Blade-type chain tensioner

Abstract: A blade-type chain tensioner includes a blade shoe (2) having a chain sliding face (20a), a blade spring (3) biasing the blade shoe toward an associated chain, and a bracket (4) to rotatably support the fixed end of the blade shoe. The length of the blade spring (3) is shorter than that of the chain sliding face (20a) of the blade shoe (2). The first end (3b) of the blade spring is attached onto the fixed end of the blade shoe and slidably contacts the distal end of the bracket at a contact point located between the fixed and free ends of the shoe.

Description: This invention relates to a blade-type tensioner having a blade shoe with a chain sliding face and a blade spring for application of spring force onto the blade shoe, as disclosed in JP57134055A and corresponding to the preamble of claims 1 and 2. FIG. 6 shows one example of a conventional blade tensioner, used for tensioning an associated chain. As shown in the figure, conventional blade tensioner 100 includes a blade shoe 101 of resin that extends in a curved line form, multiple blade springs 102 that extend along blade shoe 101 and are attached onto the blade shoe, and a metal bracket 120 as the bracket member that supports blade shoe 101. Projection 110, having curved face 110a, is formed at the tip of blade shoe 101 and the projection 110 has concavity 111 that stores one end of blade spring 102. A nearly triangular projection 112 is formed at the fixed end end of blade shoe 101 and a concavity 113, that stores the other end of blade spring 102, is formed in the projection 112. Holes for attaching, 121, 122, are formed in bracket 120. Sliding face 125, on which projection 110 at blade shoe tip 101 can contact and slide, is formed at the tip of bracket 120. One end of pin 130 is fixed at the center of bracket 120. Projection 112, as the fixed end side of blade shoe 101, is inserted rotatably onto pin 130. During operation of the chain, the chain runs on sliding face 101 a of blade shoe 101 and the press-down load, due to blade shoe 101 and deformation of blade spring 102, acts on the chain at such time. The conventional blade tensioner is used where the center-to-center distance of the chain is relatively short, such as a chain to drive the oil pump of an engine. On the other hand, because of the demand to lower the cost of the engine, it is desired to use a blade tensioner of relatively low manufacturing cost, for a cam chain that drives between the crankshaft and the camshaft. In the case of a cam chain, the center distance is long, generally, so that the length of the blade tensioner needs to be long to match the center distance. However, when the total length of the blade tensioner is long, the resonant frequency becomes low due to its lower natural frequency and, as a result, the blade tensioner resonates within the rpm range of the engine and fatigue damage can occur. GB 505746 discloses an improved tensioning device for transmission chains including a blade shoe having a fixed end which is rotatably disposed on a mounting and a free end opposite the fixed end. A blade spring is attached to the blade shoe for biasing the shoe against a chain in use, the free end of the spring being bent to form a V-shaped channel in which the tip of a screw engages, the screw being adjustable to vary the biasing force applied by the spring. This invention addresses such a conventional problem. The objective is to offer a blade tensioner that can prevent resonance in the rpm range and fatigue damage. It is a first object of the invention to provide a blade tensioner which applies tension to a chain. The tensioner includes a blade shoe with a chain sliding face, a blade spring that applies the spring force to the blade shoe and a bracket upon which to attach the blade shoe. A fixed end, portion, or proximal end of the blade shoe is rotatably attached to the bracket. The blade spring contacts the tip or distal end of the bracket at a contact point located between the free end and the fixed end of the blade shoe. According to one aspect of the present invention there is provided a blade-type chain tensioner comprising: a bracket; a blade shoe having a chain sliding face, a fixed end and a free end opposite said fixed end, said blade shoe being rotatably disposed on said bracket at said fixed end of said blade shoe; and a first blade spring mounted on a face opposite the chain sliding face of said blade shoe, characterised in that said first blade spring extends from said fixed end to said free end of said blade shoe so as to urge said blade shoe, in use, toward an associated chain, and in that a protrusion is formed on said blade shoe at an intermediate position between said free end of said blade shoe and said fixed end thereof, which protrusion slidably contacts a distal end of said bracket. In accordance with another aspect of the present invention there is provided a blade-type chain tensioner comprising: a bracket; a blade shoe having a chain sliding face, a fixed end and a free end opposite said fixed end, said blade shoe being rotatably disposed on said bracket at said fixed end of said blade shoe; and a first blade spring mounted on a face opposite the chain sliding face of said blade shoe, characterised in that said first blade spring extends in use, from said fixed end to said free end of said blade shoe so as to urge said blade shoe toward an associated chain, and in that a protrusion is formed on the bracket proximate to a distal end thereof, which protrusion slidably contacts said first spring at an intermediate position between said free end of said blade shoe and said fixed end thereof. In this invention, the chain runs on the chain sliding face of the blade shoe. Proper tension is applied to the chain by the action of the blade shoe activated by the force of the deformed blade spring. The natural frequency of the blade tensioner is determined by the location where the tip of the bracket and the blade spring come into contact. As the contact point between the spring and the bracket moves toward the tip of the blade shoe, the natural frequency of the shoe becomes lower. On the other hand, as the contact point moves toward the fixed end of the blade shoe, the natural frequency of the shoe and tensioner becomes higher. The objective is to raise the natural frequency of the blade tensioner higher than the frequency of vibrations generated by the engine. In the present invention, the location of the contact point between the tip portion of the bracket and blade spring or blade shoe is located between the blade shoe tip or free end and its fixed end, so that the natural frequency of the blade tensioner is made relatively high. Thereby, the resonant frequency of the blade tensioner can be set relatively high compared to those frequencies generated by the engine and, as a result, the resonance of the blade tensioner within the rpm range of the engine can be prevented and fatigue damage due to resonance can be prevented. The length of the blade spring is preferably shorter than the length of the sliding face of the blade shoe. A first end of the blade spring is attached to the fixed end of the blade shoe and the second end is located apart from the blade shoe and, at the same time, the second end slidably contacts the tip of the bracket. The overall length of the blade spring is shorter than the length of the sliding face of the blade shoe and the second end of the blade spring (i.e. the tip), located apart from the blade shoe, slides on the tip of the bracket. The tip of the bracket is in contact with the second end of the blade spring and the position of this contact point is located between the free and the fixed ends of the blade shoe and, in one example, it is offset from a mid position between the ends of the blade shoe and located nearer to the blade shoe tip. In this manner, the resonance frequency of the blade tensioner can be set high and, as above, the resonance in the engine rpm range and fatigue damage due to resonance can be prevented. In a preferred embodiment of the invention, the blade tensioner includes a further or second blade spring that runs along the face opposite the chain sliding face of the blade shoe. Thus, the deformation per unit load is small. That is, a blade tensioner with a high spring constant is offered. The projection at the bracket tip contacting the blade spring in the one aspect of the invention or the projection on the blade shoe side by the bracket tip in the other aspect of the invention, this contact point being located approximately midway between the blade shoe free end and its fixed end, has the advantage that the resonance frequency of the blade tensioner can be set high and, as above, the resonance in the engine rpm range and fatigue damage due to the resonance can be prevented. In a development of the invention, the blade spring includes a first blade spring that is provided on the side opposite to the chain sliding face of the blade shoe and a second blade spring which is shorter than the chain sliding face, and a first end of which is attached to the fixed end of the blade shoe and the second end is positioned away from the blade shoe. At the same time, the other end of the second blade spring is attached to the projection that is provided to the bracket. The projection of the bracket contacts the second or free end of the second blade spring and this point of contact is located between the blade shoe free end and its fixed end. Thereby, the resonance frequency of the blade tensioner can be set high and the resonance in the engine rpm range and resulting fatigue damage are prevented. The protrusion can be located between the ends of the element (the shoe or bracket) upon which it is formed. The location of the protrusion defines the location of the point of contact between the shoe and the bracket. It can be seen that as the point of contact between the shoe and bracket is moved from a location near the middle of the shoe to the end of the shoe the free span of tensioner shoe thus created is lengthened and thus, the natural resonant frequency of the shoe becomes lower. It is therefore an object of the invention to locate the point of contact between the shoe and the bracket via the protrusion operating therebetween at a middle location between the ends of the shoe. Thus, the natural frequency of the shoe is maintained at a higher frequency relative to lower engine vibrations and reduces the susceptibility of the tensioner to damage from resonant vibrations originating from the engine and associated mechanisms. In order that the invention may be well understood, there will now be described some embodiments thereof, given by way of example, reference being made to the accompanying drawings, in which: FIG. 1 is a side view of a blade tensioner which does not form part of this invention; FIG. 2 is the sectional view along line II-II of FIG. 1; FIG. 3 is a side view of a second blade tensioner which does not form part of this invention; FIG. 4 is a side view of a blade tensioner of a first embodiment of this invention; FIG. 5 is a side view of the blade tensioner of the second embodiment of this invention; and FIG. 6 is a side view of a conventional blade tensioner. FIG. 1 is a side view of the blade tensioner wich does not form part of of this invention; FIG. 2 is its cross-section along II-II, As shown in FIG. 1, blade tensioner 1 includes a blade shoe 2 of resin which is curved in an arc form, a blade spring 3 that pushes blade shoe 2, and a metal bracket 4 that acts as the bracket to attach blade shoe 2. As shown in FIG. 2, blade shoe 2 has a generally U-shaped cross-section and is composed of bottom wall 20 and side walls 21 that stand on both its sides. Outer face 20a of bottom wall 20 is a chain sliding face. Fixed end 2b of blade shoe 2 is attached to bracket 4 rotatably via pin 5. Blade spring 3 separates gradually from inside face 20b of bottom wall 20 of the blade shoe 2 from its rear part 3b, which is in contact with inside face 20b, to its tip 3a and it is curved in an arc form as a whole. The length of blade spring 3 is shorter than blade shoe 2. Rear part 3b of blade spring 3 is attached to boss 22 formed in fixed end 2b of blade shoe 2 and its tip 3a is placed away from blade shoe 2. Curved face 31 is formed on tip 3a and said curved face 31 contacts tip 4a of bracket 4 slidably. Contact of the tip 4a of bracket 4 with tip 3a of blade spring 3 is made at a point C located between tip 2a and fixed end 2b of blade shoe 2. Bolt hole 40 in FIG. 1 is a bolt hole for attachment of bracket 4 onto the engine. Blade tensioner 1 is attached by an attachment bolt (not shown) inserted into the bolt hole and by pin 5 to the engine via bracket 4. FIG. 3 is a side view of a second blade tensioner which does not form part of this invention and the same reference characters are assigned to the same or corresponding parts as in FIG. 1. Here, the point of provision of the blade shoe and blade spring and the shape of the blade shoe are different from the first embodiment above. As shown in FIG. 3, blade shoe 2 has a rectangular cross-section and blade spring 6 is mounted on inside face 20b opposite to chain sliding face 20a of blade shoe 2 along the inside face 20b. Tip 6a of blade spring 6 is attached to concavity 23 formed at tip 2a of blade shoe 2 and its rear end 6b is attached to concavity 24 formed at fixed end 2b of blade shoe 2. In this second embodiment, too, contact between tip 4a of bracket 4 with tip 3a of blade spring 3 is located at a point C approximately midway between tip 2a of blade shoe 2 and its fixed end 2b. FIG. 4 is a side view of a blade tensioner of a first embodiment of this invention and the same or corresponding parts as FIG. 3 are assigned the same reference characters. Here, a projecting member, which is the contact point with the bracket tip, is provided on the side of the blade shoe. As shown in FIG. 4, a projection 25 projecting toward bracket 4 is formed at the mid point between tip 2a and fixed end 2b of blade shoe 2. Projection 25 has a curved face 25a and the curved face 25a contacts tip 4a of bracket 4 slidably. In this third embodiment, contact between tip 4a of bracket 4 with projection 25 is at point C located at the mid point between tip 2a and fixed end 2b of blade shoe 2. Alternately, the projection can be formed at tip 4a of bracket 4, the curved face can be formed on the projection towards blade shoe 2 and the curved face can contact blade spring 6 slidably. FIG. 5 is a side view of the blade tensioner of the second embodiment of this invention and the same or corresponding parts as FIG. 4 are assigned the same reference characters. The projection is provided at the tip of the bracket and additional blade spring are provided. As shown in FIG. 5, projection 42 projecting toward blade shoe 2 is formed at tip 4a of bracket 4. A curved face 42a is formed on projection 42 and the curved face contacts blade spring 6 mounted slidably on blade shoe 2. Blade spring 3 gradually separates in the lengthwise direction from its rear end 3b to its tip 3a , from inside face 20b, starting from its contact with inside face 20b of blade shoe 2 and it is in an arc-curved form as a whole. The length of blade spring 3 is shorter than the chain sliding face 2a of blade shoe 2. Rear end 3b of blade spring 3 is attached to boss 22 at fixed end 2b of blade shoe 2 and tip 3a is placed away from blade shoe 2 and is attached slidably to through-hole 42b (attachment part) formed on projection 42. Thereby, tip 3a of blade spring 3 is slidable against projection 42 of bracket 4. Incidentally, a groove can be formed instead of through-hole 42b to slidably attach blade spring 3. In the second embodiment, contact of projection 42 of bracket 4 with blade spring 4 on the side of blade shoe 2 is at point C located at or near the mid point between tip 2a and fixed end 2b of blade shoe 2. When the chain is in operation, the chain runs on chain sliding face 20a of blade shoe 2 and proper tension is applied to the chain by blade shoe 2 as well as the elastic repulsive force of deformed blade springs 3, 6. In such case, the natural frequency of blade tensioner 1 is determined by the position of contact point C. The closer the contact point C is to tip 2a of blade shoe 2, the lower the natural frequency and, conversely, the closer the contact point C is to fixed end 2b of blade shoe 2, the higher the natural frequency of the tensioner. In the embodiments above, contact point C is located between tip 2a and fixed end 2b of blade shoe 2 and is closer to tip 2a, so that the natural frequency of blade tensioner 1 is relatively high. Thereby, the resonance frequency of blade tensioner 1 can be set high and, as a result, the resonance of blade tensioner 1 in the engine rpm range and the resulting fatigue damage can be prevented. In the embodiments above, one of two members that contact at contact point C has a curved face (see codes 31, 25a, 42a). Thereby, blade shoe 2 and blade springs 3, 6 do not interfere with other members and their deformation is smooth. As a result, the chain is tensioned properly during its operation. As detailed above, the blade tensioner contact point of the tip of the bracket with the blade spring or blade shoe is at the mid point between the tip and fixed end of the blade shoe and, thereby, the resonance frequency of the blade tensioner can be set high. As a result, the resonance of the blade tensioner in the engine rpm range and the resulting fatigue damage can be prevented. In one embodiment, the blade spring of the blade tensioner is shorter than the sliding face of the blade shoe and the other end of the blade spring (i.e. the tip), placed away from the blade shoe, is slidable against the tip of the bracket. The tip of the bracket is in contact with the other end of the blade spring and the contact point is located at the mid point between the tip and fixed end of the blade shoe. Thereby, the resonance frequency of the blade tensioner can be set high and the resonance of the blade tensioner in the engine rpm range and resulting fatigue damage can be prevented. In another embodiment, an additional blade spring is provided on the face opposite the chain sliding face of the blade shoe, therefore, the amount of deformation per unit load is small, that is, the spring constant of the blade tensioner is high. In a further embodiment, the other end of the blade spring has a curved face and the curved face contacts the tip of the bracket slidably. In such case, the tip of the bracket does not interfere, so that the deformation of the blade spring is smooth and a proper tension is applied to the operating chain. In a further embodiment, an outward projection is formed at the tip of the bracket or blade shoe at the mid point between the tip and fixed end of the blade shoe and the projection is provided slidably against the blade spring or bracket tip. The projection at the bracket tip contacts the blade spring or the projection on the side of the blade shoe contacts the bracket tip. This contact point is at the mid point between the tip and fixed end of the blade shoe. Thereby, the resonance frequency of the blade tensioner can be set high and the resonance in the engine rpm range and resulting fatigue damage can be prevented. In a further embodiment, the projection has a curved face and the curved face slidably contacts the blade spring or bracket tip. Therefore, deformation of the blade spring is made smooth. In a further embodiment, the blade spring is composed of a first blade spring provided on the face opposite to the chain sliding face of the blade shoe and a second blade spring is provided, which is shorter than the chain sliding face and one end of which is attached to the fixed end of the blade shoe and the other end is located away from the blade shoe. The other end ofthe second blade spring is attached to the projection of the bracket. The projection of the bracket is attached to the other end of the second blade spring and the contact point is between the tip and the fixed end of the blade shoe. Thereby, similarly to the first embodiment, the resonance frequency of the blade tensioner can be set high and resonance in the engine rpm range and resulting fatigue damage can be prevented. In a further embodiment, the projection of the bracket has a curved face and the curved face slidably contacts the first blade spring. The projection of the bracket has an attachment part to which the other end of the second blade spring can be slidably attached. Thereby, deformation of the blade spring is smooth. Certainly modifications which are within the ordinary skill in the art are considered to lie within the scope of this invention as defined by the following claims.

Claims: A blade-type chain tensioner comprising: a bracket (4); a blade shoe(2) having a chain sliding face (20a), a fixed end (2b) and a free end (2a) opposite said fixed end (2b), said blade shoe (2) being rotatably disposed on said bracket (4) at said fixed end (2b) of said blade shoe (2); and a first blade spring (6) mounted on a face opposite the chain sliding face (20a) of said blade shoe (2); wherein said first blade spring (6) extends from said fixed end (2b) to said free end of said blade shoe (2) so as to urge said blade shoe, in use, toward an associated chain, characterised in that a protrusion (25) is formed on said blade shoe (2) at an intermediate position between said free end (2a) of said blade shoe and said fixed end (2b) thereof, which protrusion slidably contacts a distal end (4a) of said bracket (4), at a contact point. A blade-type chain tensioner comprising: a bracket (4); a blade shoe (2) having a chain sliding face (20a), a fixed end (2b) and a free (2a) end opposite said fixed end (2b), said blade shoe (2) being rotatably disposed on said bracket (4) at said fixed end of said blade shoe (2); and a first blade spring (3) mounted on a face opposite the chain sliding face (20a) of said blade shoe (2); wherein said first blade spring (3) extends in use, from said fixed end (2b) to said free end (2a) of said blade shoe (2) so as to urge said blade shoe (2) toward an associated chain, characterised in that a protrusion (42) is formed on the bracket (4) proximate to a distal end thereof, which protrusion slidably contacts said first spring (3) at a contact point located at an intermediate position between said free end (2a) of said blade shoe and said fixed end(2b) thereof. A blade tensioner according to claim 2, further comprising a second blade spring (3) having a shorter length than the length of the chain face (20a) of said blade shoe (2), a first end (3a) of said second blade spring (3) being attached onto said fixed end (2b) of said blade shoe (2), and a second end (3a) of said second blade spring (3) being disposed apart from said blade shoe (2), said second end (3a) of said second blade spring (3) being fitted onto said protrusion (42) on the distal end (4a) of said bracket (4). A blade tensioner according to any of the preceding claims, wherein the protrusion (25;42) has a curved face (25a;42a). A blade tensioner according to any of the preceding claims, wherein said intermediate position is at a midpoint between said free end of said blade shoe and said fixed end thereof.

Inventors: TADA NAOSUMI, TADA, NAOSUMI
Applicants: BORGWARNER MORSE TEC JAPAN KK, BORGWARNER MORSE TEC JAPAN K.K.
Application year: 2000
Main classification: F16H7
IPC codes: F16H7