A gearbox assembly including a housing supporting an input shaft to drive a first shaft that includes drive gears that correspond to driven gears on a second shaft. According to the present invention, gray scale display is performed by combining time ratio gray scale and voltage gray scale in a liquid crystal display device which performs display in OCB mode. Images acquired from a number of samples are combined, enhancing the systematic defects and suppressing random features such as variations in material quality. Also, a number of rounds for each bout and a time duration for each round are selected. When the intake air amount falls within the high amount region, the hybrid electronic control unit detects a rich imbalance in air-fuel ratio among the cylinders by comparing the detected value with a third threshold corresponding to the intake air amount. The cleaning liquid is discharged to the outside of the watertight cap through discharge holes, which are formed between the external cylinder and the internal cylinder.