Continuously Variable Transaxle (CVT) Operation

This is a demonstration of a continuously variable transmission a belt-driven continuously variable  transmission, this is a General Motors V T25  trans axle it has a drive pulley  right here and a driven pulley over here  it has a still belt that seems to be the  weak point in these transmissions  because the steel belts tend to break at  times we have an input shaft from the  torque converter that's connected to the engine, so our power comes in.

We have a  reverse clutch that if we help this  solid with the engine turning the drive  pulley would turn backwards we have a  forward clutch that when it applies with  the engine turning will connect the  forward clutch to the drive pulley and  turn the drive pulley causing the driven  pulley over here to also rotate  connected to the driven pulley as our  output shaft with this gear right here  this gear connects to the final drive and propels the the front tires so the  way a CVT which is continuously variable  transmission.

The way that works is to  continuously vary the gear ratio of the  input to the output the gear ratio in  the low range that we're in right now is  about . to   takes about 2.6 terms of the input shaft  to equal one turn of the output shaft  but we can control the width of this  pulley and the width of this other  pulley which makes the still belt shift  positions and we can have gear ratios  that go anywhere from that 2.6 to 1 all the way up to an overdrive gear ratio of  clear up to about 0.4 to 1 which I'll demonstrate here in just a moment so  we're going to have power coming in.

We want to move forward  apply the forward clutch and turn the  the drive pulley in this demonstration we're actually going to hook a socket to  the output and turn the driven pulley but that's not really how it's done in  the vehicle but we're doing that in this demonstration to show you the different  gear ratios as we change it with compressed air on the Pistons that are  in these housing so we've got a very large socket and drill motor we're going  to hook up to the driven pulley let's go  ahead and start turning that notice that  as the drive pulley turns very quickly .

The driven pulley is turning very slowly  and it's a gear ratio of about 2. 6 to 1 now if I come in I want to change the  gear ratio I'm gonna apply hydraulic  pressure with a piston that controls  this pulley and I'm gonna use the air  pressure in this demonstration and it's  going to be noisy but you'll see the  pulley come down to a smaller width and  that's gonna cause the driven pulley to  go wider so I'm gonna do that right now  we play where the output is turning  class that can overdrive position, so  we're in overdrive right now the engines  turning really slow but the output shaft  is turning really fast.

Now we're going  to come in and change the ratio back to under drive situation so now we've got  the engine turning really fast and the  wheels are the output turning really  slowly and that's those are the two extremes of the CVT transmission and  what's cool is that we can vary the gear  ratio anywhere between this low and the  high that we had we can even have a 1 to 1 gear ratio of direct drive so once again.

This is a continuously variable  transaxle CVT and this particular one is  out of a General Motors product of Saturn but Honda Nissan Chrysler all use  continuously variable belt driven  transmissions transaxles the hybrid  electric vehicles use an electronic continuously variable transaxle that  uses electric motors and the planetary gearset in place of these pulleys.