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AV propulsion: it’s all about ‘pinpoint levels of control’

What are the potential challenges and opportunities for propulsion systems in autonomous vehicles? Michael Nash investigates

While human drivers in conventional cars seek responsiveness and driving pleasure, users of autonomous vehicles (AVs) expect to be able to sit back, relax and access entertainment. To enable this, however, the ride must be smooth and the interior of an AV must be comfortable and quiet. Much of this can be influenced by the powertrain.

As such, powertrain engineers are faced with a long list of challenges, from mimicking a natural but smooth driving style to dramatically reducing noise, vibration and harshness (NVH).

Heightened senses

A 2015 study by Michael Sivak and Brandon Schoettle of the University of Michigan Transportation Research Institute (UMTRI) listed some of the activities that people could do while travelling in a fully self-driving vehicle. These included reading, texting, watching movies or television, playing games and working.

Any one of these activities may result in either a moderate or a severe level of motion sickness, argued Sivak in the report: “Motion sickness is expected to be more of an issue in self-driving vehicles than in conventional vehicles. The reason is that the three main factors contributing to motion sickness – conflict between vestibular (balance) and visual inputs, inability to anticipate the direction of motion and lack of control over the direction of motion – are elevated in self-driving vehicles.”

“When an AV goes over a pothole it can be very startling for the vehicle occupants. We’re working on technology that can detect potholes and adjust the shock absorption on the required side of the vehicle so that the occupants don’t feel it at all” – Gerard DeVito, Eaton

Speaking to Megatrends, Gerard DeVito, Vice President and Chief Technology Officer at Eaton’s Vehicle Group, suggested that this issue could be addressed with the development of intelligent powertrain systems. “As soon as somebody is on a computer and not driving, they will have a heightened sense of what the vehicle is doing,” he said. “To combat this, the acceleration and deceleration will have to be smoother and dampened.”

Limiters can be installed to ensure the AV can only accelerate at a certain pace, while sensors on the vehicle can be linked to the powertrain to make sure the AV keeps sufficient distance between itself and the vehicle in front. If the car ahead brakes suddenly, the greater the distance, the smoother the AV’s braking process.

Linking the powertrain to various sensors and using artificial intelligence (AI) could also enable AVs to produce a ‘natural’ driving style, similar to that of a human driver. This, DeVito claimed, could also reduce motion sickness.

“You’d be surprised how hard it is to emulate what a driver is doing and ensure the ride is smooth so the vehicle occupants don’t feel like the AV is doing something it shouldn’t,” he mused. “There will be considerable interaction with camera systems, radar and LiDAR. We will have to use the information from these to provide data that will be fed through very sophisticated algorithms, allowing the system to act accordingly.”

Motion sickness may only be a cause for concern in Level 4 and Level 5 highly automated cars, and not in AVs that require a significant contribution to the driving task from a human, like Level 2 and Level 3 autonomous cars. That’s the view of Mark Buchanan, Senior Manager of Advanced Engineering at BorgWarner, who told Megatrends that drivers of Level 2 and Level 3 AVs will likely “expect and require a more traditional performance and response from the propulsion systems in these vehicles.”

Enhanced levels of control

Another issue that could be challenging when considering propulsion systems in AVs is manoeuvrability. “Consider moving an autonomous 80,000lb truck in close proximity, just by a few inches,” DeVito said. “This is often the case when loading or unloading heavy-duty vehicles (HDVs), or even when squeezing a passenger car into a tight spot at a busy urban car lot. How do we do this? There are some unique algorithms that Eaton holds as intellectual property giving us the ability to manoeuvre with pinpoint levels of control.”

“Efficiency of AV powertrains will be a major concern. As the trend towards hybrid and EVs continues to pick up pace, efficiency regarding high battery-powered driving range will be key for those vehicles to be successful” – Mark Buchanan, BorgWarner

The development of electrified powertrain architectures can have an impact on this level of control. Like many experts, DeVito thinks that there will be some form of electrification present in the majority of new vehicles in the near future, which could mean mild hybrids using 48-volt (48v) systems, plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs) or fuel cell electric vehicles (FCEVs).

Joel Maguire, BorgWarner’s Director of Electrification, agrees with this view. “The future we see is that all vehicles will have some form of electrification,” he explained to Megatrends. And this, he added, includes AVs.

The marriage of electrification and self-driving technology is one that DeVito described as mutually beneficial. “We see this trend happening in both the passenger car and commercial vehicle space,” he predicted. “Once these vehicles include a reasonably-sized electric motor, it becomes much easier to control the propulsion of the vehicle. This is because they are inherently less complex than internal combustion engines (ICEs).”

DeVito believes the level of control AVs have when it comes to propulsion must be greater than the level of control that a human driver would have over a conventional, non-autonomous vehicle.

He provides an example to justify this, describing a scenario whereby a person can see that he or she is about to drive over a pothole: “The driver acknowledges the pothole and knows exactly when the car will ride over it, and when to expect it. One company came to us for help with this, because they found that when an AV goes over a pothole it can be very startling to the vehicle occupants. We’re working on technology that can detect potholes and adjust the shock absorption on the required side of the vehicle so that the occupants don’t feel it at all.”

Unusual silence

This type of technology can also be beneficial when considering NVH. When coupled with electrification, DeVito thinks that this will allow AVs to operate in a smooth and quiet manner.

“You’d be surprised how hard it is to emulate what a driver is doing and ensure the ride is smooth so the vehicle occupants don’t feel like the AV is doing something it shouldn’t” – Gerard DeVito, Eaton

For Christopher Robinson, Analyst at Lux Research, the rollout of AVs will change the characteristics that OEMs look for when designing new models. “Although chassis, suspension and engine design varies between vehicle segments and OEMs, most consider driving feel as an important quality, making sure the vehicle is responsive and fun to drive,” he told Megatrends. “This is true even for hybrid vehicles, as the fourth-generation Prius moved to a double wishbone rear suspension to improve handling. But without someone behind the wheel, the design focus can move towards comfort and smoothness.”

While it greatly reduces NVH, electrification also causes issues as the noise of the electric motor fails to mask other noises in the vehicle that would otherwise be drowned out by the ICE. DeVito described the autonomous EV as a “much quieter environment,” and thinks that occupants may be more aware of moving parts such as windscreen wipers.

He also highlighted the fact that some first-time EV drivers are highly conscious of the ‘whine’ that comes from the electric motor. This, he added, will be a difficult challenge to overcome, but one that is being mitigated with sound dampening techniques.

Saving or consuming energy

Some AV demonstrations to date have highlighted numerous advantages of using self-driving technology, one of which is a potential reduction in fuel consumption. “We’ve already seen this with some semi-autonomous driving features, like platooning,” DeVito observed. “Taking that human element of unpredictability out of the equation leads to fuel savings, and I think we can get much more out of highly automated vehicles.”

The autonomous car or truck could be linked to street furniture, such as traffic lights, with vehicle-to-infrastructure (V2I) technology. On-board computers that link to the powertrain would then adjust the speed of the vehicle to make sure that it does not need to stop at any traffic lights on its intended route.

Buchanan, however, has reservations about AV efficiency; he believes the number of electrical systems used in an autonomous vehicle will mean they are less efficient than those that are not autonomous. “Efficiency of AV powertrains will be a major concern,” he stated. “As the trend towards hybrid and EVs continues to pick up pace, efficiency regarding high battery-powered driving range will be key for those vehicles to be successful. Already today, cars do feature plenty of technology that consumes large amounts of electrical energy. With autonomous cars, the energy demands increase significantly due to the huge volume of data that is being processed and all the assistance systems needed to allow secure autonomous driving.”

“Most OEMs consider driving feel as an important quality, making sure the vehicle is responsive and fun to drive. This is true even for hybrid vehicles, but without someone behind the wheel, the design focus can move towards comfort and smoothness” – Christopher Robinson, Lux Research

Kyle Landry, another analyst at Lux Research, thinks an intelligent link between the powertrain and autonomous driving systems could make the powertrain more efficient. “It’s definitely possible through the clever usage of power and fleet connectivity,” he said. “For example, the US SuperTruck programme is investigating the use of 3D mapping to better decide how to modulate the throttle up and down hills for optimum efficiency. But only minor improvements can realistically be expected from these types of systems.”

With bumps, jerks, sudden acceleration and sharp braking accounted for in the earliest stages of an autonomous vehicle’s development cycle, and the development of an appropriate – and clean – propulsion system seen as no larger challenge, some of the major hurdles to delivering the perfect autonomous vehicle can quickly be overcome. However, a “greater level of control” will be required for an AV powertrain than for a manually-driven car, as AVs require precise and accurate regulation of throttle and deceleration.

As the automotive industry moves into into an era in which manually-driven cars share the roads with AVs, powertrain development will become polarised. Human drivers will continue to expect responsiveness and driving pleasure; those in the AVs they drive alongside, though, will expect to derive their pleasure from comfort, blissfully ignorant of the vehicle’s propulsion system.

This article appeared in the Q3 2017 issue of Automotive Megatrends Magazine.