Technique: automatic transmission

Transmissions for Dummies

Automatic gearbox, sequential gearbox, robotic gearbox, dimmers, dual clutch, hydrostatic gearbox ... the bike now offers several gearbox alternatives. It is enough to lose your Latin. The bikers' den offers you a small overview to see it more clearly.

A universal panacea in motorsport, the sequential transmission is our daily batch. Because Monsieur Jourdain makes prose without knowing it, the worst of 125 Chinese user has a sequential box like the latest Porsche. In fact, it is a box, reports of which occur "in sequence", i.e. in a precise and unaltered order.

Indeed, unlike a car, where you can go straight from second to 4th or 5th, if you like, on a motorcycle, steps 3, 4 and finally 5 must be followed. An error in the barrel selection mechanism, which imposes the order of passage, as opposed to the gear lever, which is located in the place of your choice in the car.

Consistent

On a conventional gearbox, the gear change order is superimposed by a selection barrel. The gearbox is said to be sequential because we change gears one by one without being able to skip gears.

Robotic boxes

It is currently found on Yamaha FJR AS and 1200 VFR DTCs handled otherwise. This is a conventional "barrel" box, where the control is mechanized by means of an electric drive. The pilot pulls the trigger and makes the passes go through when he wants.

The control acts simultaneously on the selector and clutch, allowing gears to be engaged or disengaged.

Basically, the gear of the motorcycle does not change, it is just its control, which is automated. To avoid having to disengage when stopped, the clutch is also slave or can be centrifugal like on a scooter so that it automatically disengages below a certain engine rpm. From a performance standpoint, no change, nothing changes. The dual clutch is even slightly better. Only the energy used by the pilot to disengage and operate the selector is now supplied by the engine.

WORK Cup

The 1300 FJR box is a robotic serial box. It can be operated by hand or legs. The clutch lever is gone. It is a form of an automatic transmission.

CVT "Continuous Gear Variations"

Continuously variable transmissions, or "variators", are found on scooters and beyond Aprilia Mana. We're talking continuous variation because there are no intermediate bearings like there is on the gearbox.

To make an analogy, the box is a ladder, the dimmer is an inclined plane. Movement is transferred from the drive pulley to a pulley headed through the belt. As the setting is done by tapering the pulleys, the belt moves there, sliding continuously without stopping the transmitting torque.

In fact, the pilot keeps the throttle open under all circumstances, which guarantees him "cannon" acceleration. Disadvantage of the process: its low efficiency, materialized by the large cooling system it needs and high consumption. Compare the mana appetite of 850 and 900 CT and you'll see. Sliding along the cones, the belt rubs and wears out, dissipating energy that turns into heat. That is why, with rare exceptions (Daf, Fiat, Audi), it is not used or is used little in the car.

The dimmer can be purely centrifugal, as in 95% of the cases, or electronic, as in the Mana or Burgman 650. In the latter case, the dimmer movements are controlled by electronic actuators that determine the ideal gear ratio in accordance with engine speed and throttle opening. The advantage is to be able to combine the dimmer display with the injection display in favor of increased performance and slightly lower consumption compared to a centrifugal dimmer. Unlike a centrifugal dimmer, which only reacts to engine speed, an electronic dimmer can select a very long ratio when driving quietly on the gas network because you don't need power. Hence, lower consumption. On the contrary, you suddenly open wide, the dimmer is in a very short gear to offer you optimal acceleration. The advantage of this process is also that it allows the pilot to select himself using a switch for specific positions corresponding to "speed". This is what the Mana, Gilera 800 GP and Burgman 650 offer. From the user's point of view, it is quite close to Rs 1300, but in principle it is fundamentally different, hence the confusion in the minds of people.

Electronic drive Burgman 650

Unlike other scooters equipped with purely centrifugal dimmers, the Burgman 650 is equipped with an electronic dimmer that is controlled according to speed, speed and throttle opening.

The first automatic roadster, Aprilia Mana, also features an electronically controlled dimmer. Pay attention to important vents, synonymous with heat and therefore low efficiency.

Hydrostatic transmission

The arrival of the VFR 1200 DTC should not make us forget another Honda automatic transmission present at DN 01 and named HFT (Human Friendly Transmission)

Human friendly transmission

Motor Driven The hydrostatic transmission is equipped with a pump and hydraulic motor. In this pump, the tilt plate (gray left) pushes pistons that convert engine power into hydraulic pressure (red fluid). There is a hydraulic motor on the same axis that will drive the reverse conversion, i.e. converts pressure into energy. The electric drive (visible in purple in the diagram) allows you to change the tilt of the hydraulic motor tray. This action changes the stroke of the pistons, which cause the LED plate to rotate (gray on the right). Changing the stroke also means changing the displacement of the pistons, which decreases or increases the number of revolutions of the output shaft at the same number of revolutions as the input pump. This leads to a constant change in the gear ratio between the input shaft and the output shaft. Thus, the HFT is a CVT (Continuous Variable Transmission) as well as a dimmer. Finally, to avoid losses, the input and output shafts can be locked directly, which means a direct connection between the combustion engine and the transmission shaft, with almost no loss of efficiency (96% according to Honda).

Honda's compact hydrostatic transmission competes with electronic drives. As with the Burgman or Aprilia Mana, you can choose from 6 predefined positions corresponding to 6 different box ratios, from the infinity of combinations available.

Other

Basically, these are the "automatic" transmissions available on motorcycles. On two wheels, except in the distant past (400 and 750 Hondamatic and guzzi 1000 convert), very few torque converters have been used as we know them in automobiles. Heavy, bulky and rather low yield, they saved us.