Photo: Catalin Garmacea
BMW is not new to the all-wheel drive car scene. Actually, their first car that ever sent its power to all four wheels was unveiled back in 1985 and it was an E30 325i model. However, a lot of things changed since then and the aim has gone from simply sending the power to the wheels to doing it efficiently.
In this regard, BMW launched xDrive back in 2004 on the X3 and X5 models and talked about efficiency, lightweight construction and driving dynamics, things that weren’t particularly interesting back then to the audience. Changing times brought along a need for a new approach.
On the 2 Series Active Tourer, BMW is actually launching its first all-wheel drive system developed for a front-wheel drive platform. It’s also the first such system created for a transversely mounted engine, but that’s not all that’s interesting about it.
The xDrive system for the car weighs just 61 kg (134 lbs) and features technology that allows to save the amount of losses per the drivetrain to a minimum.
Power from the front drive to the rear axle is transferred thanks to an angular gear on the front differential and a two-part cardan shaft that are called ‘Power Take-Off’. The heart of the entire system is an electro-hidraulic multiple-disk clutch (Hang-On) fitted inside the rear axle drive. Its job is to vary the torque distribution between the front and rear wheels via a hydraulic pump.
The input shaft is a hollow shaft construction and directly connected to the front axle differential. This way, part of the drive force is transferred from the differential basket to the cardan shaft via the hollow shaft, the crown wheel and the pinion shaft.
What makes this system stand out compared to others is that the pressure inside the pump is not measured by a sensor but rather by means of voltage and power alignment.
Furthermore, in case AWD is needed, the valve will open in a matter of milliseconds to build up maximum operating pressure in the clutch and deliver torque to the rear wheels. All of this happens without the driver or the passenger noticing it.
At the same time, all the electronics on board are adapted to the new system, including DSC, DTC, EDLC (Electronic Differential Lock Control) and Performance Control. The new xDrive system will only be available on the 225i and 220d models.
On the 2 Series Active Tourer, BMW is actually launching its first all-wheel drive system developed for a front-wheel drive platform. It’s also the first such system created for a transversely mounted engine, but that’s not all that’s interesting about it.
The xDrive models weigh just 61 kg more than FWD ones
The Active Tourer range is aiming at offering both space and luxury and the BMW badge and all that should come with it. That means drivers will expect the car to handle in a certain way. FWD doesn’t allow the car to be particularly dynamic, but with all-wheel drive things change.The xDrive system for the car weighs just 61 kg (134 lbs) and features technology that allows to save the amount of losses per the drivetrain to a minimum.
Power from the front drive to the rear axle is transferred thanks to an angular gear on the front differential and a two-part cardan shaft that are called ‘Power Take-Off’. The heart of the entire system is an electro-hidraulic multiple-disk clutch (Hang-On) fitted inside the rear axle drive. Its job is to vary the torque distribution between the front and rear wheels via a hydraulic pump.
Power Take-Off
We know BMW likes to use all sorts of weird names for its technologies so we had to know what Power Take-Off actually meant. As far as we can tell, it’s an angular gear mounted behind the engine, on the automatic transmission and crankcase.The input shaft is a hollow shaft construction and directly connected to the front axle differential. This way, part of the drive force is transferred from the differential basket to the cardan shaft via the hollow shaft, the crown wheel and the pinion shaft.
Hang-On
As far as ‘Hang-On’ goes, this is the multiple disk clutch located in the rear axle drive. It directs a proportion of torque to the rear wheels, depending on the driving situation. It can send up to 100 percent of the power to one axle and is operated by a hydraulic pump which, in turn, is controlled by a pulse-width-modulated signal from the ECU.What makes this system stand out compared to others is that the pressure inside the pump is not measured by a sensor but rather by means of voltage and power alignment.
The cars are front-wheel drive when all-wheel drive is not needed
In order to be as efficient as possible, the xDrive system deactivates the pump that controls the multiple disk clutch when all-wheel drive is not needed, turning the car into a front-wheel drive vehicle. Thanks to a spring-loaded valve, the oil level in the clutch is lowered, reducing friction losses, making the car run even more efficiently.Furthermore, in case AWD is needed, the valve will open in a matter of milliseconds to build up maximum operating pressure in the clutch and deliver torque to the rear wheels. All of this happens without the driver or the passenger noticing it.
At the same time, all the electronics on board are adapted to the new system, including DSC, DTC, EDLC (Electronic Differential Lock Control) and Performance Control. The new xDrive system will only be available on the 225i and 220d models.
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