A confluence type pressure increasing gerotor pump

Abstract

A kind of converging type pressure increasing gerotor pump.This application relates to the improvement of gerotor internal gear pump structure.By staggered compensation, avoid the flow pulsation caused by pump cavity volume change, and then realize the output pressure boost, and run smoothly.This application includes high pressure pump body, low pressure pump body and main shaft, the axis of outer rotor A and outer rotor B is arranged on one side of the main shaft, the axis of high pressure pump outer rotor is arranged on the other side of the main shaft, and the axis of outer rotor A is + alpha angle relative to horizontal line, the axis of outer rotor B is - alpha angle relative to horizontal line, alpha = 360 ° / 2N, N is the number of inner rotor teeth.This application adopts the ingenious design of rotor eccentric installation, realizes the pressure boost of pump, and the staggered compensation solves the flow pulsation caused by pump cavity volume change, provides stable flow for high pressure booster pump inlet.This application can be widely used in new energy vehicles, wind power, air conditioning, generator, industrial production, chemical industry, petroleum, metallurgy, water treatment and other fields, for conveying various liquids.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of positive displacement hydraulic pumps, in particular to the improvement of the structure of a cycloid internal gear pump. BACKGROUND

[0002] The current gear pump generally adopts involute straight gear, involute helical gear, cycloid gear, straight line conjugate gear, circular arc involute circular arc gear, etc. By using the meshing characteristics of the corresponding gear, different types of gear pumps are designed to complete the pumping of the medium. Due to the development of the host equipment in the direction of high power, high efficiency and multiple working conditions, the weight, volume, efficiency, pressure, pulsation, vibration and noise of the gear pump are required to be higher, and only the cycloid internal gear pump can meet the comprehensive performance of small volume, high efficiency, small pulsation, strong self-priming and low vibration and noise. However, in actual application, the cycloid internal gear pump has the problems of low pressure, small flow and shaft misalignment. The existing cycloid internal gear pump cannot meet the application requirements of high-end mechanical equipment in the aviation industry, new energy vehicles, high-power wind power and other equipment.

[0003] In order to increase the application field of the cycloid internal gear pump and meet the development of industrial equipment, the pressure of the cycloid internal gear pump needs to be improved, and the flow needs to be increased. However, due to the structural characteristics of the cycloid pump, simply increasing the pressure will cause the problem of shaft misalignment, which will further cause the wear of the pump cavity rotor and a series of problems such as vibration and noise.

[0004] Therefore, how to combine the structural characteristics of the cycloid pump to alleviate the shaft misalignment when increasing the pressure of the cycloid pump, and effectively improve the overall stability of the equipment, has become a technical problem to be solved in the field. SUMMARY

[0005] The present application provides a kind of by misplacement compensation, avoids the flow pulsation caused by the volume change of pump cavity, and then realizes the output pressure increase, and the running stable confluence type pressure increasing cycloid pump.

[0006] The technical scheme of the present application is: including high pressure pump body, low pressure pump body and main shaft, the low pressure pump body includes pump body A and pump body B arranged on the left and right sides of the high pressure pump body, and a communication plate is arranged between the pump body A and the high pressure pump body.

[0007] A pump cavity A is arranged in the pump body A, an outer rotor A and an inner rotor A are movably arranged in the pump cavity A, an axial pump body A flow channel is arranged at the upper part of the pump body A, the pump body A flow channel communicates with the pump cavity A, and a pump body A inlet communicating with the pump body A flow channel is arranged at the top of the pump body A.

[0008] A through-type communication plate flow channel is arranged at the lower part of the communication plate.

[0009] The high-pressure pump body has a high-pressure pump chamber on the end face facing the connecting plate, and a high-pressure pump outer rotor and a high-pressure pump inner rotor are provided in the high-pressure pump chamber; a through-type high-pressure pump flow channel is opened in the lower part between the bottom surface of the high-pressure pump chamber and the other end face of the high-pressure pump body, a high-pressure outlet flow channel is opened in the upper part between the bottom surface of the high-pressure pump chamber and the other end face of the high-pressure pump body, and a high-pressure pump outlet communicating with the high-pressure outlet flow channel is opened in the top of the high-pressure pump body;

[0010] The pump body B is provided with a pump chamber B, and an outer rotor B and an inner rotor B are movably arranged in the pump chamber B. An axial pump body B flow channel is provided at the upper part of the pump body B, and the pump body B flow channel communicates with the pump chamber B. A pump body B inlet communicating with the pump body B flow channel is opened at the top of the pump body B.

[0011] The axes of the outer rotor A and the outer rotor B are located on one side of the main shaft, and the axis of the outer rotor of the high-pressure pump is located on the other side of the main shaft. The axis of the outer rotor A forms an angle of +α with respect to the horizontal line, and the axis of the outer rotor B forms an angle of -α with respect to the horizontal line. α = 360° / 2N, where N is the number of teeth of the inner rotor.

[0012] Furthermore, the thickness of the inner rotor A and the inner rotor B is t, and the thickness of the inner rotor of the high-pressure pump is 1.5~2.0t.

[0013] Furthermore, a flow channel guide groove L and a flow channel guide groove R are respectively provided at both ends of the flow channel.

[0014] Furthermore, sealing structures are provided on both ends of the connecting plate.

[0015] Furthermore, positioning shoulders are provided on both ends of the connecting plate.

[0016] Furthermore, a high-pressure pump body positioning step circle coaxial with the main shaft is formed at the edge of the high-pressure pump cavity for fitting with the positioning shoulder on the connecting plate.

[0017] Furthermore, a positioning structure and a sealing structure are provided between the high-pressure pump body and the pump body B.

[0018] Furthermore, the pump body A, the connecting plate, and the high-pressure pump body are each provided with their own central holes, and the pump body B is provided with a central blind hole for accommodating the main shaft; a sliding bearing is provided between the main shaft and each of the central holes and the central blind hole.

[0019] This invention utilizes the unique eccentric structure of the inner and outer rotors of a cycloidal pump, employing a clever design of eccentric rotor installation to achieve pump boosting. By designing the rotor eccentricity angle, it achieves misalignment compensation between the output chambers of the two low-pressure pumps, converging hydraulic oil into the high-pressure pump. This innovative misalignment compensation measure resolves flow pulsation caused by changes in pump chamber volume, providing a stable flow rate at the inlet of the high-pressure booster pump. Through the design of the rotor parameters for the high-pressure booster pump and the low-pressure pump, and the structural layout of the two low-pressure pumps and the high-pressure booster pump, the radial force on the pump shaft is effectively alleviated, achieving high-flow boosting and also auxiliaryly compensating for flow pulsation, thus improving the overall performance and lifespan of the pump.

[0020] This invention can be widely applied in new energy vehicles, wind power, air conditioning, generators, industrial production, chemical industry, petroleum, metallurgy, water treatment and other fields for transporting various liquids. Due to its advantages such as compact structure, stable operation, low noise level, small vibration amplitude, strong self-priming ability, small flow pulsation, high volumetric efficiency, high transfer efficiency, and strong viscosity, it can ensure safety and reliability in various fields. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a three-dimensional exploded view of the present invention;

[0023] Figure 2 This is a schematic diagram of the structure of the present invention;

[0024] Figure 3 This is a schematic diagram of the structure of pump body A in this invention;

[0025] Figure 4 yes Figure 3 The right view;

[0026] Figure 5 This is a three-dimensional schematic diagram of the connecting plate in this invention;

[0027] Figure 6 This is a schematic diagram of the connecting plate of the present invention.

[0028] Figure 7 yes Figure 6 The left view;

[0029] Figure 8 This is a three-dimensional schematic diagram of the high-pressure pump body in this invention;

[0030] Figure 9 This is a schematic diagram of the high-pressure pump body in this invention;

[0031] Figure 10 yes Figure 9 The left view;

[0032] Figure 11 This is a schematic diagram of the structure of pump body B in this invention;

[0033] Figure 12 yes Figure 11 The left view;

[0034] Figure 13 This is the working principle of the invention. Figure 1 ;

[0035] Figure 14 yes Figure 13 Sectional view of AA;

[0036] Figure 15 yes Figure 13 BB section view;

[0037] Figure 16 yes Figure 13 CC section view.

[0038] In the picture:

[0039] 1 is pump body A, 11 is outer rotor A, 12 is inner rotor A, 10 is pump body A inlet, 100 is pump body A flow channel, 101 is pump chamber A, and 102 is positioning step circle A.

[0040] 2 is the connecting plate, 200 is the connecting plate flow channel, 2001 is the connecting plate flow channel guide groove L, 2002 is the connecting plate flow channel guide groove R, 201 is the positioning shoulder, and 202 is the sealing groove.

[0041] 3 is the high-pressure pump body, 30 is the high-pressure pump outlet, 300 is the high-pressure pump flow channel, 3001 is the high-pressure pump flow channel guide groove L, 3002 is the high-pressure pump flow channel guide groove R, 301 is the high-pressure pump chamber, 302 is the high-pressure outlet flow channel, 303 is the high-pressure pump body positioning shoulder, 304 is the high-pressure pump body positioning step circle, 31 is the high-pressure pump outer rotor, and 32 is the high-pressure pump inner rotor.

[0042] 4 is pump body B, 40 is pump body B inlet, 400 is pump body B flow channel, 401 is pump chamber B, 402 is positioning step circle B, 41 is outer rotor B, and 42 is inner rotor B.

[0043] 5 is the main axis.

[0044] In the diagram, P0 is the inlet pressure of the low-pressure pump, P1 is the outlet pressure of the low-pressure pump, and P2 is the outlet pressure of the high-pressure pump.

[0045] F1 is the radial force acting on the main shaft from the low-pressure pump outlet; F2 is the radial force acting on the main shaft from the low-pressure manifold of the high-pressure pump; and F3 is the radial force acting on the main shaft from the high-pressure zone of the high-pressure pump.

[0046] t is the rotor thickness.

[0047] O0 is the center of the main axis, O 31 O is the center of the outer rotor of the high-pressure pump. 11 Centered on outer rotor A, O 41 Center of outer rotor B;

[0048] Figure 13 The double-dotted arrowhead indicates the flow trajectory of the fluid. Figures 13-16 A hollow arrow filled with a diagonal line indicates the direction of fluid flow. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0050] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this patent. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0051] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0052] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0053] likeFigures 1-12 As shown, it includes a high-pressure pump body 3, a low-pressure pump body, and a main shaft 5. The low-pressure pump body includes pump body A1 and pump body B4, which are respectively located on the left and right sides of the high-pressure pump body 3. A connecting plate 2 is also provided between the pump body A1 and the high-pressure pump body 3, so that the pump body A1, the connecting plate 2, the high-pressure pump body 3 and the pump body B4 are connected in sequence.

[0054] Pump body A1 is provided with pump chamber A101. An outer rotor A11 and an inner rotor A12 are movably arranged in pump chamber A101. An axial pump body A flow channel 100 is provided at the upper part of pump body A1, and the pump body A flow channel 100 is connected to pump chamber A101. A pump body A inlet 10 is opened at the top of pump body A1, which is connected to pump body A flow channel 100.

[0055] The lower part of the connecting plate 2 is provided with a through-type connecting plate channel 200;

[0056] The high-pressure pump body 3 has a high-pressure pump chamber 301 on the end face facing the connecting plate 2. The high-pressure pump chamber 301 has an outer rotor 31 and an inner rotor 32. A through-type high-pressure pump flow channel 300 is opened in the lower part between the bottom surface of the high-pressure pump chamber 301 and the other end face of the high-pressure pump body 3. A high-pressure outlet channel 302 is opened in the upper part between the bottom surface of the high-pressure pump chamber 301 and the other end face of the high-pressure pump body 3. A high-pressure pump outlet 30 is opened at the top of the high-pressure pump body 3, which connects to the high-pressure outlet channel 301.

[0057] Pump body B4 is provided with pump chamber B401. An outer rotor B41 and an inner rotor B42 are movably arranged in pump chamber B401. An axial pump body B flow channel 400 is provided at the upper part of pump body B4, and pump body B flow channel 400 is connected to pump chamber B401. A pump body B inlet 40 is opened at the top of pump body B4, which is connected to pump body B flow channel 400.

[0058] The shafts of outer rotors A11 and B41 are located on one side of the main shaft 5, and the shaft of the high-pressure pump outer rotor 31 is located on the other side of the main shaft 5. The shaft of outer rotor A11 forms an angle of +α with respect to the horizontal line, and the shaft of outer rotor B31 forms an angle of -α with respect to the horizontal line. α = 360° / 2N, where N is the number of teeth of the inner rotor.

[0059] like Figures 14-16 As shown, this invention utilizes the meshing principle of the internal and external gears of the cycloidal pump to ensure that the centers of the inner rotor A12, inner rotor B42, and high-pressure pump inner rotor 32 are coaxial with the main shaft 5 (i.e., Figures 14-16 (O0) The inlet and outlet are set by adjusting the eccentric position of the outer rotors of the three pump bodies. It should be noted that each outer rotor is coaxial with the pump chamber. Figures 14-16 China and Israel O 31 Indicates the center of the outer rotor 31 of the high-pressure pump, O 11 Indicates the center of the outer rotor A11, O 41 This indicates the center of the outer rotor B41.

[0060] The shaft O of the outer rotor A11 11 and the shaft O of the outer rotor B41 41 Located to the left of the axis O0 of the main shaft 5, the axis O of the high-pressure pump outer rotor 31 31 Located on the opposite side, hydraulic oil enters through pump body A inlet 10 and pump body B inlet 40 respectively, and then flows into pump chamber A101 and pump chamber B401 through pump body A flow channel 100 and pump body B flow channel 400 respectively. The hydraulic oil in pump chamber A101 and pump chamber B401 merges into high-pressure pump chamber 301, and then, under the action of the inner and outer rotors of the high-pressure pump, the flow is combined and pressurized, flowing from high-pressure outlet channel 302 to high-pressure pump outlet 30, realizing two-stage oil supply.

[0061] Based on the inherent meshing characteristics of gears, this invention utilizes the relative motion between two specially shaped gears (an internal gear and an external gear) to transport fluid. The size of the meshing cavity changes periodically, resulting in unstable oil flow at the inlet of the high-pressure booster pump. Taking a six-tooth inner rotor as an example, the outer rotor A11 is deflected 30° to the upper left and the outer rotor B41 is deflected 30° to the lower left, thus achieving compensation for the misalignment of the two low-pressure pump output cavities. This solves the flow pulsation caused by changes in pump cavity volume and provides a stable flow rate at the inlet of the high-pressure booster pump.

[0062] like Figure 13 As shown, the thickness of the inner rotor A12 and the inner rotor B42 is t, and the thickness of the inner rotor 32 of the high-pressure pump is 1.5~2.0t.

[0063] The booster cycloidal pump of this invention adopts a two-inlet, one-outlet design. Sufficient input flow is provided to the booster pump through two inlets. The inner and outer rotors of pump bodies A1 and B4 are exactly the same size. The inner and outer rotors of the high-pressure pump body 3 are designed with the same parameters as the inner and outer rotors of pump bodies A1 or B4, calculated based on input flow and efficiency. However, the rotor width of the high-pressure pump body 3 is 1.8 times the rotor width of pump bodies A1 or B4. The input flow of pump bodies A1 and B4 is 2Q, while the input flow of the high-pressure pump body 3 is 1.8Q. This design not only alleviates the inherent flow pulsation problem of gear pumps but also achieves a large flow rate for the cycloidal pump during the boosting process. Each cycloidal pump has a high-pressure zone, and the corresponding shaft is subjected to radial force, which can lead to shaft misalignment. This invention can alleviate the total radial force F0 of the shaft to the greatest extent. In this invention, according to... Figure 13 As shown, the forces acting on the main shaft 5 are as follows: the radial force F1 from the outlets of the low-pressure pump bodies A and B acting on the main shaft, the radial force F2 from the low-pressure junction area of ​​the high-pressure pump acting on the main shaft, and the radial force F3 from the high-pressure area of ​​the high-pressure pump acting on the main shaft.

[0064] Taking the above-mentioned rotor width embodiment as an example, F2 is calculated from the pressure P1 and the area to obtain F2=1.8F1, and F0=F3-(F1+F2+F1)=F3-3.8F1. This design can not only alleviate the inherent flow pulsation problem of gear pumps, but also realize the large flow of cycloidal pumps during the pressurization process. Through the layout design of two low-pressure pumps and a high-pressure booster pump, the alternating force layout of the main shaft of the existing multi-stage cycloidal pump is avoided, which alleviates the misalignment problem caused by the radial force imbalance of the main shaft, thereby maintaining a relatively stable alignment state, increasing the speed of the main shaft, and reducing vibration and leakage caused by misalignment during operation; reducing pump vibration noise and improving stability.

[0065] Furthermore, flow channels L3001 and R3002 are respectively provided at both ends of the flow channel 200, which can provide a specific flow direction for the hydraulic oil, ensure smoother hydraulic oil flow, avoid irregular turbulence of hydraulic oil, and help improve the working efficiency and stability of the booster cycloidal pump.

[0066] Furthermore, sealing grooves 202 are provided on both ends of the connecting plate 2.

[0067] Furthermore, positioning shoulders 201 are provided on both ends of the connecting plate 2.

[0068] Furthermore, a high-pressure pump body positioning step circle 304 coaxial with the main shaft 5 is provided at the edge of the high-pressure pump chamber 301 for fitting with the positioning shoulder 201 on the connecting plate 2.

[0069] Furthermore, a positioning structure and a sealing structure are provided between the high-pressure pump body 3 and the pump body B4.

[0070] The positioning step circle A102 is fitted onto the positioning shoulder 201 on one side of the connecting plate 2. The positioning shoulder 201 on the other side of the connecting plate 2 is connected to the positioning step circle 304 of the high-pressure pump body. The positioning shoulder 303 of the high-pressure pump body is connected to the positioning step circle B402 to form the positioning of the booster cycloidal pump.

[0071] The sealing structures at both ends of the connecting plate 2 and the sealing structure between the high-pressure pump body 3 and the pump body B4 can effectively prevent oil from leaking out from the pump body connection, ensure that the oil in the pump body can circulate in the system, reduce oil loss, maintain stable oil volume, and prevent the normal operation of the equipment from being affected by oil leakage.

[0072] Furthermore, pump body A1, connecting plate 2 and high-pressure pump body 3 are each provided with their own central holes, and pump body B4 is provided with a central blind hole for accommodating the main shaft 5; sliding bearings are provided between the main shaft 5 and each central hole and the central blind hole.

[0073] This invention has the following characteristics:

[0074] First, a booster cycloidal pump is adopted to effectively increase the working pressure and flow rate of the existing cycloidal pump during operation, thereby improving the pump's mechanical efficiency and volumetric efficiency.

[0075] Secondly, the booster cycloidal pump of the present invention can alleviate shaft misalignment, thereby improving the working stability and volumetric efficiency of the booster cycloidal pump and reducing pump leakage and vibration.

[0076] Third, by using the eccentric design of the outer rotor, the misalignment compensation between the two low-pressure pump output chambers is achieved, which solves the flow pulsation caused by changes in pump chamber volume and provides a stable flow at the inlet of the high-pressure booster pump.

[0077] This invention can effectively increase the working pressure and flow rate of cycloidal pumps, reduce volumetric losses and gear wear, and significantly reduce vibration and noise caused by pressure pulsation. Overall, it improves the comprehensive performance of existing gear pumps and extends their service life.

[0078] It should be stated that the above-described specific embodiments are merely preferred embodiments of the present invention and the technical principles employed. Those skilled in the art should understand that various modifications, equivalent substitutions, and variations can be made to the present invention based on the technical content disclosed in this application. However, such variations, as long as they do not depart from the spirit of the present invention, should be within the protection scope of the present invention. Furthermore, some terminology used in this specification and claims is not limiting but merely for ease of description.

Claims

1. A manifold type booster cycloidal pump, comprising a high-pressure pump body, a low-pressure pump body, and a main shaft, characterized in that, The low-pressure pump body includes pump body A and pump body B, which are respectively located on the left and right sides of the high-pressure pump body, and a connecting plate is provided between pump body A and the high-pressure pump body. The pump body A has a pump chamber A inside, and an outer rotor A and an inner rotor A are movably arranged inside the pump chamber A. An axial pump body A flow channel is provided at the upper part of the pump body A, and the pump body A flow channel is connected to the pump chamber A. A pump body A inlet is opened at the top of the pump body A, which is connected to the pump body A flow channel. The lower part of the connecting plate is provided with a through-type connecting plate flow channel; The high-pressure pump body has a high-pressure pump chamber on the end face facing the connecting plate, and a high-pressure pump outer rotor and a high-pressure pump inner rotor are provided in the high-pressure pump chamber; a through-type high-pressure pump flow channel is opened in the lower part between the bottom surface of the high-pressure pump chamber and the other end face of the high-pressure pump body, a high-pressure outlet flow channel is opened in the upper part between the bottom surface of the high-pressure pump chamber and the other end face of the high-pressure pump body, and a high-pressure pump outlet communicating with the high-pressure outlet flow channel is opened in the top of the high-pressure pump body; The pump body B is provided with a pump chamber B, and an outer rotor B and an inner rotor B are movably arranged in the pump chamber B. An axial pump body B flow channel is provided at the upper part of the pump body B, and the pump body B flow channel communicates with the pump chamber B. A pump body B inlet communicating with the pump body B flow channel is opened at the top of the pump body B. The axes of the outer rotor A and the outer rotor B are located on one side of the main shaft, and the axis of the outer rotor of the high-pressure pump is located on the other side of the main shaft. The axis of the outer rotor A forms an angle of +α with respect to the horizontal line, and the axis of the outer rotor B forms an angle of -α with respect to the horizontal line. α = 360° / 2N, where N is the number of teeth of the inner rotor.

2. The manifold type booster cycloidal pump according to claim 1, characterized in that, The thickness of the inner rotor A and inner rotor B is t, and the thickness of the inner rotor of the high-pressure pump is 1.5~2.0t.

3. A manifold type booster cycloidal pump according to claim 1 or 2, characterized in that, A flow channel guide groove L and a flow channel guide groove R are respectively provided at both ends of the flow channel.

4. A manifold type booster cycloidal pump according to claim 3, characterized in that, Sealing structures are also provided on both ends of the connecting plate.

5. A manifold type booster cycloidal pump according to claim 3, characterized in that, Positioning shoulders are provided on both ends of the connecting plate.

6. A manifold type booster cycloidal pump according to claim 5, characterized in that, A high-pressure pump body positioning step circle, coaxial with the main shaft, is provided at the edge of the high-pressure pump cavity for fitting with the positioning shoulder on the connecting plate.

7. A manifold type booster cycloidal pump according to claim 1 or 2, characterized in that, A positioning structure and a sealing structure are also provided between the high-pressure pump body and the pump body B.

8. A manifold type booster cycloidal pump according to claim 1 or 2, characterized in that, The pump body A, the connecting plate and the high-pressure pump body are each provided with their own central holes, and the pump body B is provided with a central blind hole for accommodating the main shaft; a sliding bearing is provided between the main shaft and each of the central holes and the central blind hole.

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