[brian_]

No electric OEM cars have a shiftable gearbox today, they just don't need it... that said however, you may find it simplifies the conversion...

Well, no mass-production pure battery electric cars have a multi-speed gearbox, since the original Tesla Roadster transaxle failed and is long gone, the Rimac cars are nearly custom exotics, the cars using GKN's two-speed eTwinsterX are all hybrids, and no one is currently using any of the several available two-speed transaxles intended for electric drive in production.

I agree that with a modern motor (not so much for a forklift motor) only one ratio is needed, and that's the current normal practice.

I also agree that

• you likely need some gear reduction between the motor and the final drive, and the stock transmission may be the cheapest and easiest (although not lightest or most compact) way to get it, and
• you may not know the best gear ratio in advance, and shifting the stock transmission is an effective way to change ratios.

 

[brian_]

Yes, that's true that no current EVs have a gearbox...

Just to be clear: they all have a gearbox, but they don't have a multi-speed gearbox (just a single ratio or "single speed" gearbox).

...this would only be for simplicity sake. That being said though, would there not be a benefit to keep the electric motor in a certain RPM range to extend the battery life? Or is that completely irrelevant for electric motors, and they use the same amount of power regardless at what RPM they're running at?

Motor speed does matter both to available power and to efficiency. In most production EVs, the manufacturers have decided that the efficiency benefit of changing ratios is not sufficient to justify the cost, weight, and complexity.

To me, the main reasons for wanting multiple ratios would be:

• use of a motor which does not have as wide an effective speed range as the high-voltage motors used in production EVs, or
• wanting to operate well at both highway speeds and very slowly, such as crawling off-road.

For just crawling off-road, the low range of a typical "transfer case" (which is really a multi-function device with auxiliary transmission, front drive disconnect, and "drop" or "transfer" gear or chain set) would provide the desired reduction gearing... especially if extra-low gearing is available, such as 4:1 rather than the more typical 2.5:1 or so.

The other option which I forgot to mention is getting rid of the gearbox, and replacing it with a 2 speed over drive unit which would give 2 speeds.

A more compact and simpler two-speed gearbox - intended as an auxiliary unit behind a conventional transmission but used in this case as the only transmission - is an appealing idea. A couple of notes, though:

• You probably need an underdrive (with one direct ratio and one reduction ratio) rather than an overdrive (which has one direct ratio and one overdrive ratio), since you probably want the motor to run faster, not slower.
• These are not nearly as easy to find as they were a few decades ago.

 

[brian_]

Personally it's alot of work but I'd build a custom independent suspension subframe for the front and also the rear and mount entire leaf motor into subframe in the rear.

At that point, wouldn't it be a completely custom chassis which happens to have a Defender body - and perhaps some of the frame - on top? Like this:

Im working on a few small bits and pieces for my other "project car", a 73 Firebird, and one of those is working with a metal shaping guy (http://www.chris-isaacs.com) who also does customs chassis work so a completely new chassis with IFS and only rear wheel drive would be the ticket! Some other time

Some people do stuff like that, but it's pretty extreme.

 

[brian_]

Ideally Id love a front driven accessory plate like the one EV West does which includes the AC compressor and such.

This one?
EV West Accessory Plate & Pump System For HPEVS AC-34/35/50/51
I can't imagine wanting power steering that doesn't work under 5 MPH or air conditioning that shuts off when stationary or creeping. I suspect that they built this for people using Powerglide transmissions (which make the motor turn all of the time), and then decided that it was usable even without idling.

In contrast to what EV West says, a separate motor for each accessory - suited specifically to that accessory and running only as required - makes far more sense to me. Even using their accessory mounting and drive set with a single motor dedicated to the accessories (and running at constant speed) would be more effective.

 

[brian_]

I was thinking the older style Toyota/Jeep transfer cases.

... and lots of current pickup truck and Jeep transfer cases, too.

 

[brian_]

... it would need to be powerful enough to deal with the Defender's steering torque which is huge. I'd be wary of getting one off a production car that has EPAS like a Vauxhall as it might not have the grunt for the Defender application.

That raises a question: if you want to use the original hydraulic rack and just provide electrically-pumped fluid, what's the heaviest car that came with electro-hydraulic power steering (EHPAS or EHPS)? My Mazda 3 has it, along with all the other cars built on the Ford C1 platform, probably using TRW pumps, and maybe all the same model of pump; however, TRW does offer different pumps with different capacities. The 2006–2013 Volvo V70 isn't small, and the Defender probably has slower steering which would reduce the load on the pump.

Toyota pioneered production use of this system in the W20-generation MR2 (to avoid long hydraulic lines between the steering rack and the mid-rear mounted engine); however, I don't know what else they have used it on, and I have read that Toyota has discontinued this system. They apparently don't even sell the fluid for it any more, so the system probably hasn't been used in new Toyota vehicles for at least a decade.

The trend for a decade has been away from this system of steering boost, which was an interim step between engine-driven hydraulics and directly powering the rack or column with an electric motor (Electric Power Assisted Steering or EPAS). There will now be a huge selection of non-hydraulic EPAS systems from production cars, some with the motor in the column and others with the motor on the rack, but any of them will be a challenge to control unless offered as an already sorted-out aftermarket solution because they expect commands over CAN. Even the pumps for electro-hydraulic systems can be difficult to control; the simple operation of the Toyota W-20 system is one reason for its popularity in EV conversions and engine swap projects.

 

[brian_]

Defenders don't have rack & pinion steering have a PAS steering box .

Good catch... but the electrically-pumped hydraulic assist option is still available... it's just a hydraulic steering box instead of hydraulic steering rack. The hydraulic cylinder in the Land Rover PAS box is very short, so it may need a lot of pressure to be effective, compared to a typical hydraulic rack.

Of course in the straight electric assist, the only option would be the column-mounted motor, since no one builds a motorized worm&sector box. It could be done, of course, but powering the column is the more obvious solution.

 

[brian_]

I think I have read somewhere that for Range Rover electric they have used electric steering pump from new Mini One which also adjusts the assistance based on car’s speed.

Although a simple pump with no variable assistance would make things easier perhaps.

Any recent steering pump should be able to change pressure to vary assistance. The challenge is telling it what to do, which is usually a CAN communication.

It looks like control the unit in the first BMW Mini might be unusually simple, according to this discussion from a BMW forum:
Mini Electric Power Steering Pump...
That discussion is somewhat questionable, because it states that there is no control logic needed, but includes a document showing that the pump's output pressure varies with steering action. It also mentions response to steering action, but not road speed.

Another article suggests only a simple low/high assist logic, based solely on steering activity:

The electric pump has circuitry which is used to control or "modulate" the power drawn from the car's electrical system as well as control the hydraulic fluid flow according to the steering system demand. This allows the motor to run slower (and draw less power) when there is little or no need for assistance, such as when driving on straight roads or idling in traffic. When the driver turns the steering wheel, the control circuitry built into the pump's motor increases current flow to the motor, making it spin faster and subsequently moving more hydraulic oil through the steering rack at a higher pressure. Sharp turns and tight maneuvering such as city driving, parking and autocross events keep the motor/pump running in an elevated power state. Once the road straightens out, the system returns to a reduced power state to cool off, save power and increase component life.

I also wonder about the motor for this pump - from various Mini forum discussions it appears to be a brushed (presumably PM DC) design, which has wear problems. Surely this thing which runs all the time should be brushless, right?

The whole early BMW Mini setup looks a generation out date in technology to me... but maybe that suits a Defender.

 

[brian_]

Many of these systems use the Vauxhall Corsa (GM) power steering assembly...

Good tip! That certainly looks like the same hardware.

For those in North America, the Opel/Vauxhall Corsa has never been sold here under any name. Perhaps the same powered column appears in another model? In any case, lots of cars (including GMs) have electrically powered columns here, and have for many years, even if not exactly the same unit.

For example, EV West offers an Electric Power Steering Unit for Electric Vehicles, which appears to be based on a GM unit (but not the one from the Corsa), and they provide quite a bit of information linked to that page about how it works.