Patent Publication Number: US-6993428-B1

Title: Detecting leakage of engine exhaust gas using exhaust mass flow measurement

Description:
FIELD OF THE INVENTION 
   This invention relates generally to internal combustion engines that propel motor vehicles and have exhaust systems that include exhaust gas treatment devices. In particular the invention relates to the measurement of the mass flow of engine exhaust gas and the further use of that measurement for the purpose of measuring exhaust gas leakage from the exhaust system. 
   BACKGROUND AND SUMMARY OF THE INVENTION 
   Exhaust gas treatment devices in the exhaust systems of internal combustion engines that propel motor vehicles prevent significant amounts of undesired products of combustion from being emitted to the surrounding atmosphere. For assuring full effectiveness whatever after-treatment device or devices is or are present in an exhaust system, it is important for integrity of the exhaust system to be assured. 
   The present invention is directed to a system that includes devices for placement in an engine exhaust system to obtain measurements of certain physical characteristics of exhaust gas flowing through the exhaust system and processing equipment for processing data related to exhaust gas flow past those devices to yield data representing the mass flow of exhaust gas through the exhaust system. 
   The invention further relates to processing the exhaust mass flow data with data representing mass flow introduced into engine combustion chambers for combustion to yield data indicative of any leakage from the exhaust system upstream of the devices placed in the exhaust system. 
   The invention still further relates to obtaining the exhaust mass flow data both upstream and downstream of an exhaust gas treatment device and processing the obtained data to yield data indicative of any leakage from the exhaust gas treatment device. 
   By monitoring for leakage in such ways, compliance with any relevant laws and/or regulations can be proven. Alternatively, detection of leakage can be signaled, enabling early correction of a leak. 
   Principles of the invention can be embodied in an engine by the exposure of two devices to exhaust gas flow, in conjunction with suitable algorithms in on-board processing apparatus, such as apparatus present in a processor-based engine control system. 
   One of the two devices comprises a sensor having the capability for accurately sensing exhaust gas temperature. The other device comprises an electric heater having the capability to be heated to a temperature in excess of exhaust gas temperature. By using an existing exhaust gas sensor as the other device, the invention can be cost-effectively implemented in a motor vehicle. 
   Execution of an algorithm that processes temperature data provided by the sensor and power data representing power required to maintain heater temperature yields data representing mass flow through the exhaust system past the temperature sensor and the electric heater. 
   Execution of a further algorithm that processes the exhaust mass flow data and data obtained from mass flow measuring apparatus that measures mass flow entering the engine for combustion yields data representing any leakage in the exhaust system occurring upstream of the exhaust system sensor and heater. 
   Principles of the invention can also be embodied in an engine by the exposure of a first pair of the two devices to exhaust gas flow upstream of an exhaust gas treatment device and a second pair of the two devices downstream of the exhaust gas treatment device, in conjunction with suitable algorithms in on-board processing apparatus, and processing data obtained through use of the four devices to yield data representing any leakage from the exhaust gas treatment device. 
   Accordingly, one general aspect of the present invention relates to a method of measuring mass flow of exhaust gas through an exhaust system of an internal combustion engine. The method comprises developing temperature data representing temperature of exhaust gas flowing past a temperature sensor disposed in temperature sensing relation to the exhaust gas flow, and developing power data representing power required to heat an electric heater disposed in heat exchange relation with the exhaust gas flow to a temperature in excess of temperature of exhaust gas flow past the heater. The temperature data and the power data are then processed according to an algorithm for yielding data representing mass flow of exhaust gas. 
   Another general aspect relates to an engine that embodies the method just described. 
   Still another general aspect of the invention relates to a method of measuring leakage of exhaust gas from an exhaust system of an internal combustion engine. The method comprises developing temperature data representing temperature of exhaust gas flowing past a temperature sensor disposed in temperature sensing relation to the exhaust gas flow, and developing power data representing power required to heat an electric heater disposed in heat exchange relation with the exhaust gas flow to a temperature in excess of temperature of exhaust gas flow past the heater. A processor processes the temperature data, the power data, and data representing mass flow through the engine upstream of the temperature sensor and heater according to an algorithm for yielding data representing the difference between mass flow of exhaust gas past the temperature sensor and heater and mass flow upstream of the temperature sensor and heater. 
   Another general aspect relates to an engine that embodies the method just described. 
   The foregoing, along with further aspects, features, and advantages of the invention, will be seen in this disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, briefly described below, and contains a detailed description that will make reference to those drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a general schematic diagram of an engine having an exhaust system containing devices used in practice of the present invention. 
       FIG. 2  is more detailed view of the portion of the engine exhaust system showing placement of devices used in a representative implementation of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates general elements of a multi-cylinder internal combustion engine  10  that powers a motor vehicle. An example of such a vehicle and engine is a truck having a fuel-injected diesel engine. 
   Engine  10  comprises an intake system  12 , including an intake manifold  14 , through which charge air is delivered to engine cylinders  16 . Charge air enters each engine cylinder  16  from manifold  14  via a corresponding intake valve or valves. Individual fuel injectors  18  inject diesel fuel into individual engine cylinders in properly timed relation to engine operation. 
   Engine  10  also comprises an exhaust system  20 , including an exhaust manifold  22 , for conveyance of exhaust gases created by combustion within cylinders  16  from the engine. Exhaust gases pass out of each cylinder  16  via a respective exhaust valve or valves into exhaust manifold  22 . From manifold  22  the exhaust gases pass through piping to an exhaust gas treatment system  24  that contains one or more treatment devices. 
   An electronic engine control  26  that possesses digital processing capability is associated with engine  10 . Control  26  may comprise one or more processors that process data from various input data sources in accordance with one or more programmed algorithms to provide control of various functions associated with operation of engine  10  and/or provide certain information about engine operation. Certain data processed by control  26  represents variables and may originate at external sources (input variables) and/or be generated internally of control  26  (local variables). Other data may be programmed into and stored in control  26  for processing by algorithms. 
   In accordance with principles of the invention, data representing the temperature of the exhaust gas passing through exhaust system  22  after treatment by treatment system  24  is provided by a temperature sensor  28 . An electric heater  30  is placed in the exhaust system proximate sensor  28  for obtaining additional data. Heater  30  can be the heater of an exhaust gas sensor present in the exhaust system. 
   Control  26  acts via suitable electric circuitry to control the delivery of electric current to heater  30  such that heater  30  is heated to a temperature in excess of exhaust gas temperature flowing past the heater. The flow of exhaust gas past heater  30  tends to cool the heater. In order to maintain heater temperature, control  26  must regulate the electric current flow through heater  30 . 
   For a constant exhaust gas flow rate, less electric current is needed to maintain heater temperature as exhaust gas temperature rises, and more current is needed as exhaust gas temperature falls. For a constant exhaust gas temperature, less electric current is needed to maintain heater temperature as exhaust gas flow rate decreases, and more current is needed as exhaust gas flow rate increases. 
   Because current flow through heater  30  correlates with power input to the heater, and because power input to the heater correlates with mass flow rate of exhaust gas, a measurement of the current flow to the heater, a measurement of temperature of exhaust gas flow, and knowledge of the heater temperature collectively provide sufficient data for obtaining a measurement of mass flow rate of exhaust gas. Where the current flow is regulated in such a manner as to maintain a known heater temperature, data representing that known temperature may be used as knowledge of the heater temperature. Where the current flow is not necessarily regulated in such a manner, a measurement of heater temperature must be obtained to provide the knowledge of the heater temperature. 
   Processing of these various pieces of data by control  26  is performed using appropriate algorithms to yield mass flow rate of exhaust gas. While heater  30  is proximate sensor  28 , it should be placed so that it does not influence the exhaust gas temperature being sensed by sensor  28 . 
   Any leakage from exhaust gas treatment system  24  can be measured by placement of a second pair of devices, namely temperature sensor  28 ′ and electric heater  30 ′, upstream of system  24 . Temperature data obtained from sensor  28 ′ and power data representing the power input to heater  30 ′ are processed to yield the upstream exhaust gas flow rate data. The downstream exhaust gas flow rate data is then subtracted from the upstream exhaust gas flow rate data to yield a measurement of any leakage from system  24 . 
   Commercially available devices may be used for sensors  28 ,  28 ′ and for heaters  30 ,  30 ′. Appropriate circuitry interfaces each with control system  26 . Heaters  30 ,  30 ′ can be a heated exhaust gas sensor, such as a NOx sensor, HEGO (Heated Exhaust Gas Oxygen), UEGO (Universal Exhaust Gas Oxygen), or any other sensor which can be heated to temperatures above typical exhaust gas temperatures. 
   While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention are applicable to all embodiments and uses that fall within the scope of the following claims.