GEARBOX FOR MOTOR VEHICLE

Abstract: A mechanical stepped gearbox comprises a number of gear wheel pairs (25-34) which interact with one another and are arranged on an input shaft (19), an output shaft (22) and a first side shaft (24). The gear wheel pairs can be selectively coupled in, in order to form different gear ratios. In addition to this, the gearbox comprises, arranged on a second side shaft (40), a gear wheel (39) which is used both in order to bring about a reverse gear and in order to transmit driving force to the first side shaft (24). The gearbox can thus be designed with short axial extent even when the gearbox comprises many gear steps.

Description: Gearbox for motor vehicle The invention relates to a gearbox for a motor vehicle according to the introduction to attached Patent Claim 1. State of the art Gearboxes for use in passenger cars are dimensioned in order to permit driving at different speeds at the same time as combustion engines for use in vehicles permit the most economical driving within a limited engine speed range. In association with an increased requirement for performance and at the same time a requirement for economical driving, there is an increased requirement for more gear steps in the gearboxes. More gear steps can be arranged by mounting more gear wheels in the gearbox on its existing shafts. This means that the gearbox is given an axially longer extent. For vehicles with a longitudinally mounted gearbox, this is no great problem. On the other hand, for vehicles with a transverse gearbox, the space in the transverse direction of the vehicle is critical, since an increased gearbox length is not usually possible without the width of the vehicle having to be increased. The use of a transverse gearbox affords the possibility of building the gearbox together with the drive engine of the vehicle, so that a complete drive aggregate is obtained. This in turn makes it possible to build the drive aggregate compactly and to use the available space in the vehicle effectively. The possibilities for increasing the number of gears while retaining the axial length of the gearbox are limited and presuppose that it is possible in another manner to reduce the axial length of other components in order thus to create new space for more gear wheels in the gearbox. For modern vehicles, which to a great extent are already optimised in said respect, there are problems in creating such space. This problem is further aggravated by the fact that it is usually the cars with the most powerful engines which, with a view to increasing the maximum speed of the vehicle, it is most important to provide with more gear steps. Since these cars can transmit a great driving torque, gear wheels, couplings and other components in the gearbox must be dimensioned for these torques, which further increases its axial extent. A known manner of reducing the axial extent of a gearbox is to replace the conventional synchronising couplings with other, narrower types of non- synchronised couplings in order thus to make space for further gear wheels. However, the requirement thus arises to arrange synchronising in another manner, for example by suitable engine control or by arranging a so-called central synchronising arrangement. Such solutions comprise both expensive and complicated control systems and have not come into practical use in series-produced vehicles. Aim of the invention The aim of the invention is to make it possible that a gearbox can be designed with more gear steps without its axial extent increasing. The gearbox is particularly advantageously to be capable of being used in transverse drive aggregates for use in motor vehicles. Moreover, the gearbox is to be capable of comprising synchronising couplings which are usual for gearboxes, as well as also being constructed around conventional and proven components. The gearbox is to be based on usual gearwheel technology with its possibilities for manufacturing the gearbox at low cost and to have a high degree of efficiency, at least in the majority of driving conditions. Brief description of the invention The abovementioned aim is achieved in that the gearbox is designed with the features which are indicated in the characterising part of attached Patent Claim 1. By virtue of, according to the invention, arranging a separate gear wheel in order to transmit driving torque to a side shaft, it is made possible that certain gears are operated on the side shaft. The length of the input shaft of the gearbox can thus be reduced. According to the invention, the same gear wheel is used in order to bring about a reverse gear. Further gear wheels are not required for this, which allows further reduction of its axial length. Advantageous embodiments are indicated in the attached subclaims. Further advantages and features which characterise the invention emerge from the attached exemplary description of an advantageous embodiment of the invention. Brief description of the drawings The exemplary description is given with reference to the attached drawings, in which: Figure 1 shows a diagrammatic vehicle with a gearbox according to the invention, and Figure 2 shows diagrammatically a gearbox according to the invention. Description of an exemplary embodiment A motor vehicle is exemplified in Figure 1 by a diagrammatically shown front-wheel drive passenger car 1 1 which comprises a transverse drive aggregate 12 in the front end of the vehicle 11. The drive aggregate consists of a combustion engine 13 built together with a mechanical stepped gearbox 14, which gearbox 14, via a differential gear 15 and drive shafts 16, transmits driving force to the front, driving wheels 17 of the vehicle. The car also comprises freely rotating rear wheels 18. Attached Figure 2 shows diagrammatically in greater detail the design of the gearbox 14. The gearbox 14 comprises an input shaft 19 which, via a clutch 20, is connected to and driven by an output shaft 21 of the engine 13. The gearbox 14 also comprises an output shaft 22 connected to the differential gear 15 via a toothed gear 23, from which differential gear 15 driving forces are transmitted to the drive shafts 16 of the driving wheels 17. The input shaft 19 and output shaft 22 of the gearbox 14 are parallel to one another and to the crankshaft of the engine 13. Also included in the gearbox 14 is a side shaft 24. Arranged in a fixed manner on the output shaft 22 are five different gear wheels 25-29, four gear wheels 25-28 of which are in constant engagement with four gear wheels 30-33 which are mounted rotatably around the input shaft 19. By means of coupling members 3-6 arranged on the input shaft 19, the four gear wheels 30-33 can be selectively coupled together in a fixed manner with the input shaft 19. The four gear wheels 30-33 and 25-28 respectively on the input shaft 19 and the output shaft 22 respectively form different gear wheel pairs which form different gear ratios for the gearbox 14. In the same manner, two gear wheels 34, 35 are rotatably mounted around the side shaft 24, one 34 of which engages with the gear wheel 29 on the output shaft 22 and forms a gear wheel pair. The second gear wheel 35 on the side shaft 24 engages with the gear wheel 27 on the output shaft 22 and forms with it a gear wheel pair. This gearwheel 27 on the output shaft 22 is thus used in order to form two gear wheel pairs. The gear wheels 34, 35 on the side shaft 24 can also, by means of coupling members 1 , 2, be coupled together with the side shaft 24. In the figure, the same reference designations are used for the coupling members 1-6 as correspond to the gear position when the coupling 1-6 in question is activated. The two couplings 1 , 2 on the side shaft 24 are thus used in order to couple in the gear positions 1 and 2 while the four couplings 3-6 on the input shaft 19 are used for gear positions 3, 4, 5 and 6. The gearbox 14thus has six gears for forward operation. In addition to this, arranged in a fixed manner on the input shaft 19 is a first gear wheel 36 and arranged in a fixed manner on the side shaft 24 is a second gear wheel 37. Arranged on the output shaft 22 is a rotatably mounted third gear wheel 38 which, by means of a coupling R, can be connected in a fixed manner to the output shaft 22. Said coupling R is used in order to couple in the reverse position of the gearbox 14 according to what is to be described in greater detail below. The first, second and third gear wheel 36-38 all engage with a fourth gearwheel 39 which is freely mounted around a second side shaft 40. In Figure 2, the first side shaft 24 is shown in a lowered position. In reality, this side shaft 24 is arranged partly behind the output shaft 22 and the input shaft 19. The gear engagement between the second gear wheel 37 and the fourth gear wheel 39 is therefore shown diagrammatically with a broken line. For the same reason, the gear engagement between the third gear wheel 38 and the fourth gear wheel 39 is also shown by means of a broken line. By virtue of the fact that Figure 2 in this manner makes clear in principle the different gear engagements of the fourth gear wheel, the axial extent of the fourth gearwheel comes to be shown as exaggerated in relation to its actual extent. In reality, the gear engagements are, for example, arranged so that the gear engagement between the first and fourth gearwheel 36 and 39 respectively in relation to the second and the fourth gear wheel 37 and 39 respectively takes place essentially in the same axial plane. The couplings R and 1-6 are constituted by synchronising couplings which are usual for vehicle gearboxes and which are operated with the aid of conventional coupling forks (not shown). Only one of the couplings R, 1-6 can be activated at a time. The gearbox 14 also has a neutral position N, in which none of the couplings R, 1-6 is activated. The first, second and third gear wheel 36, 37 and 38 respectively are arranged at one end of their respective shafts 19, 24 and 22 respectively. This end is opposite the end at which the input of the gearbox 14 via the input shaft 19 and its output via the output shaft 22 are arranged. The input and output of the gearbox 14 are thus arranged on the same side. The functioning of the gearbox 14 described is as follows. Upon activation of one of the couplings 3, 4, 5 or 6, one of the gear wheels 30, 31, 32 and 33 respectively comes to be coupled together in a fixed manner with the input shaft 19. Driving force is transmitted through the gearbox 14 by interaction with corresponding gear wheels 25-28 on the output shaft 22. At the same time as the input shaft 19 rotates, the fourth gear wheel 39 is driven by the fixed, first gear wheel 36. The second gear wheel 37 on the side shaft 24 thus also comes to be driven with the result that the entire side shaft 24 also rotates. The third gear wheel 38 on the output shaft 22 is also driven but, since the reverse coupling R is not activated, the output shaft 22 is not acted upon by this. Upon activation of one of the couplings 1 or 2, the gear wheels 34 and 35 respectively come in a corresponding manner, by iteraction with corresponding gear wheels 29 and 27 respectively on the output shaft 22, to transmit driving force to the output shaft 22. The driving torque from the input shaft 19 is in this connection transmitted via the first gear wheel 36, the fourth gear wheel 39 and the second gear wheel 37 to the side shaft 24. Upon activation of the reverse coupling R, the third gear wheel 38 is coupled together with the output shaft 22. The gear wheel 38 is driven by the gear engagement with the fourth gear wheel 39 in a direction of rotation which is counter to the direction in which the output shaft 22 rotates when any one of the couplings 1 to 6 inclusive is activated. Activation of the coupling R thus has the effect that the output shaft 22 is driven in the opposite direction and the vehicle can be reversed. When the reverse gear is engaged in this manner, the other gear wheels 30-35 also come to be driven in their opposite directions via the gear wheels 25-29. As, however, none of these is connected in a fixed manner to its respective shaft, this has no effect. The use of the fourth gear wheel 39 according to the present invention means that the entire gearbox 14 can be given axially small dimensions despite a large number of gears. The fourth gearwheel 39 is used on the one hand in order to transmit torque to the side shaft 24 and on the other hand in order to bring about a reverse gear. As a result of this, no further gear wheels or shafts are required in order to bring about a reverse gear. Instead of, as is conventional, arranging the gears 1 and 2 also on the same shafts as the other gears, the gearbox according to the invention results in a slightly worse degree of efficiency of gears 1 and 2. This is because of the extra gear engagement between the gear wheels 36, 39 and 37. However, the gear positions 1 and 2 are used in normal driving only on starting and thus for very short periods of time. The reduced degree of efficiency, under these driving conditions, is therefore negligible on the whole. Within the scope of the attached patent claims, the invention can be modified and designed differently from what is indicated in the above exemplary description. For example, the couplings for the different gear positions R, 1 to 6 inclusive, and the gear wheels likewise, can be arranged in another manner. Similarly, the gearbox can be modified for both fewer and more gear steps than the number in the example.

Claims: P A T E N T C L A I M S 1. Gearbox for a motor vehicle, comprising an input shaft (19), an output shaft (22), at least one first side shaft (24) and a number of coupling members (1-6), by means of which coupling members (1-6) different interacting gear wheel pairs (25-34) arranged on the input shaft (19), the output shaft (22) and the side shaft (24) can be selectively coupled in, in order to form different gear ratios for driving forwards, there being arranged on the input shaft (19) of the gearbox (14) a first gear wheel (36) and on the side shaft (24) of the gearbox (14) a second gear wheel (37), characterised in that a third gear wheel (38) is rotatably mounted on the output shaft (22) of the gearbox, in that a fourth gear wheel (39) is arranged on a second side shaft (40), in that the first, second and third gear wheel (36, 37, 38) are in engagement with the fourth gear wheel (39), and in that there is arranged on the output shaft (22) a coupling (R), by means of which the third gear wheel (38) can be coupled together with the output shaft (22) in order to form a reverse gear. 2. Gearbox for a motor vehicle according to Patent Claim 1, characterised in that the first gear wheel (36) is connected in a fixed manner to the input shaft (19). 3. Gearbox for a motor vehicle according to Patent Claim 1, characterised in that the second gear wheel (37) is connected in a fixed manner to the first side shaft (24). 4. Gearbox for a motor vehicle according to Patent Claim 1, characterised in that the fourth gear wheel (39) is mounted freely rotatably around the second side shaft (40). 5. Gearbox for a motor vehicle according to any one of the preceding patent claims, characterised in that the gear wheels (25-29), which form the gear wheel pairs, on the output shaft (22) are connected in a fixed manner to the output shaft (22), and in that the gear wheels (30-35), which interact with these gear wheels, on the input shaft (19) and on the first side shaft (24) are mounted freely rotatably around the respective shaft (19, 24) and can, by means of respective coupling members (1-6), be selectively connected in a fixed manner to the respective shaft (19, 24). 6. Gearbox for a motor vehicle according to Patent Claim 1, characterised in that the coupling member (R), by means of which the third gear wheel (38) can be coupled together with the output shaft (22), is designed as a synchronising coupling. 7. Gearbox for a motor vehicle according to Patent Claim 1, characterised in that the first gear wheel (36) on the input shaft (19), the second gear wheel (37) on the first side shaft (24) and the third gear wheel (38) on the output shaft (22) are arranged at one end of the respective shaft. 8. Gearbox for a motor vehicle according to Patent Claim 7, characterised in thatthere are arranged atthe respective other ends of the input shaft (19) and the output shaft (22) connections from the drive engine (13) of the vehicle and to the driving wheels (17) of the vehicle (17).

Inventors: NORDKVIST KJELL, NORDKVIST, KJELL
Applicants: SAAB AUTOMOBILE, SAAB AUTOMOBILE AKTIEBOLAG
Application year: 1991
Main classification: B60K17
IPC codes: F16H3