To Shift or Not to Shift
Ford Five Hundred buyers can choose between a CVT or 6-speed automatic transmission. Hereís why.
|Craig Renneker sees a future for CVTs in mid-size front-wheel-drive vehicles.|
Executive Engineer, Craig Renneker is in charge of the engineering and development of all new automatic transmissions for future Ford, Lincoln and Mercury vehicles. We talked to Renneker on the eve of the launch of the new Ford Freestyle crossover and Ford Five Hundred and Mercury Montego, a program that supports both CVT and 6-speed automatic transmissions.Q. Why both CVT and 6-speed on the same program?A.
Essentially, amongst the transmission community there are three new transmission architectures out there and itís not really clear to us which one of those is going to be dominant in this type of vehicle. Those three architectures are the CVT, the planetary 6-speed and the dual-clutch (found on the Audi TT and Volkswagen R32). We believe that the CVT or the planetary 6-speed are going to be the dominant for front-wheel-drive in North America coming forward. And this program gave us the opportunity to work with both of them. We developed the CVT with joint venture partner ZF and we were able to purchase the 6-speed from Aisin AW as sort of an off-the-shelf item. Weíve now been able to really get some deep experience with both the CVT and the 6-speed and that will set us up to make a longer-term architecture decision.Q. What are some of the differences between the CVT and 6-speed?A.
Letís start with fuel economy. By our computer calculations they should be about neck in neck, with the CVT possibly being a little bit better. Yet, when we run the actual fuel economy testing it comes out with the 6- speed a little bit better. So itís still not completely clear which one, long term, is going to deliver better fuel economy.
The other issue is performance. This has actually been very interesting. Our computer simulations show that the CVT should be faster 0 to 60 and, in fact, it is. Thatís why weíve got the CVT mated to the all-wheel-drive system and why we use CVT only in the Freestyle ,which is a little bit bigger and heavier vehicle. However, 0 to 60 times do not always correlate with the customerís perception of which one of these cars is faster. Thatís been an interesting thing for us to analyze as well.
The 6-speed tends to be a little bit quicker off the line, and yet the CVT beats it 0 to 60. And that really is going to come down to a customer perception issue as to which is the best way for customers to measure performance.Q. All Freestyles will be equipped with a CVT, while the FWD Five Hundred base model will have either CVT or 6-speed as options. Why that choice?A.
Since we knew we wanted to use the CVT with the AWD system, we never developed a 6-speed AWD package, we just never did the engineering work for it. And as we launch we canít really predict exactly how many customers are going to order AWD. We can make a projection, which we have, but itís going to come down to the customer at the end of the day voting as to how many AWDs we build.
Because every AWD requires a CVT, we need a little flexibility in the system to change the mix management between CVTs and 6-speeds based on the number of AWDs that we sell. For front wheel drive we can either use a CVT or a 6-speed.Q.What technologies have advanced the CVT into this torque range?A.
There are two key technologies in my mind that helped advance CVTs into this torque range. One of them is the loop chain, thereís no question about that. Audi worked with LUK originally to help develop that chain and weíve just built upon that. Weíve made some improvements to the manufacturing process and weíre actually running our chain at a little bit lower stress level than Audi. The other major enabler is the inclusion of an on-board microprocessor. Weíve got full electronic control over all the pressures in the CVT. That gives us a lot more flexibility and a lot quicker response time to the changing environment of the CVT.Q. What are the differences in size, weight and cost between the two?A.
The CVT tends to be a bit heavier and a bit more expensive to manufacture than the 6- speed. I canít share all of the exact manufacturing cost numbers with you. Honestly, I donít know because we buy the 6-speed from a supplier and theyíre not going to tell us how much it costs them to make it. But it is fair to say that the CVT is a bit more expensive to manufacture than the 6-speed.Q. How much more expensive? 5 percent, 10 percent, 30 percent?A.
Well again, I canít really share with you an exact number but itís not double or anything like that. The question we have is, are customers willing to accept a higher price for the transmission because of that. I donít know that they are.Q. What are the torque limits for CVTs and will we ever see rear-drive CVT transmissions? A.
Letís take that in two steps, first, letís talk about front-wheel-drive and going higher in torque. Iím not going to talk much about any future programs, however what we have said in the past and I think itís still fair to say, that the 3.0L engine is about as far as I see it practical to take a CVT. CVTs tend to be a little larger and heavier and that gets worse as they go higher in torque capacity. Iím confident that we can make a CVT work at the next higher level torque capacity. However, the weight and package size gap is going to get bigger.
AS for rear-drive CVTs, the chain or belt driven-type of CVT just doesnít package very well in a RWD application. It just doesnít fit under the body very well.