| 摘要 |
Disclosed is a method of diagnosing cam profile switching and the resultant variable valve control in an internal combustion engine without reducing fuel efficiency or effecting exhaust emissions. The method involves changing between a normal mode and a diagnostic mode which changes the cam profile to adjust valve timing whilst also changing the amount of fuel introduced in to the cylinder so that a stoichiometric air to fuel ratio is maintained during the test. The exhaust gas is measured by an exhaust gas sensor and the measurement is then compared with the expected result. If the variable valve timing (VVT) and/or variable valve actuation (VVA) arising from the cam profile switching is operating correctly then the exhaust sensor measurements should be relatively unchanged between the two operating modes. A further embodiment allows for feedback control of the fuel injection amount. In this case, since the feedback amounts would be expected to be different for the two modes an error signal indicating cam profile switching failure and associated VVT/VVA failure is generated when the feedback correction factors in the two different modes are substantially the same. |
