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Custom design: Warner releases the brakes

01 May 2012

Warner Electric has been supplying brakes and clutches to Yale Lift Trucks for many years. When developing its next generation of three-wheel trucks, Yale approached the company with a new design brief: to customise its standard PK-35 brake to fit within a confined space whilst providing parking and manual release braking functions to help increase manoeuvrability.

Warner's standard PK-35 brake is used in many forklift and materials handling applications around the World. However, Yale's latest approach to the company called for certain design features that required significant customisation of the standard product, as Warner's Mathieu Ruault explains:

“The level of re-design for this project was such that the finished components were virtually one hundred percent bespoke to the customer's requirements. Development was extremely fast-paced to keep to the project's short schedule; during this time we worked closely with Yale to review the performance of existing brakes and incorporate a manual override function.”

The main function of the brake is to lock the traction motor shaft when the truck is parked. This is done with springs pushing against a moving armature, which clamps a friction disc linked to the motor shaft. When power is applied to the brake, a coil acts as an electromagnet to pull the moving armature and to compress the springs.

There are two motors, back-to-back, with each one linked to the front wheels of the truck. The brakes, which are mounted on the back of the traction motors, on the opposite side to the gearbox, had to meet specific performance requirements, in line with the regulations, whilst also fitting within a confined space. Warner also factored easy-removal into the design to allow for servicing without the removal of the drive unit or traction motor.

Prototypes were created as each specification was addressed, and each was thoroughly tested, both on the bench and in the field. Life-cycle tests were run, simulating a fully laden truck travelling at certain speeds, as well as with air gap tests and pull-in/holding tests. This latter programme determined the air gap limits and demonstrated that the brake would pull-in to release as required. The effects of temperature on pull-in responsiveness and timing was also studied. Mr Ruault again:

"The test rigs were designed to simulate different braking energies with various speeds, to be as close as possible to the application; this also allowed us to monitor the torque of the unit through the whole life of the friction disc. The brake included new features like the hand release lever and an enclosed design to prevent entry of environmental contaminants. These options exist on other forklift brakes, but were usually added at a significant cost. The redesign work challenged us to come up with a solution which allowed these features to be integrated in the easiest way possible, allowing the design to remain cost competitive compared with the older version with these options."

The newly modified PK-35 brake is an integral component on several different series of Yale and Hyster brand 1,300 - 1,800kg capacity sit down counterbalance trucks. It is also being installed on a series of three-wheel stand trucks.

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