Force Control Low-Speed High-Torque Dynamometer Slashes Testing Time and Cost


A Force Control dynamometer featuring the Positorq® Oil Shear Load Brake slashed a manufacturer’s testing time from 62 days of in-field testing to just 21 days of round-the-clock lab testing. In addition to completing testing in roughly 1/3 the time, the new dyno eliminated the need to ship heavy equipment to remote sites and have 2 operators on site for the duration of testing, further reducing testing costs. This unique project has unusual requirements – continuous torque up to 750 Nm (554 lb ft), momentary torque up to 1,127 Nm (831 lb-ft), and maximum statis lock-up torque to 1,502 Nm (1,108 lb ft).

Furthermore, the system cycles between minimum to maximum torque within 100 ms at a cycle rate of 500 cycles per minute. The Positorq® load brake features oil shear technology which enables it to meet all project requirements and provide smooth, controlled, high torque loads down to 0 rpm. It can absorb full horsepower continuously for as long as the test requires, making it ideal for a wide range of high-torque, low-speed testing applications.

Easy to use programming developed by Force Control engineers allows independent adjustment of acceleration rate, deceleration rate, and cycle rate. This system also provides on-screen setup for all parameters – acceleration rate, deceleration rate, time at maximum torque, time at minimum torque, number of cycles per sequence, and number of sequences. 

How Oil Shear Technology Works
Oil Shear Technology is a system of providing a film of transmission fluid between the friction discs and drive plates of a mechanical multiple disc type of friction brake. As the discs and plates are brought together, squeezing the fluid film, it goes into hydroviscous shear. This phenomenon transmits torque through the fluid through laminar flow.

This phenomenon is based on the laminar flow of the fluid film between the friction discs and drive plates. The fluid tends to flow in layers with each layer moving at consistently different speeds between the rotating friction disc and the static drive plate. As the pressure squeezing the disc and plate together increases the hydroviscous force of the molecules sliding past each other, it increases the torque. Therefore, simply controlling the pressure on the friction stack controls the torque.

The torque is proportional to pressure on the friction stack which is controlled by actuation pressure. This pressure can be provided by a proportional regulator for pneumatically actuated units, or a proportional regulator or servo valve in hydraulically actuated, more responsive systems.

With the fluid layer between the friction disc and drive plate there is no tendency to stick slip or chatter at very low differential speed, providing a smooth transfer of torque down to 0 rpm.

The second part of the equation is heat energy that must be dissipated from the system. Using Oil Shear Technology, the fluid is circulated through the friction stack and is cycled out of the brake to a forced lube cooling system. The cooled fluid cools the brake components including the friction material, eliminating the typical degradation found in dry friction brakes. This also allows for a more compact load brake that can, in many cases, be directly mounted to the axle, or output of the test device. The cooling system typically includes cooling oil pumps, motors, filters, over temperature switches, optional hydraulic actuation pump and motor, flow switches, fluid level sight gauge, optional tank heater, and heat exchangers. Heat exchangers can be oil-to-water or oil to air.

The cooling system can be designed for one load brake or several. Some cooling systems are designed multiple load brakes, such as 4-wheel vehicles utilizing 4 brakes. The hydraulic actuation system can be built into the cooling unit utilizing the same fluid.

The Force Control Industries Positorq load brakes utilizing Oil Shear Technology are available in a variety of sizes ranging from 68 Nm (5 lb ft) to 406,700 Nm (300,000 lb ft) and can absorb up to 2237 kW (3000 thermal horsepower). Mountings vary from flange mount, to foot mounts, to shaft mount. Custom designs and load carrying capacity are commonly developed for specific applications.

Force Control Industries Supplies Complete Dyno Stands
Force Control Industries can furnish a complete test stand including base fabrication, controls, data acquisition, and support. This can be a benefit to many companies who often build testing facilities in-house, but either lack the ability or time to design and support the complete system. Force Control will work with customers to provide any level of design and support from just a load brake, to design and build of the mounting structure, to a complete control system.

Source: Force Control Industries Inc.

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