Exhaust Gas Recirculation System

• US 20080178853A1
• Filed: 11/20/2007
• Published: 07/31/2008
• Est. Priority Date: 01/26/2007
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: HOSHIKA, Hiroaki, KUBO, Jun, OTSUKI, Toshiki, TOKUYASU, Noboru, OHATA, Eiichiro, YAMAOKA, Shiro
• Granted Patent: US 7,681,560 B2
• Time in Patent Office: Days
• US Class Current: 123/568.11
• CPC Class Codes: F02B 2275/14 Direct injection into combustion chamber
• CPC Class Codes: F02B 29/0406 Layout of the intake air cooling or coolant circuit
• CPC Class Codes: F02D 2041/0075 by using flow sensors
• CPC Class Codes: F02D 41/005 according to engine operating conditions
• CPC Class Codes: F02M 26/05 High pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust system upstream of the turbine and reintroduced into the intake system downstream of the compressor
• CPC Class Codes: F02M 26/06 Low pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust downstream of the turbocharger turbine and reintroduced into the intake system upstream of the compressor
• CPC Class Codes: F02M 26/28 with liquid-cooled heat exchangers
• CPC Class Codes: F02M 26/35 with means for cleaning or treating the recirculated gases, e.g. catalysts, condensate traps, particle filters or heaters
• CPC Class Codes: F02M 26/47 the characteristics being temperatures, pressures or flow rates
• CPC Class Codes: F02M 26/49 Detecting, diagnosing or indicating an abnormal function of the EGR system
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

The present invention prevents an EGR sensor installed in an engine'"'"'s EGR path from being soiled by soiling substances in exhaust. A catalyst is positioned upstream of the EGR sensor to purify the soiling substances in EGR gas. The status of the EGR sensor is properly controlled in accordance with the conditions of the catalyst. This ensures the EGR sensor is less likely to be affected by the soiling substances in the exhaust under any circumstances of the EGR path and allows the EGR sensor to avoid a decrease in the accuracy of EGR gas detection. An alternative configuration may be employed such that the EGR gas recirculates from the downstream side of a catalyst installed in a main exhaust path.

Claims

1. An exhaust gas recirculation system for an engine, comprising:

an exhaust gas recirculation path for establishing communication between an exhaust path and an intake path of an engine and recirculating part of exhaust gas back into the intake path;

exhaust gas flow rate detection means for detecting the rate of an exhaust gas flow in the exhaust recirculation path;

an exhaust gas flow control valve for controlling the rate of an exhaust gas flow in the exhaust recirculation path; and

a catalyst that is installed upstream of the exhaust gas flow rate detection means to purify soiling substances in the exhaust gas.

2. An engine control device for controlling the system according to claim 1, wherein the operating status of the exhaust gas flow rate detection means is controlled while using a signal in accordance with the conditions of the catalyst as one input.

3. The engine control device according to claim 2, wherein, when the catalyst is inactive, an exhaust gas flow rate detection function of the exhaust gas flow rate detection means is disabled.

4. The engine control device according to claim 2, wherein, when the catalyst is inactive, control is exercised to place the exhaust gas flow rate detection means in a soilure protection mode.

5. The engine control device according to claim 2, wherein, when the catalyst is active, control is exercised to place the exhaust gas flow rate detection means in a flow rate detection mode.

6. The engine control device according to claim 2, wherein, when a diagnosis indicates that the catalyst is faulty, the exhaust gas flow rate detection function of the exhaust gas flow rate detection means is disabled.

7. The engine control device according to claim 2, wherein, when a diagnosis indicates that the catalyst is faulty, control is exercised to place the exhaust gas flow rate detection means in the soilure protection mode.

8. The engine control device according to claim 2, wherein the exhaust gas flow rate detection means includes a hot wire resistor that is exposed to an exhaust gas flow and detects the flow rate of the exhaust gas in accordance with a change in the hot wire resistor.

9. The engine control device according to claim 2, wherein the exhaust gas flow rate detection means calculates an exhaust gas flow rate from a pressure difference between pressures detected before and after the exhaust gas flow control valve.

10. The engine control device according to claim 2, wherein the exhaust gas flow rate detection means is flow detection means of an ultrasonic type.

11. The exhaust gas recirculation system for an engine according to claim 1, wherein the exhaust gas recirculation path includes an exhaust gas temperature control device for controlling exhaust gas temperature.

12. The exhaust gas recirculation system for an engine according to claim 1, wherein the exhaust gas flow rate detection means is positioned in an area exposed to the exhaust gas recirculation path in the exhaust gas temperature control device.

13. The exhaust gas recirculation system for an engine according to claim 1, wherein the exhaust gas flow rate detection means is positioned in the exhaust gas recirculation path that is located downstream of the exhaust gas temperature control device.