A portable ventilator uses a Roots-type blower as a compressor to reduce both the size and power consumption of the ventilator. Various functional aspects of the ventilator are delegated to multiple subassemblies having dedicated controllers and software that interact with a ventilator processor to provide user interface functions, exhalation control and flow control servos, and monitoring of patient status. The ventilator overcomes noise problems through the use of noise reducing pressure compensating orifices on the Roots blower housing and multiple baffling chambers. The ventilator is configured with a highly portable form factor, and may be used as a stand-alone device or as a docked device having a docking cradle with enhanced interface and monitoring capabilities.

Portable ventilator system

A portable mechanical ventilator having a Roots blower is configured to provide a desired gas flow and pressure to a patient circuit. The mechanical ventilator includes a flow meter operative to measure gas flow produced by the Roots blower and an exhalation control module configured to operate an exhalation valve connected to the patient circuit. A bias valve connected between the Roots blower and the patient circuit is specifically configured to generate a bias pressure relative to the patient circuit pressure at the exhalation control module. The bias valve is further configured to attenuate pulsating gas flow produced by the Roots blower such that gas flowing to the mass flow meter exhibits a substantially constant pressure characteristic. The bias pressure facilitates closing of the exhalation valve at the start of inspiration, regulates positive end expiratory pressure during exhalation, and purges sense lines via a pressure transducer module.

Mechanical ventilation system utilizing bias valve

A method and apparatus for controlling a brushless DC (BLDC) motor over a wide range of angular speeds is presented Analog magnetic sensors provide continuous signal measurements related to the rotor angular position at a sample rate independent of rotor angular speed In one embodiment, analog signal measurements are subsequently processed using an arctangent function to obtain the rotor angular position The arctangent may be computed using arithmetic computation, a small angle approximation, a polynomial evaluation approach, a table lookup approach, or a combination of various methods In one embodiment, the BLDC rotor is used to drive a Roots blower used as a compressor in a portable mechanical ventilator system

Compressor control system for a portable ventilator

A Roots-type blower has first and second meshed, lobed rotors disposed in first and second chambers of a housing. Each lobe has first and second axially facing end surfaces defining a twist angle that is a function, at least partially, of the number of lobes on each rotor, and each lobe further defines a helix angle that is a function of the twist angle and an axial length between the first and second axially facing end surfaces of said lobe. The lobes cooperate with an adjacent surface of the housing to define at least one blowhole that defines a control volume, occurs in a cyclic manner, and moves linearly in a direction toward the outlet port. The blowhole provides communication between adjacent control volumes.

Optimized helix angle rotors for roots-style supercharger

A positive displacement, recirculating Roots-type rotary gas compressor which operates on the basis of flow work compression. The compressor includes a pair of large diameter recirculation conduits (24 and 26) which return compressed discharge gas to the compressor housing (14), where it is mixed with low pressure inlet gas, thereby minimizing adiabatic heating of the gas. The compressor includes a pair of involutely lobed impellers (10 and 12) and an associated port configuration which together result in uninterrupted flow of recirculation gas. The large diameter recirculation conduits equalize gas flow velocities within the compressor and minimize gas flow losses. The compressor is particularly suited to applications requiring sustained operation at higher gas compression ratios than have previously been feasible with rotary pumps, and is particularly applicable to refrigeration or other applications requiring condensation of a vapor.

Recirculating rotary gas compressor

A high ratio positive displacement recirculating rotary compressor is disclosed. The compressor includes an integral heat exchanger and recirculation conduits for returning cooled, high pressure discharge gas to the compressor housing to reducing heating of the compressor and enable higher pressure ratios to be sustained. The compressor features a recirculation system which results in continuous and uninterrupted flow of recirculation gas to the compressor with no direct leakage to either the discharge port or the intake port of the compressor, resulting in a capability of higher sustained pressure ratios without overheating of the compressor.

High ratio recirculating gas compressor

A positive displacement, transverse flow, internally refluxing, rotary gas compressor which operates on a constant volume, variable mass, near-isothermal compression cycle. The compressor includes a pair of involutely lobed, intermeshed impellers that sweep gas from an intake port through the compressor housing to a discharge port in constant volume displacement cavities that are defined by the lobes of the impellers and the compressor housing walls. The cavities are effectively sealed against both the intake and discharge ports over upstream interior housing sidewall portions that extend from the intake port over an angle at least as great as the angle between adjacent lobes of the impellers. Downstream therefrom the interior housing sidewalls are spaced radially from the rotating impellers so as to allow limited reflux counterflow of discharge gas back into the advancing displacement cavities. The refluxing gas isentropically expands into the constant volume displacement cavities so that the pressure of the gas contained in the displacement cavities approaches that of discharge. The final pressure increase with accompanying volume reduction into discharge is gained by adiabatic compression at a low pressure ratio as each cavity opens into discharge. The resulting process is noncontaminating and more energy efficient than compression by volume reduction alone.

Reflux gas compressor

A new technology for the positive displacement compression of refrigerant vapors, air, and other gases is described. The technology integrates an open flow recirculation system operating at output pressure with a multi-lobed Root's type rotary compressor. The compressor feeds input pressure fluid into the recirculation system at constant temperature through flow work, Power for the flow work is supplied by equivalent shaft work. Displacement cavities in the compressor rotors convey input pressure fluid into the recirculation system. After closing to inlet they open to intermediate refill ports, and recirculation fluid flows !n. Pressure increases to within a few percent of discharge level before the cavities close to refill and then open into discharge. Final pressure increase is gained through adiabatic compression at a ratio which is near unity. The associated temperature rise is minimal, Compressor units based on this technology are quiet and highly energy efficient. With the recirculation system there is no significant pressure pulse into discharge. At the same time there are no valves and no reciprocating, rubbing, or contact parts in the flow stream. The inherent simplicity of the Root's type rotary compressor has been preserved.

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John F. Weinbrecht

Papers

Recirculating rotary gas compressor

High ratio recirculating gas compressor

Reflux gas compressor

The Flow Work Compressor