WO2004076222A1

WO2004076222A1 - Power transmission with range gear separated from a main gear

Info

Publication number: WO2004076222A1
Application number: PCT/SE2004/000220
Authority: WO
Inventors: Lars Eklund
Original assignee: Scania Cv Ab (Publ)
Priority date: 2003-02-26
Filing date: 2004-02-19
Publication date: 2004-09-10
Also published as: SE521643C2; SE0300500L; DE112004000316T5; SE0300500D0

Abstract

Power transmission of a motor vehicle, particularly a truck (2), in which a multi-speed main gear (10) and a range gear (24) which is driven from the latter form part of the driveline between the vehicle’s engine (4) and a central gear (16) of a vehicle axle (14) which comprises driveshafts (20,22) for powered wheels (12), which central gear is driven via a propeller shaft system (30). In the driveline, the range gear (24) is arranged separately from the main gear (10) and situated directly adjacent to the central gear (16), and the propeller shaft system (30) is drivingly connected between an output shaft (26) from the main gear (10) and an input shaft (28) to the range gear (24).

Description

Power transmission with range gear separated from a main gear

The present invention relates to a power transmission of a motor vehicle, particularly a truck, in which a main gear section and a range gear which is driven from the latter form part of the driveline between the vehicle's engine and a central gear on a vehicle axle (comprising driveshafts for powered wheels), which central gear is driven via a propeller shaft system (comprising at least one propeller shaft). The propeller shaft system may comprise either a single undivided propeller shaft or two or more propeller shafts connected in series.

State of the art

The power transmission in a modern heavy truck incorporates a multi-speed gearbox (with, for example, 14 or 16 gears) which may comprise a three-speed or four-speed main gear section (with integrated split gear and crawling gear) and a range gear. The range gear is usually a planetary gear with a low-speed region and a high-speed region. In such cases, the split gear integrated in the main gear section is situated in the forward region of the main gear section (i.e. in the main gear section's input region which is connected to the vehicle's clutch), while the range gear is situated in the rear region of the main gear section. In practice, the sun wheel of the planetary gear is mounted directly on the rear end of the continuous mainshaft of the main gear section.

The fact that the range gear in the form of a planetary gear is situated rearwards on the continuous mainshaft of the main gear section results in high torque being transmitted via the propeller shaft system, with the consequence that the propeller shaft system components concerned will of physical necessity be heavy and therefore expensive to manufacture. These heavy components do of course have a high moment of inertia, which is also a disadvantage. Objects of the invention

A primary object of the present invention is therefore to provide a novel type of power transmission so designed that the torque which the propeller shaft system has to transmit (in the case of a vehicle engine with a given maximum torque) can be substantially lower than in the case of a version in which the range gear is situated in the abovementioned traditional manner, i.e. rearwards on the mainshaft of the main gear section. An object directly relating to the primary object is to provide a power transmission whose propeller shaft system can be made significantly lighter than is possible when using the abovementioned traditional mode of construction.

Another object is to provide a power transmission whose contribution to the vehicle's unsprung weight is as small as possible.

A further object is to provide a power transmission which is well suited to the use of universal joints of the constant speed type, i.e. universal joints with constant angular velocity. Such universal joints are also called "correct-angle universal couplings". In this context it may be mentioned that traditional universal joints of the ball-and-socket joint type give rise to angular velocity pulsations (speed fluctuations) on shafts or shaft ends which are mutually angled out and connected together by such a universal joint. Such angular velocity pulsations risk causing undesirable oscillations of the shafts connected together, particularly in the case of long propeller shafts.

Summary of the invention

The abovementioned objects are achieved according to the invention by the power transmission of the kind indicated in the introduction exhibiting the features indicated in the characterising part of claim 1.

A primary characteristic of the invention is therefore that the range gear incorporated in the driveline is arranged separately from the main gear and situated directly adjacent to the central gear. At the same time, the propeller shaft system comprising either a single undivided propeller shaft or two (or more) propeller shaft sections connected in series is drivingly connected between an output shaft from the main gear and an input shaft to the range gear.

In the case of a motor vehicle/with powered rear wheels, central gear means the rear axle gear, i.e. the final gear combined with the differential.

Embodiments of the power transmission according to the invention which are suitable or preferred for various vehicle versions may further exhibit the features particularly indicated in the dependent claims.

If the range gear (planetary gear) thus connected to the central gear is directly integrated with the central gear and accommodated in a gear housing common to both the range gear and the central gear, the result is significant advantages in terms of reduced space requirement and lower weight. Such a common vehicle housing may further be advantageously integrated with shaft casings which enclose the wheel driveshafts to the powered wheels.

Both at its end connected to (and hence driven by) the output shaft of the main gear and at its end connected to (and hence driving) the input shaft of the range gear, the propeller shaft system may preferably be provided with driving joints in the form of constant speed joints. Alternatively, it is of course possible instead to use universal joints (ball-and-socket joints) of the kind commonly used in truck propeller shafts. Constant speed joints have previously been used mainly in front wheel drive passenger cars. Examples of such joints include, for example, the Rzeppa coupling and the Birfield joint.

It has in practice not been possible to use constant speed joints at the ends of propeller shafts or propeller shaft sections in propeller shaft systems of trucks because the large torque which in trucks is transmitted via the propeller shaft or propeller shaft system would have led in such cases to constant speed joints which were structurally too large and bulky (and hence too expensive). The fact that the range gear according to the invention is situated directly adjacent to the central gear (instead of at the output side of the main gear section), i.e. situated after the propeller shaft system, reduces the torque which the propeller shaft system has to transmit by a factor of l/n_range, in which n_rang_e is the gear ratio of the range gear. An example which may be quoted of a normal range gear ratio is the value 3.2, which means that said reduction factor then becomes 0.31, which therefore means that the torque transmitted by the propeller shaft system decreases by 69%. It thus becomes perfectly possible for constant speed joints to be used also in propeller shaft systems for trucks without becoming too bulky and heavy and hence too expensive.

As well as the possibility of using constant speed joints in the propeller shaft system according to the invention, the invention affords the great advantage that the propeller shaft system concerned (or the propeller shaft sections or propeller shafts connected in series to form the propeller shaft system) can be made far slenderer and hence far lighter and less expensive than would be possible with the current range gear location forward of the propeller shaft system. The vehicle's weight may thus be reduced and the risk of vibrations occurring in the propeller shaft system is also likely to decrease radically, particularly when using constant speed joints, since speed pulsations of the components of the propeller shaft system are thereby completely eliminated.

The possibility of using constant speed joints in the propeller shaft system also makes it possible to build trucks with the engine at an angle of 0°, i.e. the angle between the engine's crankshaft and a horizontal plane of the vehicle (e.g. the plane formed by the longitudinal side-members). Such a 0° engine angle also creates the possibility of building a truck with a flatter and lower floor in the driver's cab, which is desirable for several reasons. If the driver's cab can be placed lower and the vehicle's height can therefore be reduced, the air resistance and the truck's total weight are reduced.

With a power transmission according to the invention it is also possible to provide the output shaft of the main gear with a flanged coupling for the connection to one end of the propeller shaft which takes the form of a constant speed shaft. In such cases the input shaft to the range gear is provided with a similar flanged coupling for the connection to the opposite other end of the propeller shaft, which means that an output shaft from the range gear can then be coupled directly to a pinion which forms part of the central gear.

Brief description of the drawings

The invention will now be made clearer and exemplified with reference to the attached drawings which illustrate very schematically a power transmission according to the invention and are as follows:

Fig. 1 depicts a schematic side view of a motor vehicle with a power transmission of the kind to which the present invention relates; and

Fig. 2 depicts a schematic plan view of a power transmission of the same general type as depicted in Fig. 1.

Description of the embodiment depicted in the drawings

Fig. 1 depicts very schematically the external contours of a motor vehicle 2 in the form of a truck which is provided with a power transmission corresponding to the type defined in the claims below.

The vehicle has an engine 4 with a clutch 6 and, connected thereto, a gearbox 8 comprising a multi-speed main gear 10. The main gear may in a conventional manner be provided with a split gear situated at the main gear's input end which is connected to the engine/clutch. For the sake of simplicity, the vehicle in this case is regarded as having only one rear axle 14 provided with two powered wheels 12. The rear axle 14 is provided in a usual manner with a central gear 16 (with differential 18) which serves as final gear. The rear axle 14 incorporates driveshafts 20 and 22 for the powered wheels 12.

A traditional truck gearbox usually incorporates a range gear in the form of a planetary gear which is then situated at the output end of the main shaft. To achieve the design advantages discussed above, however, the power transmission in such cases is so constructed that the range gear 24 which forms part of the power transmission is situated entirely separately from the main gear 10, more specifically directly adjacent to the central gear 16. The driving power (the torque) from the engine 4 is transmitted in a conventional manner from the output shaft 26 of the main gear 10 to the input shaft 28 of the range gear 24 via a propeller shaft system 30 connected between the shafts 26 and 28.

The propeller shaft system comprises preferably at least two drivingly connected propeller shafts 34 and 36 connected in series by a universal joint 32 connected between them. These two propeller shafts are drivingly connected in their turn to the shafts 26 and 28 by universal joints 38 and 40 respectively.

The universal joints 32,38,40 may take the form of, for example, traditional ball-and- sockets joints but it is preferable, with a view to preventing the occurrence on the propeller shafts 34 and 36 of rotation speed fluctuations (speed variations) which would cause vibrations in situations when said propeller shafts are not entirely coaxial (without being mutually angled), to use some suitable type of constant speed joints, e.g. Rzeppa couplings, Birfield joints, Bendix-Tracta or Bendix- Weiss couplings or Thompson couplings. These types of constant speed joints have previously been used mainly in front wheel drive passenger cars.

The range gear 24 in the form of a planetary gear is integrated and combined with the central gear 16 and accommodated in a gear housing 42 which is common to the range gear and the central gear. This gear housing may also be integrated with shaft casings 44,46 which surround the wheel driveshafts 20,22.

If the propeller shaft system takes the form of a constant speed system, it is possible to conceive of using flanged couplings instead of the universal joints 38, 40. In that case the output shaft 26 of the main gear is provided with a flanged coupling element for the connection to a cooperating flanged coupling element at the connecting end of the propeller shaft system, while the input shaft 28 of the range gear 24 is provided with a similar flanged coupling element for the connection to a corresponding flanged coupling element at the relating end of the propeller shaft system. The output shaft 48 from the range gear may further be advantageously connected directly to, or even form part of, the input pinion 50 of the central gear 16.

Claims

1. A power transmission in a motor vehicle (2), particularly a truck, in which a multi- speed main gear (10) and a range gear (24) which is driven from the latter form part of the driveline between the vehicle's engine (4) and a central gear (16) of a vehicle axle (14) which comprises driveshafts (20,22) for driven wheels (12), which central gear is driven via a propeller shaft system (30) which comprises at least one propeller shaft, characterised in that in the driveline the range gear (24) is arranged separately from the main gear (10) and situated directly adjacent to the central gear (16), and the propeller shaft system (30) is drivingly connected between an output shaft (26) from the main gear (10) and an input shaft (28) to the range gear (24).

2. A power transmission according to claim 1, characterised in that the range gear (24) is a planetary gear integrated with the central gear (16) and accommodated in a gear housing (42) which is common to the range gear and the central gear.

3. A power transmission according to claim 1 or 2, characterised in that the propeller shaft system (30) is drivingly connected to the output shaft (26) of the main gear (10) and the input shaft (28) of the range gear (24) via universal joints (38,40), e.g. ball- and-socket joints.

4. A power transmission according to claim 3, characterised in that the universal joints (38,40) are constant speed joints, e.g. Rzeppa couplings, Birfield joints or Thompson couplings.

5. A power transmission according to claim 4, characterised in that the output shaft (26) of the main gear (10) is provided with a flanged coupling for connection to one end of a propeller shaft (30) which takes the form of a constant speed shaft, and the input shaft (28) of the range gear (24) is provided with a similar flanged coupling for the connection to the propeller shaft's opposite other end, and an output shaft (48) from the range gear (24) is connected directly to an input pinion (50) in the central gear (16).

6. A power transmission according to any one of claims 2-5, characterised in that the gear housing (42) common to the range gear (24) and the central gear (16) is integrated with shaft casings (44,46) which surround the wheel driveshafts (20,22).

7. A power transmission according any one of the foregoing claims, characterised in that the vehicle axle (14) is a rear axle of the motor vehicle (2).

8. A power transmission according to any one of the foregoing claims, characterised in that a propeller shaft system (30) comprising two or more propeller shafts (34,36) connected in series forms part of the driveline.