Thermostat malfunction detecting system for engine cooling system

• US 6,957,570 B2
• Filed: 03/03/2004
• Issued: 10/25/2005
• 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:
  US10/790,779
• Publication Number:
  US 20040168510A1
• Time in Patent Office: 601 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:

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

determining whether the first temperature is less than an opening temperature of the thermostat;

detecting an intake air amount;

calculating a value based on the intake amount;

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

detecting an open-malfunction of the thermostat based on the calculated value and the second engine side coolant temperature in case the first temperature is determined to be lower than the opening temperature.

2. A method as in claim 1, wherein said detecting an open-malfunction determines whether the second engine side coolant temperature fails to reach a reference temperature before the calculated value reaches a reference value, for detecting the open-malfunction of the thermostat.

3. A method as in claim 1, wherein said detecting an open-malfunction determines whether the calculated value reaches a reference value before the second engine side coolant temperature reaches a reference temperature.