Hydraulics define the evolution of construction machinery. Article updated on April 15, 2016 with new text and images.
If you asked my 20-year-old self to describe the typical day on a construction site, I’d probably have described the stereotypical scene: five guys standing around watching a sixth dig a ditch. Even if there was ever any truth to that statement, I have a hard time believing the mammoth construction industry could survive if it didn’t keep pace with the rest of the exponentially advancing modern world.
A critical piece of the construction puzzle is the machinery used to make the work faster, safer and more efficient. Excavators, loaders, graders and dump trucks are common at every construction site, and some of these machines rely on hydraulics for every part of their operation, including the drive wheels in most cases. Although the case for hydraulics in off-highway machinery is strong even without the influence of technology, construction companies want to do the job faster and more efficiently.
Although my knowledge of fluid power is decent, I’m no construction industry expert. To help me with this specialty, I’ve employed the help of Wouter Leusden. Leusden started his career as an electrical engineer, but soon found himself incapable of solving non-electrical related issues. He took the opportunity to study mechanical engineering, and soon found a job as a service engineer on board vessels equipped with hydraulic driven cargo pumps, where his experience guided his fluid power career.
At Bosch Rexroth, Leusden specialized in safety of machinery and European Guidelines, and part of his extensive training was product driven. Next to designing the safety related control systems, he had the opportunity to present his knowledge at trade fairs, and also trained customers as well as colleagues in machine safety.
At present, he works for Wärtsilä as product warranty manager, which requires that he supports all departments involved in product sales, development and so on, with market information gained in the warranty period. Also, he has been closely involved in development of supplier related equipment for Wärtsilä during his previous employment at Denison Hydraulics and Parker Hannifin.
I asked Leusden what he feels are the current popular trends in hydraulic technology for construction equipment. “Currently, there is a very strong development of control by wire instead of the conservative direct control,” he said. “The reason for this is electronics are easier to implement, and manufacturing costs are decreasing with the amount of products becoming available.
“Manufacturers of construction equipment are also focusing on cutting costs during manufacturing of their machinery, and a great part in which costs can be reduced is the assembly of machinery components. In addition, manufacturers of construction equipment components have realized being able to offer plug-and-play solutions greatly enhances selling opportunities. Nowadays, suppliers offer electronic solutions for issues that could not have been dealt with hydraulically, such as with hitch control (EHR electrohydraulic hitch control),” Leusden continued. EHR provides benefits to tractors, such as improved highway performance when the tractor is hitched to an implement, and reduces soil compaction on sensitive fields.
The advantage of power density
The mobile hydraulic industry prides itself in using high-pressure systems to take advantage of the power density of hydraulics, which is the primary reason construction machinery relies exclusively on hydraulic actuators. I asked Leusden what the current standard for construction machinery hydraulic pressure is, and where he sees it going in the future.
“Power density is directly related to effort of equipment manufacturers to minimize space and weight and at the same time be able to increase the power capacity,” he said. “Component suppliers are able to offer pumps that can handle higher pressures while being able to save on weight and dimensions. The current standard rises up to 450 bar nominal pressure for closed circuit pumps.
“In addition, component suppliers are developing products based on the market requirements instead of equipment suppliers designing according to what suppliers can offer,” Leusden continued. “Power density is not the only positive development, as electrohydraulic dynamics are becoming more important. The realization of stable, dynamically efficient electrohydraulic control systems will provide users more precise cultivation and smoother operation, increasing safety while providing less wear and tear of auxiliary equipment.”
The industrial hydraulic machine market has long been integrated with advanced electronics in the control of fluid power, which was a natural evolution since industrial hydraulics have long been electrically operated. I asked him if construction machinery has adopted electronic control in the same way industrial hydraulics has, and if there is any potential for electric pump control, such as with a servomotor and fixed pump combination.
“In fact, due to the low cost of electronic controls on pumps in particular, manufacturers of pumps are able to offer pump controls that normally are taken care of by separate valves, thus eliminating the need of extra equipment, and also saving on customer costs,” Leusden said. “This knowledge is directly derived from the experience component manufacturers have gained from the industrial solutions.
“An important part of these developments is the implementation of safety-related control systems, which are already commonly used in industrial (hydraulic) controls. Equipment on mobile platforms is regarded as ‘machines’ according to the definition of the European Machinery Directive 2006/42 EC. To reduce risks (and liability of manufacturers), safety-related control systems are becoming part of mobile machinery as well. The European Directive on Machinery forces manufactures to look at the state of the art. With electrical/hydraulic safety related components available on the market specifically designed to protect personnel and also bystanders from risks, mobile machinery equipment manufacturers are able to combine electronic controls with a certain level of reliability.
“This reliability is established by the manufacturer of the components by means of test and/or simulation of faults,” he continued. “In addition, performance history of components is used to determine the reliability as well. Often, these components perform the tasks (process and safety) without the use of additional equipment. A simple example is an electronic joystick connected to a controller that activates a hydraulic valve. When an operator lets go of the joystick due to a safety breech in the surrounding area of the construction machine, the controller will de-energize the power to the hydraulic valve safely and the valve will return to a safe, de-energized position creating a safe stop of the machine.
“The reliability of the complete loop—joystick, controller and valve—can be evaluated with the safety standard ISO 13849. The reliability of the components in the loop is then calculated and a so-called Performance Level (PL) is derived. The height of the Performance Level (a to e) is to match the required Performance Level (PLr) set during the obligatory risk assessment. If all is done well, the manufacturer of the construction equipment has done everything in his power to manufacture a safe machine corresponding to the environment in which it is to be used. Included in the manufacturer’s evaluation is also the reasonably foreseen misuse of the machinery. The risk assessment can be done also with the use of a standard, ISO 12100. Needless to say, these two standards make a strong duo.
“The cherry on the cake is that these two standards are also harmonized under the European Machinery Directive, which actually means that the use of these standards gives the manufacturer of the equipment a presumption of conformity according to the Machinery Directive requirements,” Leusden concluded.
Hybrid technology on the rise
Because construction machinery are mostly wheeled vehicles, I posit that some form of hybrid technology would be beneficial to the construction industry, especially because of the rapid stop/start cycles of equipment such as front-end loaders. I asked Leusden if he agrees with my assumption that there is a future in hybridization in the construction industry, either with hydro-pneumatic accumulators, or perhaps electric hybridization, to which he responded:
“The future is here already! Bosch Rexroth, for example, can deliver hydraulic drive solutions with CVT (continuously variable transmissions) specifically developed for energy savings. Another type of energy saving principle is the use of the flywheel with which suppliers are not only able to save on fuel consumption, but also able to meet the regulatory requirements such as TIER 4 final and Euro Stage IV.”
In this application, the flywheel is spun up to speed by absorbing inertial energy from the machine, such as has been used on F1 cars.
Other examples of hybridization have already been developed in garbage trucks. They use a combination of a central pump/motor and hydro-pneumatic accumulators. The accumulator(s) will provide extra energy to the pump/motor—which is attached to the transmission—during acceleration. During braking, the fluid then pumps back into the accumulator(s), storing energy that would typically just be lost as heat from the vehicles brakes. This type of hybrid system can be seen on front-end loaders as well.
Finally, I gave Leusden the chance to peer into his crystal ball, and tell me what he sees coming in the next 20 years of construction equipment technology.
“Hydraulics in the construction industry will continue to be more safe, more reliable and especially more fuel efficient,” he predicted. “Main drivers for this are the regulatory requirements on safety, fuel consumption and total cost of ownership. The latter point will trigger (if not already present) suppliers of parts and equipment to develop components that last longer, need less service and are more robust. With technology evolving, suppliers also will develop tools to troubleshoot the equipment from distance through the Internet. With being able to monitor or even control equipment remotely, security of data and control will follow suit.”
So it’s clear hydraulically driven construction machinery will not only stay current, but also lead some other industries in the use of electronics and other technologies. So much depends economically and environmentally, that obsolescence is just not an option.