EPICYCLIC GEAR SPEED CHANGE SYSTEM

Abstract: In a speed change gear wherein sun gears, carriers and ring gears of a plurality of epicyclic gear devices are selectively fixed by respective clutches to perform switching between the forward and rearward movements and a gear change, a brake (29) is connected to the output shaft (21) of this speed change gear, whereby energy absorptions of the clutches are shared and the oil pressure of the brake (29) is controlled in accordance with the rotary speed of the output shaft (21), so that the respective clutches can be rendered compact in size. Furthermore, supply of lubricant oil is decreased when the brake (29) is released, whereby the stirring resistance of the oil is low, so that transmission efficiency is satisfactory.

Description: Field of the Invention The present invention relates to a gear speed change system as defined by the features of the preamble of claim 1 and which are well known for the skilled person. Such a prior art, as shown in a schematic diagram or a epicyclic gear speed change system 51 shown in Fig. 4, specifies to provide a driving source 52 such as an engine or a torque converter, an input shaft 53 which is driven by the drive source 52, and a reverse sun gear 54 and a forward sun gear 55 which are coupled to the input shaft 53. In addition, the epicyclic gear speed change system has a reverse planetary gear 57 which is carried by the reverse carrier 56 and engaged with the reverse sun gear 54, a reverse clutch 58 which fixes the reverse carrier 56 to a case 59 or releasing the reverse carrier 56 from the case 59, a ring gear 60 which engages with the reverse planetary gear 57, and a carrier 61 coupled to the ring gear 60. Furthermore, the epicyclic gear speed change system has a forward planetary gear 62 which is carried by the carrier 61 and engaged with forward sun gear 55, a ring gear 63 which is engaged with the forward planetary gear 62, and a forward clutch 64 for fixing the ring gear 63 to the case 59 or releasing the ring gear 63 from the case 59. The above gear speed change system is provided with a third planetary gear 67 which is carried by the carrier 61 and engaged with a third sun gear 65 and a third ring gear 66, a third clutch 68 which fixes or releases the third ring gear 66 to or from the case 59, and an output shaft 71 which connects the third sun gear 65, the second sun gear 69 and the first sun gear 70. In addition, a second planetary gear 73 which is carried by the carrier 61 and engaged with the second sun gear 69 and the second ring gear 72, a second clutch 74 which fixes or releases the second ring gear 72 to or from the case 59, and a carrier 75 which is coupled with the second ring gear 72 are provided. Furthermore, a first planetary gear 77 which is carried by the carrier 75 and engaged with the first sun gear 70 and the first ring gear 76 and a first clutch 78 which fixes the first ring gear 76 to the case 59. 79 denotes an inertial member of a vehicle. In case of changing over movement of a vehicle from forward shift to rearward shift in the above described arrangement of the system, the forward clutch 64 and the second clutch 74 are released immediately after a speed changing operation. The second clutch 74 is engaged in advance. Under this condition, the output shaft 71 is rotating due to inertia 79 of the vehicle and therefore the reverse carrier 56 is also rotating. As the hydraulic pressure of the reverse clutch 58 is gradually increased, the rotation of the reverse carrier 56 is gradually slowed down and finally stopped, and the input side rotation and the output side rotation coincide with the speed changing ratio for the rearward shift. At this time, the reverse clutch 58 absorbs a large energy to reversely rotate the inertia member 79 of the vehicle. The following describes the changeover of forward to rearward movement, for example, from the rearward shift to the forward shift. For rearward shift, the reverse clutch 58 is engaged with the first clutch 78, the reverse carrier 56 and the first ring gear 76 are fixed to the case 59 and other clutches are kept released. The reverse clutch 58 and the first clutch 78 are released and the second clutch 74 is engaged. In this case, an energy to be absorbed by the second clutch 74 is approximate to an inertia, which is a small value, of the gear speed change system 51. Then the clutch 64 is engaged. At this time, the clutch 64 absorbs a large energy to reversely rotate the inertial member 79 of the vehicle. There is a problem that the areas of the forward clutch which absorbs such large energy and the reverse clutch 58 should be increased and therefore the gear speed change system need be large-sized. In addition, the clutches which are not engaged perform idle rotation during operation and stir the lubrication oil and such stirring resistance causes a horse power loss to deteriorate transmission efficiency. Disclosure of the Invention The present invention is made in view of the above problems of the related art is intended to share energy absorption of the clutches with the output shaft of a gear speed change system coupled to the brake in a gear speed change system for changing over forward movement to rearward movement of a vehicle and changing a speed of the vehicle by selectively fixing the sun gears, carriers and ring gears of a plurality of epicyclic gear devices with respective mating clutches. The gear speed change system in accordance with the present invention is provided with the features of claim 1. In addition a rotary wheel is coupled to the output shaft. In addition, the gear speed change system is provided with a piping supplying a lubrication oil to the brake, a pilot changeover valve installed in this piping and a piping guiding a pilot pressure of the hydraulic pressure control valve to this pilot changeover valve to reduce the quantity of lubrication oil when releasing the brake. Since the brake absorbs the energy when forward movement is to be changed over to rearward movement, the areas of respective clutches can be reduced to be compact in dimensions. When the brake clutch is released, the quantity of lubrication oil to be supplied to the clutches is reduced to lessen the stirring resistance of lubrication oil, thus improving the transmission efficiency. Brief Description of the Invention Fig. 1 is a schematic illustration of an epicyclic gear speed change system in accordance with the present invention, Fig. 2 is a flow chart illustrating the operation of this gear speed change system; Fig. 3 is a diagram illustrating the correlation of the output shaft rotation rate, the hydraulic pressure for the clutches and the hydraulic pressure for the brake, and Fig. 4 is a schematic diagram of an epicyclic gear speed change system according to the prior art which is well-known for the skilled person. Referring to Fig. 1 schematically illustrating the present invention, an epicyclic gear speed change system 1 is provided with an input shaft 3 which is driven by a driving source 2 such as an engine or a torque converter and a reverse sun gear and a forward F sun gear which are connected to the input shaft 3. In the following the capital R indicates reverse and F indicates forward. This epicyclic gear speed change system 1 is provided with an R planetary gear 7 which is carried by an R carrier 6 and engaged with an R sun gear 4, an R clutch 8 which fixes or releases the carrier 6 to or from a case 9, a ring gear 10 which is engaged with the R planetary gear 7 and a carrier 11 which is coupled to the ring gear 10. It also has an F planetary gear 12 which is carried by the carrier 11 and engaged with the F sun gear 5, a ring gear 13 which is engaged with the F planetary gear 12, and an F clutch 14 which fixes or releases the ring gear 13 to or from the case 9. It is also provided with a third planetary gear 17 which is carried by the carrier 11 and engaged with the third sun gear 15 and the third ring gear 16, a third clutch 18 which fixes or releases the third ring gear 16 to or from the case 9, and an output shaft 21 which connects the third sun gear 15, the second sun gear 19 and the first sun gear 20. It is further provided with a second planetary gear 23 which is carried by the carrier 11 and engaged with the second sun gear 19 and the second ring gear 22, a second clutch 24 which fixes or releases the ring gear 22 to or from the case 9, and a carrier 25 which is coupled to the second ring gear 22. It has a first planetary gear 27 which is carried by the carrier 25 and engaged with the first sun gear 20 and the first ring gear 26 and a first clutch 28 which fixes the first ring gear 26 to the case 9. A brake 29 and a rotary wheel 30 are connected to the output shaft 21. A rotation sensor 31 for measuring the rotation rate of the rotary wheel 30, a controller 34 which receives signals from the rotation sensor 31 and a speed change lever 32 and controls a hydraulic pressure control valve 33, and piping 35, 36, 37, 38, 39 and 40 for supplying a hydraulic oil to the hydraulic cylinders of respective clutches through the hydraulic pressure control valve 33. The system is also provided with piping 41 for supplying a lubrication oil to the brake 29, a pilot changeover valve 42 provided in the piping 41 and piping 43 for guiding a pilot pressure to the pilot changeover valve 42. 44 denotes an inertial member of the vehicle. The clutches which engage with respective speed steps carry a correlation as shown with circles in Table 1. In other words, the F clutch 14 engages with the first clutch 28 for forward shift a, the F clutch 14 engages with the second clutch 24 for forward shift b, and the F clutch 14 engages with the third clutch 18 for forward shift c. The R clutch 8 engages with the first clutch 28 for rearward shift a, the R clutch 8 engages with the second clutch 24 for rearward shift b, and the R clutch 8 engages with the third clutch 18 for rearward shift c. The operation of the speed change gears system is described below, referring to the flow chart shown in Fig. 2. In step 101, a speed change signal is generated from the speed change lever 32 to the controller 34. Changeover from forward movement to rearward movement or from rearward movement to forward movement is determined in step 102 and, if YES is given, the hydraulic pressure control valve 33 operates to release the F clutch 14 or the R clutch 8 which is currently engaged and the operation advances to step 103. In step 103, the hydraulic pressure control valve 33 operates and supplies a hydraulic oil to the piping 40 to actuate the brake 29. At this time, the hydraulic oil is supplied to the piping 43 and the pilot changeover valve 42 is changed over and the lubrication oil is supplied to the brake 29. Simultaneously, the R clutch 8 or the F clutch 14 is engaged. In step 104, it is determined from a signal of the rotation sensor 31 for measuring the rotary wheel 30 whether or not the rotation rate of the output shaft 21 is smaller than a specified value ε approximate to 0 (zero). If NO is given, the operation returns to a step before step 103 and, if YES is given, the operation advances to step 105. In step 105, the hydraulic pressure control valve 33 operates to stop a hydraulic oil to the piping 40 and releases the brake 29. When the supply of the hydraulic oil to the piping 40 is stopped, the pressure of the pilot piping 43 is canceled and the pilot changeover valve 42 is changed over, thus reducing the quantity of lubrication oil to be supplied to the brake 29. If NO is given in step 102, the operation advances to step 106, the hydraulic pressure control valve 33 operates with a signal from the controller 34 to release a speed changeover clutch being engaged, that is, one of the first clutch 28, second clutch 24 and third clutch 18, the hydraulic pressure for the other clutch is gradually increased to cause the clutch to be engaged, and the operation advances to step 107. In step 107, speed change is finished and the hydraulic pressure of the clutch being engaged is further boosted up to a specified pressure (step 108). Fig. 3 shows the correlation of the rotation rate of the output shaft 21, the hydraulic pressure for those clutches such as the F clutch 14, R clutch 8, first clutch 28, second clutch 24 and third clutch 18, and the hydraulic pressure for the brake 29. When the hydraulic pressure for the clutches is reduced according to a speed change signal from the speed change lever 32, the hydraulic pressure for the brake increases. When the hydraulic pressure for the brake 29 reaches a specified value, the hydraulic pressure for the clutches gradually increases. When the rotation rate of the output shaft 21 approaches 0, the hydraulic pressure for the brake begins to reduce. When the rotation rate of the input shaft 3 and the rotation rate of the output shaft 21 coincide with the speed change ratio, the hydraulic pressure for the brake is 0. The hydraulic pressure for the clutches rises up to the predetermined value. For the epicyclic gear speed change system 1, the F clutch 14 and the R clutch 8 can be small-sized with addition of the brake 29 since the clutch energy is absorbed by the F clutch 14 or the R clutch 8 and the brake 29. In addition, the F clutch 14, the R clutch 8 and the speed control clutches such as the first, second and third clutches which share the energy can be small-sized. When the brake 29 is released, the stirring resistance of hydraulic oil can be small to reduce the quantity of lubrication oil to be supplied and the transmission efficiency can thus be increased. Industrial Applicability The speed change gear system in accordance with the present invention is useful as an epicyclic gear speed change system which employs small-sized clutches and provides less stirring resistance of lubrication oil and higher transmission efficiency.

Claims: An epicyclic gear speed change system to change between forward and rearward movement of a vehicle and to change speed of the vehicle, said system comprising: an input and an output shaft (3 and 21) and a plurality of epicyclic gear devices selectively providing a connection between said shafts (3 and 21), each of the epicyclic gear devices having a sun gear, a planetary gear and an associated carrier, a ring gear, and a respective mating clutch (8,14,18,24,28) associated therewith, whereby speed change and a changeover between forward and rearward movement is accomplished by selectively fixing carriers and ring gears of said epicyclic gear devices with respective mating clutches, whereby a hydraulic pressure control valve is provided to supply and stop delivery of hydraulic oil to respective clutches, characterised in the provision of a brake (29) connected to said output shaft (21) to share energy absorption, and a control system to control said brake in accordance with a rotation rate of the output shaft so that said brake is actuated from the start of a changeover between forward and rearward movement until the rotation of the output shaft becomes smaller than a specified value; wherein said control system comprises: -- a speed change lever (32) to provide a speed change signal, -- a rotation sensor (31) measuring a rotation rate of said output shaft (21) to provide a rotation signal, and -- a controller (34) receiving said signal from said rotation sensor and said signal from said speed change lever to provide a control signal to control the supply of hydraulic pressure to said brake in accordance with the rotation rate of said output shaft. The epicyclic gear speed change system of claim 1, comprising a rotary wheel (30) coupled to said output shaft (21), said rotation sensor (31) measuring the rotation rate of said rotary wheel. The epicyclic gear speed change system of claim 1, comprising a piping to supply hydraulic oil to said brake (29), a pilot changeover valve (42) installed in said piping, and a piping to guide a pilot hydraulic pressure of said hydraulic pressure control valve (33) to said pilot changeover valve, wherein a quantity of lubrication oil to be supplied is reduced when said brake is released.

Inventors: KUSE TAKASHI, SATO MASAYUKI, KUSE, TAKASHI, SATO, MASAYUKI
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1992
Main classification: B60K41
IPC codes: F16H63, F16H59, F16H3, F16H61, B60W10, B60W30