GB2193766A

GB2193766A - Transmission comprising mechanical gearbox and torque converter

Info

Publication number: GB2193766A
Application number: GB08714466A
Authority: GB
Inventors: Eric Albert Whateley
Original assignee: BROWN GEAR IND; David Brown Gear Industries Ltd
Current assignee: BROWN GEAR IND; David Brown Gear Industries Ltd
Priority date: 1986-06-21
Filing date: 1987-06-19
Publication date: 1988-02-17
Anticipated expiration: 2007-06-19
Also published as: GB2193766B; GB8714466D0; GB8615209D0

Abstract

A hydrodynamic torque convertor (11) is located on the input side of a reversing stepped speed- change gearbox (12,13) with sliding clutches. A first friction clutch (44) is engageable to drive the torque convertor impeller (30) and also a pump (38) for filling the torque convertor with oil, a first freewheel (32) is interposed in a driving connection between the torque convertor turbine (31) and the gearbox, a second friction clutch (45) is engageable to provide a direct driving connection to the gearbox thus by-passing the torque convertor, and a second freewheel (40) is interposed in said direct driving connection. The driver selects forward or reverse drive, after which microprocessor control means automatically actuate the friction clutches and the speed-change sliding clutches so that the torque convertor is operative in low gear but is by-passed in higher gear. The microprocessor control is preferably responsive to speed and may operate to throttle back the engine during clutch engagement and ratio change. The turbine drives the gearbox input shaft via an epicyclic gear train in an alternative embodiment. <IMAGE>

Description

SPECIFICATION Transmission This invention relates to a transmission, and more particularly to a transmission for a vehicle such as a railcar.

The object of the invention is to provide a smooth take-up of drive and smooth gear changes.

According to the invention, a transmission comprises a gearbox, a torque converter on the input side of the gearbox, a first friction clutch engageable to drive the torque converter, a first freewheel interposed in a driving connection between the torque converter and the gearbox, a second friction clutch engageable to provide a direct driving connection to the gearbox and thereby by-pass the torque converter, a second freewheel interposed in said direct driving connection, and control means for disengaging the second friction clutch if necessary, engaging the first friction clutch and filling the torque converter when low speed ratio is required and for disengaging the first friction clutch, engaging the second friction clutch and emptying the torque converter when higher speed ratios are required.

The invention will now be described, by way of example, with reference to the accompanying drawings of which: Fig. 1 is a diagrammatic sectional side elevation of one embodiment of a transmission for a railcar; and Fig. 2 is a corresponding elevation of a modification thereof incorporating additional epicyclic gearing.

Referring now to Fig. 1, a transmission for a railcar comprises a casing (not shown) containing a gearbox indicated generally at 10 and a hydrodynamic torque converter indicated generally at 11, the torque convertor 11 being disposed on the input side of the gearbox 10.

The gearbox 10 has a forward and reverse section indicated generally at 12 in series with a stepped speed-change section indicated generally at 13; a single layshaft 14; and a plurality of sliding clutches hereinafter referred to. More specifically, the gearbox 10 includes an input shaft 15, an intermediate shaft 16 and an output shaft 17 which are all co-axial with one another, the layshaft 14 being parallel to said co-axial shafts. Four toothed gears of appropriately different pitch circle diameters are integral with or rigidly secured to the layshaft 14. One of said gears indicated at 18 meshes constantly with a reverse idler gear 19 which also meshes constantly with a gear 20 rotateably mounted on the input shaft 15.

Another of the gears indicated at 21 on the layshaft 14 meshes constantly with a gear 22 integral with or rigidly secured to the intermediate shaft 16. The two other gears indicated at 23 and 24 on the layshaft 14 mesh constantly with respective gears 25 and 26 rotateably mounted on the output shaft 17. A forward and reverse sliding clutch 27 is adapted to connect the input shaft 15 driveably either to the gear 20 rotateably mounted thereon or to the intermediate shaft 16. Another sliding clutch 28 is adapted to occupy a neutral, disengaged position or to connect the output shaft 17 driveably either to the gear 25 rotateably mounted thereon or to the intermediate shaft 16. A further sliding clutch 29 is adapted to occupy a neutral, disengaged position or to connect the output shaft 17 driveably to the gear 26 rotateably mounted thereon.The torque converter 11 includes an impeller 30, a turbine 31 driveably connected to the input shaft 15 of the gearbox 10 by way of a first freewheel 32, and a stator 33 rigidly secured to the casing of the transmission. The impeller 30 is driveably connected to the output member 34 of a first multi-plate friction clutch indicated generally at 44 the input member 35 of which is adapted to be driveably connected to the railcar's engine (not shown). The output member 34 has integral with or rigidly secured to it a toothed gear 36 which meshes constantly with a driving gear 37 of a pump 38 for filling the torque converter 11 with oil. The input member 35 constitutes also the input member of a second multi-plate friction clutch indicated generally at 45 the output member 39 of which is driveably connected to the input shaft 15 of the gearbox 10 by way of a second freewheel 40.The input member 35 has integral with or rigidly secured to it a toothed gear 41 which meshes constantly with a driving gear 42 of a pump 43 for supplying oil for lubrication and other purposes. The transmission is provided with microprocessor control means linked to speed sensor means, both of said means being conventional and therefore not shown.

In operation, the driver starts the engine and engages the forward or reverse sliding clutch 27, whereupon the microprocessor control means engage the sliding clutch 29 and then engage the first friction clutch 44. In the drawings, the sliding clutch 27 is shown in forward position, the sliding clutch 29 is shown in engaged position, and the sliding clutch 28 is shown in neutral position. The first friction clutch 44 drives the pump 38 for filling the torque converter 11 with oil, and as the engine speed is increased, drive accordingly commences to be transmitted from the engine through the first friction clutch 44, the torque converter 11 and the first freewheel 32 to the gearbox 10 which is in condition to transmit low speed ratio of, say, 1.67:1.The torque converter 11 has a start-up speed reduction ratio of, say, 2.85:1, and thus the overall speed reduction ratio of the transmission increases progressively from, say, 4.76:1 until it approaches 1.67:1 when the torque converter 11 reaches its minimum slip condi tion. The microprocessor control means then disengage the first friction clutch 44, throttle back the engine to its idling speed, engage the second friction clutch 45 when the engine speed is lower than the speed of the gearbox input shaft 15, and increase the engine speed.

The second freewheel 40 takes up the drive as the engine speed exceeds the speed of the gearbox input shaft 15. The pump 38 for fill ing the torque converter 11 with oil is no longer driven, and the inoperative torque con verter 11 empties. The speed reduction ratio of the transmission is the gearbox low speed ratio of 1.67:1. When conditions dictate an up-change, the microprocessor control means throttle back the engine to its idling speed, disengage the sliding clutch 29, cause the sliding clutch 28 to connect the output shaft 17 to the intermediate shaft 16 when the speeds of said shafts are synchronous, and increase the engine speed whereupon the sec ond freewheel 40 takes up the drive.Whilst the sliding clutch 27 is in forward position, a direct drive of 1:1 speed ratio through the three co-axial shafts 15, 16 and 17 is effected, but whilst the sliding clutch 27 is in reverse position, the drive path must always include the layshaft 14 and drive is effected through the input shaft 15, the reverse idler gear 19, the layshaft 14, the intermediate shaft 16 and the output shaft 17 at a speed ratio of approximately 1:1. When conditions dictate a further up-change, the microproces sor control means throttle back the engine to its idling speed, shift the sliding clutch 28 into neutral position and then cause it to connect the output shaft 17 to the gear 25 rotateably mounted thereon when the speeds of said shaft and said gear are synchronous, and in crease the engine speed whereupon the sec ond freewheel 40 takes up the drive.An over drive speed ratio of, say, 0.719:1 is thereby effected. When conditions dictate a down change, the microprocessor control means throttle back the engine to its idling speed, shift the sliding clutch 28 into neutral position, increase the engine speed so that the speed of the intermediate shaft 16 is higher than that of the output shaft 17 and then throttle back the engine to its idling speed again, cause the sliding clutch 28 to connect the output shaft 17 to the intermediate shaft 16 when the speeds of said shafts are synchro nous, and increase the engine speed whereu pon the second freewheel 40 takes up the drive.When conditions dictate a further down change, the microprocessor control means throttle back the engine to its idling speed, disengage the sliding clutch 28, increase the engine speed so that the speed of the gear 26 rotateably mounted on the output shaft 17 is higher than the speed of said shaft and then throttle back the engine to its idling speed again, cause the sliding clutch 29 to connect the gear 26 to the shaft 17 when their speeds are synchronous, and increase the engine speed whereupon the second freewheel 40 takes up the drive. When conditions dictate a down-change into low speed ratio, the microprocessor control means throttle back the engine to its idling speed, disengage the second friction clutch 45 and engage the first friction clutch 44.This causes the torque converter 11 to fill with oil, and as the engine speed is increased the first freewheel 32 takes up the drive transmitted thereto by way of the first friction clutch 44 and the torque converter 11. When it is desired to coast in any speed ratio, the engine is simply throttled back to its idling speed and the appropriate freewheel 32 or 40 overruns. The provision of the first and second freewheels 32 and 40 rules out any engine braking, but this is not disadvantageous in rail vehicle usage. The control means are arranged to disengage the appropriate friction clutch 44 or 45 if the speed of the gearbox input shaft 15 approaches the idling speed of the engine, in order to prevent stalling.

Referring now to Fig. 2, the transmission of Fig. 1 is modified by interposing epicyclic gearing indicated generally at 50 between the turbine 31 of the torque converter 11 and the first freewheel 32. The gearing 50 comprises an annular gear 51 rigidly secured to the turbine 31, a sun gear 52 rigidly secured to the casing, and a set of planet pinions 53 meshing constantly with the sun gear 52 and the annular gear 51 and rotateably mounted on a planet carrier 54 driveably connected to the gearbox input shaft 15 by the first freewheel 32. The speed reduction ratio of the epicyclic gearing 50 is, say, 1.67:1 so that when the torque converter 11 is operative the overall speed reduction ratio of the transmission is variable between, say, 8:1 and approaching 2.8:1.

In another modification, which is equally well applicable to the transmissions of both Fig. 1 and Fig. 2, a brake engageable by the microprocessor control means is provided on the layshaft to facilitate synchronisation. In a further modification, which is likewise applicable to the transmissions of both Fig. 1 and Fig. 2, any other gearbox having a forward and reverse section in series with a speed-change section, for instance a multi-layshaft or epicyclic gearbox, can be employed.

In addition to smooth operation, the transmission provides low-speed manoeuvreability and fuel economy.

Claims

1. A transmission comprising a gearbox, a torque converter on the input side of the gearbox, a first friction clutch engageable to drive the torque converter, a first freewheel interposed in a driving connection between the torque converter and the gearbox, a second friction clutch engageable to provide a direct driving connection to the gearbox and thereby by-pass the torque converter, a second freewheel interposed in said direct driving connection, and control means for disengaging the second friction clutch if necessary, engaging the first friction clutch and filling the torque converter when low speed ratio is required and for disengaging the first friction clutch, engaging the second friction clutch and emptying the torque converter when higher speed ratios are required.

2. A transmission according to claim 1, wherein said driving connection includes epicyclic gearing.

3. A transmission according to either of the preceding claims, wherein the gearbox has a forward and reverse section in series with a speed-change section.

4. A transmission according to any one of the preceding claims, wherein the gearbox has sliding clutches.

5. A transmission according to claims 3 and 4, wherein the control means are of microprocessor type linked to speed sensor means and arranged to control also the sliding clutches in the speed-change section of the gearbox.

6. A transmission according to any one of the preceding claims, wherein the gearbox is of singie-layshaft type.

7. A transmission constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated by, Fig. 1 of the accompanying drawings.

8. A transmission constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated by, Fig. 2 of the accompanying drawings.