric pressure, the valve rod is raised to allow the valve to open to a controlled degree, while as the pressure in the upper chamber is elevated to nearly the atmospheric pressure with the pressure in the lower chamber falling substantially below the atmospheric pressure, the valve rod is lowered to tightly close the valve and completely shut off the recirculation of the exhaust gas. It will thus be noted that during the cranking, idling, deceleration or high-load operation of the vehicle, when no recirculation of exhaust gas is required, or diaphragm valve is tightly closed to shut off the recirculation of the exhaust gas completely, while during the acceleration of normal operation of the vehicle which requires recirculation of exhaust gas preferably at a controlled rate, the valve is opened with its opening controlled depending upon the pressure in the Venturi portion of the carburetor to thereby regulate the quantity of the gas to be recirculated.

According to another preferred embodiment of this invention, there is provided an exhaust gas recirculating apparatus similar to that hereinabove described but further including a solenoid valve operationally associated with means for detecting the temperature of engine cooling water, the ambient temperature or the vehicle speed and adapted to open in response to an electric signal transmitted from the detecting means when the engine cooling water temperature, the ambient temperature or the vehicle speed has reached a predetermined level. The solenoid valve has an open port communicating with the open air, and another port communicating with both the intake manifold and the chamber of the changeover device. When the engine cooling water temperature, the ambient temperature or the vehicle speed has reached a predetermined level, the solenoid valve is actuated to open and thereby allow air to flow through the valve into the chamber of the changeover device, which in turn actuates the diaphragm valve for closing to shut off the recirculation of exhaust gas completely.

In a diaphragm type regulating valve known in the art, spring means has been solely relied upon to close the valve and maintain it in closed position. Consequently, the valve is unavoidably caused to open and thereby allow an undesirable recirculation of exhaust gas when the pressure in the upstream of the valve has become relatively high or alternatively the pressure in the downstream of the valve has become relatively low from time to time during operation of an engine. According to the apparatus of this invention, however, the regulating valve can be kept in closed position as long as necessary, since the upper diaphragm disposed between the two chambers is sized considerably larger than the lower diaphragm, and is capable of exerting a considerably larger force on the valve rod to urge it downwardly than the lower diaphragm can exert on the rod to urge it upwardly.

The foregoing and other objects, features and advantages of this invention will become more apparent from the following detailed description, and the accompanying drawings, in which:

FIG. 1 is a schematic diagrammatical view showing a preferred embodiment of this invention with an engine on a motor vehicle and its associated parts;

FIG. 2 is a vertical cross-sectional view of a preferred form of a diaphragm type regulating valve for the apparatus of this invention;

FIG. 3 is a vertical cross-sectional view of a form of a changeover device for actuating the diaphragm type regulating valve;

FIG. 4 is a vertical cross-sectional view of another form of the changeover device;

FIG. 5 is a cross-sectional view taken along the line A--A of FIG. 4;

FIG. 6 is a cross-sectional view taken along the line B--B of FIG. 5;

FIG. 7 is a cross-sectional view taken along the line C--C of FIG. 5;

FIG. 8 is a cross-sectional view taken along the line D--D of FIG. 5;

FIG. 9 is a view similar to FIG. 1, but showing another preferred embodiment of this invention further including a two way solenoid valve; and

FIG. 10 is a view similar to FIG. 9 showing a similar preferred embodiment with a three way solenoid valve.

Referring to FIG. 1, a pressure changeover device is indicated at 2, a diaphragm valve for regulating the flow of the gas being recirculated at 3, an air strainer at 4, and the Venturi portion of a carburetor at 5. The reference numeral 6 denotes a hole provided in te Venturi portion 5 for extracting a negative pressure signal from the Venturi portion 5. A butterfly valve in the carburetor is shown at 7. The numeral 8 indicates a hole provided adjacent to the butterfly valve 7 for extracting a negative pressure signal which varies depending on the opening of the butterfly valve 7. An intake manifold 9 is provided with a hole 10 through which a negative pressure signal is continuously extracted from the intake manifold 9. An exhaust manifold 11 is connected to the opposite side of an engine 12 from the intake manifold 9. A conduit 13 interconnects the exhaust manifold 11 and the diaphragm valve 3, and is adapted to transfer a portion of the exhaust gas from the exhaust manifold 11 to the valve 3. Another conduit 14 is provided between the valve 3 and the intake manifold 9 to recirculate a portion of the exhaust gas into the engine 12. A tube 15 is connected to the hole 8 of the carburetor at one end, and the other end thereof is connected with a hole 211 of the pressure changeover device 2 to transmit a negative pressure signal from the carburetor to the device 2. One end of a tube 16 is connected to the hole 6 of the Venturi portion, and the other end of the tube 16 is divided into two branches. One of those branches is connected to a hole 26 of the diaphragm valve 3, and the other branch is connected to a hole 251 of the pressure changeover device 2. A tube 17 is connected to the hold 10 of the intake manifold 9 at one end, and the other end of the tube 17 is connected to a hole 231 of the pressure changeover device 2 to transmit a negative pressure signal from the intake manifold 9 into the pressure changeover device 2. A tube 18 is connected to an outlet hole 241 of the pressure changeover device 2 at one end and to an inlet hole 27 of the diaphragm valve 3 at the other end to transmit a negative pressure signal from the device 2 to the valve 3. The pressure changeover device 2 is further provided with a hole 221 opening into the atmosphere and adapted to communicate with either the outlet hole 241 or an inlet hole 251 of the device 2 depending on the operation of the device 2, as best shown in FIG. 3.

Referring to FIG. 2, the diaphragm valve 3 will be described in further detail. The valve 3 comprises a pair of negative pressure chambers 28 and 30 separated by a diaphragm 29. The upper chamber 28 is adapted to regulate the flow of the exhaust gas being recirculated, while the lower chamber 30 is adapted to shut off the flow of the gas completely. Another diaphragm 31 is provided below the diaphragm 29 and has a considerably smaller effective area than the diaphragm 29. A valve rod 32 is integrally formed with the two diaphragms 29 and 31. A valve member 34 is attached to the lower end of the rod 32 and is rotatable about the rod 32. The valve member 34 is adapted to rest on a valve seat 35. A spring 37 is provided in the upper chamber 28 to control the pressure of the chamber 28. An adjust screw 36 is provided at the top of the valve to closely regulate the pressure required to lift the valve member 34 from the seat 35. The chamber 28 is supplied with a negative pressure signal through the inlet hole 26, while the lower chamber 30 is fed with a negative pressure signal through the inlet hole 27. All the functioning elements of the valve 3 are enclosed in a housing 38. The valve housing 38 is provided at its bottom end with an inlet 40 for the exhaust gas to be recirculated through the engine, and an outlet for the exhaust gas is indicated at 39. A seal member 33 encircles the valve rod 32 intermediate the ends thereof.

Reference is now made to FIG. 3 for further description of the pressure changeover device 2. The device 2 comprises a body 50 provided with a plurality of bores for the purpose to be hereinafter described. A shaft 51 is received in the central cavity of the body 50 and provided with a pair of horizontally extending bores 71 and 72. The shaft 51 is slidable relative to the body 50, so that the bores 71 and 72 of the shaft 51 may be selectively aligned with the bores of the body 50. A diaphragm 421 is connected to the top of the shaft 51 and defines a negative pressure chamber 411. An inlet hole 211 is provided adjacent to the top of the device 2 to introduce a negative pressure signal into the chamber 411. A spring 491 is interposed between the diaphragm 421 and the top of the device 2 to control the pressure of the chamber 411. An adjust screw 471 is provided at the top of the device 2 to act on the spring 491 and adjust and set the initial position of the shaft 51. The adjust screw 471 is held in position by a nut 481. Another adjust screw 45 is fitted in the adjust screw 471 and extends along the longitudinal axis thereof to adjust the stroke of movement of the shaft 51. The screw 45 is held in position by a nut 46. The hole 221 opening into the atmosphere is provided with an air strainer. The hole 221 may be selectively communicated with either the outlet hole 241 or the inlet hole 251 on the opposite side of the device 2 when the bores 71 and 72 of the shaft 51 are selectively aligned with the bores of the body 50. The bores of the body 50 and the bores 71 and 72 of the shaft 51 are disposed in such a relation that the inlet hole 231 provided below the hole 221 may be communicated with the outlet hole 241 but will never communicate with any other hole of the body 50. The outlet hole 241 may be communicated with either the inlet hole 231 through the bore 71 as shown in FIG. 3 or the hole 221 opening into the atmosphere upon elevation of the shaft 51. The inlet hole 251 may be communicated only with the oppositely disposed hole 221 through the upper bore 72 of the shaft 51 as shown in FIG. 3. A plurality of 0-rings 44 encircle the shaft 51 to provide a seal between the shaft 51 and the body 50. An annular chamber 43 of the atmospheric pressure is located below the diaphragm 421 and encircles the uppermost portion of the shaft 51. The bore provided in the body 50 communicates the chamber 43 with the hole 221.

FIGS. 4 through 7 show a different form of a pressure changeover device generally designated at 2'. The major difference of the device 2' shown in FIGS. 4 through 7 from the device 2 of FIG. 3 lies in the use of leaf springs 52 and 56 versus the bores 71 and 72 in the shaft 51 selectively alignable with the bores provided in the body 50. The reference numerals indicating various elements of the device 2' in FIGS. 4 through 7 will be listed in contrast to those of the corresponding elements of the device 2 shown in FIG. 3:

negative pressure chamber 412 to 411;

spring 492 to 491;

adjust screw 472 to 471; nut 482 to 481;

air holes 222 and 223 to 221 (the hole 223 being provided on a vehicle body frame 73);

inlet hole 232 to 231; inlet hole 252 to 251;

outlet hole 242 to 241; and diaphragm 422 to 421.

The leaf springs 52 and 56 are formed with diminishing portions 63 and 64, respectively, at one end thereof, which may be suitably shaped to produce the bending stress required of the springs 52 and 56. A sealing member 53 is thermally bonded to the free end of the spring 52, and a pair of similar sealing members 55 and 65 are secured in a like manner to the other spring 56 as shown in FIG. 7. The sealing members 53, 55 and 65 may be made of any appropriate organic material, such as rubber. A pair of rods 54 and 58 are erected on the upper surface of the diaphragm 422 as shown in FIG. 4 and extend upwardly through the bores formed in a body 66. The upper ends of the rods 54 and 58 are located in abutment against the free ends of the leaf springs 52 and 56 respectively, and the rods 54 and 58 are slidable vertically so as to raise the free ends of the springs 52 and 56 respectively upon elevation of the diaphragm 422. A shaft 59 is connected to the center of the diaphragm 422 and extends downwardly, and a guide member 60 encircles the shaft 59 adjacent to the lower end thereof. The shaft 59 and the guide member 60 are provided for the purpose of preventing the diaphragm 422 from shifting sideways and regulating the stroke of vertical movement of the diaphragm 422. The spring 52 is rivetted to the body 66 at 61, while the other spring 56 is rivetted to the body 66 at 62.

Another embodiment of this invention is shown in FIG. 9 and includes a two-way solenoid valve 1 interposed between the carburetor and the pressure changeover device 2. The solenoid valve 1 has an open port 19 communicating with the atmosphere, and an inlet hole 20 provided for receiving a negative pressure signal thereinto. The tube 15 connected to the outlet hole 8 of the carburetor at one end is connected to the inlet hole 20 of the solenoid valve 1 at the other end. A tube 151 is connected to the tube 15 at one end, and the other end of the tube 151 is connected to the inlet hole 211 or 212 of the device 2. The solenoid valve 1 is adapted to be actuated to establish communication between the atmosphere and the interior of the tube 15 through the ports 19 and 20 in response to an electric signal transmitted when the temperature of engine cooling water, the ambient temperature or the vehicle speed has reached a predetermined level. It will be noted that a three-way solenoid valve may be used in place of the two-way valve, wherein one end of the tube 151 is connected to the third port of the valve instead of the tube 15 and the third port of the three-way valve serves as an outlet for the signal to be transmitted into the device 2.

The mode of operation of the apparatus according to this invention will be described for different operating conditions of the vehicle on which the apparatus is installed. Description will first be made of the operation of the apparatus provided with a pressure changeover device as shown in FIG. 3, in combination with or without a solenoid valve.

1. Cranking, idling, deceleration or high-load operation (no solenoid valve is required)

Under these operating conditions, the vehicle requires no recirculation of exhaust gas. Substantially no negative pressure exists at the outlet port 8 of the carburetor; in other words, the pressure at the outlet port 8 is nearly atmospheric. Thus, the pressure in the chamber 411 of the device 2 which communicates with the outlet port 8 is considerably higher than a predetermined level, so that the spring 491 is caused to expand and lower the shaft 51 to its lowermost position as shown in FIG. 3. As seen in FIG. 3, the inlet port 251 of the device 2 is communicated with the atmosphere through the bore 72 of the shaft 51 and the open air port 221. Likewise, the inlet port 231 communicating with the intake manifold 9 is communicated with the outlet port 241 through the lower bore 71 of the shaft 51. Thus, the upper chamber 28 of the diaphragm valve 3 is communicated with the port 251 of the device 2 through the tube 16, and air is allowed to get into the chamber 28 until the pressure in the chamber 28 becomes equal to the atmosphere, so that the spring 37 is allowed to expand and lower the valve rod 32 and the valve member 34. At the same time, air is allowed to flow through the tube 16 into the outlet port 6 of the Venturi portion 5 of the carburetor. Simultaneously, as the lower chamber 30 is communicated with the intake manifold 9, the pressure in the chamber 30 is equallized to that of the intake manifold 9, so that the amount of force equal to the neqative pressure in the chamber 30 multiplied by the difference in effective surface area between the two diaphragms 29 and 31 acts downwardly upon the valve rod 32 to lower the valve member 34 onto the seat 35 and thereby stop the recirculation of exhaust gas completely.

2. Acceleration or normal operation. (No solenoid valve 1 is required.)

Under these operating conditions, recirculation of exhaust gas is required or desirable, and a negative pressure exists at the outlet port 8 of the carburetor. The pressure in the chamber 411 of the device 2 communicating with the outlet port 8 of the carburetor is considerably lower than a predetermined level, so that the spring 491 is allowed to contract and thereby raises the shaft 32 to its uppermost position. Thus, the communication between the inlet port 251 and the open port 221 of the device 2 is broken. The elevation of the lower bore 71 severs communication between the outlet port 241 and the inlet port 231 and instead communicates the outlet port 241 with the open port 221 so that air is allowed to flow through the open port 221 into the outlet port 241. At the same time, the upper chamber 28 of the diaphragm valve 3 is solely communicated with the Venturi portion 5 of the carburetor through the outlet port 6 thereof, so that the pressure in the upper chamber 28 is equalized to that of the Venturi portion 5. On the other hand, air is allowed to flow into the lower chamber 30 and lifts the upper diaphragm 29 overcoming the resistance of the spring 37, so that the valve member 34 is lifted from the seat 35 defining therebetween a gap through which recirculation of exhaust gas is accomplished. The width of the gap defined between the valve member 34 and the seat 35 is determined solely by the level of the negative pressure in the upper chamber 28, hence of the Venturi portion 5, so that the flow of the exhaust gas to be recirculated through the apparatus may be regulated in accordance with variation in the negative pressure of the Venturi portion 5.

Operation of the apparatus as shown in FIG. 9

A switch not shown detects the temperature of engine cooling water, the ambient temperature or the vehicle speed and transmits an electric signal to the two-way solenoid valve 1 when the engine cooling water temperature, the ambient temperature or the vehicle speed has reached a predetermined level, whereupon air is allowed to flow into the Venturi portion of the carburetor through the conduit 15. Accordingly, the pressure in the Venturi portion is equalized to the atmosphere, and the pressure in the chamber 411 of the device 2 is also raised to the atmospheric pressure as it is communicated with the outlet port 8 of the Venturi portion, so that the diaphragm 421 and the shaft 51 are lowered to establish the operative position of the device 2 as shown in FIG. 3. The diaphragm valve 3 is thus allowed to shut off the flow of the exhaust gas therethrough completely. It will be noted that a switch adapted for both detecting the temperature of the engine cooling water, the ambient temperature or the vehicle speed and directly causing the device 2 to switch over its operational position may be used on the apparatus without departing from the scope and spirit of this invention.

Attention is now directed to the operation of the apparatus provided with a pressure changerover device changeover shown in FIGS. 4 to 8, in combination with or without a solenoid valve.

1. Cranking, idling, deceleration or high-load operation (No solenoid valve 1 is required)

The pressure in the chamber 412 of the device 2' is not sufficiently low, as compared with the pressure in the space above the diaphragm 422, to cause the spring 492 to contract, so that the rods 54 and 58 are kept in their uppermost position urging the leaf springs 52 and 56 upwardly. Accordingly, communication is established between the lower open port 222 and the inlet port 252 and allows the flow of air into the inlet port 252. At the same time, communication is established between the inlet port 232 communicating with the intake manifold 9 and the outlet port 242 communicating with the valve 3, while the outlet port 242 is severed from communication with the upper open port 223. Thus, the pressure in the upper chamber 28 is raised to the atmospheric pressure and allows the spring 37 to expand and thereby lower the valve member 34. Simultaneously, the pressure in the low chamber 30 is equalized to that of the intake manifold 9, so that the amount of force equal to the negative pressure in the chamber 30 multiplied by the difference in effective surface area between the two diaphragms 29 and 31 acts upon the valve rod 32 to completely close the valve and stop the recirculation of exhaust gas.

2. Acceleration or normal operation. (No solenoid valve 1 is required)

Under these operating conditions, the pressure in the carburetor becomes sufficiently lower than the atmospheric pressure, and therefore, the pressure in the chamber 412 of the device 2' becomes sufficiently low, as compared with the pressure in the space above the diaphragm 422, to cause the spring 492 to contract, so that the rods 54 and 58 are lowered to their lowermost position. The rods 54 and 58 are disengaged from the springs 52 and 56 respectively, and the resiliency of the spring 52 brings the free end of the spring 52 into close contact with the upper end of the bore of the body 66 through which the rod 54 extends, so that the communication between the open port 222 and the inlet port 252 is severed. At the same time, due to its resiliency, the other spring 56 moves away from the inner end of the upper open port 223 upon withdrawal of the rod 58 to establish communication between the port 223 and the outlet port 242, while the sealing member 65 affixed to the spring 56 intermediate the ends thereof closes a bore provided to establish the communication between the inlet port 232 and the outlet port 242. Accordingly, the pressure in the upper chamber 28 of the diaphragm valve 3 is equalized to the pressure at the outlet port 6 of the Venturi portion 5, while the pressure in the lower chamber 30 is raised to the atmospheric pressure, so that the valve rod 32 is raised to lift the valve member 34 from the seat 35 and thereby allow recirculation of exhaust gas through the valve 3. The width of the gap defined upon separation of the valve member 34 from the seat 35 is variable with variation in the negative pressure of the chamber 28 of the valve 3, hence of the Venturi portion 5, so that recirculation of exhaust gas through the valve 3 amy be automatically regulated in response to change in the negative pressure of the Venturi portion 5.

3. Operation of the apparatus provided with a two-way solenoid valve as shown at 1 in FIG. 9. The apparatus operates in a like manner to the apparatus provided with a pressure changeover device as shown in FIG. 3 and a solenoid valve as hereinbefore described, and the diaphragm valve 3 completely shuts off the recirculation of the exhaust gas therethrough.

While the invention has been described with reference to some preferred embodiments thereof, it is to be understood that variations or modifications may be made by those skilled in the art without departing from the scope of the invention which is defined by the appended claims.

Claims

What is claimed is:

1. An exhaust gas recirculating apparatus associated with an engine on a motor vehicle or the like, comprising:

a regulating valve, the inlet of which is communicated with an exhaust manifold and the outlet of which is communicated with an intake manifold, said regulating valve including:

an actuating rod member,

an upper diaphragm secured to the upper end of said rod member,

a lower diaphragm smaller than said upper diaphragm and secured to said rod member in a position below said upper diaphragm,

an upper actuating chamber defined above said upper diaphragm,

and a lower actuating chamber defined between said upper and lower diaphragms;

and a changeover device for selectively actuating said regulating valve, including

a diaphragm defining an actuating chamber provided with a first port communicating with a carburetor,

a second port communicating with said upper actuating chamber of said regulating valve and further with a Venturi portion of said carburetor,

a third port communicating with said intake manifold,

a fourth port communicating with the open air,

and a fifth port communicating with said lower actuating chamber of said regulating valve and communicatable with said third port;

said regulating valve being adapted to open to a controlled degree upon elevation of the pressure in said lower actuating chamber to nearly the atmospheric pressure, while closing upon elevation of the pressure in said upper actuating chamber to nearly the atmospheric pressure.

2. Apparatus as defined in claim 1, wherein said regulating valve includes:

a valve seat member,

a closure member attached to the lower end of said actuating rod member and sealingly engageable with said seat member,

adjustable spring means disposed in said upper actuating chamber and engaged at its lower end with said upper diaphragm,

a port communicating said upper actuating chamber of said regulating valve with said second port of said changeover device through appropriate conduit means,

and a port communicating said lower actuating chamber of said regulating valve with said fifth port of said changeover device through appropriate conduit means,

said actuating rod member being vertically movable to move said closure member to or away from said seat member.

3. Apparatus as defined in claim 1, wherein said changeover device includes:

a housing defining said actuating chamber above said diaphragm and a vertically extending eleongate cavity below said actuating chamber,

a shaft member slidably received in said cavity and secured at its upper end to said diaphragm,

a first transverse bore provided across said shaft member intermediate the ends thereof and opening at the diametrically opposite sides of said shaft member,

a second transverse bore provided across said shaft member in a position below said first bore and opening at the diametrically opposite sides of said shaft member,

a second actuating chamber defined below said diaphragm, encircling the upper end of said shaft member and communicating with said forth port,

and adjustable spring means disposed in said firstmentioned actuating chamber and engaged at its lower end with said diaphragm,

said first transverse bore being alignable with said second and fourth ports to communicate said second and fourth ports with each other and said second transverse bore being alignable with said third and fifth ports to communicate said third and fifth ports with each other when said shaft member is lowered to its lowermost position, while said first transverse bore is closed by the peripheral wall of said cavity and said second transvere bore is aligned with said fourth and fifth ports to communicate said fourth and fifth ports with each other when said shaft member is raised to its uppermost position.

4. Apparatus as defined in claim 1, wherein said changeover devices includes:

a housing defining said actuating chamber below said diaphragm and secured at its upper end to a vehicle body frame, the upper end of said housing being shaped to form a first cavity and a second cavity between said housing and said vehicle body frame,

a shaft member carrying said diaphragm at its upper end and vertically slidably received in a guide member attached at its lower end to the bottom of said housing,

a second actuating chamber defined between said diaphragm and the upper end of said housing and communicating with said fourth port,

adjustable spring means disposed in said first-mentioned actuating chamber, encircling said shaft member and engaged at its upper end with said diaphragm,

a first vertical bore formed in said housing and opening into said first cavity at its upper end and into said second actuating chamber at its lower end,

a second vertical bore formed in said housing and opening into said second actuating chamber at its lower end, the upper end of said second vertical bore being closed by a resilient sealing member,

a first rod member attached to said diaphragm at its lower end and having a smaller diameter than said first vertical bore to define a path establishing communication between said second actuating chamber and said first cavity, said first rod member being vertically movable through said first vertical bore and projectable into said first cavity,

a second rod member attached to said diaphragm at its lower end and vertically movable through said second vertical bore, said second rod member being capable of pushing up said resilient sealing member and projecting into said second cavity,

a first leaf spring positioned in said first cavity and secured to said housing at one end, the other end of said first leaf spring being positioned over said first vertical bore and engageable by said first rod member,

a second leaf spring positioned in said second cavity and secured to said housing at one end, the other end of said second leaf spring being positioned over said second vertical bore and engageable by said second rod member,

a sixth port provided in said vehicle body frame and opening into the open air at one end and into said second cavity at the other end,

the inner end of said third port being positioned below an intermediate portion of said second leaf spring and closable thereby,

said first and second leaf springs being adapted to be be lifted from said first and second vertical bores, respectively, to establish communication between said second and fourth ports while establishing communication between said third and fifth ports and closing said sixth port, when said first and second rod members are raised to their uppermost position,

said first and second leaf springs being allowed to return to their original position to close said first vertical bore while closing the inner end of said third port and opening said sixth port to thereby establish communication between said fifth and sixth ports, when said first and second rod members are lowered to their lowermost position.

5. Apparatus as defined in claim 1 and further including a solenoid valve interconnecting said changeover device and said carburetor and provided with an open port communicating with the open air, said solenoid valve being operable in response to an electic signal transmitted by means detecting the temperature of engine cooling water, the ambient temperature or the vehicle speed, whereby said actuating chamber of said changeover device is selectively communicated with said carburetor and the open air.

6. Apparatus as defined in claim 5, wherein said solenoid valve is a two-way valve.

7. Apparatus as defined in claim 5, wherein said solenoid valve is a three-way volve. valve.