AUTOMATIC CONTROL DEVICE FOR CONTROLLING THE LOCK OF A DIFFERENTIAL

Abstract: An automatic control device for controlling the lock of a differential is formed by a sensor (V₁) which senses the speed of the input element (15) of the differential (10) and a second sensor (V₂) which senses the speed of the driven element (18) of the differential (10); the two sensors (V₁, V₂) supply the detected signals to a microprocessor (20) which prosesses them and, when the difference between said values exceeds a preset activation threshold, activates an electrovalve (E) which, by drawing oil under pressure from the lubrication circuit (24) of the motor (13), controls a cylindre (21) which engages a clutch (22) located between the crown wheels (17) of the differential, thereby locking it.

Description: The invention relates to a automatic control device for controlling the lock of a differential. Among the various types of differential lock devices we remember, for example, a device with manual insertion at will of the driver, comprising a slidable grooved sleeve which rigidly connects to one another the two axel shafts of the driving wheels so as to render inoperative the differential; alternati veldt the sleeve, when sliding, may lock the planetary gears on their own axes or one of the crown wheels to the spider box thereby still obtaining the same result, i.e. the disactivation of the differential. It is obvious that all these systems, being manual and entrusted to the discretion of the driver, give rise first of all to difficulties in the insertion and then may remain inserted even when their use is not necessary, with the consequence of damages to the vehicle because of overcharges due to the power distribution. In other cases a selflocking differential is used pro-.- vided with a series of pins or radially sliding rollers, inserted into the driving member of the differential, or clutch discs are inserted between the elements rigidly connected to the crown wheels and the spider. In the first case, when one of the two driven elements tends to accelerate relative to the other, the pins move radially by following the undulations of the profiles of the driven elements thereby transmitting different torques. In the second case, when a certain difference in the speed of the two axel shafts is exceeded, a periodical intervention of the clutches is produced with an intensity which is as greater as higher is the rotation speed of the pivots of the planetary gears. The selflocking differentials of this type have the disadvantage consisting in that they imply pre-established locking values and operate even in conditions in which their intervention is not required. Another device is the differential with viscous clutch lock which takes advantage of the action of viscous forces proportional to the speed variation between the input and the output of the differential; disadvantageous in this case is the fact that the transmitted torque is affected by the temperature of the viscous element, and moreover it is impossible to adjoust the locking degree, and since there is no operation threshold the lock intervenes alwais, even in cases in which such intervention is not necessary, as for example in case of very sharp curves. The object of the invention is to provide an automatic control device for controlling the lock of a differential, free from the typical disadvantages of the above-mentioned cor.ventic- nal devices and having the particular advantage of to become operating in an automatical manner only when certain conditions arrise, i.e. for certain speed difference values between the input and the output of the differential. The device proposed allows transferring the torque onto the wheel in conditions of adhesion, thus ensuring the necessary propulsive thrust for the vehicle. In addition, the device proposed is simple to manufacture and can be mounted on vehic- les which utilize the transmission on two or all four wheels, and in this second case, with a central differential. Finally, the proposed device does not give rise to serious problems as regards either the installation or the maintenance, unlike the analogous devices utilized at present time. For these and further objects which will be better understood later, the invention proposes to provide an automatic control device for controlling the lock of a differential, charac= terized in that it comprises sensor means (V1) for sensing the speed of the member (15) of input into the differential (10) and sensor means (V2) for sensing the speed of the driven member 18 of output from the differential (10); comparator means (20) being provided for comparing the values detected by the sensors (V1 ,V2) , arranged to activate differential lock members (22) when the difference between said values exceeds a threshold of activation of said lock members (22). The subject of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic sectional view of a differential provided with the device according to the invention; Figure 2 is a block diagram of the device; Figure 3 is a diagram of the hydraulic circuit utilized, Figure 4 is a diagrammatic sectional view of a group of two differentials and a central differential, utilized on vehicles with four driving wheels, utilizing the device according to the invention; Figure 5 is a block diagram of the device utilized in the technical solution shown in Figure 4; Figures 6 and 7 show two alternative technical solutions of the hydraulic circuit used for the technical solution shown in Figure 4. Figure 1 is a diagrammatic representation of a conventional differential 10 in which the spider box 11 receives the motion from the driving shaft 12 of the motor 13 through the gearbox 14 and a gear 15. The box 11 encloses the planet wheels 16 meshing with the crown wheels 17 keyed on the axle shafts 18 of the wheels 19. According to the invention, a sensor V1 for sensing the speed of the input element of the differential is mounted in register with the gear 15, and a sensor V2 sensing the speed of the driving element of the differential is mounted in register with an axle shaft 18. As can be seen from Figure 2, the data detected by the sensors V1 and V2 are supplied to a microprocessor 20 which in its turn controls an electrovalve E whose function consists in actuating the operating cylinder 21 (Figure 3) of a diffe- rential lock clutch 22 (Figures 1 and 3). By way of example, the hydraulic circuit (Figure 3) comprises the conventional lubrication oil carter 24 of the motor 13, provided with a pump 23, and into which there is inserted the electrovalve E which, as said before, controls the operating cylinder 21 of the clutch 22 inserted between the crown wheels 17 of the differential. The operation of the device is as follows. when. the difference between the speed of the input ene- ment and the speed of the driven element is higher than or equal to 2 predetermined value A, the said activation threshold, i.e. in formula lVl#V2I > /A, the microprocessor 20 which processes said data sensed by the respective sensor V1 and V2, supplies current to the electrovalve E which introduces oil under pressure into cylinder 21 which inserts the clutch 22, thus locking the differential. The difference V1 - V2 is in absolute value, so that a single sensor V2 may bemountedon a axle shaft 18 instead of a sensor for each axle shaft, thus, a value V1 - V2 is obtained independently from whether the right-handwheelor the left-hand wheel is slipping. Obviously, when |V1 - V2|@(A - #), wherein #is defined as threshold between the opening and the closure of the clutch (delay), the system is prepared for taking off current from ¯ the electrovalve E and therefore, the clutch 22 is disconnected and thus activates again the differential, Accordingly, the device automatically becomes operating when certain conditions arise, i.e. for certain values of tSV between the input and the output of the differential; it will be up to the manufacturer and the designer to dimension the microprocessor and to calculate the values of A (activation threshold) and ± (delay threshold) in order that the device becomes operating only under determined operation conditions of the vehicle, namelysof the--kind of the slipping of a wheel, but only when the conditions are such as to require the lock of the differential. It is also possible to subject the degree of locking to the ss V by means of a continuous series of pressure pulses having the duration t t (t=time), to which corresponds a certain pressure P onto the cylinder 21 which controls the clutch closure ; the value of P will depend on the value of At and ss t1 (interval between two successive pressure pulses). Generally, with this system it is possible to program different types of actuation of the differential lock (for example the lock in connection with the position of the brake pedal. The more general technical solution shown in Figures 1,2 and 3 may be applied, for example, to a vehicle with four driving wheels with a central differential. This technical solu tion is diagrammatically shown in Figure 44.in which the three differentials 10 , 10 , 10 ,i.e. the front, central and a c d back differentials, respectively, can be seen. The common reference numbers of these three differentials and that of the technical solution of Figure 1 have as the only difference the letter a, c and p which indicates frontal, central and back. In this case, sensor V1 is applied to the input element of the central differentia3.20 while sensor V2 is applied to the driren element 18 of the central differential connected to the c back axle 18p. p In this solution, the microprocessor 20 Verifies the ine quality V1 > in fact, two cases may take place, namely V2 > V1 and therefore a slipping of the back carriage, or V1 > V2 and therefore a slipping of the forecarriage. In the first case (V27 V1), the microprocessor 20 operates according to the logic|V2 - V1|@ B (wherein B is the activation threshold as A in the case of Figure 1, but with a different value) , so that current is supplied to the electrovalves E1 ann E2 pf the circuit shown in Figures 5 and 6, which supply oil under pressure to the respective cylinders 21 and 21 which c p close the clutch 22 and 22 , thereby locking the central dif c p ferential 10 and the back differential 10 , respectively. When c p |V2 - V1|@ (B - #B),#B being the delay threshold, i.e. there is an acceptable slipping of the back carriage, the current s taken off from the electrovalves E1 and F7 with the consequent opening of the clutches 22 and 22 and reactivation of the cen c p trawl differentIal 10 and the back differential 10 c p In the second case (V1 > V2), in which the forecarriage slips, the microprocessor 20 operates in accordance with the logic |V1 - V2|@ A so that current is supplied to the electrovalve E1 which, through the cylinder 21 , activates the clutch 21 , thereby locking the central differential 10 . In case of c c an acceptable slipping of the forecarriage, i.e. |V1 - V2|@ (A - #), # being the delay threshold, current is taken off A' A from the electrovalve E1 with consequent opening of the clutch 22 and reactivation of the central differential 10 c c Resuming the functions, the microprocessor 20 verifies the inequalities V1@V2 and in accordance with the two cases: : First ase V2 > V1 (the back carriage slips) the microprocessor acts in accordance with the logic |V2 - V1|@B --)closes the clutches 22C and 22p locking the respec tive differentials |V2 - V1|@(B - #) --) opens the clutches 22c and 22p, thus releasing the respective differentials. Second case V1)V2 (the forecarriage slips) the microprocessor acts in accordance with the logic 1 1 21 > r closes the clutch 22 thus locking the central differential |V1 - V2|@(A - #) --) opens the clutch 22c thus releasing the central differential. In an alternative technical solution of the circuit represented in Figure 7, the electrovalve E is single, so that, de pending-on the existing conditions described hereinabove and name |V1 - V2|@A (slipping ot the forecarriage) or |V2 - V1|@B (slipping of the back carriage) the microprocessor 20 will be adjusted so as to detect whether the first or the second situation is taking place in relation to the two threshold values A or B and will supply oil under pressure to the cylinders 21 c and 21 in order to close the clutches 22 and 22 . Once the p c p intervention condition has been terminated, i.e. in the situ ation|V1 - V2|@(A - #A) or |v2 - V1|@ (B - #B) respectively current will be disinserted from the electrovalve E with conse quent opening of the clutches 22 and 22 c p The example of only two sensors V1 and V2 has been cited, but it is understood-that these sensors may be even more than two and mounted, for example, on both driven axle shafts, in the case of the single differential for a traction on only two wheels, or on both axle shafts connected to the two front and back differentials in the case of a traction on all four wheels. Also the hydraulic circuit shown in Figures 3, 6,and 7 is given by way of non limiting example.

Claims: CLAIMS 1.- An automatic control device for control device for controlling the lock of a differential, characterized in that it comprises sensor means -LV1) for sensing the speed of the member (15) of input into the differential (10) and sensor means (V2) for sensing the speed of the driven member (18) of output from the differential (10); comparator means (20) being provided for comparing the values detected by the sensors (V1/ V2), arranged to activate differential lock members (22) when the difference between said values exceeds a threshold of activation of said lock members (22). 2.- A device according to Claim 1 in which the differen- tial (10 ) is a central dIfferential connected to two diffe c rential (10 , 10 ) inserted, respectively, on the front ax-le a p (18 ) and the back axle (18 ) for a vehicle with four driving a p wheels, characterized in that the sensor (V1) senses the speed of the input member (15) of the central differential (10c), and the sensor \T2) Is positioned on the transmission shaft (18 ) which connects the central differential (10c) to the back differential (10 ); on both said differentials (10 ) and p c (10 ) there being mounted a locking member (22) for locking p the differential,actuated, concomitantly or separately, by comparator means (20) which compare values sensed by the sensors (V1,V2),when the difference between said values exceeds an activation threshold od said locking members (22). 3.- A device according to Claims 1 and 2, characterized in that the comparator means (20) are formed by a microprocessor which controls at least an electrovalve (E) which,inserted into the lubrication circuit (24) of the motor of the vehicle, actuates at least a cylindre (21) which actuates a respective locking member (22) formed by a clutch. 4.- A device according to Claims 2 and 3, characterized in that the electrovalves (E) are tWOr each of which actuates a cylindre (21) which activates a locking member (22)

Inventors: CANDELLERO, GIOVANNI
Applicants: ITALDESIGN S.P.A.
Application year: 1984
Main classification: F16H1
IPC codes: B60K17, B60K23, F16H48