GB2131920A - Hydrostatic transmissions - Google Patents

Abstract

To prevent jamming of a working element driven by a hydrostatic transmission, eg the main rotor of a combine harvester, the displacement of the transmission pump is varied when pressure of the fluid delivered by the pump exceeds a predetermined value to increase the speed of the working element. In a split torque transmission with direct drive to the planet carrier of a planetary gear set (11) and hydrostatic drive to the annulus gear, the displacement of the pump (15) is normally controlled by a manually- operated servo-valve (55), but when valve (75) detects a predetermined rise in pump output pressure it admits fluid to servo-piston (56) to reduce pump displacement. If the pressure continues to rise, valve (80) admits fluid to servo- piston (57) to increase pump displacement and thereby stop the drive. <IMAGE>

Description

SPECIFICATION Anti-plug control This invention relates to an anti-plug control for a drive which drives a working element, such as the main rotor of a rotary combine harvester that can be jammed by excessive material. More particularly, the invention relates to the control of a variable displacement unitofa hydrostatic transmission used independently as the drive means or as part of a hydromechanical transmission drive means with the change of the displacement of the variable displacement unit upon the occurrence of a jam effecting an increase in the speed oftheworking element.

In rotary combine harvesters, there is a driven main rotorto which the crop is fed. The main rotor can be subjectto plugging which occurswhenthe main rotor becomesjammedwith crop because the crop is fed thereto in larger quantities than can be passed by the main rotor. The control of this invention senses the pressure in the closed circuit ofthe hydrostatic transmission and, when the pressure reaches a predetermined value, the control operates to adjust the variable displacement unit of the hydrostatic transmission to increase the speed ofthe main rotor. It is known in the artto sense the pressure in the closed circuit of a hydrostatic transmission and, at some levei of pressure, causes a change in the displacement of the variable displacement unit.However, such a control has been to reduce the torque applied to the motor, ratherthan cause a change in the speed of the motor ofthe transmission to increase the speed ofthe working element driven bythetransmission.

The present invention relates to a new and improved anti-plug control fora drive to prevent jamming of a driven working element in response to an overload by varying the displacement of the variable displacement unit of a hydrostatictransmissimon to increase the speed of the working element.

This working element can be the main rotor of a rotary combine harvester or other conveying devices, such as a belt conveyor or an auger, which could be subject to jamming by an excess quantity of material being handled.

The invention accordingly provides an anit-plug control fora drive to prevent jamming of a driven working element in response to an overload, wherein the drive includes a fluid motor and a variable displacementfluid pump for supplying fluid to the motor comprising, servo means including a servo control cylinderfor controlling displacement of the pump, means for sensing the pressure ofthe fluid delivered by the pump to the motor, and means responsive to an increase of the pressure beyond a predetermined value for modifying the displacement ofthe pump to increase the speed ofthe drive.

In one application of the invention, the drive is a hydromechanical transmission, ofwhich the fluid pump and motor comprise a hydrostatic transmission component. The variable displacement pump has a swash plate controlled by the servo means. The pump and motor are connected in closed hydraulic circuit. A fluid line extends from the high pressure side ofthe closed ci rcuit to the servo control cylinder and a normally closed pressure-responsive valve in the fluid line opens when the predetermined pressure is reached and causes pressure fluid to act on the servo control cylinderto vary the displacement of the variable displacement pump with the resultthatthe spedeed of the working element is increased.Advan tageouslythe hydromechanical transmission is such that a decrease in the displacement ofthe pump causes a decrease in the speed of the fluid motor and the desired increase in the speed oftheworking elementwhich istheoutputshaftofthehydromechanical transmission.

Preferably the control of the invention further comprises additional means responsive to an increase in the fluid pressure delivered by the pump of a predetermined amount beyond the predetermined value for modifying the displacement of the pump to decrease the speed of the drive.

Fig. lisa diagrammaticview of a hydromechanical transmission; and Fig. 2 is a schematic drawing ofthe hydrostatic components of the transmission.

Fig 1 illustrates a conventional hydromechanical transmission wherein a driven input shaft 10 extends toaplanetarygearsetll 11 and a drive shaft 12 extends from the planetary gear set. The planetary gear set typically has a sun gear and a ring gearwith intermediate planet gears carried on a planetcarrier. A hydrostatic transmission having a variable displacement unit 15 and a fixed displacement unit 16 are connected together in a closed circuit, with the variable displacement unit 15 having an input shaft 17 driven by the input shaft 10 and the fixed displacement unit having an output shaft 18 connected to an element of the planetary gear set. A hydromechanical transmission is shown in Ross US Patent No.

3,396,607 and the disclosure thereof is incorporated herein by reference. As evident from the Ross Patent, the input shaft 10 can connect to the planet gear carrier of the planetary gear set and the output shaft 18 of the fixed displacement unit connects to the ring gear and with the drive shaft 12 being connected to the sun gear. In a hydromechanical transmission, the speed of the planetary gear set element driven by the ouput shaft 18 of the hydrostatictransmission can be either added orsubtractedtothe rotational speed of the planetary gear set element driven at a constant input speed bythe input shaft 10.

With the variable displacement unit 15 at maximim displacement at one side of neutral, the speed ofthe drive shaft 12 is ata minimum and, as the displace mentofthevariable displacement unit 15 is de- creased, the speed of the drive shaft 12 increases.

The hydrostatic transmission utilized in Fig. 1 is shown more particularly in Fig. 2.

The variable displacement unit 15, identified as a variable displacement pump in Fig. 2, and the fixed displacement unit 16, identified as a fixed displacement motor in Fig. 2, are each constructed as an axial piston unit, with the stroke ofthe pistons controlled by a swash plate.

The variable displacement pump 15 has a casing 20 which rotatably mounts on bearings the input shaft 17. A cylinder block 21 is rotatable within the casing and is splined at 22 tothe input shaftfor rotation therewith. A series of pistons 23 are movable in cylinders within the cylinder block and the stroke thereof is controlled by a movable swash plate 24 with shoes carried by the pistons in sliding contact with the swash plate.

The fixed displacement motor 16 has a casing 30 which rotatably mounts the output shaft 18 on bearings and a cylinder block 31 is splined at 32 to the outputshaft. The cylinder block31 has cylinders in each of which a piston 33 is movable with the stroke thereof being controlled by a fixed swash plate 34.

With the pump swash plate 24 positioned as shown in Fig. 2, pistons 23 are stroked for maximum displacementduring rotation of the cylinder block and fluid under pressure is delivered from a pump outlet 40 to a fluid line connection 41 extending to the motor 16 and which forms the high pressure side of a closed circuit connecting the pump and motor. The low pressure side of the closed circuit is through a fluid line connection 42 whereby fluid can return from the motortothe inlet ofthe pump. This structure is conventional and the conventional structure further includes a charge pressure circuit including a charge pump 45 which draws fluid from a reservoir 46 which passes through a filter 47.The charge pump 45 functions to provide make-up fiuid to the closed circuit between the pump and motor by supply to the low pressure side through either ofthe charge check valves 48 and 44 which, at their upstream ends, are connected to a fluid line 50 connected to the outlet side of the charge pump and, at their downstream ends, are connected to thefluid line connections 41 and 42, respectively. A charge relief valve 51 operates to relieve the charge pressure when it exceeds the setting of the charge relief valve. The reservoir 46 is supplied from fluid within the casing of the motor 16 through a line 52 which extends to the reservoir 46 and has a heat exchanger 53 therein for cooling the fluid, such as oil.

Another conventional part of a hydrostatictransmission is the displacement control which includes a control valve, indicated generally at 55, and which is supplied with charge pressure fluid through the line 50. The displacement control valve 55 is positionable to control the fluid connections of a pair of servo control cylinders 56 and 57 mounted in the pump casing 20 and which, through pivotally connected links 58 and 59 extended to the swash plate 24, control the position ofthe swash plate.

Displacement control cylinders with either a charge pressure port or tank ports at the displacement control valve. More particularly, servo control cylinder 56 is connected to a port of the displacement control valve by lines 61 and 62 and the servo control cylinder 57 is connected to a port of the displacement control valve by lines 63 and 64.

The displacement ofthe swash plate 24 is established by initially setting a position ofthe displacement control valve member 60 which, as shown, can be underthe control of a handle 68 which is pivotally mounted and which, through linkage, is connected to the valve member In the use of the variable displacement pump as part ofthe hydromechanical transmissionforthe purposes described herein, onlythe servo control cylinder 56 need be used to position the swash plate 24 since only one side ofthe hydrostatic closed circuit is pressurized throughout the speed range of the working element driven bythetransmission and the internal forces within the variable displacement unitalwaystendtotilttheswash plate toward a clockwise extreme position.As the handle 68 is pivoted from the position shown in a direction to shift the valve membertoward the left, as viewed in Fig. 2, charge pressure is delivered through lines 61 and 62 to the servo control cylinder 56, acting to extend the piston within the cylinder and thereby move the swash plate from the maximum displacement position shown towards a reduced displacement position.

The linkage interconnecting the handle 68 and the valve member 60 includes a feedback linkage connected to the swash plate whereby the valve member is caused to return to a position where lands of the valve member blockthe servo control cylinder 56 from both charge pressure and a tank port at the displacement control valve. This feedback linkage includes a link 70 pivotally connected to an end ofthe valve member and having pivot connections to link71 and 72 which pivotally connect to the handle 68 and the swash plate, respectively.

With the swash plate 24 positioned as shown in Fig.

2, the pump is at maximum displacement and thereby the motor 16 is operating at maximum speed. Within the planetary gear set 11 there is a maximum subtraction of speed from the input speed derived from the input shaft 10 whereby the drive shaft 12 is rotating at minimum speed and, in fact, could be non-rotating. As the swash plate is caused to move from maximum displacement toward zero displacement position, the speed ofthe motor 16 is reduced with the resulting increase in speed of the drive shaft 12.

With the drive shaft 12 driving a main rotor in a rotary combine harvester, or driving some other working element which can become overloaded, there is an increase in pressure in the high pressure side of the closed circuit between the pump and motorwhen overloading occurs. Meansforsensingthepressure on the high pressure side comprises a pressure limiter sensing valve 75which is normally closed by having a valve member spring-urged to a closed position to close a fluid line 76 connected to the fluid outlet 40 of the pump and which has a section 77 extending to the line 61 connected to the servo control cylinder 56.The pressure limiter sensing valve can either be pre-setor remotely selectively set to open ata predetermined value of pressure in the fluid line connection 41 between the pump and motor and, when opened, high pressure fluid is directed to the servo control cylinder 56. This results in moving the swash plate 24to a reduced displacement position whereby the speed of the motor output shaft 18 reduces and the speed of the drive shaft 12 from the planetary gear set increases.

For illustrative purposes, the predetermined value or level ofthe pressure at which the pressure limiter sensing valve 75 will open can be 5,000 psi. Ifthe increase in speed of the drive shaft 12 is sufficientto dischargethe excess material from the working element, the pressure in the closed circuit will ultimately reduce and the hydrostatic transmission will return to the speed of operation set bythe displacement control valve 55.

In the unlikely event that the working element is unable to discharge excess material and the working element does jam, then the pressure limiter sensing valve 80, which is set to open at a pressure higherthan the pressure limiter sensing valve 75, will open. This valve has an inlet connected to the pump outlet 40 buy a line81 and an outlet connected by a line 82 to a line 83 which connects to the servo control cylinder 57. Each ofthe pressure limiter sensing valves 75 and 80 are of the type having a valve member urged to a closed position by a spring and with the force ofthe spring being settableto control the pressure at which the valve will open.The pressure limiter sensing valves can beofatypewhich can be remotely adjustable.

When the pressure limitersensing valve 80 opens,the swash plate 24 moves to a maximum displacement position, with the result that the drive shaft 12 stops rotation. An optionally usable orifice 85 in the line 76 can be used to insure that pressure limiter sensing valve 80 will be effective to override the operation of the pressure limiter sensing valve 75.

Commonly mounted pressure limitercheckvalves 90 and 91 have their downstream sides connected to the charge pressure line 50 and their upstream ends connected to the lines 77 and 63, respectively, whereby the pressure in either of the latter lines in excess ofthe setting of a spring connecting the valve members 90 and 91 and charge pressure acting on the backside of the valve members will cause a valve member to open to discharge fluid to the charge pressure line 50.

If the working element, such asthe main rotor of a rotary combine harvester, is driven by a hydrostatic transmission output to the rotor usually via reduction gearing rather than by a hydromechanical transmission, the same control can be used since the main rotor normally operates in one direction only and one side of the main hydrostatic loop is pressurized. In such control in a hydrostatictransmission,the press ure-limitersensing valve 75 when opened would cause delivery of fluid pressure to the servo control cylinder which would actto move the swash plate to increase the displacement of the pump and thereby increase the speed ofthe motor 16. The pressure limitersensing valve 80 would be connected to the servo control cylinder which, when activated, would move the swash plate to a zero displacement position.

With the anti-plug control disclosed herein, pressure in the closed circuit of a hydrostatic transmission can be sensed when a working element becomes overloaded and the hydrostatictransmission adjusted in respoaseto an increase in pressure in the closed circuit of the hydrostatic transmission to increase the speed of the drive of the working element in an effort to clearthe overload of material and prevent a jam.

Claims (8)

1. An anti-plug control for a drive to prevent jamming of a driven working element in response to an overload, wherein the drive includes a fluid motor and a variable displacementfluid pumpforsupplying fluid to the motor comprising, servo means including a servo control cylinder for controlling displacement ofthe pump, means for sensing the pressure of the fluid delivered by the pump to the motor, and means response to an increase of the pressure beyond a predetermined value for modifying the displacement ofthe pump to increase the speed ofthe drive.

2. A control as defined in claim 1, including means operable in response to an increase in the fluid pressure of a predetermined amount beyond the predetermined value for modifying the displacement ofthe pump to decrease the speed of the drive.

3. A control as defined in claim 2, wherein the last-mentioned means is operable to stop the drive.

4. A control as defined in claim 1, wherein there is a pair ofthe servo control cylinders and the means operable to increase the speed of the drive includes a fluid line extended between the pump outlet and one of the servo control cylinders and a pressure-responsive valve normally closing the fluid line and openable when the fluid pressure reaches the predetermined value.

5. Acontrol asdefined in claim 4, including means for slowing the speed of the drive when thefluid pressure goes a predetermined amount beyond the predetermined value, comprising a second fluid line between the pump outletandthe otherofthe servo cylinders and asecond normally closed pressure responsive valve in the second fluid line set to open at a fluid pressure value higherthan the predetermined value.

6. A control as defined in claim wherein a flow restriction in the first fluid line ensures preferential flow th rough the second fluid line to the other servo control cylinderwhen the second pressure-responsivevalve opends.

7. A control according to any preceding claim, wherein the drive is a hydromechanical transmission ofwhich the fluid pump and motor comprise a hydrostatic transmission component, the variable displacement pump being at maximum displacement when the drive is at minimum speed and the displacement of the variable displacement pump being decreased when the fluid pressure exceeds the predetermined value to decrease the speed of the fluid motor and increasethespeed ofthe drive.

8. A control according to claim 1, substantially as described herein.