Exhaust gas purifying apparatus

Abstract

A throttle unit placed in an exhaust gas passage controls an opening-ratio of each of first and second valve members to control a gas-flow sectional area of the exhaust gas passage. When the temperature of a three-way catalyst is low, the throttle unit introduces the exhaust gas flow into a part of an outer-periphery of the three-way catalyst. This control can rapidly increase the temperature of the three-way catalyst from an early period of starting an internal combustion engine within a short period of time. The throttle unit increases the gas-flow sectional area of the exhaust gas passage according to increasing the temperature of the three-way catalyst. When the three-way catalyst reaches its activation temperature, the throttle unit instructs the first and second valve members to fully open. This decreases a pressure loss of the exhaust gas because the exhaust gas is supplied into the entire of the three-way catalyst.

1 . An exhaust gas purifying apparatus comprising:
 an exhaust gas pipe that forms an exhaust gas passage in which an exhaust gas emitted from an internal combustion engine flows;   a catalyst unit having a catalyst placed in the exhaust gas passage;   catalyst temperature detection means capable of detecting a temperature of the catalyst placed in the catalyst unit; and   a throttle unit, placed in at least one of an upstream side and an downstream side of the catalyst unit, capable of introducing the exhaust gas flowing in the exhaust gas passage into a part of the catalyst unit when the temperature of the catalyst detected by the catalyst temperature detection means is lower than an activation temperature of the catalyst.   
   
   
       2 . The exhaust gas purifying apparatus according to  claim 1 , wherein the throttle unit decreases a gas-flow sectional area of the exhaust gas passage in the exhaust gas pipe. 
   
   
       3 . The exhaust gas purifying apparatus according to  claim 2 , wherein the throttle unit increases the gas-flow sectional area of the exhaust gas passage according to the temperature rise of the catalyst detected by the catalyst temperature detection means. 
   
   
       4 . The exhaust gas purifying apparatus according to  claim 3 , wherein the throttle unit gradually increases the gas-flow cross section of the exhaust gas passage from the outer peripheral side toward the inner side of the catalyst unit along a diameter direction of the catalyst unit according to the temperature rise of the catalyst in the catalyst unit. 
   
   
       5 . The exhaust gas purifying apparatus according to  claim 4 , wherein the throttle unit comprises:
 a rotary shaft placed in the diameter direction of the exhaust gas passage in the exhaust gas pipe;   a first valve member that rotates around the rotary shaft to open and close the exhaust gas passage at the upstream side of the rotary shaft in the upstream side of the catalyst unit;   a second valve member that rotates around the rotary shaft to open and close the exhaust gas passage at the downstream side of the rotary shaft in the upstream side of the catalyst unit; and   a throttle drive means that independently drives the first valve member and the second valve member.   
   
   
       6 . The exhaust gas purifying apparatus according to  claim 3 , wherein the throttle unit expands the gas-flow sectional area of the exhaust gas passage from the central side toward the outer peripheral side in the diameter direction of the catalyst unit according to the temperature rise of the catalyst. 
   
   
       7 . The exhaust gas purifying apparatus according to  claim 6 , wherein the throttle unit comprises:
 a throttle member that expands from the inner wall of the exhaust gas pipe toward the catalyst unit side; and   a valve drive means that drives the throttle member between the central side and the outer peripheral side in the diameter direction of the catalyst unit.   
   
   
       8 . The exhaust gas purifying apparatus according to  claim 1 , further comprising an exhaust gas heating means that is placed at the upstream side of the catalyst unit in order to heat the exhaust gas before it reaches the catalyst unit. 
   
   
       9 . The exhaust gas purifying apparatus according to  claim 1 , further comprising a control means capable of controlling the operation of the throttle unit, wherein the control means is an electronic control unit composed a microcomputer that comprises a central control unit, a read only memory, and a random access memory. 
   
   
       10 . The exhaust gas purifying apparatus according to  claim 1 , wherein the catalyst is a three way catalyst placed in the catalyst unit.