I am still trying to get used to the tranny in my FEH. Couple things that seem very odd to me based on my other car/trucks that I have owned.

1) When traveling down the road at about 70mph the tach can be any place from 2000 RPM going down a hill and then 4,000 RPM going up a hill/incline. Do these transmisions not "lock up" like a normal tranny?

2) can some one explain to me the difference between D and L? I shift mine and it does not seem to really make much of a difference.

Jon

 

The drive train has a continuously-variable transmission in it (CVT). The computer controls the RPM of the engine via the setting of the CVT and the throttle and attempts to optimize the torque output for the load demand. The load is either the drive shaft, which can drive the wheels and the torque electric motor, and independently from that the Motor-Generator. By regulating the current flow, both electric motors may be a load (charging the battery) or a negative load (driving the drive train).

Complicated? Yep. I haven't been able to find any source for exactly how the system tries to optimize, but you can derive much of it if you know about optimal torque/RPM settings of the Atkinson-cycle ICE. I think it is a trade secret to Ford.

I have observed that the algorithm is fairly stable -- on my FEH I don't get varying RPMs unless I change the setting of the accelerator pedal or the terrain changes. If you are seeing that there might be something wrong.

It was a surprise to me that the difference between D and L is just a signal input to the computer, but that's what it is. You will get no difference on accel, but when your foot is off the accel pedal the L signal will slow the car faster in regenerative braking mode.

 

I try to be very careful about using the term CVT when describing how the system works.

To someone with experience with an actual CVT they would find that it drives very similarly. But technically you can't call it a CVT. Much less even calling it a transmission!

There are two places I have seen a good explanation of the system. The first one is a side-bar article in the January 2004 Motor Trend. The 2004 Prius was their car of the year. In the side-bar they gave a good explanation without getting too technical.

The other place is here:

http://prius.ecrostech.com/original/PriusFrames.htm

Click on "understanding the Prius" on the sidebar. In there Graham Davies explains how the Prius system works.

Except for a few minor differences, Ford uses the exact same architecture as Toyota does in their hybrids. So learning about how the Prius works will give you a very good understanding of how your Escape works.

 

You guys are spelling it wrong!

The Ford Escapes do not have a CVT, they have an eCVT.
Both are "continuously variable" but are two different beasts.

A CVT uses belts between two beveled, or varius diameter pullys.
A CVT is like a 21-speed bicycle, but with more than 21 combos.

An eCVT is a planetry gear set. There are no belts or pullys.
The "e" stands for electronic.

In the eCVT all gears are always in mesh all the time. Even in "Neutral" which I put in quotes because it is a pretend neutral. This car has no neutral in the traditional sense.
Neutral in the Ford with eCVT is just an unpowered coast, that's it. The car has no "Low" gear either. As mentioned, the gear selector is only a joystick to a computer. There's no mechanical link, except to the parking pawl when you put the car in Park.

To prove the shifter is only a joystick, put the car in REVERSE when moving forward at 55 miles per hour. Absolutely nothing happens. The computer sees this as an unreasonable request, a "human error" and ignores it. I'm not full of it, and this will not harm your car in the slightest. Hundered of people have tried this, and some Ford spokes-persons used to do this when they Demo'd the car for the media when it first came out in late 2004.

Also, not many owners live in the Rocky Mountains. I do. I have noticed the car will also go into L gear mode ( which is only for stopping, not pulling ) if I ride my brake pads too long coming down a grade. The car predicts my brakes 'should' be getting hot by now, and converts to engine brake even in D gear position.

As another example, on said hills, going downhill at 70 MPH I tried to put the car into "pretend neutral" so I could coast even faster. Well, the computer also saw this as an unreasonable request, and kept the power alive at this speed. N, by computer, is only supposed to cut all electric power to the motors, and allow them to "freewheel".

The "e" means an electric motor, the generator, which is the sun gear controls the engine speed. Since this transmission has 3 parts, one part can do whatever it wants, irrespective of the other two. The traction motor is the outer ring gear, and the gas engine is the carrier gear for the planets ( the "orbit"). The planet gears are just there like rollers to transfer power.

This is a good visual. http://homepage.mac.com/inachan/prius/planet_e.html

For example, you can have any engine speed at any wheel speed, if the generator speed changes. You can have any generator speed at any wheel speed if the engine speed changes.

You can only "lock up" the transmission and have engine speed "locked" to wheel speed if you lock up the generator first. This could happen, but generally is not the case.

It is very simple mechanically, but difficult to explain in words!
In summary, it is normal to have "RPM all over the place".
Happy driving!

-John

 

Jon-

Here is the torque curve for the 2.3 ICE, the link was posted earlier by GaryG.

http://www.cleanmpg.com/photos/showp...to/864/cat/508

You can see the "deadband" between 3000 and 3500 rpm where additional power is not added by the ICE. You can feel it if you look for it while you drive.

With your questions - you have only 'scratched the surface' of the differences between this drive train and a traditional engine/transmission.
I keep learning things all the time and I've been driving mine for 2 years.

 

I know that in many acceleration scenarios in my 08 FEH, the computer will put the engine at 4000 RPM and hold it there. Looking at the torque curve, I think it's obvious that Ford programmed and engineered for this scenario. By having the eCVT, Ford can put take advantage of the engine's most efficient (and possibly the more clean) power zones.

 

Please be aware there are some limitations.
http://john1701a.com/prius/presentat...ntation_06.htm

Ken@Japan

 

A photo is worth a thousand words but article does refer to the Toyota Prius not Ford Escape. The Escape might be similar but also different because it is a Ford.

 

Here's the graphs for FORD.



4 examples are given. Of course, there are nearly infinite possibilites between the lines.

At ICE speed of 1000 RPM for example, the generator will be between 4000 and -12,000 RPM.

At ICE speed of 4000 RPM, for example, the generator will be between 15,000 and -1000 RPM.

Since the Max. speed allowed is 12,500 with brief excursions to 13,000, you can now say it is not allowed to have the ICE at 4000 RPM with the car standing still.

Normally, the soonest you will see engine speed of 4000 RPM will be @ 17 MPH.
The Ford can have 3000 RPM at a stop. That does not mean it does, but it can.

Notice the "best" line, (least extreeme) orange line, in the center, is ICE 2000 RPM.
What RPM ( or close ) does this car run at most often????

 

[quote=MyPart;166576]I know that in many acceleration scenarios in my 08 FEH, the computer will put the engine at 4000 RPM and hold it there. Looking at the torque curve, I think it's obvious that Ford programmed and engineered for this scenario. By having the eCVT, Ford can put take advantage of the engine's most efficient (and possibly the more clean) power zones.[/quote]

What makes this situation more interesting is that hypermilers such as GaryG attempt to keep the RPMs below 2000 as much as possible for best fuel efficiency.