CHAIN TENSIONER

Abstract

To provide a simple-structured chain tensioner that reduces the burden of work required for assembling and maintenance, sufficiently damps the motion of the plunger, and helps reduce machining costs and size increases of the plunger and tensioner body. The chain tensioner includes a tensioner body with a plunger bore, a plunger, and a biasing member that biases the plunger. The plunger has raised portions with which a locking member engages. The plunger bore is provided with a locking member holding part on one side that is open. The locking member holding part is provided with an inclined surface at one end in the plunger entry direction, the inclined surface becoming progressively shallower in the plunger entry direction. The locking member can deform elastically in a cross section when engaging with the raised portion of the plunger.

Claims

1. A chain tensioner comprising: a tensioner body with a plunger bore that is open on one side; a cylindrical plunger slidably inserted in the plunger bore; and a biasing member that biases the plunger in an extension direction, the plunger including on an outer circumferential surface thereof a plurality of raised portions with which a locking member engages, the plunger bore being provided with a locking member holding part on one side that is open, the locking member holding part being open toward a center axis of the plunger and holding the locking member, the locking member holding part being provided with an inclined surface at least at one end in a plunger entry direction in which the plunger enters into the plunger bore, the inclined surface becoming progressively shallower in the plunger entry direction, the locking member being allowed to deform elastically in a cross section inside the locking member holding part when engaging with the raised portion of the plunger.

2. The chain tensioner according to claim 1, wherein the raised portions of the plunger are formed on an outer circumferential surface of the plunger in an annular form.

3. The chain tensioner according to claim 1, wherein the locking member holding part has a volume that is equal to or larger than that of the locking member.

4. The chain tensioner according to claim 1, wherein the locking member holding part is formed in an annular form, and the locking member has a ring-like shape.

5. The chain tensioner according to claim 1, wherein the locking member holding part is formed as a plurality of holes open toward the center axis of the plunger bore, and the locking member has a spherical shape.

6. The chain tensioner according to claim 1, wherein the locking member holding part is formed as a groove open toward the center axis of the plunger bore, and the locking member has a bar-like shape with ends.

7. The chain tensioner according to claim 1, wherein the locking member is at least partly fixed to the locking member holding part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a partial cross-sectional view of a chain tensioner 100 according to one embodiment of the present invention;

[0033] FIG. 2 is a schematic enlarged view of part A of the chain tensioner 100 according to one embodiment of the present invention;

[0034] FIG. 3 is a schematic enlarged view of part A of the chain tensioner 100 according to one embodiment of the present invention, illustrating a state when the plunger 120 has moved in the plunger entry direction; and

[0035] FIG. 4 is a schematic enlarged view of part A of the chain tensioner 100 according to one embodiment of the present invention, illustrating a state when the plunger 120 has moved to the open side of the plunger bore 111.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Hereinafter, a chain tensioner 100 according to one embodiment of the present invention will be described with reference to the drawings.

[0037] For ease of explanation, illustration of components other than the tensioner body 110, plunger 120, and locking member 130 is omitted in FIG. 2 to FIG. 4.

[0038] The chain tensioner 100 includes a tensioner body 110 with a plunger bore 111 that is open on one side, a cylindrical plunger 120 slidably inserted in the plunger bore 111, and a biasing member S that biases the plunger 120 in the extension direction, as shown in FIG. 1 and FIG. 2.

[0039] The tensioner body 110 has an oil supply path 112 in the back of the plunger bore 111. A check valve V shuts off flow between the oil supply path 112 and the plunger bore 111. Pressure from the oil supply path 112 side opens the check valve V to allow the oil to be supplied.

[0040] A locking member holding part 113 in the form of an annular groove is provided on the inner circumferential surface on the open side of the plunger bore 111. The groove opens toward the center axis of the plunger bore 111.

[0041] The locking member holding part 113 is composed of a locking wall 115 on the open side of the plunger bore 111 and an inclined surface 114. The inclined surface 114 is formed such that the locking member holding part becomes progressively shallow inwards of the plunger bore 111.

[0042] The locking member holding part 113 has a volume that is at least larger than that of the locking member 130 to be described later.

[0043] The plunger 120 includes a plunger hole 121, and a plurality of raised portions 122 and depressed portions 123 on its outer circumferential surface.

[0044] The plunger hole 121 is configured to allow the biasing member S to fit in, which constantly biases the plunger 120 towards the open side of the plunger bore 111.

[0045] The locking member 130 is an annular elastic member made of rubber for example and able to elastically change its cross-sectional shape upon application of an external force. The locking member 130 has an inside diameter that is at least smaller than the outside diameter of the raised portions 122 of the plunger.

[0046] Next, the process of mounting the plunger 120 and locking member 130 of the chain tensioner 100 according to one embodiment of the present invention is described with reference to FIG. 1 and FIG. 2.

[0047] First, the check valve V is attached to shut off flow between the plunger bore 111 and the oil supply path 112 of the tensioner body 110.

[0048] Next, the biasing member S, plunger 120, and locking member 130 are assembled into the plunger bore 111.

[0049] The locking member 130 is positioned between the plunger's depressed portion 123 that is located nearest the open end of the plunger bore 111 and the locking member holding part 113.

[0050] Next, how the plunger 120 of the chain tensioner 100 according to one embodiment of the present invention provides the vibration damping effect is explained with reference to FIG. 1 to FIG. 4.

[0051] The plunger 120 is constantly biased in the extension direction by the biasing member S, i.e., towards the open side of the plunger bore 111 to apply tension via a guide shoe (not shown) to the chain (not shown) passed around in the engine (not shown).

[0052] The space between the plunger bore 111 and the plunger hole 121, which is filled with oil supplied from the oil supply path 112 via the check valve V when the engine (not shown) is running, functions as an oil pressure chamber or hydraulic damper, and damps the vibration applied from the guide shoe (not shown) to the plunger 120. The vibration energy of the plunger 120 is thus reduced, which effectively prevents the chain from rattling or minimizes noise generation.

[0053] The oil inside the oil pressure chamber is allowed to flow out slightly through an oil flow passage (not shown) provided in the plunger bore 111 or the plunger 120.

[0054] When the engine is started for the first time, or immediately after the engine that has not been operated for a while is started, the oil pressure chamber may not be fully filled with oil. When this is the case, the oil pressure chamber cannot serve the function of a hydraulic damper and may fail to damp the vibration energy of the plunger 120, so that unstable movement of the plunger 120 may result in chain rattling or noise generation.

[0055] Now, how the locking member 130 behaves in response to the vibration of the plunger 120 at the start of the engine will be described.

[0056] When the plunger 120 moves into the plunger bore 111 (hereinafter plunger entry direction), the locking member 130 moves in the plunger entry direction along with a raised portion 122 of the plunger as shown in FIG. 3.

[0057] The locking member 130 between the inclined surface 114 and the depressed portion 123a elastically deforms and changes its cross section to some extent. However, since the inclined surface 114 of the locking member holding part 113 is formed such that the holding part becomes progressively shallow inwards of the plunger bore 111, the locking member 130 soon applies a reaction force to the plunger 120 via the depressed portion 123a of the plunger, gradually slowing down, and eventually stopping, the movement of the plunger 120 in the plunger entry direction.

[0058] Therefore, even in a situation where the oil pressure chamber is not fully filled with oil such as when the engine is started, the movement of the plunger 120 in the plunger entry direction can be sufficiently damped by the reaction force generated by the cross-sectional elastic deformation of the locking member 130 so that chain rattling and noise generation can be minimized.

[0059] When the plunger 120 moves out from the plunger bore 111 (hereinafter plunger extension direction), the locking member 130 moves in the plunger extension direction along with the plunger 120 until the locking member contacts the locking wall 115, as shown in FIG. 4.

[0060] The locking member 130 is stopped when it comes into contact with the locking wall 115. However, as the plunger 120 keeps moving in the plunger extension direction, the locking member 130 gradually increases in diameter along the contour between the depressed portion 123a and the raised portion 122 of the plunger, and elastically changes the cross-sectional shape in conformity to the locking member holding part 113.

[0061] The locking member 130 thus disengages from the depressed portion 123a and raised portion 122 of the plunger, allowing the plunger 120 to keep moving in the plunger extension direction and press the chain via the guide shoe without resistance from the locking member 130.

[0062] If the chain has worn due to wear by then, the plunger 120 moves out further so that the locking member 130 rides over the plunger's raised portion 122 and fits into the depressed portion 123b.

[0063] The locking member holding part 113 has a larger volume than that of the locking member 130. Therefore, the locking member 130, when riding over the plunger's raised portion 122, can shift into the locking member holding part 113 almost entirely so that the locking member 130 hardly applies a resisting force to the plunger 120 moving in the plunger extension direction.

[0064] When the plunger 120 moves in the plunger entry direction again, the locking member 130 held between the plunger's depressed portion 123b and the inclined surface 114 restricts the amount of movement of the plunger 120 while also damping the kinetic energy of the plunger.

[0065] This way, the vibration amplitude of the plunger 120 is kept within the range where the plunger can sufficiently press the chain, and therefore the plunger can keep the correct chain tension even when the chain has stretched due to wear.

[0066] The locking member 130 does not have to be in an annular form. For example, the locking member may have a bar-like shape with ends, or a spherical shape, and a plurality of locking member holding parts in the form of recessed grooves or holes may be formed in the inner circumferential surface of the plunger bore 111 in conformity to the shape of the locking member. Raised portions and depressed portions in the form of protrusions and grooves may be formed on the outer circumferential surface of the plunger in conformity to the number and shape of the locking member.

[0067] In the case with a spherical locking member 130, for example, the resisting force applied by the locking member to the plunger can be readily tailored by adjusting the number or arrangement of the locking member holding parts and locking members. In the case with a segmented bar-like locking member 130, the resisting force applied by the locking member to the plunger can be readily tailored by adjusting the number or arrangement of the locking member holding parts and locking members, as well as the amount of oil flow between the outer circumferential surface of the plunger and the plunger bore can be tailored by adjusting the orientation or position of the locking member holding parts in the form of grooves.

[0068] Optionally, the locking member 130 may be partly fixed to the locking member holding part 113 by bonding or welding. This ensures that at least a part of the locking member 130 will remain inside the locking member holding part 113 when the locking member 130 is compressed between the raised portion 122 of the plunger and the inclined surface 114 and undergoes a large elastic deformation in cross section. The locking member 130, when released from the compression, can then restore its shape reliably, as it is located inside the locking member holding part 113.

[0069] Moreover, fixing the locking member 130 will prevent it from misalignment, detachment, or entanglement between the plunger 120 and the plunger bore 111, during the assembly of the chain tensioner 100.

[0070] While one embodiment of the present invention has been described in detail, the present invention is not limited to the embodiment described above and may be carried out with various design changes without departing from the scope of the present invention set forth in the claims.

[0071] The configuration of the locking member holding part is not limited to the one with an inclined surface and a locking wall described in the embodiment above. For example, there may be a connecting wall that connects the inclined surface and the locking wall. Optionally, the inclined surface may include some parts with inclination angles varied stepwise.

[0072] The locking member is not limited to the annular, or segmented bar-like or spherical shape mentioned in the embodiment above. For example, the locking member may be formed in a tubular, prismatic, or pyramid shape.

[0073] In the embodiment described above, an oil flow passage is provided in the plunger bore and the plunger. The configuration of the oil flow passage is not limited to this example. For example, a slight gap between the plunger bore and the plunger may serve as an oil flow passage, or a groove may be provided on the surface of the locking member to serve as an oil flow passage.