Driving on a frozen ice lake is a strange experience at any time, but never more so than when the towering Volvo XC90 T8 that we're piloting on the treacherous surface of a frozen lake starts to do a convincing impression of a Focus RS.
-Look closely and you'll see that, despite obviously being an XC90, this car has had its badges covered by black tape. That's because it's not a Volvo as much as a hard-working prototype vehicle belonging to British engineering company GKN, built to help with the development of a radical new electric rear axle.
-The clue is in the name: e-Twinster. Which is an electric version of the existing GKN Twinster axle that's fitted to the Focus RS, among others—and which uses separate electronically controlled clutches for each rear wheel to bias torque across the axle. It's what gives the Ford its understeer-cancelling ability, and also its hoontastic Drift Mode.
-The idea of the e-Twinster is to offer the same ability to manufacturers who use either an electrically powered rear axle in a hybrid, or even a full EV. As with the Twinster, each coupling can go from open to fully locked in less than a tenth of a second, allowing torque to be shifted between wheels very quickly.
-GKN makes the electric motor module that sits at the rear of the standard XC90 T8 hybrid, making it the perfect test bed for the e-Twinster. This is currently powered by a 60-kW motor (80-hp) which also produces 177 lb-ft of torque. However, a 10:1 gearing ratio within the unit multiplies this to a potential peak 1770 lb-ft, with up to 885 lb-ft going to each axle. The system has a key advantage over the existing Twinster in that it can operate even when there's no power coming from the engine, quickening response time.
-That's the theory, anyway. Putting it into practice takes place at GKN's Winter Test in Arjeplog, northern Sweden. This is where the company shows off new technology to its executives, potential customers, and also scuzzy journalists like ourselves. It's not the best place to find out how a car handles, but it is actually an ideal location to reveal the differences between the prototype and a standard XC90 T8 that has been brought along for comparison.
-The standard car tries its best on the frozen surface but ultimately understeers like an elk on ice skates, pushing wide as you apply power in a turn. The rear motor is trying to neutralize the car's line as the front starts to run out of grip, but it lacks the ability to mitigate more than a small part of the front-end push.
-The e-Twinster prototype feels radically different. It has been made with three different levels of assistance to demonstrate how the system works, and the engineers on hand warn that it isn't an indication of how a finished car would drive (hence the polite covering up of the Volvo's badging). Even in the most gentle setting it feels vastly more responsive than the standard T8, with much less understeer on turn-in and the sensation of the rear end sharpening the car's line with throttle applied. It's easy to persuade the XC90 into a sideways cornering attitude that is almost as much fun as it is unlikely.
-The more aggressive settings are selected by a touchscreen on the dashboard, which also displays how much torque is being sent to each rear wheel. The "Maximum Plus" setting is basically a rally mode; selecting it gets the XC90 oversteering like an overgrown Focus RS pretty much as soon as you turn the wheel, yet still allowing you to retain impressive control as it crabs across the ice. Like the standard T8's electric motor, the e-Twinster works at speeds of up to 100 mph.
-More practically, the e-Twinster dramatically improves traction in split-grip situations where there is more adhesion on one side than the other, as 100 percent of available electric power can be directed to one side. It also boosts stability during extreme maneuvers with the throttle closed, as it gives the ability to create a braking torque from the electric motor's regenerative capacity, something the standard Twinster can't do.
--
- -
- First Drive: Ford Focus RS
- -
- Volvo XC90 T8 Plug-In Hybrid Powertrain Detailed: 400 hp and 59 MPGe
- -
- 2016 Volvo XC90 Tests, Reviews, Specs, Pricing, and More
- -
-
GKN says that several major automakers have already expressed an interest in the system, though we're taking the choice of the XC90 as a prototype as a broad hint of where it might end up first. With a wave of performance hybrid and EVs approaching, it's good to know that somebody is working on making them handle as well as—if not better than—the cars they are set to replace.
-
No comments:
Post a Comment