US3881456A

US3881456A - Exhaust gas recirculation system

Info

Publication number: US3881456A
Application number: US474351A
Authority: US
Inventors: Hidetaka Nohira; Kiyoshi Kobashi
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1973-05-30
Filing date: 1974-05-29
Publication date: 1975-05-06
Anticipated expiration: 1992-05-06
Also published as: DE2425673A1; JPS5213249B2; DE2425673B2; CA1002835A; JPS507932A

Abstract

An exhaust gas recirculation system including pressure controlling means provided in the exhaust gas recirculation passage, said pressure controlling means having a pressure controlling section adapted to control air pressure in the pressure source with pressure of exhaust gas flowing into said pressure controlling means, and wherein pressure controlled by said pressure controlling section is led into a controlled pressure chamber defined by a diaphragm operable to open or close said pressure controlling means. A valve operated by pressure around a butterfly valve is provided in a conduit connecting said pressure source and said pressure controlling section. A chamber formed in said pressure controlling section for effecting pressure control is selectively communicated with said pressure source or with a part downstream of said butterfly valve. In the valve provided in the conduit connecting said pressure source and said pressure controlling section is provided a diaphragm chamber for operating said valve, the diaphragm chamber being communicated with a location adjacent said butterfly valve through a solenoid valve.

Description

United States Patent 1 [111 3,881,456 Nohira et a1. 1 1 May 6, 1975 EXHAUST GAS RECIRCULATION SYSTEM [75] Inventors: Hidetaka Nohira; Kiyoshi Kobashi, ABSTRACT both of Susono, Japan [73] Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha, Toyota, Japan [22] Filed: May 29, 1974 21 1 Appl. No.: 474,351

Primary ExaminerWendell E. Burns Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher CONTROL DEVICE An exhaust gas recirculation system including pressure controlling means provided in the exhaust gas recirculation passage, said pressure controlling means having a pressure controlling section adapted to control air pressure in the pressure source with pressure of exhaust gas flowing into said pressure controlling means, and wherein pressure controlled by said pressure controlling section is led into a controlled pressure chamber defined by a diaphragm operable to open or close said pressure controlling means.

A valve operated by pressure around a butterfly valve is provided in a conduit connecting said pressure source and said pressure controlling section.

A chamber formed in said pressure controlling section for effecting pressure control is selectively communicated with said pressure source or with a part downstream of said butterfly valve.

In the valve provided in the conduit connecting said pressure source and said pressure controlling section is provided a diaphragm chamber for operating said valve, the diaphragm chamber being communicated with a location adjacent said butterfly valve through a solenoid valve.

4 Claims, 4 Drawing Figures PATENTEUHAY' ems 3,881,456

sum 2 BF 2 FIG. 3

EXHAUST GAS RECIRCULATION SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention:

This invention relates to an exhaust gas recirculation system for purifying exhaust gas released from engines, and more particularly to a system of the type just recited whereby exhaust gas recirculated is always controlled by pressure to stay substantially at the same level as atmospheric pressure regardless of variation of negative pressure in the intake system of the engine and wherein particularly positive and reliable operation of the valve in the pressure control means controlling the exhaust gas recirculation rate is ensured.

2. Description of the Prior Art:

In the conventional pressure control devices designed to control the supply of exhaust gas into the intake system, recirculated exhaust gas pressure itself is introduced into a pressure chamber having a diaphragm so as to operate the valve in the pressure control unit by the action of said diaphragm. Accordingly, pulsation of exhaust gas pressure is directly picked up, and hence in case only a small amount of recirculated exhaust gas is controlled, the valve and its seat hit or rub against each other to cause early wear thereof. It was therefore essential to use a rubber-like material for the valve or for the valve seat, and for this reason, there is a certain limitation to heat resistance of such parts. Also, since pressure in the pressure chamber having the diaphragm is substantially equalized with atmospheric pressure, the valve itself is opened or closed with a weak force, so that if such control valve is used, the exhaust gas flow characteristic of the control valve may be changed by the deposit material in exhaust gas, and further, as the valve is greatly affected by negative pressure in the intake pipe, it needs to additionally provide a certain negative pressure compensating means for improving responsiveness, but such means itself involves the problem of heat resistance or sticking. There is also known an automatic pressure controlling mechanism in which pressure in the pressure chamber having a diaphragm is detected by utilizing intake pipe negative pressure and air is introduced into the intake pipe to raise up the negative pressure in the intake pipe to a suitable level to produce a controlling negative pressure signal so as to operate the valve in the pressure controlling means in response to such signal to thereby maintain pressure in the pressure chamber substantially equal to atmospheric pressure. However, as this mechanism is of the type in which air is flown into the intake pipe, there is a possibility that intake pipe negative pressure may be dropped below the lowest permissible level. Therefore, intake pipe negative pressure is low at the high load operating range of the engine, and hence although it is desirable to enlarge the valve opening for allowing exhaust gas recirculation in great quantity at one time, it is actually impossible to obtain a satisfactorily large valve opening due to small intake pipe negative pressure. There is also proposed a device in which the valve is closed by the action of air pressure given by an engine-driven air pump, but according to this device, it is impossible to perfectly close the control valve because the engine speed is low in the running condition where perfect shut-off of exhaust gas recirculation is desired, as during cranking or idling, and also because air pump pressure is weak.

SUMMARY OF THE INVENTION:

The present invention provides an improved exhaust gas recirculation system of the type in which the pressure of exhaust gas recirculated from the exhaust system into the intake system is maintained substantially equal to atmospheric pressure and the valve for controlling the exhaust gas recirculation rate can perform its opening and closing operations positively and reliably. According to the present recirculation system, a pressure control unit having a fixed throttle, a pressure chamber and a valve are provided in the exhaust gas recirculation conduit, and pressure in the controlled pressure chamber acting to open said valve is controlled by releasing compressed air from an air pump according to the pressure of the recirculated exhaust gas, thereby to maintain exhaust gas recirculated into the intake system at substantially the same level as atmospheric pressure, and further, when negative pressure in the intake system indicating the running condition of the engine drops below a certain level, supply of compressed air from the air pump into the controlled pressure chamber in the pressure control unit is shut 011'. Also, positive pressure from the air pump and negative pressure from the intake system are selectively supplied into the controlled pressure chamber in the pressure control unit with operation of a pressurechangeover valve in response to the engine running condition such that strong negative pressure working to the intake system will act when the valve is closed while high positive pressure of the air pump will act when the control valve is opened. Further, a solenoid-energized changeover valve is provided in a conduit through which negative pressure in the intake system is sent into the controlled pressure chamber, such that when there is no need of recirculating exhaust gas, as during warmup of the engine, the pressure-changeover valve maintains the shut-off condition of the air pump and the controlled pressure chamber in the pressure control unit by the operation of said solenoid-energized changeover valve.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a schematic diagram of an exhaust gas recirculation system according to the present invention;

FIG. 2 is a vertical sectional view of a pressure control unit in the exhaust gas recirculation system according to the present invention;

FIG. 3 is a vertical sectional view of a modification of pressure control unit; and

FIG. 4 is a vertical sectional view of a pressurechangeover valve in the exhaust gas recirculation sys tem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

An exhaust gas recirculation system embodying the present invention is described in detail with reference to FIG. 1. Air is supplied into the engine I from an air cleaner 2 while fuel-air mixture is supplied through a Venturi 3, butterfly valve 4 and intake pipe 5, and the exhaust gas is discharged out from an exhaust pipe 6. Provided adjacent the engine 1 is an air pump 8 which is driven by a crank shaft through a belt 7. The exhaust pipe 6 is connected to the intake pipe 5 through a conduit 10 provided with pressure controlling means 9 so that a part of the exhaust gas will flow into a section of the intake pipe 5 adjacent the engine 1. Compressed air from the air pump 8 is conducted through a conduit 11 into a pressure inlet port 13 in a pressure-changeover valve 12, and a pressure outlet port 14 of the valve 12 is connected through a conduit 17 to a pressure inlet port 16 in a pressure controlling section of a pressure control unit 9. The conduit 17 is also connected through its branch conduit 17' to a pressure inlet port 19 of a controlled pressure chamber 18 in the pressure control unit 9. Another pressure inlet port 20 of the pressure-changeover valve 12 is connected through a conduit 22 to a negative pressure outlet port 21 which opens into a section of the intake pipe 5 located slightly downstream of the closed butterfly valve 4. The negative pressure inlet port 24 of a negative pressure chamber 23 in the pressure-changeover valve 12 is connected to a negative pressure outlet port 25 opening into a section of the intake pipe 5 adjacent the closed position of the butterfly valve 4 through a conduit 27 which is provided with a solenoid-energized changeover valve 26. This solenoid-energized changeover valve 26 is electrically operated by a control device 28 which converts the engine speed into an electric signal and produces an output signal corresponding to the engine speed. That is, the pressure-changeover valve 12 is arranged such that when there is no need of recirculating exhaust gas, the negative pressure chamber 23 in the changeover valve 12 is communicated with an opening 29 (opened into the atmosphere) in the solenoid-energized changeover valve 26, and when exhaust gas recirculation is required, the negative pressure chamber 23 is communicated with the negative pressure outlet port 25 in the intake pipe 5. The input signal to the control device 28 may be the warm-up condition of the engine or atmospheric temperature.

The pressure control unit 9 is now described in detail with particular reference to FIG. 2. There is provided a valve body 32 having an exhaust gas inlet 30, an L- shaped passage and an outlet 31. In the L-shaped passage are provided a fixed throttle 33, a pressure chamber 34 and a valve 35 arranged in that order in the direction from the exhaust pipe 6 to the intake pipe 5. The valve 35 consists of a valve seat 36 and a valve member 37, the latter being mounted slidably at the lowermost end of a shaft 38 so that the valve member 37 can seal the valve seat 36. The upper end of the shaft 38 extends through an air-bleeding hole 39 upward of the valve body 32 and is secured to a diaphragm 40 by a nut. The air-bleeding hole 39 is adapted to prevent deposition of oil particles to the shaft 38. In an atmosphere-communicated chamber 41 below the diaphragm 40 is provided a spring 42 adapted to push up the diaphragm 40, and the controlled pressure chamber 18 is provided on the upper side of the diaphragm 40. In a side wall of the valve body 31 is provided a detected pressure chamber 46 having a diaphragm 45, the chamber 46 being communicated with the pressure chamber 34 in the pressure control unit 9 through a passage 44 formed in the valve body 32 and provided with a throttle 43. The passage 44 opens in a lower end portion of the detected pressure chamber 46 to flow down condensed water into the pressure chamber 34. Defined by the diaphragm 45 on the opposite side from the detected pressure cham ber 46 is a chamber 47 which is communicated with the atmosphere through an air-bleeding hole 48. On the chamber 47 side of the diaphragm 45 is provided a plate-like valve 49 which has rubber-type synthetic resin layer on its surface and is fixed by a nut. In opposition to this valve 49 is provided an air-bleed pipe 52 which is connected to the pressure inlet port 16 through a throttle and a check valve 51. The diaphragm 45 is arranged to be moved by a spring 53 provided in the detected pressure chamber 46 and a spring 54 provided in the chamber 47 so as to maintain a small space between the valve 49 and the air-bleed pipe 52 when no exhaust gas pressure works in the detected pressure chamber 46. The pressure controlling section 15 is constituted in this way. When pressure in the detected pressure chamber 46 rises higher than the atmospheric pressure, the air-bleed pipe 52 is closed by the valve 49. The diaphragm 45 in the pressure control section 15 is disposed parallel to the direction of lateral vibration of the engine so that the diaphragm 45 may be isolated from vibration of the engine.

FIG. 3 shows a modified form of pressure control unit 9. In this modification, the parts assigned the same reference numerals as in the unit of FIG. 2 operate in the completely same way as the counterparts of FIG. 2. The valve 35' is arranged such that the valve member 37' will engage with the valve seat 36' from its upper side, and two

diaphragms

57 and 58 are secured by a nut to the upper end of the shaft 38' in such a manner that they are spaced apart a predetermined distance from each other by a strut and a spring 56. The upper diaphragm 57 is greater in area than the lower diaphragm 58, and a controlled pressure chamber 18 having a pressure inlet port 19 is defined between said both

diaphragms

57 and 58. In a chamber 41' formed on the upper side of the diaphragm 57 in communication with the atmosphere is provided a spring 59 adapted to urge the diaphragm 57 downwardly, said spring 59 being adjusted in its pushing force by an adjusting screw 60. Means corresponding to the check valve 51 in FIG. 2 is constituted by a check ball 62 hiased by a spring 61 and a valve seat section 63 which are adapted to check introduction of atmospheric pressure into the side of the throttle 50. Beneath the diaphragm 58 is defined a chamber 64 communicated with the atmosphere.

The pressure-changeover valve 12 is shown in detail in FIG. 4. In the valve body 65 is formed a chamber 66 connected to the

pressure inlet ports

13, 20 and pressure outlet port 14, and a valve seat 67 is provided between the pressure inlet port 13 and outlet port 14, with a valve seat 68 being provided between the pressure outlet port 14 and inlet port 20 in opposition to the valve seat 67. The valve seats 67 and 68 are selectively closed by a valve 69 secured to the lower end of a shaft 70 which is secured at its top end to a diaphragm 72 by a nut through a seal 71 provided in the valve body 65 to seal the upper end of the chamber 66. Below the diaphragm 72 is defined a chamber 73 communicated with the atmosphere, while a negative pressure chamber 23 connected to the negative pressure inlet port 24 is formed on the upper side of the diaphragm 72. In the negative pressure chamber 23 is provided a spring 74 adapted to push the diaphragm 72 downwardly, the spring 74 being adjusted in its pressing force by an adjusting screw 75.

Now, the operation of the exhaust gas recirculation system having the above-described arrangement will be described. Let it here be assumed that the control device 28 is issuing a signal requiring recirculation of exhaust gas in response to a factor such as engine speed or atmospheric temperature, and accordingly, the solenoid-energized changeover valve 26 is in operation to communicate the negative pressure outlet 25 in the intake pipe 5 with the negative pressure inlet 24 in the pressure-changeover valve 12. When no negative pressure is acting to the negative pressure outlet port 25 in the intake pipe 5 as when the engine is cranking, idling, decelerated or heavily loaded, no negative pressure works to the negative pressure 23 in the pressurechangeover valve 12, and hence the valve 69 keeps the valve seat 67 closed through the shaft 70 under the force of the spring 74. In this condition, since the pres sure-changeover valve 12 communicates the pressure inlet port with the pressure outlet port 14, a high negative pressure is loaded to the check valve 51 in the pressure controlling section 15 of the pressure control unit 9 from the negative pressure outlet port 21 in the intake pipe 5, thus keeping the check valve 51 closed, and hence a negative pressure acts to the controlled pressure chamber 18 from the conduit 17' irrespective of pressure in the detected pressure chamber 46. Consequently, the valve seat 36 is closed by the valve member 37 through the shaft 38 under the force of negative pressure acting to the diaphragm 40 and the force of spring 42, thus perfectly inhibiting flow of exhaust gas into the intake pipe 5 from the exhaust pipe 6 through the conduit 10.

When the engine is accelerated or brought into stationary run, with the solenoid-energized changeover valve 26 being kept in the above-said condition, the negative pressure acting into the negative pressure outlet port in the intake pipe 5 is now introduced into the negative pressure chamber 23 in the pressurechangeover valve 12 through conduit 27 to move upwardly the valve 69 against the force of spring 74 to thereby close the valve seat 68. As this situation is brought about, the pressure-changeover valve 12 is operated to communicate the pressure inlet port 13 with the outlet port 14 so that compressed air from the air pump 8 is led to the pressure controlling section 15 in the pressure control unit 9 through said pressurechangeover valve 12 and conduit 17. On the other hand, exhaust gas which has flown into the pressure chamber 34 in the pressure control unit 9 is further introduced through the passage 44 into the detected pressure chamber 46 to equalize pressure in said pressure chamber 34 with that in said detected pressure chamber 46. Therefore, if pressure in the detected pressure chamber 46 is only slightly higher than atmospheric pressure, there is created a small space between the valve 49 mounted on the diaphragm 45 and the opening of the air-bleed pipe 52 by the force of

springs

53 and 54, causing compressed air in the conduit 17 to flow out into the chamber 47 through the throttle 50, check valve 51 and the air-bleed pipe 52 to raise the pressure of the exhaust gas in said conduit 17 close to atmospheric pressure. Accordingly, pressure in the controlled pressure chamber 18 in the pressure control unit 9 also remains low and the diaphragm keeps the valve 37 closed under the force of spring 42, inhibiting any flow of exhaust gas through the valve 35 in the control unit 9. However. when exhaust gas pressure in the pressure chamber 34 rises up to cause corresponding rise of pressure in the detected pressure chamber 46. the diaphragm is urged to move toward the chamber 47 to actuate the valve 49 to close the air-bleed pipe 52. This causes pressure rise in the conduits l7 and 17' as well as pressure rise in the controlled pressure chamber 18, forcing the diaphragm 40 downwardly against the opposing force of spring 42. Consequently, the valve member 37 separates from the valve seat 36, allowing exhaust gas in the exhaust pipe 6 to flow into the intake pipe 5 through conduit 10 and pressure control valve 9. Such flow of exhaust gas into the intake pipe 5 causes a drop of pressure in the pressure chamber 34 and in the detected pressure chamber 46, allowing compressed air to flow out into the chamber 47 from the air-bleeding pipe 52 to lower the pressure in the controlled pressure chamber 18 to thereby close the valve 35. Pressure in the pressure chamber 34 is thus maintained substantially equal to atmospheric pressure, and hence the amount of exhaust gas flowing to the outlet 31 from the fixed throttle 33 is kept proportional to the amount of air introduced into the engine I from the Venturi 3.

When the engine speed is such that no exhaust gas recirculation is required, or when the engine is not yet sufficiently warmed up, the control device 28 operates to switch the solenoid-energized changeover valve 26 to communicate the negative pressure chamber 23 in the pressure-changeover valve 12 with the atmosphere, and no matter how much negative pressure acts to the negative pressure outlet 25 of the intake pipe 5, the operation of the pressure changeover valve 12 is not the least affected. This condition induces the same behavior as when the engine is cranking, idling, decelerated or heavily loaded, and the valve 35 of the pressure control unit 9 is perfectly closed to inhibit recirculation of exhaust gas in the exhaust pipe 6 into the intake pipe.

Now, the operation of the pressure control unit shown in FIG. 3 will be described. This control unit operates substantially same as that of FIG. 2, but in this unit, two diaphragms are provided above and below the controlled pressure chamber 18', and pressure in the chamber 18' for operating the valve 35 acts to the differential area between the upper and

lower diaphragms

57 and 58 to operate the valve member 37'. This valve member 37 is positioned above the valve seat 36' to prevent the deposition of carbon or the like in exhaust gas on the valve member 37'.

As described above, in the exhaust gas recirculation system of the present invention, pressure of compressed air supplied into the pressure controlling section from the air pump is controlled according to pressure of the exhaust gas introduced into the pressure control unit, and the operation of the valve in the control unit is accomplished by the controlled compressed air to maintain pressure of exhaust gas recirculated into the intake system from the exhaust pipe at the substantially same level as atmospheric pressure. However, since the pressure acting to open the valve is a strong positive pressure, it is possible to strengthen the acting force of the spring used for maintaining the valve in its closed position, and the exhaust gas recirculated does not pulsate. Also, although compressed air introduced into the pressure controlling section is released into the atmosphere from the valve, there is posed no problem in operating the valve of the pressure control unit as air discharge from the air pump is great in amount. Further, said opening and closing operation of the valve is little affected even if compressed air from the air pump is used for re-combustion of exhaust gas. Still further, the area where air pump scharge pressure is weak,

that is, where the engine speed is low, coincides with the area where it is desired to shut off exhaust gas recirculation for securing safety of the engine. in such area, it is possible to perfectly shut off exhaust gas recirculation by converting the weak air pump discharge pressure into a strong intake pipe negative pressure by use of a pressure-changeover valve.

It is to be further noted that the pressure controlling section of the pressure control unit is secured directly to the valve body so that even if the atmospheric temperature drops to an extremely low level, no freezing of condensed water in the detected pressure chamber takes place owing to radiation of heat from the control valve body. However, since little exhaust gas flows into the detected pressure chamber, the pressure controlling section does not rise so high in temperature and hence long durability of the diaphragms is ensured. Also, since closure of the valve in the pressure control unit is accomplished by the resilient force of springs, it is not essential in some applications to utilize negative pressure in the intake system when closing the valve.

What we claim is:

I. An exhaust gas recirculation system in which the exhaust system and intake system of an internal combustion engine are connected to each other by a conduit so as to recirculate a part of exhaust gas from the exhaust system into the intake system, said system comprising:

a pressure control unit provided in said conduit and having a fixed throttle,

a pressure chamber and valve arranged successively in that order in the direction from the exhaust system to the intake system,

a pressure control section comprising:

a first chamber communicated with said pressure chamber,

a second chamber separated from said first chamber by a diaphragm and communicated with a pressure source and also with the atmosphere, and

a valve assembly secured to said diaphragm and adapted to control communication between said second chamber and said pressure source,

and a controlled pressure chamber communicated with said second chamber in said pressure control section and compartmented by a diaphragm joined to said valve in said pressure control unit, whereby compressed air supplied into said second chamber in said pressure control section from said pressure source is released into the atmosphere corresponding to pressure in said pressure chamber to control pressure in said chamber in the pressure control section, and said valve in the pressure control unit is operated responding to the thus controlled pressure so as to maintain pressure in said pressure chamber substantially equal to atmosphere pressure.

2. The exhaust gas recirculation system as set forth in claim 1, wherein a valve is provided in the conduit connecting the pressure source with said second chamber in the pressure control section and with said controlled pressure chamber in the pressure control unit, and a negative pressure chamber operable to open or close said valve is connected to that part of the intake system which is located adjacent a butterfly valve so that said valve will be opened or closed according to the running condition of the engine.

3. The exhaust gas recirculation system as set forth in claim 1, wherein said pressure source and a section of the intake system downstream of the butterfly valve are communicated with said second chamber in the pressure control section through a valve, and a negative pressure chamber operable to switch said valve is communicated with a part of the intake system adjacent said butterfly valve, and wherein said pressure source and said intake system are selectively communicated with said second chamber by said valve according to the running condition of the engine.

4. The exhaust gas recirculation system as set forth in claim 2, wherein a solenoid-energized valve operated according to the running condition of the engine is provided in the conduit connecting the negative pressure chamber in said valve with a part of the intake system adjacent the butterfly valve, and when there is no need of recirculating exhaust gas, said negative pressure chamber in said valve and the intake system are shut off from each other by said solenoid-energized valve.

Claims

1. An exhaust gas recirculation system in which the exhaust system and intake system of an internal combustion engine are connected to each other by a conduit so aS to recirculate a part of exhaust gas from the exhaust system into the intake system, said system comprising: a pressure control unit provided in said conduit and having a fixed throttle, a pressure chamber and valve arranged successively in that order in the direction from the exhaust system to the intake system, a pressure control section comprising: a first chamber communicated with said pressure chamber, a second chamber separated from said first chamber by a diaphragm and communicated with a pressure source and also with the atmosphere, and a valve assembly secured to said diaphragm and adapted to control communication between said second chamber and said pressure source, and a controlled pressure chamber communicated with said second chamber in said pressure control section and compartmented by a diaphragm joined to said valve in said pressure control unit, whereby compressed air supplied into said second chamber in said pressure control section from said pressure source is released into the atmosphere corresponding to pressure in said pressure chamber to control pressure in said chamber in the pressure control section, and said valve in the pressure control unit is operated responding to the thus controlled pressure so as to maintain pressure in said pressure chamber substantially equal to atmosphere pressure.