Acura first put Super Handling All-Wheel Drive (SH-AWD) onto the road in 2005. Back then, the system bowed in the RL, Acura’s flagship sedan. At its launch, SH-AWD was the world’s first all-wheel drive system with active torque vectoring technology.
The idea was to create an AWD system that delivered the all-weather driving confidence that shoppers expected, while also deploying some trick new technology that enhanced handling and agility.
In 2005, the crossover market was exploding, and more Canadians were buying more AWD-equipped cars than ever. With SH-AWD, those shoppers could now choose a system that improved all-weather confidence, while simultaneously improving the overall dynamics and response of the vehicle.
Most shoppers opted for AWD to improve traction and grip in wintery or off-road conditions. With SH-AWD, they could now opt for an AWD system that also provided significant benefits to handling and response across a wide range of driving conditions.
Acura MDX Photo by Acura
Acura MDX Photo by Acura
The first generation SH-AWD system in 2005 was born of an evolution and combination of two earlier Honda technologies.
The first of these was the VTM-4 AWD system. Initially engineered for the 2001 Acura MDX, VTM-4 was designed to push current engineering boundaries with the goal of creating an AWD system that was as lightweight, efficient, and compact as possible. Abbreviated from Variable Torque Management, VTM-4 used a single-speed transfer unit bolted to the transaxle up front, and a driveshaft to connect it to the rear differential, itself positioned between the rear wheels. When required, clutches built into that rear differential could clamp down, immediately transferring power to the rear wheels, on demand.
By 2005, the VTM-4 system was evolved and enhanced to create SH-AWD. New tricks were added to the system’s capabilities, including new hardware and software that enabled something called torque vectoring.
Imagine four people paddling a boat, one at each corner. If a single paddler starts paddling faster than the rest, the boat will begin to steer and rotate in the opposite direction. That’s a simple illustration of how torque vectoring works.
1998 Honda Prelude Photo by Honda
1997 Honda Prelude transfer case Photo by Honda
1997 Honda Prelude Photo by Honda
For an early example of torque vectoring in a car, we can go back to the 1997 Honda Prelude.
After dozens of patents, this year marked the debut of its Active Torque Transfer System (ATTS) — basically, a front differential that could send up to 80 percent of the engine’s power to the outer wheel in a corner, and over-drive that wheel by 15 percent — that is, spinning it up to 15 percent faster than the inside wheel.
The ATTS system allowed this front-drive sports car to split engine power across its front axle in a way that helps rotate and steer the car, while reducing understeer. It’s an early example of torque vectoring, a means of precisely controlling how engine power is split across a vehicle’s axle or axles in real time, to help it steer and handle more eagerly.
When the SH-AWD system debuted in the 2005 Acura RL, it tapped into these earlier technologies using the more compact and highly evolved VTM-4 system, as well as applying the benefits of the Honda Prelude’s torque-vectoring ATTS system to its rear axle.
The evolution and eventual combination of these two earlier technologies formed the basis of the first-generation SH-AWD system. The active torque vectoring, via the ability to over-drive a single wheel, was the star of the show.
Since its introduction, SH-AWD has evolved over four generations, and the most current of those can be found bolted up beneath models like the Acura TLX, MDX, and RDX.
Today, SH-AWD works with an open front differential and a pair of electronically actuated clutch packs on the rear drive unit, bolted between the rear wheels. Each clutch pack controls the delivery of power to a single, corresponding rear wheel. Power is always being transferred to the rear axle, and the individual motor-driven clutch packs clamp down with millisecond accuracy at the direction of a computer monitoring system which controls how much power is transmitted to each rear wheel at any given moment.
Importantly, the hardware can overdrive the rear axle by 2.7 percent, giving the system the important ability to spin one or both rear wheels faster than the front wheels. When cornering, the outside rear wheel is driven faster than the average speed of the two front wheels, in effect using drive torque to help steer the car from the rear axle.
With rear-axle torque vectoring helping to rotate and steer the car from behind, the workload of the front tires is reduced– which helps balance handling and enhance steering response. The result is an AWD car that feels more nimble and handles more like a rear-drive vehicle, especially when drivers push the car out of a corner with the throttle down.
2019 Acura RDX SH-AWD Differential Photo by Honda
Acura SH-AWD Differential Photo by Honda
Acura SH-AWD Differential Photo by Honda
Acura SH-AWD Differential Photo by Honda
2016 Acura TLX-2 3.5L SH-AWD Rear Differential Photo by Honda
I asked Honda Canada’s Hayato Mori, AVP, Business Development and Customer Engagement at Honda Canada to provide some more information on the latest SH-AWD system.
“The system’s main inputs come from the yaw sensor, throttle position, and vehicle speed. The system looks at the inputs to determine how much power to send to each wheel, in order to maximize grip when powering through a corner” he explains.
“It can also anticipate front wheel slippage when the vehicle is stopped. More power is sent to the rear axle, depending on how hard you accelerate. There’s no delay in traction”.
The latest version of SH-AWD is also smarter and faster-acting than ever, thanks to some improvements to its hardware and programming.
“The latest system can transfer 40 per cent more torque to the rear axle at launch, and there’s three times more torque available at 100 km/h. The response time is also 30 per cent faster. To achieve this, certain mechanical components were beefed up, and software was re-written. This allows the driver to experience faster and better response when pushed to the limit” Mori says.
Acura RDX Photo by Justin Pritchard
Acura RDX Photo by Justin Pritchard
Acura RDX Photo by Justin Pritchard
Acura RDX Photo by Justin Pritchard
After 16 years and thousands of kilometres spent testing SH-AWD equipped Acuras in a wide range of conditions, the sensation this generates from the driver’s seat has always been a source of smiles.
The system works invisibly in most situations, but dial in SPORT mode and hit your favourite roundabout, merge ramp or winding backroad with your foot down, and you can feel the system working beneath you to make the vehicle handle like something smaller, lighter, and more rear-driven.
The sporting benefits of the SH-AWD system are most apparent when the equipped vehicle is driven with intent, which is exactly what driving enthusiasts love.
Keyword: Deep Dive: Acura’s 4th-generation SH-AWD system