Oil Circuit Bypass Cooling for Variable-Speed Oil-Free Compressors

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional oil circuits for oil-free compressors with variable speed drives face challenges in maintaining optimal lubrication and cooling, leading to issues such as excessive oil viscosity at low speeds, hydraulic losses, and overheating, which result in increased costs and complexity due to the need for adjustable coolers and separate motor-driven rotary oil pumps.

Innovation Solution

An oil circuit design where the rotary oil pump is driven by the compressor motor, featuring a bypass pipe with an integrated oil cooler and a pressure-actuated bypass valve, allowing for variable oil flow through the cooler based on compressor speed, ensuring consistent oil temperature and reduced viscosity, and incorporating an inlet channel with a dam to maintain oil volume for smooth startup.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the rotary oil pump is driven by a separate motor, then the oil pump can be controlled independently, but the compressor becomes more expensive, larger, and requires additional maintenance

Engineering Contradiction:

Improvecontrollability of oil pumpVSAvoidnumber of motors and control units

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent combines the oil pump drive function with the existing compression motor by coupling the oil pump to the motor shaft. This eliminates the need for a separate motor while ensuring the oil pump operates whenever the compressor is running, thus reducing device complexity and maintenance requirements while maintaining adequate oil delivery control

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If the rotary oil pump delivers more oil at higher speeds, then lubrication and cooling are improved, but oil pressure becomes too high causing excessive oil consumption and hydraulic losses

Engineering Contradiction:

Improvelubrication and cooling effectivenessVSAvoidhydraulic losses and oil consumption

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent segments the oil flow path by introducing a bypass line with a pressure-regulating valve. This divides the oil flow into two paths: one through the main lubrication points and another through the bypass that regulates excess pressure, thereby preventing hydraulic losses while maintaining adequate lubrication at high speeds

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses a pressure-regulating valve in the bypass line to dynamically adjust oil pressure parameters based on operating conditions. This ensures that oil pressure remains within optimal ranges across varying compressor speeds, preventing both insufficient lubrication and excessive pressure-related losses

Inventive Principle:

Principle #35Parameter changes

3Temperature

If the oil cooler cools all oil at low speeds, then oil temperature is controlled, but oil viscosity becomes too high leading to oil losses in bearings

Engineering Contradiction:

Improveoil temperature controlVSAvoidoil losses in bearings

Core Design Contradiction:

TemperatureVSLoss of substance

Solution Approach 1:

The patent makes the cooling system dynamic by positioning the oil cooler in the bypass line rather than in the main oil path. This allows the cooler to operate selectively based on bypass flow conditions, providing cooling when needed while avoiding excessive cooling at low speeds that would increase viscosity and cause bearing oil losses

Inventive Principle:

Principle #15Dynamics

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

This design maintains consistent oil temperature and viscosity, reducing losses and the need for large coolers, while ensuring efficient lubrication and cooling across varying compressor speeds, and allows for a compact and cost-effective oil circuit with improved startup performance.

Implementation Method 1

the oil is brought to an oil cooler, where the oil is cooled

Methodology Applied

Scientific EffectHeat transfer: Heat Exchanger

Implementation Method 2

a rotary oil pump configured to drive oil from the oil reservoir through an inlet channel upstream the rotary oil pump to the compressor element and/or the motor

Methodology Applied

Scientific EffectMechanical pumping: Pump

Implementation Method 3

a bypass valve which is configured to guide a portion of the oil back to the oil reservoir

Methodology Applied

Scientific EffectPressure-actuated flow control: Valve

Data Source

PatentUS11085448B2Oil circuit, oil-free compressor provided with such oil circuit and a method to control lubrication and/or cooling of such oil-free compressor via such oil circuit

Publication Date: 2021.08.10 ATLAS COPCO AIRPOWER NV

AI summary

An oil circuit for lubrication and cooling of an oil-free compressor with an oil reservoir and a rotary oil pump to drive oil to the compressor element and/or the motor via an oil pipe. The rotary oil pump has a rotor mounted on a rotation shaft, and is driven by the motor of the compressor. The oil circuit is provided with a bypass pipe and a pressure-actuated bypass valve which guide a portion of the oil back to the oil reservoir without this portion of the oil passing through the compressor element and/or the motor during its way back to the oil reservoir. The oil circuit is further provided with an oil cooler in the bypass pipe. The bypass valve is in the oil pipe.