Patent ID: 8746189

Claim:
A control system of an internal combustion engine comprising: a variable compression ratio mechanism able to change a mechanical compression ratio; a variable valve timing mechanism able to control a closing timing of an intake valve; the closing timing of the intake valve approaching an intake bottom dead center as an engine load becomes higher, a detection device for detecting the mechanical compression ratio; and a compression ratio control device controlling the mechanical compression ratio on the basis of the mechanical compression ratio detected by the detection device; wherein when an abnormality occurs in the detection device, the mechanical compression ratio is lowered to a minimum mechanical compression ratio, the closing timing of the intake valve is fixed to a closing timing at the time of an engine high load operation, and control of an amount of intake air by the variable valve timing mechanism is switched to control of an amount of intake air by a throttle valve, said detection device is provided with a detection sensor which detects the mechanical compression ratio and generates an output signal which shows the detected mechanical compression ratio, said compression ratio control device receives an output signal of said detection sensor as an input signal showing said detected mechanical compression ratio and, based on said input signal, lowers the mechanical compression ratio when said detected mechanical compression ratio is higher than a target mechanical compression ratio and increases the mechanical compression ratio when said detected mechanical compression ratio is lower than the target mechanical compression ratio; said control system is provided with input signal switching means for switching said input signal to an input signal indicating a predetermined mechanical compression ratio of a high compression ratio side regardless of the output signal of the detector sensor when an abnormality occurs in said detection device; and due to this input signal switching action, the mechanical compression ratio is lowered toward the minimum mechanical compression ratio.