A few generations ago (let’s call it Industry 3.0), fluid flow and pressure weren’t just the muscle of hydraulic systems, but also the brain. These purely hydraulic systems did not rely on electronics for automatic control. Instead, systems used circuit blocks made up of a network of flow passages and logic valves to control machine sequences, direction, speed, and other work functions. Electronic components were also used, but they were mainly relays and switches to trigger some external function or control indicator lights and other monitoring devices.
But even with the birth of electronic control in hydraulic systems, many machines still used hydraulic logic control, especially in the machine-tool industry. AND, NOR, NAND, and other logic elements commanded control sequences, and if a malfunction occurred, troubleshooting required specialized knowledge not only of machine logic, but of hydraulics as well.
Then solid-state electronics found its way into hydraulics. Solid-state analog devices and microprocessors quickly replaced industrial hydraulic control because these electronic devices could quickly and easily be reprogrammed. Plus, they were much more compact, faster, more energy-efficient, and easier to maintain. But it didn’t stop there: Electromechanical drives began being specified not only to control hydraulics, but to replace hydraulics altogether. However, troubleshooting an electrohydraulic system still requires the skills of a highly trained and experienced technician. That’s because a loose electrical connection, burned-out solenoid, or bad switch is just as likely to cause a machine malfunction as a faulty hydraulic component.
More recently, though, hydraulics has been winning back applications that had been replaced by electromechanical drives in some industrial sectors. Machines that undergo extended dwell periods seem to benefit from this technology the most. For example, hydraulic drives in small- to medium-size injection-molding machines had been replaced by variable-speed electromechanical drives. Continued technical advancements gave these electromechanical drives increasingly higher power ratings, threatening to replace even larger hydraulic drives.
That trend has been slowed—and maybe even reversed somewhat—by what some call hybrid drives. Instead of using a fixed-speed motor driving a variable-displacement pump, these newer drives use a variable-speed electric drive and fixed-displacement pump. These hybrid drives are much more energy efficient than fixed-speed drives and can transmit much higher power than electromechanical drives.
I bring this all up because a similar trend seems to be happening in mobile hydraulics for both on- and off-highway equipment. However, instead of replacing hydraulics, these variable-speed electric drives—run by high-power batteries—are replacing diesel and gas engines. The benefits are zero emissions, quieter operation, and less maintenance. The main drivers of this trend are advances in battery technology and power management that improve power density and for longer periods of time.
We have published in-depth articles on this topic over the last several years, and we have more in the works for our Dec. and Jan. issues—just in time for IFPE and ConExpo. Read the latest by clicking here, and look for more coverage in our next two issues and, of course, on our website.