GB1558432A - Differntial devices for motor vehicles - Google Patents

Description

(54) IMPROVEMENTS IN DIFFERENTIAL DEVICES FOR MOTOR VEHICLES (17) 1, VALERIO COLOTTI, an Italian citizen, of 305 Via Agnini, Modena, Italy, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to differential safety devices for motor vehicles. Such devices act to assist in avoiding dangerous skidding while the vehicle is moving, particularly where the ground causes difficulties in roadholding, or in certain stretches of road.

Prior to this invention, two main types of such differential gears were available: the first, the so called "braked torque" device, providing predetermined resistance moment, the other the so-called "self locking" device; the first, with predetermined resistance moment, has, besides the conventional differential gears, friction discs alternatively keyed on the crown wheel hubs and on the internal surface of the box, distributed in two groups and biased inwards by a series of metalelad set springs housed in the two end plates of the differential; the second, self locking device has two aligned couplings for the keying of the half shafts of the wheels, the couplings having external surfaces which are of undulating or cammed profile and between which are positioned' rollers supported by an intermediate cage. This earlier stage of the technique has several deficiencies and drawbacks due to the fact that the differential with groups of spring-biased discs, besides being expensive, does not give a satisfactory performance in low gears, since in these gears torques greater than determined value resistance torques developed by the spring biased discs are created, so much so as to determine, by the effect of the inertial mass of the wheel rotating on the land with a low adhesive force, the loss of arranged balance and skidding of the vehicle in spite of the safety differential gear; as regards the roller differential, which is particularly cheap because it does not employ gears, it is true that the incipient angular rotation of one of the couplings due to the beginning of skidding of the corresponding wheel is locked by means of rollers inserted in the respective cavities with an opposed corrugated profile, but it is also true that, since the skidding wheel tends to lift, as happens for example with the internal wheel on a bend, the wheel itself goes on skidding, making the differential gear completely useless. Because of such deficiences and drawbacks it is necessary to solve the above discussed problem by finding a differential device which allows side skids to be avoided even at lower speeds and when the wheel tends to lift; this differential device must be economical and balanced.

This invention consists in a differential device for motor-vehicles, comprising a casing adapted to be rotated by the propeller shaft of the vehicle, two coaxial driving elements rotatable relative to the casing and adapted to be connected to the half-shafts driving the vehicle wheels, one or more clutch disks rotatable with a respective one of the driving elements and adapted to engage a corresponding disk or disks rotatable with the casing, the clutch disk or disks on the casing being axially movable relative to those of the driving elements, springs biasing into engagement the disk or disks on the casing and the associated disk or disks on each driving element, one of the two driving elements having a radially out wardly facing surface surrounded by a radially inner face of the other driving element, a plurality of rollers supported by a cage rotatable with the casing and interposed between the said surfece of driving elements, which surfaces each have an undulating profile engaged by the rollers and arranged to permit only a limited relative rotation between the driving elements.

The invention thus solves the above mentioned problem through the adoption of a differential device made up of the combination of a disk and spring differential device having a predetermined resisting moment, with a roller differential having rollers between cylindrical surfaces with opposed undulating profile; when running at lower speeds, the rollers can act to stop the initial wheel skidding due to the resisting moment being exceeded, this moment being determined by the springs, while, if there is any tendency for the wheel to lift, the clutch plates prevent skidding of the wheel itself.

The extraordinary result of this is that the disk and spring device not only gives the differential device the known advantageous characteristics of such disk and spring devices but also acts as an equaliser of the roller device, while the roller device not only gives the differential device the known advantageous characteristics of such roller devices, but also acts as an equalizer of the disk and spring device: there is, in such a way, a continuous exchange between the two devices, thus ensuring safety in any condition of running of the vehicle.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a vertical longitudinal section through a differential device in accordance with the invention; Figures 2 and 3 are enlarged crosssections through a self-locking roller of the device of Figure 1, showing the roller in two limiting draft positions between an outer and inner ring of the device: Figure 4 is a longitudinal section through a cage carrying the self locking rollers of the device; Figure 5 is a section on line V-V of Figure 1.

Referring to the drawings, reference numeral 1 indicates the inner ring of the self locking device equipped with hub 2, the ring being internally toothed to provide a splined profile 3 for the left wheel drive shaft clutch of the motor vehicle; reference numerals 4 indicate the generatrices of an undulating track forming the outer surface of ring 1; 5 is an outer splined profile of hub 2; 6 is a hub, internally equipped with a splined profile 7 for the right wheel drive shaft clutch of the motor vehicle; 8 is a flange whose base is formed in hub 6, and from whose outer end there projects, parallel to the axis of hub 6 and extending towards the left as seen in Figure 1, an outer ring 9 of the self locking device; reference numerals 10 indicate the generatrices of an undulating track forming the inner surface of ring 9 itself: it should be noted that the number and the form (shapes) of the cams defined by generatrices 4 and 10 are determined by well-known formulae; 11 are the self locking device rollers inserted in seats 12 of cage 13; 14 is a flange of cage 13, which is cenored on the outer surface of hub 2; the surface of the inner end of hub 2 being centred on the surface of the outer end of hub 6; 15 is an internal splined profile of flange 14; 16 and 17 are two clutch disks respectively internally and externally toothed to be inserted respectively into splined profiles 5 and 15 so as to be axially slidable relative to those gears; 18 is a cap equipped with hub 19 for the passage of the left-hand drive shaft, the cap being fixed to flange 14 by means of screws 20; 21 are recesses in cap 18, peripherally distributed in a symmetrical manner, each of them containing a calibrated spring 22 to urge clutch disk 17 against clutch disk 16 and against a shoulder formed on cage 13; 23 is an external toothing of hub 6 acting as a splined profile in which there is inserted splined profile of a clutch disk 24, so that clutch disk 24 is axially slidable on hub 6; 25 and 26 are two more clutch disks, equipped with peripheral splined profiles for the axially slidable keying in splined profile 27 of ring 28 which is integral with disk 29 of hub 30, which receives the right-hand drive shaft; 31 are the seats uniformly distributed on the outer surface of disk 29, each one housing a spring 32 capable of urging disks 26, 24, 25 against a shoulder of flange 8; 33 and 34 are two possible thrust bearings; 35 is a casing, or differential box, fixed by means of screws 36 and plugs 37 to disk 29; 38 and 39 are aligned holes of flange 14 and disk 35, distributed peripherally to allow the passage of bolts securing to the casing the crown gear (not shown) of the differential, the crown gear transmitting to casing 35 the rotation of the propeller shaft of the vehicle; 40 and 41 are the seats for the internal rings of bearings; 42 are the holes for receiving screws 20 and 36: 43 is the centring hole of cage 13 on hub 2; 44 are the holes for both oil lubrication.

The operation of the device is as follows: When the vehicle is travelling in a straight line, the components 14 and 35 rotate as a whole on the axis of components 1 and 6 causing rotation of cage 13 whose rollers 11, engaging profiles 4 and 10, apply torque to outer ring 9 and inner ring 1: therefore, through keyings 3 and 7, the wheel drive shafts (not shown) are rotated; in such a situation, the series of calibrated springs 22 and 32 press axially disks 16, 17 and 24, 25, 26, respectively, against cage. 13 and flange 8; these springs determine, because of disk friction, a condition of resistance to relative motion between cage 13 and hub 2 and between disk 29 and flange 8 of hub 6, respectively, i.e. in the differential device, for both wheels, there a resisting or braking movement such as to prevent skidding of a wheel if the wheel is running on ground having, within certain limits, smaller adhesion than that of the ground on which the other wheel is running: in such a way skidding is avoided since the torque imparted to components 13 and 29 does not correspond to the adhesion torque on the wheel having least adhesion and therefore does not increase the number of revolutions of the corresponding wheel; in such a way, the effect of a side skid caused by a wheel skidding is avoided; moreover, if the adhesion moment of a wheel went below the predicted limit, for this resisting moment, the inertial moment of the wheel would overcome the resisting moment determined by springs 22 or 32, which would otherwise tend to give said wheel a relative speed compared to the other and produce, even if limited, a certain skidding: in such a situation, disk 24 would assume, compared with disks 25, 26 and ring 28, and also compared with disk 17 and cage 13 a relative speed; this would be in the same relation as the speed of ring 9 to ring 1: but ring 9 can rotate, relative to ring 1, only through a very narrow angle, depending on the number of cams having generatrices 10 and 4; e.g., if we imagine we are initially in the situation of Figure 2 and that the wheel inertial mass, without adhesion, makes ring 1 rotate in a clockwise direction, the final self-locking device situaion will be that of Figure 3; from this figure it can be noted that the angular sliding of ring 1 is very limited and the undulation 4 itself of the track provides for stopping the skidding of ring 1: in such a way the effect of unbalance due to the inertial wheel mass ceases and disks 24 and 16 resume the initial position, in balance with components 25, 26, 28 and components 17 and 13 respectively; in this way, the balance disturbance has been limited to a negligible quantity and for such a short time as not to allow the motor vehicle to experience the initial effect of skidding; it, therefore, goes not running without any adverse effect; the same balancing effect is possible when the conditions caused by change in road adhesion occur when the vehicle is negotiating a curve or in any wet, slimy, snowy, iced, sandy or muddy conditions: it should be noted that the self-locking component of the device acts on the resisting or braking component of the device itself in order to re-balance it; in the same way as the resisting or braking component tends to re-balance the self-locking component.

It will be appreciated that various modifications could be made in the described embodiment. For instance, the number of disks such as 16, 17, 24, 25, 26, the number of rollers 11 and of cams having generatrix lines 4 and 10 and the number of springs 22 and 32 can vary according to particular requirements.

WHAT I CLAIM IS: 1. A differential device for motorvehicles, comprising a casing adapted to be rotated by the propeller shaft of the vehicle, two coaxial driving elements rotatable relative to the casing and adapted to be connected to the half-shafts driving the vehicle wheels, one or more clutch disks rotatable with a respective one of the driving elements and adapted to engage a corresponding disk or disks rotatable with the casing, the clutch disk or disks on the casing being axially movable relative to those of the driving elements, springs biasing into engagement the disk or disks on the casing and the associated disk or disks on each driving element, one of the two driving elements having a radially outwardly facing surface surrounded by a radially inner face of the other driving element, a plurality of rollers supported by a cage rotatable with the casing and interposed between the said surfaces of the driving elements, which surfaces each have an undulating profile engaged by the rollers and arranged to permit only a limited relative rotation between the driving elements.

2. A differential device as claimed in claim 1, in which the clutch disks are connected by splined connections to the associated driving elements or casing.

3. A differential device as claimed in claim 1 or claim 2, in which the springs biasing the clutch disks are helical compression springs housed in peripherally spaced recesses formed in the axial end walls of the casing.

4. A differential device as claimed in any preceding claim, in which the axially inner faces of the axially inner clutch disks of the sets of clutch disks associated respectively with each driving element engage respectively a flange supporting the roller cage and a flange supporting a cylindrical portion of one of the driving elements which carries the said radially inwardly facing surface.

5. A differential device as claimed in any preceding claim, in which one end of one of the driving elements is rotatably supported on one end of the other driving element.

6. A differential device for a motor vehicle, constructed, arranged and adapted to operate substantially as described with reference to, and as shown in, the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   6, respectively, i.e. in the differential device, for both wheels, there a resisting or braking movement such as to prevent skidding of a wheel if the wheel is running on ground having, within certain limits, smaller adhesion than that of the ground on which the other wheel is running: in such a way skidding is avoided since the torque imparted to components 13 and 29 does not correspond to the adhesion torque on the wheel having least adhesion and therefore does not increase the number of revolutions of the corresponding wheel; in such a way, the effect of a side skid caused by a wheel skidding is avoided; moreover, if the adhesion moment of a wheel went below the predicted limit, for this resisting moment, the inertial moment of the wheel would overcome the resisting moment determined by springs 22 or 32, which would otherwise tend to give said wheel a relative speed compared to the other and produce, even if limited, a certain skidding: in such a situation, disk 24 would assume, compared with disks 25, 26 and ring 28, and also compared with disk 17 and cage 13 a relative speed; this would be in the same relation as the speed of ring 9 to ring 1: but ring 9 can rotate, relative to ring 1, only through a very narrow angle, depending on the number of cams having generatrices 10 and 4; e.g., if we imagine we are initially in the situation of Figure 2 and that the wheel inertial mass, without adhesion, makes ring 1 rotate in a clockwise direction, the final self-locking device situaion will be that of Figure 3; from this figure it can be noted that the angular sliding of ring 1 is very limited and the undulation 4 itself of the track provides for stopping the skidding of ring 1: in such a way the effect of unbalance due to the inertial wheel mass ceases and disks 24 and 16 resume the initial position, in balance with components 25, 26, 28 and components 17 and 13 respectively; in this way, the balance disturbance has been limited to a negligible quantity and for such a short time as not to allow the motor vehicle to experience the initial effect of skidding; it, therefore, goes not running without any adverse effect; the same balancing effect is possible when the conditions caused by change in road adhesion occur when the vehicle is negotiating a curve or in any wet, slimy, snowy, iced, sandy or muddy conditions: it should be noted that the self-locking component of the device acts on the resisting or braking component of the device itself in order to re-balance it; in the same way as the resisting or braking component tends to re-balance the self-locking component.

   It will be appreciated that various modifications could be made in the described embodiment. For instance, the number of disks such as 16, 17, 24, 25, 26, the number of rollers 11 and of cams having generatrix lines 4 and 10 and the number of springs 22 and 32 can vary according to particular requirements.

   WHAT I CLAIM IS:

   1. A differential device for motorvehicles, comprising a casing adapted to be rotated by the propeller shaft of the vehicle, two coaxial driving elements rotatable relative to the casing and adapted to be connected to the half-shafts driving the vehicle wheels, one or more clutch disks rotatable with a respective one of the driving elements and adapted to engage a corresponding disk or disks rotatable with the casing, the clutch disk or disks on the casing being axially movable relative to those of the driving elements, springs biasing into engagement the disk or disks on the casing and the associated disk or disks on each driving element, one of the two driving elements having a radially outwardly facing surface surrounded by a radially inner face of the other driving element, a plurality of rollers supported by a cage rotatable with the casing and interposed between the said surfaces of the driving elements, which surfaces each have an undulating profile engaged by the rollers and arranged to permit only a limited relative rotation between the driving elements.

   2. A differential device as claimed in claim 1, in which the clutch disks are connected by splined connections to the associated driving elements or casing.

   3. A differential device as claimed in claim 1 or claim 2, in which the springs biasing the clutch disks are helical compression springs housed in peripherally spaced recesses formed in the axial end walls of the casing.

   4. A differential device as claimed in any preceding claim, in which the axially inner faces of the axially inner clutch disks of the sets of clutch disks associated respectively with each driving element engage respectively a flange supporting the roller cage and a flange supporting a cylindrical portion of one of the driving elements which carries the said radially inwardly facing surface.

   5. A differential device as claimed in any preceding claim, in which one end of one of the driving elements is rotatably supported on one end of the other driving element.

   6. A differential device for a motor vehicle, constructed, arranged and adapted to operate substantially as described with reference to, and as shown in, the accompanying drawings.