Working Vehicle Reverse Switch Segmentation for PTO Safety
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Solution Overview
Problem
In agricultural tractors, the reverse switch's coupler removal or wiring disconnection leads to difficulty in distinguishing between abnormal states and normal operation, resulting in uncertain prevention of PTO shaft drive during rearward traveling, compromising safety and reliability.
Innovation Solution
A working vehicle with an actuator-controlled PTO clutch and a reverse switch featuring interlocking normally closed and opened contacts, which shifts the PTO clutch to an interruption state based on voltage inputs from these contacts, ensuring the PTO shaft is not driven during rearward traveling or when abnormalities occur, and allows drive when both the PTO switch and overriding switch are turned ON.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a normally opened contact is used in the reverse switch to detect rearward traveling operation, then the circuit opens when rearward traveling is detected, but the system cannot distinguish between abnormality (coupler removal or wiring disconnection) and normal forward traveling operation, compromising reliability
Solution Approach 1:
The reverse switch is segmented into two independent contact systems: a first contact (normally closed) that opens during rearward traveling or abnormality, and a second contact (normally opened) that closes during rearward traveling. This segmentation allows the control device to distinguish between abnormality and normal operation by evaluating both contact states simultaneously, thereby resolving the reliability issue while maintaining ease of operation
Solution Approach 2:
The control device receives feedback from both the first and second contacts of the reverse switch and uses this feedback to determine the operational state. By monitoring the combined state of both contacts, the system can reliably distinguish between rearward traveling (first contact open, second contact closed) and abnormality (both contacts open), ensuring safe PTO shaft drive prevention
2Adaptability or versatility
If the reverse switch coupler is removed or wiring is disconnected, then the circuit opens, but the system cannot distinguish this abnormality from normal forward traveling, resulting in uncertain PTO shaft drive prevention
Solution Approach 1:
The detection system is segmented into two independent contact circuits that provide complementary information. The first contact provides one state signal while the second contact provides a contrasting state signal, allowing the control device to detect abnormalities through state inconsistency, thereby maintaining reliability even when the switch configuration is modified
Solution Approach 2:
The system monitors changes in the electrical state parameters of both contacts. By comparing the expected parameter relationship (first contact open, second contact closed during rearward traveling) with the actual parameters, the control device can detect abnormalities such as coupler removal or wiring disconnection, ensuring reliable abnormality detection regardless of switch configuration variations
3Device complexity
If a single normally opened contact is used in the reverse switch, then the structure is simple, but the system lacks the capability to reliably distinguish between abnormal states and normal operation, compromising safety
Solution Approach 1:
The reverse switch structure is segmented into two contact systems (first normally closed contact and second normally opened contact) that work together to provide state distinction capability. This segmentation increases the information content of the switch output, allowing reliable differentiation between abnormal states and normal operation while maintaining relatively simple switch construction
Solution Approach 2:
The dual-contact reverse switch structure serves multiple functions: it detects rearward traveling operation, detects forward traveling operation, and detects abnormalities (coupler removal or wiring disconnection). This multi-functionality is achieved through the coordinated operation of the two contacts, providing comprehensive safety monitoring without requiring separate detection systems
Data Source
AI summary
The purpose is to provide a working vehicle such that, when a reverse switch coupler is detached, or when a wire connecting a reverse switch to a control device is disconnected, driving of a PTO shaft can be reliably prevented and reliability of the reverse switch can be improved. In a tractor, a reverse switch includes a normally closed type first contact, and a normally open type second contact that is switched in association with the first contact. When an input voltage from the first contact is higher than a set voltage, and when the input voltage from the first contact is lower than the set voltage and an input voltage from the second contact is equal to or lower than the set voltage, a control device controls the actuator such that the PTO clutch is disconnected.