Method and apparatus for reducing noise in a roots-type blower

Abstract

A Roots-type blower comprises a housing defining a rotor chamber and an inlet and outlet to the rotor chamber. First and second rotors are mounted in the rotor chamber, each rotor defining a plurality of lobes, adjacent lobes and the housing cooperating to define gas transport chambers. The blower is configured so that a net flow rate of gas into a gas transport chamber is generally or approximately constant, whereby a change in gas pressure in the gas transport chamber is generally or approximately linear, as the gas transport chamber approaches the outlet. In one embodiment, this is accomplished by providing flow channels extending from the outlet towards the inlet, and from the inlet towards the outlet, corresponding to each rotor. The flow channels permit gas to flow from the high pressure outlet to a gas transport chamber and from the gas transport chamber to the low pressure inlet. The resulting amelioration of pressure spikes associated with flow back substantially reduces the operational noise level of the blower.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This patent application claims the benefit of the filing date of pending U.S. patent application Ser. No. 10 / 912,747, filed Aug. 4, 2004, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60 / 492,421, filed Aug. 3, 2003. FIELD OF THE INVENTION [0002] The present invention relates to Roots-type blowers and, more particularly, to a method and apparatus for reducing the noise generated by such a blower. BACKGROUND OF THE INVENTION [0003] Roots-type blowers have potential application in a wide variety of environments. They are relatively efficient, and can produce a wide range of delivery pressures and volumes. However, they produce a high level of noise. The high noise level produced by Roots blowers has limited their use in environments where such high noise levels are unacceptable. One such environment is providing breathing assistance to patients by means of a mechanical ventilator. [0004] For a variety of reasons, ...

AI Technical Summary

Benefits of technology

[0021] The invention is a method and apparatus for reducing the noise generated by a Roots-type blower. The invention has particular use in mechanical ventilators, though the advantages thereof may be realized in many different noise-sensitive blower applications.

[0022] The blower of the present invention comprises a housing defining a rotor chamber and an inlet and outlet to the rotor chamber. First and second rotors are mounted in the rotor chamber, each rotor defining a plurality of spaced lobes. Adjacent lobes of a rotor cooperate with the housing to define a series of generally closed chambers that move from the inlet to the outlet as the rotors are rotated. These chambers are referred to herein as “gas transport chambers.” In one or more embodiments, the blower is configured with helical rotors as known in the art to reduce noise caused by pulsing flow.

Problems solved by technology

However, they produce a high level of noise.

The high noise level produced by Roots blowers has limited their use in environments where such high noise levels are unacceptable.

However, heretofore it has not been possible to reduce the noise created by a Roots blower to the level that is acceptable for a mechanical ventilator.

One type of noise is caused by pulsing flow.

These pulses generate a substantial amount of noise.

This reverse gas flow is very sudden.

The resulting series of pressure spikes creates continuous noise at a level that is unacceptable for many applications, including mechanical ventilators.

However, this lobe design does not address the problem of flow back, since the relative pressure between the gas at the outlet and gas being delivered from the inlet is still the same.

Heretofore, however, it has not been possible to reduce the noise of a Roots blower to the extent required for use in a noise sensitive application such as a mechanical ventilator.

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