The lack of a driver in an autonomous vehicle (AV) re-writes the rules on many aspects of vehicle design, including the powertrain and driveline. Continuing just-auto/QUBE's series of interviews, we asked Lee Sykes of powertrain engineering consultancy, Drive System Design, what the future might bring.
How are the OEMs and Tier 1 suppliers approaching transmission and driveline design for AVs?
Most companies are still concentrating on the AI aspects of making AVs work.
It's early days yet. The impact of AVs on transmission and driveline design is still a new question for the automotive industry; most companies are still concentrating on the Artificial Intelligence (AI) aspects of making AVs work and haven't really got to grips with it yet at this level.
Drawing up a specification for an AV means addressing the different requirements of the various levels of autonomy, understanding the transitions from level 1 to 2, 3, 4 and 5 and their impact on the functional priorities in order to apply appropriate solutions.
The first question for OEMs is whether to focus on level 5 or the interim steps which lead there. This will affect how much vehicle architecture will be carried over and how much will be purpose designed. A clearer picture emerges when designing for fully autonomous vehicles where the systems can be fully optimised, without the constraint of accommodating legacy systems.
How do the design priorities differ from a vehicle with a human driver?
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By GlobalDataTransmission design is steered by a number of key attribute targets, including package, durability, NVH, performance, safety and cost. Traditionally, some of these are driver demanded but, if there is no driver, the attribute may have no relevance or, at the very least, the relative weightings of the design priorities will change substantially.
Package size is inevitably related to durability and the required duty cycle. An AV 'summoned on demand' like a taxi could operate 24/7, clocking up a very high mileage and increasing the duty; on the other hand, eliminating the human driver will avoid abuse or frequent demands for peak performance, so reducing the duty cycle.
AV occupants will be more demanding than aircraft and train passengers, who accept relatively poor levels of comfort and NVH.
Driveline NVH and refinement is more challenging in vehicles with an electric powertrain, autonomous or not, because noise issues that would be masked by an IC engine become more significant and smooth progress will be expected at all times, with no manual driver to blame for any irregularities in acceleration in an AV. Refinement expectations include vertical as well as horizontal accelerations, so ride comfort needs to be tailored accordingly. I suspect AV occupants will be more demanding than aircraft and train passengers, who accept relatively poor levels of comfort and NVH.
Driving pleasure, derived from the handling or responsiveness of the vehicle, is irrelevant if no driver is in control; provided the vehicle has safe and adequate roadholding, the suspension can be optimised for ride comfort. Driveline technologies, such as torque vectoring, used on manually driven vehicles to combine safety with responsive handling, may well be replaced by AI algorithms which prevent the vehicle getting into trouble in the first place.
Shuttling into a parking space or inching forward in stop-start traffic will be more challenging for a robot driver because it lacks human intuition.
At low speeds, the vehicle must have the ability to carry out manoeuvres in a controlled yet timely manner, without discomfort to the occupants. Shuttling into a parking space or inching forward in stop-start traffic typically require precise clutch modulation, which will be more challenging for a robot driver because it lacks human intuition. This has implications for powertrain design; it may be more effective to use motor current control than conventional clutch control. If so, it will be important to evolve the motor design concurrently with the transmission.
Are there any similarities in the design priorities?
Achieving performance through lightweighting remains a priority but, whereas a conventional vehicle is looking for faster acceleration or lower fuel consumption, the AV needs maximum range. Weight reduction throughout all the vehicle systems reduces the energy drain on the battery pack during acceleration, and extends range.
Designing for the appropriate price point is just as important for an AV as a normal vehicle and is heavily influenced by the ownership model envisaged by the manufacturer. Is the AV intended to be a low cost consumer product for individual ownership or a more expensive commercial product, made to higher standards as a revenue generator on a rental basis?
Without a driver to cater for, will the roles of driveline and chassis engineers be diminished?
The complex interactions between the different attributes of an AV mean that the driveline and chassis engineers will still have important roles, but with different priorities to today. Instead of maximising straight line performance and juggling comfort against handling, there will be new challenges and opportunities to trade-off. For example, wheel motors improve cabin packaging space, but their unsprung weight adversely affects road holding, so clever ways of achieving package requirements whilst limiting these negative impacts will be required. Similarly, soft suspension improves ride comfort but diminishes control; connectivity with road furniture and other road users enables an AV to avoid situations requiring extreme dynamic manoeuvres; using condition monitoring to make lightweight designs realistic could improve range by reducing powertrain weight. There will be plenty for engineers to get their teeth into.
What can an engineering consultancy like DSD contribute?
You have to know what questions to ask in order to have any hope of coming up with the right answers.
You have to know what questions to ask in order to have any hope of coming up with the right answers. Independent companies like ours often make excellent catalysts, impartially helping the OEMs and Tier 1 suppliers focus their energies; sometimes through participation in a consortium with others during pre-competitive phases; at other times through more product-specific activities such as modelling or brainstorming.
When faced with a disruptive technology, such as the arrival of AVs, the most effective course is to use an attributes-driven approach to establish vehicle requirements then cascade these down to system and component level specifications. We have a number of sophisticated tools and techniques to support this, enabling us to conceptualise inventive architectures applicable to both autonomous and electric vehicles, to minimise any compromises and so achieve the best balance of attributes.
