Exhaust gas recirculation system
United States Patent 11 1 1111 3,877,452 Nohira et al. Apr. 15, 1975 EXHAUST GAS RECIRCULATION SYSTEM 3,774,583 11/1973 King 123/119 A 3.796049 3 1974 1+ -11&#34; 123 119 A 75 1111761110151 Hidetaka Nohira; Kiyoshi Kobashi, I  
 both of Susono Japan Primary ExaminerWendell E. Burns [73] Assignee: Toyota Jidosha Kogyo Kabushiki Attorney, Agent, or Firm-Stevens, Davis, Miller &amp;  
 Kaisha, Toyota, Japan Mosher 22 Filed: Mar. 28, 1974 21 Appl. No.2 455,880  
 [57] ABSTRACT An exhaust gas recirculation system comprising a flow rate control valve provided in the recirculation pas- [30] Foreign Application Priority Data sage for the exhaust and suction systems of the engine, May 24, 1973 111 11111 48-57239 a diaphragm Chamber adapted for Controlling the flow rate control valve and arranged to be selectively con- 521 US. Cl 123/119 A nected to the Suction system and to prsssure p 511 111:. CI. P021111 25/06 fier through a Pressure change-Over valve, and an air [58] Field of Search 123/119 A; 60/278 bleeding mechanism Provided in Said Pressure p fier for converting negative pressure variation in the [56] 7 References Cited suction system into an amplified positive pressure vari- UNITED STATES PATENTS 3,739,797 6/1973 Caldwell 123 119 A 3 laims, 7 Drawing Figures I I 85 98 1| 1 l 3 ll 1 l 88 2 J 7| l 7 1 I00 l 99 97 22 2| l l l l l l PATENTEDAPR 1 51975 sumaqr&#39;g EXHAUST GAS RECIRCULATION SYSTEM BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to an exhaust gas recirculation system in which a variable weak negative pressure in the suction system of an internal combustion engine is converted into a proportional strong positive pressure by a pressure amplifier so as to open or close the exhaust gas flow rate control valve in the recirculation system with said positive pressure.  
 2. DESCRIPTION OF THE PRIOR ART In most of the existing exhaust gas recirculation systems for vehicles, the control valve used for controlling the recirculation rate of exhaust gas is controlled by a pressure signal, and usually a diaphragm type valve is used for the control valve because such diaphragm type valve provides a relatively large valve shaft driving force. Also, negative pressure in a venturi is utilized as a controlling signal for the control valve. This has the advantage that proper controlling of the recirculation rate of exhaust gas is provided. However, such negative pressure of a venturi is a little too weak to directly actuate the diaphragm of the control valve. There is known a mechanism for amplifying such venturi negative pressure for use as an energy source. However, such negative pressure amplifying mechanism has the problem that negative pressure varies frequently according to the operating condition of the engine as negative pressure in the suction pipe is used as energy source. Therefore, there is used a negative pressure storage tank for constantly obtaining negative pressure signal by amplifying the venturi negative pressure, but this still involves the problems that air could leak from the ampli fying mechanism and that the negative pressure storage tank would prove short of capacity when negative pressure in the suction pipe is weak. Thus, in order to meet various operating conditions of the engine, the negative pressure storage tank must be of a fairly large capacity, and loading of such large capacity tank to a passenger vehicle would pose another problem.  
 SUMMARY OF THE INVENTION The present invention provides an exhaust gas recirculation system featuring an arrangement by which the exhaust gas flow rate control valve is operated by positive pressure. According to the recirculation system of the present invention, compressed air is introduced into a controlled pressure chamber in a pressure amplifier from a positive pressure source, and the introduced compressed air is released into the atmosphere correspondingly to pressure in said controlled pressure chamber and negative pressure in the vicinity of the venturi in the suction system. There is thus formed a pressure amplifying mechanism producing the same effect as would be obtained when variation of negative pressure around the venturi is amplified by pressure in the controlled pressure chamber, and such pressure amplifying mechanism is used to practice positive opening and closing of the control valve provided in an exhaust gas recirculation passage. Opening of the control valve is effected by said pressure amplifier while closing of the valve is accomplished by negative pressure in the suction system. Also, the control valve is kept closed according to the operating condition of the engine.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram of an internal combustion engine adapted with an exhaust gas recirculation system of the present invention;  
  FIG. 2 is a longitudinal sectional view of a pressure amplifier and a pressure change-over valve according to the present invention;  
  FIG. 3 is a longitudinal sectional view of a control valve;  
  FIG. 4 is a longitudinal sectional view of another control valve;  
  FIG. 5 is a system diagram of an internal combustion engine adapted with an exhaust gas recirculation system according to another embodiment of the present invention;  
  FIG. 6 is a longitudinal sectional view of a pressure amplifier and a control valve in the system of FIG. 5; and  
  FIG. 7 is a longitudinal sectional view of a pressure change-over valve used in the above system.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is now described in detail by way of an embodiment illustrated in FIGS. 1 to 3 of the drawings.  
  The engine body 1 is provided with an intake manifold 2 and an exhaust manifold 3. The fuel-air mixture is supplied into said intake manifold 2 through an air cleaner 4, a venturi 5 in the carburetor and a throttle valve 6, and exhaust gas is discharged out from the engine 1 into the atmosphere through said exhaust manifold 3. Said exhaust mainfold 3 and intake manifold 2 are connected to each other by a conduit 8 provided with a control valve 7 at a suitable location thereof so that a portion of exhaust gas will be guided back into the intake manifold 2. In the body portion 51 of said control valve 7 is provided a passage 52 for passing exhaust gas, and in said passage 52 is provided a fixed orifice 54 which is opened or closed by a valve 53. Disposed above said valve body 51 is a housing provided with two diaphragms 58 and 59 of different sizes defining in said housing an atmospheric pressure chamber 55, a controlled pressure chamber 56 and an atmospheric pressure chamber 57 successively in that order upwardly. Between said two diaphragms 58 and 59 is provided a strut 61 adapted for maintaining a constant distance therebetween, and in the atmospheric pressure chamber 57 is provided a spring 62 adapted for pressing the diaphragm 59 toward the controlled pressure chamber 56. The opening-closing valve 53 is joined to the two diaphragms 58 and 59 by a shaft 64 which extends through a seal 63 of the valve body 51 and is arranged to open the fixed throttle 54 when a positive pressure is introduced into the controlled pressure chamber 56 from a pressure amplifier 11 which is described later. The control valve 7 may also be arranged such that the opening-closing valve 53 is provided upstream of the fixed orifice 54 and the controlled pressure chamber 56 is defined by one diaphragm 65 and housing 66 so that said valve 53 will be opened or closed by the operation of said diaphragm 65, as shown in FIG. 4.  
  The presssure amplifier unit 11 is provided so that a positive pressure corresponding to negative pressure in the suction system will be supplied into the controlled pressure chamber 56 in the control valve 7. A diaphragm 15 pressed by a spring 14 is provided between a housing portion 12 and another housing portion 13 of said unit 11, said both housing portions 12 and 13 being joined by bolts 16 to define a controlled pressure chamber 17 on the housing portion 12 side and an atmospheric pressure chamber 18 communicated with the atmosphere on the housing portion 13 side. In the housing portion 12 is provided a conduit 20 having a orifice 19, said pipe 20 being connected to an engine-driven air pump 21 and a conduit 22 so that a positive pressure will be supplied into the controlled pressure chamber 17. Also provided in said housing portion 12 is a pressure outlet port 23&#39; which is communicated with an inlet port 24 of a pressure change-over valve 41 to be described later, said valve 41 being further communicated with the controlled pressure chamber 56 in the control valve 7 through a conduit 71 so that a positive pressure controlled by the pressure amplifier unit 11 will be selectively supplied to the control valve 7. A hole 25 is formed in the diaphragm 15 in the pressure amplifier unit 11, and an air bleeding portion 26 is provided in said hole on its side closer to the atmospheric pressure chamber 18. Said air bleeding portion 26 has a bleeding hole 27 for discharging positive pressure into the atmospheric pressure chamber 18, and a check ball 29 pressed by a spring 28 is positioned in said bleeding hole 27. Disposed above and joined integral to said housing portion 13 are another housing portion 33 and a diaphragm 32 pressed by a spring 31. Defined by said diaphragm 32 and said housing portion 33 is a negative pressure chamber 35 into which negative pressure is introduced through the conduit 36 provided in the housing portion 33 which communicates with a section near the venturi of the carburetor by a conduit 37. The pressing force of the spring 31 is adjusted by an adjusting screw 38 to regulate the position of the diaphragm 32. Joined to the underside of the diaphragm 32 and secured by a nut 40 is a stick 39 against which the check ball 29 in the air bleeding portion 26 is pressed against the force of spring 28 corresponding to the positions of said diaphragms and 32. The pressing force of the respective springs 14 and 31 and position of the air bleeding portion 26 are suitably regulated so that the distances of movement of said both diaphragms 15 and 32 will be equal to each other. That is, when negative pressure in the negative pressure chamber 35 of the pressure amplifier unit 11 is strong, the diaphragm 32 is raised up against the force of the spring 31 to let the stick 39 separate from the check ball 29 so that the bleeding hole 27 is closed by the check ball 29. Therefore, pressure in the controlled pressure chamber 17 is intensified by the air pump 21, causing the diaphragm 15 to rise up with the air bleeding portion 26. However, if said diaphragm 15 rises up too much, the check ball 29 is forced down by the stick 29 so that positive pressure in the controlled pressure chamber 17 is released out through the bleeding hole 27, and consequently, pressure in said controlled pressure chamber 17 is weakened to let the diaphragm 15 descend. If said diaphragm descends too much, the  
 bleeding hole 27 is closed by the check ball 29 as said pressure chamber 35. This may be expressed by the following formula:  
 [N THE ABOVE FORMULA:  
 S effective area of diaphragm 32; S effective area of diaphragm 15; P negative pressure in negative pressure chamber 35; P positive pressure in controlled pressure chamber 17; P initial setting value of negative pressure in negative pressure chamber 35; P initial setting value of positive pressure in controlled pressure chamber 17; x: diplacement of diaphragm 32; y: displacement of diaphragm 15; K spring constnat 31; K spring constant 14; a proportional constant (amplification rate). (Diaphragm displacement is effected such that x y). A pressure change-over valve 41 is provided integral with the pressure amplifier unit 11 so that a controlled positive pressure in the pressure amplifier unit 11 will be selectively supplied to the control valve 7. The housing 81 of said pressure change-over valve 41 is provided on the side of the housing portion 12 of said pressure amplifier unit 11 opposite from the controlled pressure chamber 17, and the chamber 82 in said housing 81 is communicated with the pressure outlet port 23&#39; of the controlled pressure chamber 17 through a valve seat 83. At a location in the chamber 82 opposed to the valve seat 83 is provided another valve seat 84 which is connected to a part of the suction pipe 2 positioned downstream of the throttle valve 6 through a conduit 85. A passage 86 provided in the housing 81 is communicated with the controlled pressure chamber 56 by said conduit 71 so that said chamber 82 will be always in communication with controlled pressure chamber 56 in the control valve assembly 7. On the side of the housing 81 opposite from the pressure amplifier unit 11 is mounted a housing 91 provided with a diaphragm 89 defining an atompsheric pressure chamber 87 and a negative pressure chamber 88, and a valve 92 adapted for selectively closing said valve seats 83 and 84 is connected to the diaphragm 89 by a shaft 93 which extends through the housing 81. Also a seal 94 is provided at the parts where the shaft 93 passes through the housing 81. in the negative pressure chamber 88 is provided a spring 95 adapted for pressing the diaphragm 89 to the atmospheric pressure chamber side and arranged to be adjusted in its pressing force by an adjusting screw 96. The negative pressure chamber 88 in the pressure change-over valve assembly 41 is connected to a part of the suction pipe 2 adjacent the throttle valve 6 through a conduit 98 provided with a solenoid valve 97. Thus, when negative pressure in the negative pressure chamber 88 in said pressure change-over valve assembly 41 is elevated, positive pressure in the pressure amplifier unit 11 is supplied to control valve 7, while when said negative pressure is reduced, negative pressure in the suction pipe 2 is supplied to said control valve 7. The solenoid valve 97 functions to selectively supply negative pressure in the suction pipe 2 or atmospheric pressure into the negative pressure chamber 88 in the pressure change-over valve assembly 41. The solenoid valve 97 comprises a magnet coil 99 and a valve body 100 actuated by said magnet coil 99 which receives a control signal from a control device 101 corresponding to the engine speed, atmospheric temperature and other factors.  
  Let us now see the operation of the just described exhaust gas recirculation system of the present invention in a situation where the solenoid valve 97 connects the pressure change-over valve 41 with the suction pipe 2 and the engine is in a cranking, idling, decelerated or high-loaded state. Under such operating condition, negative pressure in the neighborhood of and adjacent the throttle valve 6 is weak and such negative pressure is introduced into the negative pressure chamber 88 in the pressure change-over valve assembly 41 through conduit 98 and acts weakly on the diaphragm 89, so that the valve seat 83 closes the valve 92 under the stronger force of spring 95 thereby communicating conduit 85 with conduit 71. Consequently, negative pressure in the suction pipe 2 is introduced into the controlled pressure chamber 56 in the control valve assembly 7 through conduit 85, pressure change-over valve 41 and conduit 71, and a face pressure equivalent to the difference in effective area between the diaphragms 58 and 59 works in the same direction as the pressing force of spring 62, closing the fixed orifice 54 with the valve 53. Therefore regardless of the pressure in the controlled pressure chamber 17 in the pressure amplifier unit 11, the valve seat 83 in the pressure change-over valve assembly 41 stays closed by the valve 92 to inhibit supply of said pressure to the control valve 7, so that no exhaust gas is recirculated from the exhaust manifold 3 back into the intake manifold 2.  
  When the operating pattern of the engine is changed into an accelerated or constant-speed operation, negative pressure around and adjacent the throttle valve 6 is intensified and such intensified negative pressure is introduced into the negative pressure chamber 88 in the pressure change-over valve assembly 41 through conduit 98 to press the diaphragm 89 against the force of spring 95 to close the valve seat 84 with the valve 92, thus communicating the controlled pressure chamber 17 in the pressure amplifier unit 11 with the conduit 71. During this time since negative pressure around the venturi 5 is being introduced into the negative pressure chamber 35 in the pressure time, unit 11 and also positive pressure in the controlled pressure chamber 17 is being amplified proportional to the change of negative pressure as said above, the controlled strong positive pressure in the controlled pressure chamber 17 is ggided into the controlled pressure chamber 56 in the control valve assembly 7 through pressure change-over valve 41 and conduit 71, and hence a face pressure corresponding to the difference in effective area between the diaphragms 58 and 59 works against the pressing force of spring 62, opening the fixed orifice 54 with the valve 53. Therefore, exhaust gas is recirculated from the exhaust manifold 3 into the intake manifold 2 through the control valve 7. As the variation of negative pressure in the suction pipe 2 conforms to the running condition of the engine, the exhaust gas recirculation rate also conforms to the operating pattern of the engine. During this period, no negative pressure in the intake manifold 2 is introduced into the control valve 7 as the valve seat 84 is closed by the valve 92 in the pressure change-over valve assembly 41.  
  When the engine operation is under the conditions other than above-said, that is, when the factors such as engine speed, engine cooling water temperature, atmospheric temperature and vehicle speed are in a state where recirculation of exhaust gas is not required, the control device 101 operates to transmit a signal to the magnet coil 99 of the solenoid valve 97 to switch the solenoid valve 97 to communicate the negative pressure chamber 88 in the pressure change-over valve assembly 41 with the atmosphere, so that the valve seat 83 in said valve assembly 41 is closed by the valve 92 which is pressed by spring 95 through diaphragm 89 and shaft 93. Thus, the pressure change-over valve 41 always communicates the control valve 7 and suction pipe 2, keeping the fixed orifice 54in the control valve 7 closed by the valve 53, and hence no exhaust gas is recirculated into the intake manifold 2.  
  Referring now to FIGS. 5 to 7, there is shown another embodiment of the present invention. This embodiment difiers from the preceding one in that the pressure amplifier unit 11 is formed integral with the control valve assembly 7 and the pressure change-over valve assembly 41 is separated therefrom. The route for communication of the intake manifold 2, pressure change-over valve 41, pressure amplifier unit 11, air pump 21, control valve 7 and solenoid valve 97 is same as in the preceding embodiment. Both embodiments are also identical in the manner in which negative pressure in the intake manifold 2 is amplified by the pressure amplifier unit 11 and the control valve 7 is opened by the action of the amplified positive pressure. In the drawings, the parts which are the same as those in the preceding embodiment are assigned the same reference numerals. The pressure amplifier unit 11, as in the foregoing embodiment, has formed therein a negative pressure chamber 35, an atmospheric pressure chamber 18, a controlled pressure chamber 17 and an air bleeding section 26&#39;. The controlled pressure chamber 17 doubles as the controlled pressure chamber 56 for the control valve 7, and at a part of the air bleeding portion 26 opposed to said controlled pressure chamber 17 is provided a check valve 102 adapted for allowing release of only positive pressure from the controlled pressure chamber 17 into the bleeding hole 27&#39;. The openingclosing valve 53 in the control valve assembly 7 is connected to a diaphragm 65&#39; through a shaft 64 extending through seal 63 in the valve body 51 and further to a lower part of the air bleeding portion 26 so that said valve 53 will be opened and closed in accordance with the behavior of the diaphragms l5 and 32. The pressure change-over valve assembly 41 is separate from the pressure amplifier unit 1 1. It has a valve 92 adapted for selectively closing the valve seats 83 and 84 and a negative pressure chamber 88 operable to switch the valve 92. Conduit connecting to the suction pipe 2 and conduit 22 leading into the air pump 21 are selectively connected with the controlled pressure chamber l7 in the pressure amplifier unit 11.  
  In the above-described mechanism, as in the preceding embodiment, the pressure amplifier unit 11 performs an amplifying operation to recirculate exhaust gas in the exhaust pipe into the intake manifold 2, but when positive pressure in the air pump 21 is introduced into the controlled pressure chamber 17 in said unit 1 1 through change-over valve 41, a pertinent amount of positive pressure is released into the atmosphere from the bleeding hole 27 through check valve 102 so that positive pressure in the controlled pressure chamber 17 will become same as produced by amplifying variation of negative pressure around the venturi 5, thus opening the fixed orifice 54 by the operating valve 53 in&#39; the control valve assembly 7. However, when negative pressure in the downstream of the throttle valve 6 is introduced into the controlled pressure chamber 17 in the amplifier unit 11 through change-over valve 41, the controlled pressure chamber 17&#39; develops a negative pressure as no air is flown into said chamber 17 from the bleeding hole 27 through check valve 102, so that the fixed orifice 54 is closed by the valve 53 in the control valve assembly 7.  
  According to the present invention, as described above, the negative pressure in the suction pipe representing the operating condition of the engine is amplified into a positive pressure proportional to the absolute value of the negative pressure by a pressure amplifier unit consisting of two pieces of diaphragms and an air bleeding mechanism, and such positive pressure is introduced into a controlled pressure chamber in the control valve assembly which controls the exhaust gas recirculation rate, thus allowing opening of the control valve with a large positive pressure while controlling the exhaust gas recirculation rate corresponding to the operating condition of the engine. No problem is posed in the opening of the control valve even when using a spring with a strong pressing force in the control valve closing direction. Also, when it is desired to close the control valve in a certain operating condition of the engine, negative pressure in the intake manifold is introduced into the controlled pressure chamber in said control valve so that closing of the control valve is secured by such negative pressure and the force of the spring. Further, exhaust gas recirculation is automatically stopped when the engine operation is under other conditions where recirculation of exhaust gas is not required. Also, though compressed air in the controlled 40 pressure chamber in the pressure amplifier unit is released into the atmosphere from the air bleeding portion, no problem arises in such matter as the air pump of the pressure source is of a sufficiently large capacity.  
 What we claim is:  
  1. An exhaust gas recirculation system for an internal combustion engine in which the exhaust and suction systems are communicated with each other by a conduit provided with a control valve, characterized in that said control valve is opened or closed by a pressure amplifying unit so as to recirculate exhaust gas into the suction system corresponding to variation of negative pressure in the suction system, said pressure amplifying unit comprising a first diaphragm and a second diaphragm arranged to divide the interior of the housing into three chambers, a first chamber defined by said first diaphragm so that compressed air will be introduced thereinto from a pressure source, said first chamber having a pressure outlet portion, a second chamber defined between said first and second diaphragms and communicated with the atmosphere, a third chamber defined by said second diaphragm so that negative pressure adjacent a venturi in the suction system will be introduced thereinto, a valve mounted on said first diaphragm to control communication between said first and second chambers, and an operating member mounted on said second diaphragm to operate said valve.  
  2. The exhaust gas recirculation system as set forth in claim 1, further including a pressure switch-over valve by which a pressure outlet port in the pressure amplifying unit and a part of the suction system located downstream of a throttle valve are selectively communicated with the controlled pressure chamber in said control valve, said pressure switch-over valve having a negative pressure chamber communicating with a part of the suction system located adjacent the throttle valve.  
  3. The exhaust gas recirculation system as set forth in claim 2, further including a valve means provided in a conduit communicating the negative pressure chamber in the pressure switch-over valve with a part of the suction system adjacent the throttle valve, said valve means being adapted to operate corresponding to the operating condition of the engine and whereby communication between said negative pressure chamber in the pressure switch-over valve and the suction system is shut off when recirculation of exhaust gas is not required.