Hydrostatic CVT Hydraulic Control for Pump-Motor Volume Timing
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Solution Overview
Problem
Conventional stepless speed change structures with hydrostatic transmissions face challenges in adjusting timing without interruption between the movement of motor-directed and pump-directed operating arms, and require complex mechanical link mechanisms to adjust the volume of hydraulic pumps and motors efficiently.
Innovation Solution
A simplified and compact stepless speed change structure that uses a hydrostatic transmission with a single speed change operating member, incorporating a pump operation piston, neutral spring mechanism, slide oil chambers, motor operation piston, larger volume operation spring, and pressure control valves to manage the volume changes of both the hydraulic pump and motor, allowing for bidirectional movement and independent operation of the pump and motor volume adjusting members.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mechanical link mechanisms are used to connect the speed change operating member with the pump-directed and motor-directed operating arms, then volume changes of both hydraulic pump and motor can be achieved, but the structure becomes large and complicated
Solution Approach 1:
The patent replaces the mechanical link mechanism with a hydraulic control system. Pressure oil supplied to the slide oil chambers actuates the pump operation piston and motor operation piston, which in turn control the pump volume adjusting member and motor volume adjusting member. This hydraulic substitution eliminates the need for complex mechanical linkages while maintaining the ability to change volumes of both pump and motor through a single speed change operating member.
Solution Approach 2:
The invention uses hydraulic pressure oil to transmit control forces from the speed change operating member to the pump and motor volume adjusting members. The pressure oil is supplied to slide oil chambers that move the operation pistons, which are engaged with the volume adjusting members. This hydraulic transmission mechanism allows for simplified structure while achieving coordinated volume changes of both pump and motor.
2Ease of operation
If first and second flexible mechanisms are provided to move pump-directed and motor-directed operating arms, then speed change from zero to predetermined speed is enabled, but the timing adjustment becomes difficult and the mechanism becomes complicated
Solution Approach 1:
The patent replaces the flexible mechanisms with a hydraulic control system using pressure oil and slide oil chambers. The pump operation piston and motor operation piston are actuated by pressure oil supplied to their respective slide oil chambers, allowing for smooth and continuous movement of the volume adjusting members without the need for complex flexible linkages.
Solution Approach 2:
The invention changes the control parameter from mechanical linkage geometry to hydraulic pressure. By controlling the pressure oil supply to the slide oil chambers, the system can adjust the timing and extent of volume changes of the pump and motor. The biasing forces of the neutral spring mechanism and larger volume operation spring are specifically set to enable coordinated movement, replacing the need for complex flexible mechanism timing adjustments.
3Device complexity
If a single speed change operating member is used to control both pump and motor volumes, then structure simplification is achieved, but precise timing control becomes difficult
Solution Approach 1:
The patent introduces pressure oil as an intermediary to transmit and differentiate the control signals from the single speed change operating member. The pressure control valve and slide oil chambers act as intermediaries that can independently control the timing of pump and motor volume changes. The biasing forces of the neutral spring mechanism and larger volume operation spring are specifically set to ensure that the motor operation piston starts moving in the smaller volume direction after the pump operation piston moves and the neutral spring mechanism is brought into a predetermined retained-elastic state, achieving precise timing control.
Solution Approach 2:
The invention uses parameter changes in the hydraulic system to achieve precise timing control. By adjusting the biasing forces of the neutral spring mechanism and larger volume operation spring, the system can precisely control when the motor volume changing starts relative to the pump volume changing. This parameter-based control through hydraulic pressure allows for accurate timing without needing multiple operating members.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient and compact volume changes of both hydraulic pump and motor with a single speed change operating member, simplifying the structure and eliminating the need for complex mechanical linkages, while maintaining precise control over speed changes.
Implementation Method 1
a neutral spring mechanism that holds the pump operation piston at a neutral position when no external force is added to the pump operation piston and generates a biasing force toward the neutral position when the pump operation piston is moved in the first and second slide directions from the neutral position
Implementation Method 2
first and second slide oil chambers that are so configured that pressure oil, which has been supplied thereinto, presses and moves the pump operation piston in the first and second slide directions, respectively, against the biasing force of the neutral spring mechanism
Implementation Method 3
a larger volume operation spring that biases the motor operation piston in the larger volume direction
Implementation Method 4
a smaller volume operating oil chamber that is so configured that pressure oil, which has been supplied thereinto, presses and moves the motor operation piston in the smaller volume direction against the biasing force of the larger volume operation spring
Data Source
AI summary
A pump operation piston biased by a neutral spring mechanism and a larger volume operation spring biased by a larger volume operation spring in a larger volume direction operatively move pump and motor volume adjusting members, respectively, is provided. A first pressure control valve commonly controls supply-discharge of pressure oil that presses the pump operation piston in a first slide direction and the motor operation piston in a smaller volume direction. A second pressure control valve controls supply-discharge of pressure oil that presses the pump operation piston in a second slide direction. Biasing forces of the neutral spring mechanism and the larger volume operation spring are so set that, after the pump operation piston is moved in the first slide direction by a predetermined distance, the motor operation piston starts moving.