Hydrostatic Stepless Speed Change with Hydraulic Pump-Motor Timing
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Solution Overview
Problem
Conventional stepless speed change structures with hydrostatic transmissions face challenges in simplifying and compacting the mechanical link mechanism, making it difficult to adjust timing without interruption between the movement of pump and motor operating arms, and require complex mechanical linkages to connect speed change operating members with swash plates in hydraulic pumps and motors.
Innovation Solution
A stepless speed change structure that includes a hydrostatic transmission with a variable displacement hydraulic pump and motor, utilizing a pump operation piston and motor operation piston that are bidirectionally movable, along with neutral springs and pressure control valves, to adjust volumes independently or together with a single speed change operating member, allowing for simplified and compacted design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mechanical link mechanisms are used to connect speed change operating members with pump and motor swash plates, then volume changes of both hydraulic pump and motor can be achieved, but the mechanism becomes large and complicated
Solution Approach 1:
The patent replaces complex mechanical link mechanisms with a hydraulic control system. A single speed change operating member controls a spool valve that directs hydraulic fluid to operate both the pump swash plate and motor swash plate independently or together, eliminating the need for complex mechanical linkages while maintaining volume change capability
Solution Approach 2:
The patent introduces a spool valve as an intermediary element between the speed change operating member and the hydraulic pump/motor. This spool valve acts as a mediator that distributes hydraulic fluid to different chambers, enabling independent or combined operation of pump and motor volume adjustment without direct mechanical connection
2Adaptability or versatility
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 mechanism becomes complicated and timing adjustment becomes difficult
Solution Approach 1:
The patent replaces flexible mechanical mechanisms with a hydraulic control system using a spool valve. The spool valve controls hydraulic fluid flow to operate the pump and motor volume adjusting members independently through hydraulic chambers, achieving the same speed range capability without complex flexible linkages and with easier timing adjustment
Solution Approach 2:
The patent uses hydraulic chambers and hydraulic fluid to transmit force and control the operation of pump and motor volume adjusting members. The spool valve directs hydraulic fluid to different chambers to achieve different operational modes, replacing mechanical flexible mechanisms with a hydraulic control system that provides smoother operation and easier timing control
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 realization of first and second speed change states with a single speed change operating member, improving the timing and complexity of volume adjustments in hydraulic pumps and motors, thereby enhancing the operational efficiency and reducing mechanical complexity.
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
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
A pump operation piston (110,310) biased by a neutral spring mechanism (120,33) and a larger volume operation spring (150) biased by a larger volume operation spring (150) in a larger volume direction (VL) operatively move pump and motor volume adjusting members (30;60), respectively. A first pressure control valve (171) commonly controls supply-discharge of pressure oil that presses the pump operation piston in a first slide direction (S1) and the motor operation piston in a smaller volume direction (VS). A second pressure control valve (172) controls supply-discharge of pressure oil that presses the pump operation piston in a second slide direction (S2). 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.