By Bryan McGehee
Parker Hannifin Corp.
Global Accumulator Div.

Figure 1. Integrated hydraulic circuit technology for construction and other types of off-highway equipment need not incorporate multiple functions. A simple integrated accumulator manifold, inset, can yield the same cost-saving benefits on a smaller scale.

A hot topic in all sectors of hydraulics continues to be integrated hydraulic circuits (IHCs). IHCs bring together multiple valves to serve multiple functions into a single manifold or assembly of manifolds. IHCs allow the elimination of many of the hose and tubing assemblies, fittings, and line-mounted valves that would otherwise be used in a conventional system. The result is a compact assembly with much less potential for leakage, that can be more reliable, durable, less expensive to produce, and which requires less maintenance.

But IHCs don’t have to incorporate multiple functions. Integrating functions into a manifold used with a major component, such as an accumulator, can also be of benefit. Integrated accumulator manifolds (IAMs) for mobile equipment are proving to be an excellent way to provide a wide variety of simple circuit functionality within a single assembly.

Each IAM is designed to fit a specific custom-engineered application. Importantly, an IAM does not have to follow a fixed mold design — it can be as simple as installing a valve into the extended end cap of the accumulator, Figure 1. This example represents a simple, yet effective IAM. Extending the length of the accumulator end cap allows it to serve double duty: as an end cap and as a valve manifold.

Conversely, an IHC manifold containing multiple components can also serve as the end cap of an accumulator, Figure 2. This type of solution could be used where a single component assembly is most practical, but the manifold functionality is too complex to fit inside an extended accumulator end cap. In this case, the geometry that normally would be machined into the internal surface of the accumulator end cap is machined onto the outer surface of the manifold.

Figure 2. An accumulator can be integrated with an IHC by machining the manifold surface to double as the end cap of the accumulator.

In applications that require small accumulators, an IAM can become even more innovative. Figure 3 shows a transparent 3-D model of an IHC incoorporating an integral accumulator. A main cavity is drilled to house the accumulator piston. Channels connect the volume on the dry side of the psiton to gas chambers, which are charged with pressurized gas, usually nitrogen. Of course, the IHC also contains a variety of control valves.

A case in point
An equipment manufacturer had manufactured a line of machines incorporating an accumulator and single valve manifold mounted separately and plumbed together. On rare occasions, physical contact between the hydraulic components and a moving part of the machine caused significant damage to the hydraulic system. However, limited available space prevented relocating the components to a different area of the machine.

Figure 3. An accumulator can be integrated within the confines of the IHC manifold by machining cavities and connective channels into the manifold.

The problem was resolved by extending the accumulator end cap and integrating the valve manifold within the accumulator, Figure 4. Reducing the envelope of the assembly by several cubic inches provided the clearance to eliminate the interference.

Although this application example had specific needs for reducing envelope, IAMs, in general, can also reduce:

• total number of components used,
• plumbing complexity,
• potential leak points,
• envelope size requirements,
• installation labor,
• shipping costs, and
• overall installed cost.

Plus, IAMs provide the benefits
of a single source for the entire assembly. Going along for the ride Many applications can benefit from IAM solutions, but they lend themselves especially to ride control systems. Because of their short wheel base and large pneumatic tires, wheel loaders and backhoes tend to undergo a fore and aft oscillation motion, or bouncing. This condition worsens when the vehicle travels at higher speeds. A ride control system might use an accumulator between the lift cylinder and its directional control valve to allow the cylinder to float. As a result, the machine remains level and steady, even when operating over rough terrain. This provides added safety and comfort for the operator and improved vehicle control, which translates to greater equipment productivity.

Figure 4. By integrating a valve manifold with an accumulator, an OEM was able to reduce the size of the assembly enough to prevent impact from a moving structure of the machine.

With ride control in place, machines can travel faster with less risk of losing a portion of the load they are carrying. Reducing shock in the system, can offer additional benefits, including reduced vibration for less structural fatigue and longer hydraulic component life.

Most ride control systems use a 2-way solenoid-operated poppet valve so the operator can isolate the accumulator from the lift cylinder for better control when the vehicle is in a loading or digging mode. With the flip of a switch, the operator can turn ride control on when the vehicle needs to travel.

The accumulator and valve should be located near the boom cylinder, but the additional mounting and plumbing present a challenge. By integrating the valve and the accumulator, ride control systems can be offered within a single assembly to simplify installation.

Endless variations
Design of integrated hydraulic circuits has tended to focus on valves — and with good reason. IHCs provide multiple benefits, not only to OEMs, but to end users as well. However, limiting component integration only to directional- and pressure-controlvalves causes you to miss out on similar benefits that can be gained with accumulators.

But why stop there? Don’t settle only for the benefits of component integration. Go a step further by also integrating functions. For example, providing position feedback of the accumulator piston using a linear displacement transducer allows electrohydraulic control systems to monitor system operation. You could also incorporate a proximity switch to detect low precharge pressure. The variations and opportunities are endless.

Brian McGehee is application engineer at Parker Hannifin’s Global Accumulator Div., Machesney Park, Ill. For more information, visit www.parker.com/accumulator.