The present invention relates to compressors and, more particularly, to electrically driven axial compressors.
Electrically driven compressors must convert rotary motion from a motor into linear motion to actuate a piston or a series of pistons to generate compressed gas. Most compressors accomplish this task by means of a crankshaft and connecting rod assembly, similar to that found in internal combustion engines. Some advantages to this design are the proven reliability and the high operating efficiency. One major disadvantage is the space required by the connecting rod throughout the complete cycle. This disadvantage becomes particularly evident in multistage compressors used for compressing gas to high pressures, typically greater than 1000 psig. Often, the pistons and cylinders used in the higher stages of these compressors are not large enough to accommodate the connecting rod and the dynamic space it occupies. As a result, many designs limit the piston travel to under 0.5 inches, and use stepped pistons in the higher pressure stages. These actions reduce the compressor efficiency and add components to the assembly.
Other designs for compressors utilize nutating heads to convert rotary motion into linear motion. In these designs, the piston travel is parallel to the axis of rotation. Automotive air conditioning compressors commonly use this type of compressor. An advantage of this style compressor is the low amount of package space required by the compressor. In addition, the connecting rods, if any are used at all, articulate less than those used with crankshafts. This allows more travel in small diameter pistons than with crankshaft designs. One disadvantage to this style of compressor is the piston reciprocation relies mostly on sliding action than rolling action. This increases the amount of friction in the system, and lowers overall compressor efficiency.
It is a principal object of the present invention to combine the rolling action from crankshaft driven compressors with the high piston travel found in nutating head compressors.
Briefly described, a cam driven piston compressor of the present invention includes one or more cams powered by a motor, the cams being adapted to rotate through 360 degrees, and one or more cam followers, each of which is in contact with one of the cams. The compressor also includes one or more pistons wherein each of the pistons is attached to one of the cam followers, one or more cylinders wherein each of the cylinders encloses one of the pistons, and a compressor head in contact with the cylinders.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become appreciated and be more readily understood by reference to the following detailed description in conjunction with the accompanying drawings, wherein:
Referring to
In operation the axial cam 40 converts rotary motion from the electric motor and gearbox 12 into linear motion used to drive the three pistons 54, 56, and 58. As the cam 40 rotates, cam followers 32, 42, and 44 are forced into reciprocal motion by means of bearings 64 and 66 that are attached to the cam followers and ride against the upper surface and lower surface, respectively, of the lip 46 of the cam 40. The cam followers 32, 42, and 44 are restrained to only move linearly by means of the inner and outer guide bearings 62 and 34 that ride in the guide slots 70 and 30, respectively, machined into the upper housing 16. Since the cam follower motion is purely linear, even small diameter pistons can be actuated over a large distance without risk of the cam follower contacting the cylinder wall. Although gas pressure from the small amount of gas that isn't pushed out of the cylinder will be used to start the retraction of the piston, it is the incoming gas pressure, when present, that is the principal retracting force. For the first stage (piston 54 and cylinder 18) this is gas pressure coming into the compressor, but for the latter stages (piston 56 and cylinder 20, piston 58 and cylinder 22), it is the pressurized gas from the previous stage (e.g. as stage 1 completes its compression cycle, the gas flowing out of stage 1 forces the stage 2 piston to fully retract). This effect requires proper cam timing to work efficiently. In case of insufficient pressure entering stage 1, the compressors 10 and 100 shown in
As shown in
As best shown in
In the embodiment shown in
The individual shapes and offsets of the cams 130-134, and the relative diameters of the cylinders 104 and 108 determine the magnitude of the torque variations on the motor of the motor and belt reduction assembly 142. Those skilled in the art will appreciate that if the torque variations are minimized a lower torque motor can be used with the compressor than if the torque variations are greater.
These designs have several advantages over prior art. First, the cams can be shaped in such a way to dedicate more rotary motion into piston extension than piston retraction. In both embodiments approximately 240 degrees of input rotation is used to extend the pistons, and 120 degrees to retract the pistons. Since it takes more force to extend the pistons, spreading the force over a larger amount of rotary motion helps to lessen the torque requirements on the drive motor. This option is not available on crankshaft driven or nutating head compressors.
A second advantage to this design is the housing guide grooves and cam follower bearings in the first described embodiment and the guide rings in the second described embodiment that combine to restrict the cam followers to purely linear motion. With respect to the first described embodiment the inner and outer guide grooves help balance the forces acting on the cam follower. Since all non-axial forces on the cam followers are transmitted through rolling bearings, losses due to friction are minimized. In addition, the rolling contact helps reduce heat build-up, reduces the wear rate of the components, and reduces the need for lubrication.
A third advantage to this design is the long piston stroke made possible by the combination of the cam profile and the linear motion of the cam followers. In the preferred embodiment, the piston stroke is approximately 1.5 inches, three times longer than comparable crankshaft-drive compressors. The long piston stroke helps improve efficiency of the compressor by minimizing the effect of dead volume in the cylinders. It also allows the compressor to run slower, helping to reduce the compressor's operating temperatures, which extends seal life.
A fourth advantage is the adaptability of this design to meet the requirements of different applications. The same motor and drive section can be used to drive different arrangements of multiple piston compressors. In the preferred embodiment, the compressor utilizes three pistons connected in series, the first stage being approximately two inches in diameter, the second stage being approximately one inch in diameter, and the third stage being approximately one-half inch in diameter. However, the compressor could easily be adapted to utilize three pistons of the same diameter acting in parallel without needing to modify the drive section. Other options could include using anywhere from two to six pistons, acting in series or in parallel, of various sizes. Those skilled in the art will understand that at least some of these options would advantageously use a cam with a different cam profile from that shown in
The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, the foregoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the following claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2006/030739 | 8/4/2006 | WO | 00 | 2/5/2008 |
Publishing Document | Publishing Date | Country | Kind |
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WO2007/019452 | 2/15/2007 | WO | A |
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