PSA Reefer Car Access Platform
PSA Reefer Truck
In January of this year, Well Engineered was approached by PSA Halifax to Design a bespoke truck body in order to more efficiently access the refrigeration units on shipping containers while loaded on train cars. This custom truck body is a two-story platform to be mounted to the back of a 3/4-ton pick-up truck frame, replacing the bed of the truck while preserving the truck cab. The platform will have elevations at 5.5' and 8.5', allowing access to the top and lower container in the railcar. The lower 5.5' platform is level with the top of the railcar and allows the user to walk onto the railcar and access the lower container. The 8.5' platform will actuate out 7' and allow the user to walk out onto a catwalk and access the top container. Due to the top platform having to extend 7' from the side of the truck, the truck body design must also incorporate a stabilization leg to prevent the truck tipping. The system will be fully integrated into the truck with appropriate switches and sensors to prevent driving while the platform is in operation. The customer requires that the platform is made from Aluminum to decrease weight and is made so that it can be mounted to any suitable truck frame, with minor modifications.
As the lead designer for this project, my first step was to outline the most important and most challenging aspects of the project and design around those; for this project in particular that would be the 7' actuating platform. Aluminum, although a lot lighter than steel, it is also weaker and welds poorly. Due to this, when creating structures using aluminum sheet there is a level of creativity required in order to create strength through bent plate geometry and rivets. Luckily, we do a lot of work with bent aluminum, so I have had some experience working and designing structures using bent aluminum sheets. Using aluminum sheet bent into channel I was able to construct a suitable catwalk that could support a 400lb worker at the full extension of 7' with very little deflection. The catwalk extends but also needs to retract 7', therefore when designing the catwalk it was important to keep in mind the mechanism that will move the platform back and forth.
After some brainstorming, I was able to come up with a roller system that is driven by an electric motor mounted on the side of the platform. The motor was sized in order to handle the mass of the platform (the platform will not be actuated with a person onboard) and move the platform at an effective and time efficient speed. The roller design consists of two sets of staggered rollers that are sized to handle the moment forces in the max use case. Only one set of rollers will be drive rollers and output power; these will be direct driven by the motor. Secondary rollers are also included in this design to make the movement and positions more favorable, especially when stored. Side rollers have also been integrated in to keep the platform centered and on track with the primary and secondary rollers.
In actuality the truck body has three platforms, where one platform is the housing for the actuating platform and sits about 7" above the 8.5' high moving platform. Therefore, we have a platform that sits inside another platform when stored. The actuating platform sits 8.5' from the ground and therefore requires handrails all around. At the same time, the stationary platform that exist on top of the moving platform housing must also be guarded by a handrail. Therefore, the platform must be designed in a way so that both platforms are surrounded by handrails at all positions, regardless of how far the platform is actuated. Due to this I decided to design a telescoping handrail that extends and retracts with the platform; where smaller, thinner rails mounted on the moving platform will telescope into larger railings that are mounted on the stationary upper platform.
In order to keep the truck body within an appropriate footprint, the moving deck will only have a linear actuation of 4.5'; the additional 2.5' will be achieved using an extension that will flip down, creating a catwalk 7' long. Due to the nature of the design, the total length of the moving deck must be long enough to allow for sufficient engagement on the primary drive wheels when extended the full 7'; while also being able to retract and store in an envelop of just over 8'. The folding extension is mechanized by a linkage driven by a linear actuator. The linear actuator for the extension and side motor for the rollers are sized so that they can both run in tandem. The linkage for the deck extension is independent of the primary moving platform and can be flipped up or down at any time, no matter the position of the moving platform between stored and fully actuated.
The design of the lower platform was less of a challenge due to no moving parts. When designing with bent sheet metal, creating a closed section increases the stiffness of the member. The base or bed of the truck body, that will be bolted to the truck frame, will be a closed rectangular section of bent aluminum sheet by design. Keeping in mind the largest sheet of aluminum that can be sourced, I designed a closed section base with appropriate bends and flanges to develop stiffness across the entire bed. As previously mentioned, the truck must also have a stabilizer leg to prevent it from tipping when the catwalk is in use. About a year ago I designed a hydraulic stabilization leg for our company truck. We have been using this hydraulic leg consistently since it was installed, and the design has proved to be robust and reliable. Due to the success of the previous leg, I implemented the same tube in tube design and scaled it down for use on a 3/4-ton truck. The stabilization leg will be made out of steel which will be bolted to bent aluminum sheet stringers that run the entire width of the bed. To prevent galvanic corrosion of the aluminum, the steel will first be painted and then assembled to the aluminum stringers.
We are currently waiting for the truck that will be used in the project so that the final details can be completed, and drawings released. Once the sheet metal parts are laser cut and bent, they will come back to the Well Engineered shop to be assembled.