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The DynaMax AWD coupling is basically like some others in that an electric motor operates an oil pump to pressurize a housing with a multidisc clutch. The hydraulic pressure applies the clutch so required torque is transferred from the front-drive-based system to the rear differential—the greater the pressure, the more torque is shifted to the rear.
However, there are numerous differences vs. other systems, both within the coupling and with the high level of active control that speeds response, to improve overall performance.
First, the CAN bus (Controller Area Network) monitors signals, principally throttle position, steering angle, vehicle speed, and road texture (an algorithm that includes wheel speed sensor signals). The signals go to the AWD computer, which calculates the ideal front-rear torque split that it anticipates.
The computer then operates the motor at up to 10 rpm to run the pump, to build up the required hydraulic pressure (maximum of 320 psi/2.0 MPa) for the clutch. This is accomplished with the aid of a feedback signal from a pressure sensor on the clutch housing. The motor stops when the correct clutch-apply pressure is reached.
At start-up the system presets the front-rear torque distribution so there is no slip on the front axle. As the vehicle moves down the road, the DynaMax computer continuously monitors sensor readings, to anticipate changes in upcoming driving conditions.
The computer recalculates impending torque split requirements from the CAN bus data and, if necessary, makes instantaneous adjustments in motor-pump-to-clutch-housing system oil pressure with the help of the housing pressure sensor.
Because Magna engineers designed the DynaMax system to react quickly in changing traction conditions, such as encountering an icy road patch, it never starts from an "off" position.
If the pressure must be increased (for more torque transfer to the rear), the motor turns forward to operate the pump. If the front-end traction is good, the computer simply backs off the motor-pump assembly to reduce clutch-apply pressure. Then more torque (and if it's appropriate, all the torque) is delivered to the front wheels. There are no pump valves to open and close.
The pump is a gerotor type. Engineers note that its tight internal tolerances enable it to maintain commanded pressure for a short duration, as effectively as a plunger- or valve-type pump. If the time period for steady state becomes extended, so that leakage starts to reduce the apply pressure, the pump runs to reload the hydraulic circuit as required.
As a result, the DynaMax computer's typical response time to "tune" for an impending change in torque-split requirement is 50-100 ms. If a torque increase is needed from the engine, it takes up to 300 ms to build up, observed Walter Sackl, Magna Powertrain's global product manager, so in some cases the engine may determine the actual time period.
In any event, the response of the DynaMax itself should occur well within 150 ms, Sackl said.
The computer algorithm for the clutch looks for consistently good front-end traction and when possible will maintain 100% to the front wheels for fuel economy. The algorithm, however, is adaptive; in "sporty driving" it will apportion torque as needed between front and rear, Sackl said, and it will transfer 100% to the rear if appropriate.
The up-to-100% front-or-rear torque split, in conjunction with the AWD computer's active control approach, also minimizes oversteer and understeer in normal driving situations, he added. In addition, the system has a manual-select position for a 50-50 torque split.
The DynaMax coupling was sized for light weight and engineered for minimum energy use. Its 727 lb·ft (1000 N·m) peak torque design capacity is more than adequate, even with a generous safety margin, because the new Sportage's 2.4 L engine's rated peak torque is 168 lb·ft (228 N·m). However, Kia intends to use this coupling in forthcoming vehicles.
The Sportage has a tow capacity of 2000 lb (907 kg); Kia's testing showed that even with maximum loads, including hill climbing, the coupling's internal temperature never reached a thermal shutoff level. A contributing factor is the cooling provided by the large oil capacity of the DynaMax housing, Sackl said.
The fluid fill, unlike competitive designs, is life of vehicle, he added.
Kia has an exclusive arrangement with Magna Powertrain that with required competitive development times should last for two model years. The DynaMax coupling is being built in Korea in a plant that is a joint venture between Magna Powertrain and Hyundai WIA, a parts manufacturing affiliate.
