Abstract:
A geartrain for a five-speed automatic transmission including first and second compound planetary gear units. The first compound planetary gear unit includes first and second simple planetary gearsets having first, second and third operating elements. The first operating element acting as an input element. The second compound planetary gear unit includes third and fourth simple planetary gearsets having fifth, sixth, seventh and eighth operating elements. The fifth operating element acts as an output element. The sixth operating element is variably connected to either the first operating element or the second operating element. The seventh operating element is fixedly connected to the fourth operating element. Clutches for variably connecting the sixth operating element to either the first operating element or the second operating element are provided. Brakes for selectively connecting the third and eighth operating element to a transmission housing are provided.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a geartrain, and more particularly, to a geartrain for a five-speed automatic transmission used in vehicles, which can be designed to be compact in size and lightweight by reducing the number of frictional elements and planetary gearsets. 
     2. Description of the Related Art 
     Generally, automatic transmission systems for vehicles comprise a transmission control unit (TCU) which automatically controls shift ratios according to changes in a running condition of the vehicle. 
     The above-described TCU controls a plurality of friction elements provided in a geartrain to either operative or inoperative states to select one of the three essential elements of the planetary gearset (a sun gear, a ring gear, and a planet carrier) to be an input element, another a reaction element, and the last an output element, thereby controlling the number of output revolutions. 
     The geartrain is generally designed to realize four forward speeds and one reverse speed. However, with the development of high-power engines, geartrains have been developed to realize five forward speeds and one reverse speed. 
     The 5-speed geartrain is comprised of three simple planetary gearsets and at least six friction elements. 
     However, in such a geartrain for a 5-speed automatic transmission, to drive the vehicle in fourth or fifth speed-overdrive, there is a need for an element which rotates at a higher speed than that of a final output element. This results in power loss. In addition, the large number of friction elements results in a heavy and large-size automatic transmission. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to solve the problems associated with the above described conventional geartrain. 
     It is an object of the present invention to provide a geartrain for a five-speed automatic transmission used in vehicles which, by omitting an element which rotates at a higher speed than a final output element needed in the prior art during overdrive, can minimize power loss. 
     It is another object of the present invention to provide a geartrain for a five-speed automatic transmission which can be designed to be compact in size and lightweight by reducing the number of friction elements. 
     To achieve the above objects, the present invention provides a geartrain for a five-speed automatic transmission, comprising: 
     a first compound planetary gear unit comprising first and second simple planetary gearsets having first, second, third, and fourth operating elements, said first operating element acting as an input element; 
     a second compound planetary gear unit comprising third and fourth simple planetary gearsets having fifth, sixth, seventh and eighth operating elements, said fifth operating element acting as an output element, said sixth operating element being variably connected to either the first operating element or the second operating element, and said seventh operating element being fixedly connected to the fourth operating element; 
     clutch means for variably connecting said sixth operating element to either the first operating element or the second operating element; and 
     brake means for selectively connecting the third and eighth operating element to a transmission housing. 
     The first simple planetary gearset is a double pinion planetary gearset, and the second simple planetary gearset is a single pinion planetary gearset. 
     The first operating element is a sun gear of the second simple planetary gearset; the second operating element is a combination of a planet carrier of the first simple planetary gearset and a planet carrier of the second simple planetary gearset; the third operating element is a ring gear of the first simple planetary gearset; and the fourth operating element is a combination of a sun gear of the first simple planetary gearset and a ring gear of the second simple planetary gearset. 
     The third simple planetary gearset is a double pinion planetary gearset, and the fourth simple planetary gearset is a single planetary gearset. 
     The fifth operating element is a combination of a sun gear of the third simple planetary gearset and a ring gear of the fourth simple planetary gearset; the sixth operating element is a planet carrier of the fourth simple planetary gearset; the seventh operating element is a combination of a ring gear of the third simple planetary gearset and a sun gear of the fourth simple planetary gearset; and the eighth operating element is a planet carrier of the third simple planetary gearset. 
     The clutch means comprises a first clutch interposed between the planet carrier of the second simple planetary gearset and the planet carrier of the fourth simple planetary gearset, and a second clutch interposed between the sun gear of the second simple planetary gearset and the planet carrier of the fourth simple planetary gearset. 
     The brake means comprises a first brake interposed between the ring gear of the first simple planetary gearset and the transmission housing and a second brake interposed between the planet carrier of the third simple planetary gearset and the transmission housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention: 
     FIG. 1 is a schematic diagram illustrating a geartrain according to a preferred embodiment of the present invention; 
     FIG. 2 is a lever analogy representation which can be obtained through a geartrain according to a preferred embodiment of the present invention depicted in FIG. 1; 
     FIG. 3 is a schematic diagram illustrating an operation of forward first, second and third speeds of a geartrain according to a preferred embodiment of the present invention through a lever analogy; 
     FIG. 4 is a schematic diagram illustrating an operation of forward fourth and fifth speeds of a geartrain according to a preferred embodiment of the present invention through a lever analogy diagram; 
     FIG. 5 is a schematic diagram illustrating an operation of reverse speed of a geartrain according to a preferred embodiment of the present invention through a lever analogy diagram; and 
     FIG. 6 is a chart illustrating the operation of friction elements in each shift range of a power train according to a preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 
     Referring first to FIG. 1, there is shown a schematic diagram of a geartrain according to a preferred embodiment of the present invention. 
     The geartrain of this embodiment comprises an engine 100 for generating power, a torque converter T for multiplying torque generated from the engine, and first and second compound planetary gear units 1 and 3 for receiving converted torque through an input shaft 10 and for outputting five forward speeds and one reverse speed to a transfer drive gear TD. 
     The first compound planetary gear unit 1 has a first simple planetary gearset PG1 that is a double pinion planetary gearset and a second simple planetary gearset PG2 that is a single pinion planetary gearset. 
     In the first compound planetary gear unit 1, a sun gear S1 of the first simple planetary gearset PG1 is fixedly connected to a ring gear R2 of the second simple planetary gearset PG2, and a planet carrier Ca1, connecting pinion gears P1 to each other, of the first simple planetary gearset PG1 is fixedly connected to a planet carrier Ca2, connecting pinion gears P2 to each other, of the second simple planetary gearset PG2. 
     Therefore, the first compound planetary gear unit 1 consists of four operating elements, i.e., a sun gear S2 of the second simple planetary gearset PG2, which is fixedly mounted around the input shaft 20 to act as an input element, a ring gear R1 of the first simple planetary gearset PG1 which is variably connected to a transmission housing 20 to selectively act as a reacting element, a combination of the sun gear S1 and ring gear R2, and a combination of the planet carrier Ca1 and planet carrier Ca2. 
     The second compound planetary gear unit 1 has a third simple planetary gearset PG3 that is a double pinion planetary gearset and a fourth simple planetary gearset PG4 that is a single pinion planetary gearset. 
     In the second compound planetary gear unit 3, a sun gear S3 of the third simple planetary gearset PG3 is fixedly connected to a ring gear R4 of the fourth simple planetary gearset PG4, and a ring gear R3 of the third simple planetary gearset PG3 is fixedly connected to a sun gear S4 of the fourth simple planetary gearset PG4. 
     Therefore, the second compound planetary gear unit 3 consists of four operating elements, i.e., a planet carrier Ca3, connecting pinion gears to each other and being variably connected to the transmission housing 20 to selectively act as a reacting element, of the third simple planetary gearset PG3, a planet carrier Ca4, connecting pinion gears P4 to each other, of the fourth simple planetary gearset PG4, a combination of the sun gear S3 and ring gear R4, and a combination of the ring gear R3 and sun gear S4. 
     The above described first and second compound planetary gear units 1 and 3 are combined to each other. That is, the combination of the sun gear S1 and ring gear R2 of the first and second simple planetary gearsets PG1 and PG2 is fixedly connected to the combination of the ring gear R3 and sun gear S4 of the third and fourth planetary gearsets PG3 and PG4; the combination of the planet carriers Ca1 and Ca2 of the first and second simple planetary gearsets PG1 and PG2 is variably connected to the planet carrier Ca4 of the fourth simple planetary gearset PG4; and the sun gear S2 of the second simple planetary gearset PG2 is variably connected to the planet carrier Ca4 of the fourth simple planetary gearset PG4; and the combination of the sun gear S3 and ring gear R4 of the third and fourth simple planetary gearsets PG3 and PG4 is fixedly connected to the transfer drive gear TD which transmits shifted rotating force to a final reduction gear (not shown). 
     A first clutch C1 is interposed between the combination of the planet carriers Ca1 and Ca2 of the first and second simple planetary gearsets PG1 and PG2 and the planet carrier Ca4 of the fourth simple planetary gearset PG4. The first clutch C1 is operated in forward first, second and third speeds to interconnect the combination of the planet carriers Ca1 and Ca2 and the planet carrier Ca4. A second clutch C2 is interposed between the sun gear S2 of the second simple planetary gearset PG2 and the planet carrier Ca4 of the fourth simple planetary gearset PG4. The second clutch C2 is operated in forward third, fourth and fifth speeds to interconnect the sun gear S2 and the planet carrier Ca4. 
     In addition, a first brake B1 is interposed between the ring gear R1 of the first simple planetary gearset PG1 and the transmission housing 20. The first brake B1 is engaged to fix the ring gear R1 in forward first and fifth speeds and reverse speed. A second brake B2 is interposed between the planet carrier Ca3 of the third simple planetary gearset PG3 and the transmission housing 20, such that it can operate in the forward second and fourth speeds and the reverse speed to fix the planet carrier Ca3. 
     The above described geartrain can be illustrated as a lever representation as shown in FIG. 2. In FIG. 2, levers L1 and L2 indicate the first and second compound planetary gear units 1 and 3, respectively. The four operating elements of the first compound planetary gear units 1 are indicated as first, second, third and fourth operating elements A, D, E and F on the first lever L1, and the four operating elements of the second compound planetary gear unit 3 are indicated as first, second, third and fourth operating elements G, H, I and J on the second lever L2. 
     Describing the first lever L1 more in detail, the first operating element A indicates the sun gear S2 of the second simple planetary gearset PG2, the second operating element D indicates the combination of the planet carriers Ca1 and Ca2 of the first and second simple planetary gearsets PG1 and PG2, the third operating element E indicates the ring gear R1 of the first simple planetary gearset PG1, and the fourth operating element F indicates the combination of the sun gear S1 and ring gear R2 of the first and second simple planetary gearsets PG1 and PG2. 
     In addition, in the second lever L2, the first operating element G indicates the combination of the sun gear S3 and ring gear R4 of the third and fourth simple planetary gearsets PG3 and PG4, and the second operating element H indicates the planet carrier Ca4 of the fourth simple planetary gearset PG4. The third operating element I indicates the combination of the ring gear R3 and sun gear S4 of the third and fourth simple planetary gearsets PG3 and PG4, and the fourth operating element J indicates the planet carrier Ca3 of the third simple planetary gearsets PG3. 
     As described above, the first operating element A of the first compound planetary gear unit 1 is fixedly connected to the input shaft 10 to act as an input element, the third operating element E of the first compound planetary gear unit 1 is variably connected to the transmission housing by the first brake B1 to selectively act as a reacting element. 
     In addition, the first operating element G of the second compound planetary gear unit 3 is fixedly connected to the transfer drive gear TD to act as an output element, and the fourth operating element J of the second compound planetary gear unit 3 is variably connected to the transmission housing by the second brake B2 to selectively act as a reacting element. 
     The first clutch C1 is interposed between the second operating element D of the first compound planetary gear unit 1 and the second operating element H of the second compound planetary gear unit 3, and the second clutch C2 is interposed between the first operating element A of the first compound planetary gear unit 1 and the second operating element H of the second compound planetary gear unit 3. 
     In the forward first, second and third speeds D1, D2 and D3, since the first clutch C1 is operated as charted in FIG. 6, the lever representation of FIG. 2 can be illustrated as a single third lever L3 having first, second, third, fourth, fifth and sixth nodes N1, N2, N3, N4, N5 and N6 as shown in FIG. 3. 
     That is, in the third lever L3, the first node N1 indicates the first operating element A of the first compound planetary gear unit 1, the second node N2 indicates the first operating element G of the second compound planetary gear unit 3, the third node N3 indicates the combination of the second operating elements D and H of the first and second compound planetary gear units 1 and 3, the fourth node N4 indicates the third operating element E of the first compound planetary gear unit 1, the fifth node N5 indicates the combination of the fourth operating element F of the first compound planetary gear unit 1 and the third operating element I of the second compound planetary gear unit 3, and the sixth node N6 indicates the fourth operating element J of the second compound planetary gear unit 1. Through this lever analogy, shift ratios of the forward first, second and third speeds can be demonstrated. 
     FORWARD FIRST SPEED 
     In the forward first speed D1, the first clutch C1 and the first brake B1 are operated as charted in FIG. 6. Accordingly, the first node N1 indicating the sun gear S2 of the second simple planetary gearset PG2 becomes the input element, and the fourth node N4 indicating the ring gear R1 of the first simple planetary gearset becomes a reacting element. Accordingly, the first forward speed is outputted through the transfer drive gear TD connected to the ring gear R4 of the fourth simple planetary gearset PG4 of second node N2. 
     Therefore, when assuming that the output revolution number of the ring gear R4 is &#34;1&#34;, a line connecting the output point of the second node N2, acting as the output element, to the fourth node N4, acting as the reacting element, becomes the first speed line 11. At this point, the number of input revolution D1 of the first node N1 becomes the first input speed which is higher than the output speed &#34;1&#34;. This shows that speed reduction is realized. 
     In the first speed state, the elements of the third node N3 idle in the output direction, while the operation elements of the fifth and sixth nodes N5 and N6 rotate in the opposite direction of the output. 
     FORWARD SECOND SPEED 
     If throttle opening is increased in the forward first speed state, the first brake B1 is disengaged, while the second brake B2 is operated. Accordingly, the reacting element is changed from the fourth node N4 to the sixth node N6 indicating the planet carrier Ca3 of the third simple planetary gearset PG3. Accordingly, the second speed is outputted through a transfer drive gear TD fixed to the ring gear R4 of the fourth simple planetary gearset PG4. 
     That is, when assuming that the output revolution number of the ring gear R4 is &#34;1&#34;, a line connecting the output speed point of the second node N2, acting as an output element, to the sixth node N6, acting as the reacting element, becomes the second speed line 12. At this point, the number of input revolution D2 of the first node N1 becomes the second input speed which is higher than the output speed &#34;1&#34;. This shows that speed reduction is realized. 
     In this forward second speed state, all operating elements of the third, fourth and fifth nodes N3, N4 and N5 rotate in the output direction at a number of revolutions less than that of the output. 
     FORWARD THIRD SPEED 
     If the throttle opening is increased in the forward second speed state, the second brake B2 is released, while the second clutch C2 is operated. Accordingly, since the first and second compound planetary units 1 and 3 are locked as the input is realized through the first node N1, the forward third speed is outputted through the transfer drive gear TD connected to the ring gear R4 of the fourth simple planetary gearset PG4. 
     That is, when assuming that the output revolution number of the ring gear R4 is &#34;1&#34;, a line connecting the output speed point of the second node N2 to the equal level of the first node N1, acting as the input element, becomes the third speed line 13. At this point, the number of input revolution of the first node N1 becomes the third input speed D3 which is equal to that of the output speed &#34;1&#34;. This shows that neither speed reduction nor speed increase occurs. 
     In this forward third speed state, all operating elements of the nodes N1 through N6 rotate in the output direction at the same number of revolutions as that of the output. 
      Forward Fourth and Fifth Speeds! 
     In the forward fourth and fifth speeds, since the second clutch C2 is operated as charted in FIG. 6, the first and second levers L1 and L2 can be illustrated as a single fourth lever L4 having first through sixth nodes N1, N2, N3, N4, N5 and N6 as shown in FIG. 4. 
     That is, in the fourth lever L4, the first node N1 indicates the first operating element G of the second compound planetary gear unit 3, the second node N2 indicates a combination of the first operating element A of the first compound planetary gear unit 1 and the second operating element H of the second compound planetary gear unit 3, the third node N3 indicates the second operating element D of the first compound planetary gear unit 1, the fourth node N4 indicates the second operating element E of the first compound planetary gear unit 1, the fifth node N5 indicates a combination of the fourth operating element F of the first compound planetary gear unit 1 and the third operating element I of the second compound planetary gear unit 3, and the sixth node N6 denotes the fourth operating element J of the second compound planetary gear unit 3. Through this lever analogy, shift ratios of the forward fourth and fifth speeds can be demonstrated. 
     FORWARD FOURTH SPEED 
     If the throttle opening is increased in the third speed state, the first clutch C1 is disengaged, while the second brake B2 is operated. Accordingly, the second node N2 indicating the sun gear S2 of the second simple planetary gearset PG2 becomes an input element, while the sixth node N6 indicating the planet carrier Ca3 of the third simple planetary gearset PG3. 
     Therefore, the forward fourth speed is outputted through the first node N1 indicating the ring gear R4 of the fourth simple planetary gearset PG4. 
     That is, when assuming that the output revolution number of the ring gear R4 is &#34;1&#34;, a line connecting the output speed point of the first node N1 to the sixth node N6, acting as the reacting element, becomes a fourth speed line 14. At this point, the number of input revolution D4 of the second node N2 becomes the fourth input speed which is less than the output speed &#34;1&#34;. This shows that speed increase is realized. That is, the fourth speed state is an overdrive in which output speed is higher than the input speed. 
     In the fourth speed state, all the operating elements of the third, fourth and fifth nodes N3, N4 and N5 rotate in the output direction at a number of revolutions less than that of the output. Therefore, since there is no operating element which idles at a number of revolutions higher than that of output, power loss is prevented. 
     FORWARD FIFTH SPEED 
     If the throttle opening is increased in the fourth speed state, the second brake B2 is disengaged, while the first brake B1 is engaged as charged in FIG. 6. Accordingly, the second node N2 becomes the input element, while the fourth node N4 indicating the ring gear R1 of the first simple planetary gearset PG1 becomes the reacting element. Therefore, the forward fifth speed is outputted through the transfer drive gear TD fixed to the ring gear R4 of the fourth simple planetary gearset PG4. 
     That is, when the output revolution number of the ring gear R4, i.e., the node N1, is assumed to be &#34;1&#34;, a line connecting the output speed point of the first node N1 to the fourth node N4, acting as the reacting element, becomes a fifth speed line 15. At this point, the number of input revolution D5 of the second node N2 becomes the fifth input speed which is less than the output speed &#34;1&#34;. This shows that speed increase is realized. That is, the fifth speed state is an overdrive state in which the output speed is higher than the input speed. 
     In the fifth speed state, the operating element of the third node N3 rotates in the output direction at the number of revolutions less than that of the output, while the operating elements of the fifth and sixth nodes N5 and N6 rotate in the opposite direction of the output direction. Therefore, since there is no operating element which idles at a number of revolutions higher than that of output, power loss is prevented. 
     REVERSE SPEED 
     When a shift mode is selected to a reverse mode, the first and second clutches C1 and C2 are disengaged, and the first and second brakes B1 and B2 are operated. 
     Accordingly, in the reverse mode, the first and second levers L1 and L2 can be illustrated as a single lever L5 having first through sixth nodes N1 through N6 as shown in FIG. 5. 
     That is, in the fifth lever L5, the first node N1 indicates the first operating element G of the second compound planetary gear unit 3, the second node N2 indicates the second operating element H of the second compound planetary gear unit 3, the third node N3 indicates a combination of the fourth operating element F of the first compound planetary gear unit 1 and the third operating element I of the second compound planetary gear unit 3, the fourth node N4 indicates a combination of the third operating element E of the first compound planetary gear unit 1 and the fourth operating element J of the second compound planetary gear unit 3, the fifth node N5 denotes the second operating element D of the first compound planetary gear unit 1, and the sixth node N6 indicates the first operating element A of the first compound planetary gear unit 1. Through this lever analogy, the reverse speed can be demonstrated. 
     In the reverse mode, the first and second clutches C1 and C2 are disengaged, while the first and second brakes B1 and B2 are operated. Accordingly, the sixth node N6 indicating the first operating element A of the first compound planetary gear unit 1 becomes the input element, while the fourth node N4 indicating the combination of the third operating element E of the first compound planetary gear unit 1 and the fourth operating element J of the second compound planetary gear unit 3 becomes the reacting element. In addition, the first node N1 indicating the ring gear R4 of the fourth simple planetary gearset PG4 become the output element. 
     That is, when assuming that the output revolution number of the ring gear R4 is &#34;1&#34;, a line connecting the output speed point of the first node N1 to the fourth node N4, acting as the reacting element, becomes the reverse speed line 16. At this point, the number of input revolution REV of the sixth node N6 becomes the reverse input speed. That is, the direction of the input speed is opposite to the output speed. 
     In this disclosure, there is shown and described only the preferred embodiment of the invention, as aforementioned, it is to be understood that the invention is capable of use in various other combinations and environments and is capable of change or modification within the scope of the inventive concepts as expressed herein.