Under the skin: How steer-by-wire can still give engaging handling

Titan steering rack

Titan’s steer-by-wire system can provide meaningful driver feedback

Systems are now becoming so advanced they have driving involvement engineered in – here’s how

Steer-by-wire is one of those technologies that has remained on the fringes for a couple of decades, but as these systems become increasingly sophisticated, they can be used to engineer driver involvement into a car’s handling and performance capabilities.

Steer-by-wire systems retain the familiar steering rack, driven by an electric motor like a conventional electric power steering system (EPAS), but with no steering column or other mechanical connection to the driver.

The latest steer-by-wire electric systems give engineers the opportunity to get exactly the characteristics they need for a particular car, from dawdling around town to a brisk drive on B-roads or a motorway cruise.

Steer-by-wire also fits the bill for utilitarian applications, such as commercial and autonomous vehicles.

It is due in the Toyota bZ4X this year, and will be in the Lexus RZ 450e in 2024. Infiniti introduced it in the Q50 almost 10 years ago but the ‘redundancy’ was mechanical, with a steering column remaining in place, just in case.

True steer-by-wire has no mechanical connection between the steering wheel and steering rack, just an electronic link, and that’s what the Toyota and Lexus One Motion Grip system will have.

Although it may seem like a dodgy idea, there are many benefits, both for manufacturers and drivers. Steer-by-wire comes under the broader category of drive-by-wire elements, such as electronic throttle control, which have been in production for years. One advantage for manufacturers of by-wire systems is the potential to produce a ‘dry’ chassis, with no hydraulic fluid involved.

The idea is for each suspension corner of the car to be pre-assembled and bolted on to the car on a production line and literally plugged in, doing away with messy hydraulic fluid and all that entails. The ratio is reduced as the car gathers speed, slowing the response right down at motorway speeds to avoid the car becoming twitchy.

UK firm Titan, which started life in the 1960s developing racing cars, is now a specialist in advanced steering systems. It has recently developed a precision steer-by-wire system aimed at lower-volume manufacturers that not only work with smaller numbers but also may need a bespoke system tailored for, say, a sports car or an autonomous delivery van.

Autonomous vehicles need autonomous steering, but there are advantages for human drivers too. An example is a variable steering ratio and variable weight. With no mechanical connection, the ratio can be lowered when cruising in the straight-ahead, making the steering less sensitive to unwanted inputs.

A full steer-by-wire system is also quite mechanically simple. The steering wheel directly works a control unit like a gaming machine and motors on the steering rack actually move the wheels.

Linking the two, a computer brain takes the signals from the driver’s steering input and relays them to the steering rack. The caveat is that the computer decides what the wheels will do and not necessarily the driver, but the benefit is that steering lock can be almost infinitely variable, reducing turns in the case of the Toyota and Lexus to a mere 150deg in either direction at parking speeds.

That last aspect is true of more conventional variable-ratio steering, but steer-by-wire also opens up the possibilities for semi-autonomous safety systems like accident avoidance, where a car can literally steer out of trouble if the driver isn’t quick enough.

Titan’s technical director, Paul Wilkinson, thinks a big benefit is the ease of tuning that steer-by-wire gives. An algorithm that can differentiate between a thrash around the lanes or a drive in the city can adapt the feedback to suit.

Alternatively, drivers can choose modes as they might now between, say, Sport and Comfort for suspension, or Normal, Sport and Eco for a powertrain.

EPAS once had drawbacks compared with hydraulic systems when it first emerged, lacking feel and feedback. Since then, advances in electronics have enabled engineers to compensate for internal friction and even changes in ambient temperature.

Wilkinson says one of the biggest problems with providing feedback from the road to the steering wheel was the inertia of the electric motor working the steering rack, in effect blocking it so little if any reached the driver.

Titan solves that problem by creating a digital model of the motor’s inertia, and compensating for that in the control software. The motor then reacts in a way that the feedback can travel back from the road wheels to the driver’s hands.

It also means that for less able drivers, cars could be steered by a mini wheel or a joystick. Like some aeroplanes, which have relied on fly-by-wire systems for years in both civilian and military aviation, the systems are fully redundant, which means that if any critical hardware or software parts fail, there’s a back-up ready to take over

Source: Autocar

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