Ko ra n e ’s O u t L o o k Ken Korane • Contributing Editor
The practical side of mobile electrification
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Manufacturers of construction equipment are falling over each other in the scramble to introduce electrified off-road vehicles that eliminate diesel engines and, in some cases, hydraulic drives. A number of such machines were on display at this year’s bauma, and predicting more of the same at Conexpo 2020 will be the safest bet in Las Vegas. Although limiting greenhouse gas emissions and combating climate change are laudable goals, OEMs need to step back and consider the engineering practicalities and underlying economics before jumping head first into electrification. In terms of power density, performance and price, in most applications electric drives absolutely won’t match hydraulics in the next few years. Take the case of hydrostatic wheel drives. While granted, they’re less efficient than their electric or mechanical counterparts, they have a lot going for them in mobile settings — starting with compact size, high Hydraulic drives are built to handle rugged operating conditions. torque capacity, rugged construction, relatively low cost and proven durability. despite that, in most cases, the machines will cost substantially more There’s lots of talk of electric replacements for hydraulic drives. yet provide laggard performance. Unfortunately, systems where conventional electric motors generate Like it or not, conventional diesel engines and hydraulic systems the same torque are much larger, and space is at a premium in a mobile will continue to be used in mobile equipment for a long time because machine. One proposed solution is ultrahigh-speed electric motors that they offer a robust, reliable and well-known option served by a operate at around 20,000 rpm. This makes the units smaller and lighter. wide network of suppliers. And fluid-power technology, thanks to But then engineers need to integrate a complex planetary gearbox into innovations like digital control, continues to improve in terms of the motor to reduce output speed and connect to standard drive-train efficiency and power. components. Moreover, a traction motor typically requires an inverter that takes up space. That said, a number of factors could upset this status quo, including: This motor/gearbox system faces a difficult development path • A substantial and worldwide tightening of air pollution to ensure it’s protected against vibration, shock, corrosion and regulations temperature extremes, and operates reliably for a long time. And • Punitive taxes on carbon emissions worse, high-speed permanent-magnet electric motors and the • Long-term spike in the price of oil accompanying gearboxes are expensive, and inverters aren’t cheap, • Serious innovations that upgrade electric-drive performance either. and slash costs One engineer at a major component supplier related that OEMs • Breakthroughs in advanced battery chemistries are beating down their door for help with electrification, for the most part to satisfy marketing hype, not to solve practical applications. “In Such changes would open the door to major opportunities for terms of dollars and cents, it’s nuts.” Thus, over the near term the main electric powertrains. Over the long term fluid-power suppliers need focus of electrification will be for sites and cities that mandate local zero to be attuned to potential market shifts, as it’s risky to be unprepared emissions – today mainly in Europe. Then OEMs have to get on board for the adoption of new technology. FPW
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8/19/19 12:24 PM
