Integrated pump and motor

Abstract

An integrated motor pump for use in medical devices and the like.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 60/793,508, filed Apr. 20, 2006.

FIELD OF THE INVENTION

The present invention relates generally to small pumps for moving air and other gases. The low pressure pump uses a brushless DC motor to drive a reciprocating air pump. This type of device is used in various applications including medical devices such as automatic blood pressure monitoring devices where the pump inflates the blood pressure cuff.

BACKGROUND OF THE INVENTION

Small motor driven reciprocating air pumps have been widely used for a variety of application and are typically used for sampling gases or inflating blood pressure measuring cuffs in the medical device field. The availability and advent of brushless DC motors have made such pumps very controllable, reliable and safe and which has greatly increased their use in the field.

In pumps of the prior art design the pump includes a pump frame with a motor mounting aperture to receive a brushless DC motor. Motors and pump capacity are matched to the particular application. Typically the motor is positioned in the frame and retained in the frame by a setscrew or other retainer device. An eccentric crank mounted to the motor shaft couples with the “big end” of connecting rod of a piston assembly that drives the piston in the pump. Most pumps rely on a rubber membrane to position and seal the piston head in the bore of the pump. Air is admitted and exhausted from the pump through a pair of flap valves that cooperate together with the reciprocating piston to form an air moving assembly.

Even when the pumps are of modest size the piston assembly forms a dynamically unbalanced element in the construction and efforts are made in the prior art to eliminate some vibration modes from the system. The most common form of balance is a simple counterweight screw, which balances the crank. Although such a system is an advantage over an unbalanced assembly it does not permit vibration free operation of the pumps nor does it permit quiet operation.

SUMMARY OF THE INVENTION

In contrast to the existing architecture for small pumps the present invention incorporates at least a portion of the motor assembly into the frame of the pump assembly simplifying motor construction and reducing the parts count of the overall device. This form of assembly also permits more accurate location and alignment of the reciprocating assembly, which is advantageous. In addition to the integration of motor elements into the pump frame, the reciprocating piston is balanced by an eccentric balancing construction that provide better “balance” or dampening of vibration modes in the device. This counter-weighted assembly addresses vibration modes and produces a pump that is quieter and smoother in operation, which is desirable in most applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the figures identical numerals indicate identical structure wherein:

FIG. 1 is a perspective view of the assembled device;

FIG. 2 is an exploded view of the components of the device;

FIG. 3 is a perspective view of the motor/pump frame;

FIG. 4 is a cross section of the motor/pump frame;

FIG. 5 is a perspective view of the counterweight rotor; and,

FIG. 6 is a cross section of the completed motor/pump assembly.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows the general layout of the motor/pump assembly 10. The pump portion is generally designated 32 while the motor portion is generally designated 30. In operation DC current is supplied to the motor and it drives the pump. Air is admitted through port 12 and emitted from port 14.

FIG. 2 shows the assembly 10 exploded to show the individual components. The pump portion includes the cylinder head 13, which sandwiches the flap valve sheet 34 between the cylinder head 13 and the cylinder plate 37. Screws typified by screw 48 holds the cylinder head valve plate 24 and cylinder to the to the motor/pump frame 15. The connecting rod/piston 38 is positioned in to the cylinder.

FIG. 3 shows the motor/pump frame 15 in isolation. FIG. 4 is a cross-section of the motor/pump frame 15 showing the stator assembly 56 that is placed in the mold and molded into position in the motor/pump frame 15. In the figure the axial motor shaft 20 is shown in isolation intersecting at 90° the axis 50 of the pump assembly.

FIG. 5 shows the eccentric weight and crank used to balance the reciprocating assembly of the motor pump device in isolation. It is generally designated 16 and it consists of an eccentric shaft rotating around axis 58 and having a counter weight 60 and an eccentric weight 62 disposed around the axis 58. Stepped surfaces around the shaft 66 provide location indexes for bearing and the like.

FIG. 6 shows the motor pump assembly completely assembled in cross section. In this figure the rotor 70 has been placed in the assembly forming a motor with the imbedded stator 71. The motor shaft lying along axis 20 is a press fit into the eccentric balance mechanism 16. The connecting rod 38 has a big end with a pressed on ball-bearing race 39 positioned for rotational motion around the eccentric balance weight 16. The connecting rod terminates in a piston 40 assembly which includes a rubber gasket 36 sandwiched between the head of the piston 40 and a piston plug 41. This assembly reciprocates in the cylinder 37 and admits and exhausts gases through the cylinder head 13 out of the complimentary ports typified by outlet port 14.

In contrast is a design of conventional motor pumps. The present invention incorporates an eccentric weight 16 that is relatively large and massive in comparison to the weights of the connecting rod and piston assembly. Primary rotational balance is achieved by having an offset motor shaft hole within the weight so that the weight 60 is balanced by the mass 62. Although the mass 62 is placed closer to the center of the radius of gyration it is larger and therefore is an effective counter weight to the mass 60. The attention to achieving primary balance produces a motor with reduced vibration, which is desirable in most applications, especially those associated with medical devices.

Claims

1. An integrated motor pump comprising:

a) a unitary frame having a aperture for mounting a pump head and having a integrated stator winding;

b) a rotor mounted within said pump frame concentric with said stator; said rotor having an axel;

c) said rotor axel coupled to a connecting rod; said connecting rod holding a gasket;

d) said gasket forming a piston in a cylinder plate.

2. The device of claim 1 wherein said motor frame is injection molded from a high temperature plastic.

3. The device of claim 1 wherein said stator and rotor together form a brushless DC motor.

4. The device of claim 1 further comprising a pump head located proximate said aperture for regulating gas flow through an inlet and an outlet coupled to said pump head.

5. The device of claim 1 further comprising a reciprocating piston pump of the type having a rubber diaphragm forming a pump head seal and forming a first and a second leaf-a-valve for admitting an exhausting air from said pump chamber.