Clever Cars: Infiniti Q50 can steer by wire

  • A triple backup system is in place for the fast-acting actuators that channel driver inputs from the steering wheel to the road wheels. In the event of total electrical failure, a normally disengaged clutch clamps shut, providing a mechanical steering link.
Date:13 January 2014 Author: Anthony Doman Tags:, , , ,

Infiniti Q50’s steer-by-wire system transforms the way you drive – and the way you feel about driving

Steering mechanisms have remained essentially unchanged since the days of the horseless buggy. The driver manipulates a control device – usually a wheel – that, by means of a system of gearing, turns the front wheels in the desired direction.

Power assistance can be used to make it easier to turn, and damping can be used to make it more comfortable. Some systems adapt power assistance according to vehicle speed, and some allow the driver to choose the level of assistance. But one thing remains immutable: steering involves solid assembly with minimal scope for adjustability.

Unless you’re driving an Infiniti Q50. That’s because this new compact sports sedan from the Japanese manufacturer is the world’s first production model to steer by wire. What Infiniti calls Direct Adaptive Steering (DAS) replaces the conventional mechanical connection between steering wheel and the road wheels with electronics.

Accomplishing this has been a surprisingly tough challenge that has taken the company’s engineers 15 years to bring to production. Not only has DAS given Infiniti the opportunity to do away with entire sub-assemblies of belts, pumps and what not. It’s also given them the opportunity to do things that you simply can’t do with conventional, mechanically linked steering. (See “Towards a driverless future”).

We went hands-on with the Infiniti in Barcelona, Spain. That’s because the new car, due here in early 2014, is the spearhead for a new, Euro-oriented line-up from the Japanese company. A compact sports sedan aimed at the likes of BMW’s 3 Series and Mercedes’ C-Class, it also signifies Infiniti’s new “Q” nomenclature.

Our time with the Infiniti involved a mix of driving on freeways, urban and rural roads, much of it in a downpour that would have done the Highveld proud.

On the road, the Infiniti feels remarkably solid and poised, with an overall ride quality that I’d rate as firm. We drove both the hybrid and diesel variants. (DAS is standard on some versions and an option on others.) But, of course, we were too busy concentrating on the traffic, the route and the weather to pay too much attention to the car’s formidable array of technology.

That’s why we were directed to the race track. Not that we were let loose on the swoops and switchbacks of the FAST Parcmotor Castelloli track.

Nestled near the Montserrat mountains, a short distance north of the Catalonian capital, this challenging circuit was designed for motorcycle racing and features a mix of elevation changes and tight corners in some ways reminiscent of Kyalami. Instead, we were put through three sessions to highlight aspects of the new steering system, and to experience what the hybrid engine was capable of.

1. Mix and match
Test 1 was the Response Test. This began with a pretty straightforward simulated obstacle avoidance – a quick left/right S-bend manoeuvre. Following it was slalom with gradually shrinking distances between the direction change indicator cones. All of this was done under a speed limiter at around 30 km/h, and on completion the limiter was disengaged so we could feel the steering loading and feedback through a moderately fast-ish uphill right-hander.

Nothing out of the ordinary there.

Then it was the same again, but with some different steering settings dialled in. (Direct Adaptive Steering makes all options available via simple touch-screen controls as part of the Infiniti Drive Mode Selector.)

Up to four dedicated modes provide preset combinations of steering weight and response – for parking, say, a blend of lower gearing and lighter feel; for high-speed cornering, say, quicker gearing combined with much heavier feel. For the purpose of our run, we selected the Custom alternative. This allows mixing and matching of steering weight and response. Our chosen blend combined light steering weight and quick response (the settings can be memorised). Well, they did warn us that it might feel different.

A leisurely flick of the steering wheel into the first left-hander nearly had us wiping out half the cones.

The ensuing right-hander was only marginally more dignified. In my defence, by the time we reached the slalom, I was sufficiently acclimatised to be able to make a passable attempt at threading my way through with minimal damage to the trackside furniture. Cranking it up through the fast sweep, the steering felt just fine.

OK, I was convinced. DAS does the feel/weight thing spectacularly well. Best of all, it doesn’t seem disconnected from the wheels – although, of course, it is. Infiniti’s unique ability to tailor both weight and response doesn’t detract from driver involvement.

2. What bumps?
Up the road, we turned off the track on to a short, specially constructed concrete strip crossed with little humps rather like speed bumps. Only, these bumps didn’t stretch across the entire surface, and alternated left and right. With DAS switched out, the Q50 handled the uncomfortable jiggling with quite decent poise.

But release the steering wheel, and its wild gyrations indicated that the running gear was working very hard indeed. A second pass, this time with DAS engaged, was an eye-opener. “It’s a trick,” I muttered. Holding the wheel, road shocks seemed totally damped out. “Let go the wheel,” my guide suggested. It was uncanny. No steering wheel movement worth mentioning. Yet, when you needed to make steering inputs, the feel was all there.

Conclusion so far: DAS is able to adjust the steering feel to the driver’s preference, and transmit his inputs to the wheels faithfully. It’s also able to sense inbound impulses – that is, from the road surface – and filter out unnecessary inputs, improving both comfort and control. Impressive.

3. On the straight and narrow
You’ll find “lane keeping assistance” systems in many cars these days, though admittedly mostly high-end ones. Using sophisticated imaging methods – from cameras to radar – these systems are able to detect that a car is veering out of its lane, to warn the driver and to correct the car’s direction of movement by means of the stability control system.

Lately, they’ve even been able to steer the car back into line. Thanks to the Q50’s steer-by-wire system, which incorporates Active Lane Control, this form of driver assistance is able to be even more accurate and refined.

Our session involved driving in a defined lane, marked out by cones, above 80 km/h. We confirmed that the ALC graphic in the car’s display changed to a tunnel-like picture, indicating that the system had recognised we were in a lane. We then deliberately allowed the road camber to cause the car to drift to one side. As we approached the “lane marking”, the steering eased us back into line, and eerily kept us in line.

This exercise illustrated that Direct Active Steering is most definitely a waypoint en route to autonomous driving. For the moment, though, it’s a support system: the driver retains control and can override it. This is a good thing.

Direct Active Steering is available on certain models as standard and as an option on others.

Towards a driverless future?
Infiniti’s parent company Nissan spent a decade developing DAS and a further 5 years preparing it for production. It covered over 400 000 km on the road undergoing real-world testing.

At the front wheels, a fast-acting actuator drives the steering rack. There are no response-slowing mechanical losses. There is also no refinement-impairing vibration, because the forces feed both ways – from the driver to the wheels and from the wheels back to the driver.

“The advantage of DAS is that at first you can have a different kind of personalisation, a different wide range of adjustment,” an Infiniti official told me. “Steering ratio can be changed, and effort as well.”

A second advantage is that you can filter most of the inputs that you don’t want to have on your steering. “You feel the road input produced by irregularities or you can also filter side wind or road camber. You clean all these inputs from your steering and keep purely all the feeling that relates to your handling, grip or lateral acceleration, or your road-holding.”

Associated with DAS is Active Lane Control, which Infiniti claims is the most effective and sophisticated lane-keeping system yet developed, because it is the only one to use the steering to ensure the car stays between lane markings. Other systems rely on a vehicle’s Electronic Stability Program (ESP) to apply braking force on one side of the car in order to alter its course. The driver always has the choice of how the car is set up – ALC intervention can be mild or full, depending on preference.

ALC uses a camera sensor to detect that the vehicle is travelling in a lane. Control systems process this information and, via the steering control unit, instruct the steering actuator to make any necessary corrections.

Aside from being a safety feature, ALC contributes to a firm on-centre steering feel that benefits overall control. A spin-off of this is the potential to make driving less tiring by reducing the need for continuous steering input owing to crosswinds or minor camber changes in the road surface.

Fantastic, but just how safe is it? What if the electronics fail? There’s a triple-mode backup involving three separate electronic control units. In the event of a total systems failure, a failsafe kicks in: a mechanical steering linkage. It’s disengaged by a clutch in normal use.

Infiniti Q50
Engine:
2,2 diesel 14 hybrid 3,5 V6
Power: 125 kW 268 kW (total)
Torque: 400 N.m 546 N.m (total)
Transmission: 7A or 5M 7A
Drive: rwd or awd
Top speed: 230 km/h (A) 250 km/h 0-100 8,5 s (A) 5,1 s
Economy: 4,8 L/100 km (A) 6,8 L/100 km (awd)
Co2: 124 g/km 159 g/km (awd)

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