Control system for variable valve timing apparatus

Abstract

A control system for a variable valve timing apparatus that changes a valve timing of an internal combustion engine using a motor which is controlled by operating a switching element includes: an oil temperature estimating portion; a substrate temperature estimating portion; and a current limit controller. The oil temperature estimating portion estimates a temperature of lubricating oil of the engine. The substrate temperature estimating portion estimates a temperature of a substrate to which the switching element is mounted based on the temperature of the lubricating oil. The current limit controller limits a current flowing through the switching element based on the temperature of the substrate in a manner that a temperature of the switching element is restricted from exceeding a predetermined upper limit value.

What is claimed is: 
     
         1 . A control system for a variable valve timing apparatus that changes a valve timing of an internal combustion engine using a motor which is controlled by operating a switching element, the control system comprising:
 an oil temperature estimating portion that estimates a temperature of lubricating oil of the internal combustion engine;   a substrate temperature estimating portion that estimates a temperature of a substrate to which the switching element is mounted based on the temperature of the lubricating oil estimated by the oil temperature estimating portion; and   a current limit controller that limits a current flowing through the switching element based on the temperature of the substrate estimated by the substrate temperature estimating portion in a manner that a temperature of the switching element is restricted from exceeding a predetermined upper limit value.   
     
     
         2 . The control system according to  claim 1 , wherein
 the current limit controller limits the current flowing through the switching element from exceeding a predetermined upper limit guard value when the temperature of the substrate estimated by the substrate temperature estimating portion becomes higher than a predetermined determination value.   
     
     
         3 . The control system according to  claim 1 , further comprising:
 a switching element temperature estimating portion that estimates the temperature of the switching element based on the temperature of the substrate estimated by the substrate temperature estimating portion, wherein   the current limit controller limits the current flowing through the switching element from exceeding a predetermined upper limit guard value when the temperature of the switching element estimated by the switching element temperature estimating portion becomes higher than a predetermined determination value.   
     
     
         4 . The control system according to  claim 3 , wherein
 the switching element temperature estimating portion computes an increase of the temperature of the switching element, which is caused by self-heat-generation of the switching element, based on the current flowing through the switching element, and   the switching element temperature estimating portion computes the temperature of the switching element by adding the increase of the temperature of the switching element to the temperature of the substrate estimated by the substrate temperature estimating portion.   
     
     
         5 . The control system according to  claim 1 , wherein
 the substrate temperature estimating portion computes a base temperature for the temperature of the substrate based on the temperature of the lubricating oil estimated by the oil temperature estimating portion and a temperature of cooling water of the internal combustion engine, and   the substrate temperature estimating portion computes the temperature of the substrate by mathematically processing the base temperature for the temperature of the substrate.   
     
     
         6 . The control system according to  claim 1 , wherein
 the oil temperature estimating portion computes an increase of the temperature of the lubricating oil with respect to a temperature of cooling water of the internal combustion engine based on an operational status of the internal combustion engine,   the oil temperature estimating portion computes the temperature of the lubricating oil by mathematically processing a value calculated by adding the increase of the temperature of the lubricating oil to the temperature of cooling water.   
     
     
         7 . The control system according to  claim 1 , wherein
 the oil temperature estimating portion computes a combustion temperature of the internal combustion engine based on an operational status of the internal combustion engine,   the oil temperature estimating portion computes an increase of the temperature of the lubricating oil with respect to a temperature of cooling water of the internal combustion engine based on the combustion temperature, and   the oil temperature estimating portion computes the temperature of the lubricating oil by mathematically processing a value calculated by adding the increase of the temperature of the lubricating oil to the temperature of cooling water.