Drivetrains of the future

[freebeard]

How One Company Can Turn Normal Cars Into Affordable Hybrids Using Supercar Tech

An un-attributed quote in the article:

The new eAxle is an evolution of the system GKN designed for the Porsche 918 Spyder. The single-speed design minimises weight to just 20.9kg while optimising efficiency, installation space and costs for mass-market vehicle applications. A two-staged geartrain with a gear ratio of 12.5 provides up to 2000Nm torque and 65kW power for a dynamic pure-electric mode and balanced wheel torques for all-wheel drive mode. An electromechanically actuated dog clutch disconnects the electric motor at higher vehicle speeds and an open coupling minimises rotating losses when disengaged. Precision engineering of the gear teeth and other acoustic measures ensure noise emissions are minimal.

I like the Toyota MGR at 98lb and 68hp. The Aricmoto SRK has two motors in a single drive unit. It has 40hp; but I'm not sure of the weight. This article appears to say, in non-metric terms, 46lb and 85hp and that torque vectoring is built into the unit.

As cars like the BMW i3 and Smart EV populate junkyards, some drive axles will be preferable over others. I suspect the complete Tesla subframe, at 300lb will be most popular. What other candidates are there.

[user removed]

The solution is not more complexity.

regards
mech

[freebeard]

That's why I like the Toyota MGR. Four moving parts and two of those are splined together. All the complexity is in creating the rotating magnetic fields.

[e*clipse]

I agree w/ Old Mechanic.

I also have severe doubts about the weight. I don't think it's possible, unless titanium and carbon parts are used, to get a "two stage" AWD drivetrain WITH a 65 kW motor that weighs only 20kg. If you take the motor parts ( rotor & stator ) out of the MGR, you're left with a one speed gearbox and differential that weighs about 20kG. ( I need to dig up my notes on that ) Toyota did an excellent job at keeping the MGR light; I'm having a difficult time finding excess weight to remove.

Now they're claiming that they can get twice as many gears and differentials, etc with the same weight??? Oh yeah, and a motor too?

It may be possible to get a 65kW electric MOTOR that light, especially if they are spinning it REALLY FAST, like the 12.5:1 gear ratio would imply. To get the 6.86:1 MGR to move a "sporty car" at 130mph, the motor needs to spin @ about 12,000 rpm. I would guess by their gearing they have a motor spinning well over 20,000 rpm. That's the "easy" way to get a light electric motor...

The problem, we're finding with the MGR is that the BEMF requires a very high voltage power supply. For the MGR, it's 650V.

- E*clipse

[samwichse]

I like how they quote the weight of the drive axle/motor... but wait, what about the weight of the batteries to power the thing? That's going to be another 100kg and a chunk of your trunk space if you want a plugin hybrid from this thing.

Also, 65kw from a 20.9kg motor means it's going to need to be water cooled. So radiator, piping, water fill, pump to add to that weight.

All in I'm going to say you're going to add 200-220kg to your car and take up half the trunk if you want to use it.

Sam

[e*clipse]

That's probably a stretch; although it's the opposite side of that argument.

Case in point, my 1G Honda Insight - reasonable comparison, since they were talking about a hybrid vs a pure EV. Similar things could be said of the Prius.

The Insight's electric motor takes virtually no space. Think of it as a thicker than normal flywheel.

The motor in my MGR is also very small - about 10" in diameter and 5" thick. For the power they're talking about, refer to my statement about its power and spinning it faster. The entire MGR takes a tiny bit more space as a standard differential.

You're probably right about the battery. The battery pack of my Insight is very small - yes it doesn't store much energy, but it is made of air-cooled NiMh cells. High power Lithium cells would significantly boost the storage capacity with no weight or volume gain.
Something about 1/3 the size of the Nissan Leaf's pack would give 6kWh at 100kg.

Cooling system? The Prius and the Insight, as well as many other examples, use the existing cooling system. The 50kW MGR doesn't have an external cooling system.

If we're talking about a pure EV, you're right - partially, because a much larger battery pack is needed.

But to be fair, consider how much stuff you remove first. Engine, transmission, gas tank, replace large cooling system with small one, etc etc. In my EV, the net space AND weight is equal, so there's no net loss.

- E*clipse

Originally Posted by samwichse

I like how they quote the weight of the drive axle/motor... but wait, what about the weight of the batteries to power the thing? That's going to be another 100kg and a chunk of your trunk space if you want a plugin hybrid from this thing.

Also, 65kw from a 20.9kg motor means it's going to need to be water cooled. So radiator, piping, water fill, pump to add to that weight.

All in I'm going to say you're going to add 200-220kg to your car and take up half the trunk if you want to use it.

Sam

[freebeard]

Water or oil cooled.

I like how they quote the weight of the drive axle/motor... but wait, what about the weight of the batteries to power the thing?

What about the weight of the gas tank, shift lever, etc.? The thing about electricity as a source of energy is it's fungible. It could come from batteries—of some chemistry and energy density—or from a turbine generator, super-capacitors in a KERS, or a little brass ball on a miniature Eiffel tower in the middle of the roof if you can figure out a way to make that work.

[freebeard]

Here's another example.

The Toyota/Lexus hybrids with the electric rear axle were limited to a few years of production and 10Ks of examples. As they move through the recycling system, the prices for an unit are going up. Acura has announced a new hybrid version of their 2017 MDX. It uses the Sport Hybrid (SH-AWD) system from the new NSX.

Acura Shows New Beakless Face And Hybrid Drivetrain On Refreshed MDX

They ditch the driveshaft of the non-hybid version for an electric axle:

At the front are two more, grouped together as the Twin Motor Unit. Effectively, each drives one of the front wheels, though there's actually a complex one-way clutch, double-pinion gear mechanism used for torque multiplying, and a brake in-between them. Each has 36 HP and 54 lb-ft. of torque, the latter kicking in at 0-2,000 rpm.

2017 Acura NSX First Drive - SlashGear

So while the NSX will have low production numbers, the MDX will be driven in larger numbers by less capable drivers. We shall see if all the driver assist features can keep the parts out of the junkyards.

[freebeard]

Today I was bicycling around town so I stopped in at the Toyota dealer down the street and talked to a few of the half-dozen salespeople on the floor. They had one example of the 2016 RAV4 hybrid, and I took a peek underneath.

It does appear that, while the early CA-only compliance cars use a Tesla drive, the current RAV4 has an electric rear axle sourced from ZF:


http://www.autoevolution.com/news/zf-s-new-modular-rear-axle-has-steering-and-electric-drive-options-104410.html#agal_0

Like that without the rear-wheel steering. What I'm really liking a lot though, is this system from a proposed urban car:


http://www.zf.com/corporate/en_de/products/product_range/cars/cars_electric_twistbeam.shtml

This would be awesome in the back of a Baja Bug, with the twist beam located where the rear torsion bar housing is.