Planetary gear vs. CVT transmission

CVT is a generic term, so both cars are CVT-equipped. The Prius uses a planetary-gear system, Honda uses cones and belts.

I'm sure each has its advantages regarding power performance, economy, and cost.

 

I don't know about Nissan mechanical CVT...

Toyota has their own comparison of mechanical CVT (Allion) versus eCVT Planetary (Prius).

http://www.toyota.co.jp/en/tech/environment/ths2/output.html

 

It's not really about the Prius planetary gear transmission, which by itself is no more than a fixed gear ratio, but it's all about the HSD, which combines the MGs, ICE, and a very sophisticated control system. The HSD is by far more elegant than an ordinary CVT, but does offer some losses when power is forced to go through the mechanical-electrical-mechanical transformation cycle.

Tom

 

<div class='quotetop'>QUOTE(jamarimutt @ Aug 1 2007, 12:57 PM) [snapback]488704[/snapback]</div>

Don't know about the Sentra, but the Prius has the most throttle lag of any car I've ever driven, including a 1980 Ford Mustang turbo (which I thought would forever be the king of throttle lag, until now).

Yellow light in a Prius? Mash the throttle to the floor, take your time deciding if you'll go through the intersection or come to a stop...the PSD will still be gathering itself up and you'll be feeling only the first hints of acceleration...so if you DO decide to stop, it's still not really a problem.

I'm exaggerating a bit, but not much. I sometimes floor the throttle until I'm sure that I *won't* need the power, just to give the car a chance to spool up. It's like that.

Same with cornering...if you want to balance the chassis with power, you need to be WAAAAAY ahead of it, or it'll be too late. Fun, but challenging.

 

Yeah I've almost been rear ended a couple of times in the Prius when I do a fast lane change in heavy traffic and the throttle lag doesn't let me accelerate fast enough. I just need to remember to press the throttle down a lot sooner when I change lanes. It's not like a normal car at all in that regard.

 

I've driven the Nissan CVTs. They are smooth. Not much difference in feel to the Prius. They don't have the range the HSD has though. At 105 km/hr (about 65 MPH) I've seen 1200 RPM engine speed, and 5000 RPM engine speed, depending on load. You don't get that with a mechanical CVT!

I don't know how long the mechanical CVTs will last. Seems to me that belt will eventually fail, or the cones will wear, or something bad will happen. It just looks too fragile!
In the HSD the belt is straight and simple. The gears just turn, they don't slide on shafts. There is a lot less to fail. The electronics has proven to be more reliable than any mechanical system.

As far as the lag, I only see that if the engine has shut down. If you force it to keep running you get little or no lag. Not good for fuel economy, of course, but if you want to play, you have to pay!

 

<div class='quotetop'>QUOTE(Pinto Girl @ Aug 1 2007, 04:52 PM) [snapback]488845[/snapback]</div>

You can't compare Otto and atkinson cycle engine like that. It is how atkinson ICE response. That's why Prius has 28 hp instant battery power available.

 

<div class='quotetop'>QUOTE(Pinto Girl @ Aug 1 2007, 04:52 PM) [snapback]488845[/snapback]</div>

Ehh, I don't know. Avis gave me a '07 Mustang this week and it has its own issues with throttle lag. It may be the fault of the automatic transmission more than anything else but it needs at least as much time to downshift and spool up as the Prius. At least with the Prius you get **something** (though not much) from the hamsters (battery) while the ICE is winding up. Then again the end result in the Mustang is a bit more satisfying due to the combined noise of the engine thumping away and the transmission screaming at me to merge already and then leave me alone!

What can I say, it's a rental. Probably been abused by every business traveller in Connecticut by now.

 

hi guys,

From my understanding the HSD is a whole package of the eCVT and the electronic motor + ICE. So by saying the HSD is the gear, i think this is partially correct. Like tom said, there will be power(energy) loss when switching from mechanical/electronic. My experience on my 2004 350z convertible automatic gear also have lag too. I am pretty sure the 350z has larger lag then my 2007 prius. When I floor the gas, there is usually a big lag with load engine roar before the car accelerate. So my feeling is that the lag is acceptable provided that Z is almost 50% more weight then my prius.

 

"the Prius has the most throttle lag of any car I've ever driven,"

Well, last timer I described the lag, I got flamed by some who deny the lag exists. Be warned! ;-)

 

I have never notice any lag. When I hit the accelerator, it goes right away. Just today, I jumped from my lane that was at a complete stop into a lane that was going 25 MPH, and I didn't give it a second thought. I will start looking for it, but I have had cars with a lag before, and I definately noticed it and thought carefully before merging out in front of semis.

<div class='quotetop'>QUOTE(Pinto Girl @ Aug 1 2007, 01:52 PM) [snapback]488845[/snapback]</div>

Pinto Girl, All this time, I thought your name was in reference to the Ford Pinto, but now I am convinced it is in reference to real horses. Obviously, you have never driven a stock Ford Pinto if you think a 1980 Ford Mustang Turbo has the most throttle lag of any car.

<div class='quotetop'>QUOTE(jamarimutt @ Aug 1 2007, 10:57 AM) [snapback]488704[/snapback]</div>

I think it would have been less confusing if Toyota had not elected to say Prius has a CVT. I think it is more acurate to state that a similar function to a CVT is achieved by all the HSD components throughout the whole drive train working together, including the ICE. I guess they could have called it CVD for Continuously Variable Drivetrain.

The acutal Planetary Gear Set portion of the HSD system is almost as simple as the differential on a rear wheel drive car. They pretty much last forever (well, lets say 250,000 miles).

I will talk about my understanding ot the Prius Power Split Device and HSD in generalities. If you are a Prius Technician, or have done extensive research, you may be able to fine tune my description, and I welcome the dialog.

I think that if Toyota calls the Power Split Device an eCVT, it was a marketing decision based on how the car buying public would best accept the new technology. It is not like any other CVT or Automatic Transmission. As has been said, it has a fixed gear ratio, and I am not aware of any other transmission that uses a fixed gear ratio. The actual planetary Gear Set is very passive. Where the power flows is controlled by the computer by controlling loads and RPMs on the ICE, Motor and Motor Generator. I could not do anything without all the other unique HSD components and the Computer. THey work as a team.

I believe the name Power Split Device is more descriptive for the Panetary Gear Set as utilized in Prius, and the name Continuosly Variable Transmission is missleading, as that function can only be achieved by all parts of the HSD working together.

The Planetary Gear Set has no clutch surfacess and therefore should be more reliable than any Automatic Transmission including CVT that uses clutches where parts slide against each other with friction and resulting heat and wear.

The clutch disk in a manual (stick shift) transmission is covered with lining material similar to brake pads or shoes, that is sandwitched between steel Flywheel and sping loaded pressure plate and operate in a dry environment very similar to brakes. They are locked tightly together until you push in the manual clutch in. When you shift gears, the clutch plate and flywheel are then moving at different speeds, and are designed to slip against each other as you begin to let out the clutch untill it is fully engaged and they are locked together once the clutch is let all the way out. This is why you need to develope a technique of letting the clutch out gradually.

A regular Automatic Transmissions also has clutches and drums with bands that slide against each other but they operate in an oil bath, and the friction is minimized by the hybraulic torque convertor mounted on the engines flywheel. The clutches, drums and bands slip against each other when they are first activated until the lock together. This friction causes heat and wears away clutch material that darkens the transmission fluid and makes it stink. Incidently, the drums and clutch packs are typically connected with two or more Planetary geasets. As was said earlier, Planetary Gear Sets. As was said earlier, this is a very generic term to describe a particular arrangement of gears that I beleive have been used since the some of the earliest, if not the first automatic transmissions.

A CVT with cones and a belt has the friction material on the belt and it rubs on the cones in the oil bath causing friction and heat. The cones move in and out the vary the size of the pulleys. As the cones move together, the belt has to ride out further on the cones creating a larger circle while at the same time, the cones at the oposite end of the belt are moving appart so that the belt runs around a smaller circle. Like the different sizes of spokets on a bicycle, but with a belt instead of a chain, and able to make any size circle in between.

In the Prius Power Split Device, there is a fixed gear ratio, no clutches that ship at all. The chain in the Power Split device is on sprokets like a timing chain in the engine or a bycycle chain. It cannot slip, so their are no clutch materials wearing off and mixing with the oil.

The magic is in the computer, motor, Motor/generator and how they all work together. The computer operates Motors, Motor Generator and ICE in continuosly variable combinations to keep the battery between 60 to 80 percent charged, keep ICE in the most efficient operating range and maximize economy as much as posible.

The RPM of the engine is controlled by the computer, and is not directly based on the accelerator pedal. When you don't need much power, the computer operates the motor generator and ICE to charges the batteries or if they are already charge enough, shuts down the ICE once the Catelytic Convertor is warmed up. When you need more power, the computer can top the generator and use the motor at full power to assiist the ICE.

 

Here's a *shocking* $.02 I've experienced a +1s delay when I push the pedal to the metal. I don't believe this has anything to do w/ the eCVT. I don't have enough experience w/ it since I do try to drive more conservatively on my prius. My biggest gripe is the ICE shutting down 30-60s after a full stop. It happens no matter how slow I stop. And *yes* the car was 10min into the trip (80F outside)

 

<div class='quotetop'>QUOTE(ACORNBLUES @ Aug 2 2007, 02:42 PM) [snapback]489540[/snapback]</div>

What is wrong with that?

 

If the car is warm and the battery is charged and no heat is required to the cabin, the car should shut down 10s after a full stop the first time, upon deceleration thereafter. The only time I ever see the engine shut down that long after a full stop is when it's stone cold. Nearly a minute of warm-engine idling doesn't sound right.

Now, if you come to a full stop and then keep creeping forward to catch up with the next car's bumper you might have a problem. You need to be stopped continuously for 10s.

 

I said:<div class='quotetop'>QUOTE(Vebev @ Aug 2 2007, 04:20 PM) [snapback]489611[/snapback]</div>

and then I see:<div class='quotetop'>QUOTE(brick @ Aug 2 2007, 04:26 PM) [snapback]489617[/snapback]</div>

I see the error of my question... I somehow thought ACORNBLUES was asking why the engine shut off rather than why it stayed on. My apologies.