Electrohydraulics Aid Performance of New John Deere Excavators

Robert Moore, Global Director Construction Engineering at John Deere, told Power & Motion that a lot of thought was put into what strategy to use for the hydraulics system on the P-Tier excavators.

He explained that traditional excavator hydraulics use an open center system with what is termed negative flow control. In these systems, the load on the machine is what told the pumps and the rest of the hydraulics to work. An electrohydraulic system, on the other hand, utilizes positive flow control in which “we're sensing what the operator is asking for with the joysticks in advance of what the machine feels for a load,” said Moore.

“The hydraulic pump and the rest of the hydraulics actually get a little bit of a jump start into what's going to happen next based on what the operator is asking the machine to do, instead of waiting for a load to be put on the machine and then have the machine react,” he continued.

To achieve this, the hydraulics went from a hydromechanical system to an almost entirely electronic one driven by sensors and software. Moore said there are pressure transducers in every circuit and decisions are being made by software when it comes to machine tuning and determining the flow a hydraulic pump will deliver. “All of those things are now driven by interrogating those sensors [on] the condition of the circuit and having software make a decision based on [those conditions],” he said.

Moore went on to explain that the previous hydromechanical system was pilot controlled, meaning joysticks in the operator cab sent a low-pressure hydraulic signal to the main hydraulic control valve to initiate various machine functions. The load on the tip of the bucket drove up the back pressure to the main control valve and the negative flow control system would then hydromechanically tell the system’s hydraulic pump to stroke.

John Deere’s electrohydraulic system on the P-Tier excavators differs by sending an electrical signal from the joysticks to proportional solenoids which then vary the pilot signal delivered to the main hydraulic control valve. Moore said this enables the positive flow approach used in the excavators by electronically controlling the system’s hydraulic pump.

The same electrical signal that's influencing the proportional solenoids is also telling the hydraulics that flow is needed in a few milliseconds. “Instead of waiting serially for a whole bunch of stuff to happen, now it's all happening in parallel,” he said. “[This is] really good from a manual operation standpoint and incredibly important from an automation perspective.”

The electrohydraulics also enable integration of various technologies, such as the EZ Control feature on the P-Tier excavators which adjusts the hydraulics with the push of a button to create smoother boom and arm movements and an automatic coupler option that allows hydraulic tool changes to be made without leaving the operator cab.

Features like these are becoming increasingly important to help overcome the labor challenges the construction industry is facing as well as maintain the comfort and safety of machine operators.

Moore also noted that the ability to add automation and autonomy to a machine is a significant and necessary capability which is feasible with electrohydraulics. While technically feasible to hydromechanically automate something, he said from a practicality standpoint it makes no sense to do so. “You must invest in the infrastructure, the platform that you’re going to put automation on top of and electrohydraulics is that platform,” he said.

He said that when using excavators, it is common for operators to have to switch between manual and automated control. An operator may be using automated control for grading but if a rock or other object is suddenly in the way, quickly needs to switch to manual operation which is not always easy to do. “You want that to be seamless,” said Moore. “When you’ve got the right system to build on top of, [like electrohydraulics] it can seem really easy to the operator.

“We want it to be completely transparent to the operator. It should not be a mental load on them,” he continued. “They've got a job to do [and] it's our job to make it as easy as possible for them to stay focused on doing their job exactly the way they want to.”

Read the article "How Automation is Impacting Hydraulic and Pneumatic Designs" to learn more about how fluid power systems are evolving to meet automation requirements. 

In general, Moore anticipates use of electrohydraulic control to continue growing. It may not be used on all hydraulic circuits, he noted, but will likely make its way into most machine types in some capacity over the coming years.

The overall efficiency and automation potential of electrohydraulics will drive their continued uptake by John Deere, and other construction equipment manufacturers who want to take advantage of those benefits. “[Electrohydraulics are] a very capable tool…and the answer to a lot of the things our customers want,” he concluded.