Thermostat malfunction detecting system for engine cooling system

• US 7,010,967 B2
• Filed: 11/10/2004
• Issued: 03/14/2006
• Est. Priority Date: 12/17/1996
• Status: Expired due to Term

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Wakahara, Keiji, Ichikawa, Akira
• Primary Examiner(s): MCCALL, ERIC SCOTT
• Application Number:
  US10/984,931
• Publication Number:
  US 20050102093A1
• Time in Patent Office: 489 Days
• Field of Search: 374/145, 374/144, 123/41.01, 123/41.15, 340/450.3, 340/450, 340/449, 340/438, 731/19.R, 731/181, 731/173, 731/172, 731/16
• 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 an abnormality of a thermostat in a cooling system of an internal combustion engine, comprising:

detecting a coolant temperature on the engine side of the thermostat after an engine start in a temperature range in which the thermostat normally is closed; and

detecting an abnormality of the thermostat by using the detected coolant temperature and a heat radiation amount of the coolant.

2. The method as in claim 1, wherein the abnormality is detected based on a period required for the detected coolant temperature to reach a predetermined temperature after the engine start, a predetermined value and the heat radiation amount.

3. The method as in claim 1, further comprising:

correcting, by the heat radiation amount, a period required for the detected coolant temperature to reach a predetermined temperature after the engine start,

wherein the abnormality is detected based on the corrected period and a predetermined value.

4. The method as in claim 1, further comprising:

correcting, by the heat radiation amount, a predetermined value,

wherein the abnormality is detected based on the corrected predetermined value and a period required for the detected coolant temperature to reach a predetermined temperature after the engine start.

5. The method as in claim 2, wherein the period is calculated based on integration of amounts of intake airflow supplied to the engine.

6. The method as in claim 1, wherein the abnormality is detected based on the coolant temperature detected after a predetermined period from the engine start, a predetermined temperature and the heat radiation amount.

7. The method as in claim 6, further comprising:

correcting, by the heat radiation amount, the coolant temperature detected after the predetermined period,

wherein the abnormality is detected based on the corrected coolant temperature and a predetermined temperature.

8. The method as in claim 6, further comprising:

correcting, by the heat radiation amount, the predetermined temperature,

wherein the abnormality is detected based on the corrected predetermined temperature and the coolant temperature detected after the predetermined period.

9. The method as in claim 6, wherein the predetermined period is calculated based on integration of amounts of intake airflow supplied to the engine.

10. The method as in claim 1, wherein the heat radiation amount of the coolant is based on a vehicle speed.

11. The method as in claim 1, wherein the heat radiation amount of the coolant is based on an ambient temperature outside a vehicle.

12. The method as in claim 1, wherein the heat radiation amount of the coolant is based on an intake airflow temperature of the engine.

13. The method as in claim 1, wherein the heat radiation amount of the coolant is based on an operating condition of a blower fan of a vehicle.