Speed reducer

A speed reducer includes a first transmission shaft, an eccentric wheel, a first roller assembly, a rotating wheel, a second roller assembly and a second transmission shaft. The rotating wheel includes a main body and an axle hole. The main body includes a convex structure and a concave structure. The convex structure is protruded from an outer periphery of the main body and has outer teeth. The outer teeth are contacted with the corresponding first rollers. The concave structure is concavely formed in a surface of the main body and includes inner teeth. The inner teeth are contacted with plural second rollers of the second roller assembly. Since the speed reducer is designed to have four operating situations, the speed reducer can have various reduction ratios.

FIELD OF THE INVENTION

The present invention relates to a speed reducer, and more particularly to a speed reducer with the benefits of a RV reducer and a harmonic drive reducer.

BACKGROUND OF THE INVENTION

Generally, a motor is operated at a high speed and a low torsion force. In other words, it is difficult to drive a large-sized load. Consequently, for allowing the motor to drive a heavy object, a speed reducer is used for reducing the rotating speed of the motor and increasing the torsion force.

Conventionally, the speed reducers are classified into several types, including rotary vector (RV) reducers and harmonic drive reducers. For example, the RV-E series reducer is a two-stage speed reducer produced by Nabtesco. The RV-E series reducer comprises a first speed reduction stage with a spur gear and a second speed reduction stage with an epicyclic gear. The gears of the first speed reduction stage and the second speed reduction stage are made of metallic material. The RV-E series reducer is a two-stage reduction design to reduce vibration and inertia while increasing ratio capabilities. The RV-E series reducer provides high-end performance in highly rigid and high reduction ratio configurations, and the rolling contact elements of the RV-E series reducer have high efficiency and long life. However, since the RV-E series reducer has larger volume and weight and has many components, the cost of the RV-E series reducer is high.

The harmonic drive reducer comprises a wave generator, a flex element (e.g., a flex spline) and a rigid gear. The elastic deformation of the flexible element can be controlled to result in a pushing action so as to transmit motion and power of mechanical transmission. The harmonic drive reducer has smaller size, lighter weight and higher precision when compared with the RV reducer. However, since the rigidity of the flex element of the harmonic drive reducer is lower than the metallic element, the harmonic drive reducer is unable to withstand high impact and has a problem of causing teeth difference friction. In other words, the use life of the harmonic drive reducer is shorter. Moreover, since the input speed of the harmonic drive reducer is not high, the reduction ratio of the harmonic drive reducer is lower.

Therefore, there is a need of providing a speed reducer with the characteristics of a RV reducer and a harmonic drive reducer in order to the overcome the above drawbacks.

SUMMARY OF THE INVENTION

An object of the present invention provides a speed reducer. The speed reducer comprises a rotating wheel, a first roller assembly and a second roller assembly. The rotating wheel comprises a convex structure and a concave structure. The convex structure is contacted with plural first rollers of the first roller assembly. The concave structure is contacted with plural second rollers of the second roller assembly. The cooperation of the rotating wheel and associated components can achieve the speed reducing purpose. By the speed reducer of the present invention, the problems of the conventional RV reducer (e.g., high volume, weight and cost) and the problems of the conventional harmonic drive reducer (e.g., the deformation of the flex spline and the teeth difference friction) will be overcome.

In accordance with an aspect of the present invention, there is provided a speed reducer. The speed reducer includes a first transmission shaft, an eccentric wheel, a first roller assembly, a rotating wheel, a second roller assembly and a second transmission shaft. The first transmission shaft has a first end and a second end. The eccentric wheel is eccentrically fixed on the second end of the first transmission shaft. The first roller assembly includes a first wheel disc and plural first rollers. The first wheel disc is arranged between the first end and the second end of the first roller assembly. The plural first rollers are disposed on the first wheel disc. The plural first rollers are selectively self-rotated. The rotating wheel includes a main body and an axle hole. The eccentric wheel is rotatably disposed within the axle hole. The main body includes a convex structure and a concave structure. The convex structure is protruded from an outer periphery of the main body and has one or plural outer teeth. The outer periphery of the main body is contacted with the corresponding first rollers. The concave structure is concavely formed in a surface of the main body and includes one or plural inner teeth. The second roller assembly includes a second wheel disc and plural second rollers. The plural second rollers are disposed on the second wheel disc. The plural second rollers are selectively self-rotated. The second rollers are contacted with the corresponding inner teeth. The second transmission shaft has a third end and a fourth end. The second wheel disc is fixed on the third end of the second transmission shaft. The number of the outer teeth and the number of the inner teeth are different. The number of the first rollers is at least one greater than the number of the outer teeth. The number of the second rollers is at least one greater than the number of the inner teeth.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a schematic exploded view illustrating a speed reducer according to an embodiment of the present invention. The speed reducer1can be applied to motors, machine tools, robotic arms, automobiles, motorcycles or other motive machines in order to provide a speed reducing function. As shown inFIG. 1, the speed reducer1comprises a first transmission shaft10, an eccentric wheel11, a first roller assembly12, a rotating wheel13, a second roller assembly14, a second transmission shaft15and a bearing16.

Preferably but not exclusively, the first transmission shaft10is a shaft lever that is made of metallic material or alloy. The first transmission shaft10has a first end100and a second end101. The first end100is a power input end for receiving an input power from a motor (not shown). The eccentric wheel11is a circular disc structure that is made of metallic material or alloy. Moreover, the eccentric wheel11has an eccentric hole110. The geometric center of the eccentric hole110is deviated from the geometric center of the eccentric wheel11. The second end101of the first transmission shaft10is penetrated through the eccentric hole110. Consequently, the eccentric wheel11is eccentrically fixed on the second end101of the first transmission shaft10. When the input power received by the first end100of the first transmission shaft10results in rotation of the first transmission shaft10, the eccentric wheel11is driven by the second end101of the first transmission shaft10. Consequently, the eccentric wheel11is eccentrically rotated relative to an axle center of the first transmission shaft10.

The first roller assembly12comprises a first wheel disc120and plural first rollers121. The first wheel disc120is a circular disc structure or a hollow cylindrical structure that is made of metallic material or alloy. Moreover, a bearing (not shown) is disposed within a center hole (not shown) of the first wheel disc120. The central hole is at the geometric center of the first wheel disc120. An example of the bearing includes but is not limited to a ball bearing, a needle bearing or an oil-retaining bearing. The first end100of the first transmission shaft10is penetrated through the bearing that is disposed within the center hole of first wheel disc120. Consequently, the first end100and the second end101of the first transmission shaft10are located at two opposite sides of the first wheel disc120. Preferably but not exclusively, the plural first rollers121are circular posts, which are made of metallic material or alloy. Moreover, the plural first rollers121are circumferentially and discretely arranged on a mounting surface122of the first wheel disc120at regular intervals. That is, the plural first rollers121and the second end101of the first transmission shaft10are located at the same side of the first wheel disc120. Optionally, the plural first rollers121are rotated about their own axles (i.e., self-rotation). That is, the plural first rollers121can be selectively rotated about fixed positions of the mounting surface122.

The rotating wheel13is made of metallic material or alloy. In this embodiment, the rotating wheel13comprises a main body130and an axle hole133. The axle hole133is located at the geometric center of the main body130. The bearing16is disposed within the axle hole133. Through the bearing16, the eccentric wheel11is rotatably disposed within the axle hole133. Consequently, when the eccentric wheel11is rotated, the rotating wheel13is synchronously rotated with the eccentric wheel11. The main body130comprises a first surface1300and a second surface1301, wherein the first surface1300and the second surface1301are opposed to each other. Moreover, the main body130comprises a convex structure131and a concave structure132. The first surface1300of the main body130is arranged between the plural first rollers121and located beside the mounting surface122of the first wheel disc120. The convex structure131is protruded from an outer periphery of the main body130. Moreover, the convex structure131comprises at least one outer tooth. In this embodiment as shown inFIG. 1, the convex structure131comprises plural outer teeth. Due to the plural outer teeth, the convex structure131has a blunt teeth profile, a wavy profile or a petal profile. Moreover, the outer peripheries of the outer teeth are contactable with the corresponding first rollers121. The concave structure132is concavely formed in a middle region of the second surface1301of the main body130. Moreover, the concave structure132comprises at least one inner tooth. In this embodiment as shown inFIG. 1, the concave structure132comprises plural inner teeth. Due to the plural inner teeth, the concave structure132has a wavy profile or a petal profile. An example of the bearing16includes but is not limited to a ball bearing, a needle bearing or an oil-retaining bearing. Moreover, the region between the concave structure132and the convex structure131is defined as a wall region.

The second roller assembly14comprises a second wheel disc140and plural second rollers141. The second wheel disc140is a circular disc structure that is made of metallic material or alloy. The second wheel disc140comprises a third surface1400and a fourth surface1401, wherein the third surface1400and the fourth surface1401are opposed to each other. The third surface1400is located beside the second surface1301of the rotating wheel13. Moreover, a fixing hole (not shown) is located at a geometric center of the second wheel disc140. Preferably but not exclusively, the plural second rollers141are circular posts, which are made of metallic material or alloy. The plural second rollers141are circumferentially and discretely arranged on the third surface1400of the second wheel disc140at regular intervals. Moreover, the plural second rollers141are partially accommodated within the concave structure132and contacted with the corresponding inner teeth of the concave structure132of the rotating wheel13. Consequently, when the rotating wheel13is synchronously rotated with the eccentric wheel11, the plural second rollers141are pushed by the corresponding inner teeth of the concave structure132and thus rotated. Optionally, the plural second rollers141are rotated about their own axles. That is, the plural second rollers141can be selectively rotated about fixed positions of the third surface1400.

Preferably but not exclusively, the second transmission shaft15is a shaft lever that is made of metallic material or alloy. The second transmission shaft15has a third end150and a fourth end151. The third end150of the second transmission shaft15is fixed in the fixing hole of the second wheel disc140of the second roller assembly14. Consequently, when the second wheel disc140of the second roller assembly14is rotated, the second transmission shaft15is synchronously rotated with the second wheel disc140. Moreover, the fourth end151of the second transmission shaft15is a power output end.

In this embodiment, the number of the first rollers121is at least one more than the number of the outer teeth of the convex structure131of the rotating wheel13, and the number of the second rollers141is more than the number of the inner teeth of the concave structure132of the rotating wheel13. In case that the plural first rollers121are rotated about the fixed positions of the mounting surface122, the plural second rollers141are not rotated about the fixed positions of the third surface1400of the second wheel disc140. Whereas, in case that the plural second rollers141are rotated about the fixed positions of the third surface1400of the second wheel disc140, the plural first rollers121are not rotated about the fixed positions of the mounting surface122. Moreover, the number of the outer teeth of the convex structure131and the number of the inner teeth of the concave structure132are different. In the embodiment ofFIG. 1, the number of the outer teeth of the convex structure131is at least one more than the number of the inner teeth of the concave structure132. Alternatively, in another embodiment, the number of the inner teeth of the concave structure132is at least one more than the number of the outer teeth of the convex structure131. For example, as shown inFIG. 2, the number of the outer teeth of the convex structure131is four, and the number of the inner teeth of the concave structure132is five.

Since the reduction ratio of the speed reducer1is determined according to the difference between the number of the outer teeth and the number of the inner teeth and the self-rotation of plural first rollers121or the plural second rollers141. According to the above designing concepts, the speed reducer1can be designed to have four operating situations. For understanding the present invention, the following presuppositions are made: (a) the number difference between the number of the outer teeth of the convex structure131and the number of the inner teeth of the concave structure132is one, (b) the number of the first rollers121is at least one more than the number of the outer teeth of the convex structure131of the rotating wheel13, and (c) the number of the second rollers141is at least one more than the number of the inner teeth of the concave structure132of the rotating wheel13. In the following drawings, the dotted circles indicate that the first rollers121or the second rollers141are not self-rotated, and the solid circles indicate that the first rollers121or the second rollers141are self-rotated.

In the first operating situation of the speed reducer1, the number of the outer teeth of the convex structure131is one more than the number of the inner teeth of the concave structure132, the plural first rollers121are not rotated about the fixed positions of the mounting surface122, and the plural second rollers141are rotated about the fixed positions of the third surface1400of the second wheel disc140. For example, in case that the number of the outer teeth of the convex structure131is N, the number of the inner teeth of the concave structure132is equal to (N−1), the number of the first rollers121is equal to (N+1), and the number of the second rollers141is equal to N. In the first operating situation, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are identical. Moreover, the reduction ratio of the speed reducer1is equal to N×N, wherein N is an integer greater than 1.

Hereinafter, the operating principles of the speed reducer1in the first operating situation will be illustrated with reference toFIGS. 3-7.FIG. 3schematically illustrates the sequential actions of the speed reducer of the present invention in the first operating situation. For example, the number of the outer teeth of the convex structure131is 4, and the number of the inner teeth of the concave structure132is 3. InFIG. 3, the time interval between every two adjacent actions is equal to the time period of rotating one-fourth turn of the first transmission shaft10. When the first transmission shaft10is driven by an external driving mechanism (e.g., the shaft lever of the motor) and rotated in a counterclockwise direction, the eccentric wheel11is synchronously rotated with the first transmission shaft10in the counterclockwise direction. InFIG. 3and the following drawings, the symbol A denotes the axle center of the first transmission shaft10, and the symbol B denotes the axle center of the eccentric wheel11. When the first transmission shaft10is rotated one turn, the eccentric wheel11is eccentrically rotated one turn. Since the eccentric wheel11is rotatably disposed within the bearing16, the eccentric rotation of the eccentric wheel11will result in a pushing force to push the rotating wheel13to be slowly rotated in a clockwise direction. Moreover, since the plural first rollers121are not rotated about the fixed positions of the mounting surface122, the inner teeth of the concave structure132and the plural second rollers141of the second roller assembly14are pushed against each other. Under this circumstance, the plural second rollers141are self-rotated in the clockwise direction and rotated about the common axis in the counterclockwise direction so as to result in an epicyclic motion. In response to the epicyclic motion of the plural second rollers141, the second wheel disc140is correspondingly rotated in the counterclockwise direction. Consequently, the second transmission shaft15is synchronously rotated with the second wheel disc140in the counterclockwise direction. As the second transmission shaft15is rotated, an external driven mechanism (e.g., a belt pulley or a gear) is driven to be rotated at a reduced speed. In this embodiment, the number of the outer teeth of the convex structure131is 4, and the number of the inner teeth of the concave structure132is 3. In response to one-fourth turn of the first transmission shaft10in the counterclockwise direction, the epicyclic motion of the plural second rollers141results in one-sixteenth turn of the second transmission shaft15. Consequently, the reduction ratio of the speed reducer1is 16.

In the first operating situation, if the number of the outer teeth of the convex structure131is N, the reduction ratio of the speed reducer1is equal to N×N.FIG. 4schematically illustrates three examples of the speed reducer of the present invention in the first operating situation, in which the numbers of the outer teeth of the convex structure are 2, 3 and 4, respectively. If the number of the outer teeth is 2 and the number of the inner teeth is 1, the reduction ratio of the speed reducer1is equal to 4 (i.e., 2×2=4). If the number of the outer teeth is 3 and the number of the inner teeth is 2, the reduction ratio of the speed reducer1is equal to 9 (i.e., 3×3=9). If the number of the outer teeth is 4 and the number of the inner teeth is 3, the reduction ratio of the speed reducer1is equal to 16 (i.e., 4×4=16).FIG. 5schematically illustrates three examples of the speed reducer of the present invention in the first operating situation, in which the numbers of the outer teeth of the convex structure are 5, 6 and 7, respectively. If the number of the outer teeth is 5 and the number of the inner teeth is 4, the reduction ratio of the speed reducer1is equal to 25 (i.e., 5×5=25). If the number of the outer teeth is 6 and the number of the inner teeth is 5, the reduction ratio of the speed reducer1is equal to 36 (i.e., 6×6=36). If the number of the outer teeth is 7 and the number of the inner teeth is 6, the reduction ratio of the speed reducer1is equal to 25 (i.e., 7×7=49).FIG. 6schematically illustrates three examples of the speed reducer of the present invention in the first operating situation, in which the numbers of the outer teeth of the convex structure are 8, 9 and 10, respectively. If the number of the outer teeth is 8 and the number of the inner teeth is 7, the reduction ratio of the speed reducer1is equal to 64 (i.e., 8×8=64). If the number of the outer teeth is 9 and the number of the inner teeth is 8, the reduction ratio of the speed reducer1is equal to 81 (i.e., 9×9=81). If the number of the outer teeth is 10 and the number of the inner teeth is 9, the reduction ratio of the speed reducer1is equal to 100 (i.e., 10×10=100).FIG. 7schematically illustrates two examples of the speed reducer of the present invention in the first operating situation, in which the numbers of the outer teeth of the convex structure are 20 and 30, respectively. If the number of the outer teeth is 20 and the number of the inner teeth is 19, the reduction ratio of the speed reducer1is equal to 400 (i.e., 20×20=400). If the number of the outer teeth is 30 and the number of the inner teeth is 29, the reduction ratio of the speed reducer1is equal to 900 (i.e., 30×30=900).

From the above descriptions, the pushing action of the speed reducer1of the present invention is similar to the conventional harmonic drive reducer. Consequently, in comparison with the RV reducer, the speed reducer1of the present invention has simplified structure and less number of components, and is easily assembled and cost-effective. Moreover, for achieving a high reduction ratio (e.g.,900), the gap between every two adjacent teeth of the gear of the conventional harmonic drive reducer is very small. Consequently, it is difficult to produce the conventional harmonic drive reducer with high reduction ratio. In other words, the reduction ratio cannot be largely increased. In contrast, if the number of the outer teeth of the convex structure131is 30 and the number of the inner teeth of the concave structure132is 29, the speed reducer1of the present invention can achieve the reduction ratio of 900. Moreover, the rotating wheel13can be easily produced, and the reduction ratio of the speed reducer1is largely increased. Moreover, due to the wall region between the concave structure132and the convex structure131of the rotating wheel13of the speed reducer1, the overall rigidity of the speed reducer1is increased to withstand high impact and the use life of the speed reducer1is prolonged. Consequently, the problems of the conventional harmonic drive reducer (e.g., the deformation of the flex spline and the teeth difference friction).

In the second operating situation of the speed reducer1, the number of the outer teeth of the convex structure131is at least one more than the number of the inner teeth of the concave structure132, the plural first rollers121are rotated about the fixed positions of the mounting surface122, and the plural second rollers141are not rotated about the fixed positions of the third surface1400of the second wheel disc140. For example, in case that the number of the outer teeth of the convex structure131is N, the number of the inner teeth of the concave structure132is equal to (N−1), the number of the first rollers121is equal to (N+1), and the number of the second rollers141is equal to N. In the second operating situation, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are different. Moreover, the reduction ratio of the speed reducer1is equal to (N+1)×(N−1), wherein N is an integer greater than 1.FIG. 8schematically illustrates the sequential actions of the speed reducer of the present invention in the second operating situation. For example, the number of the outer teeth of the convex structure131is 4, and the number of the inner teeth of the concave structure132is 3. InFIG. 8, the time interval between every two adjacent actions is equal to the time period of rotating one-fourth turn of the first transmission shaft10. Under this circumstance, the reduction ratio of the speed reducer1is (4+1)×(4-1)=15.

In the third operating situation of the speed reducer1, the number of the inner teeth of the concave structure132is at least one more than the number of the outer teeth of the convex structure131, the plural first rollers121are not rotated about the fixed positions of the mounting surface122, and the plural second rollers141are rotated about the fixed positions of the third surface1400of the second wheel disc140. For example, in case that the number of the outer teeth of the convex structure131is N, the number of the inner teeth of the concave structure132is equal to (N+1), the number of the first rollers121is equal to (N+1), and the number of the second rollers141is equal to (N+2). In the third operating situation, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are different. Moreover, the reduction ratio of the speed reducer1is equal to N×(N+2), wherein N is an integer greater than 1.FIG. 9schematically illustrates the sequential actions of the speed reducer of the present invention in the third operating situation. For example, the number of the outer teeth of the convex structure131is 4, and the number of the inner teeth of the concave structure132is 5. InFIG. 9, the time interval between every two adjacent actions is equal to the time period of rotating one-fourth turn of the first transmission shaft10. Under this circumstance, the reduction ratio of the speed reducer1is 4×(4+2)=24.

In the third operating situation, if the number of the outer teeth of the convex structure131is N, the reduction ratio of the speed reducer1is equal to N×(N+2).FIG. 10schematically illustrates three examples of the speed reducer of the present invention in the third operating situation, in which the numbers of the outer teeth of the convex structure are 2, 3 and 4, respectively. For example, if the number of the outer teeth is 2 and the number of the inner teeth is 3, the reduction ratio of the speed reducer1is equal to 8 (i.e., 2×4=8). If the number of the outer teeth is 3 and the number of the inner teeth is 4, the reduction ratio of the speed reducer1is equal to 15 (i.e., 3×5=15). If the number of the outer teeth is 4 and the number of the inner teeth is 5, the reduction ratio of the speed reducer1is equal to 24 (i.e., 4×6=24).FIG. 11schematically illustrates three examples of the speed reducer of the present invention in the third operating situation, in which the numbers of the outer teeth of the convex structure are 5, 6 and 8, respectively. If the number of the outer teeth is 5 and the number of the inner teeth is 6, the reduction ratio of the speed reducer1is equal to 35 (i.e., 5×7=35). If the number of the outer teeth is 6 and the number of the inner teeth is 7, the reduction ratio of the speed reducer1is equal to 35 (i.e., 6×8=48). If the number of the outer teeth is 8 and the number of the inner teeth is 9, the reduction ratio of the speed reducer1is equal to 80 (i.e., 8×10=80).

In the fourth operating situation of the speed reducer1, the number of the inner teeth of the concave structure132is at least one more than the number of the outer teeth of the convex structure131, the plural first rollers121are rotated about the fixed positions of the mounting surface122, and the plural second rollers141are not rotated about the fixed positions of the third surface1400of the second wheel disc140. For example, in case that the number of the outer teeth of the convex structure131is N, the number of the inner teeth of the concave structure132is equal to (N+1), the number of the first rollers121is equal to (N+1), and the number of the second rollers141is equal to (N+2). In the fourth operating situation, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are identical. Moreover, the reduction ratio of the speed reducer1is equal to (N+1)×(N+1), wherein N is an integer greater than 1.FIG. 12schematically illustrates the sequential actions of the speed reducer of the present invention in the fourth operating situation. For example, the number of the outer teeth of the convex structure131is 4, and the number of the inner teeth of the concave structure132is 5. InFIG. 12, the time interval between every two adjacent actions is equal to the time period of rotating one-fourth turn of the first transmission shaft10. Under this circumstance, the reduction ratio of the speed reducer1is (4+1)×(4+1)=25.

As mentioned above, the number difference between the number of the outer teeth of the convex structure131and the number of the inner teeth of the concave structure132is one. The parameters of the speed reducer1in the four operating situations are listed in the following table.

It is noted that the number difference between the number of the outer teeth of the convex structure131and the number of the inner teeth of the concave structure132may be more than one. Regardless of the number difference, the speed reducer1can be designed to have the above four operating situations. Consequently, the speed reducer1can have various reduction ratios.

In the first operating situation of the speed reducer1, the following presuppositions are made: the plural first rollers121are not rotated about the fixed positions of the mounting surface122, the plural second rollers141are rotated about the fixed positions of the third surface1400of the second wheel disc140, and the number of the outer teeth of the convex structure131minus the number of the inner teeth of the concave structure132is K. Under this circumstance, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are identical. In case that the number of the outer teeth of the convex structure131is N, the reduction ratio is equal to |N×(N−K+1)/K|, wherein N is an integer greater than 1 and the difference (N−K) is greater than 1.

FIG. 13schematically illustrates two examples of the speed reducer of the present invention in the first operating situation, in which N=8 (K=1, 2). If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 1 (i.e., K=1), the reduction ratio of the speed reducer1is equal to 8×(8−1+1)/1=64. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 2 (i.e., K=2), the reduction ratio of the speed reducer1is equal to 8×(8−2+1)/2=28.FIG. 14schematically illustrates three examples of the speed reducer of the present invention in the first operating situation, in which N=8 (K=3, 4, 5). If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 3 (i.e., K=3), the reduction ratio of the speed reducer1is equal to 8×(8−3+1)/3=16. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 4 (i.e., K=4), the reduction ratio of the speed reducer1is equal to 8×(8−4+1)/4=10. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 5 (i.e., K=5), the reduction ratio of the speed reducer1is equal to 8×(8−5+1)/5=6.4.

In the third operating situation of the speed reducer1, the following presuppositions are made: the plural first rollers121are not rotated about the fixed positions of the mounting surface122, the plural second rollers141are rotated about the fixed positions of the third surface1400of the second wheel disc140, and the number of the outer teeth of the convex structure131minus the number of the inner teeth of the concave structure132is equal to K, wherein K is negative. Under this circumstance, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are different. In case that the number of the outer teeth of the convex structure131is N, the reduction ratio is equal to |N*(N−K+1)/K|, wherein N is an integer greater than 1 and the difference (N−K) is greater than 1.

FIG. 15schematically illustrates two examples of the speed reducer of the present invention in the third operating situation, in which N=8 (K=−1, −2). If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −1 (i.e., K=−1), the reduction ratio of the speed reducer1is equal to 8×(8+1+1)/(−1)=80. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −2 (i.e., K=−2), the reduction ratio of the speed reducer1is equal to |8×(8+2+1)/(−2)|=44.FIG. 16schematically illustrates three examples of the speed reducer of the present invention in the third operating situation, in which N=8 (K=−3, −4, −5). If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −3 (i.e., K=−3), the reduction ratio of the speed reducer1is equal to 8×(8+3+1)/(−3)=32. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −4 (i.e., K=−4), the reduction ratio of the speed reducer1is equal to 8×(8+4+1)/(−4)=26. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −5 (i.e., K=−5), the reduction ratio of the speed reducer1is equal to 8×(8+5+1)/(−5)=22.4.

In the first operating situation or the third operating situation of the speed reducer1, the reduction ratio is equal to |N×(N−K+1)/K|, wherein N is an integer greater than 1. Since the number of the outer teeth of the convex structure131and the number of the inner teeth of the concave structure132are different, K is an integer that is not equal to 0. Moreover, the number difference (N−K) is greater than 1. In case that the term N×(N−K+1)/K is positive, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are identical. Whereas, in case that the term N×(N−K+1)/K is negative, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are different.

In the second operating situation of the speed reducer1, the following presuppositions are made: the plural first rollers121are rotated about the fixed positions of the mounting surface122, the plural second rollers141are not rotated about the fixed positions of the third surface1400of the second wheel disc140, and the number of the outer teeth of the convex structure131minus the number of the inner teeth of the concave structure132is K. Under this circumstance, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are different. In case that the number of the outer teeth of the convex structure131is N, the reduction ratio is equal to |(N+1)×(N−K)/K|, wherein N is an integer greater than 1 and the difference (N−K) is greater than 1.

FIG. 17schematically illustrates two examples of the speed reducer of the present invention in the second operating situation, in which N=8 (K=1, 2). If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 1 (i.e., K=1), the reduction ratio of the speed reducer1is equal to (8+1)×(8−1)/1=63. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 2 (i.e., K=2), the reduction ratio of the speed reducer1is equal to (8+1)×(8−2)/2=27.FIG. 18schematically illustrates three examples of the speed reducer of the present invention in the second operating situation, in which N=8 (K=3, 4, 5). If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 3 (i.e., K=3), the reduction ratio of the speed reducer1is equal to (8+1)×(8−3)/3=15. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 4 (i.e., K=4), the reduction ratio of the speed reducer1is equal to (8+1)×(8−4)/4=9. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is 5 (i.e., K=5), the reduction ratio of the speed reducer1is equal to (8+1)×(8−5)/5=5.4.

In the fourth operating situation of the speed reducer1, the following presuppositions are made: the plural first rollers121are rotated about the fixed positions of the mounting surface122, the plural second rollers141are not rotated about the fixed positions of the third surface1400of the second wheel disc140, and the number of the outer teeth of the convex structure131minus the number of the inner teeth of the concave structure132is equal to K, wherein K is negative. Under this circumstance, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are identical. In case that the number of the outer teeth of the convex structure131is N, the reduction ratio is equal to |(N+1)×(N−K)/K|, wherein N is an integer greater than 1 and the difference (N−K) is greater than 1.

FIG. 19schematically illustrates two examples of the speed reducer of the present invention in the fourth operating situation, in which N=8 (K=−1, −2). If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −1 (i.e., K=−1), the reduction ratio of the speed reducer1is equal to |(8+1)×(8+1)/(−1)|=81. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −2 (i.e., K=−2), the reduction ratio of the speed reducer1is equal to |(8+1)×(8+2)/(−2)|=45.FIG. 20schematically illustrates three examples of the speed reducer of the present invention in the fourth operating situation, in which N=8 (K=−3, −4, −5). If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −3 (i.e., K=−3), the reduction ratio of the speed reducer1is equal to |(8+1)×(8+2)/(−3)|=33. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −4 (i.e., K=−4), the reduction ratio of the speed reducer1is equal to (8+1)×(8+2)/(−4)=27. If the number N of the outer teeth is 8 and the number difference between the outer teeth and the inner teeth is −5 (i.e., K=−5), the reduction ratio of the speed reducer1is equal to |(8+1)×(8+2)/(−5)∥=23.4.

In the second operating situation or the fourth operating situation of the speed reducer1, the reduction ratio is equal to |(N+1)×(N−K)/K|, wherein N is an integer greater than 1. Since the number of the outer teeth of the convex structure131and the number of the inner teeth of the concave structure132, K is an integer that is not equal to 0. Moreover, the number difference (N−K) is greater than 1. In case that the term (N+1)×(N−K)/K is positive, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are different. Whereas, in case that the term (N+1)×(N−K)/K is negative, the rotating direction of the first transmission shaft10and the rotating direction of the second transmission shaft15are identical.

In some embodiments, the eccentric wheel11and the second transmission shaft15are connected with each other through a coupling (not shown). Moreover, the wall region between the concave structure132and the convex structure131may have cavities. Due to the cavities, the dynamic balance of the rotating wheel13during rotation can be achieved. Moreover, the dynamic balance of the speed reducer may be achieved by adjusting the weight of the first transmission shaft10or providing an eccentric design of the rotating wheel13.

In the above embodiment, the first transmission shaft10is the power input end, and the second transmission shaft15is the power output end. It is noted that those skilled in the art will readily observe that numerous modifications and alterations may be made while retaining the teachings of the invention. For example, in another embodiment, the first transmission shaft10is the power output end, and the second transmission shaft15is the power input end. Under this circumstance, the speed reducer1is a speed increaser in fact.

From the above descriptions, the present invention provides a speed reducer. The speed reducer comprises a rotating wheel, a first roller assembly and a second roller assembly. The rotating wheel comprises a convex structure and a concave structure. The convex structure is contacted with plural first rollers of the first roller assembly. The concave structure is contacted with plural second rollers of the second roller assembly. The pushing action of the speed reducer of the present invention is similar to the conventional harmonic drive reducer. Consequently, the speed reducer of the present invention has simplified structure and less number of components, and is easily assembled and cost-effective. Moreover, due to the concave structure of the rotating wheel, the volume and weight of the overall speed reducer are reduced. Moreover, since the wall region of the rotating wheel is clamped by the plural first rollers and the plural second rollers, the gaps between the rotating wheel and the plural first rollers and the plural second rollers can be effectively controlled. Moreover, due to the wall region, the overall rigidity of the speed reducer is increased to withstand high impact, and the use life of the speed reducer is prolonged. Moreover, since the speed reducer of the present invention is designed to have four operating situations, the speed reducer can have various reduction ratios. That is, the speed reducer of the present invention can provide a high reduction ratio. In conclusion, the speed reducer of the present invention has the benefits of a RV reducer and a harmonic drive reducer.