General Motors plans to roll out a new 10-speed automatic transmission in its 2017 Chevrolet Camaro ZL1. Designed for rear-wheel-drive applications, the transmission will be available in eight yet-to-be-named vehicles by 2018.
Earlier this month, Ford announced select trim levels F-150 would get a 10-speed transmission, so the trail is already blazed to drop the new trans into select members of Chevy and GMC’s pickup lineup.
GM says its new 10-speed is an all-new design – and the first-ever application in a car – with a wider, 7.39 overall gear ratio spread, that enables the ZL1’s supercharged engine to remain at optimal engine speeds during upshifts.
“With world-class shift times on par with the world’s best dual-clutch transmissions and the refinement that comes only from a true automatic, the 10-speed delivers incomparable performance on and off the track,” says Dan Nicholson, vice-president, GM Global Propulsion Systems. “It also leverages the experience of our other multispeed transmissions to deliver that performance with greater efficiency as its use expands into other vehicles.”
The wider overall ratio enables a lower numerical top gear ratio – an attribute that reduces engine speed on the highway, which contributes to greater fuel efficiency than a comparable eight-speed transmission. Improvements in spin loss complement the optimized gearing, further enhancing efficiency.
The 10-speed is approximately the same size as the six- and eight-speed transmissions, minimizing changes to vehicle interfaces.
Testing has shown faster upshift times than the Porsche PDK dual-clutch transmission. In fact, the 1-2 upshift is 36-percent quicker than the PDK, while the 2-3 and 3-4 upshifts are 27-percent and 26-percent quicker, respectively.
Thanks to only two non-applied clutches – the same number as the eight-speed – as well as other design features, the 10-speed automatic has lower friction that contributes to greater fuel efficiency over GM’s six- and eight-speed automatics. New ultra-low viscosity transmission fluid also reduces friction, while an internal thermal bypass allows the transmission to warm up faster – attributes that enhance fuel efficiency
It is the latest transmission to use an all-new, GM-developed control system, with performance calibrations tailored specifically for different vehicles.
Architectural features and packaging
Thousands of hours of computer-aided engineering analyses were made during the development of the Hydra-Matic 10-speed transmission, resulting in a design envelope comparable to the eight-speed automatic.
A one-piece aluminum case with an integral bell housing helps reduce weight and enhance powertrain stiffness, while a unique 260mm, integral turbine clutch torque converter design reduces complexity and helps make the converter thinner, which contributes to the transmission’s packaging.
The 10-speed has four simple gearsets and six clutches: two brake clutches and four rotating clutches – one more clutch than the eight-speed, despite having two more forward gears.
A unique triple-clutch assembly in the middle of the 10-speed’s architecture is a primary enabler for packaging 10-speed content in the same space as GM’s six- and eight-speed transmissions.
The 10-speed also features a variable-displacement vane pump, which optimizes transmission fluid pressure, based on speed and load, to enhance efficiency.
7.39 ratio spread and faster upshifts
The new 10-speed’s performance and efficiency are due primarily to its wider 7.39 overall gear ratio spread, which GM says enhances off-the-line performance with a more aggressive first gear ratio than the company’s eight-speed automatic. Smaller steps between the gears also help the engine maintain the optimal speed for maximum power at almost all speeds, especially when exiting a corner on a track.
Adaptive shift controls such as Performance Algorithm Shifting and Driver Shift Control enhance performance driving. Performance Algorithm Shifting (PAS) monitors how assertively the driver is using engine output to determine at what engine speed to upshift or downshift. Driver Shift Control allows the driver to shift the transmission via the steering wheel-mounted paddle shifters. Electronic safeguards prevent over-revving if the wrong gear position is selected, but relies on the driver to make upshifts or downshifts.
Gear changes are mainly executed with clutch-to-clutch action, where an on-coming clutch is engaged and an off-going clutch is released in a precise manner to achieve the ratio change. Certain key shifts, however, are made with a freewheeling action, such as 3-1 downshifts, where a plate clutch is actively disengaged while a mechanical freewheeler clutch automatically engages with optimum synchronization.
The torque converter is 260mm in diameter and features a lock-up clutch. It also uses electronic controlled capacity clutch (ECCC) technology, which employs a small, regulated amount of slip to dampen out engine pulses for a smoother running drivetrain, especially during shifting.
Reduced spin losses and new transmission fluid
Friction-reducing design features, including all-new ultra-low viscosity transmission fluid, internal thermal bypass, minimal number of non-applied clutches and other lower mechanical spin losses, contribute to the 10-speed’s effect on improved vehicle efficiency.
The low-viscosity fluid helps reduce fraction across the full temperature operating range, which enhances fuel efficiency. Additionally, the internal thermal bypass allows the transmission to warm up faster to its optimal operating temperature, further contributing to fuel efficiency.
GM control system
Shift time quickness and responsiveness are accomplished by leveraging the base transmission hardware in concert with GM exclusively developed algorithms, software and calibrations. An externally mounted electronic control module executes millions of controls instructions every second.