JP2012233542A - Power transmission shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power transmission shaft with a low-cost structure, that can prevent variations of an inner pressure in a boot.SOLUTION: A drive shaft 1, end 1a of which is covered by the boot 3, includes; a cylinder 20 extending in an axial direction so that a rotational center axis Oof the drive shaft 1 corresponds to a center axis; a piston 30 that is slidably housed in the cylinder 20; and an inner biasing spring 41 and an outer biasing spring 42, which are pressed by the piston 30. The cylinder 20 has an internal communication hole 21a and an outer communication hole 22a. The piston 30 has a first air passage 31 that connects the outer communication hole 22a with the inside of the cylinder 20, when the piston 30 moves to the other axial end 22 and presses the outer biasing spring 42, and a second air passage 32 that connects the internal communication hole 21a with the inside of the cylinder 20, when the piston 30 moves to one axial end 21 and presses the inner biasing spring 41. The first air passage 31 has a first inner opening 31a provided to be separated from an inner wall surface of the cylinder 20.

Description

  The present invention relates to a power transmission shaft, and more particularly, to a power transmission shaft such as a drive shaft or a propeller shaft in which a connection portion with a joint is covered with a boot.

  In a drive shaft or the like for transmitting a driving force to a driving wheel of a vehicle, a structure in which joints are attached to both ends of the intermediate shaft is employed. Specifically, the inboard joint attached to the inboard side of the intermediate shaft includes, for example, a tripod type constant velocity joint. The outboard joint attached to the outboard side of the intermediate shaft includes a barfield type constant velocity joint.

  In such a drive shaft, boots that close the opening are used for the inboard joint and the outboard joint, respectively, in order to prevent leakage of grease filled in the joint and entry of foreign matter from the outside of the joint. Specifically, these boots have a body portion formed in a conical cylinder shape that gradually increases in diameter from one end side in the axial direction toward the other end side, and this body portion is large from the small diameter end portion side. It is formed in a bellows shape that undulates toward the radial end side.

  By the way, the joints and boots described above are exposed to high temperatures due to the effects of self-heating generated during operation of the joints and radiant heat from the engine, the exhaust pipe and other heating elements. Thus, when the boot is repeatedly subjected to a temperature change between a high temperature state and a normal temperature state or a low temperature state, the boot internal pressure greatly fluctuates. Such a change in the boot internal pressure can cause deformation of the boot or abnormal wear due to contact with members around the drive shaft, for example.

  In recent years, for the purpose of preventing such troubles due to fluctuations in the internal pressure of the boot, a craze that allows the passage of gas but prevents the passage of liquid on at least one of the inner and outer surfaces of the boot. A boot having a breathable film formed thereon is known (for example, see Patent Document 1). According to the boot described in Patent Document 1, even if a pressure difference occurs inside and outside the boot, the pressure difference inside and outside the boot can be relaxed by allowing air to pass through the breathable film. Moreover, since the air permeable film does not allow liquid, that is, the lubricant in the boot to pass therethrough, leakage of the lubricant to the outside can be prevented.

JP 2008-232302 A

  However, in the boot described in Patent Document 1 described above, if a lubricant such as grease sealed inside the boot covers the entire breathable film, air cannot pass through the breathable film. In particular, when the joint is in operation, the intermediate shaft also rotates at a high speed, so that the lubricant is scattered on the inner surface of the boot and easily covers the entire breathable film. For this reason, the temperature in the boot rises during operation of the joint, and even if the boot internal pressure increases, the pressure in the boot cannot be released, and as a result, the above-described fluctuation in the boot internal pressure may occur. Thus, in the boot described in Patent Document 1, there is still room for improvement with respect to preventing fluctuations in the boot internal pressure.

  In addition, for example, if a vent is provided in the boot to communicate with the inside and outside of the boot, the pressure inside the boot can be maintained at atmospheric pressure and fluctuations in the boot internal pressure can be prevented, but a lubricant such as grease is sealed in the boot. Can not do. Thus, simply providing the vent hole in the boot requires a new structure for sealing the lubricant, and there is a problem that the cost increases.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power transmission shaft that can prevent fluctuations in boot internal pressure with a low-cost configuration.

  In order to achieve the above object, the power transmission shaft according to the present invention is (1) a power transmission shaft whose end connected to the joint is covered with a boot, and the rotation center axis and the center axis of the power transmission shaft are A cylinder internally provided to coincide and extend in the axial direction, a piston slidably received in the cylinder, and the piston when the piston reaches one end in the axial direction of the cylinder. An inner biasing member biasing toward the other axial end of the cylinder, and when the piston reaches the other axial end of the cylinder, the piston is biased toward one axial end of the cylinder. An external urging member that urges the cylinder, and the cylinder communicates with the inside of the boot at the one end in the axial direction, and communicates with the outside of the boot at the other end in the axial direction. With holes, The piston moves to the other axial end of the cylinder and presses the outer urging member, and a first air passage that communicates the external communication hole and the inside of the cylinder; A second air passage that communicates with the communication hole in the boot and the inside of the cylinder when the inner urging member is pressed by moving to one end in the axial direction, and the first air passage includes: It has the structure which has the opening part opened to the axial direction one end part side of the said cylinder, and the said opening part was provided in the position spaced apart from the inner wall face of the said cylinder.

  With this configuration, the power transmission shaft according to the present invention has a cylinder inside the power transmission shaft, and a piston having first and second air passages is slidably accommodated inside the cylinder. For this reason, for example, when the internal pressure of the boot becomes positive with respect to the atmospheric pressure, the piston moves to the other end side in the axial direction inside the cylinder and presses the outer biasing member, whereby the first air passage The external communication hole communicates with the inside of the cylinder through the. As a result, the air inside the boot can escape to the outside of the boot. As a result, the boot internal pressure can be maintained at atmospheric pressure.

  On the contrary, when the internal pressure of the boot becomes negative with respect to the atmospheric pressure, the piston moves inside the cylinder toward one end in the axial direction and presses the inner urging member. The in-boot communication path and the inside of the cylinder communicate with each other through the path. Thereby, the air outside the boot can be taken into the boot. As a result, the boot internal pressure can be maintained at atmospheric pressure.

  Thus, the power transmission shaft according to the present invention functions as a pressure control valve in which the piston inside the cylinder maintains the boot internal pressure at atmospheric pressure even when the boot internal pressure rises and falls. Therefore, the boot internal pressure can be prevented from changing with a simple configuration, that is, a low-cost configuration. Therefore, it is possible to prevent the occurrence of abnormal wear due to the deformation of the boot or the contact with the members around the power transmission shaft due to the fluctuation of the boot internal pressure.

  Further, since the power transmission shaft according to the present invention is provided at a position where the opening of the first air passage is separated from the inner wall surface of the cylinder, lubricant such as grease that has flowed into the cylinder is supplied to the power transmission shaft. Only the air inside the boot can be discharged to the outside by being pressed against the inner wall surface of the cylinder by the action of the centrifugal force according to the rotation of.

  ADVANTAGE OF THE INVENTION According to this invention, the power transmission shaft which can prevent the fluctuation | variation of boot internal pressure with a low-cost structure can be provided.

It is a partially expanded sectional view of the joint part containing the drive shaft which concerns on embodiment of this invention. It is a figure which shows the piston which concerns on embodiment of this invention, Comprising: (a) is an axial sectional view, (b) is an axial front view. It is explanatory drawing of operation | movement of the pressure regulator which concerns on embodiment of this invention, Comprising: (a) is a figure which shows the movement of the piston at the time of boot internal pressure rise, (b) is an axial direction other end of a piston. It is a figure which shows the state which reached the part, (c) is a figure which shows the state which the piston reached the axial direction one end part. It is a figure which shows the state in which boot internal pressure is a positive pressure with respect to atmospheric pressure, Comprising: (a) is a figure which shows the state just before opening of a 1st air path, (b) is a 1st air path. It is a figure which shows the state by which was opened. It is a figure which shows the state where boot internal pressure is a negative pressure with respect to atmospheric pressure, Comprising: (a) is a figure which shows the state just before opening of a 2nd air path, (b) is a 2nd air path. It is a figure which shows the state by which was opened. It is the graph which compared the change of the boot internal pressure at the time of using the drive shaft which concerns on embodiment of this invention with the change of the conventional boot internal pressure.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present embodiment, an example in which the power transmission shaft of the present invention is applied to a vehicle drive shaft whose end connected to a joint is covered with a boot will be described.

First, the configuration will be described.
As shown in FIG. 1, the drive shaft 1 according to the present embodiment is provided in a power transmission path between a vehicle differential and a drive wheel (not shown).

  Specifically, a drive shaft 1 as a power transmission shaft has one end 1a connected to a constant velocity joint 2 as a joint on the drive wheel side. Further, the other end (not shown) of the drive shaft 1 is connected to a constant velocity joint on the differential side. The constant velocity joint 2 is composed of a fixed constant velocity joint that mainly supports vertical movement, such as a Rzeppa type or a Barfield type. On the other hand, the differential-side constant velocity joint is composed of a sliding constant velocity joint that mainly responds to changes in the axial direction of the drive wheels, such as a tripod type and a double offset type.

  The end 1 a of the drive shaft 1 is covered with a bellows-like boot 3 fixed to the drive shaft 1 and the constant velocity joint 2. In the present embodiment, the end portion 1a refers to a part of the drive shaft 1 located inside the accommodation space including the accommodation chamber 2a defined by the expansion / contraction portion 3c of the boot 3 described later and the constant velocity joint 2. . Similarly to the end portion 1a, the other end portion of the drive shaft 1 is covered with a bellows-like boot (not shown).

  The boot 3 is made of a resin material or a rubber material, and has a large-diameter end portion 3a (right end in the drawing) fixed to the constant velocity joint 2 and a small-diameter end portion 3b (left end in the drawing) fixed to the drive shaft 1. And the expansion / contraction part 3c formed in a bellows shape. The large-diameter end 3a is fixed to the outer periphery of the constant velocity joint 2 by a fastening band (not shown) so as to cover the opening of the constant velocity joint 2. The small-diameter end 3b is fixed to the outer periphery of the drive shaft 1 by a fastening band (not shown). The expansion / contraction part 3c is integrally formed with the large-diameter end part 3a and the small-diameter end part 3b so that the diameter gradually decreases from the large-diameter end part 3a toward the small-diameter end part 3b. The extendable portion 3c can be expanded and contracted according to the vertical displacement of the drive shaft 1.

  The boot 3 configured in this manner seals the accommodation chamber 2 a of the constant velocity joint 2. That is, the storage chamber 2 a communicates with the inside of the boot 3. Grease as a lubricant is sealed inside the storage chamber 2 a and the boot 3. The encapsulated grease is used for lubricating each member of the constant velocity joint 2.

  By the way, the constant velocity joint 2 and the boot 3 described above are exposed to high temperatures due to self-heating generated during operation of the constant velocity joint 2 and radiant heat from an engine, an exhaust pipe and other heating elements (not shown). Accordingly, when the boot 3 is repeatedly subjected to a temperature change between a high temperature state and a normal temperature state or a low temperature state, the boot internal pressure greatly fluctuates. Such a change in the boot internal pressure may cause deformation of the boot 3 or abnormal wear of the boot 3 due to contact with members around the drive shaft, for example.

  Therefore, in the present embodiment, the following configuration is added to the drive shaft 1 in order to prevent the fluctuation of the boot internal pressure as described above.

  That is, the drive shaft 1 includes a pressure adjusting device 10 on the constant velocity joint 2 side for preventing fluctuations in boot internal pressure. The pressure adjusting device 10 can be applied not only on the constant velocity joint 2 side but also on the differential velocity constant joint side.

  Specifically, the pressure adjusting device 10 includes a cylinder 20, a piston 30, an inner biasing spring 41 as an inner biasing member, and an outer biasing spring 42 as an outer biasing member. Yes.

The cylinder 20 is formed inside the drive shaft 1 and extends in the axial direction so that the rotation center axis O _{D of} the drive shaft 1 coincides with the center axis O _S of the cylinder 20 (see FIG. 2A). . Cylinder 20, together with the central axis O _S away from the rotation center axis O _D, so as to be parallel to the rotational center axis line O _D, may be formed inside the drive shaft 1.

Further, an in-boot communication hole 21 a that communicates the inside of the boot 3, that is, the inside of the storage chamber 2 a and the inside of the cylinder 20, is formed at one axial end portion 21 (right end in FIG. 1) of the cylinder 20. The in-boot communication hole 21 a is formed by a through hole formed in a direction orthogonal to the axial direction of the cylinder 20 at the axial one end 21. The in-boot communication hole 21a is formed in a direction orthogonal to the axial direction of the cylinder 20, but is not limited thereto, and is inclined at a predetermined inclination angle with respect to the central axis O _S of the cylinder 20 (see FIG. 2A). You may let them.

Furthermore, an external communication hole 22 a that communicates the outside of the boot 3 and the inside of the cylinder 20 is formed at the other axial end portion 22 (left end in FIG. 1) of the cylinder 20. The external communication hole 22 a is configured by a through hole formed in a direction orthogonal to the axial direction of the cylinder 20 at the axial one end portion 21. The external communication hole 22a is formed in a direction orthogonal to the axial direction of the cylinder 20, but is not limited thereto, and is inclined at a predetermined inclination angle with respect to the central axis O _S of the cylinder 20 (see FIG. 2A). May be.

The piston 30 is accommodated in the cylinder 20 so as to be slidable in the axial direction. As shown in FIG. 2 (a), (b) , the piston 30 have a first air passage 31 and the second air passage 32 which is inclined at a predetermined inclination angle with respect to the central axis O _S of the cylinder 20 doing. The central axis of the piston 30 coincides with the center axis line O _S of the cylinder 20.

  The first air passage 31 connects the external communication hole 22a (see FIG. 1) and the inside of the cylinder 20 when the piston 30 moves to the other axial end 22 of the cylinder 20 and presses the outer biasing spring 42. It comes to communicate. Further, the first air passage 31 has a first inner opening 31a that opens to the axial one end 21 side (right side in FIG. 2) of the cylinder 20 and an axial other end 22 side (see FIG. 2). 2 and the first outer opening 31b that opens on the left side. The first inner opening 31a in the present embodiment constitutes an opening according to the present invention.

The first inner opening 31a is provided at a position separated from the inner wall surface of the cylinder 20 (see FIG. 1). Specifically, the first inner opening 31 a is formed on the inner surface 30 a of the piston 30 so that the center thereof coincides with the center axis O _S of the cylinder 20, that is, the center axis of the piston 30. The first outer opening 31b is formed of a groove formed along the outer peripheral surface of the piston 30 and opens over the entire circumference toward the radially outer side of the piston 30.

  When the piston 30 moves to the one axial end 21 of the cylinder 20 and presses an inner biasing spring 41 to be described later, the second air passage 32 and the inside of the cylinder 20 are connected to the communication hole 21a in the boot (see FIG. 1). It is supposed to communicate with. The second air passage 32 has a second outer opening 32a that opens to the other axial end 22 side (left side in FIG. 2) of the cylinder 20 and an axial one end 21 side of the cylinder 20 (FIG. 2 on the right side) and a second inner opening 32b.

  Similar to the first inner opening 31a, the second outer opening 32a is formed on the outer surface 30b of the piston 30 so that the center thereof coincides with the central axis of the piston 30. Similar to the first outer opening 31b, the second inner opening 32b is composed of a groove formed along the outer peripheral surface of the piston 30 and opens over the entire circumference toward the radially outer side of the piston 30. doing.

  The inner biasing spring 41 is a compression coil spring, and one end (left end in FIG. 2) is fixed to the inner side surface 30 a of the piston 30. As shown in FIG. 5 (b), the inner biasing spring 41 has one end in the axial direction of the cylinder 20 when the piston 30 reaches one end 21 in the axial direction of the cylinder 20. By abutting on the side end surface 21 b of the portion 21, the piston 30 is urged toward the other axial end portion 22 side of the cylinder 20.

  The outer biasing spring 42 is formed of a compression coil spring like the inner biasing spring 41, and one end (right end in FIG. 2) is fixed to the outer surface 30 b of the piston 30. As shown in FIG. 4B, the outer biasing spring 42 has the other end (the left end in FIG. 2) in the axial direction of the cylinder 20 when the piston 30 reaches the other end 22 in the axial direction of the cylinder 20. By abutting on the side end surface 22 b of the other end portion 22, the piston 30 is urged toward the one end portion 21 side in the axial direction of the cylinder 20.

  Next, the operation of the pressure adjusting device 10 will be described.

  First, as shown in FIG. 3A, as the temperature inside the boot 3 (hereinafter referred to as the boot internal temperature) increases, the boot internal pressure P (kPa) increases, that is, positive pressure with reference to the atmospheric pressure (0 kPa). Then, the piston 30 moves in the cylinder 20 toward the other end 22 in the axial direction. When the boot internal pressure P (kPa) becomes equal to or higher than the predetermined pressure, the piston 30 presses the outer urging spring 42 as shown in FIG. 3B, and the external communication hole 22a is passed through the first air passage 31. And the inside of the cylinder 20 communicate with each other. Thereby, the air inside the boot 3 is discharged to the outside of the boot 3, and the inside of the boot 3 is maintained at atmospheric pressure.

  On the other hand, when the boot internal pressure P (kPa) decreases as the boot internal temperature decreases, that is, when the atmospheric pressure becomes negative (0 kPa) as a reference, the piston 30 moves inside the cylinder 20 toward the axial one end 21 side. To do. When the boot internal pressure P (kPa) is equal to or lower than the predetermined pressure, the piston 30 presses the inner biasing spring 41 and the boot internal communication hole via the second air passage 32 as shown in FIG. 21 a communicates with the inside of the cylinder 20. Thereby, outside air is introduced into the boot 3 and the inside of the boot 3 is maintained at atmospheric pressure.

  Here, with reference to FIG. 4 (a), (b) and FIG. 5 (a), (b), the operation | movement at the time of the air discharge mentioned above and air introduction is demonstrated in detail.

  4A and 4B are diagrams showing a state in which the boot internal pressure is positive with respect to the atmospheric pressure, and FIGS. 5A and 5B are diagrams in which the boot internal pressure is negative with respect to the atmospheric pressure. It is a figure which shows the state of.

First, as shown in FIG. 4A, when the boot internal pressure P becomes a positive boot internal pressure P _P1 (for example, 10 kPa) with reference to the atmospheric pressure (0 kPa), the load F ₁ is shown on the inner side surface 30a of the piston 30. Acts in the direction of the middle arrow. As a result, the piston 30 moves to a position where the other end (the left end in the drawing) of the outer biasing spring 42 contacts the side end face 22b of the cylinder 20. At this time, the outer biasing spring 42 is not yet pressed by the piston 30 and is in an uncompressed state. Here, the load F ₁ (N) is obtained by multiplying the boot internal pressure P _P1 (kPa) by the area S (mm ² ) of the inner side surface 30a (F ₁ = P _P1 × S).

The outer biasing spring 42 of the present embodiment has a spring constant k that can be displaced (compressed) by an amount corresponding to the thickness t (mm) when the load F ₁ (N) acts on the inner side surface 30a. Those having (= F ₁ / t) are employed. Alternatively, the thickness t (mm) may be set according to the spring constant k (N / mm) of the outer biasing spring 42. That is, in the present embodiment, when a load F ₂ (N) larger than the load F ₁ (N) is applied to the inner surface 30a, the piston 30 is moved as shown in FIG. The spring constant k (N / mm) or the thickness t (mm) is appropriately selected so as to move by a distance d (mm) from the position shown in FIG. Here, the load F ₂ (N) is obtained as a value obtained by multiplying the positive boot internal pressure P _P2 (kPa) larger than the boot internal pressure P _P1 (kPa) by the area S (mm ² ) of the inner side surface 30a ( F ₂ = P _P2 × S). The thickness t (mm) is the axial thickness between the outer surface 30b of the piston 30 and the first outer opening 31b. The distance d (mm) is larger than the thickness t (mm).

Therefore, when the load F ₂ (N) acts on the inner side surface 30a, the piston 30 moves from the position shown in FIG. 4A to the position shown in FIG. 4B, and presses the outer biasing spring 42. The displacement amount δ (mm) of the outer biasing spring 42 at this time is the same as the thickness t (mm).

  As a result, as shown in FIG. 4B, the first outer opening 31b and the external communication hole 22a communicate with each other. As a result, the air inside the boot 3 is discharged to the outside of the boot 3 through the first air passage 31.

  At this time, grease may enter the inside of the cylinder 20, but since the drive shaft 1 is rotating, the entered grease is pressed against the inner wall surface of the cylinder 20 by centrifugal force. For this reason, grease does not flow into the first air passage 31 from the first inner opening 31a. Therefore, the grease does not leak out of the boot 3.

On the other hand, in the state shown in FIG. 4B, when the boot internal pressure P becomes equal to or less than the boot internal pressure P _P1 (kPa), the load acting on the inner side surface 30a of the piston 30 also becomes equal to or less than the load F ₁ (N). Due to the urging force of the outer urging spring 42, the piston 30 is pushed back toward the axial end portion 21 side (right side in the drawing) of the cylinder 20. Thereby, as shown to Fig.4 (a), the 1st outer side opening part 31b will be in a closed state, and the inside of the boot 3 (refer FIG. 1) will be in a sealed state.

On the other hand, as shown in FIG. 5A, when the boot internal pressure P _M1 becomes negative (for example, −10 kPa) with reference to the atmospheric pressure (0 kPa), the inside of the piston 30 The load acting on the side surface 30a is negative. That is, a load −F ₁ (N) opposite to the above-described load F ₁ (N) acts on the outer surface 30 b of the piston 30. As a result, the piston 30 moves to a position where the other end (the right end in the figure) of the inner biasing spring 41 comes into contact with the side end surface 21b of the cylinder 20. At this time, the inner biasing spring 41 is not yet pressed by the piston 30 and is in an uncompressed state. Here, the load −F ₁ (N) is obtained as a value obtained by multiplying the boot internal pressure P _M1 (kPa) by the area S (mm ² ) of the outer surface 30b (−F ₁ = P _M1 × S). The areas of the inner side surface 30a and the outer side surface 30b are both S (mm ² ).

The inner biasing spring 41 of the present embodiment is the same as the outer biasing spring 42 described above, and the axial thickness between the inner side surface 30a and the second inner opening 32b is the above thickness. It is the same as t (mm). Therefore, when a load −F ₂ (N) larger than the load −F ₁ (N) is applied to the outer surface 30b, the piston 30 is positioned as shown in FIG. 5 (a) as shown in FIG. 5 (b). Is moved by a distance d (mm). Here, load _-F 2 (N), said boot pressure _P M1 (kPa) determined by a value obtained by multiplying the area S (mm ²⁾ to a large negative boot pressure _P M2 (kPa) than (-F ₂ = P _M2 × S). The distance d (mm) is larger than the thickness t (mm).

Therefore, when the load −F ₂ (N) acts on the outer side surface 30b, the piston 30 moves from the position shown in FIG. 5A to the position shown in FIG. 5B, and the inner biasing spring 41 is moved. Press. The displacement amount δ (mm) of the inner biasing spring 41 at this time is the same as the thickness t (mm). As a result, as shown in FIG.5 (b), the 2nd inner side opening part 32b and the communication hole 21a in a boot come to communicate. Thereby, outside air is introduced into the boot 3 through the second air passage 32. On the other hand, in the state shown in FIG. 5B, when the boot internal pressure P is equal to or higher than the boot internal pressure P _M1 (kPa), the load acting on the outer surface 30b of the piston 30 is also equal to or lower than the load −F ₁ (N). The piston 30 is pushed back to the other axial end 22 side (left side in the figure) of the cylinder 20 by the biasing force of the inner biasing spring 41. Thereby, as shown to Fig.5 (a), the 2nd inner side opening part 32b will be in a closed state, and the inside of the boot 3 (refer FIG. 1) will be in a sealed state.

  Next, the relationship between the boot internal temperature and the boot internal pressure will be described with reference to FIG.

  In the graph showing the boot internal pressure in FIG. 6, the thin solid line is a graph showing the boot internal pressure when the conventional drive shaft not including the pressure adjusting device 10 according to the present embodiment is applied, and the thick solid line is the pressure It is a graph which shows the boot internal pressure at the time of applying the drive shaft 1 of this invention provided with the adjustment apparatus 10. FIG.

As shown in FIG. 6, when the vehicle starts running, the boot internal temperature rises from the boot internal temperature K ₁ (° C.) to the boot internal temperature K ₂ (° C.). Then, during running of the vehicle, the boot in temperature, to remain at the travel start of the boot in the temperature K _{1 (°} C.) higher than boots the temperature K _{2 (℃).}

At this time, the conventional boot internal pressure temporarily rises to the positive pressure P ₂ (kPa) with respect to the atmospheric pressure as the boot internal temperature rises (between time T ₀ (h) and time T ₁ (h)). Thereafter, the air inside the boot begins to escape, and the conventional boot internal pressure decreases to atmospheric pressure (between time T ₁ (h) and time T ₂ (h)). Next, when the vehicle stops, the conventional boot internal pressure temporarily decreases to the negative pressure P ₄ (kPa) with respect to the atmospheric pressure as the boot internal temperature decreases (from time T ₃ (h) to time T ₄ (h). )while). Thereafter, air begins to enter the boot, and the conventional boot internal pressure rises to atmospheric pressure (between time T ₄ (h) and time T ₅ (h)).

On the other hand, the boot internal pressure of the present invention once rises to the positive pressure P ₁ (kPa) as the vehicle travels, as in the conventional boot internal pressure. However, the positive pressure P ₁ (kPa) is sufficiently lower than the positive pressure P ₂ (kPa). Then, after the boot internal pressure reaches the positive pressure P ₁ (kPa), the air inside the boot 3 is quickly discharged by the pressure adjusting device 10, so that the boot internal pressure is increased at an early stage compared to the conventional case. Maintained at atmospheric pressure. Next, even after the vehicle stops, the boot internal pressure of the present invention temporarily decreases to the negative pressure P ₃ (kPa) as the boot internal temperature decreases, as with the conventional boot internal pressure. However, the negative pressure P ₃ (kPa) is sufficiently lower than the negative pressure P ₄ (kPa). Then, after the boot internal pressure reaches the negative pressure P ₃ (kPa), air is quickly introduced into the boot 3 by the pressure adjusting device 10, so that the boot internal pressure is increased at an early stage compared to the conventional case. Maintained at atmospheric pressure.

  As described above, the boot internal pressure of the present invention has a longer period (time) of maintaining the atmospheric pressure than the conventional boot internal pressure. For this reason, fluctuations in the boot internal pressure of the present invention are significantly reduced compared to the conventional boot internal pressure.

  As described above, the drive shaft 1 according to the present embodiment has the cylinder 20 inside the drive shaft 1, and the piston having the first air passage 31 and the second air passage 32 inside the cylinder 20. 30 is slidably accommodated. For this reason, for example, when the internal pressure of the boot becomes a positive pressure with respect to the atmospheric pressure, the piston 30 moves inside the cylinder 20 toward the other end 22 in the axial direction and presses the outer biasing spring 42, thereby The external communication hole 22 a communicates with the inside of the cylinder 20 through one air passage 31. Thereby, the air inside the boot 3 can escape to the outside of the boot 3. As a result, the boot internal pressure can be maintained at atmospheric pressure.

  On the contrary, when the internal pressure of the boot becomes negative with respect to the atmospheric pressure, the piston 30 moves inside the cylinder 20 toward the one end 21 in the axial direction and presses the inner biasing spring 41. The in-boot communication hole 21 a and the inside of the cylinder 20 communicate with each other through the second air passage 32. Thereby, the air outside the boot 3 can be taken into the boot 3. As a result, the boot internal pressure can be maintained at atmospheric pressure.

  Thus, in the drive shaft 1 according to the present embodiment, the pressure control valve in which the piston 30 inside the cylinder 20 maintains the boot internal pressure at atmospheric pressure even when the boot internal pressure rises and falls. Therefore, it is possible to prevent fluctuations in the boot internal pressure with a simple configuration, that is, a low-cost configuration. Therefore, it is possible to prevent the boot 3 from being deformed or caused to be abnormally worn due to contact with members around the drive shaft, for example, due to fluctuations in the boot internal pressure. As a result, deterioration of the boot 3 can be suppressed and the life can be extended.

  Further, the drive shaft 1 according to the present embodiment is provided at a position where the first inner opening 31 a of the first air passage 31 is separated from the inner wall surface of the cylinder 20. The applied grease is pressed against the inner wall surface of the cylinder 20 by the action of a centrifugal force according to the rotation of the drive shaft 1, and only the air inside the boot 3 can be discharged to the outside.

  In the present embodiment, the inner biasing spring 41 and the outer biasing spring 42 are fixed to the piston 30. However, the present invention is not limited to this. For example, the inner biasing spring 41 is attached to the side end surface 21b of the cylinder 20. The outer biasing springs 42 may be fixed to the side end surfaces 22b of the cylinders 20, respectively.

Further, in the present embodiment, as shown in FIG. 1, the cylinder 20 is driven so that the rotation center axis O _D of the drive shaft 1 and the center axis O _S of the cylinder 20 (see FIG. 2A) coincide. was formed in the interior of the shaft 1 is not limited to this, for example, such that the center axis O _S is inclined at a predetermined inclination angle with respect to the rotation center axis O _D, be formed cylinder 20 inside the drive shaft 1 Good.

  Further, in the present embodiment, an example in which the power transmission shaft according to the present invention is applied to a drive shaft provided between a differential and a drive wheel has been described. However, the present invention is not limited to this, and for example, a propeller shaft of an FR vehicle It is also possible to apply to.

  As described above, the power transmission shaft according to the present invention has an effect that it is possible to prevent fluctuations in the boot internal pressure with a low-cost configuration, and the connection portion with the joint is covered by the boot, for example, a drive It is useful for all power transmission shafts such as shafts and propeller shafts.

1 Drive shaft (power transmission shaft)
1a end 2 constant velocity joint (joint)
DESCRIPTION OF SYMBOLS 3 Boot 10 Pressure adjusting device 20 Cylinder 21 Axial direction one end part 21a Boot internal communication hole 22 Axial other end part 22a External communication hole 30 Piston 31 1st air passage 31a 1st inner side opening part (opening part)
31b First outer opening 32 Second air passage 32a Second outer opening 32b Second inner opening 41 Inner biasing spring (inner biasing member)
42 Outer biasing spring (outer biasing member)
O _D rotation center O _S central axis

Claims (1)

A power transmission shaft whose end connected to the joint is covered with boots,
A cylinder provided inside so that the rotation center axis of the power transmission shaft and the center axis coincide with each other and extend in the axial direction;
A piston slidably housed inside the cylinder;
An inner biasing member that biases the piston toward the other axial end of the cylinder when the piston reaches one axial end of the cylinder;
An outer biasing member that biases the piston toward one end in the axial direction of the cylinder when the piston reaches the other end in the axial direction of the cylinder;
The cylinder has an in-boot communication hole that communicates with the inside of the boot at the one axial end, and an external communication hole that communicates with the outside of the boot at the other axial end.
The piston moves to the other axial end of the cylinder and presses the outer urging member, the first air passage communicating the external communication hole and the inside of the cylinder, and the cylinder A second air passage that communicates with the communication hole in the boot and the inside of the cylinder when moving to one end in the axial direction and pressing the inner urging member;
The first air passage has an opening that opens to one end side in the axial direction of the cylinder,
The power transmission shaft, wherein the opening is provided at a position separated from an inner wall surface of the cylinder.

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