JP2000291575A - Root type fluid machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of noise and seizure by arranging an off-set part for preventing interference of a counterpart rotor or a rotor chamber, when inclining is generated on a foundation curvature for forming a tooth profile of a pair of rotors, whose crest gear and trough gear are engaged with each other by a torque or a load. SOLUTION: A root blower 1 is composed of an input pulley, a drive rotor 3, a driven rotor 5, and rotor shafts 7, 9. Each of rotors 3, 5 are composed of rotor shafts 7, 9 and rotor main bodies 19, 21. Two crest gears 23, 25 are formed on the rotor main bodies 19, 21, and trough gears 27, 29 are formed on both sides of each of the crest gears 23, 25, and are engaged with the crest gears 23, 25 as the counterparts. In this case, off-set parts 37, 39 are crowning- worked on both end sides of the rotor main body 19 of the drive rotor 3 from a foundation curvature to an inside. The axial direction cross sectional shape of each off-set part 37, 29 is formed in such a shape that an offset quantity is gradually increased toward an end part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roots type fluid machine used for a supercharger for a vehicle, for example.

[0002]

2. Description of the Related Art A roots type fluid machine 201 as shown in FIG. 5 is described in Japanese Patent Application Laid-Open No. Hei 8-200360, and another roots type fluid machine is disclosed in Japanese Patent Application Laid-Open No. 60-75793. Has been described.

[0003] A roots type fluid machine 201 shown in FIG. 5 has a pair of rotors 20 meshing with each other with teeth running parallel to the rotation center axis.
3, 205, and a rotor chamber 2 for rotatably accommodating them.
07, a timing gear set 209 that rotates the rotors 203 and 205 synchronously in opposite directions and engages them so as not to contact each other, and an input pulley 211.

The rotor 203 has bearings 213 at both ends.
The rotor 205 is supported at both ends by bearings 217 and 219.

A gap 22 is provided between the rotors 203 and 205.
1 are provided to prevent mutual interference and burn-in. The gap 221 is made as small as possible to minimize fluid leakage and efficiency loss.

The input pulley 211 is fixed to a rotor shaft 223 of the input rotor 203 and is connected to a pulley on the engine side via a belt. The rotation of the input pulley 211 is controlled by the rotor 20 via the timing gear set 209.
3. Rotate 205.

When the rotors 203 and 205 rotate, the fluid is sucked into the rotor chamber 207 from the suction port and is discharged from the discharge port.

A roots type fluid machine disclosed in Japanese Patent Application Laid-Open No. 60-75793 is disclosed in FIG.
In order to prevent interference between the rotors 225 and 227 and between the rotors 225 and 227 and the rotor chamber, the respective outer circumferences are offset inward from the basic curves.

As shown in FIG. 6, a normal 231 passing through a point 229 on the basic curve, a rotor 225,
227 are determined according to the intersection angle α between a line 237 connecting the center points 233 and 235 and the point 229.

As shown in FIG. 7, in the basic curves of the rotors 225 and 227, the peak teeth 239 are epicycloidal curves and the valleys 241 are hypocycloidal curves.

These curves intersect each other at a position where the rotation angle β of the rotors 225 and 227 becomes 45 °, and the intersection angle α becomes maximum at a position where the rotation angle 45 °.

Also, as shown in FIG. 6, when an error of the rotation angle γ occurs in the rotor 227, as shown by a broken line, the rotor 225 at the rotation angle of 45.degree. Approach and interference is likely to occur.

Therefore, the largest offset is performed at the position where the rotation angle is 45 °.

[0014]

In the root type fluid machine 201 shown in FIG. 5, a load due to the tension of the belt is applied to the rotor shaft 223 of the input-side rotor 203 via the input pulley 211. The rotor 203 is inclined by a slight clearance (play) between the bearings 213 and 215.

Further, even when a roots-type fluid machine is used as a turbine (expander), the rotor from which the rotation is taken out receives a torque from an output pulley or an output gear, thereby causing an inclination.

When such an inclination occurs, the rotor 20
3 and 205 easily interfere with each other, generating noise and burning.

However, in order to prevent interference, the rotor 2
When the gap 221 between 03 and 205 is widened, leakage of fluid increases, and efficiency decreases.

The inclination and phase error of the rotor change under the influence of many factors such as the dimensional accuracy of each rotor, the accuracy (grade) of the bearing, and the backlash. In the case of the root type fluid machine shown in FIG.
5 and 227, the interference between the mountain tooth 239 and the valley tooth 241 (hypocycloid curve portion) of the mating rotor starts from the rotation angle of about 20 ° before the rotation angle β becomes 45 °. .

Also in this case, if the offset amount is further increased in order to prevent such interference, fluid leakage increases and efficiency decreases.

Further, in any of the conventional examples, in order to reduce the inclination of the rotor, the dimensional accuracy of the rotor is particularly increased,
Alternatively, using a bearing with a small clearance greatly increases the cost.

Accordingly, an object of the present invention is to provide a roots-type fluid machine that prevents interference due to the inclination of the rotor.

[0022]

According to a first aspect of the present invention, there is provided a roots type fluid machine in which each of the root-type fluid machines has an axial mountain tooth and a valley tooth alternately in a rotational direction, and meshes with each other. A pair of rotors, a timing gear set for synchronously rotating the rotors and meshing with each other so as not to contact each other, a rotor chamber for rotatably housing each rotor, and a rotor chamber And a casing having a fluid inlet and a fluid outlet communicating with the fluid, for inputting torque via one of the rotors or extracting torque therefrom. The basic curve forming the tooth profile of the rotor to be formed is provided with an offset portion for preventing interference with the counterpart rotor or the rotor chamber when the torque or load causes an inclination. Features.

As described above, in the roots-type fluid machine according to the first aspect, since the basic curve of the rotor for transmitting and receiving the torque is provided with the offset portion (relief portion) in the inward direction, the rotor has the torque or the torque. Even if it is inclined by receiving a load, interference with the other rotor or the rotor chamber is prevented, and noise and image sticking are prevented.

Therefore, it is not necessary to increase the gap between the rotors to prevent interference, so that leakage of fluid and reduction in efficiency are prevented.

Also, according to the displacement amount accompanying the inclination of the rotor,
If the amount of offset is selected to be minimum, interference can be prevented while minimizing fluid leakage and reduction in efficiency.

Further, in order to reduce the inclination of the rotor, it is not necessary to particularly increase the dimensional accuracy of each rotor and it is not necessary to use a bearing having a small clearance, so that a large increase in cost can be avoided.

According to a second aspect of the present invention, there is provided the roots type fluid machine according to the first aspect, wherein the offset portion of the rotor for transmitting and receiving the torque has an axial end receiving the torque or the load and the other end. Are provided at one or both of the axial end portions, and an effect equivalent to the configuration of claim 1 is obtained.

When the rotor is inclined due to the application of torque or load, the clearance between the rotor and the counterpart rotor becomes smaller at the axial end on which the rotor is applied. In addition, if an inclination occurs around the center in the axial direction, the other end in the axial direction may be rotatable.
The gap with the rotor or the gap with the rotor chamber may be reduced.

Therefore, this configuration in which offset portions are provided at both ends in accordance with the amount of displacement generated at both ends in the axial direction of the rotor can provide a large interference prevention effect.

In addition, since an offset is given only to a necessary portion according to the displacement amount due to the inclination of the rotor,
While minimizing fluid leakage and reduced efficiency,
Can be prevented.

[0031] The invention of claim 3 is claim 1 or claim 2.
3. The root-type fluid machine according to claim 1, wherein an offset portion of the rotor for transmitting and receiving torque is provided at a crossing point between a mountain tooth and a valley tooth. The same effect as that of the configuration is obtained.

In addition to this, as shown in FIG. 7, the rotor interference occurs at the intersection (the inflection portion where the type of the basic curve changes) where the basic curve of the mountain tooth and the basic curve of the valley cross. Since it is the largest, the configuration of claim 3 in which an offset portion is provided at this location can provide a large interference prevention effect.

Furthermore, since the necessary amount of offset is applied to the portion where the displacement amount due to the inclination of the rotor is the largest, the leakage of the fluid and the decrease in the efficiency are minimized while minimizing the leakage. Can be prevented.

According to a fourth aspect of the present invention, there is provided the first to third aspects.
5. The roots-type fluid machine according to claim 1, wherein the rotor for transmitting and receiving torque has a cross-sectional shape in the axial direction in which an offset amount increases toward an axial end. Thus, the same effect as any of claims 1 to 3 is obtained.

In addition, since the amount of displacement of the rotor due to the inclination becomes larger toward the end in the axial direction, the amount of offset increases toward the end in the axial direction. This configuration has a large effect of preventing interference.

As described above, the necessary offset amount is determined to the minimum according to the displacement amount due to the inclination of the rotor.
While minimizing fluid leakage and reduced efficiency,
Can be prevented.

According to a fifth aspect of the present invention, there is provided a roots-type fluid machine having a pair of rotors each having axially toothed teeth and valley teeth alternately in the rotational direction, and meshing with each other. A timing gear set for rotating the respective rotors so as to be engaged with each other so as not to contact each other, and a rotor for rotatably accommodating the respective rotors.
A rotor having a rotor chamber and a casing having a fluid suction port and a discharge port communicating with the rotor chamber, and a torque type for inputting torque or extracting torque through one of the rotors. A fluid machine, wherein an offset portion for preventing interference with a mating rotor is provided on a basic curve forming a valley portion of the rotor.

As described above, according to the roots type fluid machine of the fifth aspect, the basic curve (for example,
The hypocycloid curve) is provided with an offset portion for preventing interference with the counterpart rotor. Therefore, even if the rotor is inclined or a phase error is generated in the rotor, FIGS. Unlike the conventional example, even when the rotation angle is smaller than 45 degrees (for example, a rotation angle of 20 degrees), interference between the offset valley teeth and the mountain teeth of the mating rotor does not occur.

Therefore, in order to prevent rotor interference,
Since it is not necessary to particularly increase the offset amount, it is possible to prevent the rotor from interfering with the minimum offset amount while minimizing fluid leakage and efficiency reduction.

Further, in order to reduce the inclination of the rotor, it is not necessary to particularly increase the dimensional accuracy of each rotor and it is not necessary to use a bearing having a small clearance, so that a large increase in cost can be avoided.

[0041]

1 and 2 show a first embodiment of the present invention.
An embodiment (root blower 1) will be described.

This root blower 1 (root type fluid machine)
Has the features of claims 1, 2, 3, and 4, and is used for a supercharger of a vehicle. FIG. 1 shows a roots blower 1, and members and the like without reference numerals are not shown.

The root blower 1 includes an input pulley, a drive rotor 3 (rotor for transmitting and receiving torque), a driven rotor 5, rotor shafts 7, 9, a casing 11, and a timing gear assembly. It is composed of

The input pulley is connected to the rotor shaft 7 of the drive rotor 3. The input pulley is connected to a pulley on the engine side via a belt, and is driven to rotate by the driving force of the engine.

The casing 11 is provided with a rotor chamber 13 and a suction port 15 and a discharge port 17 communicating therewith.

Further, a gear chamber provided with an oil reservoir is formed adjacent to the casing 11, and the timing gear set is accommodated in this gear chamber.

The rotors 3, 5 are housed in a rotor chamber 13.

The drive rotor 3 comprises a rotor shaft 7 and a rotor body 19, and the driven rotor 5 has a rotor.
It comprises a rotor shaft 9 and a rotor body 21.

The rotor bodies 19 and 21 are formed with two mountain teeth 23 and 25 parallel to the rotation center axes of the rotors 3 and 5, respectively. The valley teeth 27, 29 are formed on both sides of each of the mountain teeth 23, 25.
5 meshes with the valley teeth 29 and 27 of the other party.

The basic curve of each mountain tooth 23, 25 is a theoretical cycloidal curve, and the basic curve of each valley tooth 27, 29 is a hypocycloidal curve.

The mountain teeth 23 and 25 are formed with hollow portions 31 and 33 penetrating in the axial direction, respectively, to reduce the moment of inertia of the rotors 3 and 5 and to reduce the root blower 1.
(Supercharger) efficiency and engine fuel efficiency are improved.

Each of the rotor shafts 7 and 9 is provided with a rotor body 19 and 2
On both sides of 1 are mounted bearings 11 on the casing 11.

By forming these bearings in the form of seals or by disposing seals between the rotor shafts 7 and 9 and the casing 11, air from the rotor chamber 13 to the outside can be obtained. Leakage and oil leakage from the gear chamber to the rotor chamber 13 are prevented.

The timing gear set is composed of a pair of timing gears meshing with each other, and these timing gears are connected to the rotor shafts 7 and 9, respectively.

The driving force of the engine input from the pulley is
The rotors 3 and 5 are rotated via a timing gear set, and the timing gear set synchronously rotates the rotors 3 and 5 in opposite directions so as not to contact each other.

The root blower 1 discharges the air sucked from the suction port 15 through the discharge port 17 and supplies the air to the engine.

As shown in FIG. 1, a load 35 due to the tension of the belt is applied to the drive rotor 3 via the input pulley.
The drive rotor 3 is inclined in the direction of the load 35 by the clearance of the bearing. Further, since the inclination is generated at a substantially central portion in the axial direction, displacement occurs in the opposite direction at the opposite end of the drive rotor 3.

FIG. 1 shows that the rotation angle β of each of the rotors 3 and 5 is 45 °.
When the rotor 3 is tilted, the rotors 3 and 5 come closest to each other at a position where the rotation angle is about 45 ° as described above, and interference easily occurs.

FIG. 2 is a drawing showing the drive rotor 3 cut along a plane having a rotation angle of 45 °. This cutting part is a tooth 23
And the connecting portion of the valley teeth 27. Therefore, it becomes an intersection (inflection portion) between the theoretical cycloid curve portion and the hypocycloid curve portion.

As shown in FIG. 2, the drive rotor 3 has crown portions on both ends of the rotor body 19 and offset portions 37 and 39 inward from the basic curve.

The axial cross-sectional shape of each of the offset portions 37 and 39 is such that the offset amount gradually increases toward the end.

The offset unit 37 is on the input pulley side,
The offset portion 39 is on the opposite side. Since the displacement amount due to the inclination is larger in the input side offset portion 37 than in the opposite side offset portion 39, the offset amount and the axial offset range are smaller than the offset portion 39.
Are enlarged.

Therefore, even if the drive rotor 3 is inclined under the load 35, the provision of the offset portions 37 and 39 prevents the drive rotor 3 from interfering with the driven rotor 5.

The offset amount of the offset portions 37 and 39 and the range of the offset (width from the end face) are minimized in accordance with the displacement amount of both ends of the rotor body 19 due to the inclination of the drive rotor 3. Has been selected.

Further, a relief portion is provided on the inner periphery of the rotor chamber 13 so that even if the drive rotor 3 is inclined, interference with the rotor chamber 13 is prevented by the relief portion. .

Further, a coating is applied to the surface of each of the rotor bodies 19 and 21 so that the gap between the rotor bodies 19 and 21 and the teeth 23 and 25 are formed. The gap with the rotor chamber 13 is adjusted to a predetermined value.

This gap adjustment by coating reduces air leakage and improves the volumetric efficiency of the roots blower 1.

The root blower 1 (supercharger) is thus constructed.

As described above, even if the drive rotor 3 is tilted by the input torque, the root blower 1
The offset portions 37 and 39 provided in the rotor body 19 prevent interference with the driven rotor 5, and the relief portions provided in the rotor chamber 13 also prevent interference with the rotor chamber 13. .

Therefore, to prevent interference, each rotor 3, 5
Since there is no need to unnecessarily widen the gap between them, air leakage and reduction in efficiency are prevented.

Further, since the offset portions 37 and 39 are provided at both ends of the rotor main body 19 in which the displacement occurs with the inclination of the drive rotor 3, the effect of preventing interference is large.

As described above, the interference between the rotors 3 and 5 is caused by the intersection (inflection) at which the respective basic curves of the mountain tooth and the valley cross.
Since the offset portions 37 and 39 are provided at this position corresponding to a rotation angle of 45 °, the effect of preventing interference increases accordingly.

Since the displacement of the drive rotor 3 due to the inclination becomes larger toward the end in the axial direction, the offset portion 3
By increasing the offset amounts of 7 and 39 toward the end in the axial direction, a greater interference prevention effect can be obtained.

As described above, the offset portions 37, 3
Since the offset amount 9 is set to the minimum necessary value in accordance with the displacement amount of each part of the drive rotor 3, interference can be prevented while minimizing fluid leakage and reduction in efficiency.

Further, in order to reduce the inclination of the drive rotor 3, it is not necessary to particularly increase the dimensional accuracy of the rotors 3, 5 or to use bearings having a small clearance. Large rises in the air are avoided.

Next, a second embodiment (root blower) of the present invention will be described with reference to FIGS.

This roots blower (roots type fluid machine) has the features of claim 5. FIG. 3 shows a rotor 41 used in the root blower, and members and the like not given reference numerals are not shown.

FIG. 3 shows the outer shape (cross-sectional shape: tooth shape) of the rotor 41 (rotor main body).

The rotor main body is formed with two mountain teeth 43, 43 parallel to the rotation center axis of the rotor.
The valleys 45, 45 are formed between 3, 43.

The basic curve of the mountain tooth 43 is a theoretical cycloidal curve, and the basic curve of the valley tooth 45 is a hypocycloidal curve.

The outermost curves 47 show the respective basic curves, in which there is no gap between the rotors.

The inner curve 49 is offset from the curve 47 inward to provide a constant gap between the rotors.

A curve 51 corresponds to the conventional example shown in FIGS. 6 and 7 and shows a state in which the curve 49 is further offset, and as indicated by an arrow 53, at a position where the rotation angle β = 45 °. The offset amount is maximum.

On the other hand, the curve 55 is of this embodiment, and the hypocycloid curve portion of the valley 45 is further offset from the curve 51.

FIG. 4 is a graph in which the change in the rotor gap with respect to the rotation angle β of the rotor 41 is actually measured and plotted.

The straight line graph 57 shows the gap when the outer shape of the rotor is set to the curve 49. Thus, the gap between the rotors is constant (0.degree. 08m
m).

The graph 59 shows the gap when the outer shape of the rotor is set to the curve 51 of the conventional example.

The graph 61 shows the rotor 41 of the embodiment.
(Curve 55).

The graph 61 of the embodiment and the graph 5 of the conventional example
In comparison with No. 9, in the rotor 41 of the embodiment in which the valley teeth 45 are offset, the gap is wider than the conventional example between the rotation angle of 0 ° smaller than the rotation angle of 45 ° and the rotation angle of about 25 °. You can see that it is.

Therefore, the rotor 41 is inclined by factors such as the dimensional accuracy of the rotor 41 and the mating rotor, the accuracy (grade) of the bearing, the backlash, or the like, or
Even if a phase error occurs in the rotor 41, the hypocycloid curve portion (valley tooth 45) is offset so that the rotation angle β before the rotation angle β becomes 45 °, for example, the rotation angle 20
The rotor does not interfere even with the angle of about.

Thus, the roots blower of the second embodiment is configured.

This roots blower, as described above,
Since the hypocycloid curve forming the valley teeth 45 of the rotor 41 is offset to prevent interference with the counterpart rotor, even if the rotor 41 is inclined, the hypocycloid curve differs from that of the prior art shown in FIGS. In contrast, in a small rotation angle range of 20 ° or less, no interference occurs between the valley tooth 45 and the mountain tooth of the mating rotor.

Therefore, in order to prevent rotor interference,
Since there is no need to make the overall offset amount particularly large,
The minimum offset minimizes fluid leakage and loss of efficiency while preventing rotor interference.

Further, in order to reduce the inclination of the rotor, it is not necessary to particularly increase the dimensional accuracy of each rotor or to use a bearing having a small clearance, so that a large increase in cost can be avoided.

In the present invention, the torque transmission mechanism for connecting the rotor for transmitting and receiving torque to the outside may be any of a belt type transmission mechanism, a gear type transmission mechanism, and a chain type transmission mechanism.

Therefore, the torque transmitting member connected to the rotor may be any of a pulley, a gear and a sprocket.

The root-type fluid machine of the present invention can be used not only for applications such as a blower for transferring a fluid by rotating the rotor but also for moving the fluid through the casing. It may be used for a rotating turbine (expander).

With such a configuration, the rotation take-out side row
Even if the rotor is tilted by receiving torque from an output pulley, an output gear, an output sprocket, etc., as described above, in the roots type fluid machine of the present invention, the interference of the rotor is prevented by the offset. You.

[0099]

According to the roots type fluid machine of the first aspect, the offset portion is provided in the basic curve of the rotor for transmitting and receiving the torque. −
Interference with the rotor or the rotor chamber is prevented.

Therefore, it is not necessary to widen the gap between the rotors to prevent interference, so that leakage of the fluid and reduction in efficiency are prevented.

If the minimum offset amount is selected according to the displacement amount due to the inclination of the rotor, interference can be prevented while minimizing the leakage of the fluid and the decrease in efficiency.

Further, in order to reduce the inclination of the rotor, it is not necessary to particularly increase the dimensional accuracy of each rotor and it is not necessary to use a bearing having a small clearance, so that a large increase in cost can be avoided.

According to the second aspect of the present invention, the same effect as that of the first aspect is obtained, and a large interference preventing effect is obtained by providing offset portions on both sides according to the amount of displacement generated at both ends of the rotor. Is obtained.

Further, by offsetting only necessary portions in accordance with the displacement amount, it is possible to prevent the rotor from interfering while minimizing the leakage of the fluid and the decrease in efficiency.

The invention of claim 3 is the invention of claim 1 or claim 2.
In addition to obtaining the same effect as the configuration described above, a great interference prevention effect can be obtained by providing the offset portion at the intersection of the mountain tooth and the valley tooth where the basic curve of the mountain tooth and the basic curve of the valley cross.

Further, since a necessary amount of offset is applied to a portion where the displacement amount of the rotor is the largest, it is possible to prevent the interference of the rotor while minimizing the leakage of the fluid and the decrease in the efficiency. it can.

The invention of claim 4 is the invention of claims 1 to 3
By obtaining the same effect as any one of the above, and increasing the offset amount toward the axial end where the displacement amount increases, a large interference prevention effect can be obtained.

Further, since the necessary offset amount is determined according to the displacement amount due to the inclination of the rotor, the interference of the rotor can be prevented while minimizing the leakage of the fluid and the decrease in the efficiency. .

The roots-type fluid machine according to the fifth aspect is different from the prior art shown in FIGS. 6 and 7 in that the basic curve of the valley tooth portion is offset, so that the rotor can be rotated even in a small rotation angle range. Interference is prevented.

Therefore, it is not necessary to particularly increase the offset amount in order to prevent the rotor interference. Therefore, it is possible to minimize the leakage of the fluid and the decrease in the efficiency by the minimum offset while minimizing the interference of the rotor. Can be prevented.

Further, in order to reduce the inclination of the rotor, it is not necessary to particularly increase the dimensional accuracy of each rotor and it is not necessary to use a bearing having a small clearance, so that a large increase in cost can be avoided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a view showing tooth forms of a rotor and the like used in a second embodiment of the present invention and a conventional example.

FIG. 4 is a graph showing a gap between rotors of the second embodiment and a conventional example.

FIG. 5 is a sectional view showing a first conventional example.

FIG. 6 is a view showing a tooth form of a rotor used in a second conventional example.

FIG. 7 is a view showing a tooth form of a rotor used in a second conventional example.

[Explanation of symbols]

Reference Signs List 1 root blower (root type fluid machine) 3 drive rotor (rotor for transmitting and receiving torque: input side rotor) 5 driven rotor (partner rotor) 11 casing 13 row Chamber 15 suction port (inflow port) 17 discharge port (outflow port) 23, 25 mountain tooth 27, 29 valley tooth 37, 39 offset part 41 rotor 43 mountain tooth 45 valley tooth 55 hypocycloid curve part of valley tooth 45 Offset part provided in

Claims (5)

[Claims] 1. A pair of rotors each having an axial mountain tooth and a valley tooth alternately in the rotation direction, and a pair of rotors meshing with each other with a mountain tooth and a valley tooth, and rotating each rotor synchronously. A timing gear set that meshes with each other so as not to contact each other; a rotor chamber that rotatably houses each rotor; and a casing that has an inlet and an outlet for a fluid that communicates with the rotor chamber. A root-type fluid machine that inputs torque through one of the rotors or takes out the torque, the basic curve forming the tooth profile of the rotor that transmits and receives the torque,
A roots type fluid machine having an offset portion for preventing interference with a counterpart rotor or a rotor chamber when an inclination occurs due to the torque or load. 2. The invention according to claim 1, wherein the offset part of the rotor for transmitting and receiving the torque is provided at one or both of the axial end receiving the torque or the load and the axial end on the other side. A roots-type fluid machine provided. 3. The invention according to claim 1, wherein an offset portion of a rotor for transmitting and receiving torque is provided at a crossing point between a mountain tooth and a valley tooth. Roots type fluid machine. 4. The invention according to claim 1, wherein an axial cross-sectional shape of the rotor for transmitting and receiving torque increases an offset amount toward an axial end. A roots-type fluid machine characterized by having a shape of 5. A pair of rotors each having an axial mountain tooth and a valley tooth alternately in the rotational direction, and a pair of rotors meshing with each other with a mountain tooth and a valley tooth, and rotating each rotor synchronously. A timing gear set that meshes with each other so as not to contact each other, a rotor chamber that rotatably houses each rotor, and a casing that has a suction port and a discharge port for a fluid that communicates with the rotor chamber. A root-type fluid machine for inputting torque or extracting torque via one of the rotors, wherein a mating rotor is formed on a basic curve forming a valley tooth portion of the rotor. A roots type fluid machine comprising an offset portion for preventing interference with the fluid.