ARJEPLOG, Sweden – From a 7-speed Getrag dual-clutch hybrid-electric transmission to a 3-motor electric-axle layout enabling torque vectoring and improved dynamic handling for battery-powered cars, Magna’s powertrain division is preparing for the next generation of sophisticated propulsion systems.
Magna acquired transmission specialist Getrag just last year, and already the company is shopping to potential automaker customers prototype cars integrating the latest Getrag transmissions, such as the new 6MTI550 manual for torque applications up to 590 lb.-ft. (800 Nm).
Installed on a BMW 340i, the 6MT is intended for low-volume inline engine applications and is compatible with all-wheel drive and stop/start systems. Maximum input speed is 7,000 rpm, and Magna says the modular design can be scaled for torque density, gear number, spread and synchronizer technology. The transmission also is suited for light-duty commercial vehicles.
Also available during recent test drives in Arjeplog, Sweden, was a series-production Renault Mégane IV with a Getrag dual-clutch 7DCT300 transmission, which was designed for high fuel efficiency and to accommodate torque up to 236 lb.-ft. (320 Nm).
The 7-speed DCT works with most front-transverse engines and stop/start, consumes little power, mates with AWD, integrates a mechanically actuated parking brake and can achieve a gear ratio spread as high as 8.5.
The FWD Mégane IV, with a 1.6L 4-cyl. and an open differential, launched this year with the Getrag DCT, but the transmission first appeared in the larger Renault Espace in 2015.
The Mégane test drive was intended to demonstrate the three available modes that change drivetrain behavior. On the open road, switching between Sport, Neutral and Comfort modes significantly alters the drive experience. That flexibility is much more difficult to achieve with a conventional automatic transmission with a torque converter, Magna engineers say.
In comfort mode, upshifts with the Getrag DCT occur quickly, at low engine speeds, improving fuel economy and ensuring ultra-smooth cycling through gears. The driver arrives in fifth gear without even realizing it.
In Sport mode, the DCT holds gears longer, allowing the engine to rev higher and route more power and torque to the road. The two wet clutches enable much quicker shifting: 200 milliseconds in Sport, compared with up to 350 milliseconds in Comfort. In all modes, the DCT will downshift up to three gears, depending on pedal position and vehicle speed.
“We don’t use a classical hydraulic system for this transmission,” says Thomas Holle, Magna Powertrain teamleader for transmission testing.
“We use smart actuation that combines small electric motors and small pumps for each clutch. Each single clutch has its own e-motor pump system, an on-demand actuation pump. We only need to turn the electric motors when we need to keep a clutch closed or change status of the clutches.”
The next step is to further electrify the DCT for hybrid applications by integrating within the transmission housing an electric motor rated as low as 15 kW for stop/start and up to 75 kW for a plug-in hybrid, Holle says.
“And the installation length will not change for the (OEM) customer,” he says of the hybrid DCT, which is 14.5 ins. (369 mm) long. “It’s easy for the customer to build up a platform” with either the DCT or hybrid HDT version.
The hybrid transmission integrates all the necessary cooling, power inversion and electronic controls.
Estimating the fuel-economy gain with the hybrid transmission depends on battery size and other parameters, but Holle says an automaker could see a 20% reduction in fuel consumption relative to the standard non-hybrid DCT.
The hybrid transmission weighs about 198 lbs. (90 kg) while the non-hybrid DCT weighs in at 148 lbs. (67 kg), Holle says.
The hybrid version is intended for FWD architectures, but Holle says Magna is considering adapting it for AWD.
Tesla Model S Adapted For Torque Vectoring
A further demonstration of Magna Powertrain’s electric-drive capabilities is a Tesla Model S modified to use torque vectoring for greater vehicle stability during aggressive driving.
The production Model S, a sleek and sporty all-electric sedan, is known for excellent straight-line acceleration but not maneuverability, partly because torque and the speed of both rear wheels cannot be controlled independently.
So the Magna team removed the two electric motors (one at each axle) of the production model and replaced them with three induction motors (one at the front, two at the rear).
With special control algorithms, Magna’s eTelligentDrive system can read steering inputs and direct additional torque to whichever wheel needs it, achieving side-to-side torque vectoring through the drivetrain, rather than through the brakes or electronic stability control system.
“We are kind of steering the vehicle on a dynamic level with the power of the wheels,” says Werner Ness, Magna Powertrain’s eMobility product manager. “That’s exactly the purpose of our system.”
He’s not aware of any electric vehicles on the market with such capability. For now, the eTelligentDrive system is in prototype form only on the Model S, and Ness says it will be ready for production in 2020. The modified Model S is set up for AWD, but a RWD version also can achieve the same torque-vectoring effect with one motor on each rear wheel.
Magna’s highly integrated eDrive system contains the gearbox, e-motor and inverter and can be applied for hybrid vehicles as well. In the prototype Model S, all three axle drives have peak power of 140 kW, although Ness says 200 kW is feasible.
On a frozen lake in Sweden recently – with traction control and stability control off – the modified Model S is a blast to drive in a large circle as the system determines the driver’s intended direction and constantly varies the amount of torque between front and rear and from side to side (on the rear axle), while monitoring wheel slip along the way.
For demonstration purposes, the “40/60” mode functions like a standard differential with a fixed torque split and no torque vectoring. The vehicle tends to oversteer and understeer, and spin-outs on the ice are common.
In “Automatic” mode, the system constantly monitors where torque is needed to keep the vehicle headed in the intended direction, making adjustments in milliseconds. If understeer is detected, more torque will be routed to the outside rear wheel. Oversteer triggers the opposite response.
“Sport” mode is great fun as it maintains vehicle stability but allows a certain degree of drifting as the rear wheels can slip a bit more before the system intervenes.
Walter Sackl, director-product management for Magna Powertrain, says the technology introduces a new level of dynamic driving for electric cars.
“It’s not just throttle on and straight ahead. You can also easily go through those handling courses with this torque vectoring,” Sackl says. “We can show how the battery-electric vehicle can outperform other vehicles with regard to vehicle dynamics.”