A semi-automatic car features a transmission that combines manual and automatic gearboxes - offering the best of both worlds.
The system affords the driver easy control over gear selection, by providing steering wheel-mounted paddle shifters (or a modified shift lever). This means the driver can control gears in "manual mode", usually with an upshift/downshift method.
Crucially, in a semi-automatic there is no clutch pedal. Instead, the car’s CPU and sensors operate the clutch when the driver changes gear.
A set of actuators and a hydraulic motor sit where the gear lever and clutch pedal would be in a manual.
The vehicle's computer manages engine torque; speed; accelerator pedal position; and other functions.
When the CPU detects a scenario that requires a gear change, it engages the clutch and temporarily disconnects the semi automatic gear system. After this the shift actuators will shift gears and disengage the clutch so the connection between transmission and engine is re-established.
- Better fuel efficiency (like a manual)
- Easy to use (like a fully automatic)
Autos usually have the gear box layout "PRND" (Park, Reverse, Neutral, and Drive). Meanwhile, a semi-automatic might be operated via a lever or a push-button system on the wheel. A semi-auto will not have a Park mode and there will be an Automatic mode replacing the Drive mode.
In an automatic, gear changes are carried out by the vehicle, rather than the driver. In a semi-automatic, the driver decides when to change gear while helping them navigate through the gears.
Semi-automatic gearboxes are not common, but do feature in a number of cars:
- Many Ferraris, including the 599 GTO.
- Vauxhall - in smaller cars such as the Corsa.
Ford - the firm’s early semi-auto appeared in the 1970 Maverick, and has developed into the Easytronic gearbox, which is used in some Fiesta models.