Maybe this should be in the newbie forum. I'm very interested in a 2010 and having never driven a Prius before I'm interested in what the experience is like with the transmission. I know its a CVT. Does it feel like a normal auto (which I know has a torque converter) in that when you take you foot off the pedal it will creep forward? Or is it more like a manual that it will stay still or roll if on a hill? Thanks
It creeps like a normal auto but it doesn't feel like a normal auto, it's heaps better! There are no shifts, the engine revs are always as low as they can be to deliver just as much power as needed that is you never have the engine hunting up and down because you are right between where the engine is happy in a gear, there is no noise when stopped, there is no energy used when stopped with your foot firm on the brake pedal(except to run accessories), there are no bumps as you put the car in drive, there is no delay in selecting drive or reverse, the shift lever movements are light but precise and it will put itself in park when you shut down the car! The system still provides engine braking for steep long hills, and you will love it! You can drive a Prius just like you drive any car, you don't even need to turn a key to start it!
It's not a conventional CVT. The only reason to use that name is that it is continuously variable. Instead the car controls the road speed and engine speed by varying the rate of rotation of two motors, referred to as MG1 and MG2. It can vary the rate of rotation either by applying power to the motor, or taking off power by configuring it as a generator. It may send some of the power generated to the other MG, depending on power and torque requirements. The transmission does not mechanically creep or provide drag. To feel more like a conventional automatic, the HV ECU software drives MG2 at low speed, to a target speed of 7 mph on the flat, to simulate creep. At higher speeds, it takes some power off MG2 to simulate mild engine braking. As you press the accelerator, the regen is reduced until at zero, then power is applied. This zero spot is what the hypermilers call the 'glide' position. The simulated creep is sufficient to keep the car from rolling back on most shallow and medium hills. If you're coming from a manual, slow speed manoeuvring can be a bit tricky as you're braking against the creep, which may be low speed, but can provide a fair bit of torque. The friction brakes are quite grabby when braking against the creep, particularly as they are used so little in normal service braking - the car prefers regeneration to friction braking, where possible, and friction braking normally only kicks in when the ECU switches to creeping. At around 6mph, and slowing to a stop, I reckon the wheels don't even complete one whole revolution (the circumference of the 2G tyre is a little under two metres). Regen doesn't actually provide that much energy relative to the amount of energy required to accelerate and maintain speed, but it's better than wasting it by heating brake pad material.
Thanks guys! I've only ever had 2 cars. My first was an auto (with a large V8 engine) and my current is a little manual city car. I sure miss that auto around London, so much easier to drive. I tried an automated manual but found it a little weird, as it didn't simulate creep at all. So I'm pleased the Prius drives like this. I think I read in one of the reports that on the 2010 if you hold the brake right down for a few seconds it beeps and then will hold the brake for you for a few seconds to allow you to press the accelerator pedal and so not roll on hills. If so, this is a great feature. Nothing worse than hill starts on the handbrake!
there is an huge, huge, difference between best CVT's and Prius... and you should be glad for it . Prius and other toyota hybrids have, hands down, the best transmission you can get in the vehicle. On the other hand, even advanced CVT's have very, very strange driving feel. It is just very, very different experience.
Two things to add on the creep: * Target speed on my 2004 is 6mph. I've allowed the wheels to freely spin while lifted in the air to verify, and this is the speed at which the car settles from slower or faster. * Pressing the brake pedal with moderate pressure beyond a certain point switches off MG2. If stopped @ a light and you want to "conserve" battery, just hold the brakes more than "lightly". This can be verified on the energy flow screen. Once the brakes are released, creep is re-enabled. * No pedal coasting is similar to an automatic - you get a light braking effect through regeneration down to about 12 mph, after which point you'll coast to the 6mph creep target. * B-mode - consider it like low gear in an automatic - it's used for downhill "engine" braking by using maximum regeneration. This too is effective down to 12mph. Note - when the battery becomes full, the excess energy will be used to spin the engine up to it's max RPM. Don't be concerned, the car will not "overrev", though the noise can be disconcerting at first. Otherwise, the car drives just like any other automatic, minus the annoying shift shock. The sensation you'll get is seamless acceleration to the point where you're at your target speed w/o realizing it. Granted, at 140,000 cumulative Prius miles, I've grown more used to it ;-)
Even tougher doing a hill start with a foot operated handbrake but it can be done. I just hold my left foot on the brake to do a hill start. Oh, I actually brake with my right foot, left foot braking is only for steep hill starts.
The 2010 will have Hill Start Assist, which has something to do w/ holding the brakes for a bit until the gas is applied. Not sure how hard you have to press on the gas at first though. The current Prius "can" roll back slightly if the hill is steep enough and you're not quick on the gas. Nothing like a manual transmission though.
Hill assist works like this. If you are on a hill, and the vehicle starts to roll back with the vehicle in drive, the brakes will engage. At that point, as soon as you have ANY pressure on the gas pedal, the brakes disengage and away you go. It isn't like you have to mash the gas to have the brake release.
Hi Wooski, The best way to describe the Prius transmission, is that is an electric torque converter. There are two motors, the torquer, MG2 (Stands for Motor Generator 2) and the speeder, MG1. MG2 is fixed geared to the wheels. MG1 can vary in speed forward and reverse by a large amount. When the car is going slow, and you want to accellerate, the engine comes on, but the torque load at the wheels is too large for all of the engine RPM to go directly to the wheels. The overspeed is sent to MG1 turns backwards generating AC electricity, which is rectified into DC electricity, and feeds MG2. As the car gets faster and faster, more and more of the engine power can go to the wheels, and less to MG1. Eventually, the engine can run the car down the road without any electrical assist with MG1 stationary. Check out http://prius.ecrostech.com/original/PriusFrames.htm for in depth descriptions.
its like on Rav4... to activate the feature, you need to hold brake all the way for 2-3 seconds, it will beep and then it will be active (and brakes will hold your car).when you release the brake, you have several seconds to press gas at which point it will automatically shut off. so it is not automatically activated feature because of course it does not know what you want to do...
You can run AC motors from a DC source, all you need is an inverter. And indeed the Hybrid battery is a DC source that is fed to MG2 on occaision. So, MG1 output is converterd by its inverter bridge to DC, wherein the inverter bridge for MG2 reconverts the DC to AC..... My take on the OP was that he did not have a motor technician/electrical engineer level of understandng of motor controls. So, I simplified things to make the big picture easier to understand... I never said or implied MG2 was a DC motor. You read that into what I wrote, yourself..... And the terminology is loose in this regard anyway. A brushless DC motor is very similar to a AC permanent-magnet synchronous motor. A better description for the motor in the Prius is a hybrid-field AC motor, but that is not official terminology of any of the motor people. Hybrid, because at slow speeds the majority of the magnetic field is from the permanant magnets, and at higher speeds, the majority is from induction...
I think you did imply MG2 was a DC motor, hence my post. Whether I read extra into your post or not does not really matter. At least I wasn't condescending toward Wooski. I did not make any assumptions about Wooski's ability to understand the operation of the Prius' drivetrain which, conceptually at least, is not that difficult.
Thanks to all contributors on the 'trans' post! I plan to purchase a IV or V soon after delivery to U.S. Only concern is how difficult it may be to do business with the dealers. MSRP is just fine and I plan to include a few dealer options - but please...do not plug in the unwanted dealer packages before delivery... Honestly --- anytime my thoughts have swayed to potentially another vehicle (Insight or any other variety of hybrid on the market now) I always seem to read something on this forum that simply places the Prius technology so far ahead of any other hybrid on the market. And because of your information, my decision will be simple - can't wait for the '10 test drive....one of thousands here to be sure. Thanks again folks!
The terminology does get a little funny. A brushless DC motor is really an AC motor with a built-in inverter. For larger motors, like those of the Prius, it still works in a similar fashion, except now the inverter is placed in its own package. Draw the box around the inverter *and* motor and you can still consider it a brushless DC motor. Draw two boxes and you have an inverter and AC motor. Either way it's the same system. I do like the term hybrid synchronous motor. It's a good description of how they work. Just to be clear for other readers, the hybrid synchronous part is not directly related to the discussion about brushless DC. You can make any motor technology brushless with proper electronics. The hybrid synchronous part is simply a compromise between cost, size, and efficiency. The permanent magnet portion is very efficient, but not very powerful. The induction portion is very powerful for the cost and size, but not as efficient. Combining the two allows for good efficiency at lower power outputs, but larger power when needed, but at the expense of efficiency. Tom
