Cab Coming-Off Prevention Structure for Working Machines
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Solution Overview
Problem
Existing cab coming-off prevention devices for working machines, such as hydraulic excavators, face issues with the rod-shaped member detaching due to cracking at the welded portion when subjected to loads exceeding the load-bearing capacity, leading to potential failure and loss of the cab during overturns.
Innovation Solution
A cab coming-off prevention structure featuring a shaft-shaped stopper shaft with a notched portion and a key member, where the stopper shaft is inserted through holes in both the cab and machine body frame, with the key member fitted into the notched portion, ensuring the stopper shaft remains locked and preventing detachment, even if the key member is temporarily disengaged, thereby reinforcing the cab's attachment to the machine body frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the rod-shaped member is fixed by welding to the bottom frame of the cab, then the coming-off prevention device can be securely attached, but the welded portion may crack under excessive load causing the device to detach
Solution Approach 1:
The rod-shaped member is segmented into two parts: a stopper shaft portion inserted through holes in both the cab and machine body frame, and a key member fitted into a notched portion of the stopper shaft. This segmentation allows the key member to act as a separate locking element that prevents detachment even if the welded portion fails, thereby resolving the contradiction between attachment strength and reliability under excessive load.
Solution Approach 2:
The key member acts as an intermediary element between the stopper shaft portion and the cab/machine body frame. It provides an additional mechanical connection that mediates the load transfer, ensuring that even if the welded connection fails, the key member maintains the attachment, thus improving reliability under excessive load conditions.
2Device complexity
If a simple rod-shaped member is used for the coming-off prevention device, then the device complexity is reduced, but the device may detach due to welding failure under excessive load
Solution Approach 1:
The device is segmented into the stopper shaft portion and the key member, where the key member serves as a simple yet effective locking element. This segmentation adds minimal complexity while significantly improving reliability by preventing detachment through the notched portion-key member interface, resolving the contradiction between device simplicity and reliability under excessive load.
Solution Approach 2:
The notched portion in the stopper shaft portion creates an asymmetric geometry that engages with the key member. This asymmetric design provides a simple mechanical interlock that prevents detachment, adding minimal complexity while ensuring reliability under excessive load conditions.
3Force
If the rod-shaped member is made to withstand high loads, then the load-bearing capacity is improved, but the welded portion becomes more susceptible to cracking under excessive load
Solution Approach 1:
The key member serves as an intermediary that shares the load-bearing function with the welded portion. By distributing the load through both the welded connection and the key member engagement, the stress concentration on the welded portion is reduced, thereby improving resistance to welding failure while maintaining high load-bearing capacity.
Solution Approach 2:
The load-bearing function is segmented between the stopper shaft portion (welded connection) and the key member (mechanical interlock). This segmentation allows the system to withstand high loads while reducing the risk of welding failure, as the key member provides an alternative load path that prevents complete failure even if the welded portion cracks.
Data Source
AI summary
To provide a cab coming-off prevention structure of a working machine capable of preventing a coming-off prevention device from falling off.One end side of a stopper shaft portion 51 of a coming-off prevention device 16 is inserted through a through-hole 37a. The other end side of the stopper shaft portion 51 is inserted through an insertion hole 23b. A stopper main body portion 52 is provided on the other end of the stopper shaft portion 51. A portion of the key member 53 is fitted into a notched portion 51c provided along a direction crossing an axial direction of one end side the stopper shaft portion 51. The other part of the key member 53 protruding from the stopper shaft portion 51 is fixed to the one of the cab 14 and the revolving frame 23. Even if the key member 53 is disconnected from the cab 14 or the revolving frame 23, the coming-off prevention device 16 can be prevented from falling off, without the stopper shaft portion 51 coming off the through-hole 37a, because a portion of the key member 53 is fitted into the notched portion 51c of the stopper shaft portion 51.