Exhaust gas recirculation system for internal combustion engine

Claim 1

An exhaust gas recirculation system for an internal combustion engine comprising: an exhaust gas recirculation passage (21) communicating an exhaust pipe of an engine with an intake pipe of said engine at a position downstream of a throttle valve disposed in said inake pipe for recirculating a portion of exhaust gases from said exhaust pipe to said intake pipe; a restriction (22) and a valve seat (23) respectively disposed in series in said exhaust gas recirculation passage (21) for forming a pressure chamber (24) in said recirculation passage between said restriction (22) and said valve seat (23); a control valve (8) having a first diaphragm chamber (85), a first deformable diaphragm (82) responsive to the pressure in said first diaphragm chamber (85), and a valve body (83) connected to said first diaphragm for cooperating with said valve seat (23) to form a variable orifice; a pressure pipe (31) communicating said first diaphragm chamber (85) of said control valve (8) with a source of negative pressure in said intake pipe (3); a modulator (7) having a second diaphragm (71) and a second and a third diaphragm chambers (74, 75) divided by said second diaphragm (71), said second diaphragm chamber (74) being communicated with said pressure chamber (24), said third diaphragm pressure chamber (75) being communicated with said intake pipe through a throttle port (4a) for modulating the pressure in said first diaphragm chamber (85) in response to the pressures in said second and third diaphragm chambers (74, 75) of said modulator (7), said throttle port (4a) being positioned such that it is upstream of said throttle valve (4) when it is closed and it is downstream of said throttle valve (4) when it is opened by a predetermined angle; and a negative pressure control valve (9) having a third diaphragm (91), and a fourth and fifth diaphragm chambers (92, 94) divided by said third diaphragm (91), said fourth diaphragm chamber (92) being communicated with said intake pipe downstream of said throttle valve, said fifth diaphragm chamber (94) being communicated with the atmosphere and with said third diaphragm chamber (75) of said modulator (7), and means (95, 96) connected to said third diaphragm (91) for controlling the communication between said fifth diaphragm chamber (94) of said negative pressure control valve (9) and said third diaphragm chamber (75) of said modulator (7) to introduce air to said third diaphragm chamber (7) in response to the pressure in said fourth diaphragm chamber (92), so that the amount of air introduced into said third diaphragm chamber (75) is increased in accordance with the increase of the negative pressure in said intake pipe, whereby the pressure in said pressure chamber (24) is decreased in accordance with the increase of the negative pressure in said intake pipe and increase of a rotational speed of said engine.