Variable Charge Pump System for Hydrostatic Circuits
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Solution Overview
Problem
Existing charge pump systems in closed hydrostatic circuits face parasitic losses due to fixed displacement pumps, which generate excessive flow rates at high rotational speeds and insufficient flow rates at low speeds, leading to inefficiencies and power wastage.
Innovation Solution
A charge pump system incorporating a planetary gear set connected to the charge pump's input shaft and driven by a motor that adjusts the ring gear's rotational speed, allowing for variable charge pump flow rates independent of the main pump's rotational speed, enabling efficient flow rate adjustment and minimizing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed displacement charge pump is used to maintain hydraulic fluid pressure in the closed hydrostatic circuit, then the charge pump capacity is sufficient at low rotational speeds, but the charge pump flow rate exceeds hydraulic fluid losses at high rotational speeds, causing parasitic losses
Solution Approach 1:
The patent applies a planetary gear set with variable transmission ratio to the charge pump, enabling the pump's rotational speed to be dynamically adjusted relative to the main pump. This allows the charge pump to operate at optimal speeds across different load conditions, maintaining sufficient pressure at low speeds while avoiding excessive flow rates at high speeds, thus eliminating parasitic losses from over-pumping.
2Loss of energy
If a variable displacement charge pump is used to reduce excess charge flow at high rotational speeds, then parasitic losses are reduced, but the pump requires high volumetric size to provide enough charge flow at low rotational speeds
Solution Approach 1:
Instead of varying displacement, the patent varies the rotational speed of the charge pump through a planetary gear set with adjustable transmission ratio. This allows a compact fixed-displacement pump to deliver appropriate flow rates at all speeds by optimizing the speed ratio between main pump and charge pump, avoiding the need for oversized pump components.
Solution Approach 2:
The patent separates the control of charge pump speed from main pump speed using an independent planetary gear mechanism. This segmentation allows the charge pump to be optimized for compact size while its actual output is controlled by the variable transmission ratio, decoupling pump size requirements from flow rate requirements across different operating conditions.
3Productivity
If a variable displacement charge pump is used to adjust charge flow rate, then flow rate can be reduced at high speeds, but the pump operates at low displacement during most operation, causing parasitic losses from driving a high volumetric pump
Solution Approach 1:
The patent dynamically adjusts the charge pump's rotational speed through the planetary gear set's variable transmission ratio, allowing the pump to operate at high speed when needed for rapid charging while maintaining compact size. This eliminates the energy waste of driving an oversized pump at low displacement, as the actual pump size matches the maximum required flow rate.
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
The system achieves efficient hydraulic fluid circulation by adjusting the charge pump's rotational speed to match the hydrostatic circuit's needs, reducing parasitic losses and energy consumption, while maintaining a compact and cost-effective design.
Implementation Method 1
a planetary gear set, whose planet wheel carrier is connected to an input shaft of the charge pump, and whose sun wheel is driveable by a driving shaft
Implementation Method 2
a charge pump motor capable to drive the ring gear of planetary gear set
Data Source
AI summary
The invention relates to a charge pump system (190) comprising a hydrostatic charge pump (12) capable to generate a hydraulic flow rate to be fed into a closed circuit of a hydrostatic transmission, a planetary gear set (20), whose planet wheel carrier (22) is connected to an input shaft (11) of the charge pump (12), and whose sun wheel (21) is driveable by a driving shaft (3); and a charge pump motor (30) capable to drive the ring gear (23) of planetary gear set (20).