The need to meet increasing fuel efficiency and emissions standards is breathing new life into an old design.
I remember my 1966 Ford Mustang fondly. It had a 200 cubic inch 6 cylinder, so it wasn't a "hot rod" by any means. It did have a Hurst shifter mounted to its three speed manual gearbox, and guys looking in through the window thought there was more under the hood than there really was. Shifting through the gears on an open stretch of road supplied plenty of exhilaration to a then young driver, and learning how to ease the clutch out for a smooth take off, especially on an upslope, are lessons that weren't learned easily.
Maybe that's the reason manual transmissions have lost their appeal to the average consumer. They certainly can't compete with an automatic in ease of use. But the world, and our industry, is changing as the need to improve fuel economy, reduce vehicle emissions and lower our carbon footprint continues to rise.Manuals Revisited: The Automatic Manual
Manual transmissions will be an important element in meeting future fuel economy and emissions standards, worldwide. In terms of efficiency, manual transmissions are nearly 97 percent efficient in transferring engine power from the engine to the drive line, while automatics come in around 86 percent. They are much simpler in design than their automatic cousins, with fewer moving parts making them easier — and cheaper — to manufacture.
But to make manual transmissions acceptable to the average consumer, the OEMs will have to address the consumer perceived problems of difficulty of use and perceived drivability issues caused by missed or improper shifting technique.The answer lies in modern electronics. First is the transmission control unit (TCM), mated to the network communications bus so it receives the driver's inputs and information it needs on how the vehicle is currently operating. Second is an electronically controlled clutch actuator to replace the driver's left foot on the clutch pedal. This actuator can be electro-mechanical (using an electric motor to move the clutch linkage) or electro-hydraulic.
Last is an electro-mechanical shift actuator that takes the place of the shift linkage. These components allow a conventional manual transmission to shift like an automatic, with no additional effort required by the driver. These designs are appropriately named Automatic Manual Transmissions, or AMTs.The software programmed into the TCM gives the driver a choice of shift options, allowing them to select a "sport" mode that allows manual shifting much like you're already familiar with on some planetary automatic transmission offerings.
When compared to a conventional manual, an AMT completes a shift in about half the time (300 to 500 milliseconds as compared to 500 to 1,000 milliseconds), with an efficiency gain of 2 to 4 percent even though it weighs slightly more. It also reduces emissions levels 3 to 5 percent and costs about the same as its conventional counterpart.A variant on the AMT is the Zeroshift transmission designed by Zeroshift Ltd. The Zeroshift design addresses the perceived poor shift quality of some AMTs. It does this by further reducing the time between shifts to, as the name implies, near zero seconds! How it works is pretty unique.
The Zeroshift hub assembly takes the place of the synchronizer pack used in a conventional transmission. It essentially is a simple torque hand-over from one drive gear to another. According the company's literature, "Two drive rings (dogs) with alternating faces share a common hub and allow drive in one or the other direction; one ring takes up the drive, the other eliminates the backlash that is common in dog shift transmissions.""When conducting a Zeroshift, the unloaded ring is moved with considerably less force to that of existing transmissions. Engine synchronization is conditioned by a control system to ensure a seamless torque transition." Seeing it in action makes the process easier to understand and you can see a video animation of it at www.zeroshift.com/animation.
Eliminating the time between shifts not only improves efficiency and reduces emissions, it adds to performance.According to company literature, "On average, a vehicle equipped with Zeroshift will take one second less to accelerate from 0 to 60 (mph) than an identical vehicle with a (conventional) manual transmission." It also addresses the drivability and shift quality issues. Because there is no perceptible time between shifts, the normal vehicle pitch experienced by occupants driving a conventional manual transmission is eliminated.
Not One, But Two!
Another variant on the standard manual is the dual clutch manual transmission (DCTs). DCTs essentially are two manual transmissions in one. One side handles the even gears, and the other side takes care of the odd gears, with some DCTs having seven total gear combinations. The heart is a dual, multiplate, wet or dry clutch separated into an inner and outer assembly.One clutch relays power to one side of the trans, and the other relays power to the opposite side. An electronic control unit anticipates which gear will be needed next, and engages that gear to its shaft, but no power flows until the corresponding clutch is engaged. The result is a seamless shift from one gear to the next.
Manufacturers like Getrag have been working on the technology since the 1980s. The Porsche PDK DCT competed in the Porsche 956/962 racecar back in 1983, but limits of then current electronics prevented it from reaching production.
"My first prototype dual clutch transmission was in 1987. At that time the electronics were not as powerful as today," says Ulrich Remmlinger, head of product engineering at ZF Getriebe, GmbH.
Shift times for a typical DCT range from 150 to 300 milliseconds, even faster than an AMT. Fuel consumption savings are comparable to an AMT, but overall emissions savings are almost double over the automatic manual. The biggest drawback, from a manufacturing standpoint, is the current cost of the design. There are few suppliers providing components, and manufacturers are seeking to recoup engineering costs.
However, the costs are comparable to many conventional automatic transmissions, and this cost spread should become lower over time as more companies compete for the business.
There is an additional advantage a DCT offers over a conventional automatic transmission. Gearing is independent in a DCT, allowing a larger spread of ratios as compared to a planetary automatic and just as many of them. There are 6-, 7- and even an 8-speed dual clutch transmission offered in the market place. As with 7- and 8-speed automatics, it's all about keeping the engine in its most efficient rpm range. As a comparison, the 7-speed DCT in the Porsche 911 cuts engine rpm from 2,450 at 62 mph (using the 5-speed automatic) to 1750.
What about Automatics?
The stated goal is improved efficiency. Newer multispeed automatics like the ZF 8-speed are proving that the planetary automatic can be made to meet those goals. It is expected to be used in production of the new BMW 5-series GT and possibly in other model lines as well.
Dr. Klaus Draeger was quoted in an article on DCTfacts.com as saying, "The 8-speed ZF is now able to shift as fast as a good DCT." It also offers other advantages according to Draeger. "If you want to shift quickly from sixth to fourth or from seventh to fifth, you can do this in a single step with the eight speed. On the DCT it takes longer as the shifts are sequential."
In addition, he says that because a DCT essentially is a manual tranny, high output models would require beefier gearing and internal parts, adding to the size and weight of the assembly.
Constant variable transmissions (CVTs) are popular with many Japanese auto makers, and they too continue to evolve. The Nissan XTRONIC CVT transmission, for example, has a unique supplementary two speed planetary sub-transmission that operates in series with the CVT variator. This innovation increases the ratio spread over a typical CVT and allows lower rpm at cruising speeds while still maintaining low speed drivability. Size and mass are also, surprisingly, reduced and the manufacturer claims a 30 percent reduction in internal friction with a corresponding increase in fuel economy of 10 percent.
A slightly different take on a DCT is the new Nissan 1MC2 system, to be introduced on the 2012 Infiniti M35 hybrid. This powertrain uses a single electric motor-generator and two clutches in place of the torque converter to drive its 7-speed planetary automatic.
The motor is a 50 kW permanent magnet design with a clutch on either side, allowing multiple driving modes. During conventional highway driving, both clutches are engaged and the gas engine drives the tranny directly. The rear clutch is a wet design that allows some degree of slippage for smooth operation, and the motor can operate as a generator to charge the HV battery.
On full acceleration, both clutches are engaged and the motor adds its torque to the engine's output. Nissan says that the absence of a conventional torque converter adds a "direct feeling driveline" that should appeal to sporty drivers. When slowing down, the front clutch disengages while the rear remains engaged to take advantage of regenerative braking. Low speed operation is electric drive, with the front clutch open to separate the engine from the driveline.
Today and Tomorrow
All of these new transmissions have a few things in common. One, they are all being developed to increase the overall efficiency of the modern automobile and many have applications to future hybrid and electric vehicle (EV) designs. Two, they are all electronically controlled. That means that we, as the guys and gals charged with keeping them on the road, must continue our own education in order to keep up with changing times and technology.
We at Motor Age are pledging to do all we can to help you do just that. Additional resources can be found online in our community site at www.SearchAutoParts.com, and through our dedicated e-newsletters. You can get the latest information from us on the 'net by joining me on Facebook and/or Twitter. Just search me, Pete Meier.
