Thermostat malfunction detecting system for engine cooling system

• US 6,725,710 B2
• Filed: 02/06/2003
• Issued: 04/27/2004
• 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:
  US10/359,266
• Publication Number:
  US 20030131659A1
• Time in Patent Office: 446 Days
• Field of Search: 731/16, 731/172, 731/173, 731/181, 731/19.R, 340/438, 340/449, 340/450, 340/450.3, 123/41.01, 123/41.15, 374/144, 374/145
• 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 diagnosing an open-malfunction of a thermostat of an internal combustion engine upon start of the engine, comprising the steps of:

a) measuring a coolant temperature of a coolant on an engine side of the thermostat;

b) determining an accumulated value of quantity of heat generated by the engine since engine start;

c) comparing a starting time coolant temperature measured upon starting the engine with a predetermined temperature which is set to be lower than an opening temperature of the thermostat;

d) comparing the accumulated value of quantity of heat with a predetermined quantity of heat generated by the engine; and

e) diagnosing whether the thermostat has an open-malfunction based on the engine side coolant temperature, when the starting time coolant temperature is lower than the opening temperature of the thermostat and the accumulated value of quantity of heat has reached a predetermined quantity.

2. The method of claim 1, wherein step e) comprises diagnosing whether said thermostat has an open-malfunction based on the engine side coolant temperature at the time when the accumulated value of quantity of heat reaches the predetermined quantity.

3. The method of claim 2, wherein step e) comprises diagnosing whether said thermostat has an open malfunction based on the starting time coolant temperature and the temperature at the time when the accumulated value of quantity of heat reaches the predetermined quantity.

4. The method of claim 1, wherein step e) comprises diagnosing that the thermostat has no open-malfunction when the coolant temperature has increased corresponding to the accumulated value of quantity of heat.

5. The method of claim 1, wherein step e) comprises diagnosing that the thermostat has open-malfunction when the coolant temperature has not increased corresponding to the accumulated value of quantity of heat.

6. A method for diagnosing an open-malfunction of a thermostat of an internal combustion engine upon start of the engine, comprising the steps of:

a) measuring a coolant temperature of a coolant on an engine side of the thermostat;

b) determining an accumulated value of quantity of heat generated by the engine since engine start;

c) comparing a starting time coolant temperature measured upon starting the engine with a predetermined temperature which is set to be lower than an opening temperature of the thermostat;

d) comparing the engine side coolant temperature with a predetermined temperature;

e) diagnosing whether the thermostat has an open-malfunction based on the accumulated value of quantity of heat, when the starting time coolant temperature is lower than the opening temperature of the thermostat and the engine side coolant temperature reaches a predetermined temperature.

7. The method of claim 6, wherein step e) comprises diagnosing that the thermostat has open-malfunction when the accumulated value of quantity of heat is greater than a predetermined quantity of heat to increase the engine side coolant temperature to said predetermined temperature.

8. The method of claim 6, wherein step e) comprises diagnosing that the thermostat has no open-malfunction when the accumulated value of quantity of heat is smaller than a predetermined quantity to increase the engine side coolant temperature to said predetermined temperature.

9. A method for diagnosing an open-malfunction of a thermostat of an internal combustion engine upon starting of the engine, comprising:

a) setting a target temperature for a coolant of the cooling system of the engine;

b) measuring a starting time temperature of the coolant upon starting of the engine;

c) comparing said starting time coolant temperature with a pre-determined temperature that is set below an opening temperature of the thermostat;

d) determining a value representing a quantity of heat generated by the engine following engine start;

e) measuring a current coolant temperature of a coolant on an engine side of the thermostat; and

f) diagnosing whether the thermostat has an open-malfunction based on the current engine side coolant temperature, when the starting time coolant temperature is lower than said predetermined temperature and the value corresponding to the quantity of generated heat has reached a predetermined value.

10. A method as in claim 9, wherein said step d) comprises measuring an intake air amount.

11. A method as in claim 10, wherein said step d) comprises reading engine speed and intake air amount and then calculating the quantity of heat generated for the engine speed and engine load from stored data.

12. A method as in claim 9, further comprising the step of determining an accumulated value representing generated heat by adding a latest value representing the quantity of heat generated by the engine to a previously accumulated value representing the quantity of heat generated by the engine.

13. A method as in claim 9, wherein said step f) comprises diagnosing that there is no malfunction when the engine side coolant temperature has increased in correspondence to the value determined in step d).

14. A method as in claim 9, wherein step f) comprises diagnosing that the thermostat has an open-malfunction when the current engine side coolant temperature is less than said target temperature when the value determined in step d) reaches the predetermined value.

15. A method as in claim 9, wherein when a malfunction is diagnosed, an alarm lamp is illuminated to warn the driver of the malfunction.

16. A method as in claim 15, wherein the warning light is illuminated after a single malfunction detection.