GB2125121A - Gearboxes - Google Patents

Abstract

A gearbox has a casing (1) formed in two substantially identical dished halves (10A, 10B) abutted at their edges in a plane of symmetry (11) perpendicular to the input, output and layshafts (15, 18 and 22) whose opposite ends are respectively journalled in bearings (17A, 17B, 20A, 20B and 23A, 23B) in the two casing halves. Friction clutches (35, 36) controlled by a hydraulic selector valve (29) are selectively engageable to transmit forward and reverse drive between the input and output shafts (15, 18). The selector valve (29) is a rotary spool valve housed in a bore in the casing half 10A with its axis parallel to the three shafts (15, 18, 22) and selectively supplies pressure fluid from a pump (25) to fluid delivery passageways (54, 55) formed in the wall of the casing half (10A) and leading to the two clutches (35, 36) for selective actuation thereof. The need for a separate selector valve block secured to the exterior of the gearbox casing with external pressure fluid connections to the clutches is thereby avoided. <IMAGE>

Description

SPECIFICATION Gearboxes This invention relates to gearboxes, and particularly although not exclusively, to a small forward/reverse gearbox for marine use.

According to the present invention from one aspect, a gearbox comprising an input shaft, an output shaft and a layshaft parallel to the input and output shafts, and alternatively-selectable transmission trains between the input and output shafts, includes a casing made in two dished parts having a common joint face in a plane perpendicular to the three shafts whose opposite ends are supported in bearings respectively carried by the two casing parts.

Preferably the two dished casing parts are substantially identical. This enables both casing halves to be castings made successively in the same mould, the castings being identical apart from minor machining differences.

The gearbox may provide alternativelyselectable forward speeds and neutral between the input and output shafts, but in a preferred form the gearbox provides aiternatively-selectable forward and reverse drive and neutral between the input and output shafts.

The gearbox may also include a selector valve for controlling hydraulically-operated clutches to select the different transmission ratios or drive directions, the valve being housed in a bore in one of the two casing parts. The bore for the valve is preferably axially-parallel to the three shafts. The selector valve may communicate with the clutches via fluid passageways formed in the said one casing part, instead of using passageways in a separate distribution casting or assembly.

In a gearbox embodying the invention, the casing may be provided with a separate attached cover plate incorporating at least one passageway for the distribution of pressure fluid. A pump may be provided, driven by one of the three shafts, which supplies pressure fluid for the hydraulic actuators of the clutches and/or supplies pressurised lubricating fluid for distribution. The cover plate may incorporate a fluid feed passage leading from the pump outlet to a selector valve for clutch operation. The cover plate may also incorporate a feed passage for distributing lubricating fluid to the clutches and/or other parts of the gearbox.

According to another aspect of the invention, in a gearbox having an input shaft, an output shaft and a layshaft, with alternatively-selectable transmission trains including selector clutches associated with the input and layshafts for selecting the operative transmission train, each clutch includes a clutch pinion which is mounted on the respective shaft and secured for rotation therewith by an interface fit between its bore and the respective shaft, without additional securing means. It has been found that it is possible to use the technique of interference fits to affix these clutch pinions to the shafts in a manner capable of transmitting the tongue corresponding to the maximum power which the gearbox is designed to transmit.

In a method of assembling a gearbox embodying this last aspect of the invention, the clutch pinions may be forced onto their respective shafts by means of a power press which records the load imposed, during the assembly.

The invention may be carried into practice in various ways, but one specific construction embodying all of its aspects will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a side view of a small forward/ reverse marine gearbox; Figure 2 is a view in section on the line A-B-C-D-E in Figure 1; and Figure 3 is a scrap view in section on the line Ill-Ill in Figure 1 showing details of the oil pump.

In the illustrated embodiment, the gearbox comprises a casing 10 formed in two substantially-identical halves 1 OA and 1 OB and joined together along a pane joint face 11 by means of bolts 12. A distribution plate 1 3 is bolted to the outside of one casing half 1 OA. An input shaft 1 5 with a protruding splined end 1 6 is journalied at its opposite ends in bearings 1 7A and 17B respectively housed in coaxial bores in the opposite side walls of the two casing halves 1 0A, 108.An output shaft 1 8 with an external coupling flange 1 9 is journalled at its opposite ends in bearings 20A, 20B respectively housed in two further coaxial bores in the side walls of the two casing halves 1 OA and 1 OB. A layshaft 22 is journalled at its opposite ends in bearings 23A, 238 housed in two further coaxial bores in the opposite side walls of the two casing halves 1 OA, 10B, the layshaft being parallel to the input and output shafts. In axial view the relative positions of the input and layshafts with respect to the output shaft are indicated by the letters B and C in Figure 1. An oil pump 25 of intermeshing gear type is housed in a protruding portion 26 of the distribution plate 13, and is driven by a dog coupling 27 directly from the layshaft 22.The pump supplies pressure oil via a channel 28 to a rotary selector valve 29 whose valve spool is housed in a further bore in the casing half 1 OA, that bore also being parallel to the bores of the three shafts 1 5, 18 and 22.

The two halves 1 OA and 10B of the casing 10 are castings which are substantially identical, apart from various bores and minor final machining operations, and have in fact been made by repetition casting in a single mould. This enables the casing 10 to be made up of pairs of virtually-identical castings drawn from stock, thus simplifying production. The three pairs of bores for the three shafts 1 5, 18 and 22 and the fourth bore for the spool of the control valve 29, all being parallel, can be machined in one operation on the same multi-spindle drill using one setting.

The output shaft 1 8 carries a pinion 30 secured for rotation therewith by a spline connection 31, the pinion 30 being in permanent mesh with a pair of pinions 32, 33 respectively journalled on the input shaft 1 5 and the layshaft 22, and free to be rotated thereon. Two hydraulically-operated oilimmersed multi-disc clutches 35 and 36 are mounted respectively on the input and layshafts and can be selectively engaged to couple the shaft 1 5 or 22 to the respective pinion 32 or 33 for transmitting respectively reverse and forward drive to the output shaft 1 8 via its pinion 30.The two pinions 32 and 33 have the same number of teeth which in this case is less than that of the teeth on the pinion 30, thus providing a speed reduction between the input and output shafts 1 5 and 18. Each of the clutches 35 and 36 includes a clutch pinion 37 or 38 which is secured on the respective shaft 1 5 or 22 solely by an interference fit, without any further keying or pinning. In assembly the two clutch pinions 37, 38 are forced onto their associated shafts by means of a hydraulic press provided with means for recording the load being imposed on the press rams. This method and the resultant record provides an automatic check on the dimensional accuracy of the parts, and consequently the reliability of the joint between the shafts and the bores of the pin;ons, since a recorded pressure below a certain value would indicate insufficient interference.No further securing of these pinions 37,38 on their shafts is necessary.

The two clutch pinions 37 and 38 are in permanent mesh with one another, and hence the drive of the input shaft 1 5 is transmitted to both clutch pinions to rotate them in opposite directions. Each of the clutches 35 and 36 incorporates hydraulic actuation by means of an annular piston 39 slidably mounted on and sealed against the circumference of the respective shaft 15 or 22 and also sliding in and sealed against the wall of a cylinder 40 formed in the respective clutch pinion 37 or 38.When actuated by the admission of high-pressure fluid from the pump 25 to the cylinder 40 in the interior of the clutch pinion 37 or 38, the respective piston 39 applied an axial compression thrust to the stack of interleaved discs and rings of its clutch to frictionally engage the clutch, thus transmitting the drive of the input shaft 1 5 to the selected pinion 32 or 33 and thence to the output shaft pinion 30 and output shaft 18, the latter being driven in the forward or reverse direction depending upon whether it is the clutch 36 or the clutch 35 which has been actuated.

The selection and control of clutch actuation is performed by means of the rotary valve 29 whose rotary valve spool 45 can be turned manually, by means of a control mechanism (not shown) linked to a lever 45, into a neutral position or into either of two operative positions constituting a forward and reverse position. A bail-catch 46 locates the lever 45 in each of these three positions. A limit switch 48 actuated by the spool 45 of the valve 29 through a fall cam arrangement 49 is provided to prevent an engine, whose drive the gearbox transmits, from being started unless neutral is selected.

The valve 29 is supplied with pressure fluid from the pump 25 via the passage 28 in the distribution plate 1 3 which leads into an annular groove 50 formed around the valve spool 45. The spool 45 has an axial bore 51 communicating via a radial inlet port 52 with the groove 50, and communicating at its other end with a cylinder 53 formed in the interior of the valve spool 45.

Depending on the angular position of the spool 45, the cylinder 53 can be placed in communication, via a radial delivery port 54 in the wall of the spool 45, with either of two passageways dulled in the wall of the casing half 1 OA. One of these passageways 55, shown in Figure 2, is a short passage which leads via a circumferential groove 56 and radial port 57 in the bush 58 for the clutch pinion 38 to a circumferential groove 59 in the spindle of the pinion 38, and thence via radial and axial passageways 60, 61, into the cylinder 40.

The second short passage, not shown, leads similarly to the inlet of the clutch 35 on the input shaft 15.

Thus depending on the angular position to which the lever 47 and valve spool 45 are set, the valve 29 delivers pressure oil from the pump 25 either to the clutch 36 to clutch in the pinion 33 to the layshaft for forward drive of the output shaft, or to the clutch 35 to clutch in the pinion 32 to the input shaft for reverse drive, or to neither clutch when neutral is selected so that both clutches are disengaged.

The delivery path of the high-pressure oil from the gear pump 25 is indicated in Figure 2 by the branching full-line X marked with arrows. The path is via passage 28 in the distribution plate 1 3 (the downstream part of the passage 28 being a groove in the plate 1 3 closed by the housing part 1 OA), port 52, passage 51 to the spool cylinder 53 and thence via the port 54 to the cylinder 40 of the selected clutch 36 or 35 to operate that clutch. The delivery pressure of the oil along the arrowed path X is regulated to 330 p.s.i.

(2275.27 kPa) by means of a pressure-regulating relief valve 65 whose spool is housed in the cylinder 53 and is loaded by a spring 66. The bypass oil at a lower pressure, in the region of 50 p.s.i. (344.74 kPa) delivered from the relief valve 65, as indicated by arrows Y, is discharged through an outlet 67 in the housing part 1 OA and is passed by a pipe connection indicated at 68 to an oil cooler 69. From the oil cooler the low pressure oil is delivered by a pipe connection indicated at 70 to an inlet 71 in the distribution plate 1 3 and is utilised for lubrication purposes.

The flow path of the lubrication oil from the inlet 71 is indicated by the branched broken line Z marked with arrows. The oil in one branch of the path Z flows through a further channei-section passage 75 in the distribution plate 1 3 to the layshaft 22 to lubricate the bearing 23A and dog coupling 27, and flows through an axial bore 76 and radial bores 77 in the layshaft 22 to the journal bearing of the pinion 33, and via ports 78 in the spindle of the pinion 33 to the clutch 36 to lubricate its plates. Another branch of the flow path Z is directly to the input shaft 1 5 to lubricate its bearing 1 7A and, via an axial bore in the shaft 1 5, to the journal bearing of the pinion 32 and to the clutch 35.The oil discharged from plates of the two clutches 35 and 36 descends to a sump 80 from which the oil pump 25 draws its intake oil (through an intake, not shown), and which provides for direct lubrication of the output shaft bearings 20A and 20B and in the teeth of the intermeshing pinions 30, 32, 33.

In the top of the casing half 1 OA there is provided an oil filter hole 81 closed by a cap 82 carrying a dipstick 84. A drain plug 85 for draining the sump 80 is provided in the bottom of the casing half 1 OA.

The item 85 shown inside the distribution cover in Figure 2 is a special tool which can be used to operate an emergency drive system in the event of hydraulic failure. It will not be described in detail since it does not relate to the present invention.

The arrangement of the hydraulic valving and hydraulic circuitry described and illustrated have various advantages, some of which will now be briefly mentioned. Firstly, the selector valve and pressure reguiating valve are both housed in one half 1 OA of the main gearbox 10, thus removing any need for a separate valve block. This then allows the use of "feed" passageways in one casing half 1 OA to supply high-pressure operating oil from the selector valve to the respective clutches 35, 36 via the simple pressed-in bushes 58, instead of a "feeder" which floats on the respective clutch shaft and is piped to a separate valve block.

The distribution plate 1 3 performs several useful functions. It provides an end cap for each adjacent shaft bearing 1 7A, 23A, and it carries the pump assembly 25 and provides the oil feed passageway to the selector valve 29. It also distributes lubrication oil from the cooler to the clutches and various bearings, without the need to use a conventional shaft "feeder" unit piped to the valve housing as mentioned.

It will be appreciated that the specific gearbox construction illustrated is described merely as being an exemplification of the various aspects of the invention set out above. According to a further aspect of the invention, also embodied in this example, a gearbox is provided with a casing housing its various shafts and pinions, the casing comprising two substantially-identical dished castings having planar joint faces secured together in a common plane of symmetry of the casing which is perpendicular to to axes of the various shafts.

According to the invention from yet another aspect, a gearbox whose transmission ratio and/or transmission direction is selectively controlled by means of a hydraulic valve which selectively actuates hydraulic clutches, for example forward and reverse clutches, incorporates passageways for pressurised oil formed in the wall of the gearbox casing and extending between the control valve and the respective clutches.

According to the invention from yet another aspect, a method of securing a pinion on a shaft comprises forcing the bore of the pinion onto the shaft with an interference fit by means of a press, and recording the thrust of the press ram as an indication of the tolerance of this interference fit.

All these last three broad aspects of the invention are embodied in the specific example described and illustrated.

Claims (12)

1. A gearbox whose transmission ratio and/or transmission direction is or are selectively controlled by means of a hydraulic selector valve which selectively actuated hydraulic clutches, for example forward and reverse clutches, the selector valve being housed in a recess in the gearbox casing, and the wall of the gearbox casing being formed with passageways for pressurised hydraulic fluid extending between the selector valve and the respective clutches.

2. A gearbox as claimed in Claim 1, whose casing is formed by two dished casing parts secured together at their edges, the said recess and the passageways being formed in one of the casing parts.

3. A gearbox which comprises a casing, an input shaft, an output shaft and a layshaft parallel to the input and output shafts, and alternatelyselectable transmission trains between the input and output shafts, and in which the casing is made in two dished parts with a joint face in a plane perpendicular to the three shafts whose opposite ends are supported in bearings respectively carried by the two casing parts, and which also includes hydraulically-operated clutches by selective operation of which different transmission ratios and/or drive directions are selected, and a selector valve for controlling the operation of the clutches, the selector valve being housed in a recess in one of the two casing parts, and communicating with the clutches for the control thereof via fluid passageways formed in the wall of the said one casing part.

4. A gearbox as claimed in Claim 3, in which the recess housing the selector valve is a bore axially-parallel to the three shafts.

5. A gearbox as claimed in Claim 2 or Claim 3 or Claim 4, in which the selector valve is a rotary spool valve whose cylindrical spool is housed in a cylindrical bore constituting the recess in the said one casing part for rotation therein about the axis of the bore, a delivery port in the external cylindrical surface of the valve spool cooperating selectively with ports formed in the internal cylindrical surface of the bore in communication respectively with the fluid passageways in the wall of the said one casing part.

6. A gearbox as claimed in any one of Claims 2 to 5, in which the casing also includes a separate cover plate attached to the said one dished casing part and incorporating at least one passageway for the distribution of pressure fluid.

7. A gearbox as claimed in any one of the preceding claims, also including a pump driven by one of the gearbox shafts and supplying pressure fluid for the hydraulic actuators of the clutches and/or pressurised lubrication fluid for distribution in the gearbox.

8. A gearbox as claimed in Claims 6 and 7, in which the pump is mounted on the cover plate and in which the cover plate incorporates a pressure fluid feed passage leading from the pump outlet to the selector valve for clutch operation.

9. A gearbox as claimed in Claim 7 or Claim 8 in which the cover plate also incorporates one or more feed passages for distributing pressurised lubricating fluid to the clutches and/or other parts of the gearbox.

10. A gearbox as claimed in any one of the preceding claims, in which the two dished parts of the casing are substantially identical.

11. A gearbox as claimed in Claim 8 in which the two dished parts of the casing are castings made in the same mould.

12. A gearbox as claimed in any one of the preceding claims, in which each clutch includes a clutch pinion which is mounted on an associated gearbox shaft and is secured for rotation therewith by an interference fit between its bore and the respective shaft without additional securing means.

1 3. A gearbox substantially as specificaily described herein with reference to the accompanying drawings.