GB2108221A - Facilitating ratio changes in vehicles with multiple wheel drive - Google Patents

Abstract

A vehicle, such as a four wheel drive agricultural or industrial tractor, in which a prime mover (10) drives a gear box (13) which in turn drives first and second pairs of driven wheels (15,11) via first and second drive trains (16,14,18;17,30). Gearbox (13) includes a gear wheel (17) which is axially slidable to effect a ratio change in the gearbox and an axially fixed gear (18) which meshes with the slidable gear (17). A disconnecting means (14) such as a multi-plate clutch is provided in one of the drive trains to disconnect the drive connection with the associated pair of driven wheels (15) during a ratio change which involves sliding of gear wheel (17) thus eliminating inter-tooth friction between the slidable gear wheel (17) and the fixed gear wheel (18) caused by transmission wind-up. The disconnecting means (14) may be actuated in response to movements of a selector means (119) which effects ratio changes in the gearbox or, when a main clutch (12) is provided between the prime mover (10) and gearbox (13), in response to operation of a main clutch control means such as a pedal. <IMAGE>

Description

SPECIFICATION Vehicles with multiple wheel drive This invention relates to vehicles with multiple wheel drive, hereinafter referred to as being of the kind specified, which comprise a prime mover; a gearbox driven from the prime mover and including a gear wheel which is axially slidable to effect a ratio change in the gearbox; selector means for effecting said ratio change; first and second pairs of driven wheels; and first and second drive-train means operatively connecting said slidable gear wheel with said first and second pairs of driven wheels respectively, at least one of said drive trains including an axially fixed gear wheel which meshes with said slidable gear wheel.

Examples of vehicles of the kind specified are four wheel drive agricultural/industrial tractors. In such vehicles difficulty can be experienced in making ratio changes which involve sliding of said gear wheel due to inter-tooth friction between said slidable gear wheel and the meshing fixed gear wheel caused by transmission wind-up. This wind-up arises since the slidable gear wheel is connected with one pair of wheels and the fixed gear with the other pair of wheels, and the two pairs of wheels are almost certainly not rotating at exactly the same speed (due, for example, to tyre diameter variations.

It is object of the present invention to provide an improved form of vehicle of the kind specified in which the above problem is mitigated.

According to the present invention the above object is achieved in a vehicle of the kind specified by providing a disconnecting means in one of said drive trains, said disconnecting means being arranged to disconnect the drive connection with the associated pair of driven wheels during a ratio change which involves sliding of said gear wheel.

As will be appreciated, since in a vehicle in accordance with the present invention the slidable gear wheel and meshing fixed gear wheel are no longer both connected with their associated driven wheels during a ratio change which involves sliding of the slidable gear wheel, the previously referred to inter-tooth friction which tends to oppose sliding of the slidable gearwheel is eliminated.

In a preferred arrangement the disonnecting means is actuated in response to movements of the selector means which indicate that a ratio change which involves sliding of said gear wheel is to be made.

In an alternative though possibly less desirable arrangement for a vehicle having a main clutch between the prime mover and gearbox which is engaged and disengaged by a main clutch control means, the disconnecting means may be actuated in response to the operation of the main control means. In such an arrangement each time the main clutch control means (which is normally a pedal) is operated to effect any ratio change the disconnecting means would be arranged to disconnect the drive connection with the associated pair of driven wheels. This arrangement thus has the disadvantage that the drive disconnection would occur even during ratio changes which do not involve sliding of said gear wheel thus causing unnecessary loss of the braking effect associated with the disconnected pair of wheels.

In a vehicle in which the disconnecting means is actuated in response to operation of the main clutch control the main clutch control may be arranged to have a normal operating range of movement necessary for full disengagement of the main clutch and a further position or range of positions beyond the normal operating range, the disconnecting means being arranged to be actuated whenever the main clutch control is in said further position or range of positions. Thus, for example, when the main clutch is pedal operated, the main clutch may be arranged to be disengaged before the pedal is fully depressed and the disconnecting means may be actuated by fully depressing the pedal.

Conveniently, when the invention is applied to a four wheel drive agricultual/industrial tractor with driven front and rear pairs of wheels and which employs a four wheel drive clutch in the drive train to the front wheels, the four wheel drive clutch may be utilised as the disconnecting means and the drive connection to the front wheels may be disconnected by disengaging the four wheel drive clutch either in response to movements of the selector means or main clutch control means as described above.

In a preferred arrangement the disconnecting means is fluid pressure operated and is actuated by a solenoid-operated fluid control valve which is triggered by the operation of the selector means or the main clutch control means.

Two embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 diagrammatically illustrates a four wheel drive agricultural tractor embodying the present invention; Figure2 diagrammatically illustrates the details of the gearbox of the tractor of Figure 1; Figure 3 illustrates the four wheel drive clutch used in the tractor of Figure 1; Figure 4 diagrammatically illustrates the shift pattern used by the transmission selector lever of the tractor of Figures 1 and 2, and Figure 5 diagrammatically illustrates the hydraulic and electrical circuitry of an alternative embodiment of the invention.

Referring to Figure 1 this shows the general layout of a four wheel drive agricultural tractor in which an engine 10 drives the wheels 11 via a main clutch 12 and gearbox 13. Front wheels 15 of the tractor are driven by a shaft 16 via a four wheel drive clutch 14 and meshing gears 17 and 18 which form part of the output stage of the gear box and are used to select the "range" of operation of tbe gearbox as will be described below.

Referring now to Figure 2 which shows the internal details of gearbox 13, it will be seen that input shaft 20, which is driven from clutch 12, is in turn coupled to a forward-reverse gear mechanism indicated generally at 21. The gear box is also provided with a 4-speed intermediate change gear mechanism indicated generally at 22 and a 2-speed or high-low range output mechanism indicate generally at 23. A main shaft 24 extends rearwardly from the input shaft 20. Both the input shaft 20 and main shaft 24 are hollow and a power takeoff shaft 25 extends through these shafts.

Acounter shaft 28 and rearwheel drive output shaft 30 are parallel to the main shaft and are coaxial to each other.

The forward-reverse mechanism 21 includes forward and reverse drive gears 32, 34, respectively, journaled about the input shaft 12, a forward input gear 36 in engagement with gear 32, input gear 36 being coupled to the countershaft 28 for rotation therewith, and a one piece idler gear set 37 including portion 38 which is rotatable with the shaft portion 40, and a further reverse idler gear portion 42 in driving engagement with the input gear 36. (It should be noted at this point that for reasons of clarity the gear set 37 is not shown in its correct position in the drawings).

A shift gear 44 is carried by the input shaft 12 for rotation therewith, the shift gear being disposed between rotatable gears 32, 34. The gears 32, 34 have splined sections 32s, 34s, respectively disposed adjacent the shift gear. A shift-collar 46 is disposed about the shift gear 44 and splines 32s and 34s. By moving the shift collate two the right as shown in the drawing the shift gear 44 becomes engaged with the forward drive gear 32 thereby causing the input gear 36 to be driven in a forward direction. If the shift collar were shifted to the left, it would pass through a neutral position to a reserve position wherein it would couple the shift gear 44 with the reverse gear 34 through idler gear set 37 thereby causing the input gear 36 to rotate in a reverse direction.The shift collar 46 is caused to be moved from its forward position to its reverse position by a shift fork 48, the shift form in turn being coupled to a shift rail and other control linkage which are not a feature of the present invention.

The input gear 36 is secured to the forward end of the counter shaft 28 and rotation of the gear 36 will cause the counter shaft to rotate. First and second drive gears 50, 52 are rotatably journaled about the counter shaft 28, the drive gears 50, 52 being in mesh with driven first and second gears 54, 56, respectively. The driven gears 54 and 56 are in turn mounted on the main shaft 24 for rotation therewith.

A synchronizing mechanism indicated generally at 58 is disposed between the first and second drive gears, the synchronizing mechanism including a synchronizer collar 60 mounted upon a hub 62 which is in turn coupled to the counter shaft 28. Disposed to either side of the hub 62 are synchro rings 64. By shifting the collar 60 from the neutral position illustrated in the drawing to the right, short spline 50s on the drive gear 50 will become engaged after the gear has been brought up to speed in a known manner. In a similar manner, movement of the collar 60 to the left will cause short spline 52s to become engaged. The synchronizing collar 60 is caused to be shifted by a fork 66 which is in turn connected to a shift mechanism not illustrated.

A second synchronizing mechanism 68 is disposed between third drive gear 70 and the fourth drive gear 72. The third drive gear 70 is journaled for rotation about the output shaft 30, and the fourth drive gear 72 is journaled for rotation about the counter shaft 28. A hub 74 is coupled to the counter shaft 28 for rotation therewith, and the hub 74 can in turn be coupled with either the third or the fourth drive gear by shifting the synchronizer collar 76 to the right or to the left from the neutral position illustrated. The third and fourth drive gears 70,72 are in turn disposed in driving relationship with the third and fourth driven gears 78 and 80, the third and fourth driven gears being fixed on main shaft 24.

The high-low range gear mechanism 23 includes output gear 17 which is splined to the output shaft 30 for sliding movement thereon. The output gear is provided with a coupler section 84 on one side which is adapted to mate with a corresponding coupler 86 on the third drive gear 70 when the output gear is shifted to its left hand or high range position by fork 88 as shown in the drawing. When the output gear 82 is shifted to the right in its low range position, the teeth on the gear 82 will become engaged with corresponding teeth on gear 90 which is integral with the main shft 24 for rotation therewith.

Gearbox 18 is axially fixed and positioned so that it remains in engagement with gear 17 in both the low and high range positions.

In operation when the output gear 82 is in its left hand position the transmission will be disposed in its high range and shifts can be made into fifth, sixth, seventh, and eigth gears. When the output gear is in its right hand position the transmission will be in its low range and shifts can be made into first, second, third and fourth gears. First gear is obtained by shifting the collar 60 to the right while maintaining collar 76 in its neutral position. A shift into second gear is obtained merely by shifting the collar 60 to the left hand position. If it is desired to shift from second into third, the collar 60 will be moved into its neutral position and collar 76 will be shifted to the right to cause third drive gear 70 to become engaged with its hub 74. Finally, fourth gear is obtained by shifting the collar 76 to the left hand position.

Clutch 14 is of the multi-plate type and is hydraulically operated from a pump 100 via a solenoidoperated valve 101 and hydraulic lines 102 and 103.

The clutch comprises a first series of axially slidable clutch plates 105a which are connected with an output shaft 1 4a (which is in turn connected with shaft 16) and a second series of axially-slidable clutch plates 1 05b which are connected with gear 18.

An annular piston 104 is provided for bringing interleaved plates 105a and 105b into engagement to engage the clutch on pressurisation of annular chamber 107 via line 103 and drillings 103a and 103b. When the clutch is in the disengaged condition shown in Figure 3 chamber 107 is connected with hydraulic sump 106 and disengagement of the clutch plates is ensured by a number of circumferentially spaced release springs 108.

Clutch 14 is engaged by activating solenoid 101a to displace valve 101 to the right against the action of springs 108.

Figure 1 shows the electrical circuit associated with valve 101. A battery 109 is connected with solenoid 101 a via two switches 110 and 111 in series.

Switch 111, which is controlled by the gear selector mechanism, is normally held closed, as explained below, except when gear 17 is being slid to change the operating range of the gearbox. Switch 110 is closed by the operator to complete the electrical circuit and thus engage clutch 14 to give four wheel drive.

Figure 3 diagramatically shows part of the gear box selector mechanism (which is of the type described and claimed in British Patent No. 1546461) in which a selector lever 115 is pivotted at 116 on a support 117 which is fixed against vertical movement but which is rotatable about a vertical axis as indicated by arrow W. Lever 115 is pivotally connected at 118 with a rod 119 which is raised and lowered in response to pivotting of lever 115 about axis 116. Lever 115 is moved in the double-H gate shown diagrammatically in Figure 4.

As will be appreciated, when the lever is moving in the right-hand H of the gate the two speed output stage 23 of the gearbox is in its low range and ratios 1 to 4 can be selected. Similar when the lever 115 is operating in the left-hand H of the gate the high range is operative and ratios 5 to 8 can be selected.

Referring to Figure 4 ratios 1,2,5 and 6 can be selected when lever 115 is moving in its higher horizontal plane A and ratios 3,4,7 and 8 when the lever is moving in its lower horizontal plane B.

Movement of lever 115 is horizontal plane X results in the sliding of gear 17 and a consequent range change.

A projection 120 associated with switch 111 is engagable in an annular groove 121 cut in rod 119 when rod 119 is in the vertical position which corresponds to range change movements of lever 115 in plane X. When projection 120 engages groove 121 contacts 11 lea and 111 b of switch 111 disengage under the action of a spring 122. When lever 115 is in plane A groove 121 is below projection 120 (as shown by dotted detail A in Figures 1 and 3) and contacts 111 a and 111 b are held engaged since projection 115 is moved to the right by rod 119.

Similarly, when lever 115 is in plane B groove 121 is above projection 120 (see dotted detail in Figures 1 and 3) and contains 11 1a and 111 bare again held engaged.

As will be appreciated from the above description, when the tractor is operating in the four wheel drive mode the electrical circuit to solenoid 101a is completed by switches 110 and 111. If the operator now attempts to change the operating range of the gearbox, selector lever 115 will enter plane X whereupon projection 120 will enter groove 121 and switch 111 will open thus causing valve 101 to dump the pressure in chamber 107 to sump 106, thereby disengaging clutch 14. When the range change is completed and lever 115 leaves plane X, switch 111 is closed and clutch 14 reengaged assuming that the operator leaves switch 110 closed. Thus during any range change in the gearbox drive to the front wheels is automatically disconnected.This ensures that the possibility of inter-tooth friction between the teeth of gears 17 and 18 (which would tend to oppose sliding of gear 17 relative to gear 18) is eliminated thereby ensuring that the effort which it is necessary to apply to lever 115 to effect a range change remains acceptable.

It will be understood that if clutch 14 were not disconnected during a range change, even if clutch 12 were disengaged, inter-tooth friction would occur betweentheteeth of gears 17 and 18 since gear 17 would be connected with the rear wheels and gear 18 with the front wheels which would almost inevitably be rotating at a different speed to rear wheels as described above.

Figure 5 shows the electrical and hydraulic circuits of an alternative form of the present invention in which clutch 14 is disengaged i response to depression of the main clutch control pedal 150.

In this arrangement switch 1 t 1is normally held closed by a spring 151 and is arranged to be opened when the clutch pedal is depressed. This arrangement has the disadvantage that the clutch 14 is disengaged each time the main clutch 12 is disengaged to change the operative ratio of the gearbox whether of not the ratio change involves a range change. This can result in the unnecessary loss of front wheel braking, which might be important, for example, if the tractor is descending a hill with a heavy trailer.

It is throught that the above disadvantage associated with the operation of switch 111 from the clutch pedal could be overcome by arranging switch 111 only to open when clutch pedal 150 was fully depressed (i.e. depressed further than is necessary to disengage clutch 12). This would mean that the operator would be required to fully depress the clutch pedal during range changes if he desired to disengage clutch 14to lower the effort required to move lever 115.

The invention thus provides an improved form of vehicle of the kind specified in which the problem of difficult ratio changes due to inter-tooth friction between the slidable gear wheel and meshing fixed gearwheel is mitigated.

Claims (7)

1. Avehicle of the kind specified having a disconnecting means in one of said drive trains, said disconnecting means being arranged to disconnect the drive connection with the associated pair of driven wheels during a ratio change which involves sliding of said gear wheel.

2. A vehicle according to claim 1 in which the disconnecting means is actuated to response to movements of the selector means which indicate a ratio change which involves sliding of said gear wheel is to be made.

3. A vehicle according to claim 1 having a main clutch between the prime mover and gearbox which is engaged and disengaged by a main clutch control means and in which the disconnecting means is actuated in response to the operation of the main clutch control means.

4. A vehicle according to claim 3 in which the main clutch control means has a normal operating range of movement necessary for full disengage ment of the main clutch and a further position or range of positions beyond the normal operating range, the disconnecting means being arranged to be actuated whenever the main clutch control means is in said further position or range of positions.

5. A vehicle according to any one of claims 1 to 4 in the form of a four wheel drive agricultural or industrial tractor with driven front and rear pairs of wheels, the tractor having a front wheel drive clutch in the drive train to the front wheels which is utilised as the disconnecting means.

6. A vehicle according to any one of claims 1 to 5 in which the disconnecting means is fluid pressure operated and is actuated by a solenoid-operated fluid control valve which is triggered by the operation of the selector means or main clutch control means.

7. A vehicle of the kind specified constructed and arranged substantially as hereinbefore described with reference to and as shown in any one of Figures 1,4 and 5 of the accompanying drawings.