The thesis is performed in order to improve the curvic coupled engagement of a dog clutch situated in the transfer case of a truck. The dog clutch is used to engage the so called all-wheel-drive system of the truck. If the driver tries to engage the all-wheel-drive when truck’s rear wheels already skid, due to a slippery surface a relative rotational speed in the dog clutch will occur. This relative rotational speed will cause the dog clutch to bounce back of itself before engagement, or to not engage at all. The dog clutch has been redesigned to prevent this. Dynamic simulations using MD Adams have been made for the existing model, for the models created in previous works, and for the new model in order to figure out which of them will show the most stable engagement, at high relative rotational speed. The implemented simulations show that better results can be obtained. Separation into two parts of the disc pushed by the fork, shows that dog clutch’s engagement is faster and more stable, comparing to the original model and the other created models. The new model shows better coupling in the whole range of the relative rotational speed from 50 up to 120rpm.

Normally the trucks with four wheel drive option will be running in rear wheel drives and the front wheels will be rotating freely. In extreme tough driving conditions, the risk for getting stopped or slipping the rear wheels in mud is high. When the driver tries to engage the four wheel drive option and due to the difference in relative rotational speed of the dog clutch parts, there is a risk for slipping off or bouncing back of the dog clutch. After studying the importance of gear geometry and a few parameters, the team ended up with a new design and the performance of the design found satisfactory when simulated in MSC ADAMS.

This thesis regards the design process of a test rig for a new type of clutch. To save excessive fuel losses in heavy vehicles, a dog clutch has been designed with elastic engagement to lower peak torque. Currently, there is no way of testing this clutch. The purpose of this thesis is therefore to design a test rig that allows physical testing of this newly developed clutch. The thesis describes how suitable tests/measurements are found to indicate clutch functionality. By following a design process, these tests/measurements are incorporated in a test rig design. Initially, requirements were set. With these requirements, concepts have been generated. After some reviewing and improving, one final concept has been chosen. This concept has been designed using separate subsystems. When integrating these subsystems, a final design is realised. The final design measures the axial positions of components inside the clutch. It also measures torque and speed of the input and output. This all while having a variable input speed, engagement force, output braking torque, and output rotational inertia. The test rig is suitable for long-term testing to test wear of the different clutch components. Advice on future works has been given to the company based on the achieved results.

The thesis is carried out in order to improve the transfer case in trucks with all-wheel-drive. When the truck loses traction at the rear wheels, due to slippery surfaces, wheel-spin occurs. If the driver engages the all-wheel-drive at a point where traction already has been lost, a relative rotational speed in the dog clutch will occur. If this relative speed is too high the dog clutch bounces of itself before coupling or it does not couple at all. To avoid this problem, the geometry of the teeth is modified. FE simulations are done for the existing model as well as for all the new models in order to find out which of them can handle the highest relative rotational speed. The results show that the original model is not the best one. Simple modifications of the teeth’s chamfer distance and chamfer angle shows that the dog clutch can handle up to 120 rpm of relative rotational speed whereas the original model only handles 50 rpm. / Examensarbetet är utfört för att försöka förbättra inkopplingen av allhjulsdrift på lastbilar. När en lastbil kör på halt eller löst väglag kan hjulspinn uppstå vid bakhjulen. Om föraren kopplar in allhjulsdriften när hjulen börjat slira uppstår en relativ rotationshastighet mellan halvorna i klokopplingen. Om denna relativa rotationshastighet är för hög kommer halvorna i kopplingen studsa mot varandra innan de kopplas ihop eller inte koppla ihop alls. För att undvika detta problem har klokopplingens tandgeometri modifierats. FE simuleringar är gjorda på den ursprungliga modellen samt alla nya modeller för att ta reda på vilken som kopplar vid högst relativa rotationshastighet. Resultaten visar att förbättringar kan göras. Enkla modifieringar på avfasningarnas avstånd och vinklar visar att klokopplingen kan klara upp till 120 rpm i relativ rotationshastighet jämfört med den ursprungliga modellen som endast klarar 50 rpm.