Nästa generations centrifugalkoppling
Typ
Examensarbete på grundnivå
Program
Publicerad
2020
Författare
Landin, Joel
Sandström, John
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
This paper aims to investigate the possibility to replace the traditional centrifugal clutch that Husqvarna Group make use of today in their 60cc chainsaw with a compliant mechanism clutch. Today Husqvarna group use a clutch which consists of a hub and three clutch shoes and corresponding springs. The scope of this paper is therefore also to establish a guide for which parameter affect which property of the clutch.
A compliant mechanism is a mechanism that bypasses springs or hinges etc. by combining these into a singular component. In this case this would represent that hub, clutch shoes and springs are combined into a singular and homogeneous piece. Some challenges arise when all parts are combined into one, if you wish to increase the weight of the shoe clutches it is inevitable to not affect the part which is to act as the spring, regardless of if this was the intent of the engineer.
There are some specific requirements by law which applies to a chainsaw. Since there is a saw chain the clutch must engage at specific rotational speed and not at idle. Chainsaws are generally products which run at a high rotational speed, therefore the clutch needs to be designed a bit differently compared to similar clutches with different applications. Also, the clutch must be easily removeable so that the chain can be changed when needed, this also applies when used by lumberjacks in the forest.
This paper includes a study of the existing clutch and the specific requirements on such a clutch. At the same time a different study took place involving compliant mechanism, how it works, advantages and disadvantages, and also some the challenges that will emerge if the clutch instead utilize compliant mechanism. This is a study of what kind of mechanics etc. would be employed to calculate the properties of the clutch.
The work continued by generating different concepts, these concepts were then evaluated and eliminated until only two concepts remained. These concepts were then tested by Husqvarna Group in house. The test showed that the clutches had the desired functionality but did not fulfil the requirements of when the clutch should engage. The test showed that it is possible to design such a clutch but there is more work to be done.
Most of the work has consisted of design of the concepts in CAD then to be evaluated with FEM-simulations. Mostly CATIA V5 has been used. Only static calculations have been available unfortunately, therefore the results will not reflect reality perfectly. The results were deemed sufficient to compare the different concepts against each other and used to continue the optimisation. How well these calculations represent reality is something the final test shows.