NO345179B1 - Multi-circuit Stirling machine - Google Patents

Description

MULTI CIRCUIT STIRLING MACHINE

Introduction

The invention relates to a multi-circuit Stirling machine, i.e. an engine, heat pump or cooling machine that works according to the Stirling cycle, which consists of two or more independent closed gas circuits, each of which works according to the Stirling cycle.

Background and known technique

Stirling machines consist of at least one closed gas circuit, divided into an expansion volume and a compression volume, connected through three heat exchangers; an expansion heat exchanger, regenerator and compression heat exchanger. Expansion volume and compression volume can be realized in different ways, usually distributed over one or more cylinder volumes, in closed cylinders, delimited by pistons. Stirling machines are classified into alpha, beta and gamma configurations, based on how the volumes are configured. Each piston in a Stirling engine will have a stroke length determined by the crankshaft, and a stroke volume given by the stroke length and cylinder diameter. Each gas circuit can be delimited by one or more pistons, and the gas circuit's stroke volume is defined as the difference between the largest and smallest volume achieved during one revolution. In stirling machines, a displaced volume is also defined, which is the average gas volume that passes through the heat exchangers in each direction during one revolution.

WO 2014/020840 A1 includes a Stirling engine and regulation method where on one end of a displacement piston (2m), including a working medium (gas) (G) and a built-in displacement piston (2mp), is heated using a heating element (3 ) and on the other end of the displacement cylinder (2m) is cooled by means of a cooling element (4). The displacer piston (2mp) is driven in an oscillating motion by means of moving and regulating a displacer actuator (5m), a working piston (6p) mounted in a working cylinder (6) which is set in motion by activating the working medium (G) in displaces the cylinder (2m), and a piston rod (6po) to the working piston (6p) affects the output unit (7).

US 2657553 describes a driving unit for transporting heat from a lower and up to a higher temperature level, built as a closed system, where the unit includes a quantity of gas consisting of a pure substance which is the working medium, consisting of a hot and a cold part, where each part communicates via a heating unit, a regenerator and a cooler with a cooling area. The volumes of the aforementioned areas, together with the total volume of the working area, are varied by coupled piston-like units that oscillate essentially harmonically with a constant phase shift.

JP S5412062 A shows a Stirling engine provided with double acting pistons, expansion pistons, a crankshaft, connecting rods and guides. Heat exchangers, regenerators and the like are connected via a compression volume and expansion volume which is formed due to the movements of said pistons.

US 4365474 A describes a module for a double-acting four-cylinder Stirling engine which includes a heat exchanger, two upper cylinder sections, two regenerator/cooler units each having a flexible interconnected regenerator and a cooler, two heating systems and two cooling piping systems. The upper cylinder parts and regenerators extend into the heat exchanger and are sealed and attached to it. The upper cylinder parts can be connected to two lower cylinder parts attached to an engine block. The coolers can be connected to two lower cylinder parts attached to the block. Each of the heat pipe systems extends in the heat module from a respective upper cylinder part to one of the engine's regenerators; and each of the cooling pipe systems extends from a regenerator, through its respective cooler and through the cooler wall for connection to one of the lower cylinder sections.

JP H07167514 A describes a Stirling unit that can generate cold to a predetermined cylinder, where the unit includes a low temperature generating cylinder, a medium temperature generating cylinder and a high temperature cylinder that receives high temperature from an external heat source, each including a piston in connection to a crankshaft via a piston rod.

US4195613A shows a 4-cylinder, 4-circuit Stirling machine where each circuit comprises one cylinder volume in one cylinder, and one cylinder volume in another cylinder, so that each cylinder consists of one volume from one circuit and one volume from another circuit, separated by a stamp. The total of 4 pistons are connected by 2 crankshafts, which are synchronized in relation to each other, so that the machine consists of 4 identical circuits, 90 degrees out of phase in relation to each other. This solution realizes a 4-circuit Stirling machine with only one piston per cylinder. The solution also means that each piston performs compression work in one circuit at the same time as expansion work in another circuit is performed on the piston. As the 4 circuits are identical, the torque becomes very even.

Due to the mechanical design, displacement volume equals cylinder stroke volume while circuit stroke volume equals cylinder stroke volume x 1.414 (root of 2). If the circuit stroke volume is 1000 ccm, the cylinder stroke volume will therefore be 707 ccm, and the displaced volume 707 ccm.

The solution of US4195613A has two disadvantages, the first disadvantage being that the ratio between displaced volume and circuit stroke volume is constant. The ratio can be process-wise favorable under some operating conditions, but especially in low-temperature applications, a large displaced volume in relation to the circuit stroke volume is often desired, and then this solution will not provide optimal performance.

The other disadvantage of US4195613A is that all the pistons separate between two circuits that have different pressures most of the time, and the piston rings on all 4 pistons must therefore seal against the pressure difference between two gas circuits. Total sealing requirement is in relation to total stroke volume for pressurized pistons, and the total stroke volume with sealing requirement is thus 0.707 x total circuit stroke volume.

The third disadvantage of US4195613A is that the forces to be transmitted mechanically between the pistons are also proportional to the stroke volume of the pressurized pistons, and both the machine in general and the mechanics in particular must be dimensioned according to these forces. This contributes to higher production costs and higher friction than would have been the case with a smaller stroke volume per circuit stroke volume.

NO333268 shows a stirling machine with two or more circuits. The solution allows the scaling of the process to an even number of circuits, with only two pistons per two circuits, and unlike the solution in US4195613A, the solution gives the freedom to choose the ratio of circuit stroke volume to displaced volume to values other than 1.414 (the root of 2 ). Displaced volume is approximately equal to one cylinder stroke volume. By choosing an angle on the crankshaft of, for example, 150 degrees, a circuit displacement of 1000 ccm can be achieved, while the displaced volume is approx. 1930 ccm.

NO333628 has five disadvantages, where the first disadvantage is in low-temperature applications, where the circuit stroke volume is small in relation to the cylinder stroke volume. Both pistons that define the gas circuit separate between two gas circuits with different pressures for most of the revolution. This means that the total stroke volume with sealing requirements is also large. In the example with a 150 degree crankshaft, the total stroke volume with sealing requirement becomes 1.93 x total circuit stroke volume. This is much larger than in the solution in US4195613A. This results in greater friction and wear on relatively expensive sealing material than if it had been sealed for a smaller stroke volume per circuit stroke volume.

The other disadvantage of NO333628 is that for each pair of circuits there will be a cylinder where the piston separates between two cold volumes, and a cylinder where the piston separates between two hot volumes. This can cause challenges where the temperatures in the circuit are outside the working range for the materials normally used in piston rod seals and piston rings.

The third disadvantage of NO333628 is that the pressure difference across both pistons in a pair of process circuits is at all times equal to the pressure difference between the circuits, and therefore significantly greater forces must be transmitted through the crank mechanism than in, for example, US4195613A. The large forces require powerful, heavy and expensive components, and larger bearings and guides, which also produce greater friction, than in a machine configuration with a smaller cylinder stroke volume per process circuit.

The fourth disadvantage of NO333628 is that the greater sealing requirement gives an increased risk of leakage between the process circuits, and leakage between process circuits in Stirling machines causes both imbalance and significant losses in efficiency.

And the fifth disadvantage of NO0333628 is that the two process circuits in a pair of process circuits get significant differences in compression and phase angle between gas transport and heat exchange and compression and expansion. The reason lies in the piston movement given by the geometry of the crank mechanics and in particular the relationship between the length of the crank arm and the radius of the crank bay. This makes it challenging to optimize both circuits for the operating conditions, and even in a 4-cylinder design, the torque variation is significantly greater than that published for machines according to US4195613A.

With stirling machines according to known technology, it is not possible to achieve a low total stroke volume with sealing requirements, full freedom in choosing the ratio between displaced volume and total circuit stroke volume, and the torque equalization that can be achieved by distributing two or four gas circuits evenly distributed over 360 degree rotation, while the machine can be designed so that only volumes with the least unfavorable temperature conditions are close to piston rod seals.

Brief summary of the invention

A main purpose of the invention is to provide a configuration for multi-circuit stirring machines which makes it possible to realize any desired ratio between circuit stroke volume and displaced volume for the gas circuits, while at the same time the total stroke volume for pressurized pistons becomes as small as possible in relation to total circuit stroke volume , and the gas circuits can be phase-shifted uniformly over a 360-degree rotation, so that the torque is as constant as possible.

Furthermore, it is an aim of the invention to enable the realization of a multi-circuit Stirling machine, where expansion volumes and compression volumes can be distributed so that both pressurized piston rings and piston rod seals can be placed in the volumes that have the most favorable temperature conditions for the performance of the piston rings and piston rod seals. These will often be temperatures between 0 degrees Celsius and 150 degrees Celsius.

Furthermore, it is an object of the invention to provide a configuration for a stirling machine with several circuits, where the least possible forces are transferred from pressurized pistons to the crankshaft, in relation to the machine's torque.

Furthermore, it is an object of the invention to provide a stirring machine with several circuits, which is better balanced than other configurations for multi-circuit stirring machines, through that both first-order and second-order mass forces can be balanced without the use of balance shafts.

Figures

The attached figures show some embodiments of the claimed invention.

Figure 1 shows the Stirling cycle in a Pressure-Volume diagram (Pv diagram).

Figure 2 shows a schematic structure of two circuits in a Stirling machine according to the invention.

Figure 3 shows a schematic structure of four circuits in a Stirling machine according to an embodiment of the invention.

Figure 4 shows the crank mechanics of the design in Figure 3.

Figure 5 shows the crank mechanism of another embodiment of the invention.

Detailed description of the figures and embodiments of the invention The invention will be described below and embodiments of the invention will be explained with references to the attached drawings.

A simplified thermodynamic description of the Stirling cycle is shown in Figure 1. The Stirling cycle is a thermodynamic cycle that consists of 4 processes: isothermal compression, temperature increase at constant volume, isothermal expansion and temperature decrease at constant volume, of a working medium in gaseous form. Heat is exchanged with external temperature reservoirs during compression and expansion. The heat that is released when the temperature drops is stored in a regenerator, and supplied when the temperature rises, at approximately the same temperature. The cycle is (like the Carnot cycle) reversible and has the highest achievable thermal efficiency.

The invention is a multi-circuit stirling machine (0) comprising at least two process circuits (1P, 2P), with

- three cylinders (D1, W12, D2),

- three pistons (5, 6, 7), coaxially arranged in each cylinder (D1, W12, D2), - a crankshaft (21) with crankcases (21a, 21b, 21c) and connecting rods (12, 16, 20), where the connecting rods are arranged and connected with each piston (5, 6, 7), - where the cylinders (D1, W12, D2), the pistons (5, 6, 7) and the crankshaft (21) are arranged in at least one cylinder bank (8),

- where two of the cylinders (D1, D2) each comprise a coaxially arranged displacement piston (5, 7), each cylinder (D1, D2) comprises two volumes (1a, 1b, 2a, 2b) separated by a displacement piston (5, 7) , and where one volume (1b, 2b) is connected to a volume (1c, 2c) in the third cylinder (W12),

- where the two volumes (1c, 2c) in the third cylinder (W12) are separated by a coaxially arranged working piston (6),

- where each process circuit (1P, 2P) comprises at least one heat exchanger arrangement (1H, 2H), and

- where each heat exchanger (1H, 2H) is additionally connected to and arranged between the two cylinder volumes (1a, 1b, 2a, 2b).

Figure 2 shows two separate process circuits (1P, 2P) in a stirling machine according to the invention. Process circuit (1P) consists of the cylinder volumes (1a, 1b, 1c), as well as the heat exchanger module (1H), consisting of the heat exchangers (1he, 1hr, 1hc).

The cylinder volumes and the heat exchangers are linked together and connected by three flow channels (1d, 1e, 1f). Process circuit (2P) consists correspondingly of the cylinder volumes (2a, 2b, 2c), as well as the heat exchanger module (2H), consisting of the heat exchangers (2he, 2hr, 2hc). The cylinder volumes and the heat exchangers are linked together and connected by three flow channels (2d, 2e and 2f).

The cylinder volumes (1a and 1b) are separated by piston (5) in cylinder (D1), the cylinder volumes (2a and 2b) are separated by piston (7) in cylinder (D2), and the cylinder volumes (1c and 2c) are separated by piston ( 6) in cylinder (W12).

The process circuits (1P, 2P) are filled with a working medium, for example consisting of hydrogen, helium or nitrogen.

When piston (5) is moved upwards, so that cylinder volume (1a) is reduced, and cylinder volume (1b) is increased, the working medium will flow from cylinder volume (1a), via flow channel (1e), through the heat exchangers (1he, 1hr and 1hc), via flow channel (1f), and to cylinder volume (1b). The overall volume is reduced as the piston rod (9) is fed into the cylinder (5).

When piston (6) is moved downwards, cylinder volume (1c) is reduced, and thus the overall volume in process circuit (1) will also be reduced.

Piston (5) is connected to a cross head (10), which runs in a cross head liner (11), via a piston rod (9). The cross head (10) is connected to a crankshaft (21), via a crank rod (12), which is stored in the cross head (10) and in the crank bay (21a). Piston (6) and piston (7) are connected to the crankshaft (21) in a similar way, in the crank bay (21b and 21c) respectively. If the angle between the crank bays (21a) and (21b) is between 0 and 180 degrees, and the temperature in the cylinder volumes (1a and 1b) is different, the process circuit (1P) will be able to perform a Stirling cycle when the crankshaft (21) is rotated. Piston (5) will do displacement work, in the form of overcoming flow friction in heat exchangers (1H) and channels (1e, 1f), and piston (5) will perform compression work and expansion work.

In one embodiment of the invention, crank bay (21b) is 90 degrees phase-shifted in relation to crank bay (21a) and crank bay (21c) is 90 degrees phase-shifted in relation to crank bay (21b). To achieve the normal stirring process, the angle between the crank bay (21a) and (21b) will be chosen close to 90 degrees, but in some applications, it may be beneficial to choose a larger or smaller angle.

If the angle between the crank bays (21b) and (21c) is chosen so that the angle between (21a) and (21c) is close to or equal to 180 degrees, and the temperature in the volumes (1a) and (2a) is relatively equal, and the temperature in the volumes ( 1b) and (2b) are relatively similar, the process in process circuit (1P) and the process in process circuit (2P) will be approximately the same, but 180 degrees phase-shifted in relation to each other.

As piston (5) will have different effective area above and below due to the piston rod (9) cross-sectional area, the two circuits will have slightly different compression, and as piston (5) will follow a normal piston movement (oscillating), compression work and expansion work will for the two circuits be slightly out of phase in relation to the flow through the heat exchangers (1H, 2H).

The difference in work and process performance is normally small.

As the two process circuits (1P, 2P) are approximately the same, and close to 180 degrees out of phase in relation to each other, the piston (5) will do compression work in one process circuit at the same time as it does expansion work in the other process circuit. If the machine is operated as an engine, the expansion work will be greatest, and the compression work for one process circuit will be performed by the expansion work from the other process circuit, so that only the difference between the two works must be transferred via piston rod (9), crosshead (10) and connecting rod ( 12) to the crankshaft (21). If the machine is operated as a heat pump, the compression work will be the greatest, and the expansion work from one circuit will perform parts of the compression work for the other circuit, so that only the difference between the two works must be transferred from the crankshaft (21), via the crankshaft (12), crosshead and piston rod to piston (5). If the crankshaft (21) is made so that the angles between the crank bays (21a, 21b, 21c) are close to 90 degrees, the mass forces on piston (5) and (7) will produce coincident torque on the crankshaft (21), while the mass forces on piston (6) will produce a torque on the crankshaft which is in opposite phase to the torque from the mass forces on piston (5) and (7). If the equivalent oscillating point mass for piston (6) is twice as high as the equivalent oscillating point mass for piston (5), and that the oscillating point masses for piston (5) and (7) are equal, torque variation from first-order mass forces on the pistons can be neutralized.

In one embodiment of the invention, the connecting rod (16) is more than 2 times as long from the center of the crank bay bearing to the center of the cross pin bearing as the stroke length of the piston (6). The greater the ratio between the connecting rod length and the stroke length for piston (6), the more similar the process becomes in the two process circuits (1P, 2P), and the torque curve becomes more equal in the two halves of a revolution. In addition, the mass forces become lower, especially higher order mass forces, such as second order and fourth order.

The advantage is that the invention allows the scaling of the process to two process circuits (1P, 2P), with three cylinders and three double-acting pistons (5, 6, 7), and an equalization of torque and reduction of friction compared to a configuration with only one process circuit . The compression work from one circuit takes place at the same time as the expansion work from the other circuit, and both work is performed by or on the same piston, so that only the difference has to be transferred mechanically to the axle.

Piston (6) is the only piston that separates the two gas circuits, and therefore the total pressurized stroke volume for a pair of gas circuits is approximately equal to the circuit stroke volume for each circuit. Thus, the total stroke volume with sealing requirements is approx. 0.5 x total circuit stroke volume. This is the smallest achievable stroke volume with sealing requirements in relation to circuit stroke volume for Stirling machines. According to known technology within Stirling applications, total displacement with sealing requirements will be greater in relation to total circuit displacement than the invention.

In addition, it enables the realization of a family of machines with different compression ratio, but equal ratio between displaced volume and heat exchanger volume, where only the working piston stroke volume changes, e.g. by changing the diameter of cylinder (W12) and piston (6).

In one embodiment of the invention, two pairs of process circuits (1P, 2P, 3P, 4P) are arranged in a cylinder bank (8) with six cylinders in a row, where the first pair of process circuits (1P and 2P) are distributed between cylinders (D1, W12 and D2), and the second pair of process circuits (3P and 4P) are distributed between cylinders (D3, W34 and D4). See Figure 3.

Process circuit (1P) consists of the cylinder volumes (1a, 1b and 1c), as well as a heat exchanger module (1H) as described in Figure 2. The flow channels (1e and 1f) lead to the heat exchanger module (1H), and the flow channel (1d) connects the aforementioned cylinder volumes. Correspondingly, the process circuits (2P, 3P and 4P) also consist of three cylinder volumes (2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b, 4c), three flow channels (2e, 2f, 3e, 3f, 4e, 4f) and at least one heat exchanger module (2H, 3H, 4H) each.

In the same way that the cylinder volumes (1a and 1b) are separated by piston (5) in cylinder (D1), the cylinder volumes (2a and 2b) are separated by piston (7) in cylinder (D2), and the cylinder volumes (1c and 2c) are separated by piston (6) in cylinder (W12), the cylinder volumes (3a and 3b) are separated by piston (22) in cylinder (D3), the cylinder volumes (4a and 4b) are separated by piston (24) in cylinder (D4) and the cylinder volumes (3c and 4c) separated by piston (23) in cylinder (W34).

The pistons are connected to a crankshaft (21), so that piston (5) is connected to the crank bay (21a), via a piston rod (9), a cross head (10) with cross pin and a connecting rod (12). Correspondingly, piston (6) is connected to crank bay (21b), piston (7) to crank bay (21c), piston (22) to crank bay (21d), piston (23) to crank bay (21e) and piston (24) to crank bay ( 21f).

Process circuit (1P), process circuit (2P) and the relationship between them are defined by the angles between the crankshaft's crank bay (21a, 21b and 21c). Similarly, process circuit (3P), process circuit (4P) and the relationship between them are defined by the angles between the crankshaft's crank bay (21d, 21e and 21f). If the angles between the crank bays (21d, 21e and 21f) are equal to the angles between the crank bays (21a, 21b and 21c), the process circuits (3P and 4P) can be made equal to the process circuits (1P and 2P).

If the angle between the crank bays (21a) and (21c), and the angle between the crank bays (21d) and (21f), are both close to 180 degrees, and the angle between the crank bays (21b) and (21e) is close to 90 degrees, the four process circuits (1P, 2P, 3P, 4P) be 90 degrees out of phase relative to each other, and the resulting torque from the four process circuits will have very little variation over one revolution.

A Stirling machine according to the invention, which is designed as shown in figure 3, will have the same advantages as the design in figure 2, with regard to pressurized stroke volume. In addition, it will be possible to distribute the four process circuits (1P, 2P, 3P, 4P) evenly over one revolution, so that the torque has little variation.

Another advantage of the invention, in the embodiment shown in figure 3, is that it enables a stirling machine with four process circuits, where all the cylinders are in a row configuration. This means that a Stirling machine with a large displacement, and thus a large distance between piston and crankshaft, can be constructed within a significantly smaller width than a V-configuration with a similar displacement.

Figure 4 shows the crank mechanics in perspective of the design described in Figure 3. Figure 4 also shows the cross pin (25) which connects the cross head (10) and the connecting rod (12), the cross pin (26), which connects the cross head (14) and the connecting rod (16), cross pin (27) which connects the cross head (18) and the crankshaft (20), and similarly for the crank mechanism which connects the pistons (22, 23 and 24) to the crankshaft (21).

The crankshaft (21) has an input or driving end (21g), with an interface to, for example, a flywheel, generator, motor or pump depending on whether the stirling machine operates as a motor, cooling machine or heat pump. If the crankshaft rotates clockwise, viewed from the driving end (21g), the crankshaft has a crank star where crank bay (21a) defines 0 degrees, crank bay (21b) is 90 degrees and crank bay (21c) is 180 degrees. Crank bay (21d) is at 270 degrees, crank bay (21e) is at 0 degrees, and crank bay (21f) is at 90 degrees. Other designs of cylinder sequence and layout of the crank star will also be able to achieve a 90 degree phase shift between 4 process circuits, but with the described crank star, it is also achieved that three crank bays lie in the plane 0 degrees - 180 degrees: (21a, 21c and 21e), and three crank bays lie in the plane 90 degrees - 270 degrees: (21b, 21d and 21f), while all crank bays in each plane have a distance of 2 x the cylinder distance, and have a symmetrical location, i.e. the middle of the three crank bays in one plane goes in the opposite direction of the two outermost crank bays in the same plane.

For kinematic analysis, the crank mechanics of a piston in a cylinder can be represented by an oscillating point mass on the cylinder axis, a rotating point mass in the crankcase axis, and a polar moment of inertia in the connecting rod. The rotating point masses can be balanced on the crankshaft and the movement of the oscillating point masses can be expressed as fourier series, where the first term gives first-order mass forces and the second term gives second-order mass forces.

If the mechanics of each cylinder are performed with equal oscillating point mass, the first order mass forces for the crank mechanics shown in Figure 4 will be reduced to 1 x oscillating point mass at 0 degrees in the crank bay (21c) and 1 x oscillating point mass at 90 degrees in the crank bay (21d). Second order mass forces will be reduced to 3 x oscillating point mass at 0 and 180 degrees in the crankcase (21c) and 3 x oscillating point mass at 90 and 270 degrees in the crankcase (21d). A proportion of the remaining first-order mass forces can, as normal, be balanced out on the crankshaft, for example 50%. The resulting mass forces in normal balancing will be a counter-rotating first-order mass force of F1 = 0.7 m �<2 >r, a counter-rotating first-order mass moment of 0.5 x F1 x cylinder distance, and a second-order mass moment, normal to the cylinder axes and the crankshaft, from 3 x oscillating point masses with 1 cylinder distance between them.

In sum, the crank mechanics as described will be able to provide the lowest possible mass forces for a six-cylinder in-line engine according to the invention. Remaining first-order and second-order mass forces and mass moments can be balanced with balance shafts, as for other machines.

This design is advantageous as it enables a narrow design of the machine, which can be important, especially with large stroke volumes. In addition, it allows for vertical cylinders only, which can be advantageous in that the pistons are not exposed to lateral forces from gravity.

This design also enables a Stirling machine with 4 independent circuits, with close to 90 degree phase shift between the circuits, in such a way that a very uniform torque is achieved over one revolution, while at the same time a good balancing of both mass forces and torque variations from mass forces is made possible.

If cylinder numbers (D2) and (D3) are constructed with twice as much oscillating mass as the other cylinders, the first-order mass forces can be completely balanced, at the expense of higher forces in the crankshaft and bearing.

If instead cylinders (D1) and (W12) switch places, and (W34) and (D4) switch places, it is also possible to achieve better balancing than with other designs, with adjusted oscillating point masses for the various cylinders, at the expense of higher forces in connecting rods and bearings.

In one embodiment of the invention, two pairs of process circuits (1P, 2P, 3P, 4P) are arranged in a six-cylinder V-configuration, so that one cylinder bank (8) consists of process circuit (1P) and process circuit (2P), and the second bank of cylinders consists of process circuits (3P and 4P), which can be performed similarly to the process circuits (1P and 2P). The six pistons (5, 6, 7, 22, 23 and 24) are all connected by a crankshaft (21), with a crank mechanism comprising piston rod, cross head, cross pin and connecting rod. See figure 5.

Piston (5) and piston (22) are both connected to crank bay (21a), piston (6) and piston (23) are both connected to crank bay (21b), and piston (7) and piston (24) are both connected to crank bay (21c).

If the angle between the crank bay (21a and 21c) is equal to or close to 180 degrees, and the angle between the cylinder bank consisting of the process circuit (P1 and P2) and the cylinder bank consisting of the process circuit (P3 and P4) is equal to or close to 90 degrees, the four process circuits (1P, 2P, 3P, 4P) could be 90 degrees offset in relation to each other, so that the torque from the four process circuits (1P – 4P) will vary very little over one revolution.

In one embodiment of the invention, each cylinder bank (8, 8') is offset by 90 degrees in relation to each other. This design allows full balancing of first-order and second-order mass forces, through that the first-order mass forces for a pair of cylinders can be balanced on the crankshaft if the angle between the cylinder banks (8. 8') is 90 degrees, and through that the second-order mass forces for the same cylinder pair works in a horizontal direction if the cylinders are positioned 45 degrees from the vertical. If the crank bays are placed at 0 degrees, 90 degrees and 180 degrees, the second order mass forces will appear at 0 degrees, 180 degrees and 360 degrees, so that the second order mass forces can be balanced by making the oscillating mass for the two middle pistons twice as high as for the other pistons, and keep the same crank ratio, or by changing only the crank ratio for the middle pistons, or by combinations of these.

If completely symmetrical cylinder placement is used, where the connecting rod to the crosshead in 3 of the cylinders has two bearings around the crank bay, one placed on each side of the connecting rod to the crosshead in the opposite cylinder, the first order mass forces are completely balanced, and the second order mass forces can be completely balanced, with one of two different techniques. If piston (6) with associated mechanics is made with twice as large oscillating point mass as each of piston (5) and piston (7), and correspondingly for piston (23) in relation to piston (22) and piston (24), the resultant of second-order mass forces for piston (6) and piston (23) together equalize the resultant of second-order mass forces for piston (5, 7, 22 and 24). Complete balancing of second-order mass forces can also be achieved by mounting two counter-rotating balance shafts with double speed in relation to the crankshaft, symmetrically placed about a horizontal plane through the shaft's axis of rotation, and with mass force vectors in the plane through the two central cylinders ( W12, W34). If the cylinder banks (8, 8') are offset corresponding to the width of a connecting rod in relation to each other, there will be a small residue of mass forces, but such a design is normally considered well balanced.

A Stirling machine according to the invention, which is designed as shown in figure 5, will have the same advantages as the design in figure 2, with regard to pressurized stroke volume. In addition, it will be possible to distribute the four process circuits evenly over one revolution, so that the torque has little variation.

A Stirling machine according to the invention, which is shown in figure 5, will also be able to be made with a relatively short crankshaft to be a 6-cylinder machine, thus achieving a moderate total length.

Another advantage of the stirling machine according to the invention, which is shown in figure 5, and mounted with the cylinder banks (8, 8') 45 degrees from the vertical, will not have first-order or second-order mass forces or mass moments in the vertical direction. This is a major advantage during installation, as it is easier to isolate horizontal vibrations that will affect the foundation, support and any associated floor.

In an embodiment of the invention where the heat exchanger arrangement (1H, 2H) comprises three heat exchangers, preferably an expansion heat exchanger (1he, 2he), a regenerator (1hr, 2hr) and a compression heat exchanger (1hc, 2hc).

According to an embodiment of the invention, the location of the heat exchanger modules (1H, 2H, 3H, 4H) can be arranged and built into the cylinder banks, be partially inside and outside the cylinder banks or be located outside the cylinder bank. Different placement of the heat exchanger modules (1H, 2H, 3H, 4H) can be advantageous in different applications of the stirling machine's application, depending on whether it is operated as a thermal power engine, cryomotor, cooling machine or heat pump.

In an embodiment of the invention, where the machine is made with 2 pairs of process circuits (1P, 2P, 3P, 4P), which are unwired so that the 4 circuits are about 90 degrees out of phase in relation to each other, the torque will have little variation over a revolution, regardless of whether the machine is used as a thermal power engine, cryomotor, cooling machine or heat pump.

In one embodiment of the invention, the stirling machine can be used as a thermal power engine, cryomotor, cooling machine or heat pump.

Claims (11)

CLAIM 1. A multi-circuit stirling machine (0) comprising at least two process circuits (1P, 2P), - three cylinders (D1, W12, D2), - three pistons (5, 6, 7), coaxially arranged in each cylinder (D1, W12, D2), - a crankshaft (21) with crankcases (21a, 21b, 21c) and connecting rods (12, 16, 20), where the connecting rods are arranged and connected with each piston (5, 6, 7), - where the cylinders (D1, W12, D2), the pistons (5, 6, 7) and the crankshaft (21) are arranged in at least one cylinder bank (8), - where two of the cylinders (D1, D2) each comprise a coaxially arranged displacement piston (5, 7), each cylinder (D1, D2) comprises two volumes (1a, 1b, 2a, 2b) separated by a displacement piston (5, 7) , and where one volume (1b, 2b) is connected to a volume (1c, 2c) in the third cylinder (W12), - where the two volumes (1c, 2c) in the third cylinder (W12) are separated by a coaxially arranged working piston (6), - where each process circuit (1P, 2P) comprises at least one heat exchanger arrangement (1H, 2H), and - where each heat exchanger (1H, 2H) is additionally connected to and arranged between the two cylinder volumes (1a, 1b, 2a, 2b). 2. A Stirling machine according to claim 1, where the crankshaft (21) is arranged 90° ± 5° between the crank bay (21b) and each of the other two crank bays (21a, 21c) 3. A stirring machine according to claim 1, comprising two pairs of process circuits (1P, 2P, 3P, 4P) where the 4 process circuits are phase-shifted by approximately 90° ± 5° between each circuit 4. A stirring machine according to claim 1 or claim 2, comprising: - four process circuits (1P, 2P, 3P, 4P), - where each pair of the process circuits (1P – 4P) constitutes its own bank of cylinders (8, 8 ́) in a V-configuration. 5. A stirring machine according to claim 4 where each cylinder bank (8, 8') is offset by 90° ± 5° in relation to each other. 6. A stirring machine according to claim 1 or claim 2, comprising: - four process circuits (1P, 2P, 3P, 4P), and - a bank of cylinders (8), where the bank of cylinders (8) is arranged in a 6-cylinder in-line configuration. 7. A stirling machine according to claim 1, where the connecting rod (12) of the working piston (6) is longer than 2 x the stroke length of the working piston (6). 8. A stirling machine according to claim 1, where the oscillating mass for the working piston (6) with associated oscillating components and oscillating proportion of the connecting rod mass is between 1.8 and 2.2 times as high as the oscillating mass for each of the displacer pistons (5, 7) with associated components and oscillating part of the connecting rod mass. 9. A stirling machine according to any one of the preceding claims, wherein the heat exchanger arrangement (1H, 2H) comprises three heat exchangers, preferably an expansion heat exchanger (1he, 2he), a regenerator (1hr, 2hr) and a compression heat exchanger (1hc, 2hc) ). 10. A stirling machine according to any one of the preceding claims, where the location of the heat exchanger modules (1H, 2H, 3H, 4H) is arranged and built into the cylinder bank (8, 8'), arranged partly inside and outside the cylinder banks (8, 8 ') or arranged outside the cylinder bank (8, 8'). 11. A stirling machine according to any one of the preceding claims, where the machine (0) can preferably be used as a thermal power engine, cryomotor, cooling machine or heat pump.