FLAT SHIFTING
IF YOU’VE EVER HIRED a car you’ll probably be familiar with flat shifting – where you keep the throttle pinned as you jab the clutch pedal and simultaneously move the gearlever as quickly as possible into the next gear. It isn’t elegant but it makes for some pleasingly rapid gearchanges. You’d never want to do it in your own car, though. Unless, that is, you have an Aston Martin V12 Vantage S fitted with the new seven-speed manual gearbox with AMSHIFT – a system that Aston has developed to allow quick and safe upshifts while keeping the throttle wide open.
Flat shifting technology has been available on motorbikes for some time. Their low-inertia engines allow for gears to be engaged without declutching at all, so their flat-shift systems simply cut the ignition momentarily. However, to allow a 5.9-litre V12 to perform a flat shift quickly and effectively, while using the clutch, the system needs to be more sophisticated than just interrupting the ignition.
Alex Wood, powertrain calibration engineer at Aston Martin, explains what is going on when you change gear using AMSHIFT: ‘The key components needed are being able to initially detect when you’ve lost grip at the clutch, to be able to cut the engine’s torque fast enough so you don’t get a flare of revs when you press the clutch, and then, when you lift back off the clutch, detecting the kiss point – the point at which the clutch plates all kiss each other and start transmitting torque again – so you can ramp the torque back in.
‘There are two sensors that are really important; they are the ones monitoring the clutch position and the clutch speed. The clutch speed sensor knows when your engine speed and your clutch speed begin to move away from each other. That’s the point at which torque will no longer be transmitted from the engine to the wheels.
‘At that point there’s obviously a big unloading on the engine, where you’d usually expect to just hit the rev limiter if you pressed the clutch. So what we have to do then is carefully manage the torque that the engine is producing so that the engine stays at exactly the right revs for the gear you’re currently in.
‘How the engine manages that torque, while you’ve got your foot on the clutch, is by retarding the ignition and cutting fuel to a specific number of cylinders. These are the fastest methods to cut torque. As soon as you lift back off the clutch you basically wind the spark back in, turn the fuel back on and you get an instant torque transition back into smooth driving.’
The AMSHIFT system not only works during full-throttle upshifts, but you can also change gear while keeping the accelerator pedal at any position. You can even miss a gear or make an embarrassingly slow change, but when you lift back off the clutch, the engine will be at exactly the right revs.
AMSHIFT isn’t as simple as it might at first seem, then. It’s not just a quick cut of the ignition: numerous aspects of the drivetrain are being monitored and the engine responds differently depending on how the driver executes the shift. It’s a fascinating feature for the driver of a manual V12 Vantage S to experience. Let’s just hope they don’t forget they still need to lift off the throttle pedal when changing gear in other cars.
It’s more sophisticated than just interrupting the ignition