JP2006316835A - Electric control valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric control valve for securing a sufficient stopper abutment height even when a feed screw has a smaller pitch while compatibly attaining valve opening control accuracy and sufficient stopper strength and durability. <P>SOLUTION: When a movable stopper piece 49 abuts on a fixed stopper piece 46 with its axial movement following the rotation of a rotor 33 and its rotation is stopped, the rotor 33 is rotated and displaced relative to a movable stopper member 42 to make a change of a cam engagement position between an end cam face 50 of an end face cam member 43 and the movable stopper piece 49 of the movable stopper member 42 provided integrally at the lower end of the rotor 33. Thus, the movable stopper member 42 is displaced in the axial direction whereby the height of an abutting portion is increased when the movable stopper piece 49 abuts on the fixed stopper piece 46. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric control valve, and more particularly to a mechanical stopper mechanism for an electric control valve.

  As an electric control valve for controlling the refrigerant flow rate and the like in the refrigeration cycle apparatus, a fixedly arranged female screw member, a male screw member that is screw-engaged with the female screw member, and a valve that is provided in the male screw member and adjusts the opening degree of the valve port And the male screw member is driven to rotate by the rotor of the stepping motor, so that the male screw member moves in the same direction as the feed screw type together with the rotor in the axial direction. In addition, there is known a type in which the valve element increases or decreases the effective opening area of the valve port in accordance with the axial position.

  As a fully-closed stopper mechanism in this type of electric control valve, a protrusion-shaped movable side stopper is provided on the end surface of the rotor of the stepping motor, and a protrusion-shaped fixed side stopper is provided on a fixed side member such as a fixed seat. Due to the downward movement in the axial direction of the feed screw type accompanying the rotation of the rotor in the valve closing direction, that is, when the movable side stopper comes into contact with the fixed side stopper by the spiral movement of the movable side stopper, There is one that restricts movement in the fully closed direction of a valve body connected through a member (for example, Patent Document 1).

  This stopper mechanism has an advantage that the structure is simple. However, in this stopper mechanism, the height dimension (area) at which the movable stopper abuts against the fixed stopper at the time of the stopper action is determined by the feed screw pitch between the female screw member and the male screw member. A sufficient stopper contact area cannot be obtained. For this reason, there is a possibility that the stopper strength is insufficient with respect to the rotational torque of the stepping motor, and sufficient durability cannot be secured.

On the other hand, if the feed screw pitch is increased to secure the stopper contact height, the amount of change in the valve opening per pulse of the stepping motor increases, resulting in increased resolution and valve opening. Control accuracy decreases. Also, the required torque of the stepping motor is increased.
Japanese Patent Laid-Open No. 11-22847

  The problem to be solved by the present invention is to ensure a sufficient stopper contact height even when the feed screw pitch is small, and to achieve both the valve opening control accuracy and sufficient stopper strength and durability. .

  An electric control valve according to the present invention includes a fixedly arranged female screw member, a male screw member that is screw-engaged with the female screw member, and a valve body that is provided in the male screw member and adjusts the opening of a valve port, When the male screw member is rotationally driven by the rotor of the electric motor, the valve body moves in the same direction as the male screw member is displaced in the axial direction in a feed screw manner together with the rotor, and is moved to the axial position. Accordingly, in the electric control valve in which the valve body increases or decreases the effective opening area of the valve port, the valve body has a fixed stopper member with a fixed arrangement having a fixed stopper piece, and a movable stopper piece that can come into contact with the fixed stopper piece. A movable stopper member provided rotatably on the rotor and displaceable in the axial direction; and fixed to the rotor and imparting displacement in the axial direction. A cam-shaped end cam surface, and a cam-side stopper surface that is provided at both ends of the end cam surface, and the movable stopper piece abuts against the rotor to regulate the rotation angle range of the movable stopper member to a predetermined angle. And a spring means for biasing the movable stopper member toward the end surface cam surface, the movable stopper member being in a state where the movable stopper piece is not in contact with the fixed stopper piece. Below, the movable stopper piece rotates with the rotor due to the engagement relation between the movable stopper piece and the end face cam surface, and the rotation stops when the movable stopper piece comes into contact with the fixed stopper piece due to the axial movement accompanying the rotation of the rotor. In this rotation stop state, the rotor is rotationally displaced relative to the movable stopper member, and accordingly, the end face cam When the cam engagement position between the movable stopper piece and the movable stopper piece is changed, the movable stopper member is displaced in the axial direction together with the movable stopper piece, and the movable stopper piece comes into contact with the fixed stopper piece to perform a stopper action. Under the condition, the contact area where the movable stopper piece comes into contact with the fixed stopper piece increases due to the displacement of the movable stopper member in the axial direction.

  In the electric control valve, preferably, the cam shape of the end face cam surface is a high cam surface portion and a low cam surface portion that are axially displaced from each other, and an inclined cam surface portion that connects the high cam surface portion and the low cam surface portion. And a cam shape that applies axial displacement to the movable stopper by an amount of displacement in the axial direction between the high cam surface portion and the low cam surface portion.

  In this electric control valve, preferably, the end face cam member is integrally formed on the end face of the rotor.

  According to the electric control valve of the present invention, when the movable stopper piece comes into contact with the fixed stopper piece and stops rotating by the axial movement accompanying the rotation of the rotor, the rotor is rotationally displaced relative to the movable stopper member. As a result, the cam engagement position between the end face cam surface and the movable stopper piece is changed, the movable stopper piece is displaced in the axial direction, and the contact area (height where the movable stopper piece comes into contact with the fixed stopper piece by this axial displacement is changed. (Dimension) increases.

  Thereby, even if the feed screw pitch is small, a sufficient stopper contact height dimension can be secured, and sufficient valve opening control accuracy, sufficient stopper strength, and durability can be achieved at the same time.

  One embodiment of an electric control valve according to the present invention will be described with reference to FIGS.

  The electric control valve has a cup-shaped valve housing 11. An inlet joint 13 communicating with the valve chamber 12 as a lateral joint is airtightly fixed to the valve housing 11 by a brazing portion 14. A protruding tubular outlet port 15 is formed at the bottom of the valve housing 11. The outlet port 15 is located at the central axis position of the valve housing 11, and an outlet joint 16 is brazed and fixed to the outlet port 15 as a lower joint by a brazing portion 17.

  A valve seat member 18 is airtightly fixed to the outlet port 15 by brazing portions 19 and 20. The valve seat member 18 is in the valve chamber 12 and has a valve port 21 that connects the valve chamber 12 and the outlet joint 16 in communication.

  In the valve chamber 12, there is a cylindrical female screw member 22 fixed to the valve seat member 18. A communication hole 23 is formed in the side periphery of the female screw member 22. A female thread 24 is formed on the female thread member 22 concentrically with the valve port 21.

  A male screw 26 of a shaft-like male screw member 25 is threadedly engaged with the female screw 24. The male screw member 25 is integrally formed with a tapered shaft-like valve element 27 at the lower part. When the male screw member 25 rotates, the valve body 27 moves in the axial direction (vertical direction) in a feed screw manner by screw engagement between the female screw 24 and the male screw 26, and the valve port 21 is effective according to the position in the axial direction. Increase or decrease the opening area.

  Thereby, the flow rate of the fluid flowing from the inlet joint 13 to the outlet joint 16 through the valve chamber 12, the communication hole 23, and the valve port 21 is measured and controlled by the position in the axial direction of the valve body 27.

  A can-shaped rotor case 31 of a stepping motor 30 is fixedly attached to the upper portion of the valve housing 11 by welding. The rotor case 31 defines an airtight rotor chamber 32 that communicates with the valve chamber 12.

  A rotor 33 is disposed in the rotor chamber 32 so as to be rotatable and movable in the axial direction. The rotor 33 is a resin molded product, and the outer peripheral surface portion 34 is multipolarly magnetized. The rotor 33 has a boss portion 35 at the center, and an upper portion 28 of the male screw member 25 is inserted through the boss hole 36 formed in the boss portion 35 as a rotor shaft.

  A connecting member 29 is fixedly attached to the upper end of the male screw member 25. As shown in FIGS. 2 and 3, the connecting member 29 has a yoke shape and engages with a parallel two-chamfered portion 37 formed on the outer peripheral surface portion of the boss portion 35. By this engagement, the rotor 33 and the male screw member 25 are connected in a torque transmission relationship, and the rotation of the rotor 33 is transmitted to the male screw member 25.

  A cylindrical stator coil unit 38 is attached to the outer periphery of the rotor case 31. The stator coil unit 38 is not shown in detail in the internal structure, but as a stepping motor, a well-known airtight mold having magnetic pole teeth, a winding portion (stator coil), an electric wiring portion, etc. therein. Of structure.

  The stepping motor 30 rotates the rotor 33 by a rotation angle corresponding to the number of pulses by applying a pulse current to the winding portion of the stator coil unit 38. As a result, the male screw member 25 rotates, and with this rotation, the male screw member 25 and the rotor 33 move in the axial direction (vertical direction) in a feed screw manner by the screw engagement between the female screw 24 and the male screw 26. Weighing control is performed.

  Next, the stopper mechanism (fully closed stopper mechanism) of the electric control valve according to the present embodiment will be described. The stopper mechanism includes a ring-shaped fixed stopper member 41 fixed to the valve housing 11, a movable stopper member 42 that is rotatable with respect to the rotor 33 and that can be displaced in the axial direction, and a lower end portion of the rotor 33. The ring-shaped end cam member 43, the spring receiving member 44, and the compression coil spring 45 are provided integrally.

  The fixed stopper member 41 has a fixed stopper piece 46 having a predetermined height. As shown in FIGS. 6 to 9, both end surfaces of the fixed stopper piece 46 are opposite to each other when viewed in the rotation direction. The contact surfaces are 46A and 46B.

  As shown in FIG. 1, the spring receiving member 44 is loosely fitted to the outer periphery of the upper portion 28 of the male screw member 25, and is shown in FIG. 4 on the outer periphery of the boss portion 47 of the spring receiving member 44. The ring portion 48 of the movable stopper member 42 is rotatably fitted. As shown in FIGS. 6 to 9, the movable stopper member 42 has a movable stopper piece 49 that protrudes radially outward from the ring portion 48 and can come into contact with the contact surfaces 46 </ b> A and 46 </ b> B of the fixed stopper piece 46. Have one.

  Both ends of the movable stopper piece 49 also have contact surfaces 49A and 49B opposite to each other when viewed in the rotational direction. Depending on the axial position of the movable stopper member 42, the movable stopper piece 49 is rotated in the clockwise direction. As shown in FIGS. 6 and 7, one contact surface 49A of the movable stopper piece 49 comes into contact with one contact surface 46A of the fixed stopper piece 46, and the movable stopper piece 49 rotates in the counterclockwise direction. As shown in FIG. 8, the other contact surface 49 </ b> B of the movable stopper piece 49 contacts the other contact surface 46 </ b> B of the fixed stopper piece 46.

  As shown in FIG. 1, the end face cam member 43 is integrally formed with a resin rotor 33. The end face cam surface 50 of the end face cam member 43 has a cam shape that gives the movable stopper member 42 an axial displacement. As shown in FIG. 4, the end face cam surface 50 includes a high cam surface portion 50A and a low cam surface portion 50B that are displaced in the axial direction, and an inclined cam surface portion that connects the high cam surface portion 50A and the low cam surface portion 50B. 50C, and in the range of the axial displacement amount D between the high cam surface portion 50A and the low cam surface portion 50B shown in FIG. 5, an amount of axial displacement corresponding to the rotational position of the rotor 33 is applied to the movable stopper 42. give.

  When the rotor 33 rotates in the clockwise direction in a state where the movable stopper piece 49 is in a rotational position corresponding to the higher cam surface portion 50A of the end face cam member 43 described later ( As long as the movable stopper piece 49 is in contact (collision) with the inclined cam surface portion 50C during the valve closing process), an external force (rotation prevention) for stopping rotation from the outside does not act on the stopper member 42. That is, as long as it does not contact the fixed stopper 46, it rotates with the rotor 33.

  Cam side stopper surfaces 51 and 52 that face each other in the rotational direction are formed at both ends of the end cam surface 50, that is, at the end of the high cam surface portion 50A and the end of the low cam surface portion 50B. When the contact surfaces 49A and 49B of the movable stopper piece 49 come into contact with the cam side stopper surfaces 51 and 52, the rotation angle range of the movable stopper member 42 with respect to the rotor 33 is restricted to a predetermined angle (the range of the end cam surface 50). The

  As shown in FIG. 4, the movable stopper member 42 has an auxiliary piece 53 at a position rotationally displaced by 180 degrees with respect to the movable stopper piece 49, and is arranged around the end face cam surface 50 of the end face cam member 43. An auxiliary end surface cam surface 54 equivalent to the end surface cam surface 50 is formed in the portion displaced in the direction corresponding to the auxiliary piece 53, and the auxiliary piece 53 abuts on the auxiliary end surface cam surface 54, so that the movable stopper member The horizontal posture of 42 is maintained.

  As shown in FIG. 1, the compression coil spring 45 is provided between the spring receiving member 44 and the upper shoulder portion 22 </ b> A of the female screw member 22, and the spring receiving member 44 is attached to the lower end surface 33 </ b> A of the rotor 33. Energized to the side.

  The action of the compression coil spring 45 depends on the axial dimension of the boss portion 47 of the spring receiving member 44, but the movable stopper piece 49 is in a rotational position corresponding to the high cam surface portion 50A of the end face cam member 43 (FIGS. 10), with the movable stopper piece 49 provided with a minute axial gap between the high cam surface portion 50A and the flange portion 44A of the spring receiving member 44, the spring receiving member 44 is placed on the lower end surface of the rotor 33. Press against 33A. Therefore, in this state, the spring force of the compression coil spring 45 does not act on the movable stopper member 42.

  On the other hand, in a state where the movable stopper piece 49 is in a rotational position corresponding to the inclined cam surface portion 50C to the lower cam surface portion 50B of the end surface cam member 43 (see FIGS. 11 to 13), the spring receiving member 44 is below the rotor 33. The spring force of the compression coil spring 45 moves away from the end surface 33A and acts on the movable stopper member 42 to press the movable stopper piece 49 against the end face cam surface 50 of the end face cam member 43, so that the upper surface 49C and the end face cam surface 50 of the movable stopper piece 49 are pressed. A predetermined frictional resistance is given between the two. The predetermined frictional resistance here means that the movable stopper member 42 that does not come into contact with the fixed stopper 46 is in a free state in which an external force (rotation prevention) that stops rotation from the outside does not act on the stopper member 42. The frictional resistance is sufficient to rotate with the rotor 33 due to the frictional resistance.

  The movable stopper piece 49 is in a rotational position corresponding to the high cam surface portion 50A of the end face cam member 43 by slightly shortening the axial dimension of the boss portion 47 of the spring receiving member 44 (see FIGS. 1 and 10). However, the spring receiving member 44 is separated from the lower end surface 33A of the rotor 33 so that the spring force of the compression coil spring 45 acts on the movable stopper member 42 and presses the movable stopper piece 49 against the end surface cam surface 50 of the end surface cam member 43. It is possible to set.

  Next, the operation of the fully closed stopper mechanism will be described with reference to FIGS. 10 to 13, the detailed structure inside the stator coil unit 38 is not shown for the sake of simplicity.

  In the valve closing process, the male screw member 25 and the rotor 33 are lowered in the axial direction while rotating by the clockwise rotation of the rotor 33. In this valve closing process, the movable stopper piece 49 is positioned on the higher cam surface portion 50A of the end face cam surface 50 as shown in FIG. 6, and the movable stopper piece 49 abuts on the inclined cam surface portion 50C ( As a result of the collision, the movable stopper member 42 rotates together with the rotor 33 in the clockwise direction.

  When close to the fully closed position, the male screw member 25 and the rotor 33 are rotating in the axial direction while rotating, so that one of the movable stopper pieces 49 of the movable stopper member 42 rotating in the same direction as the rotor 33 is provided. The contact surface 49A comes into contact with one contact surface 46A of the fixed stopper piece 46, and further rotation of the movable stopper member 42 in the clockwise direction is prevented, so that the movable stopper member 42 is stopped. The contact height a of the contact surfaces 49A and 46A at this time may be about 0.1 to 0.2 mm, although it depends on the screw leads of the female screw 24 and the male screw 26.

  As shown in FIG. 7, when the contact surface 49A of the movable stopper piece 49 abuts against the contact surface 46A of the fixed stopper piece 46 to perform the stopper action, the rotor 33 rotates in the clockwise direction. A relative rotational displacement occurs between the rotor 33 and the movable stopper member 42, and the movable stopper piece 49 is disengaged from the engagement of the high cam surface portion 50A of the end cam surface 50 and slides on the inclined cam surface portion 50C. It comes to be located in the location engaged with the surface part 50B.

  As a result, the movable stopper member 42 is displaced downward in the axial direction relative to the rotor 33 by the amount of axial displacement D against the spring force of the compression coil spring 45, and the contact surface 49A of the movable stopper piece 49 is fixed to the fixed stopper piece. The height dimension that abuts against the contact surface 46A of 46 increases. This height dimension b may be about 1.2 mm depending on the setting of the axial direction displacement amount D.

  Due to this increase in the height dimension, a sufficient stopper contact height dimension can be secured even if the feed screw pitch is small, the contact area where the movable stopper piece 49 contacts the fixed stopper piece 46 is increased, and the feed screw pitch is increased. The sufficient valve opening degree control accuracy obtained by having a small value and the sufficient stopper strength and durability by ensuring a sufficient stopper contact area are compatible.

  As shown in FIG. 7, one contact surface 49 </ b> A of the movable stopper piece 49 contacts the contact surface 46 </ b> A of the fixed stopper piece 46, and the cam side stopper surface 52 on the lower cam surface portion 50 </ b> B side of the end surface cam member 43. Is in contact with the other contact surface 49B of the movable stopper piece 49, the rotor 33 is prevented from rotating in the clockwise direction (valve closing direction), and the fully closed position of the valve element 27 is determined with good reproducibility.

  When the valve is opened from the fully closed state described above, the rotor 33 is rotated counterclockwise. By this rotation, the movable stopper member 42 is moved in the counterclockwise direction together with the rotor 33 by the frictional resistance provided by the spring force of the compression coil spring 45 while the movable stopper piece 49 is positioned at a position where the movable stopper piece 49 is engaged with the lower cam surface portion 50B. Rotate. When approximately one rotation is made from the fully closed state, the contact surface 49B of the movable stopper piece 49 comes into contact with the contact surface 46B on the opposite side of the fixed stopper piece 46, as shown in FIG. The rotation in the turning direction is stopped.

  Further, when the rotor 33 rotates in the counterclockwise direction, a relative rotational displacement occurs between the rotor 33 and the movable stopper member 42. As shown in FIG. The cam surface 50 is disengaged from the engagement of the lower cam surface portion 50B and slides on the inclined cam surface portion 50C to be positioned at a position where it engages with the higher cam surface portion 50A.

  As a result, the movable stopper member 42 is lifted and displaced in the axial direction with respect to the rotor 33 by the axial displacement amount D, and on the way, as shown in FIG. 12, from the front side of the paper surface to the contact surface 46B of the fixed stopper piece 46. While the contact height dimension of the contact surface 49B of the movable stopper piece 49 that is in contact is shortened, the sliding cam surface portion 50C of the end surface cam surface 50 is finally slid to engage with the higher cam surface portion 50A. At the stage where the movable stopper piece 49 is positioned, the contact surface 49B of the movable stopper piece 49 is detached from the state where it abuts on the contact surface 46B of the fixed stopper piece 46, as shown in FIG.

  As a result, the movable stopper piece 49 can be rotated together with the rotor 33 again, and the movable stopper piece 49 is in a state where the contact surface 49A of the movable stopper piece 49 is in contact with the cam side stopper surface 51 on the high cam surface portion 50A side. The rotor 33 rotates together with the rotor 33. As the rotor 33 rotates, the rotor 33, the movable stopper member 42, the male screw member 25, and the valve element 27 are displaced upward in the axial direction, and the valve opening increases.

  In the embodiment, the fully-closed stopper mechanism is used. However, this stopper mechanism can be similarly configured as a fully-opened stopper mechanism.

It is a longitudinal section showing one embodiment of an electric control valve by this invention. It is sectional drawing along line AA of FIG. It is a perspective view which shows the connection part of the external thread member and rotor in this embodiment. It is a disassembled perspective view of the principal part of the fully closed stopper mechanism in this embodiment. It is an expanded view of the end surface cam of the fully closed stopper mechanism in this embodiment. It is a perspective view which shows operation | movement of the fully closed stopper mechanism in this embodiment. It is a perspective view which shows operation | movement of the fully closed stopper mechanism in this embodiment. It is a perspective view which shows operation | movement of the fully closed stopper mechanism in this embodiment. It is a perspective view which shows operation | movement of the fully closed stopper mechanism in this embodiment. It is a longitudinal cross-sectional view which shows operation | movement of the fully closed stopper mechanism in this embodiment. It is a longitudinal cross-sectional view which shows operation | movement of the fully closed stopper mechanism in this embodiment. It is a longitudinal cross-sectional view which shows operation | movement of the fully closed stopper mechanism in this embodiment. It is a longitudinal cross-sectional view which shows operation | movement of the fully closed stopper mechanism in this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Valve housing 12 Valve chamber 13 Inlet joint 14, 17, 19, 20 Brazing part 15 Outlet port 16 Outlet joint 18 Valve seat member 21 Valve port 22 Female thread member 22A Upper shoulder part 23 Communication hole 24 Female thread 25 Male thread member 26 Male thread 27 Valve body 28 Upper portion 29 Connecting member 30 Stepping motor 31 Rotor case 32 Rotor chamber 33 Rotor 33A Lower end surface 34 Outer peripheral surface portion 35 Boss portion 36 Boss hole 37 Parallel chamfered portion 38 Stator coil unit 41 Fixed stopper member 42 Movable stopper member 43 End face cam Member 44 spring receiving member 44A collar 45 compression coil spring 46 fixed stopper piece 46A, 46B fixed stopper piece contact surface 46C fixed stopper piece upper surface 47 boss part 48 ring part 49 movable stopper piece 49A, 49B movable stopper piece contact Sliding surface 49C Upper surface of movable stopper piece 50 End cam surface 50A Higher cam surface portion 50B Lower cam surface portion 50C Inclined cam surface portion 51, 52 Cam side stopper surface 53 Auxiliary piece 54 Auxiliary end surface cam surface

Claims (3)

A fixedly arranged female screw member, a male screw member screw-engaged with the female screw member, and a valve body that is provided in the male screw member and adjusts an opening degree of a valve port, and the male screw member is rotated by a rotor of an electric motor By being driven, the valve body moves in the same direction as the male screw member is displaced in the axial direction in a feed screw manner together with the rotor, and the valve body moves in the valve port according to the axial position. In the electric control valve that increases or decreases the effective opening area of
A fixed stopper member with a fixed arrangement having a fixed stopper piece;
A movable stopper member that has a movable stopper piece that can come into contact with the fixed stopper piece, and that is provided on the rotor so as to be rotatable and displaceable in the axial direction;
A cam-shaped end cam surface that is fixed to the rotor and is displaced in the axial direction, and a rotation angle of the movable stopper member with respect to the rotor by contacting the movable stopper piece provided at both ends of the end cam surface. An end face cam member having a cam side stopper surface for restricting the range to a predetermined angle;
Spring means for biasing the movable stopper member toward the end face cam surface;
In a state where the movable stopper piece is not in contact with the fixed stopper piece, the movable stopper member rotates with the rotor by the engagement relationship between the movable stopper piece and the end face cam surface, and the rotation of the rotor When the movable stopper piece comes into contact with the fixed stopper piece by the axial movement accompanying the rotation, the rotation stops,
Under this rotation stop state, the rotor is rotationally displaced relative to the movable stopper member, and the cam engagement position between the end face cam surface and the movable stopper piece is changed accordingly, When the movable stopper member is displaced in the axial direction together with the movable stopper piece, and the movable stopper piece abuts on the fixed stopper piece to perform a stopper action, the movable stopper piece is displaced by the axial displacement of the movable stopper member. An electric control valve in which the contact area that contacts the fixed stopper piece increases.   The cam shape of the end face cam surface includes a high cam surface portion and a low cam surface portion displaced in the axial direction, and an inclined cam surface portion connecting the high cam surface portion and the low cam surface portion, and the high cam surface portion 2. The electric control valve according to claim 1, wherein the electric control valve has a cam shape that applies an axial displacement to the movable stopper by an amount of an axial displacement with respect to the lower cam surface portion.   The electric control valve according to claim 1, wherein the end face cam member is integrally formed with an end face of the rotor.

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