Automatic transmission for motor vehicles
This is a continuation of application Ser. No. 919,576 filed Oct. 15, 1986, which is a continuation of application Ser. No. 820,834 filed Jan. 21, 1986, which is a continuation of application Ser. No. 256,179 filed Apr. 21, 1981. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to an automatic transmission for motor vehicles having a hydraulic torque converter, an auxiliary transmission mechanism forming an overdrive or underdrive (reducing) mechanism and a main transmission mechanism with a plural number of forward ranges and a reverse range, and more particularly to an automatic transmission for front engine-front drive type motor vehicles (hereinafter referred to as &#34;F.F. vehicles&#34; for brevity) which have axle shafts of front wheels driven from a transversely mounted internal combustion engine having its rotational axis disposed transversely to the body length of the vehicle. 
     2. Description of the Prior Art 
     In an automatic transmission for motor vehicles, a hydraulic torque converter and a transmission gear mechanism with a number of forward ranges and a reverse range are generally coaxially coupled with the crankshaft of an internal combustion engine. 
     In F.F. vehicles having the crankshaft of an internal combustion engine disposed transversely of the vehicle body, it is the usual practice to mount also in a transversely oriented position a block which assembles together an internal combustion engine, a torque converter and a transmission gear mechanism. However, in a case where an automatic transmission of this sort is mounted on a small motor vehicle which has a limited engine room space, a difficulty is often encountered in finding a space for an auxiliary transmission mechanism such as an overdrive or underdrive (reducing) mechanism which serves to improve the operational efficiency or to increase the speed ranges of the transmission, or a space for mounting a direct-coupling clutch to the hydraulic torque converter for improving the fuel consumption. 
     What is needed is an automatic transmission for a front engine-front drive type motor vehicle which includes an auxiliary transmission mechanism such as an overdrive or underdrive mechanism and a direct coupling clutch for the hydraulic torque converter for improving fuel consumption. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a compact automatic transmission for motor vehicles having, along with a hydraulic torque converter and a main transmission gear mechanism with a plural number of forward ranges and a reverse range, an auxiliary transmission gear mechanism constituting an overdrive mechanism of a speed reduction ratio smaller than 1 or an underdrive mechanism having a speed reduction ratio greater than 1. 
     It is another object of the present invention to provide a compact automatic transmission for motor vehicles of the type mentioned above, in which the auxiliary transmission mechanism is provided coaxially with the hydraulic torque converter and in parallel relation with the main transmission mechanism, transmitting power from the torque converter to the main transmission mechanism through the auxiliary transmission mechanism. 
     A further object of the present invention is to provide an automatic transmission for F.F. vehicles, in which the output shaft of the main transmission mechanism, positioned in parallel with the auxiliary transmission mechanism, is coupled with axle shafts of front wheels through a differential gear device. 
     According to the present invention, there is provided an automatic transmission for motor vehicles having a hydraulic torque converter, an auxiliary transmission mechanism mounted coaxially with the torque converter, means for transmitting power from the torque converter to the auxiliary transmission mechanism, a main transmission mechanism having a rotational axis in parallel relation with the rotational axis of the auxiliary transmission mechanism and having a plural number of forward ranges and a reverse range, means for connecting the output shaft of the auxiliary transmission mechanism with an input shaft of the main transmission mechanism, and means for connecting the output shaft of the main transmission gear mechanism with axle shafts of front wheels through a differential gear device, whereby the auxiliary transmission mechanism constituting an overdrive or an underdrive (reducing) mechanism is mounted additionally to a conventional automatic transmission having a hydraulic torque converter and a transmission mechanism with a plural number of forward speed ranges and a reverse range, without increasing longitudinal dimensions of the transmission. Mounting on a small-size motor vehicle is practicable while augmenting the speed ranges of the transmission. Moreover, the transmission construction still has room for providing a direct-coupling clutch for the hydraulic torque converter, so that the fuel consumption of the motor vehicle is improved by providing the direct-coupling clutch together with the auxiliary transmission mechanism in the automatic transmission. 
     Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification. 
     The invention according comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a diagramatic representation of an automatic transmission for a motor vehicle in accordance with the invention; 
     FIGS. 2 and 3 are diagramatic representations of alternative embodiments of an auxiliary transmission gear mechanism for the transmission of FIG. 1; and 
     FIGS. 4, 5 and 6 are diagramatic representations of alternative embodiments of the main transmission gear mechanism of the automatic transmission of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention is now illustrated more particularly by way of some preferred embodiments shown in the drawings. Referring first to FIG. 1, there is shown an embodiment which applies the present invention to an F.F. type motor vehicle having a crankshaft 2 of an internal combustion engine 1 connected to a hydraulic torque converter 3. The hydraulic torque converter 3, which is of known construction, is provided with a pump impeller 4 which is coupled with the crankshaft 2, a stator 7 which is connected to a stationary portion 6 through a one-way clutch 5, and a turbine runner 8. Further, a direct-coupling clutch 90 is provided for direct coupling of the crankshaft 2 and an input shaft 11. 
     An auxiliary transmission gear mechanism 10 is provided coaxially with the crankshaft 2 to constitute an overdrive mechanism in this particular embodiment. The input shaft 11 of the auxiliary transmission mechanism 10 which extends coaxially with the crankshaft 2 is coupled with the turbine runner 8. The auxiliary transmission mechanism 10 has a planetary gear system 20 which consists of a sun gear 21, planet-pinions 22, a ring gear 23 and a carrier 24 which rotatably supports the planet-pinions 22. The carrier 24 is coupled with the input shaft 11, and a clutch 25 controls engagement between the carrier 24 and sun gear 21, while a brake 26 controls engagement between the sun gear 21 and a stationary portion 27 of the transmission housing. A one-way clutch 28 controls engagement of the carrier 24 with the sun gear 21. The ring gear 23 which forms an output element of the auxiliary transmission gear mechanism 10 is coupled with a sprocket wheel 29. 
     An oil pump 12 which is driven by the crankshaft 2 is located on the outer side of the auxiliary transmission mechanism 10 remote from the hydraulic torque converter 3. 
     A main transmission gear mechanism 30 which is located in parallel relation with the crankshaft 2 constitutes in this particular embodiment an underdrive mechanism with three forward ranges and a reverse range. An input shaft 31 of the main transmission mechanism 30 is coupled with a sprocket wheel 32 which is linked with the sprocket wheel 29 by a chain 33. Output power of the auxiliary transmission mechanism 10 is transmitted to the input shaft 31 of the main transmission mechanism 30 through the sprocket wheel 29, the chain 33 and the sprocket wheel 32. The main transmission mechanism 30 has planetary gear systems 40 and 50 which respectively consist of a sun gear 41, 51, planet-pinions 42, 52, a ring gear 43, 53 and a carrier 44, 54 which rotatably supports the planet-pinions 42, 52. The input shaft 31 is releasably coupled with the ring gear 43 through a clutch 34 and with the sun gears 41 and 51 through a clutch 35. A brake 36 controls engagement of the sun gears 41 and 51 with a stationary portion 38 of the transmission housing. A brake and a one-way clutch 45 control engagement between the carrier 54 and a stationary portion 39, of the transmission housing. The carrier 54 which is coupled with the ring gear 53 is also coupled with a sun gear 61 of a final reducer 60. The final reducer 60 consists of the sun gear 61, planet-pinions 62, a ring gear 63 and a carrier 64 which rotatably supports the planet-pinions 62. The ring gear 63 is connected to a stationary portion 65 of the transmission housing, while the carrier 64 is connected to a shaft casing 71 of a differential gear device 70. 
     The differential device 70 which is of known construction is coupled with axle shafts 72 and 73 of front wheels (not shown). The shaft casing 71 which rotatably supports pinions 76 and 77 in meshing engagement with side gears 74 and 75 is coupled with the carrier 64. 
     The operational ranges of the above-described automatic transmission are illustrated in the following table. 
     
                       TABLE                                                       
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Shift                                                                     
positions                                                                 
         25    26      28  34    35  36    37  45                         
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1st speed                                                                 
         o             x   o               o   x                          
2nd speed                                                                 
         o             x   o         o                                    
3rd speed                                                                 
         o             x   o     o                                        
4th speed      o           o     o                                        
Reverse  o             x         o         o                              
______________________________________                                    
 
    
     In the foregoing table, the respective numerals corresponds to the reference numerals of the clutches, the brakes and the one-way clutches, and the symbol &#34;o&#34; indicates the engaged state of a clutch or brake and symbol &#34;x&#34; indicates a restrained state of a one-way clutch. The engagement and release of each clutch and brake are controlled by a corresponding hydraulic servo motor (not shown) which receives supplies of pressurized operating fluid from a hydraulic control system (not shown). 
     The operations in the respective speed ranges are as follows. 
     In the forward 1st speed, the clutches 25 and 34 and the one-way clutches 28 and 45 are actuated. The power from the crankshaft 2 is transmitted to the input shaft 11 through the torque converter 3, and thus to the carrier 24 of the planetary gear system 20. At this time, since the clutch 25 and the one-way clutch 28 are in actuated state, the whole planetary gear system 20 is rotated integrally and the sprocket wheel 29 which is coupled with the ring gear 23 is also rotated. The rotation of the sprocket wheel 29 is transmitted through the chain 33 to the sprocket wheel 32 to rotate the input shaft 31 of the main transmission mechanism 30. The rotation of the input shaft 31 is transmitted to the ring gear 43 through the clutch 34. While, the carrier 54 is put in rotation in a direction reverse to the input shaft 31 but its rotation is blocked by the one-way clutch 45, so that the ring gear 53 is rotated in the same direction as the input shaft 31 to rotate the sun gear 61 of the final reducer 60. Simultaneously, the carrier 44 is rotated in the same direction, superposing its rotational force on the sun gear 61 to drive the same by combined rotational forces. The rotation of the sun gear 61 is then transmitted to the front wheel axle shafts 72 and 73 through the final reducer 60 and differential device 70. In a case where engine braking effect is desired to be applied, for example, in a downhill operation, however, brake 37 is actuated to block the rotation of the carrier 54 since it is difficult to block its rotation by the one-way clutch 45 alone. 
     In the forward 2nd speed range, the clutches 25 and 34 the brake 36 and the one-way clutch 28 are in the actuated state. The power from the crankshaft 2 is transmitted to the input shaft 31 of the main transmission mechanism 30 in the same manner as in the forward 1st speed range. The rotation of the input shaft 31 is transmitted to the ring gear 43, while the sun gear is put in rotation in a direction reverse to the ring gear 43 but its rotation is blocked by the actuation of the brake 36, so that the planet-pinions 42 revolve both round the sun gear 41 in a same direction with the input shaft 31 and on their axis respectively, thereby the carrier 44 is rotated in the same direction with the input shaft 31 to transmit the rotation to the front wheel shafts 72 and 73 through the final reducer 60 and the differential device 70. 
     In the forward 3rd speed range, the clutches 25, 34 and 35 and the one-way clutch 28 are in the actuated state. The power from the crankshaft 2 is transmitted to the input shaft 31 of the main transmission mechanism 30 in the same manner as in the forward 1st speed range. The rotation of the input shaft 31 is transmitted to the ring gear 43 and the sun gear 41 through the clutches 34 and 35. Therefore, in the planetary gear system 40, the rotations in the same direction of the ring gear 43 and the sun gear 41 cause the planet-pinions 42 to rotate together and integrally with the ring gear 43 and the sun gear 41, thereby rotating the carrier 44 to transmit the rotation to the sun gear 61 of the final reducer 60 and then to the front wheel axle shafts 72 and 73 through the final reducer 60 and the differential device 70. 
     In the forward 4th speed range, the clutches 34 and 35 and the brake 26 are in the actuated state, the power of the crankshaft 2 is transmitted to the input shaft 11 and the carrier 24 through the torque converter 3. In this instance, the sun gear 21 is held stationary by the actuation of the brake 26, so that the rotation of the ring gear 23 which is now rotated at an increased speed through the rotation of the carrier 24 is transmitted to the input shaft 31 of the main transmission mechanism 30. Similarly to the forward 3rd speed range, the rotation of the input shaft 31 is transmitted to the front wheel axle shafts 72 and 73 through the main transmission mechanism 30, the final reducer 60 and the differential device 70. 
     In the reverse range, the clutches 25 and 35 as well as the brake 37 and the one-way clutch 28 are in the actuated state, so that the power from the crankshaft 2 is transmitted to the input shaft 31 of the main transmission mechanism 30 in the same manner as in the forward 1st speed range. The rotation of the input shaft 31 is transmitted to the sun gears 41 and 51 through the clutch 35. In this instance, as the carrier 54 is held stationary by the actuation of the brake 37, the ring gear 53 is put in rotation by the sun gear 51 through the planet-pinions 52 in a direction reverse to the input shaft 31, transmitting the reverse rotation to the sun gear 61 of the final reducer 60, and then to the front wheel axle shafts 72 and 73 through the final reducer 60 and differential device 70. 
     FIG. 2 illustrates an alternate embodiment of the auxiliary transmission mechanism 10 in which like parts are designated by like reference numerals and their explanations are omitted. In this embodiment, the auxiliary transmission mechanism 10 constitutes an overdrive mechanism, with the one-way clutch 28 located between the carrier 24 and the ring gear 23. 
     FIG. 3 shows still another alternate embodiment of the auxiliary transmission mechanism 10, which constitutes an underdrive mechanism with a reduction ratio greater than 1. In this case, the input shaft 11 is coupled with the ring gear 23, and the carrier 24 is coupled with the sprocket, wheel 29. The sun gear 21 is releasably coupled with the carrier 24 through the clutch 25 and with the stationary portion 27 of the transmission housing through the brake 26 and the one-way clutch 28. Upon engaging the clutch 25, the whole planetary gear system 20 is rotated integrally, transmitting the rotation of the input shaft 11 to the carrier 24. When the brake 26 is actuated, the rotation of the input shaft 11 is transmitted to the carrier 24 at a reduced speed. 
     FIGS. 4 to 6 illustrate alternative embodiments of the main transmission mechanism 30, wherein those component parts which have correspondents in FIG. 1 are designated by similar reference numerals to avoid repetition of explanations. In these particular embodiments of the main transmission mechanism, a brake 81 is provided parallel with the brake 36 for connecting and disconnecting the sun gears 41 and 51 with the stationary portion 82 of the transmission housing through a one-way clutch 80. 
     As clear from the foregoing description, the present invention provides an automatic transmission for motor vehicles having an overdrive or underdrive mechanism parallel with the conventional 3-speed transmission mechanism. Thus, according to the present invention, it becomes possible to increase the speed ranges of automatic transmission for F.F. vehicles or to employ a torque converter with a direct-coupling clutch.