WO1994006639A1

WO1994006639A1 - Axle device provided with three differential gears for motor-driven vehicles

Info

Publication number: WO1994006639A1
Application number: PCT/IT1993/000099
Authority: WO
Inventors: Remo Sisler
Original assignee: Remo Sisler
Priority date: 1992-09-21
Filing date: 1993-09-20
Publication date: 1994-03-31
Also published as: ITVR920080A0; ITVR920080A1; IT1259199B

Abstract

The axle device (30) comprises two wheels (49, 50; 51, 52) on each side and three differential gears (31, 37, 38), of which the central differential gear (31) is normally connected to a drive from the motor shaft and carries out its normal functions. The axle shafts (33, 34) coming out from said central differential gear (31) drive into rotation the carriers of further two side differential gears (37, 38) which, on their turn, by means of respective axle shafts, drive into an interdifferentiated rotation of turns the respective wheels. In this way, on each axle side a pair of wheels is formed, in which each wheel has a reduced section and, while bending, turns at a differentiated speed relative to the adjacent wheel, in order to take into consideration the different bending radius. Each wheel has a reduced section, and this reduces the distance between the centerline of the wheel and its respective internal and external sides, thereby greatly reducing the slipping effect of said sides on the ground. This prevents in a substantial way an abnormal tyre wear and an increase of the power dissipated by the motor, thereby avoiding the use of single soft-compound and enlarged-section tyres.

Description

AXLE DEVICE PROVIDED WITH THREE DIFFERENTIAL GEARS FOR

MOTOR-DRIVEN VEHICLES.

* * * * * * *

TECHNICAL FIELD The present invention relates to an axle device provided with three differential gears for motor-driven vehicles.

More particularly, the present invention relates to an axle device which is particularly suitable for driving automotive vehicles and which allows the roadholding properties of the vehicle to be optimised, as well as an abnormal wear of the tyres and useless power dissipations to be avoided, and this to the advantage of the whole propulsive system. The invention may be mainly applied in the technical field of motor vehicle building mechanical industry.

BACKGROUND ART The automotive technique tends at present towards a constant increase of vehicles performances, both in the terms of power and speed.

In order to solve the roadholding problems deriving from the continuously increasing powers which are transferred to the road by means of the tyres, said problems being shortly summarized by higher accelerations, brakings, slippings, skiddings, centrifugal actions of the vehicle, the background art generally provides for widening the tyre section in order to widen its tread.

However, said problems are innate in the present enlarged-section tyres. At the same time, the present technique tends to use highly sophisticated compounds for the tyres in order to compensate, it is believed, by means of the tyre adhesion on the road, the unitary adhesion loss which is determined by the reduction of the specific pressure on the road, due to the increase of the contacting surface of the tyre on the ground.

However, as a matter of fact, the adoption of enlarged-section tyres is only a palliative which trys to solve the problem on the base of a reduction of the negative effects, rather than researching the reasons of the roadholding reduction; in other words, measures are taken which are useless for substantially increasing the vehicle roadholding and which lead to a premature and fast tyre wear; as a result, after a short time the tyres need to be replaced in order to avoid roadholding conditions which are still worse than those which may be obtained by means of normal, non-enlarged-section tyres. " Figures 1, 2, 3 schematically illustrate a situation that is similar to the one which has been described above, in order to show the contrasting work which is carried out by enlarged-section tyres, once they are running along a curved path. Figure 1 represents by way of example the propulsive rear axle of a motor vehicle running along a curved path about the centre of curvature O, which acts as the fulcrum of the movement.

Actually, the respective tyres 10, which is external relative to the curve, and 11, internal relative to the curve, touch their respective path sectors from 12 to 13 and from 14 to 15.

Taking into consideration the centerlines 16, 17 of tyres 10, 11, which may be considered as having a virtually cylindrical shape and an enlarged section, it may be noted that the centerlines run along an ideal and interdifferentiated path, thanks to the presence of differential gear 26, while the respective external and internal sides of tyres 10, 11 must slip against the ground, since they cannot adapt themselves to the interdifferentiated path ratio which is bound by curve arcs 18, 19; 20, 21. In other words, by considering as ideal the speed of the contacting point on the ground in correspondence of centerlines 16, 17, as a matter of fact the external points 13, 15 of respective tyres 10, 11 would require a speed which is higher than the real speed, while the internal points 12, 14 would require a speed which is lower than the real speed.

As a consequence, each tyre 10, 11 undergoes a double self-slipping action against the ground, by increasing the sliding friction on one side by advance and on the other side by lagging, thereby causing a premature and very fast tyre wear, as well as an useless and remarkable dissipation of motor power.

The motor power dissipation phenomenon is further amplified in the case where, in order to increase the tyre adhesion to the ground, softer and softer compounds are used, which merely tend to "stick" the tyres to the ground.

Moving vehicles which are provided with these soft- compound tyres obviously involves great motor power dissipations only for overcoming the chemical adhesion force of the tyres on the ground.

Figures 2 and 3 illustrate further disadvantages involved by the use of enlarged-section tyres.

Anomalies may take place also when the tyre runs along a rectilinear path. These anomalies may be represented by scratches, foreign bodies, oil spots, water stripes etc., and they may concern only one side of the tread, as for instance 22 in fig. 2. This situation may cause an about-face of the vehicle, since (see fig. 3) considering the tyre running the path indicated by arrow 25, the friction or jamming point 22 brakes the tyre run and forms a fulcrum 23 about which the free portion of the tread tends to rotate in the direction shown by arrow 24; as a consequence, the tyre may assume a sudden, incontrollable and highly dangerous orientation.

DESCRIPTION OF THE INVENTION It is the main purpose of the present invention to obviate to the disadvantages and drawbacks which are typical of the background art and to provide, thus, for a device which allows a premature tyre wear to be avoided, the motor power dissipation of a vehicle to be reduced and the roadholding properties of the vehicle to be optimised. This is achieved by an axle device provided with three differential gears for motor-driven vehicles having the features disclosed in the main claim.

The dependent claims describe advantageous forms of embodiment of the invention.

Furthermore, claim 5 discloses a differential gear device suitable for cooperating with said axle device.

The axle device according to the invention uses a pair of wheels on each side, which are mutually interdipendent in rotation from each other and which are respectively connected to a system of differential gears.

According to the invention, the axle device is characterised by two wheels on each side and three differential gears, of which the central differential gear is normally connected to a drive from the motor shaft and carries out its normal functions.

The axle shafts coming out from said central differential gear drive into rotation the carriers of further two side differential gears which, on their turn, by means of respective axle shafts, drive into an interdifferentiated rotation of turns the respective wheels. In this way, on each axle side a pair of wheels is formed, in which each wheel has a reduced section and, while bending, turns at a differentiated speed relative to the adjacent wheel, in order to take into consideration the different bending radius. Each wheel has a reduced section, and this reduces the distance between the centerline of the wheel and its respective internal and external sides, thereby greatly reducing the slipping effect mentioned above of said sides on the ground. This prevents in a substantial way an abnormal tyre wear and an increase of the power dissipated by the motor, thereby avoiding the use of single soft-compound and enlarged-section tyres.

ILLUSTRATION OF DRAWINGS Other advantages and features of the invention will become apparent by reading the following description of a form of embodiment of the invention, given as a non- limiting example, with the help of the drawings illustrated in the annexed sheets, in which: - figure 1 shows the path along a curve of a background art axle, having enlarged-type tyres; figure 2 shows a frontal view of an enlarged-type tyre contacting a foreign body on the ground; figure 3 shows a plan view of the wheel of fig. 2; - figure 4 shows, on a widely schematical and partially sectioned plan view, a driving axle device according to the present invention; figure 5 shows a shematical section of a differential gear provided with a single side outlet for the axle shafts controlling a pair of wheels.

DESCRIPTION OF A PREFERRED FORM OF EMBODIMENT In figure 4, reference sign 30 generally indicates a driving axle device according to the present invention.

The device 30 represented in the figure shows by way of example the propulsive rear axle of an automotive vehicle; however, it is clear that this form of embodiment does not limit the scope of the invention, which may easily be carried out also on the forecarriage, in the case where the motive power is transferred to the latter.

Device 30 comprises a first central differential gear

31, which is moved by a drive 32 connected to the motor.

As usual, a first shaft 33 and a second shaft 34 come out from the carrier sides of said first differential gear

31.

According to the invention, each shaft 33, 34 is respectively provided with a flange 35, 36 for coupling the shaft with the carrier of respective second (37) and third (38) differential gears.

The carrier of each of said second and third differential gears 37, 38 is provided with an aperture, which is placed opposed to the inlet side of said shafs 33, 34, and from which a pair of axle shafts come out, which are respectively indicated by reference signs 39, 40 and 41, 42; axle shafts 39, 41 are tubular, while axle shafts 40, 42 are onted inside of axle shafts 39, 41, they are concentric to shafts 39, 41 and they are coupled to shafts 39, 41 by means of suitable bearings (not shown in the figure for better understanding of the drawing) .

Particularly referring to differential gear 37, it may be remarked in the figure that tubular axle shaft 39 is driven by crown wheel 43, while axle shaft 44 is driven by crown wheel 44; these crown wheels are obviously coupled by means of side pinions 45, 46.

Furthermore, a tired wheel 49, 50, 51, 52 is connected to each axle shaft 39, 40, 41, 42 by means of respective hubs 47, 48; the wheels are fastened to the hub through check nuts.

Each tired wheel 49, 50, 51, 52 is identical to the other ones, and is monted on identical rims. Disassembly of the wheels simply takes place by using a suitable extractor 53, by means of which nut 54 that holds hub 48 together with axle shaft 40 is loosened; thereafter, wheel 49 may be removed; wheel 50 is removed by simply acting on the normal check nuts. - Similarly, by acting on the check nuts it is possible to remove hub 48 from wheel 49.

In order to complete the description of fig. 4, we may in this case outline one of the possible positions in which a pair of brakes 55, 56, in this case a pair of disk brakes, may be placed.

Thus, according to this form of embodiment, the axle device according to the invention is substantially constituted by three differential gears and two pairs of wheels placed side by side. As it may be remarked, the height of each tyre, therefore the width of the tread section contacting the ground, is practically halved in respect of the background art solutions; as a result, the distance between the centerline of each wheel and the edges of the same is halved too; this feature, joined to the fact that the motion transfer to the wheels of each pair is differentiated by means of the lateral differential gears 37, 38, immediately involves a substantial reduction of the self-slipping effect of the tyre on the ground, thereby achieving the purposes of the invention.

In fact, thanks to the presence of differential gears 37, 38, while running along a curved path each wheel gets its relevant speed by considering the bending radius.

Thus, the slipping of the tyre on the ground is substantially reduced; this fact involves an immediate improvement of the roadholding properties and a reduced wearing action on the tyre, avoiding useless dissipations of motor power.

The rotation relative to the differentiating function between the two axle shafts is in this phase negligible from the mechanical point of view and, on a rectilinear path, the two concentric axle shafts practically turn at the same speed.

The invention has been described with reference to an advantageous form of embodiment, according to which the axle is provided with two pairs of wheels.

Theoretically, the invention could be generalized to a higher number n of wheels and of differential gears; however, the increase of number n is at present effectively limited by practical considerations, i.e. by the overall dimensions from the mechanical point of view and from the accessing difficulties for mantainance operations.

While it is clear that the increas of number n is highly desirable in respect of the improvement of the device performances, therefore for obtaining a better roadholding of the vehicle and a normal wear of the tyres, the optimisation of number n is one of the fundamental problems for the engineer.

Claims

1. Driving axle device (30) provided with three differential gears (31, 37, 38) for motor-driven vehicles, comprising a first central differential gear (31) which is connected to a gearing coming from the driving shaft and which is provided with two axle shafts (33, 34) respectively disposed aside of the carrier of said first differential gear (31) , characterised in that the end of one of said axle shafts (33, 34) sets into rotation the carrier of a second differential gear (37), and the end of the other of said axle shafts (33, 34) sets into rotation the carrier of a third differential gear (38), said second and third differential gears (37, 38) being respectively provided with an aperture from which respective axle shaft pairs (39, 40; 41, 42) come out, one (39, 41) of the shafts of said pairs being tubular and the other one (40, 42) beeing mounted inside of the tubular shaft and being concentric to the latter, the free end of each of said shafts (39, 40; 41, 42) being connected to a tired wheel (49, 50; 51, 52) .

2. Device (30) according to claim 1, characterised in that each of said shafts (39, 40; 41, 42) is connected by one end thereof to one of the crown wheels (43, 44) of one of said second and third differential gears (37, 38) .

3. Device (30) .according to one of the preceding claims, characterised in that each of said wheels (49, 50, 51, 52) is identical to the other wheels which are mounted on the device.

4. Device (30) according to anyone of the preceding claims, characterised in that the hub (54) of the external wheel (49, 52) is removable from the respective shaft (40, 42) by means of a suitable extractor (53) .

5. Differential gear device (37, 38) suitable for cooperating with an axle device according to anyone of the preceding claims, comprising two conical crown wheels (43, 44) and two side pinions (45, 46) rotating about shafts (57, 57') which are rigidly connected to the differentiating box (55) of the differential gear, in which a suitable gearing (33) sets said differentiating box (55) in rotary motion, characterised in that it comprises a single side outlet, which is disposed in correspondence of the rotation axis of the crown wheels (43, 44), in that a crown wheel (43) drives a first axle shaft (39) keyed to it and the other crown wheel (44) drives a second axle shaft (40) keyed to it, both axle shafts (39, 40) coming out of the differential gear by said single side outlet, one of the axle shafts (39) being tubular and the other one (40) being mounted inside of the tubular shaft and being concentric to the same.