 2010 Acura ZDX. Click image to enlarge |
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2011 Acura ZDX
I can imagine Acura’s marketing team in 2004 huddled around a conference table somewhere in Honda/Acura’s headquarters in Tokyo debating what they would call Acura’s revolutionary new all-wheel drive system. Some bright light probably suggested that since the AWD system provided super handling, why not call it what it is?
Typically, we think of all-wheel drive as a device to improve foul weather driving. When the roads get slippery or the snow piles up deep, all-wheel drive will help get a vehicle going and to a lesser extent keep it on the road. Some all-wheel drive systems engage both the front and rear axles all the time and transfer torque between the front and rear in varying amounts depending on which wheels, front or rear, have the best traction. Other systems drive the front wheels the majority of the time and only engage the rear axle when the front wheels begin to slip. Some more sophisticated systems can anticipate front wheel slip and send torque to the rear axle before the front wheels begin to slip.
To learn more about all-wheel drive and four-wheel drive, and differences between full-time and part-time systems, see Jim Kerr’s excellent article here.
 2010 Acura ZDX. Click image to enlarge |
Debuting in the 2005 Acura RL, Super Handling All-Wheel Drive, or SH-AWD for short, differs from typical all-wheel drive systems in that it distributes the optimum amount of torque not only between the front and rear wheels but also between the left and right rear wheels. Torque to the rear wheels is continuously varied to supply up to 100 per cent to the outside wheel. This creates an inward yaw moment, significantly improving vehicle turn-in and handling precision. The result is uncanny cornering performance that provides incredibly neutral steering and outstanding vehicle stability.
Our 2010 ZDX long-term tester is one of the best handling utility vehicles we’ve ever tested. Despite its rather large size and weight – the ZDX weighs over 2,000 kg – it handles like a much smaller – and lighter – vehicle. At first you tend to take it easy on twisty roads or freeway on-ramps until you realize that the ZDX is capable of much more. Soon you will steer through the S’s and power around on-ramps to merge easily into traffic. As your confidence increases so does the fun factor.
  2010 Acura ZDX. Click image to enlarge |
SH-AWD improves handling in other ways too. Lift off the accelerator when entering a curve or brake to slow the vehicle down and torque to the outside wheel is varied to create an outward yaw movement rather than in inward movement, which helps to keep the vehicle stable. Even while cruising in a straight line, the system is working to keep the ZDX firmly planted, concentrating torque in the front wheels which saves fuel.
How does SH-AWD work? By monitoring driver input and driving conditions, the SH-AWD system determines the optimum front-rear and lateral (left-right) torque distribution. This information is then conveyed to the rear differential, where electromagnetic clutches continuously vary the front-to-rear torque by up to 70 per cent in either direction. Rear torque can also be apportioned between the left and right rear tires by up to 100 per cent on either side.
The SH-AWD system is composed of an ECU, sensors that detect steering angle, lateral g-force, and other vehicle information, and a rear differential. Electromagnetic clutches inside the rear differential, an industry first at the time, employ electromagnets to maintain precise control over the multi-plate clutches.
 2010 Acura ZDX. Click image to enlarge |
The SH-AWD system uses torque not only for propulsion, but also to increase cornering precision and dramatically enhances vehicle manoeuvrability while helping to virtually eliminate understeer and oversteer. During cornering, the speed of the outside rear wheel is greater than the average of both front wheels. This prevents the efficient transfer of torque to the outside rear wheel in a typical AWD system. To counteract this condition, the SH-AWD system’s rear differential is equipped with a built-in acceleration device that can overdrive the outside rear wheel. This acceleration device, which is another industry first, uses a planetary gear to speed up the outside rear wheel’s rotation relative to the front wheels. The result is a significant enhancement in vehicle manoeuvrability during cornering.
SH-AWD not only improves off-line traction when the roads are wet or slippery but has the potential to do what other all-wheel drive systems cannot – despite what you may think – keep you on the road.
We’ll find out when winter finally arrives. It may only be September, but it won’t be long before the snow flies. As well, we hope to get to the Outer Banks of North Carolina before Christmas, so we’ll take the ZDX out on the beach and see how it performs in the sand.
