Press Ctrl+F7 you will get below pop up.
Traverse or cycle through the views you want to close by pressing F7 key. After selecting the view to be closed in the above pop up release Ctrl key. Then the view to be closed will be activated.
Go to Window->Preferences
type keys in the search box. Check whether any short cut key is assigned to close part. Refer below picture,
In my case it is assigned to Ctrl+W. Once the view is activated press this short cut key to close the view. If any short cut key is not assigned to close part then you can assign new short-cut key for this.
Click on Binding text box(Refer second picture) and assign your own short cut key.