For its next generation of three-wheel trucks, Yale needed a customised brake to fit within a confined space whilst providing parking and manual release braking functions to help increase manoeuvrability.
When developing its latest three-wheeled product, Yale Lift Trucks, a leading global manufacturer of lift trucks, requested design parameters such as packaging, heat dissipation and special manual release that required a high degree of customisation to the standard design. Basis for this was the standard PK-35 brake, used in many forklift and materials handling applications around the World.
Mathieu Ruault, Warner Electric Forklift and Material Handling Market Manager, comments: “The level of re-design for this project was such that the finished components were virtually 100% 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 Lift Truck’s engineers to review the performance of existing brakes and incorporate a manual override function.”
As each specification was addressed, design prototypes were created to slowly build up the final solution; an enhanced brake package that would provide all the features and benefits required whilst still remaining cost-effective. 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 are mounted on the back of the traction motors, on the opposite side to the gearbox. The brakes had to meet specific performance requirements, as per regulations, whilst also fitting within the confined space on the end of the in-line traction motors. Warner also factored easy-removal into the design to allow for servicing without the removal of the drive unit or traction motor.
Each prototype was thoroughly tested, including extensive field testing. Warner ran life-cycle tests to simulate the brake life of the product and conducted air gap tests along with pull-in/holding tests. The testing determined the air gap limits and demonstrated that the brake would pull-in to release as required. It also factored in how temperature affected pull-in responsiveness and timing. The life-cycle test simulated a fully loaded truck travelling at certain speeds to test the dynamic braking capability and overall performance outcome of the brake assembly.
The modified PK-35 brake is an integral component on several different series of Yale and Hyster brand 1,300 - 1,800 kg. capacity sit down counterbalance trucks. It is also being installed on a series of three-wheel stand trucks. All platforms use independent in-line drive unit motors for manoeuvrability, and are variations of 36V and 48V trucks. The new PK-35 brakes incorporate a manual override function that allows for easy vehicle towing in case the truck needs to be moved, with no need for additional tools or power sources.