I've enjoyed electric steering for seven years this week.

 

The HAH has electric steering, electric A/C, and electric water pump...

 

Why does the electric assist need to always be fully functioning?

I know of hydraulic assist that cuts back when you are moving. The faster you go, the less assist you get. The difference is that the hydraulic power steering pump is always functioning even there is little-to-no assist going on. With electric assist, I would think that one could just switch it 'off' when not needed, instead of simply not using it.

Isn't the whole idea of a hybrid, is to reduce or eliminate the waste of energy?

 

Your steering system is ALWAYS receiving inputs. From you and from the road. The purpose of electric power steering is to translate inputs from the driver and the road and direct the system to react accordingly. The amount of correction / assist the system delivers will vary, but the system will be active whenever the vehicle is in a driving mode.

Electric power steering is not just about hybrids, although I can't think of a single hybrid that doesn't have it. It would seem to be required for ICE off operation. But there are many, many non-hybrid vehicles that have electric steering and that number will continue to grow.

Anecdote: Lexus / Toyota has a vehicle they market in Japan that has a lane keeping system that uses electric power steering. Because of government regulation, the lane keeping system is programmed to shut down if it goes more than 5 seconds without driver input. They don't want the drivers to get comfortable with the idea of the car "steering itself" while the driver text messages, shaves, or applies mascara.

Peace,

Martin

 

You are correct that the mechanical steering system is always receiving "inputs" from you thru the steering wheel.

However, the purpose of electrically assisted power steering is to add assistance or "boost" to your "inputs". The need for "boost" varies from quite a bit when you are stopped (parking) to none when you are traveling on a highway.

When you need no assistance or "boost" from the electrically assisted power steering system, there is really no need to keep it active.

On a conventional car, with hydraulically assisted power steering, the hydraulic pump is connected to the engine via belt, and therefore is always running, even when no "boost" is needed. However, with electrically assisted power steering, it is possible to just turn 'off' the "boost" when not needed.

BTW, electrically assisted power steering is not the same as drive-by-wire. I believe you are confusing the two.

 

A spring would offer a fixed pressure in the failure mode (deceleartion is also dependent on tire loading and traction).

Now during normal brake application, the air pressure is adjusted to allow the spring to exert more or less pressure to adjust for the stopping power equired. The maximum pressure is fixed by the spring rate, but that can be far greater than the pressure you can apply to the system with your foot and what ever boost system is used.

Bob's system (that he should be getting a patent on) would just use electro-magnetics to adjust the applied force if it is implemented like the air brakes. or his system would just have the failsafe brakes and the motor/generators would do almost all the stopping. I think you would still need the friction brakes for faster stops and complete stop and hold situations.

 

Walt,

I see now where you're coming from and we are actually not that far apart. You are absolutely correct in your "at park" scenario. You don't have belts and pumps running when you have electric power steering. I pretty much glossed over that in my explanations, but to your point, that is not trivial. Still doesn't come close to 8% F/E improvement.

I was addressing "vehicle in motion" operation of electric power steering. Here's where we differ. You state that at highway speeds, for example, the system should just go to sleep. In my experience, when the vehicle is in motion, EPS is constantly monitoring driver and road inputs to calculate degree of assist required. High speed lane changes will require far less assist from EPS than parking maneuvers, as you have pointed out. But there is always the potential that the EPS may need to retard the driver input to reduce the likelihood of a roll-over caused by a driver over-correcting (single most common cause of roll-overs). If the system is dormant it might not pick up the over-correcting input.

I can assure you that I am not confusing EPS with drive-by-wire. I'm familiar with both technologies. Now, there is a slight chance that the Lexus / Toyota I drove in Japan may have been equipped with drive-by-wire. I'm fairly certain, but not beyond all doubt, that it was EPS. The lane keeping technology that was being demonstrated could potentially be achieved with either.

Peace,

Martin