Compressor Head
Technical Field of Invention
This invention relates to a compressor/pump head.
Background of Invention
In recent years, linear compressors and pumps, including both diaphragm type and free- piston type, have become more and more popular. Reasons for their success include at least low costs, high efficiency, good reliability, good service life and lubricant-free operation. It is known that linear motors in such machines tend to have strokes variable with changes in electric power input or fluid dynamic load. More particularly, when input voltage rises or outlet pressure drops, a linear motor would stroke longer, which may lead to over- stroke and cause damages by direct impact. On the other hand, when outlet pressure rises or input voltage drops, the linear motor would under-stroke, leaving a large dead space inside the working chamber without producing useful output. For these reasons, linear compressors and pumps are considered not suitable to high-pressure applications.
It is known that the problem can be dealt with by having a close loop electronic control. However, such a solution requires a sensing and control system plus an adjustable power supply, making the whole system expensive and less reliable because it introduces into the system extra potential failure points.
Summary of Invention
A first object of this invention is to provide an improved compressor/pump head more suitable to a linear system. According to the present invention, there is provided a compressor head comprising: a reciprocating (piston) member and a chamber-head member defining a working chamber between them; means for connecting the reciprocating member to a reciprocating drive; and valve means for one way fluid flow into and out of the working chamber; wherein the reciprocating and chamber-head members have complementary surfaces and at least one of these two members has a compliant portion for forming a progressive contact when the reciprocating member approaches the chamber head member.
It is preferable that said contact progresses from periphery inwards, so as to concentrate the working fluid into a small central area before finally forcing it through outlet valve. In this way, the compressor head can achieve a high compression ratio by a relatively small stroke. Also, because the final compression is by a small surface area, it can achieve a high output pressure without a proportional increase of load on the drive.
It is also preferable that both the reciprocating and chamber-head members have flexible portions to allow "soft" contact and to ensure good cushioning when the parts make compliance contacts. Such "soft" contact would ensure low working noise, long service life and also minimum dead space in working chamber, which would lead to high efficiency.
It is also preferable to make fluid and/or elastomer cushioning arrangements in reciprocating and/or chamber head structures to provide extra impact protection. It is advantageous that the fluid cushioning is formed by a space closed by bellow means.
It is also preferable to have a back support member so that the reciprocating and back support members have complementary surfaces and at least one of these two members has a compliant portion for forming a progressive contact when the reciprocating member moves backwards to the back support member. A further object of this invention is to provide a compressor head with a build-in mechanism to adjust its working chamber's size by moving the chamber-head's position in response to outlet pressure changes, so as to compensate the changes in a linear drive's stroke.
Brief Description of Drawings Further features, advantages and details of the invention are to be described with reference to preferred embodiments illustrated in the accompanying drawings, in which:
Fig. 1 is a cross-section view of a compressor head according to a first preferred embodiment of the present invention;
Fig. 2 shows the first embodiment in a double acting arrangement; Fig. 3 shows the working principles of a self-adjusting chamber-head;
Fig. 4 is an enlarged local view showing diaphragm movements in progress;
Fig. 5 shows a modified version of the first embodiment;
Fig. 6 shows a second embodiment of the invention in a double acting arrangement;
Fig. 7 is an enlarged local view showing piston movements in progress; Fig. 8 shows the working principles of a self-adjusting cylinder head;
Fig. 9 shows the details of a directional bleed hole; and
Fig. 10 is an enlarged local view showing a third embodiment of the invention. Detailed Description of Preferred Embodiments
In this application, the inventive concept is described as a compressor head for the sake of easy understanding. It should be understood that the same concept could be used for gas, liquid or a mixture of both, and also for a vacuum pump. Therefore, the term "compressor head" should be interpreted as covering "pump head" for all these applications. General Structure of the First Embodiment
Fig. 1 shows a compressor head 10, which is a diaphragm type machine suitable to high flow applications. The compressor head 10 has a housing 40, formed by an end plate 41 and a casing 42 fixed to another casing 52, which is a part of a drive (not shown). Inside the housing 40, there are a piston assembly 20 including a first diaphragm 26, and a chamber-head assembly 30 including a second diaphragm 36. The two assemblies define between themselves a working chamber 60. On the other side of the chamber-head assembly 30, there is an outlet chamber 70 for receiving fluid from the chamber 60 via outlet valves 33.
The piston assembly 20 includes a piston body 21, which is fixed to and aligned with a free end of a driving shaft 51 by a bolt 22; inlet valves 23 formed by a number of through holes and a flap member secured onto the piston body by an elastomer member 24, which also provides impact protection; and a locking ring 25, which secures the inner edge of the diaphragm 26 to the periphery of the piston body 21.
Similarly, the chamber-head assembly 30 includes a head plate 31, which is secured to a leaf spring 34 by a bolt 32; outlet valves 33 formed by a number of through holes and flap members; and a locking ring 35, which secures the inner edge of the diaphragm 36 to the periphery of the head plate 31.
The outer edges of the two diaphragms 26 and 36 are clamped between the two casings 42 and 52, which also keep all the parts aligned with the driving shaft 51. Generally speaking, the diaphragms 26 and 36 are annular in shape with arched cross section, so that they form between them a closely matched complementary relationship. There is a flexible low-friction sheet 37 sandwiched between the two diaphragms 26 and 36 to avoid abrasive damages by physical rubbing. It is possible to use composite diaphragms having low friction and abrasive resistant surfaces for the same effect. The opposing faces of the piston assembly 20 and the chamber-head assembly 30 are shaped to complement each other, leaving minimum dead space between them.
In operation, the working medium comes from the drive side of the piston assembly, as shown by arrows "Flow In", enters the chamber 60 via the inlet valves 23, then passes the outlet valves 33 into the outlet chamber 70 and finally leaves the compressor head via the outlet connector in the centre of the end plate 41, as shown by an arrow "Flow Out". In this arrangement, the general flow direction is along the piston's pumping direction, so the disturbance to the fluid flow is minimised which ensures high efficiency and low flow noise. Further, since the areas for fitting inlet and outlet valves are large, flow restriction is reduced. Also, it is convenient to use the inlet flow to cool the drive, if needed.
The head 10 is a low cost design because the parts can be made of plastics with structures for simple snap fit, making it easy for mass production and assembly.
Fig. 2 shows a pair of identical heads 10 and 10' fitted to a linear drive 50 in a double acting arrangement. The drive can be a linear motor such as that disclosed in our PCT patent application no. WO-99/18649.
In Fig. 2, the driving shaft 51 is at its left-hand end position so the chamber 60 in the head 10 at the right-hand side is at its maximum volume, while the chamber at the left-hand side is reduced to virtually zero volume. At this particular position, the distance between the front surface of the piston assembly 20 and the opposing surface of the chamber-head assembly 30 is Smax, which is the maximum stroke allowable for the drive. When the shaft 51 moves in the opposite direction, the process reverses until the piston assembly 20 hits the chamber-head assembly 30. Since both heads 10 and 10' are connected to the same outlet, their outlet pressure is always the same, so the drive 50 has balanced loads in opposite directions. Now refer to Fig. 3, in which the working principles of a self-adjusting chamber-head
30 are illustrated. The chamber-head 30 is fitted inside the casing 42. The outer surface of the locking ring 35 and a corresponding inner surface of the casing 42 form a slide bearing/sealing arrangement, which restricts the chamber-head's sideways movement and seals a cushioning chamber 80. In axial direction the chamber-head 30 can move an adjustment distance Dadj when there is a pressure difference on its two sides. It works as follows. At its nature status, the chamber-head 30 is biased by the leaf spring 34 towards the casing 42 and set onto a stop edge 43, as shown by the dash line position in Fig. 3. This is the chamber-head's rest position. When the compressor head 10 starts operation, the pressure in the outlet chamber 70 gradually builds up to generate a net total force on the chamber-head 30 against the biasing force by the spring 34 to force the chamber-head away from its rest position by a distance Dadj until the net total force is balanced by an increased spring force. By matching the spring stiffness with the required range of the chamber-head adjustment, the adjustment distance Da j can be made proportional to the pressure increase in the outlet chamber 70. The cushioning chamber 80 between the diaphragm 36 and the casing 42 has fluid communication with the outlet chamber 70 via one or more one-way valves 45. When the chamber-head 30 is forced to move an adjustment distance Dadj by a pressure increase in the chamber 70, more fluid will enter the chamber 80 via the valves 45 to make its pressure to the same value as in the chamber 70. However, when in compressing phase during which the diaphragm 36 is compressed, the valves 45 will prevent the fluid in the chamber 80 from flowing out, so the chamber-head 30 will maintain its position even when the pressure in the working chamber 60 is increased beyond that in the chamber 70. If the pressure in the chamber 70 drops, the pressure in the chamber 80 comes down slowly by a small leak through the slide bearing between the locking ring 35 and the casing 42.
Now return to Fig. 2. From the above description, it is clear that each of the chamber- heads 30 and 30' will adjust its position inwards by the same distance Da j in response to the same outlet pressure increase, this will reduce the system's stroke to a length of Smax - 2Dadj- Since the linear drive 50 would generate a smaller stroke at an increased load, the stroke reduction at the drive side will be automatically compensated by the self-adjustment of the chamber-head position. In this way, the system will be able to achieve minimum dead space in each compressing cycle and to maintain good pumping efficiency over a wide operation range.
Fig. 4 is an enlarged local view showing the progressive contact between the diaphragms 26 and 36 during operation. The solid line position Po shows the piston assembly's end position. Within one compressing phase, the piston assembly 20 moves from the end position Po through positions Pj, P2 and P3 until it finally touches the chamber-head assembly 30. During this process, since the pressure in the cushion chamber 80 is always higher than that in the working chamber 60, the diaphragm 36 is stiff and capable to maintain its convex surface shape and the diaphragm 26 is bent on top of the diaphragm 36 to form a compliance contact by the force of the linear drive. As the piston movement progresses, the diaphragm 26 is bent more and more and the contact area between the two diaphragms increases progressively from the periphery inwards, forcing the fluid between them towards a central area. Finally, as the piston assembly 20 hits the chamber-head assembly 30, the complementary surfaces of the two assemblies will form a full engagement and the remaining fluid in the chamber 60 will be forced out completely. In terms of compressor performance, because the working chamber's volume change is achieved by both axial gap reduction and diameter reduction, it is made possible for the compressor head to reach a high compression ratio by a relatively small stroke. Furthermore, as the compliance contact between the two diaphragms expands inwards, the effective pumping surface becomes smaller and smaller, which would reduce the load on the linear drive, therefore the drive would be able to produce a higher outlet pressure by the same force.
It should also be noted that if for any reason the linear drive over-strokes beyond its end position, the piston assembly would go beyond the position P3 and fully engage the chamber- head assembly. The two would move forward together so the pressure in the chamber 80 would be increased further, which in turn damps the over-stroke impact. This provides an effective protection, especially when the over-stroke is caused by e.g. an electric current surge at the power input side or a pipeline burst at the fluid outlet side. Fig. 5 shows a modified version of the first embodiment, in which the cushion chamber
80 is filled with an elastomer member 81 for impact protection. The member 81 is made of an elastic material, such as foamed plastics or rubber, so that it can be easily compressed or released to maintain the convex surface of the diaphragm 36. The chamber 80 is sealed by a bellows 38 attached to the locking ring 35, which allows the chamber-head assembly's self- adjusting movement. The bellows 38 has one or more directional bleed holes 39 which maintains a high pressure in the chamber 80 during operation but allows slow bleed. Further details of the bleed holes 39 are described with reference to Fig. 9. General Structure of the Second Embodiment
Fig. 6 shows the second embodiment of the present invention, which is basically a piston type compressor head 100 or 100' suitable to high-pressure applications. More particularly, the pair of heads 100 and 100' are fitted to a linear drive 150 in a way similar to that of the first embodiment. Since the two heads are identical, only the one at the right-hand side is fully described here.
The compressor head 100 has a housing 140 formed by an end cap 141 and a cylinder 142 with a lining 143. Inside the housing 140, there is a piston assembly 120 in the cylinder 142 and a cylinder-head assembly 130 in the end cap 141, defining between them a working chamber 160. On the other side of the cylinder-head assembly 130, there is an outlet chamber 170 for receiving fluid from the chamber 160 via outlet valves 133 and a cushioning chamber 180. The piston assembly 120 has a piston core 121, which is fixed to and aligned with a free end of a driving shaft 151 by a bolt 122; a valve plate 123 having inlet valves formed by a number of through holes and a flap member 124; a locking ring 125; a piston diaphragm 126 and a piston sleeve 127. The piston diaphragm 126 is secured at its inner edge to the piston core 121 by the valve plate 123, which also serves as a locking ring, and at its outer edge to the piston sleeve 127 by the locking ring 125. The inner surface of the piston sleeve 127 and the outer periphery of the piston core 121 form a sliding bearing and a seal is fitted to the outer periphery of the piston core to form a gas tight cushioning chamber 190 inside the piston assembly 120. The piston diaphragm 126 has one or more directional bleed holes 129 which allow fluid in the chamber 160 to enter the cushioning chamber 190 easily but restrict flow in the opposite direction. Further description of the bleed holes is made below with reference to Fig. 9.
The cylinder-head assembly 130 has a head plate 131 biased by a leaf spring 134 away from the piston assembly 120; outlet valves 133 formed by a number of through holes and a flap member; and a locking ring 135, which secures the inner edge of a diaphragm 136 to the periphery of the head plate 131.
The outer edge of the diaphragm 136 is clamped between the end cap 141 and the cylinder 142 together with its lining 143, which also keep all the parts aligned with the driving shaft 151. The diaphragm 136 has a concave face opposing the piston assembly and a number of strengthen ridges on the back surface to maintain the concave shape when there is a higher pressure in the cushioning chamber 180. The working principles of the compressor head 100 or 100' and its self-adjusting cylinder head are similar to that in the first embodiment, so they do not need to be repeated here. Only the new features of the second embodiment are explained below.
Fig. 7 is an enlarged local view showing the piston assembly's movements in compressing phase. The solid line position Po is the starting point of the phase. From the position Po to Pi, the piston assembly works in a similar way as a conventional piston. When the piston assembly reaches the position P2, the leading edge of the piston sleeve 127 hits the outer edge of the cylinder-head diaphragm 136 and stops there. After this point, only the piston core 121 moves forward and carries the piston diaphragm 126 towards the cylinder head diaphragm 136, as shown at the position P . During the piston assembly's forward movement from Po to P2, there is a relative movement between the piston core 12 and the piston sleeve 127 with the effect of making the pressure in the cushioning chamber 190 roughly the same as that in the working chamber 160. From P2 to P3, since the piston sleeve 127 cannot move further, the movement of the piston core 121 will significantly reduce the volume in the cushioning chamber 190 (see the compressor head 100' in Fig. 6) and making its pressure higher than that of the chamber 160. This high pressure inside the piston assembly will ensure the piston diaphragm's convex shape therefore the progressive compliance contact between the two diaphragms 126 and 136; it also provides effective cushioning in case of the linear drive's over-stroke. At the end of the compressing phase, if the pressure in the chamber 190 becomes excessive, some of the fluid in the chamber 190 will escape through the bleed holes 129. Once the piston core starts the withdraw movement, the pressure in the chamber 190 will drop immediately and no significant leak will happen through the bleed holes 129. At the same time the working chamber 160 will start fluid intake via the inlet valve. In this way, even through the piston assembly carries a build-in dead space, which does not have adverse effects on the compressor head's operating efficiency. It is worth mentioning that when the piston assembly 120 reaches the position P , the physical contact between the leading edge of the piston sleeve 127 and the periphery of the diaphragm 136 will form a reliable seal to ensure no leak at the last stage of the compressing phase. The effects of this seal will be further enhanced when the two diaphragms form progressively increased compliance contact. It is also worth mentioning that inside the cushioning chamber 190, the locking ring 125 carries an elastomer member 128, wliich has the effects of forcing the diaphragm 126 to bend outwards to ensure a close contact between the two diaphragms.
Fig. 8 shows by solid lines the cylinder head's rest position, and by dash lines its position aftef an adjustment distance Dadj in response to an outlet pressure increase in the chamber 170. Since the working principles and possible modifications are similar to that in the first embodiment, no further description is necessary.
Fig. 9 shows the structure details of a bleed hole 39 (129) mentioned in the above two embodiments. The hole has one end with a sharp edge and the other end with a smoothly curved edge. Because of the different shapes at two ends, fluid flow in direction A has less flow resistance while that in the opposite direction B has more flow resistance, making its operation with a directional difference. Such a bleed hole can be used together with or built into a one-way valve to allow easy flow in one direction and a restricted flow in the opposite direction. Since the use of such bleed holes is known in the art, no more description is needed. General Structure of the Third Embodiment Fig. 10 shows a third embodiment of the present invention, which is a modified version of the first embodiment. In this embodiment, a compressor head 200 has a piston assembly 220 with a diaphragm 226, which is clamped between a chamber-head member 230 and a back support member 240. A working chamber 260 is formed between the piston assembly 220 and the chamber-head member 230. Both the chamber-head member 230 and the back support member 240 have complementary surface portions for forming progressive compliance contact with the diaphragm 226 during the piston assembly's forward or backward movement. By fitting the back support member 240, the total surface area exposed to backpressure is reduced progressively during the piston assembly's backward movement from position P3 to position Po, making it easier to achieve a longer stroke. This arrangement would be particularly suitable to a vacuum pump application, in which a longer stroke would help to generate a higher vacuum in the chamber 260.
Industrial Applicability
It is not difficult to understand from the above description that the compressor head according to the present invention has at least the following advantages, a) Low manufacturing costs because most of the parts can be made of plastics or rubber and can be assembled by simple snap fit. b) High efficiency over a wide operation range. c) High compression ratio and/or flow rate by a relatively small stroke. d) Lubricant-free, leak-free and maintenance-free operation. e) Low noise and vibration.
Finally, there is no need to mention that the embodiments in this application are only exemplary, which can be easily adjusted, modified or altered by those skilled in the art once the basic concepts of the invention are understood. Also, it is obvious that other reciprocating drives, such as a standard rotary motor with a crank-shaft driving mechanism can drive the compressor head of this invention. In this case, since the stroke length can be controlled precisely, it is not necessary to have the self-adjusting chamber-head or cylinder head. The other features of the invention would still be effective.