Automated manual transmission (AMT)

An AMT is not a new kind of gearbox. Inside is the same manual gearbox and single-plate clutch as the manual version of the car; what changes is who operates them. A hydraulic or electric actuator pushes the clutch release fork, a second actuator moves the selector forks, and a small control unit decides when to do both. Maruti calls it AGS (Auto Gear Shift), Tata and Renault call it AMT; the kit itself is often supplied by Magneti Marelli or Bosch.

• Sensors feed the control unit with road speed, engine rpm, throttle position, brake pedal and the lever position (R, N, D or manual).
• When a shift is due, the unit opens the clutch with the actuator, exactly as your foot would.
• The shift actuator moves the fork to the next gear while the engine management briefly trims the throttle.
• The clutch is closed again, with a controlled slip so the car does not jerk.

The sequence takes a noticeable moment, which is why AMTs have a brief pause and head-nod between gears, most obvious under hard acceleration. Driving gently, or using the manual mode to shift a little earlier, smooths it out. Creep in traffic is handled by slipping the clutch, so long crawls in stop-go traffic warm the clutch and some cars protect it by refusing to creep uphill.

The hardware sits on top of or beside the gearbox under the bonnet, which is why an AMT adds so little weight and cost. In the Swift, Celerio, Tiago, Punch, Kwid and Exter it is the affordable automatic; the same idea, with heavier actuators, appears on some trucks and buses.