We get a lot of feedback regarding the initial cost of using electro-hydraulic power units from customers in the fluid power industry. The cost to integrate is one of the long-standing reasons electro-hydraulics have been slow to gain a foot hold in this industry. This resistance is coming from distributors, and integrators, as well as, original equipment manufacturers.
There are endless combinations of components used to design hydraulic systems. Some are replicated thousands of times for OEM applications, and others are one-of-a-kind systems for a very specific use. In this article we are focusing on a single actuator schematic to keep the comparison as simple as possible. An apples-to-apples comparison of an electro-hydraulic system vs. a traditional hydraulic system with the same functionality, and sensing capabilities, shows an interesting result.
Integrated Electro-hydraulics HPU components
Integrated Electro-hydraulic power packs are being spec’d into designs in order to allow engine off hydraulics, lower noise, lower emission capabilities, and increased efficiency from combustion engines still needed for propulsion. This is done by using power-on-demand functionality, built in pressure/flow control, and lots of internal sensing of the electronics and hydraulics systems to keep them running at peak performance and efficiency. The integrated sensing gives electro-hydraulics a huge leg up on traditional systems that need to add external components to achieve the same functionality.
A digital flow meter is a great example of an add on component. A digital flow meter costs about $800, and will need a $250 controller to monitor the flow data. The controller must be programmed, by a tech or engineer, to do something useful with the data. Electro-hydraulics can measure the same data with no extra components using a bit of math. RPM x pump displacement with proper tuning will give a flow value. Temp, pressure, RPM, current, voltage, and power are also included.
One of the biggest advantages of integrated electro-hydraulics is the packaging. Almost all hydraulic components are combined into a single package including; motor, motor controller, pump, manifold, proportional/directional control, and closed loop sensing. Oil cooling components are completely omitted since there is almost no energy lost to heat. This compactness allows systems to be installed in places they may not have been able to fit otherwise.
Traditional HPU components
Traditional hydraulic power units generally consist of a 3 phase AC electric motor, gear pump, manifold, valves, and a reservoir. This combination will get you pressure and flow at a price that is hard to beat for basic applications. Things get more expensive if additional control or sensing capabilities are needed for the application. Proportional/directional valves add mechanical flow control, but at the expense of heat (lost energy), additional costs, and system complexity. Adding sensing for system feedback optimizes efficiency and precision, but again increases cost and complexity. This is usually where the added capabilities of the system are not enough to warrant the costs involved.
Consider also, these components take up a fair amount of room. For some applications space is not a problem, however, other installations may be completely dictated by the amount of space available.
Cost comparisons of both systems
The table below shows the cost equivalent of equally capable systems for both traditional HPUs and integrated electro-hydraulic HPUs. These costs are based on actual quotes from fluid power distributors at “retail markup” that is consistent with purchasing through distribution for machine integration. This example assumes an integrated electro-hydraulic system such as, a brushless permanent magnet motor and motor controller, pump, and integrated manifold. As you can see, just for components, the electro-hydraulic HPU is about $500 less expensive.
Engineering design and installation resources
One of the biggest selling points, aside from efficiency, functionality, and packaging, of integrated electro-hydraulics is the ease of installation. Most systems require voltage in, communication, and hydraulic hoses. Simple block diagram programming gets you up and running.
It takes years and years of experience to become a master fluid power engineer that can design and troubleshoot a traditional hydraulic system. There is a huge change over in the fluid power industry happening right now. As most veterans are nearing retirement, there is a skills gap that is widening. There is not much attention given to the fluid power industry from young graduates entering the work force. Electro-hydraulics are helping bridge the skills gap by having the ability to “plug and play” which does not require traditional hydraulic knowledge or decades of experience. It also brings a level of quick control and tuning ability not easily duplicated with traditional hydraulics. Most importantly, quick design and start up times get machines back to work instead of weeks of downtime.
Parts procurement resources
Tons of resources are invested in parts procurement through verified suppliers that may take years of relationship building. Once components for a system are ordered, lead times, shipping times, shipping costs, and managing all these suppliers is a full-time position. Is also takes resources to manage the orders, invoices, and payments for these components. The ability to order an integrated electro-hydraulic HPU from a single source saves time and money that is usually not directly associated with designing a system, but, none the less, effects the bottom line.
Troubleshooting and design iterations
Once a system is designed, and assembled, it must be tested, and any bugs worked out through troubleshooting. Issues almost always arise during initial testing. These could result in hours or weeks of debugging, even ordering replacement parts. It all adds up to increased costs, and downtime of the system. Once again, the installation of integrated electro-hydraulics adds the significant advantage of working correctly, right out of the box.
Hydraulic system functionality requirements vary for every application. Basic work functions performed by a high-end system are expensive. However, when added functionality is necessary, and beneficial, integrated electro-hydraulics are the answer! Reduced installation and operation costs, as well as, less resources required from engineering, procurement, and maintenance all support the decision to choose electro-hydraulics.