Bandwidth is the Holy Grail of global vehicle development. Its measure of success includes the ability to derive genuinely diverse products and even entire brands from a common set of bones. There’s also the vision to leverage key supplier technologies when model differentiation is needed. Case in point: Ford’s unibody C2 platform, the 2021 Bronco Sport, and Dana Inc.
Development of the all-new compact utility aimed at the North American market kicked off six months after its Escape/Kuga global cousin and progressed in parallel with Ford’s development of the larger, body-on-frame Bronco. There was quite a bit of know-how sharing among the three teams, explained Bronco Sport’s veteran engineering manager Eddie Kahn, whose experience was honed on the first-generation F-150 Raptor program.
“We had no intention of making a ‘soft roader,’ because the Bronco name brings higher expectations,” Kahn told SAE’s Automotive Engineering. “Our primary aim was to create an affordable vehicle that gives even novices confidence over any terrain, with a 4x4 system that is easy to use. We wanted balance: serious off-road capability to get you into and out of extreme territory with confidence, along with on-road comfort,” he said.
Conveniently, the C2 architecture was designed to be super-flexible, for a broad range of products, "from a base Escape to the Bronco Sport Badlands series [the most off-road-aggressive model] that can climb the Hell’s Gate at Moab, which we’ve done,” Kahn said. A shorter wheelbase, wider track, increased ground clearance, reduced mass (by 20 kg/44 lb), suspension upgrades and 57/43 front/rear weight distribution “allow the new vehicle to be extremely nimble and agile on any terrain, including sand,” Kahn said.
The development team, co-led by Kahn and program chief engineer Adrian Aguirre, put a premium on robustness. They ran duty cycles beyond Ford’s standard and tested in a variety of off-road environments and events, including Borrego Springs (Calif.) and Moab. Bronco Sport’s thermal reliability is ensured with a trans cooler, a PTU cooler and an engine cooler. There also is what Kahn calls “a very advanced” predictive thermal-management system that will intervene without causing a loss of 4wd capability.
The RDU, supplied by Dana, is the star of Bronco Sport’s driveline. It helps deliver surprisingly good off-road performance through a driver-selectable, multi-mode control interface and locking capability. “The Dana twin-clutch gives us so much more capability and the ability to tailor the torque application to the driving situation,” Kahn said. “We had this technology in our early assumptions when we began laying out the driveline. The challenge, however, was we’d never applied the twin-clutch RDU in an off-road-capable application before.”
Part of Dana’s AdvanTEK Ultra driveline-systems family, the twin-clutch RDU shares clutch packs with the company’s single-clutch drive unit that launched at Ford in 2019 on the CD4 Edge, then carried over to the base Escape. “Its natural evolution is into Bronco Sport, where Ford wanted something peppy,” noted Andy Perakes, director of axle engineering at Dana’s Light Vehicle Drive Systems. “Sharing identical clutch packs enables a common control interface on the vehicle, so Ford didn’t have to go in and change their CAN messaging and all their communication protocols. And the design makes it easy to scale.” The twin-clutch version includes a second actuator motor.
Dana’s design focus with the AdvanTEK family is mechanical efficiency. Its unique hypoid design, along with a purpose-formulated axle lubricant, enables the axles to deliver fuel efficiency savings equivalent to a 200-lb (90.7 kg) weight reduction, as estimated by the U.S. EPA.
‘We kind of reversed the design philosophy there. Instead of starting with the gear design and then adding the lube, we started with the lube design,” explained Perakes, himself a Ford Powertrain veteran before joining Dana. “We started with a very low-viscosity lube – its viscosity is comparable to an ATF. There are some trade-secret enablers to this, but it enabled us to use a common lube throughout the entire system, for both the clutch pack and gearset.”
The AdvanTEK Ultra is designed to minimize churning losses and, combined with the dedicated lubricant, deliver “much lower operating temperatures,” said Ryan Keeler, Dana’s engineering manager for Light Vehicle Drive Systems. “It allowed us to kill two birds with one stone. There is no need for an external cooler. Thermal is always one of the limiting factors in a driveline, and we have a cool-running unit in the Bronco Sport.”
The ‘lubed-for-life’ twin-clutch RDU adds about 10 kg (22 lb) to the mass of Dana’s single-clutch AdvanTEK unit. Dana supplies the “low level” control software that responds to vehicle-level torque commands from the AWD system, Keeler noted. High-level controls and vehicle calibrations are handled by Ford.
With attachment points shared with its single-clutch cousin, the AdvanTEK Ultra RDU required no modifications to the C2 rear subframe. “It was essentially a drop-in,” Keeler said. “And it’s easily tunable through minor design changes – addition or subtraction of clutch plates, for example, or upgraded materials, to meet customer requirements.”
And with Ford developing a unibody pickup based on the C2 architecture, the bandwidth for Dana’s RDU may be further expanding in concert with Ford’s platform.Continue reading »