The automotive x-by-wire revolution: balancing performance with value in motion system development

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For the automotive sector, the x-by-wire revolution is on the verge. Replacing mechanical linkages with electronic control has distinct demands on the motor system, essential for the actuation of acceleration, steering, braking, and in the future, 360-degree LiDAR vision systems. Precise control is required for performance and safety, and low weight to optimise fuel or battery efficiency is vital too. But as ever with the automotive sector, development must be balanced with value for the global market. So what are the options for car manufacturers and their suppliers? Thibaut Marqueyrol, maxon’s head of automotive solutions, explains.

Recently, regulators in California ruled that Cruise, the operator and manufacturer of the San Francisco driverless taxi firm, had to suspend its service. Officials blamed an accident for the decision. In one sense, this story shows that driverless technology isn’t sufficiently mature for day-to-day use in the real world. But this case is also an example of how far driverless technology has already progressed – and where it’s going.

California may be pausing its driverless taxi initiative, but this is a temporary measure. And while California has always had a reputation as a place of pioneers, the state is not alone in its openness to driverless technology. Scotland, for example, is already running an autonomous bus service. Sooner or later, driverless cars will be commonplace on our roads.

Technology essential to achieve the driverless car revolution is x-by-wire, where x represents the required aspects of vehicle control, including drive (acceleration), braking, and steering. This technology replaces traditional mechanical systems with electronic and computer-control.

x-by-Wire and human-driven vehicles

But x-by-wire technology is by no means exclusive to driverless vehicles. Furthermore, the concept is not entirely new. Electronic control is already responsible for numerous functions of a car, from engine management through to the control of passenger windows, and x-by-wire control of the throttle has already been on the market for a number of years. But what is now coming is the spread of x-by-wire technology to all areas of a car, including its critical driving and safety systems – systems that will be fundamental to autonomous vehicle control.

And while we will have to wait a little longer to see driverless vehicles on the road, x-by-wire is set to see widespread use a lot sooner. In the next three to 10 years, there will be increasing numbers of standard, human driver vehicles, equipped with x-by-wire systems that will actuate the primary means of driver input, including steering, gear shifting, and braking. Advantages include enhancements in safety, energy efficiency, as well as improving the ease of the driving experience.

While the opportunity to increase customer value is driving x-by-wire innovation, accelerated by market competition among the global vehicle manufacturers, the culmination of technology progress is pushing it further.

Advances in the power of microchips is one such enabler, alongside the increasing reliance on electronic control systems. This direction of travel has been further accelerated by the transition to EVs that has encouraged a spike in electronic management capabilities. 

Electric motors and the car market

Also integral to x-by-wire systems is the motion that powers them, based on a motor, its transmission, encoders, as well as drives and controls. Whether actuating the suspension of a vehicle and ensuring its stability, or regulating the force applied to a brake calliper, the high-performance requirements of these applications are placing new demands on motion system development.

On the one hand, around 100 electric motors are already integrated within the design of a typical modern car, for uses varying from power steering assistance to the control of door windows. Although these roles are key, car makers treat these motors as commodities. Installing motors with higher performance won’t add value, and the differentiation between these types of motors isn’t high. In reality, they are all good enough for the performance demands that the applications require.

There is another end of the scale for motion systems, where luxury car marques already need the best performance. Prestige car makers, or tier one suppliers to premium car brands, work with motor manufacturers like maxon to increase value – value that car buyers are ultimately willing to pay for. This approach also transfers to competition motorsport, including Formula One and Formula E, where constructors pay a premium for motors from brands like maxon in return for optimum performance, particularly when torque density is key.

A new role for motion systems

However, the coming generation of vehicles integrating x-by-wire technology will include the common family car, produced in high volume, and not just supercars with a premium price tag. As a result, vehicle manufacturers will not be able to pass on the value of a high-performance electric motor to the typical car customer.

At the same time, the motion performance requirements for x-by-wire are high, and these applications need precision control. To guarantee safety in steering, throttle control, and braking, the need for optimum reliability is paramount. Motion systems must also achieve low weight to optimise a vehicle’s overall fuel or battery efficiency, and they also have to fit within a compact space envelope. For these reasons, a typical ‘commodity’ motor of the type currently used in most cars, cannot fulfil the exacting requirements of x-by-wire systems.

So what directions can car manufacturers and their tier one suppliers take to achieve the motion system they need?

The most simple option is to engage a supplier that can already guarantee the required motion performance for x-by-wire applications. Motion solution designers familiar with OEM customisation and automotive applications can also seamlessly integrate the motor and its connected components into an x-by-wire application.

With this approach, the motion system designer must have IATF 16949 accreditation, the global industry standard for automotive manufacturing worldwide, which maxon has achieved. As part of this, the supplier must also be able to manufacture at high volume, which is also critical to reach the required value and cost point demanded by the highly competitive automotive market.

The other option is to bring motion solution expertise in-house. This means recruiting qualified motion solution designers, sourcing the optimum materials, as well as initiating manufacturing. Although this is an approach commonly taken by car makers and tier one OEM suppliers to develop many automotive components, for motion systems there are additional risks.

The advantage of a motion solution partnership

Compared to partnering with an existing motion solution designer, building an in-house motion specialisation will take significantly longer to achieve. Because of the complexity of the task, if the motion design can’t be optimised to the specification within a relatively short time frame, long-term costs could also spiral.

This ‘in-house or outsource’ debate could apply by degree to any system of a vehicle. However, motion development has a distinct complexity. At the most basic level, x-by-wire motion systems have a critical requirement, with a need to guarantee reliability by ensuring ‘fail-operational’ safety and the redundancy that it provides.

To further improve performance and safety, there’s also a growing requirement to integrate new and varying types of sensors, such as LiDAR, with the motion system itself. This brings its own challenges, including the need to achieve compatible feedback systems, required to close the control loop. 

Ensuring low motion system weight is also crucial, especially for the continued emergence of EVs. The ability to optimise motor torque yet still achieve a low mass envelope remains a key reason why tier one electric motor manufacturers like maxon can pass on this premium value.

Three years away?

x-by-wire technology that actuates all aspects of driver input isn’t here yet for the current generation of vehicles, but it’s fast approaching. Car manufacturers have trialled x-by-wire technology on concept cars for everyday use, and Formula One already integrates brake-by-wire. And after x-by-wire introduction for ‘standard’ cars, the emergence of driverless vehicles will certainly depend upon this technology.

Whichever approach the car marques and their tier one OEM suppliers take to realise the required motion system designs, the rules of the automotive market won’t change: the specification for performance and safety must be met, while ensuring value – and getting to market on time. At least for the motion system, there is already a straightforward, proven way to achieve this.

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