Abstract:
A method and apparatus for exhaust gas recirculation for an internal combustion engine in which exhaust gas is recirculated through a recirculation passage connecting the exhaust passage of the engine and the intake passage of the engine. A vacuum-response type recirculation control valve is disposed in the exhaust gas recirculation passage to operate in response to vacuum detected at a vacuum detection port located in the intake passage in the vicinity of a throttle valve. A vacuum tank is connected through a solenoid-actuated change-over valve to the vacuum passage interconnecting the vacuum detecting port and the recirculation control valve, the vacuum tank being in communication with the intake passage downstream from the throttle valve through a check valve. A differential pressure switch is connected between the solenoid-actuated change-over valve and a power source and is adapted to be placed in &#34;on&#34; state when the vacuum detected at the vacuum detecting port is lower than the vacuum in the vacuum tank to operate the change-over valve to connect the vacuum tank to the vacuum passage.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for controlling exhaust gas recirculation mainly for use in vehicle engines, of the type having an exhaust gas recirculation passage connecting the exhaust passage of the engine to the intake passage of the engine, and an exhaust gas recirculation control valve disposed in the exhaust gas recirculation passage to control the rate of exhaust gas recirculation to the intake passage. 
     PRIOR ART 
     In the field of automobile engines, it has been adopted to recirculate a part of the exhaust gas to the intake passage to suppress excessive increase of the combustion temperature, thereby to prevent generation of nitrogen oxides which are air polluting components. This type of exhaust gas recirculation control device incorporates an exhaust gas recirculation control valve adapted to operate in response to the intake vacuum of the engine. This known arrangement poses the problem that, as the intake vacuum is lowered by an increase of the opening of the throttle valve during heavy load operation of the engine, the vacuum for operating the exhaust gas recirculation control valve is lowered to decrease the opening of the valve, resulting in an inadequate rate of exhaust gas recirculation. 
     SUMMARY OF THE INVENTION 
     The major object of the present invention is to provide an exhaust gas recirculation control device and method capable of overcoming the above-described problem of the prior art device. 
     Another object of the invention is to provide an exhaust gas recirculation control device and method of the above type adapted mainly for use in vehicle engines, in which the exhaust gas recirculation valve disposed in the exhaust gas recirculation passage interconnecting the exhaust gas passage and the intake passage operates without fail even when the intake vacuum is lowered due to an increase of the throttle valve opening during heavy load operation, thereby to maintain an adequate rate of exhaust gas recirculation. 
     The invention will be fully described hereafter with respect to a specific embodiment applied to an internal combustion engine of an automobile by way of example, with reference to the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The sole FIGURE of the drawing is a vertical sectional view of an essential part of a device in accordance with one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     In the drawing there is seen a portion of an automobile engine E which has an intake manifold Mi and an exhaust manifold Me which are connected to one side of the engine. 
     A carburetor C is connected to the upstream end of the intake manifold Mi, through the medium of a heat insulating sleeve It. The carburetor C has a choke valve 2 and a throttle valve 3 which are respectively disposed upstream and downstream of a venturi 1a of an intake bore 1. 
     The intake bore 1, heat insulating sleeve It and the intake manifold Mi in combination constitute an intake passage of the engine E. This intake passage is provided with a first vacuum detecting port D 1  formed at a portion thereof slightly upstream of the throttle valve 3 in the idle position, a second vacuum detecting port D 2  formed in the venturi 1a and a third vacuum detecting port D 3  formed in the heat insulating sleeve It. The port D 3  could also be formed in the intake manifold Mi. 
     An exhaust gas recirculation passage 4 connects an exhaust port of the engine E to the intake manifold Mi. An exhaust gas recirculation control valve 5 is disposed in the passage 4. The exhaust gas recirculation control valve 5 is of the vacuum response type and comprises a needle valve 6, a diaphragm 7 to which the needle valve 6 is connected and a compression valve spring 9 disposed in a vacuum chamber 8 to bias valve 6 in the closing direction. A first vacuum passage L 1  and a second vacuum passage L 2  leading from the first and the second vacuum detecting ports D 1 , D 2 , respectively, are connected to the vacuum chamber 8. 
     The first vacuum passage L 1  is provided, in the direction going from upstream to downstream, with a first solenoid-actuated change-over valve V 1 , a second solenoid-actuated change-over valve V 2  and an orifice 10. The first solenoid-actuated change-over valve V 1  includes a solenoid 11, a valve body 12 adapted to be actuated by the solenoid 11 and a normally opened port 13 and a normally closed port 14 which are adapted to be opened and closed in alternation by the valve body 12. The normally opened port 13 provides, when it is opened, unblocked opening of vacuum passage L 1 , i.e. communication between the upstream and downstream portions of vacuum passage L 1  connected to valve V 1 , whereas normally closed port 14 provides, when it is opened, communication between a vacuum tank 15 and the downstream side of the first vacuum passage L 1 . The vacuum tank 15 is connected to the normally closed port 14. The vacuum tank 15 is in communication with the third vacuum detecting port D 3  through a vacuum transmitting passage 17 having a check valve 16 therein so that the tank can store the intake vacuum during the engine operation and thereby constitute a vacuum storage means. 
     The second solenoid-actuated change-over valve V 2  includes a valve body 42 adapted to be actuated by a solenoid 41, and a normally opened port 43 and a normally closed port 44 which are adapted to be opened and closed in alternation by the valve body 42. The normally opened port 43 provides, when it is opened, communication between the upstream and downstream sides of the first vacuum passage L 1 , while the normally closed port 44 provides, when it is opened, communication between the downstream side of the first vacuum passage L 1  and an atmospheric port 45 provided with a filter. 
     A vacuum control valve 18 is disposed in the second vacuum passage L 2  and is constituted by a vacuum-response type adjusting valve 19 adapted to open and close the vacuum passage L 2  and a vacuum-response type air valve 20 adapted to control the vacuum which operates the adjusting valve 19. The adjusting valve 19 includes a valve chamber 21 formed at an intermediate location along the second vacuum passage L 2 , a vacuum chamber 23 separated from the valve chamber 21 by a diaphragm 22, a flat valve body 25 on the diaphragm 22 and adapted to open and close a valve port 24 provided at a downstream portion of the second vacuum passage L 2  and a valve spring 26 biassing the valve body 25 in the closing direction. The air valve 20 includes a valve chamber 28 at an intermediate location of a third vacuum passage L 3  extending between the third vacuum detecting port D 3  and an atmospheric port 27 with a filter, a vacuum chamber 30 separated from the valve chamber 28 by a diaphragm 29, a valve body 32 on the diaphragm 29 and adapted to adjust the opening of a valve port 31 at an upstream side of the third vacuum passage L 3  and a valve spring 33 biassing the valve body 32 in the closing direction. The valve body 32 has a shape similar to the valve member 6 of the exhaust gas recirculation control valve 5. The vacuum chamber 30 is in communication with the vacuum chamber 8 of the exhaust gas recirculation control valve 5 through the downstream side of second vacuum passage L 2  and a portion common to the first and the second vacuum passages L 1 , L 2 . An orifice 34 is provided between the valve chamber 28 and the atmospheric port 27. 
     Throughout the specification, the terms &#34;upstream side of the vacuum passage&#34; and &#34;downstream side of the vacuum passage&#34; are used to refer to the port adjacent to the vacuum side and the side adjacent to the atmospheric port respectively. 
     Referring now to the control system for controlling the first and second solenoid-actuated change-over valves V 1 ,V 2 , the control system includes a full-load detecting switch Sf adapted to be turned on upon detection of the substantially fully opened state of the throttle valve 3, a cold state detecting switch St adapted to be turned on upon detection of cold state of the engine, e.g. a temperature of the engine coolant below 60° C., an output rotation detecting switch Sn adapted to be turned on upon detection of a predetermined rotational speed of the engine shaft, e.g. engine speed in excess of 2,500 R.P.M., and a differential pressure switch Sp for comparing the vacuum in the first vacuum detecting port D 1  and the vacuum in the vacuum tank 15. The differential pressure switch Sp includes an upper vacuum chamber 35 in communication with the first vacuum detecting port D 1 , a lower vacuum chamber 36 in communication with the vacuum tank 15, a diaphragm 37 separating the vacuum chambers 35, 36 and a pair of balance spring 38,38&#39; biassing the diaphragm 37 to a neutral position. The arrangement is such that the diaphragm 37 is deflected downwardly to close the switch contact 39 when the vacuum in the upper vacuum chamber 35 is lower than the vacuum in the lower vacuum chamber 36. 
     The switches Sf and St are connected in parallel with each other between a power source 40 and the second solenoid-actuated change-over valve V 2 , while the switches Sn and Sp are connected in series between the power source 40 and the first solenoid-actuated change-over valve V 1 . 
     In the drawing, reference character Si denotes an ignition switch for the engine E. 
     The embodiment operates in the manner described hereafter. 
     When the switches Sf, St and Sn (or Sp) are in the off state to cut off the power supply to the solenoid-actuated change-over valves V 1 , V 2 , the vacuum control valve 18 operates as follows. During the operation of the engine, as the throttle valve 3 is suitably opened to generate a vacuum at the downstream side thereof, this vacuum Pc is detected through the first vacuum detecting port D 1  (now located downstream of the throttle valve 3) and is transmitted to the vacuum chamber 30 of the air valve 20, via the first and second change-over valves V 1 , V 2  and the orifice 10. As this vacuum is increased to overcome the bias of the valve spring 33, the diaphragm 29 is deflected to raise the valve body 32 to provide communication of the third vacuum passage L 3  with valve chamber 28. 
     As the third vacuum passage L 3  is communicated with valve chamber 28, the ambient air sucked through the atmospheric port 27 is sucked into the intake passage of the engine E through the third vacuum passage L 3  and the vacuum P generated in the valve chamber 28 of the air valve 20 is transmitted to the vacuum chamber 23 of the adjusting valve 19. As a result, the pressure differential between the vacuum P and the vacuum Pv detected through the second vacuum detecting port D 2  acts to deflect the diaphragm 22 upwardly. As the bias of the valve spring 26 is overcome by this upward force, the diaphragm 22 is deflected upwardly to lift the valve body 25 to open the valve port 24. As a consequence, a part of the vacuum Pv is transmitted through the valve port 24 and acts to dilute the vacuum which has passed through the orifice 10 to create a vacuum Pe which is applied to the vacuum chamber 8 to actuate the exhaust gas recirculation valve 5. 
     As the vacuum is diluted as stated above, the vacuum in the vacuum chamber 30 is lowered i.e. the pressure increases so that the opening of the air valve 20 is decreased correspondingly to reduce the vacuum in the valve chamber 28 and, accordingly, the vacuum in the vacuum chamber 23 of the adjusting valve, thereby to make the valve body 25 close the valve port 24. 
     Consequently, the vacuum Pe is increased to repeat the same operation. Since this repetition is made at a high frequency, the flow rate of air in the third vacuum passage L 3  becomes proportional to the intake air flow rate of the engine E, so that the vacuum P approximates the vacuum Pv. 
     If the intake air flow rate induced by the engine E is small, the vacuum P assumes a value higher than the vacuum Pv, so that the valve body 25 of the adjusting valve 19 moves in the direction of opening port 24 to lower the vacuum Pe by which the exhaust gas recirculation valve 5 is actuated. 
     On the contrary, if the intake air flow rate is increased, the vacuum Pv is increased to move the valve body 25 in the direction to close the port 24 to increase the actuating vacuum Pe. Therefore, the air valve 20 and the exhaust gas recirculation control valve 5 operate with the same vacuum Pe. Partly because of this fact and partly because of the similar shape of valve bodies 6 and 32 of these valves 5 and 20, the rate of the exhaust gas recirculation is changed in proportion to the flow rate of air in the third vacuum passage L 3 , i.e. in proportion to the intake air flow rate. It is, therefore, possible to obtain a constant ratio of the exhaust gas to the total intake mixture induced into the engine. 
     On the other hand, as both the engine speed detecting switch Sn and the differential pressure switch Sp are turned on to permit the solenoid 11 of the first solenoid-actuated change-over valve V 1  to be energized, the valve V 1  undergoes a change-over action to provide communication between the vacuum tank 15 and the downstream side portion of the first vacuum passage L 1 , so that the exhaust gas recirculation control valve 5 is actuated by the vacuum supplied from the vacuum tank 15, irrespective of the vacuum detected through the first vacuum detecting port D 1 . Thus, during the power-generating operation of the engine, exhaust gas recirculation is performed without fail even if the vacuum detected through the first vacuum detecting port D 1  is greatly lowered due to an increase of the opening of the throttle valve 3. 
     During idling of the engine, however, the output rotation detecting switch Sn is returned to off state, so that the first solenoid-actuated change-over valve V 1  is de-energized to cut-off the operation of the vacuum tank 15 and the consequent communication with the first vacuum passage L 1 . When the throttle valve 3 assumes the idle position, the first vacuum detecting port D 1  is positioned upstream of the valve 3 so as to detect the lowered vacuum. In consequence, the vacuum actuating the exhaust gas recirculation control valve 5 is lowered to close the valve 5 thereby to stop the exhaust gas recirculation to stabilize the idling operation of the engine. 
     As the solenoid 41 of the second solenoid-actuated change-over valve V 2  is energized as a result of closing of the full-load detecting switch Sf or the cold-state detecting switch St, the change-over valve V 2  undergoes a switching action to permit the downstream side of the first vacuum passage L 1  to come into communication with the atmospheric port 45, so that the vacuum Pe for actuating the exhaust gas recirculation control valve 5 is replaced by atmospheric pressure to close the control valve 5. Therefore, during the full load operation of the engine in which the throttle valve 3 is almost fully opened or in the cold state of the engine, the recirculation of the exhaust gas is stopped to increase the engine output. 
     As has been described, according to the invention, the vacuum tank always storing vacuum is connected through change-over valve V 1  to the vacuum passage L 1  between the vacuum detecting port D 1  opening into the intake passage of the engine and vacuum response type exhaust gas recirculation control valve 5 disposed in the exhaust gas recirculation passage 4, and the vacuum tank is brought into communication with the vacuum passage L 1  when the vacuum detected at the vacuum detecting port D 1  has dropped. Therefore, the exhaust gas recirculation control valve can operate without fail even when the intake vacuum is reduced due to an increase of the throttle valve opening during heavy load operation of the engine, because the vacuum tank supplies the exhaust gas recirculation control valve with a sufficiently high vacuum to actuate the control valve. In consequence, the exhaust gas recirculation is effected at an adequate rate to greatly contribute to suppress the generation of nitrogen oxide components in the exhaust gas.