Thermostat malfunction detecting system for engine cooling system

• US 6,679,110 B2
• Filed: 03/19/2002
• Issued: 01/20/2004
• Est. Priority Date: 12/17/1996
• Status: Expired due to Term

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Oka, Tatsuya, Wakahara, Keiji, Ichikawa, Akira
• Primary Examiner(s): MCCALL, ERIC SCOTT
• Application Number:
  US10/100,039
• Publication Number:
  US 20020088274A1
• Time in Patent Office: 672 Days
• Field of Search: 731/16, 731/172, 731/173, 731/181, 731/19.R
• US Class Current: 73/114.68
• CPC Class Codes: F01P 11/14 Indicating devices; Other safety devices
• CPC Class Codes: F01P 11/16 concerning coolant temperature F01P11/20 takes precedence
• CPC Class Codes: F01P 2023/00 Signal processing; Details thereof
• CPC Class Codes: F01P 2023/08 Microprocessor; Microcomputer
• CPC Class Codes: F01P 2025/08 Temperature
• CPC Class Codes: F01P 2025/13 Ambient temperature
• CPC Class Codes: F01P 2025/62 Load
• CPC Class Codes: F01P 2025/64 Number of revolutions
• CPC Class Codes: F01P 2025/66 Vehicle speed
• CPC Class Codes: F01P 2031/00 Fail safe
• CPC Class Codes: F01P 2031/20 Warning devices
• CPC Class Codes: F01P 2060/14 Condenser
• CPC Class Codes: F01P 5/02 Pumping cooling-air; Arrangements of cooling-air pumps, e.g. fans or blowers
• CPC Class Codes: F02D 2200/0406 Intake manifold pressure
• CPC Class Codes: F02D 2200/0414 Air temperature
• CPC Class Codes: F02D 41/18 by measuring intake air flow
• CPC Class Codes: F02D 41/22 Safety or indicating devices for abnormal conditions in air/fuel ratio feedback systems F02D41/1495, in electric control linkage F02D11/107, in purge control systems F02M25/0809
• CPC Class Codes: G01K 15/00 Testing or calibrating of thermometers
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A malfunction of a thermostat in a coolant circulating path is detected from an engine side coolant temperature in consideration of the following behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes different considerably from that in the normal time in the temperature range in which the thermostat is to be normally closed. When a closure-malfunction occurs, the coolant temperature becomes different considerably from that during the normal time in the temperature range in which the thermostat is to be normally opened. Alternatively, the malfunction may be detected from a difference between the engine side coolant temperature and a radiator side coolant temperature.

Claims

1. A method for detecting a malfunction of an internal combustion engine thermostat provided in a coolant circulating path, said method comprising the steps of;

detecting a first, starting temperature of coolant on the coolant circulating path on the engine side of said thermostat at a location spaced from said thermostat upon engine starting;

determining whether said starting temperature is less than an opening temperature of said thermostat;

detecting a second engine side coolant temperature at said location spaced from said thermostat during a period in which said thermostat is normally to be closed; and

diagnosing, when the first temperature, detected upon starting, is lower than said opening temperature, whether said thermostat has an open-malfunction based on the second engine side coolant temperature.

2. A method as in claim 1, wherein said step of diagnosing comprises determining a decrease or a rate of drop of the engine side coolant temperature right after the start of the engine and diagnosing whether said thermostat has the open-malfunction based on the decrease or the rate of drop of the engine side coolant temperature.

3. A method as in claim 1, wherein said step of diagnosing comprises determining an increase of the engine side coolant temperature until one of (1) an elapsed time from the start of the engine (2) a number of times of ignition and (3) an accumulated value representative of a quantity of heat generated by the engine, reaches a predetermined value and wherein said diagnosing step diagnoses whether said thermostat has the open-malfunction based on the increase of the engine side coolant temperature.

4. A method as in claim 1, wherein said step of diagnosing includes determining any one of (1) an elapsed time after the start of the engine, (2) a number of times of ignition, and (3) an accumulated value representative of a quantity of heat generated by the engine until the increase of detected engine side coolant temperature reaches a predetermined value or until the detected engine side coolant temperature reaches a predetermined temperature and diagnosing whether said thermostat has the open-malfunction based on a reference value.

5. A method as in claim 1, wherein said diagnosing step includes correcting data used for the diagnostic process based on at least any one of vehicle speed, outside air temperature, intake air temperature and operating state of an air conditioner.

6. A method as in claim 1, wherein said step of diagnosing is carried out after the elapse of a predetermined time from the start of the engine.

7. A method as in claim 1, comprising indicating a malfunction when the coolant temperature is lower than a reference temperature after the elapse of a predetermined time from the start of the engine and wherein the reference temperature is varied with an accumulated value of heat generated by the engine.

8. A method as in claim 1, wherein said diagnosing is performed soley when said first temperature is determined to be lower than said opening temperature.

9. A method for detecting a malfunction of a internal combustion engine thermostat provided in a coolant circulating path, said method comprising:

detecting a first temperature of coolant on the coolant circulating path on the engine side of said thermostat at a location spaced from said thermostat;

determining whether said firt temperature is less than an opening temperature of said thermostat;

detecting, after the first temperature is detected, a second engine side coolant temperature at said location spaced from said thermostat during a period in which said thermostat is normally to be closed; and

diagnosing, when the first temperature is determined to be lower than said opening temperature, whether said thermostat has an open-malfunction based on the second engine side coolant temperature.

10. A method as in claim 9, wherein said diagnosing is performed solely when said first temperature is determined to be lower than said opening temperture.

11. A method as in claim 9, wherein said diagnosing comprises determining a decrease or a rate of drop of the engine side coolant temperature right after the start of the engine and diagnosing whether said thermostat has the open-malfunction based on the decrease of the rate of drop of the engine side coolant temperature.

12. A method as in claim 9, wherein said diagnosing comprises determining an increase of the engine side coolant temperature until one of (1) an elasped time from the start of the engine, (2) a number of times of ignition (3) an accumulated value representative of a quantity of heat generated by the engine, reached a predetermined value and wherein said diagnosing diagnoses whether said thermostat has open-malfunction based on the increase of the engine side coolant temperature.

13. A method as in claim 9, wherein said diagnosing includes determining any one of (1) an elapsed time after the start of the engine, (2) a number of times of ingnition, and (3) an accumlated value representive of a quantity of heat generated by the engine until the increase of detected engine side coolant temperature reaches a predetermined value or until the detected engine side coolant temperature reaches a predetermined temperature and diagnosing whether said thermostat has an open-malfunction based on a reference value.

14. A method as in claim 9, wherein said diagnosing includes correcting data used for the diagnostic process on at leasr any one of vehicle speed, outside air temperature, intake air temperature and operaring state of an air conditioner.

15. A method as in claim 9, wherein said diagnosing is carried out after the elapse of a predetermined time from the start of the engine.

16. A method as in claim 9, further comprising indicating a malfunction when the coolant temperature is lower than a reference temperature after the elapse of a predetermined time from the start of the engine and wherein the reference temperature is varied with an accumulated value of heat generated by the engine.