Oil Circuit Bypass Cooling for Variable-Speed Oil-Free Compressors
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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 additional components.
Innovation Solution
An oil circuit design that includes a rotary oil pump driven by the compressor motor, a bypass pipe with a pressure-actuated valve, and an oil cooler placed in the bypass pipe, allowing for variable oil flow through the cooler based on compressor speed, ensuring consistent oil temperature and reduced viscosity, and incorporating a dam in the inlet channel to retain oil for smooth startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a rotary oil pump is driven by a separate motor to enable independent control, then the oil pump can be controlled independently, but the compressor becomes more expensive, larger, and requires additional components that need maintenance
Solution Approach 1:
The patent combines the oil pump drive function with the existing VSD motor that drives the compressor. The VSD motor's variable speed capability is utilized to control the oil pump speed, eliminating the need for a separate motor while maintaining independent control capability through electronic speed regulation of the shared motor.
Solution Approach 2:
The VSD motor is made to serve dual functions: driving both the compressor and the oil pump. This multi-functionality approach allows one motor to perform multiple roles, reducing the total number of motors and control systems needed in the system.
2Productivity
If the rotary oil pump is driven at higher speeds to pump more oil for lubrication and cooling, then sufficient oil supply is ensured, but the oil pressure rises too high causing excessive oil consumption and hydraulic losses
Solution Approach 1:
The system dynamically adjusts the oil pump speed to match the actual lubrication and cooling requirements at different compressor operating speeds. The VSD control continuously optimizes the pump speed, preventing excessive oil pressure and flow that would cause hydraulic losses while ensuring sufficient oil supply when needed.
Solution Approach 2:
The system uses feedback from oil pressure sensors and temperature sensors to adjust the oil pump speed. When oil pressure or temperature reaches certain thresholds, the control system reduces pump speed to maintain optimal operating conditions, preventing energy losses from excessive oil circulation.
3Temperature
If the oil cooler is designed to cool oil at maximum compressor speed, then adequate cooling is provided at high speeds, but at low speeds the oil is cooled too much resulting in high viscosity and oil losses
Solution Approach 1:
The oil cooler's cooling capacity is dynamically adjusted based on compressor operating speed and actual oil temperature. The system reduces cooling at low speeds to prevent excessive viscosity increase, while providing maximum cooling capacity at high speeds when oil temperature rises due to increased friction and compression loads.
Solution Approach 2:
The system changes the cooling parameter (cooling capacity) based on operating conditions. By adjusting the cooler's operation in response to varying compressor speeds and oil temperatures, the system maintains optimal oil viscosity across the entire operating range, preventing both overheating and excessive thickening.
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, expensive coolers, while ensuring efficient lubrication and cooling across varying compressor speeds, and allows for a compact and efficient oil circuit with reduced maintenance requirements.
Implementation Method 1
the oil is brought to an oil cooler, the cooler will cool the oil before it is brought to any components to be lubricated
Implementation Method 2
a rotary oil pump configured to drive oil from an oil reservoir through an inlet channel upstream the rotary oil pump to the compressor element and/or the motor
Implementation Method 3
a bypass pipe with a pressure-actuated valve which are configured to directly guide a portion of the oil between the rotary oil pump and the compressor element and/or the motor back to the oil reservoir
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Oil circuit for lubrication and cooling of an oil-free compressor (1) comprising a motor (4) with a variable speed and a compressor element (2) driven by said motor (4), - whereby this oil circuit (5) is provided with an oil reservoir (10) with oil (11) and a rotary oil pump (13) configured to drive oil (11) from the oil reservoir (10) through an inlet channel (23) upstream the rotary oil pump (13) to the compressor element (2) and/or the motor (4) via an oil pipe (12); - whereby this rotary oil pump (13) is provided with a rotor (26) mounted on a rotation shaft (27), whereby this rotary oil pump (13) has a swept volume, and whereby this rotary oil pump (13) is driven by the motor (4) of the compressor element (2); - whereby the oil circuit (5) is further provided with a return pipe (19) configured to guide oil (11) from the compressor element (2) and/or the motor (4) back to the oil reservoir (10); - whereby the oil circuit (5) is further provided with a bypass pipe (15) and a pressure-actuated bypass valve (14) which are configured to directly guide a portion of the oil (11) between the rotary oil pump (13) and the compressor element (2) and/or the motor (4) back to the oil reservoir (10) without this portion of the oil (11) passing through the compressor element (2) and/or the motor (4) during its way back to the oil reservoir (10); and - whereby the oil circuit (5) is further provided with an oil cooler (16), characterised in that the oil cooler (16) is placed in the bypass pipe (15) and that the bypass valve (14) is placed in the oil pipe (12).