Hydrostatic Drive Pressure Balance via Closed-Loop Control

Solution Overview

Problem

Large wheel-based machines with hydrostatic drive systems face pressure imbalances between hydraulic circuits due to wheel size, calibration errors, and fluid leakage, leading to inefficient operation and energy loss, as conventional speed feedback and pressure balance valves are ineffective for machines with steerable front wheels.

Innovation Solution

A hydrostatic drive system with two hydraulic circuits, each equipped with a pump and motor, and a controller that adjusts pump displacement based on pressure differences detected by pressure sensors to maintain balance between the circuits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If pressure balance valves are used to maintain pressure balance between hydraulic circuits, then pressure balance is improved, but device complexity and cost increase

Engineering Contradiction:

Improvepressure balanceVSAvoiddevice complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The system uses pressure sensors to continuously monitor pressure in each hydraulic circuit and feeds this information back to the controller. The controller then adjusts the pump displacement in real-time based on the pressure differential feedback, creating a closed-loop control system that maintains pressure balance without requiring complex mechanical pressure balance valves

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces traditional mechanical pressure balance valves with an electronic control system consisting of pressure sensors, a controller, and variable displacement pumps. This substitution of mechanical components with sensor-based electronic control reduces device complexity while achieving the same pressure balance function

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Stability of the object's composition

If speed sensors are used to maintain pressure balance, then pressure balance is improved, but reliability deteriorates for machines with steerable front wheels

Engineering Contradiction:

Improvepressure balanceVSAvoidreliability

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The system uses pressure sensors to continuously monitor pressure in each hydraulic circuit and feeds this information back to the controller. The controller then adjusts the pump displacement in real-time based on the pressure differential feedback, creating a closed-loop control system that maintains pressure balance without requiring complex mechanical pressure balance valves

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces traditional mechanical pressure balance valves with an electronic control system consisting of pressure sensors, a controller, and variable displacement pumps. This substitution of mechanical components with sensor-based electronic control reduces device complexity while achieving the same pressure balance function

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of operation

If manual steering compensation is used to counteract pressure imbalance, then machine steering is maintained, but energy loss increases

Engineering Contradiction:

Improvesteering controlVSAvoidenergy loss

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The controller proactively adjusts the pump displacement before significant pressure imbalances develop that would require manual compensation. By continuously monitoring pressure differentials and making preemptive adjustments to pump displacement, the system prevents pressure imbalance from occurring in the first place, eliminating the need for manual steering compensation and associated energy losses

Inventive Principle:

Principle #10Preliminary action

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 effectively maintains pressure balance between hydraulic circuits, reducing unnecessary machine turning and energy loss by continuously adjusting pressures using a cost-effective closed-loop control mechanism.

Implementation Method 1

The controller is configured to maintain a pressure balance between the first and the second hydraulic circuits based on a difference between the first pressure and the second pressure

Methodology Applied

Scientific EffectPressure sensing:

Implementation Method 2

A hydrostatic drive system with two hydraulic circuits, each equipped with a pump and motor, and a controller that adjusts pump displacement based on pressure differences detected by pressure sensors to maintain balance between the circuits

Methodology Applied

Scientific EffectHydraulic pressure control: Hydraulic Press

Data Source

PatentUS9328821B2Hydrostatic drive system

Publication Date: 2016.05.03 CATERPILLAR INC

AI summary

A hydrostatic drive system for a machine is provided. The hydrostatic drive system includes a first hydraulic circuit, and a second hydraulic circuit. The first hydraulic circuit includes a first pump and a first hydraulic motor configured to selectively receive a flow of pressurized hydraulic fluid from the first pump at a first pressure. The second hydraulic circuit includes a second pump and a second hydraulic motor configured to selectively receive the flow of the pressurized hydraulic fluid from the second pump at a second pressure. The hydrostatic drive system further includes a controller configured to maintain a pressure balance between the first and the second hydraulic circuits based on a difference between the first pressure and the second pressure.