Oil free dry screw compressor including variable speed drive

• US 6,474,950 B1
• Filed: 07/13/2000
• Issued: 11/05/2002
• Est. Priority Date: 07/13/2000
• Status: Expired due to Fees

• Current Assignee: Ingersoll-Rand Company (Trane Technologies plc)
• Original Assignee: Ingersoll-Rand Company (Trane Technologies plc)
• Inventors: Waldo, Keith D.
• Primary Examiner(s): KOCZO JR, MICHAEL
• Application Number:
  US09/615,753
• Time in Patent Office: 845 Days
• Field of Search: 417/28, 417/36, 417/44.2, 417/45, 417/310, 417/12, 418/201.1
• US Class Current: 417/12
• CPC Class Codes: F04C 18/16 with helical teeth, e.g. chevron-shaped, screw type for non-parallel axes of movement F04C18/48
• CPC Class Codes: F04C 2240/403 with inverter for speed control
• CPC Class Codes: F04C 28/08 characterised by varying the rotational speed

Abstract

An oil-free dry screw compressor system is provided and includes a variable speed drive and motor along with control logic to increase or decrease the speed of the drive and motor based on sensed pressures. By using an electric motor and a rectifier/inverter drive, a variable speed compressor system is provided having a drive system that can be stopped and started an unlimited number of times over a given time period. Methods of controlling pressure in a compressor system including an oil-free dry screw compressor are also provided.

Claims

1. An oil-free dry screw compressor system comprising:

an oil-free dry screw compressor;

means for driving said compressor; and

means for varying the speed of said means for driving, the means for varying configured to provide a drive signal to the means for driving such that the means for driving is operated at a speed within a range of speeds between a maximum speed and a minimum speed when a sensed compressor output pressure is less than a maximum compressor output pressure and the means for driving operates at a speed corresponding to the minimum speed for a given time T and thereafter is stopped when the sensed compressor output pressure is substantially equal to or greater than the maximum compressor output pressure.

2. The oil-free dry screw compressor system of claim 1, wherein said means for driving is a variable speed drive comprising an electric motor.

3. The oil-free dry screw compressor of claim 2, further comprising a three-phase AC current supply for powering said variable speed drive.

4. The oil-free dry screw compressor of claim 1, wherein said means for varying the speed comprises a rectifier/inverter drive.

5. The oil-free dry screw compressor of claim 1, further comprising means for carrying compressed fluid away from said compressor, means for sensing pressure in said means for carrying compressed fluid, and means for adjusting the means for varying the speed in response to a signal received from said means for sensing pressure.

6. The oil-free dry screw compressor of claim 5, further comprising a blowdown valve in communication with said means for carrying compressed fluid, and means for controlling opening and closing of the blowdown valve in response to a signal received from said means for sensing pressure.

7. The oil-free dry screw compressor of claim 1, wherein said compressor comprises a first airend and a second airend, wherein both the first airend and the second airend are powered by said means for driving.

8. The oil-free dry screw compressor system of claim 1 wherein the drive signal is substantially directly proportional to the compressor output pressure when the sensed compressor output pressure is less than the maximum compressor output pressure.

9. The oil-free dry screw compressor system of claim 1 wherein the given time T is equal to zero seconds.

10. The oil-free dry screw compressor system of claim 1 wherein the given time T is greater than zero seconds.