HST Wheel Loader Traction Control With Table-Based Pump Pressure Limits
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Solution Overview
Problem
Existing hydraulic drive systems for loading vehicles, such as those described in Patent Literature 1, face challenges in configuring a simple and cost-effective hydraulic circuit that allows for easy and fine adjustment of traction force control. The use of hydraulic pilot type cut-off valves increases the complexity and cost of the hydraulic circuit, and the control characteristics of traction force are limited, making it difficult to adapt to varying work conditions and operator preferences.
Innovation Solution
A loading vehicle equipped with a variable displacement traveling hydraulic pump and a traveling hydraulic motor, both electronically controlled. The system includes a controller that stores predetermined characteristic tables correlating discharge pressure of the loading hydraulic pump or engine operation state with the maximum discharge pressure of the traveling hydraulic pump. This allows for precise control of traction force by adjusting the maximum discharge pressure based on vehicle speed and operational conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hydraulic pilot type cut-off valve is used to limit the discharge pressure of the traveling hydraulic pump, then the traction force can be controlled to prevent wheel slip, but the number of components in the hydraulic circuit increases and routing of hydraulic piping becomes complicated
Solution Approach 1:
The patent replaces the mechanical hydraulic pilot type cut-off valve with an electronic control system. The controller receives signals from sensors (vehicle speed sensor, discharge pressure sensor, operation state sensor) and electronically controls the traveling hydraulic pump's displacement volume, thereby substituting a complex mechanical hydraulic control system with a simpler electronic control architecture.
Solution Approach 2:
The controller serves multiple functions: it controls both the traveling hydraulic pump and the traveling hydraulic motor, processes inputs from multiple sensors, and manages traction force control based on various operating conditions. This multi-functionality reduces the need for separate dedicated components for each control function.
2Force
If the discharge pressure of the traveling hydraulic pump is limited by using a hydraulic pilot type cut-off valve, then the traction force is controlled, but the space and cost required to configure the hydraulic circuit increase
Solution Approach 1:
The electronic control system replaces the mechanical hydraulic pilot type cut-off valve, reducing the number of hydraulic components and piping required. This substitution simplifies the overall system configuration, reduces space requirements, and lowers manufacturing costs while maintaining effective traction force control.
Solution Approach 2:
The patent extracts the pressure limiting function from the complex hydraulic pilot type cut-off valve and implements it as a software-based control logic within the controller. This separates the control function from the hydraulic circuit itself, allowing for simpler hydraulic system design and easier manufacturing.
3Adaptability or versatility
If only a hydraulic pilot type cut-off valve is used for control, then the upper limit of traction force can be selected by switching positions of the dial, but the control characteristic of the traction force comprises only a characteristic in which the higher the discharge pressure of the loading hydraulic pump is, the lower the discharge pressure of the traveling hydraulic pump is made to be
Solution Approach 1:
The patent implements dynamic control characteristics through multiple predetermined characteristic tables stored in the controller. Each table represents a different control characteristic, and the controller can dynamically switch between them based on operating conditions or operator selection. This allows for flexible adaptation to different work requirements without being limited to a single control mode.
Solution Approach 2:
The system changes control parameters by selecting different characteristic tables, each defining different relationships between loading hydraulic pump discharge pressure and traveling hydraulic pump discharge pressure. This allows the control characteristic to be adjusted from a single fixed relationship to multiple configurable relationships, enhancing adaptability while maintaining ease of operation through electronic selection rather than mechanical adjustment.
4Measurement precision
If the number of hydraulic components is increased to achieve precise traction force control, then the control precision is improved, but the cost and space required to configure the hydraulic circuit increase
Solution Approach 1:
The patent substitutes electronic sensors and a controller for additional mechanical hydraulic components. The vehicle speed sensor, discharge pressure sensor, and operation state sensor provide precise feedback signals to the controller, which then precisely controls the traveling hydraulic pump's displacement volume. This electronic sensing and control approach achieves high precision without increasing the number of hydraulic components.
Solution Approach 2:
The controller acts as an intermediary between the sensors and the traveling hydraulic pump. It processes sensor inputs, determines the appropriate control action based on stored characteristic tables, and generates control signals to adjust the pump's displacement volume. This intermediary electronic control layer enables precise traction force control while avoiding the need for complex mechanical hydraulic control mechanisms.
Data Source
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AI summary
Provided is a loading vehicle in which a control characteristic of traction force can be easily and finely set and changed while a configuration of a hydraulic circuit is simple. An HST traveling driven wheel loader 1 including electronically controlled HST pump 31 and HST motor 33, comprising a solenoid proportional pressure reducing valve 36 configured to control displacement volume of the HST pump 31 based on a control signal output from a controller 5. The controller 5 stores characteristic tables T1 to T7 indicating correlation between discharge pressure of a loading hydraulic pump 32 or an operation state of an engine 4 and maximum discharge pressure of the HST pump 31, and when vehicle speed is vehicle speed that corresponds to work requiring the traction force, outputs a control signal to the solenoid proportional pressure reducing valve 36 so as to obtain the maximum discharge pressure Pm of the HST pump 31 that corresponds to one of the characteristic tables T1 to T7.