WO2022232953A1

WO2022232953A1 - Pneumatic cylinder assembly with reduced air consumption

Info

Publication number: WO2022232953A1
Application number: PCT/CH2021/000002
Authority: WO
Inventors: Alfred Rufer
Original assignee: Alfred Rufer
Priority date: 2021-05-04
Filing date: 2021-05-04
Publication date: 2022-11-10

Abstract

A pneumatic double acting cylinder assembly is described where the air consumption is strongly reduced in comparison with a classical cylinder of a volume V. The proposed cylinder assembly is composed of two different chamber pairs or chamber pairs arrangements where in the first chamber pair a constant pressure displacement work is produced in a cylinder of a volume around V/2 and where in the second chamber pair or chamber arrangement pairs of a volume of around N*V/2 the thermodynamic energy content of the pressurised air is recovered by thermodynamic expansion instead of simply releasing it in the atmosphere. The first chamber pair corresponds to a normal double acting cylinder, and the second chamber pair can be realized with one or an assembly of two, three or more identic or similar cylinders operated in parallel. After the production of displacement work in the first chambers, the air is transferred into the second chambers or chamber assemblies of a larger volume, producing so the air expansion.

Description

Pneumatic cylinder assembly with reduced air consumption

Background of the invention

Pneumatic actuators are known for their poor energy efficiency, their normal operation being based on filling the cylinder volumes with air under pressure and releasing it at the end of the stroke to the surrounding before initiating the return stroke. The mechanical work produced is obtained from the displacement of the piston under constant pressure. At the end of the stroke, the pressure in the fully deployed cylinder is released to the atmosphere by opening the exhaust valve, allowing the free return of the piston. This corresponds to renounce to the pneumatic energy content inside the cylinder.

In Fig.1 , the converting element is a conventional pneumatic actuator. Such devices usually operate at constant pressure.

The P-V diagram in Fig. 1b shows the different quantities of energy to be recovered from a reservoir at a pressure Pi in a volume Vi. The maximum amount of energy is noted with Ei and corresponds to the expansion energy from Pi down to the atmospheric pressure P_a under isothermal conditions. This value can be calculated

W2 is the mechanical work produced by the piston’s displacement while the pressure is maintained constant through the PRV valve at a value P2. It is calculated through w₂ ={P_{2 ~}P_a)-(v_{2 ~}v_x) (2)

The last surface W2d of the diagram in Fig. 1b (right side of V2) corresponds to the internal energy of the air released to the atmosphere and its isothermal expansion from P2 down to P_a corresponds to an energy (or work) value of

The energy efficiency of the classical cylinder can be defined as

when the amount of exergy loss due to the presence of the PRV valve is not considered.

The efficiency according (4) is represented in Fig. 2. This diagram shows that for such actuators an operating pressure (P2) above 20 to 50 bar is a non-sense and leads to a very poor energetic performance when the high pressure air is released to the atmosphere after the displacement.

The principle of adding an expansion chamber to a classical pneumatic actuator is described in Ref. 1. In this document, the behavior of a vane-type actuator is described where an additional actuator is added in order to elevate the value of the produced mechanical work. For a given value of consumed air under pressure, this system permits to produce a sum of displacement work and expansion work, leading to the result of an increased mechanical performance. The simulations and calculations present the main result as realizing a device with nearly doubling the energetic efficiency.

The same principle is described for a pneumatic motor using double acting linear cylinders in Ref. 2.

According to the principle of proportionality, the present invention concerns pneumatic cylinder assemblies, where instead of increasing the mechanical performance for a given value of consumed air under pressure, the air consumption of the described mechanism is reduced in comparison with a classical actuator which produces an identic mechanical work.

Summary of the invention

The aim of the present invention is to realize a cylinder assembly where the chambers of a first cylinder are alternatively filled with air at constant pressure, producing a so-called displacement work.

Then, this air is transferred into the chambers of a second cylinder assembly for expansion during the return stroke. The second cylinder assembly is designed with a volume of the chambers being equal to a given number N (for example 3-to 4) times the volume of the first cylinder, producing a thermodynamic expansion of the air during the transfer from the chambers of the first cylinder to the chambers of the second assembly. The first-and-second cylinder assembly are mechanically coupled in order to get at the output the sum of the different forces generated by the cylinders, meaning the sum of the displacement work and the expansion work.

The reduction of the air consumption is defined for the invention in relation to a normal pneumatic cylinder which would produce the same mechanical work average during one stroke. Such a cylinder would have a volume of nearly the double value of the volume of the first cylinder of the present invention. Such a cylinder would consume nearly the double quantity of air during its strokes.

The present invention concerns a specific mechanical arrangement of the first and second cylinder assemblies where the second assembly is realized with N (three or four) cylinders identic to the first one and placed around this first cylinder, running in parallel and being mechanically coupled in order to produce an equilibrated force (without torsional torque), parallel to the axial displacement of the cylinders (Fig. 3). A parallel assembly of three cylinders can be realized (Fig. 7) where one of these three is used for the generation of constant pressure displacement work and the two other cylinders generate expansion work and are placed laterally at both sides of the first one. In order to benefit from an expansion ratio (volume ratio) during the transfer from the chambers of the first cylinder to the chambers of the two others, the volume of these two others must be chosen with a higher volume than the volume of the first cylinder (for example N, but can be a non-integer value). For an expansion volume ratio of three, the sum of the volumes of the two lateral cylinders must be equal to three-times the volume of the first cylinder, so the ratio of the volume of one of both lateral cylinders to the volume of the first one must be equal to 1.5. The ratio of the diameters being sqrt (1.5) or 1.224.

Two parallel cylinders of different volumes can also be coupled (Fig. 8), their chambers generating a sum of constant pressure displacement work and of variable pressure expansion work. A system with two cylinders of different volumes can generate torsion forces which are not parallel to the displacement axis of the pistons. In such a case, an additional guiding device for the piston rods (307) or the output rod (308) must be implemented.

Two cylinders of different volumes can also be coupled coaxially (Fig. 9), their chambers generating a sum of constant pressure displacement work and variable pressure expansion work. A system with two coaxial cylinders of different volumes does not generate torsional torques. The developed acting force is parallel with the axis of the piston's displacement.

For the coupling of two coaxial cylinders, one of the two must be of the type of a double-rod cylinder, meaning that the piston rod of this cylinder must be accessible from both sides. One single rod cylinder is coupled with a double rod cylinder (Fig. 9).

Detailed description of the preferred embodiments

A first system composed of four coupled cylinders running in parallel is represented in Fig. 3, 4 and 5. In this system, one first cylinder (4) is placed in the middle of the assembly and is assuming the function of producing the constant displacement work during filling of the chambers. Three other cylinders are placed around the first one (1), (2), (3). The stators (bodies) of all four cylinders are mechanically connected with a connecting plate (5).

The moving parts (piston rods) of all four cylinders (7) are mechanically connected with another connecting plate (6) in order to compose the sum of the forces generated by all four cylinders. This output force is transmitted to the final application via a common rod (8).

The connecting plate of the piston rods (6) is moving synchronously with all pistons and piston rods.

In order to be able to replace a single cylinder operated according the classical principle of "filling and releasing" , the new system can be completed with a connecting bridge, composed of three (or more) bridge rods (10) and of a bridge plate (9). The bridge plate serves as mechanical connector of the stators of the cylinders to the final application. The output effort and movement of the piston rods is transmitted by the common rod (8) which goes through the bridge plate (9). With this connecting bridge and common rod, the new assembly can be interfaced in the same manner than a classical cylinder (Fig. 6)

The bridge plate (9) of the new system corresponding to the connecting plate of the classical cylinder (105, Fig 6) The common rod of the new system (8) corresponding to the piston rod of the classical cylinder (108, Fig. 6).

For a three-cylinder system as represented in Fig. 7, the central cylinder (204) produces the displacement work and the two lateral ones (201, 202) produce the expansion work while the air is transferred from the central cylinder to the two lateral ones. The system includes a connecting plate for the stators (205) and a connecting plate (206) for the moving piston rods (207). The output effort is transmitted through the common rod (208).

A similar system with only two cylinders of different volumes is represented in Fig. 8. In this system, the displacement work is produced with the first cylinder (304) and the expansion work is produced by the second larger cylinder. The volume ration of the cylinders must correspond to the desired expansion ratio (for example 3 or more).

The stators of the two different cylinders are connected by the connecting plate (305), and the two moving parts (piston rods (307) are connected by the connecting plate (306). The output effort is transmitted by the common rod (308).

A system with two coaxially coupled cylinders of different volumes is represented in Fig. 9. The displacement work is produced by the first cylinder (404), and the expansion work is produced by the second cylinder (401). The stators of both cylinders are connected by the connecting plate (405), and the moving parts of both cylinders (the two piston rods are connected by a piston rod coupling device (406). The output effort is transmitted by the output rod (408).

Control valves of the cylinder assemblies

The new system is controlled by the intake, transfer and exhaust valves. Each side of the cylinders (chambers a and chambers b) are fed through their corresponding valves.

The intake valves Vin_a, Vin_b are feeding the chambers of the first cylinders (4), (204), (304) from the air reservoir.

The transfer valves Vtr_a, Vtr_b, are assuming the transfer of the air from the chambers of the first cylinder (4), (204) (304) to the chambers of the second cylinder assembly (the expansion cylinders) namely (1), (2), (3) in the case of a four cylinder system (Fig. 3) and (Fig. 10), or (201), (202) in the case of a three cylinder system (Fig. 7) and (Fig. 10), or (301) in the case of a two cylinder system (Fig. 8) and (Fig. 12). The exhaust valves Vexh_a, Vexh_b are releasing the expanded air to the atmosphere after expansion in the second cylinder or second cylinder assemblies.

A schematic representation of the cylinders and air flow is given in Fig. 13. In this representation, the cylinder 1 is representing the first cylinder of the assembly and which produces the displacement work (4) or (204) or (304) or (404).

The cylinder 2 corresponds to the cylinder or cylinder assembly which produces the expansion work. This assembly corresponds to (1), (2), (3) for a four-cylinder system, or (201), (202) for a three-cylinder system, or (201) or (401) for the two-cylinder systems.

The control sequences of the new systems are represented if Fig. 14.

References

Ref. 1 Rufer A., A compressed air driven generator with enhanced energetic efficiency, Conference: IEMERA 2020, October 2020, Imperial College London (Virtual),

Ref. 2 Rufer A., A High Efficiency Pneumatic Motor Based on Double- Acting Linear Cylinders, WWJMRD 2021; 7(1): 25. https://www.researchgate.net/publication/349338737 A High Efficiency Pneumatic Moto r Based on Double- Acting linear Cylinders

Claims

Patent claims

1. Pneumatic double acting cylinder assembly composed of two different chamber pairs or chamber pair arrangements, where the stators/chambers of each pair are connected together and form the stator of the cylinder assembly and where the piston rods of each pair or pair arrangements are connected together forming the mobile part of the cylinder assembly.

2. Pneumatic double acting cylinder assembly according the description of claim 1, where the push and pull sides of the first chamber and piston are fed alternately from a compressed air reservoir through two intake valves, producing constant pressure push and pull forces on the mobile part of the assembly.

3. Pneumatic double acting cylinder assembly according description of claim 1 and 2, where the push and pull sides of the second chamber and piston pair, or chamber and piston pair arrangements, are fed from the pull and push sides of the first chamber pair through two transfer valves during the push and pull strokes of the global arrangement, and producing variable pressure push and pull forces on the mobile part of the assembly.

4. Pneumatic double acting cylinder assembly where the displacement (volume) of the second chamber pair or chamber pair arrangement has globally a greater displacement (volume) than the volume of the first chamber pair, producing a thermodynamic expansion of the air during the transfer of the air from the push (pull) side of the first chamber pair into the pull (push) sides of the second chamber pair or pair arrangement. The thermodynamic expansion corresponding to the variable pressure forces described in claim 3.

5. Pneumatic double acting cylinder assembly according description of claim 1, 2, 3, and 4 where the air of the push and pull sides of the second chamber and piston pair, or chamber and piston pair arrangements, is released to the surrounding through two exhaust valves after the air has been expanded during the transfer from the push (pull) side of the first chamber pair into the pull (push) sides of the second chamber pair or chamber pair arrangement.