Pumps, Motors

Although it worked fine for its era, you could say Buckeye Traction Ditcher Co.'s wheel trencher was in search of a heart in the 1920s. Once the tracked machine followed the Yellow Brick Road to Emerald City, it would have asked the man behind the curtain for a pump. Trenchers would eventually be given that component — the heart of today's hydraulic system — and that's one of the reasons several early mechanically driven trenchers are now spending their retirement years parked in a central Iowa field.

On those early trenchers, the energy that moved the tracks and the rear-mounted trenching wheel was directed from the prime mover (in this case an early Caterpillar gasoline engine) through a complex array of chains, cables, shafts and gears. Each of the rusty gears on the trenchers in Iowa was designed for a specific purpose.

In actual application the exposed gears were noisy and consumed much of the power they were transmitting. Open to collect dirt and grit, the gears broke teeth and grabbed operator's clothing. Wire-rope traveled through pulleys to lower the trenching wheel into the ground. The cables made the rear of the trencher look like the tangled mess of downed power lines. In those early days, machine design was restricted by what the gears, chains and cables were required to do and by their design limitations.

Descendants of the Buckeye trencher would get the strength and versatility of a hydraulic system. Today, hydrostatic transmissions help propel tracked trenchers while motors help the digging wheel slice through tough ground conditions. When off-highway equipment was finally given a heart, the positive displacement rotary pump, individual job demands began to dictate machine design rather than the components.

The pump uses mechanical energy from the engine to push fluid through the system. The pressure in the system comes from resistance due to a load on a linear (January issue) or rotary actuator. Rotary actuators, or motors, are included in this installment of the Fluid Power Series. Many motors are pumps that are being pushed by the fluid rather than doing the pushing.

"Pump and motor design has repeatedly made progress in efficiencies and capabilities since the first units were introduced" says Bob Dolwick, marketing manager, Gear Pump Div., Parker Hannifin, Cleveland, OH. "As each design stands the test of time, the envelope is pushed as design engineers look for increased output and operation efficiency. Over the years, manufacturing techniques and the development of new and improved materials continue to empower engineers to take steps forward with designs. Today's hydraulic motors are more efficient and can operate at higher pressure."

Jeff Brenner, product portfolio manager, Work Function Div., Sauer-Danfoss, Ames, IA, gave these points to sum up industry trends facing today's pump and motor supplier:

• Reduced operating costs
• Increased system efficiencies (emissions regulations)
• Higher road speeds
• Increased cooling requirements
• Increased serviceability
• High reliability, durability
• Lower warranty costs
• Faster speed to market
• Increased power density

"Our most rapidly growing motor line is the T Series [TMK, TMT, TMV motors]," says Brenner. "This line of motors was developed to address these market needs. When these motors survive in the most rugged applications, such as skid steer loaders and forestry applications, you have a field-proven product that customers can rely on and get to market quickly."

Some of the improvements made to the hydraulic system are obvious, even to by-standers. "Twenty years ago, the biggest issue with a motor or pump was that it was going to leak due to poor manufacturing standards on ports and fittings," says Wayne Wenker, new product development manager, White Drive Products, Hopkinsville, KY. "Today the machining is much better. The industry has come a long way."

Evolution