Lexus (Mostly) Fixes The Yoke With Steer-By-Wire
When Tesla switched some of its cars’ steering wheels out for an airplane-style yoke, there was a lot of controversy. Some of it was exaggerated, and in response, some of the support for Tesla was also exaggerated. As usual, the truth lies somewhere between the two extremes. There is some legitimate reasons to be concerned about the yoke, and many people just wouldn’t like it for reasons of personal taste.
One valid criticism of the yoke was its performance in low speed driving. On the highway, where you’d almost never turn the wheel more than 90 degrees or so, the yoke is fine. The same is true for most city speed driving situations. But, when you need to rapidly move the wheel to navigate in parking lots, backing trailers, and other similar scenarios, the need to go hand-over-hand when there’s no place to put the hand was a problem for some drivers and probably an inconvenience for the people who insist that it isn’t a problem (if they were honest).
A recent video at Engineering Explained shows us how Lexus solved this problem and made its yoke a much more pleasant experience.
Long story short: Lexus has eliminated the mechanical link between the steering wheel and the front wheels, or in other words, it’s a steer-by-wire system. And, it gives Lexus the ability to do some very interesting things that wouldn’t be easy or even possible with a mechanical system.
In Jason’s video, he covers five big questions about the Lexus system:
- How does it work?
- Why do this?
- Is it safe?
- How does it make Lexus yoke better than a Tesla yoke?
- What are some drawbacks to the system?
How It Works
Cars on the road today use a mechanical system to turn the front wheels and steer the car. There are assistance systems to make this job easier for the driver, like hydraulic power steering or electric power steering, but these only help you turn the wheel and don’t remove that connection between wheel and wheels.
But, in Lexus’ system, there’s no steering linkage. There’s only a sensor in the steering column that detects the steering wheel position, and this information is sent to the steering motor, which positions the wheels to match. The process is different, but ultimately you’re still getting the same kind of control over the wheels.
There are some obvious objections to this system, the chief one being safety. Nobody wants to be one software or hardware error away from having no steering control over their vehicle. So, Jason gets to that later. Another obvious problem is that the wheel could feel “lifeless,” but this wheel works like those in a decent driving simulator, giving appropriate feedback, but in response to real-world forces and not a simulation.
Why Even Do This?
Lexus told Jason that electric motors react a lot faster than gas-powered cars. With that better throttle response comes regenerative braking, which is also a lot more responsive than the usual mechanical braking systems. Lexus wanted its upcoming EVs and plugin hybrids to have the same responsiveness in the steering wheel, with minimal lag and stretch/play in the system.
One other way this system can be extra responsive is by utilizing different ratios in the steering, without having to use complex systems to provide variable ratios. This gives Toyota (Lexus’ parent company) the ability to have a lot more control over what ratio of steering wheel turn vs wheel turn happens in different situations.
Another advantage comes in packaging. If you don’t have a full steering column, the steering wheel can go almost anywhere and you can move it around a lot more to adjust for driver needs and preferences. This comfort is improved even more when you consider that not all road feedback needs to be passed to the wheel (something enthusiasts want, but other people don’t).
Is It Safe?
I have to admit as an old-school driver that I was not excited about this idea at first. Without a mechanical link, what happens if the computer system fails? Losing something like power steering or throttle probably won’t kill you, but the thought of not being able to steer your car is terrifying.
The system is actually built with a lot of redundancy to prevent loss of steering control
First off, it has three batteries to prevent power loss from taking out steering control. There’s the main EV or hybrid traction battery, the normal 12v battery, and an extra 12-volt battery to keep the system going in the event both inverter power and the normal 12v battery fails.
The steering control actuator has redundancy as well. It has two motors, two sets of sensors, two computers, two sets of wires, and even two feedback motors. If anything fails, there’s a whole second system that can keep the system running and give you a warning that you need to get the system serviced.
Why This Is Better Than Tesla’s Yoke
For yokes, this system is particularly awesome because it can eliminate the need for hand-over-hand steering. At high speeds, the ratio can be very long and loose for stability. At lower speeds, the ratio can be very tight so that you don’t have to move the yoke much to get the full turn of the wheels. This makes it a lot easier to do things like drive in parking lots and back up trailers, and eliminates any need for a round wheel.
This makes the advantages of the yoke (better visibility, less space taken up) a lot more important. When these advantages don’t have to compete with drawbacks (difficult low-speed steering), they can really shine. Steering is sensitive when needed at low speeds, and looser for high speeds to give maximum control and comfort at all speeds.
Jason also points out that Toyota still provides physical buttons and stalks, something people who don’t want everything to be a touch screen will appreciate.
Finally, Jason gives us some information on drawbacks to the system.
One of the big ones is that it could give more safety than a normal steering system, but it doesn’t. The system could be set up to not always do what the driver says. For example, at high speeds, if you whip the wheel too quickly to one side, it could decide that the wheel movement was unsafe and ignore or deaden it down to prevent loss of control. For people who aren’t trying to do things like PIT maneuvers or J-turns, this would be OK and maybe even good for safety. For enthusiasts and professionals, this system would not be great, but could probably be turned off like traction control can be turned off. But, Lexus doesn’t take advantage of that possibility.
There’s also some lag in the system, which is very visible in Jason’s video. This means that the wheel will not always match the driver’s input like a mechanical system. The final version of the system could be better, but the prototype system has this problem.
Featured image provided by Lexus.
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