Power in Flux Excerpt: Motor History

Here’s a little excerpt from Power in Flux, about the history of electric motors. For more, get the book here: Power in Flux

It’s a common refrain heard in EV discussions that although internal combustion technology has enjoyed over a century of development and evolution, EV drivetrain technology is relatively new, and, more to the point, playing catch-up. Nothing could be further from the truth.

Though their widespread application in electric-drive vehicles may be a relatively recent development, electric drive pre-dates gasoline power, was adopted immediately for industrial applications, and has been developed aggressively to enhance power, efficiency, cost and versatility since the early years of the 20^th century. Looking specifically at motor development, there’s a classic pattern of scientific discovery and many threads of manufacturing technology progressively folding into stepped leaps in electric drive performance over the entire timeline of its application.

Today, and historically, electric motor energy consumption accounts for roughly 40% of all our energy needs. When you consider how many electric motors you come in contact with throughout an average day, this number isn’t a surprise, rather, it seems a conservative estimate. Starting with residential applications, a typical home may have a handful of gasoline motors – lawnmowers and other tools using both 4-stroke and 2-stroke small displacement gas engines, and two or three large displacement engines in cars or other vehicles. An average kitchen alone uses more electric motors, considering the compressors, pumps and fans in ovens, refrigerators and small appliances, not to mention the robust drive motors in mixing, chopping and stirring devices, than the average garage houses gas engines.

Extend the scope to a residential HVAC system and even out to the number and types of electric motors in a gasoline car, (wiper motors, fuel pumps, window drive units for a small sample) and you start to understand how much we depend on electric motors, as well as how refined their development is. If your perspective extends to industrial manufacturing applications, it’s hard to make the case that our understanding of electric motors and control systems is somehow lacking.

Figure 13: Hitachi History of Motor Develpment (source: Hitachi white paper)

Hitachi published a very helpful brief history of the company’s work in electric motor development (which started in the early years of the 1900s) using a basic 5hp induction motor as an example, but also including a discussion of the development tools in play for each period. While the electric motor was first invented in 1830, in 1910 the 5hp induction motor developed by Naosaburo Takao weighed in at 150kg (330lb), with an external diameter of 400mm (15.7”). The latest 5hp induction motor offered by Hitachi is a fraction of that – 1/15^th the size, to be precise, in their prototype model shown in 2010 – 10kg (22lb), with only 1/3 the volume. This is a result of several concurrent threads in science, manufacturing and materials research.

The first group of major developments in the electric drive timeline happened in the overlapping periods of what Hitachi calls “Scientific Initiatives” and “Industrial Initiatives,” where we saw efforts to do work like systematize motor theory, incorporate advances in metallurgy and develop insulation materials and techniques resulting in examples like the use of aluminum die-cast rotors rather than copper in the late ‘40s, incorporating ball bearings rather than journal bearings in the early ‘50s, and the use of Class E insulation in the mid-‘60s. This resulted in a steady decrease in size and weight over the mid-century.

Neodymium Magnets

The most profound advance began in the mid-‘60s, however, with the discovery of the high-magnetic energy Samarium-Cobalt (SmCo5) compound by Dr. Karl J. Strnat, leading to the subsequent discovery of Neodymium-Iron-Boron (Nd2Fe14B) by General Motors, Sumitomo Special Metals and the Chinese Academy of Sciences in 1983. This yielded a magnetic material that is fully three times the strength of any previous material – commonly referred to as “rare earth” magnets.

As Motenergy’s John Fiorenza explains, “The speed and torque in a motor is proportional to the magnetic flux and the number of turns in the windings. If the magnetic flux is three times greater due to neo magnets, then there can be three times less turns around each pole for the windings. If the turns are less, then you can use thicker wire (and reduce the winding resistance to increase efficiency) or make the motor smaller (to save material cost for the steel, case, etc).” Though the application of rare-earth magnets demanded several adaptations of design beyond simply making everything smaller, it ultimately resulted in almost five times the power in a similar volume by the turn of this century.

There’s an important consideration here in addition to the cost of the motor itself. The design of an industrial application has to be able to support and enclose the motor as well. While the power-to-weight and power-to-volume considerations in industrial applications is nowhere near as critical in electric vehicles, especially motorcycles, it’s still a consideration in the final cost of the product, and a driving force to reduce weight and size.

A concurrent thread in this development is the ability to model the magnetic field in a moving motor using, first, calculations in the early ‘70s, then increasingly complex algorithms as computational power increased – something that we see in battery development as well. Rather than using theory proven by trial-and-error fabrication or continual refinement of previous designs, understanding magnetics in first a two-dimensional space, then, by the late ‘80s and early ‘90s, the ability to model in a 3D space allowed a more complete understanding of how magnetic fields respond through increasing speeds of rotation, current and frequency.

From the Hitachi document: “The arrival of the neodymium magnet saw the adoption of concentrated windings for the stator and, as shown in the figure, smaller coil end size.

“Although coil ends with concentrated windings are smaller, because they produce large harmonic components in the magnetic flux distribution, the stator and rotor shape become important design considerations.

“Consequently, advances in the electromagnetic field analysis techniques described above have been complementary with those in magnet materials and have allowed both axial length to be roughly halved and efficiency to be improved.”

And, to keep the Hitachi discussion in perspective, the example used was in their air conditioner compressor motors, a far cry from the design and performance requirements of a typical traction motor.

One of the more interesting and amusing stories to come out of rare-earth magnet and motor development comes out of Detroit, with GM’s efforts to reduce the size and weight of the Corvette – a car that, despite being considered by many the pinnacle of American sports car achievement, was not immune from the pressures of the first, early ‘70s fuel crisis and the influx of Japanese cars into the US market, and the subsequent late-70s crisis and downsizing of complete lines of products offered by virtually all American automakers. The opportunity to cut even a few pounds, as well as the physical size of their starter motors on the Corvette was something that was not ignored. Beyond that, you have to believe that GM was redoubling their R&D effort in general, in part to keep up with Japanese competitors, and in part to maintain status as a technological force to be reckoned with – a status that took a huge hit throughout the 1970s and ‘80s.

GM was working with Sumitomo Special Metals, to develop a more powerful rare-earth magnet for their starters. On one particular occasion, when they asked for a mix of Neodymium and Iron, the result was a batch with remarkably good qualities, well beyond expectations. Trying to determine the reason for this kind of unexpected performance, they stumbled on the cause. Apparently the technicians used a crucible that hadn’t been cleaned properly. The batch had been contaminated with traces of Cobalt from a previous job, resulting in a Neodymium-Iron-Cobalt mix and an astoundingly strong magnet. A patent was granted the Chinese company and lasted well into the early years of the 2000s.

While the properties of rare-earth magnets were increasingly well understood by the late ‘80s, both the manufacturing processes for the magnets, and the assembly and design processes for their use in motors had a long way to go. Rare-earth magnets were often fragile, hard to mount and adhere to motor assemblies, besides adding significant cost to the final product (although, as John Fiorenza pointed out, in many cases of motor design, the cost of the magnets is offset by the reduced overall size and cost of materials for the motor).

Lynch Motor’s William Read recalls, “We had lots of issues with magnets detaching due to surface corrosion. The early Neodimium did so as well, so we had them zinc plated, but in some cases that gave way or peeled as well. I still have a few early magnets that have done so I found as I was looking through what I still have, which includes a few of the tools from the early days, like magnet mounting jigs, motor assembly jig, etc.” Although Read doesn’t recall the exact date Lynch started using rare-earth Neodimium magnets in their production motors, the current motors – both Lynch and Agni – use them. A good guess would be by the mid-‘90s.

While in 1975, Mike Corbin resorted to using 1950’s vintage aerospace motor technology to drive the Quicksilver to its record setting speed run, (mounting two starter motors from a Douglas A-4 “Skyhawk” fighter: intermittent-duty starters turning a Pratt & Whitney J52-P8A turbojet, 9,300 lbf (41 kN), series wound DC motors modified with silver conductors, bought military surplus), a builder outfitting a bike for the 2009 TTXGP at the Isle of Man could use an Agni PMDC axial-flux rare-earth magnet equipped motor rated at 20kW peak and weighing a scant 11kg, (24lbs). Or, he could run two – which many teams tried to do. That, in round numbers, equates to a power/weight of 20/24, or .83.

By the year 2013, only four years later, the Ohio State entry to the IOM TT-Zero (as well as their 2014 entry, both years reaching the podium in third place) was powered by an EMRAX 228 – an axial-flux, rare-earth magnet, liquid-cooled brushless AC motor that weighs in at 12.25kG (27lb) and delivers an astounding 100kW of peak power. The power/weight has skyrocketed to 100/27, or 3.7 – over a four-fold increase.

Though it’s tempting to use this as an example of the notion that EV development is “catching up,” you have to keep in mind the industrial roots of these products. It’s more an example of a long history of development and innovation reaching a critical mass – science, research and development techniques along with manufacturing processes and consumer demand all contributing to technology leapfrogging itself to unprecedented levels.