GB2030239A - A synchromesh device for a transmission of an industrial truck - Google Patents

Abstract

In a synchromesh device, for a transmission of an industrial truck such as a fork lift truck, including a main shaft (1), forward and reverse change gears (2, 3), synchronizing hub (4) fixed to the main shaft by means of spline grooves, a coupling sleeve (5) axially slidably engaged with spline grooves formed in the outer circumference of the synchronizing hub (4), and balk-rings (8, 9,) formed in their inner surfaces with frusto-conical surfaces facing frusto-conical surfaces formed in the side of a clutch gear (10) integral with the forward change gear (2) and of a clutch gear (11) integral with the reverse change gear (3), respectively, the angles of the frusto-conical surfaces are more than 10 DEG and preferably less than 11 DEG , thereby reducing surface pressures acting between the synchronizing slide surfaces during the synchronization to improve the durability of the arrangement. <IMAGE>

Description

SPECIFICATION A synchromesh device for a transmission of an industrial truck The present invention relates to a synchromesh device for use in transmissions of industrial trucks, particularly fork lift trucks for transferring heavy loads.

In industrial trucks such as fork lift trucks, frequent forward and reverse gear changes are needed during working. Accordingly, synchromesh devices for forward and reverse gear changing are required to be highly durable.

In synchromesh devices for forward and reverse gear changing hitherto used, frusto-conical angles of synchronizing slide surfaces are about 6 which provide high surface pressures between the synchronizing slide surfaces during synchronization to obtain large synchronizing capacities. As the result, the slide surfaces subjected to the high pressures are rapidly worn. Forward and reverse gears are rotated in relatively opposite directions, so that the synchronization for forward and reverse gear changing is carried out between the synchronizing slide surfaces rotating at a remarkably high relative rotating speed, with resultthatthe slide surfaces are rapidly worn requiring frequent replacement of the synchromesh devices.

With fork lift trucks and the like, because of their heavy total weights, a somewhat longer period of time (2-3 seconds) is required from braking to stoppage for changing forward and reverse movements even if the travelling speed is relatively low. Accordingly, it is not necessary for industrial trucks to have a large synchronizing capacity for completing the synchronization in a short period of time (0.3 second).

In view of this, it is a principal object of the invention to provide a synchromesh device for forward and reverse gear changing, which is suitable for industrial trucks such as fork lift trucks.

It is a further object of the invention to provide an improved synchromesh device for a transmission of an industrial truck, whose synchronizing slide surfaces include frusto-conical angles of more than 10 to reduce surface pressures acting between the synchronizing slide surfaces during the synchronization, there greatly improving its durability.

In the accompanying drawings: Fig. 1 is a sectional view of a synchromesh device according to the invention; Fig. 2 is a graph illustrating the relation between conical angles of synchronizing slide surfaces and durabilities; and Fig. 3 is a diagrammatical plan view of the balkring as viewed in the direction of the arrowA in Fig. 1, for explaining the chamfer angle of the balk-ring.

Referring to Fig. 1 illustrating a synchromesh device for forward and reverse change gears according to the invention, the device comprises a main shaft 1, a forward change gear 2, a reverse change gear 3 and a synchronizing hub 4 fixed to the main shaft 1 by means of spline grooves.

A coupling sleeve 5 is axially slidably engaged with spline grooves formed in the outer circumference of the synchronizing hub 4. The synchronizing hub 4 is also formed in its circumference with notches for accommodating therein respective insert keys 6 adapted to be urged radially outwardly by means of spread springs in the form of a ring 7 to be force into grooves formed in the inner surface of the coupling sleeve 5 at the mid portion between the ends thereof.

Balk-rings 8 and 9 are formed in their inner surfaces with frusto-conical surfaces facing frustoconical surfaces formed in the sides of a clutch gear 10 integral with the forward change gear2 and of a clutch gear 11 integral with the reverse change gear 3, respectively. The balk-rings 8 and 9 are also formed in their side surfaces with notches for receiving the insert keys 6.

With this arrangement, when the coupling sleeve 5 is moved, for example, toward the forward gear 2 by means of a shift fork (not shown), the insert keys 6 are moved together with the coupling sleeve 5 with the aid of the spread springs 7, so that the end faces of the insert keys 6 urge the balk-ring 8 to bring its frusto-conical surface into contact with the frustoconical surface of the forward change gear 10.When the rotating speed of the coupling sleeve 5 becomes equal to that of the forward change gear 2 in the manner according to the well-known synchronizing function, the coupling sleeve 5 pushes the insert keys 6 inwardly and engages the splines in the outer surface of the balk-ring 8 and the clutch gear 10, thereby transmitting the driving power from the main shaft 1 driven by a power source (not shown) through the synchronizing hub 4 and the coupling sleeve 5 to the forward change gear 2.

According to the invention, angles of more than 10 are employed for the frusto-conical angles a of the conical surface of the balk-rings 8 and 9 and the change gears 2 and 3, which form the synchronizing slide surfaces.

In such a synchromesh device, the synchronizing function is effected by the contact frictional force between the frusto-conical surfaces. If the frustoconical angle a is small, the frusto-conical contact surfaces would be subjected to an excess surface pressure resulting from a shifting load, so that the frusto-conical surfaces are aptto wear, thus becoming less durable. The larger the angle a of the conical surfaces, the less the contact surface pressure.

It has been found in our experiments that the relation between the frusto-conical angles a and durability of the device can be shown as in a curve in Fig.

2 wherein the durability rapidly increase within a range more than 10 of the frusto-conical angle. The durability in this case is defined by the number of synchromesh operations until the frusto-conical surface of the balk-ring has worn to an extent that the clearance between the clutch gear and balk-ring is eliminated because the more the frusto-conical surface wears, the more the end of the balk-ring approaches the end of the change gear.

For example, in comparison of the conical surfaces of 10 30' with 6 30', the former is of 354O0/o of the latter in contact surface pressure and PV value (product of contact surface pressure and sliding move ment speed). The durability or number of sync hromeshed times of the former is 100 times longer than that of the iatter. In other words, it is clearly evident that the wear resistance of the surface having a frusto-conical angle of more than 10 is remarkably improved.

A synchronizing capacity of a synchromesh device is given by yD/2 . since, where ,u is a coefficient of friction and D is an effective diameter of a frustoconical surface. As can be seen from the relation, the larger the frusto-conical angle a, the less the synchronizing capacity and thus the longer the time required for the synchronizing operation. The time required for a synchronizing operation with a frusto-conical angle 6" 30' is 0.3 second, while a time with an angle 10 30' is 0.6 second. Such a difference does not give rise to any problem in a practical use of a fork lift truck and the like.

Synchronizing conditions are indicated by the following formula.

jIlK/sinct'tan(0-e') where K=D/D'; D'=average diameter of chamfer of balk-ring, chamfer angle of balk-ring (refer to Fig.

3) and e'=tan,a'; ,m'=coefficient of friction of chamfer.

Accordingly, it is of course preferable to reduce the chamfer angle o thereby preventing slip due to a reduced surface pressure. However, an excessively increased frusto-conical angle may give rise to a problem in synchronizing capacity and the like. In view of this, a frusto-conical angle less than 1 1" is preferable in practical use.

As can be seen from the above description, according to the invention the frusto-conical angle of the synchronizing slide surface of the synchromesh device is made more than 10 to reduce the contact surface pressure resulting in the small PV value, thereby remarkably improving the durability required in industrial trucks such as fork lifttrucks which frequently need forward and reverse gear changing. In orderto improve the wear-resistance of the frusto-conical surface of the balk-ring, the molybdenum spraying process has generally been used. The device according to the invention can dispense with the coating by such a process, as the case may be. Moreover, the device according to the invention ensures the sufficient synchronizing performance in practical use because industrial trucks need not shorten the synchronizing period of time which are different from passenger cars.

Claims (4)

1. In a synchromesh device for a transmission of an industrial truck including frusto-conical synchronizing slide surfaces whose contact frictional force performs a synchronizing operation, the improvement comprising the frusto-conical surfaces including angles of more than 10

2. A device as set forth in claim 1, wherein said frusto-conical angle is less than 11".

3. A device as set forth in claim 1 or 2, wherein a chamfer angle of a balk-ring is as small as possible to prevent slip thereof due to a reduced surface pressure.

4. A synchromesh device substantially as described with reference to, and as illustrated in the accompanying drawings.