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They almost always only vary the amount of power assistance, not the ratio. The ratio is fixed on virtually all electrically power assisted steering racks ever

by giobox 3y ago

They almost always only vary the amount of power assistance, not the ratio. The ratio is fixed on virtually all electrically power assisted steering racks ever shipped. There is still a fixed mechanical linkage - decoupling this is what allows the ratio to be dynamically adjusted. To date only a handful of Lexus production cars have had dynamic variable ratio and decoupled steering via drive by wire. Electric power steering is essentially the same in use as traditional hydraulic systems - they just replace the hydraulic assistance with electric motors. The big advantage of decoupling and steer by wire is dynamic variable ratio, as well as packaging - no steering column to worry about making space for.

inferiorhuman 3y ago
Nah, there are variable ratio mechanical systems. On a rack and pinion setup, for instance, you vary the spacing of the teeth on the rack. ZF's been doing this for decades.
- giobox 3y ago
  Generally speaking almost all mechanical steering systems are not dynamic though, you are missing the point entirely. It can't change the spacing of the teeth on the fly - steer by wire effectively does. The number of turns lock to lock on a mechanical system is almost always the same, regardless of speed. With steer by wire, you can easily implement say one turn lock to lock at low speed for easier parking, increasing to 2-3 turns at highway speeds for stability. Which is essentially exactly what the recent Lexus model with such a system does. At low speed it can turn its wheels from one extreme to the other in just 150 degrees of steering wheel rotation - no hand over hand turning etc. 150 degrees is essentially unthinkable on a mechanical rack and pinion system, as it would make the car incredibly twitchy on a highway. > https://www.motortrend.com/reviews/2023-lexus-rz450e-steer-by-wire-yoke-review/ https://www.motortrend.com/reviews/2023-lexus-rz450e-steer-b...
  - inferiorhuman 3y ago
    It can't change the spacing of the teeth on the fly. Geez, Elon really ought to start a goalpost moving company. But hey I'll play: yes, yes it can. That's precisely what BMW's active steering is, yes it's mechanical, yes it varies the ratio depending on speed, and yes it's been around for a couple decades now.
    - giobox 3y ago
      BMW active steer doesn't get remotely close to 150 degrees lock to lock when maneuvering (minimum rotation reached is ~720 degrees/2 turns), or offer the infinite and instant range of adjustability you can get with a drive by wire system. But sure, it's just the same. I couldn't care less whether the system is on a Tesla or not, its just abundantly clear there are some design and packaging advantages when you lose the mechanical link in anything with a steering wheel. The vast, vast majority of rack and pinion systems ever made, both old and modern, don't adjust number of turns lock to lock at all, whereas the ability to essentially infinitely adjust it is inherent in all drive by wire steering systems.
      - nnevod 3y ago
        As far as I know there is no technological problem for BMW system to have whatever desired rate of adjustability and speed of reaction. It uses planetary gearset with adjuster motor connected to one of the gears - a bot similar to how Toyota Prius's transmission works. So it's more a question of how manufacturer decided it should feel for the user.
      - inferiorhuman 3y ago
        Before we change the goalposts again it's worth noting that Tesla (and to a lesser extent Lexus) make vehicles where the primary focus is on the gadgets and BMW's focus is on the driver interface. BMW active steer doesn't get remotely close to 150 degrees lock to lock when maneuvering Well, no. Super fast steering ratios are not an advantage, they're a necessary evil with a square steering control. There's nothing inherent in the BMW design that would prevent such a fast ratio beyond the reputation for emulating analog interfaces with quite a bit of fidelity. It speaks more to the intended use (gadget vs car) than to the underlying technology itself. its just abundantly clear there are some design and packaging advantages when you lose the mechanical link in anything with a steering wheel. Every time I see this I wonder if the commentor has seen a hydraulic power steering pump. They're tiny as hydraulic and pneumatic drives are often quite a bit smaller than comparable electric ones (e.g. cordless vs pneumatic power tools). The only clear advantage that electric steering offers is one of efficiency (as a result of not driving a hydraulic pump all of the time). The rest is largely a series of trade offs, especially if you look at recirculating ball / worm gear vs rack and pinion drives.
m463 3y ago
and you could invert X :)

by giobox 3y ago

inferiorhuman 3y ago

Nah, there are variable ratio mechanical systems. On a rack and pinion setup, for instance, you vary the spacing of the teeth on the rack. ZF's been doing this for decades.

giobox 3y ago
Generally speaking almost all mechanical steering systems are not dynamic though, you are missing the point entirely. It can't change the spacing of the teeth on the fly - steer by wire effectively does. The number of turns lock to lock on a mechanical system is almost always the same, regardless of speed. With steer by wire, you can easily implement say one turn lock to lock at low speed for easier parking, increasing to 2-3 turns at highway speeds for stability. Which is essentially exactly what the recent Lexus model with such a system does. At low speed it can turn its wheels from one extreme to the other in just 150 degrees of steering wheel rotation - no hand over hand turning etc. 150 degrees is essentially unthinkable on a mechanical rack and pinion system, as it would make the car incredibly twitchy on a highway. > https://www.motortrend.com/reviews/2023-lexus-rz450e-steer-by-wire-yoke-review/ https://www.motortrend.com/reviews/2023-lexus-rz450e-steer-b...
- inferiorhuman 3y ago
  It can't change the spacing of the teeth on the fly. Geez, Elon really ought to start a goalpost moving company. But hey I'll play: yes, yes it can. That's precisely what BMW's active steering is, yes it's mechanical, yes it varies the ratio depending on speed, and yes it's been around for a couple decades now.
  - giobox 3y ago
    BMW active steer doesn't get remotely close to 150 degrees lock to lock when maneuvering (minimum rotation reached is ~720 degrees/2 turns), or offer the infinite and instant range of adjustability you can get with a drive by wire system. But sure, it's just the same. I couldn't care less whether the system is on a Tesla or not, its just abundantly clear there are some design and packaging advantages when you lose the mechanical link in anything with a steering wheel. The vast, vast majority of rack and pinion systems ever made, both old and modern, don't adjust number of turns lock to lock at all, whereas the ability to essentially infinitely adjust it is inherent in all drive by wire steering systems.
    - nnevod 3y ago
      As far as I know there is no technological problem for BMW system to have whatever desired rate of adjustability and speed of reaction. It uses planetary gearset with adjuster motor connected to one of the gears - a bot similar to how Toyota Prius's transmission works. So it's more a question of how manufacturer decided it should feel for the user.
    - inferiorhuman 3y ago
      Before we change the goalposts again it's worth noting that Tesla (and to a lesser extent Lexus) make vehicles where the primary focus is on the gadgets and BMW's focus is on the driver interface. BMW active steer doesn't get remotely close to 150 degrees lock to lock when maneuvering Well, no. Super fast steering ratios are not an advantage, they're a necessary evil with a square steering control. There's nothing inherent in the BMW design that would prevent such a fast ratio beyond the reputation for emulating analog interfaces with quite a bit of fidelity. It speaks more to the intended use (gadget vs car) than to the underlying technology itself. its just abundantly clear there are some design and packaging advantages when you lose the mechanical link in anything with a steering wheel. Every time I see this I wonder if the commentor has seen a hydraulic power steering pump. They're tiny as hydraulic and pneumatic drives are often quite a bit smaller than comparable electric ones (e.g. cordless vs pneumatic power tools). The only clear advantage that electric steering offers is one of efficiency (as a result of not driving a hydraulic pump all of the time). The rest is largely a series of trade offs, especially if you look at recirculating ball / worm gear vs rack and pinion drives.

m463 3y ago

and you could invert X :)