MOTOR VEHICLE TRANSMISSION SYSTEM

Abstract: A transmission system for a motor vehicle which has a transversely-mounted front engine (1) a gear box (2) also mounted transversely, and a differential (3) connecting the secondary shaft of the gear box to the two half-axles (5) of the front wheels, includes an epicyclic step-up gear train (15) housed in the differential housing and connecting the secondary shaft of the gear box (2) to the planet carrier (10) of the differential (3) and a device (25) for selectively rendering the said epicyclic step-up gear train (15) operative and inoperative.

Description: "Motor vehicle transmission system" The present invention relates to a transmission system for a motor vehicle which has a transverselymounted front engine, a gear box also mounted transversely, and a differential connecting the secondary shaft of the gear box to the two half-axles of the front wheels. The object of the present invention is to provide a transmission system of the type specified above which has a series of stepped-up transmission ratios in addition to the normal transmission ratios of the gear box and which at the same time has a simple structure of small bulk. The main characteristic of the invention lies in the fact that the transmission system includes an epicyclic step-up gear train included in the housing of the differential and connecting the secondary shaft of the gear box to the planet carrier of the differential, and a device for selectively rendering the said epicyclic step-up gear train operative and inoperative. The said gear train is rendered operative during economy cruising of the vehicle but inoperative during acceleration phases when it is necessary to use the normal speeds of the gear box. The present invention will now be described with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a perspective view of a transmission system according to the present invention, Figure 2 is a partially-sectioned view of a de tail of the transmission system of Figure 1, Figure 3 is a section taken on line III-III of Figure 2, and Figure 4 is a section, on an enlarged scale, of a detail of Figure 2. In Figure 1, an internal combustion engine is schematically indicated 1 and is intended to be mounted in the front part of a motor vehicle with its shaft disposed transversely of the longitudinal axis of the motor vehicle. The engine 1 includes a gear box 2 of the type with gears in continuous mesh and which has a primary shaft and a secondary shaft also arranged transversely of the longitudinal axis of the vehicle. A front differential indicated by 3 is driven by a pinion 4 (see Figure 2) carried by the secondary shaft 2 and transmits drive torque to the front wheels of the motor vehicle through two half-axles 5. The front differential 3 is housed in a housing 8 joined to the housing of the gear box housing 9. The differential 3 is of the known type having a planet carrier 10 (see Figure 2) including a pin 11 on which are rotatably mounted two planets 12 (only one of which is shown in Figure 2) which mesh with two pinions 13 keyed onto the facing ends of the two halfaxles 5. The pinion 4 which is keyed onto the secondary shaft of the gear box, meshes with a gear 14 which is connected to the planet carrier 10 of the differential 3 through an epicyclic gear train 15. The gear 14 and the planet carrier 10 are rotatably mounted within the housing of the gear box by means of conical bearings 16, 17. In the embodiment illustrated in the drawings, the planet carrier 10 of the differential 3 also acts as a planet carrier for the epicyclic step-up gear train 15. Thus, the pins 18 on which six planets 19 are rotatably mounted, are fixed to the planet carrier 10. As illustrated in Figure 3, the planets 19 mesh with each other in pairs, the three pairs of planets being equi-angularly spaced from each other. Moreover, one planet of each pair meshes with an internallytoothed crown wheel 20 carried by the gear 14 while the other planet of each pair (see Figure 2) meshes with the toothed ring of a sun gear 21 rotatably mounted, by means of roller bearings 22, within a hub 10a of the planet carrier 10 of the differential 3. Two cylindrical roller bearings 23 are interposed between the hub 10a of the planet carrier 10 and the hub of the gear 14, indicated by reference numeral 14a. Axial bearings 24 are also provided for transmitting axial thrust to the conical bearings 16, 17. The system illustrated in Figure 2 further includes a device 25 for selectively rendering the epicyclic step-up gear train 15 operative and inoperative. The device 25 includes a disc 26 keyed to the sun gear 21. A bell 28 is axially slidable on this disc 26 by means of a grooved coupling 27. The bell 28 has two internal conical end surfaces 29, 30 respec tively arranged to engage two conically shaped friction washers 30a, 31 which are respectively carried by a disc 32a fixed to the hub 14a and by an element 32 fixed to the gear box housing 9. A cup spring 34 serves to urge the bell 28 to wards a first operative position in which the conical surface 29 is in contact with the washer 30a so as to render the sun gear 21 and the gear 14 rigid with each other. The device 25 includes an hydraulically-controlled actuator 33, illustrated in detail in Figure 4, which is arranged to effect displacement of the bell 28 into a second operative position in which the conical surface 30 is in contact with the friction washer 31 thereby rendering the sun gear 21 rigid with the fixed structure of the gear box. The device 33 includes a piston 34 slidably mounted in a chamber 35 formed in the fixed structure of the gear box and communicating with a duct 36 for the flow of fluid under pressure. The operation of the system described above is as follows: When it is desired to use the normal speeds of the gear box, the chamber 35 is not under pressure, and the cup spring 34 maintains the bell 28 in its first operative position, illustrated in Figure 2. In this condition, the sun gear 21 of the epicyclic step-up gear train 15 is rigid with the gear 14 which carries the internally-toothed crown wheel 20. The epicyclic gear train is thus locked and the transmission from the pinion 4 to the planet carrier 10 occurs without any step-up. When it is desired to use the step up drive, fluid under pressure is caused to flow into the chamber 35 so as to displace the piston 34 towards the left (with reference to Figure 4). This displacement causes a corresponding displacement of the bell 28 towards the left (with reference to Figure 2) against the action of the cup spring 34. The bell 28 is thus brought into its second operative position in which it renders the sun gear 21 rigid with the fixed structure of the gear box. In this condition, the gear train 15 acts as a step-up gear train whereby the transmission system provides a series of transmission ratios which are stepped-up with respect to the normal transmission ratios of the gear box. This result is achieved by means of a relatively simple structure of small bulk, which is housed in the housing of the front differential of the transmission system. Naturally, in place of the cone clutch system illustrated in Figure 2, a synchroniser device of the type normally used in gear boxes with continuously meshing gears could be used as the device for selectively rendering the epicyclic step-up gear train operative and inoperative. In a variant (not illustrated) the internallytoothed crown wheel 20 is carried by the planet carrier 10 of the differential 3, while the planets 19 (there being three instead of six of these, each meshing with the crown wheel 20 and with the sun gear 21) are carried by the gear 14.

Claims: CLAIMS: 1. A transmission system for a motor vehicle which has a transversely-mounted front engine, a gear box also disposed transversely, and a differential connecting the secondary shaft of the gear box to the two half-axles of the front wheels, characterised in that this system includes an epicyclic step-up gear train (15) housed in the housing (8) of the differential (3) and connecting the secondary shaft of the gear box to the planet carrier (10) of the differential (3), and a device (25) for selectively rendering the said epicyclic step-up gear train (15) operative and inoperative. 2. A transmission system according to Claim 1,char- acterised in that the said epicyclic gear train (15) includes an internally-toothed crown wheel (20) carried by a gear (14) which meshes with a corresponding pinion (4) keyed onto the secondary shaft of the gear box, a sun gear (21) rotatably mounted relative to the planet carrier (10) of the differential (3) and relative to the said gear (14), and a series of planets (19) carried by the planet carrier (10) of the differential (3). 3. A transmission system according to Claim 1, characterised in that the planets (19) mesh with each other in pairs, and in that the planets of each pair mesh one with the sun gear (21) and the other with the internally-toothed crown wheel (20). 4. A transmission system according to Claim 2 or Claim 3, characterised in that the device for rendering the epicyclic step-up gear train (15) operative and inoperative includes a movable member (28) selectively displaceable between a first operative position in which it renders the sun gear (21) rigid with the gear (14) and a second operative position in which it renders the sun gear (21) rigid with the fixed structure of the gear box. 5. A transmission system according to Claim 4,characterised in that the said control device (25) is constituted by an hydraulically-controlled cone clutch device. 6. A transmission system according to Claim 1, char- acterised in that the hydraulically-controlled cone clutch device (25) includes a bell (28) coupled for rotation with the sun gear (21) and displaceable axially relative thereto, this bell (28) having two internal conical end surfaces (29, 30) for cooperating respectively with two conical friction washers (30a, 31) rigid with the said gear (14) and the fixed structure (9) of the gear box; resilient means (34) biassing the bell (28) axially towards a first operative position in which one of its internal conical end surfaces (29) comes into frictional contact with the friction washer (30a) rigid with the said gear (14) and hydraulic control means for pushing the bell (28) axially towards a second operative position in which the other internal conical end surface (30) comes into frictional contact with the friction washer (31) rigid with the fixed structure (9) of the gear box. 7. A transmission system according to Claim 6,char acterised in that the said hydraulic control means (33) include a piston (34) slidably mounted in a chamber (35) formed in the fixed structure (9) of the gear box and communicating with a duct (36) for the flow of fluid under pressure.

Inventors: CANDELLERO, GIOVANNI
Applicants: S.I.R.P. STUDI INDUSTRIALI REALIZZAZIONE PROTOTIPI S.P.A.
Application year: 1983
Main classification: F16H3
IPC codes: F16H3