Control system for internal combustion engine

Abstract

A control system for an internal combustion engine includes an exhaust gas purifying device, an exhaust gas temperature sensor, and temperature estimating device. The exhaust gas purifying device is provided to an exhaust duct of the internal combustion engine. The exhaust gas temperature sensor is provided in the exhaust duct on an upstream side of the exhaust gas purifying device. The temperature estimating device estimates a first exhaust gas temperature on a downstream side of the exhaust gas purifying device through a transfer function, which is expressed by a plurality of identical first-order lag elements, based on a second exhaust gas temperature on the upstream side of the exhaust gas purifying device sensed by the exhaust gas temperature sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a schematic view of an engine control system;

FIG. 2 is a chart showing a distribution of an exhaust gas temperature in a DPF;

FIG. 3 is a chart used for explanation of a selecting method for selecting an order n and a time constant T for a temperature estimation model;

FIG. 4 is an example chart showing a selection process of a order n and time constant T for the temperature estimation model;

FIG. 5 is a chart showing a relation between an engine rotation speed, a fuel injection quantity, and the time constant;

FIG. 6 is a block diagram of the temperature estimation model, which is expressed as a discrete system;

FIG. 7 is a flow chart of a temperature estimation process for estimating a temperature on a downstream of the DPF;

FIG. 8 is a flow chart of an air-fuel ratio computation process; and

FIG. 9 is a flow chart for a heater energization control process.

Claims

1. A control system for an internal combustion engine comprising: an exhaust gas purifying device provided to an exhaust duct of the internal combustion engine;an exhaust gas temperature sensor provided in the exhaust duct on an upstream side of the exhaust gas purifying device; andtemperature estimating means for estimating a first exhaust gas temperature on a downstream side of the exhaust gas purifying device through a transfer function, which is expressed by a plurality of identical first-order lag elements, based on a second exhaust gas temperature on the upstream side of the exhaust gas purifying device sensed by the exhaust gas temperature sensor.

2. The control system according to claim 1, further comprising time constant determining means for determining a time constant for the first-order lag elements of the transfer function in accordance with an operational state of the internal combustion engine.

3. The control system according to claim 1, wherein the transfer function is expressed by an offset element and the plurality of first-order lag elements.

4. The control system according to claim 1, the control system further comprising: a gas sensor that is provided in the exhaust duct on the downstream side of the exhaust gas purifying device, the gas sensor including a sensor element part, which senses a concentration of a specified component in exhaust gas, and a heater, which heats the sensor element part, wherein an energization control of the heater for energizing the heater is performed in order to maintain the sensor element part under an activation state; andcompensating means for compensating influence of exhaust gas heat to the gas sensor based on the first exhaust gas temperature estimated by the temperature estimating means.

5. The control system according to claim 4, wherein: the compensating means corrects at least one of the sensed concentration sensed by the sensor element part and an energization amount for energizing the heater in the energization control of the heater in order to compensate the influence of the exhaust gas heat to the gas sensor.

6. The control system according to claim 1, wherein the temperature estimating means is inhibited from estimating the first exhaust gas temperature when heat is generated in the exhaust gas purifying device.

7. The control system according to claim 1, wherein: the exhaust gas temperature sensor is provided on the downstream side of the exhaust gas purifying device instead of the upstream side thereof for sensing the first exhaust gas temperature; andthe temperature estimating means estimates the second exhaust gas temperature on the upstream side of the exhaust gas purifying device based on the first exhaust gas temperature on the downstream side thereof sensed by the exhaust gas temperature sensor by using an inverse transfer function of the transfer function.

8. A control system for an internal combustion engine comprising: an exhaust gas purifying device provided to an exhaust duct of the internal combustion engine;an exhaust gas temperature sensor provided in the exhaust duct on a downstream side of the exhaust gas purifying device; andtemperature estimating means for estimating a first exhaust gas temperature on an upstream side of the exhaust gas purifying device through a function based on a second exhaust gas temperature on the downstream side of the exhaust gas purifying device sensed by the exhaust gas temperature sensor, wherein:the function is an inverse transfer function of a transfer function that is expressed by a plurality of identical first-order lag elements; andthe transfer function is used for estimating the second exhaust gas temperature based on the first exhaust gas temperature.

9. The control system according to claim 8, further comprising time constant determining means for determining a time constant for the first-order lag elements of the transfer function in accordance with an operational state of the internal combustion engine.

10. The control system according to claim 8, wherein the transfer function is expressed by an offset element and the plurality of first-order lag elements.