5 Features for Safe Hydraulic Drives

5 Features for Safe Hydraulic Drives

Five factors should be considered in order to design a safe, compact, and efficient hydraulic drive, especially considering today's advanced hydraulic drives that allow machines to reach high speeds in the most arduous conditions,

Today’s electronic-control, advanced hydraulic drives allow self-propelled machines to reach high speeds even when working in the most arduous conditions. But speed isn’t worth anything unless the vehicle operates safely. That’s where designing the drive layout and specifying the hydraulic motor can mean the difference between a machine that operates safely under all conditions and one that must go back to the drawing board.

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One of the great advantages of hydraulic drives is the absence of axles that would otherwise traverse a vehicle’s undercarriage. Hydraulic drives allow designers to place more mass between the wheel centers, rather than above them. The result is a lower center of gravity, which makes the vehicle more stable on uneven ground. Another big plus for hydraulics is independent drive control. Speed, torque, or power can be directed to individual wheels to match the specific ground conditions. The result is optimum traction control. Keeping wheels engaged with the ground gives the operator greater control and helps keep loads from shifting.

Matteo Michelin, of SAI Hydraulics, Modena, Italy, expands on these concepts with five factors that should be considered when designing a safe, compact, and efficient hydraulic drive:

Center of gravity—A compact hydraulic motor keeps the drive’s center of gravity lower than with purely mechanical drive trains, resulting in high stability, even when operating on very steep slopes. The vehicle’s overall performance is thereby improved, and the risk of overturning reduced.

Furthermore, a drive layout using hydraulic wheel motors allows greater flexibility of cabin design and engine placement, resulting in more flexible equipment designs and greater comfort and safety.

Traction distribution—Distributing traction means simply transmitting the available torque to the ground in the most efficient way possible. Flow dividers or connecting motors in series are not the most efficient methods for preventing a wheel from spinning, nor do they give the fastest reaction times.

Low center of gravity and precise traction control even on steep, unstable surfaces are hallmarks of hydraulic drives for off-highway machines.

The best solution is to balance each individual wheel torque output to the torque transmissible to the ground. SAI’s variable-displacement motors adjust their displacement continuously in full power, thereby limiting torque to each individual wheel (even down to 0 displacement) to prevent spinning.

Traction control—Safety is also a major benefit of traction control. SAI’s variable-displacement wheel drive units allow fine independent output torque distribution from every individual motor. By using a continuously variable wheel motor, the machine makes the most efficient use of the power available dependent upon specific soil conditions.

Also, when maneuvering on steep slopes, increasing the displacement of motors driving the more heavily loaded wheels provides safe traction. Therefore, the hydraulic circuit will use the same power or the same flow setting and route more flow to the front or rear axle, as required by the working conditions.

Assisted braking torque—The continuously variable displacement motors produ­ced by SAI have high mechanical efficiency that supplies high braking torque from the moment the vehicle starts to decelerate, thereby guaranteeing rapid and controlled stopping. Furthermore, the operator can continuously reduce or increase the displacement as required, thereby boosting the braking torque on any individual wheel as needed.

Auxiliary traction—SAI motors used for auxiliary traction can work at high speeds by modulating the displacement. Therefore, they can be used for driving torque at low and medium speeds but set to zero displacement if the vehicle is towed. Motors without this capability must be mechanically disengaged from the drive train to prevent damaging the motor or hydraulic system.

Download this article as a .PDF
This file type includes high resolution graphics and schematics when applicable.

For more information on SAI’s fixed-, dual-, and variable-displacement motors and other components, call (610) 497-0190, or visit www.saispa.com.

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