JP2000283185A - Fluid coupling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid coupling capable of extensively reducing drag torque without extensively lowering transmission torque. SOLUTION: An impeller 412 of a pump 41 is formed inclining to the downstream in the rotating direction toward an outer end in the diametrical direction from an inner end in the diametrical direction and a runner 422 of a turbine 42 is constituted of a first part formed inclining to the downstream in the rotating direction from an outer end in the diametrical direction and a second part formed continuously with the first part and inclining to the upstream in the rotating direction toward an inner end in the diametrical direction in a fluid coupling furnished with the pump 41 installed on an input shaft and the turbine 42 arranged opposed to the pump 41.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid coupling (fluid coupling) for transmitting rotational torque of a motor.
Regarding improvement.

[0002]

2. Description of the Related Art Fluid couplings have been conventionally used as power transmission couplings for ships, industrial machines, and automobiles. The fluid coupling includes a pump connected to a crankshaft (input shaft as a fluid coupling) of a prime mover, for example, a diesel engine, and an output shaft disposed opposite to the pump and arranged on the same axis as the input shaft. A working fluid is filled in the pump and the turbine. In such a fluid coupling, the pump includes a bowl-shaped pump shell connected to the input shaft, and a plurality of impellers radially arranged in the pump shell, and the turbine is a turbine mounted on the output shaft. The turbine includes a shell and a plurality of runners radially arranged in the turbine shell. The impeller and the runner are formed in a linear radial shape. The reason that the impeller and the runner are formed linearly is that the input torque and the output torque are one pair even if the impeller and the runner are curved or bent or are linear in a fluid coupling in which the torque amplifying action is not performed. This is to prevent the flow path resistance from increasing by forming the impeller and the runner by bending or bending.

[0003]

FIG. 6 shows the relationship between the rotational speed difference between the input and output shafts in the fluid coupling and the output torque (transmitted torque). In FIG. 6, a dashed line indicates a torque transmission characteristic of a conventional fluid coupling in which an impeller of a pump and a runner of a turbine are formed in a linear radial shape. When a fluid coupling having such characteristics is installed in a vehicle drive device, the engine is driven while the vehicle is stopped and the transmission gear of the transmission is engaged, that is, the input shaft rotates and the output shaft stops. In the state in which it is on, it has a drag torque due to its characteristics. The drag torque generally refers to a transmission torque in a state where the engine is operated at an idling rotational speed (for example, 500 rpm). This drag torque sets the design point of the fluid coupling to the rotational speed ratio at which the efficiency is maximized, that is, the rotational speed ratio between the pump and the turbine from 0.95 to 0.9.
In eighth place, it will be quite large. If the drag torque is large, the idling operation of the engine becomes extremely unstable, and this unstable rotation causes abnormal vibration in the drive system. In addition, the large drag torque causes deterioration of fuel efficiency during idling operation.

In order to reduce the drag torque described above, basically, the diameter of the pump and turbine, that is, the size of the fluid coupling must be reduced. When the size of the fluid coupling is reduced to suppress the generation of the drag torque to a small value, the torque transmission characteristic becomes as shown by a two-dot chain line in FIG. As is clear from FIG. 6, in the fluid coupling with the reduced size indicated by the two-dot chain line, a sufficient output torque (transmission torque) cannot be obtained even if the rotation speed difference between the input shaft and the output shaft increases. . That is, in the conventional fluid coupling, when the size is reduced to reduce the drag torque, the transmission torque is greatly reduced, and when the size is increased to obtain the required transmission torque, the drag torque is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and a main technical problem thereof is to provide a fluid coupling capable of greatly reducing drag torque without lowering transmission torque.

[0006]

According to the present invention, a pump shell mounted on an input shaft and a plurality of impellers disposed in the pump shell are provided in order to solve the main technical problem. A turbine shell mounted on an output shaft disposed opposite to the pump and arranged coaxially with the input shaft, and a plurality of runners disposed in the turbine shell. Wherein the impeller of the pump comprises:
The runner of the turbine is formed to be inclined from the radially outer end to the radially outer end in the downstream direction in the rotational direction, and the runner of the turbine is formed to be inclined from the radially outer end to the downstream in the rotational direction. A fluid coupling is provided, comprising: a portion; and a second portion formed continuously with the first portion and inclined in a rotationally upstream direction toward a radially inner end.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of a fluid coupling constructed according to the present invention will be described below in more detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a drive device in which a fluid coupling constructed according to the present invention is disposed between an automobile engine and a friction clutch. The drive device in the illustrated embodiment includes an internal combustion engine 2 as a prime mover, a fluid coupling 4 and a friction clutch 6 configured according to the present invention. The internal combustion engine 2 is a diesel engine in the illustrated embodiment, and a pump side, described later, of the fluid coupling 4 is attached to an end of the crankshaft 21.

The fluid coupling 4 is provided in a fluid coupling housing 40 which is attached to a housing 22 mounted on the diesel engine 2 by fastening means such as bolts 23 or the like. The fluid coupling 4 in the illustrated embodiment includes a pump 41 and a turbine 4 that is disposed to face the pump 41.
2 and a casing 43 connected to the pump 41.

The pump 41 has a bowl-shaped pump shell 411.
And a plurality of impellers 412 radially arranged in the pump shell 411.
1 is attached to the casing 43 by fixing means such as welding. The casing 43 is provided with a bolt 441 and a nut 4 on an outer peripheral portion of a drive plate 44 in which an inner peripheral portion is mounted on the crankshaft 21 by the bolt 24.
42 and the like. Thus, the pump shell 411 of the pump 41 is connected to the crankshaft 2 via the casing 43 and the drive plate 44.
Connected to 1. Therefore, the crankshaft 21 is connected to the fluid coupling 4
Functions as an input shaft for In the illustrated embodiment,
As shown in FIG. 2, the impeller 412 of the pump 41 is formed so as to be inclined from the radial inner end to the radial outer end toward the downstream side in the rotational direction of the pump 41 as indicated by an arrow, and the inner surface of the bowl-shaped pump shell 411. It is provided in. A ring gear 45 for starting is engaged with the drive gear of a starter motor (not shown) on the outer periphery of the drive plate 44.

The turbine 42 includes a bowl-shaped turbine shell 421 disposed to face the pump shell 411 of the pump 41 and a plurality of runners 422 radially disposed in the turbine shell 421. Have. The turbine shell 421 is attached to a turbine hub 47 spline-fitted to an output shaft 46 provided on the same axis as the crankshaft 21 as the input shaft by welding or other fixing means. Runner 422 of turbine 42
Is a turbine 42 indicated by an arrow from the outer end as shown in FIG.
First portion 42 formed to be inclined downstream in the rotation direction of the first portion 42
2a and a second portion formed continuously with the first portion 422a and inclined toward the inner end toward the upstream side in the rotation direction of the turbine 42.
And a portion 422b of the turbine shell 421 provided on the inner surface of the bowl-shaped turbine shell 421.

Referring to FIG. 1, the fluid coupling 4 in the illustrated embodiment includes a hydraulic pump 50. The hydraulic pump 50 is connected to the fluid coupling housing 4.
The friction clutch 6 mounted on the clutch housing 60 is attached to a clutch housing 60, which will be described later, by a fixing means such as a bolt 51 and is disposed on the pump housing 52. The hydraulic pump 50 is configured to be rotationally driven by a pump hub 48 attached to a pump shell 411 of the pump 41, and supplies a working fluid into the pump 41 and the turbine 42 via a fluid path (not shown). I do. In addition, the pump hub 48 is rotatably supported by a bearing 490 on a cylindrical shaft 49 that is inserted through the periphery of the output shaft 46.

Next, the friction clutch 6 will be described. The friction clutch 6 includes a clutch housing 60 mounted on the fluid coupling housing 40 by bolts 61.
It is arranged in. The friction clutch 6 in the illustrated embodiment includes a clutch drive plate 62 mounted on the output shaft 46 of the fluid coupling 4 and a transmission shaft 63 (in the illustrated embodiment, disposed on the same axis as the output shaft 46). , An input shaft of a transmission (not shown)), a driven plate 66 attached to a clutch hub 64 spline-fitted to the transmission shaft 63 and having a clutch facing 65 mounted on the outer peripheral portion, and a clutch drive A pressure plate 67 that presses against the plate 62, a diaphragm spring 68 that urges the pressure plate 67 toward the clutch drive plate 62, and an intermediate portion of the diaphragm spring 68 that engages with an inner end of the diaphragm spring 68. Fulcrum 6
A release bearing 69 that operates as 81 and a clutch release fork 70 that operates the release bearing 69 in the axial direction are provided. In the friction clutch 6 configured as described above, the pressure plate 67 is pressed toward the clutch drive plate 62 by the spring force of the diaphragm spring 68 in the illustrated state, and therefore, the clutch facing mounted on the driven plate 66 The power transmitted to the output shaft 46 of the fluid coupling 4 when the clutch 65 is pressed by the clutch drive plate 62 is transmitted to the transmission shaft 63 via the clutch drive plate 62 and the driven plate 66. To interrupt this power transmission, hydraulic pressure is supplied to a slave cylinder (not shown) to operate the clutch release fork 70, and the release bearing 69 is moved to the left in FIG.
The operation is performed as indicated by the dashed line, and the power transmission from the clutch drive plate 62 to the driven plate 66 is shut off by releasing the pressing force on the pressure plate 67.

The drive unit equipped with the fluid coupling constructed according to the present invention is constructed as described above, and its operation will be described below. The driving force generated on the crankshaft 21 (input shaft) of the diesel engine 2 is transmitted to the casing 43 of the fluid coupling 4 via the drive plate 44. Casing 43 and pump shell 41 of pump 41
1 is formed integrally, so that the pump 41 is rotated by the driving force. When the pump 41 rotates, the working fluid in the pump 41 is centrifugally moved to the impeller 41.
It flows toward the outer periphery along 2 and flows into the turbine 42 side as indicated by the arrow. The working fluid flowing into the turbine 42 flows toward the center and returns to the pump 41 as indicated by the arrow. As described above, the working fluid in the pump 41 and the turbine 42 circulates in the pump 41 and the turbine 42, so that the driving torque of the pump 41 is transmitted to the turbine 42 via the working fluid. Turbine 42
The driving force transmitted to the side is transmitted to the output shaft 46 via the turbine shell 421 and the turbine hub 47, and further transmitted to a transmission (not shown) via the friction clutch 6.

FIG. 3 shows the relationship between the flow of hydraulic oil inside the fluid coupling and the driving torque of the pump and the turbine.
This will be described with reference to FIG. First, a conventional fluid coupling in which the impeller 101 of the pump 10 and the runner 111 of the turbine 11 are both formed in a linear radial shape will be described with reference to FIG. FIG. 5 is an exploded view of the pump 10 and the turbine 11. For simplification, only the pump 10 has an angular velocity (ω) (ω = v2x ′ / r2, where v2x ′ is the rotation of the working fluid at the outlet of the pump 10. A description will be given of a state in which the direction speed component, r2, is rotationally driven in the direction indicated by the arrow with the average radius of the outlet of the pump 10 and the turbine 11 is stopped. When the torque of T1 is given to the pump 10,
The working fluid that has flowed into the pump 10 at the inflow speed (v1 ′) from the direction of the arrow has its circumferential speed changed by the rotational speed component (v2x ′) by the pump 10 that is rotationally driven at the angular speed (ω) in the direction indicated by the arrow. Accelerated to The working fluid whose circumferential speed has been accelerated to the rotational speed component (v2x ') in this way is the outflow speed combined with the radial speed component (v2y') due to the centrifugal fluid pressure generated by the rotation of the pump 10. It flows out of the pump 10 in the direction indicated by the arrow at (v2 '). Outflow speed (v2
The working fluid that has flowed out in the direction indicated by the arrow in ′) and has flowed into the turbine 11 hits the runner 111 of the turbine 11 and has a circumferential speed (rotational speed component) of zero (0), and the outflow speed (v1 ′) It flows out of the turbine 11 in the direction indicated by the arrow and flows into the pump 10 again. At this time, the runner 111 of the turbine 11 receives the torque (T1) from the working fluid. Thus, when the torque of (T1) is given to the pump 10, the torque (T1) is transmitted to the turbine 11. The working fluid returned to the pump 10 has a torque (T
In 1), the vehicle is accelerated to the circumferential speed (v2 '), and the above operation is repeated. The conventional fluid coupling operated in this manner has a torque transmission characteristic indicated by a chain line in FIG.

Next, the fluid coupling 4 constructed according to the present invention will be described with reference to FIG. FIG. 4 shows the pump 4
1 and the turbine 42 are shown in an exploded manner. For simplicity, only the pump 41 is driven to rotate at the angular velocity (ω) in the direction indicated by the arrow, similarly to the above-described conventional one.
Will be described in a state where is stopped. When a torque of T1 is given to the pump 41, the working fluid flowing into the pump 41 becomes
The circumferential speed is accelerated to (v2x) by the pump 41 which is rotationally driven in the direction indicated by the arrow at the angular speed (ω). The working fluid whose circumferential speed has been accelerated to (v2x) in this way has an outflow speed (v2) obtained by combining the radial speed component (v2y) of the working fluid with the centrifugal fluid pressure due to the rotation of the pump 41 and the arrow. Flows out of the pump 41 in the direction indicated by. The hydraulic oil flowing out of the pump 41 at the outflow speed (v2) in the direction indicated by the arrow and flowing into the turbine 42 hits the runner 422 and transmits torque to the turbine 42.
In the illustrated embodiment, the impeller 412 of the pump 41 is moved from the radial inner end to the radial outer end.
The working fluid that has flowed into the pump 41 receives a force in the inner circumferential direction because it is formed to be inclined downstream in the rotation direction of the pump 41. The force at this time can be estimated as follows. In the following formula, (v1) is the inflow speed of the working fluid into the pump, (v2) is the outflow speed of the working fluid from the pump, (v2x) is the rotational speed component of the working fluid at the pump outlet, (V2y) is the radial velocity component of the working fluid at the pump outlet, (t) is the time when the working fluid passes through the pump, (ω) is the angular velocity of the pump, (r)
1) is the average radius of the pump inlet, (r2) is the average radius of the pump outlet, and (m) is the mass of particles of the working fluid.

The time (t) required for the working fluid to pass through the pump 41 is obtained by the following equation (1).

[0018]

## EQU1 ## t = (r2-r1) / v1

While the working fluid passes through the inside of the pump 41 (t), the rotational speed change (dv) of the working fluid particles is as follows:
Equation 2 is as follows.

[0020]

Dv = v2x

Therefore, the average acceleration (α) generated in the working fluid particles during the passage of the working fluid through the pump 41 (t)
Is obtained by the following Expression 3.

[0022]

Α = dv / t = v2x / {(r2-r1) / v1}

Assuming that the mass of the particles of the working fluid is (m),
The average force (F1) in the rotation direction that the working fluid particles receive is represented by the following Expression 4.

[0024]

F1 = m · α = m · v2x / {(r2-r1) / v1}

The rotational speed component (v2x) of the working fluid at the pump outlet is the peripheral speed (ω · r2) at the pump outlet.
Substituting the peripheral speed (ω · r2) of the pump outlet into the rotational speed component (v2x) of the working fluid at the pump outlet in equation (4) from (v2x ≒ ω · r2), the working fluid particles receive Average force in rotation direction (F1)
Is as in the following Expression 5.

[0026]

F1 = m · (ω · r2) / {(r2-r1) / v1}

Here, the turbine 42 stops and the pump 4
If only 1 is rotating at the angular velocity (ω), m, r
Since 2, r1 and v1 are considered to be constant if the working fluid to be used and the specifications of the pump 41 are determined, the above equation 5 is given by:
The following Equation 6 is obtained.

[0028]

F1 = C1 · ω (where C1 is a constant)

On the other hand, the centrifugal force (F
2) is obtained by the following equation (7).

[0030]

F2 = m · r · ω2 (where r is the pump 41
Radius of the force received by the impeller 412 to the position of the center of gravity)

In the above equation 7, since m and r are constant once the working fluid to be used and the specifications of the pump 41 are determined,
The above equation 7 becomes the following equation 8.

[0032]

F2 = C2 · ω2 (where C2 is a constant)

The inclination (θ) of the impeller 412 of the pump 41
The average force (F1 =
The component (F1 ′) of C1 · ω) toward the inner peripheral side is obtained by the following equation (9).

[0034]

## EQU9 ## F1 ′ = cos θ · sin θ · C1 · ω

In the above equation (9), cos θ, sin θ
Is constant if the inclination (θ) of the impeller 412 of the pump 41 is determined, the above equation 9 becomes the following equation 10.

[0036]

F1 ′ = C1 ′ · ω (where C1 ′ is a constant)

Therefore, the resultant force of the radial force applied by the pump 41 to the working fluid particles is expressed by the following equation (11).

[0038]

[Equation 11]

In the above equation (11), (F2-F1 ')
Is zero (0), the working fluid does not flow from the pump 41 to the turbine 42, so that no transmission torque is generated. In order to make (F2−F1 ′) zero (0) according to Equation 11, the pump angular velocity (ω) is zero (0) (ω = 0) or the pump angular velocity (ω) is (C1 ′ / C2). ) (Ω = C1 ′ / C2). Therefore, the angular velocity (ω) of the pump near the idling rotation of the engine becomes (C1 ′ / C).
By setting the inclination (θ) of the impeller 412 of the pump 41 to be equal to 2), the drag torque during idling operation can be reduced to zero (0) or significantly. In FIG. 6, the solid line shows the torque transmission characteristic of the fluid coupling 4 of the present invention configured to have the same size as the conventional fluid coupling indicated by the one-dot chain line. That is, the fluid coupling 4 of the present invention
Is 300 rpm where the rotational speed difference (rpm) of the input / output shaft is lower than the idling rotational speed (for example, 500 rpm) of the engine.
pump 4 so that the angular velocity (ω) of the pump becomes equal to (C1 ′ / C2) when the engine speed is around pm.
The inclination (θ) of one impeller 412 is set. Therefore, as can be seen from FIG. 6, in the fluid coupling 4 of the present invention indicated by the solid line, the transmission torque becomes zero (0) when the rotational speed difference between the input and output shafts is around 300 rpm, and at the idling rotational speed of the engine (for example, 500 rpm). Also, the drag torque can be greatly reduced.

Next, with respect to the fluid coupling 4 constructed in accordance with the present invention, FIGS. 2, 3 and 4 show transmission torques in a region where the difference between the rotation speeds of the input and output shafts is equal to or more than the idling rotation speed (for example, 500 rpm) of the engine. This will be described with reference to FIG. The fluid coupling 4 in the illustrated embodiment includes a pump 41
The impeller 412 is formed so as to be inclined from the inner end in the radial direction to the outer end in the radial direction on the downstream side in the rotational direction of the pump 41, so that the outflow velocity (v2) of the working fluid from the pump 41 is linear radially. 5 is slightly reduced from the outflow velocity (v2 ') from the pump in the conventional fluid coupling shown in FIG. Therefore, the runner 111 of the turbine 11
From the working fluid, slightly less than the torque (T1) (T1
´). Therefore, (T
1 ′) is transmitted. A first runner 422 is formed to be inclined downstream in the rotation direction of the turbine 42.
And a second portion 422b formed continuously with the first portion 422a and inclined toward the inner end toward the upstream side in the rotation direction of the turbine 42,
The working fluid flowing into the turbine 42 is
Is bent by flowing along the second portion 422b from the portion 422a, and flows out of the turbine 42 in an oblique direction toward the upstream side in the rotation direction of the turbine 42 at a flow speed (v1) in a direction indicated by an arrow. At this time, runner 4
22 is a flow rate of the working fluid in the direction opposite to the inflow direction (v1)
Assuming that the torque required to push back with (T2), the runner 422 receives the reaction force (T2). Therefore, the turbine 42 receives the torque of (T1 '+ T2).
The working fluid that has flowed out of the turbine 42 in the direction of the arrow at the speed (v1) flows into the pump 41 with the torque (−T2).
To accelerate the working fluid flowing into the pump 41 with the torque (−T2) to the circumferential speed again to (v2x) as in the beginning, it is necessary to give the pump 41 a torque of (T1 ′ + T2). Then, when a torque of (T1 '+ T2) is given to the pump 41, the working fluid is accelerated at the outlet of the pump 41 to a circumferential velocity of (v2x), and the above operation is repeated.

When the pumps have the same impeller shape and the same peripheral speed at the pump outlet, the rotation speeds of the pumps are considered to be the same. Further, since the rotation of the turbine is stopped, the difference in rotation speed between the pump and the turbine is also the same.
However, the output torque of the turbine is
As described above, the conventional fluid coupling in which the runner 111 of the turbine 42 is formed in a linear radial shape is as described above (T1), and the fluid coupling 4 of the present invention in which the runner 422 of the turbine 42 is bent as described above is as described above ( T1 ′ + T2), the runner of the turbine is bent as described above,
It can be said that the output torque can be changed even if the rotation speed difference between the pump and the turbine is the same. However, since the fluid coupling has no torque amplifying function, the load applied to the pump also increases to (T1 '+ T2). That is, even in the fluid coupling 4 of the present invention in which the runner 422 of the turbine 42 is bent as described above, the input torque increases by an amount corresponding to the increase in the output torque. Remains. The relationship between the rotational speed difference between the input and output shafts and the output torque (transmitted torque) in the fluid coupling 4 of the present invention is shown by a solid line in FIG. As is clear from FIG. 6, the fluid coupling 4 of the present invention has a larger transmission torque in the high rotation region than the conventional fluid coupling indicated by the dashed line. As described above, the fluid coupling 4 in the illustrated embodiment can significantly reduce the drag torque at the idling rotation speed (for example, 500 rpm) and can obtain a large transmission torque in the high rotation region.

[0042]

As described above, the fluid coupling according to the present invention has the following functions and effects.

That is, the impeller of the pump constituting the fluid coupling is formed so as to be inclined downstream in the rotational direction from the radially inner end to the radially outer end, and the runner of the turbine is rotated in the rotational direction from the radially outer end. Since it is composed of a first portion formed to be inclined downstream, and a second portion formed to be continuous with the first portion and inclined toward the radially inner end in the rotational direction upstream. By setting the inclination (θ) of the impeller so that the working fluid operated by the rotation of the pump near the idling rotation of the engine does not flow to the turbine side, the drag torque during idling operation can be reduced to zero (0) or significantly. The transmission torque can be reduced, and a large transmission torque can be obtained in the high rotation region.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a drive device equipped with a fluid coupling configured according to the present invention.

FIG. 2 is a side view of a pump constituting the fluid coupling shown in FIG. 1;

FIG. 3 is a side view of a turbine constituting the fluid coupling shown in FIG. 1;

FIG. 4 is an explanatory diagram showing a relationship between a flow of hydraulic oil and a driving torque of a pump and a turbine in the fluid coupling shown in FIG. 1;

FIG. 5 is an explanatory diagram showing the relationship between the flow of hydraulic oil and the drive torque of a pump and a turbine in a conventional fluid coupling.

FIG. 6 is a diagram showing a relationship between a rotational speed difference between input and output shafts and a transmission torque in a fluid coupling.

[Explanation of symbols]

 2: Internal combustion engine 21: Crankshaft 4: Fluid coupling 40: Fluid coupling housing 41: Pump 411: Pump shell 412: Impeller 42: Turbine 421: Turbine shell 422: Runner 43: Casing 44: Drive plate 45: Ring gear 46: Output Shaft 47: Turbine hub 48: Pump hub 50: Hydraulic pump 52: Pump housing 6: Friction clutch 60: Clutch housing 62: Clutch drive plate 63: Transmission shaft 64: Clutch hub 65: Clutch facing 66: Driven plate 67: Pressure plate 68 : Diaphragm spring 69: Release bearing 70: Clutch release fork

Claims (1)

[Claims] 1. A pump having a pump shell attached to an input shaft, a plurality of impellers disposed in the pump shell, and a pump disposed opposite to the pump and coaxial with the input shaft. A fluid turbine comprising: a turbine shell mounted on an output shaft disposed on the turbine; and a turbine having a plurality of runners disposed in the turbine shell. A first portion formed to be inclined from the end toward the radially outer end in the downstream direction in the rotational direction, and the runner of the turbine is formed to be inclined from the radially outer end to the downstream side in the rotational direction; A fluid coupling, comprising: a second portion formed continuously with the first portion and inclined toward the radially inner end toward the upstream in the rotational direction.