GB1559225A

GB1559225A - Hydrostatic transmission with differential steering

Info

Publication number: GB1559225A
Application number: GB3730777A
Authority: GB
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1977-02-02
Filing date: 1977-09-07
Publication date: 1980-01-16
Also published as: CA1054026A; JPS5396131A; DE2800487A1; JPS6124225B2

Description

(54) HYDROSTATIC TRANSMISSION WITH DIFFERENTIAL STEERING (71) We, CATERPILLAR TRACTOR CO., a corporation organized and existing under the laws of the State of California, United States of America, of 100 N.E. Adams Street, Peoria, Illinois, 61629, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to drive for vehicles, and more particularly to a fluid drive system for providing steering of a track-type vehicle.

In the use of a track-type vehicle, it is of course important that both effective driving of the vehicle in a straight direction and effective steering of the vehicle, in either the forward or reverse direction of vehicle drive, be accomplished. Generally, it is well known to provide two separate hydrostatic motor units for driving the wheels or tracks on the respective sides of the vehicle. Such a system is disclosed in U.S. Patent Specification No.

3,655.004. It will be understood that it would be advantageous to provide a system wherein a single pump can be used to provide proper driving and actuation for steering of wheels or tracks of a vehicle.

U.S. Patent Specification No. 2,560,554 discloses a drive system wherein shafts can be locked relatively together to drive a vehicle through planetary drive systems.

Such shafts can also be made to rotate in opposite directions to provide a steering effect. A relatively complicated electrical and mechanical system is used for providing the steering effect of the vehicle.

U.S. Patent Specification No. 3,612,167 discloses a hydrostatic transmission and a motor which is used to drive a differential for driving a pair of wheels. However, there is no steering system disclosed therein.

U.S. Patent Specification No. 3,782,488 discloses a pair of hydrostatic transmissions with a single control for controlling the displacement of a pair of pumps to achieve a steering effect. Thus, in a way similar to that described in U.S. Patent Specification No. 3,655,042 a pair of pumps are used in the operation of the system.

According to the present invention a drive and steering system for a vehicle having a pair of tracks comprises a hydrostatic transmission having a pump and a first fluid operated motor for driving the tracks of the vehicle through a drive transmission; a second, fluid operated motor; means for selectively supplying pressurized fluid from the pump to the second motor to drive the second motor; and means coupling the second motor to the drive transmission to provide relative differential movement between the tracks on operation of the second motor.

One example of a system according to the invention will now be described with reference to the accompanying drawing, which is a schematic drawing of a vehicle and steering system.

Shown in the drawing is the overall system 10 for providing drive and steering of a track-type vehicle, the drive sprockets of which are shown at 12, 14. As shown therein, a vehicle engine 15 drives a pump 16 through a gear train 18. The pump 16 draws fluid from a reservoir 20 and pumps such fluid through a line 21 and through a filter 22 and into and from a venturi 24 to an orifice 26 and thence to the hydrostatic controls 28 of the vehicle. The engine 15 also drives a reversible variable displacement hydrostatic pump 30. The pump 30 is connected with a variable displacement hydrostatic motor 32 by conduit 34 and conduit 36. The variable displacement pump 30 is operatively coupled with the hydrostatic controls 28 by conduit means 38 as is well known, so that actaution of the hydrostatic controls 28 in a chosen manner varies the displacement of the pump 30 to in turn drive the motor 32 in a chosen manner.

The output shaft 40 of the motor drives a gear 42 which is engaged with a gear 44 in turn driving a shaft 46. The ends of the shaft 46 are operatively associated with identical planetary gear systems 48, 50 to couple them with the respective sprockets 12, 14 of the vehicle, and consequently only one planetary gear system 48 and its association with the end of the shaft 46 will be described in detail.

The end of the shaft 46 has fixed thereto a sun gear 52, which is in engagement with a plurality of planet gears 54 rotatably mounted to an intermediate member 56.

The intermediate member 56 has fixed thereto an outwardly extending shaft 58 having a gear 60 fixed thereto. Such gear 60 is in driving engagement with a gear 62 fixed to the shaft 64 of the sprocket 12. The plurality of gears 54 is also engaged with a ring gear 66. The ring gear 66 has outwardly projecting teeth 68 which are in engagement with the teeth of a gear 70 of a pair 70, 72 thereof secured together by a shaft 74. The other gear 72 of the pair is in engagement with a gear 76 secured to a shaft 78, the opposite end of which has fixed thereto a bevel gear 80.

As set forth above, the planetary gear associated with the sprocket 14.

A relief and replenishing valve 82 generally as disclosed in U.S. Patent Specification No. 3.477.225, is in operative association with the pump 30 and motor 32 by means of conduits 84, 86. 88, 90. The relief and replenishing valve 82 is capable of supplying fluid from the line 21 through a line 92 to the low pressure conduit of the conduits 34. 36. and also of drawing additional fluid from the low pressure conduit of the conduits 34, 36 and supplying fluid from the relief and replenishin valve 82 into a conduit 94 under conditions to be further described.

The conduit 94 communicates with a 2position valve 96 which in turn communicates with : reversible fluid motor 98 through conduits 100, 102. The output drive shaft 104 of the motor 98 has a bevel gear 106 fixed thereto which is in engagement with the bevel pears XO. 801. so that the bevel gears 80, 801. 106 form a differential 108.

A conduit 110 leads from the valve 96 to a variable pressure compensated meter out flow control valve 112, which is not sensitive to vehicle loads determining pressure in the drive svstem. which valve 112 may be opened and shut by controls to be further described. If the valve 112 is in the open position, fluid from the relief and replenish ing valve 82 will be allowed to travel through motor 98 in one and the other directions to drive the motor 98 in one and the other directions, through the flow control valve 112, and into the conduit 92 back to the relief and replenishing valve 82.

A pair of pilot valves 114, 116 are in cluded, for selectively directing fluid from the conduit 118 to the valve 96 for position ing the valve 96 in one and the other respective positions. The valve 114 is a steering valve actuated by, for example, a lever in the cab of the vehicle (not shown).

The valve 114 is always in one or the other positions to direct fluid to one or the other sides of the valve 96. However, it will be understood that fluid flow cannot take place through the motor 98 and valve 96 if the valve 112 is closed. The motor 98 is thereby locked for a non-steer effect. The lever may be chosen to be, for example, in a vertical position of the valve 112. Moving the lever in one direction opens the valve 112 and moves the steering valve 114 to the chosen steering position, or if the steering valve 114 is already in such chosen position, causes such steering valve 114 to remain in such position. Moving the lever in the other direction from the neutral position of course moves the steering valve 114 to its other position and opens the orifice 112. Moving the lever back to its neutral position leaves the steering valve 114 in the position it has occupied, but closes the valve 112.

The valve 116 is in series with the valve 114 for providing an overall reversal of the flow of pilot fluid to the valve 96.

Under normal operation, with no steering effect chosen, the engine 15 drives the pump 30 which in turn drives the motor 32 to drive the shaft 46. The relief and replenish ing valve 82 supplies fluid to the lower pressure conduit of the conduits 34, 36.

Fluid cannot flow from the conduit 94 through the motor 98. since the valve 112 is closed. Thus, the differential 108 is locked, i.e., the shafts 78, 781 are held from rotation.

Thus, the shaft 46 rotates the gears 52, 521 to rotate the planet gears 54, 541. The ring gears 66, 661 are held from rotation since the shafts 78, 781 are not rotating, and consequently the planet gears 54, 541 rotate within the ring gears 66, 661 to drive the shafts 58, 581 to in turn drive the track driving sprockets 12, 14 at the same speed.

This provides straight driving of the vehicle.

It will be understood that reversal of the pump 30 drives the motor in reverse 32 to drive the track-driving sprockets 12, 14 in the reverse direction at equal speeds.

Assuming that the track-driving sprockets 12, 14 are indeed being driven at the same speed, and also assuming that steering of the vehicle is desired, the lever described above may be actuated to open the valve 112 and to move the steering valve 114 to the proper position, if it is not already in such proper position, for steering of the vehicle as chosen. Assuming, for example, that the steering valve 114 is moved upward, pilot fluid will be supplicd to the right side of the valve 96 so that the valve 96 is in its first position as shown. Fluid will then be allowed to exit from the relief and replenishing valve 82 through the conduit 94, through the valve 96, to drive the motor 98 in one direction. Such driving of the motor 98 provides a differential movement of the shafts 78, 781, rotating one in one direction and one in the opposite direction, so that through the planetary gear systems 48, 50, a differential movement is provided between the track-driving sprockets 12, 14 of the vehicle, one such drive sprocket in fact relatively slowing down. It will be seen that steering of the vehicle is thereby provided, through differential movement of the tracks being driven by the track-driving sprockets 12, 14.

It will be seen that movement of the steering valve 114 to its other position provides pilot fluid to the other side of the valve 96 to move valve 96 to its second position to provide pressurized fluid to the motor 98 to drive the motor 98 in the other direction. Thus, the track which was relatively slowed down before will speed up to the normal drive speed, and the track which was previously at normal drive speed will slow down.

If the vehicle is being operated in the reverse direction, the forward/reverse valve 116 is actuated to provide reverse flow of pilot fluid to the valve 96. This reverses the output drive of the motor 98, which is necessary when driving in the reverse vehicle mode, to provide that the same operation of the above-described lever will provide consistent left or right steering as chosen.

WHAT WE CLAIM IS:- 1. A drive and steering system for a vehicle having a pair of tracks, the system comprising a hydrostatic transmission having a pump and a first fluid operated motor for driving the tracks of the vehicle through a drive transmission; a second, fluid-operated motor; means for selectively supplying pressurized fluid from the pump to the second motor to drive the second motor; and means coupling the second motor to the drive transmission to provide relative differential movement between the tracks on operation of the second motor.

2. A system according to claim 1, wherein the second motor is a reversible fluid motor, and wherein the means for selectively providing pressurized fluid from the pump to the second motor includes means for selectively directing pressurized fluid through the second motor in a first or a second direction.

3. A system according to claim 2, wherein the means for selectively providing pressurized fluid from the pump to the second motor includes valve means movable between a first position in which pressurized fluid is directed in the first direction to the second motor to drive the second motor in one direction and a second position in which pressurized fluid is directed in the second direction to the second motor to drive the second motor in the other direction.

4. A system according to claim 3, further comprising a pilot pressure system operatively coupled with the valve means, and a selector valve operatively coupled with the pilot pressure system to provide shifting of the valve means to the first and secoIlre positions thereof.

5. A system according to claim 1, substantially as described with reference to the accompanying drawing.

6. A vehicle having a pair of tracks and a drive and steering system according to any of claims 1 to 6.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

and to move the steering valve 114 to the proper position, if it is not already in such proper position, for steering of the vehicle as chosen. Assuming, for example, that the steering valve 114 is moved upward, pilot fluid will be supplicd to the right side of the valve 96 so that the valve 96 is in its first position as shown. Fluid will then be allowed to exit from the relief and replenishing valve 82 through the conduit 94, through the valve 96, to drive the motor 98 in one direction. Such driving of the motor 98 provides a differential movement of the shafts 78, 781, rotating one in one direction and one in the opposite direction, so that through the planetary gear systems 48, 50, a differential movement is provided between the track-driving sprockets 12, 14 of the vehicle, one such drive sprocket in fact relatively slowing down. It will be seen that steering of the vehicle is thereby provided, through differential movement of the tracks being driven by the track-driving sprockets 12, 14.

It will be seen that movement of the steering valve 114 to its other position provides pilot fluid to the other side of the valve 96 to move valve 96 to its second position to provide pressurized fluid to the motor 98 to drive the motor 98 in the other direction. Thus, the track which was relatively slowed down before will speed up to the normal drive speed, and the track which was previously at normal drive speed will slow down.

If the vehicle is being operated in the reverse direction, the forward/reverse valve

116 is actuated to provide reverse flow of pilot fluid to the valve 96. This reverses the output drive of the motor 98, which is necessary when driving in the reverse vehicle mode, to provide that the same operation of the above-described lever will provide consistent left or right steering as chosen.

WHAT WE CLAIM IS:- 1. A drive and steering system for a vehicle having a pair of tracks, the system comprising a hydrostatic transmission having a pump and a first fluid operated motor for driving the tracks of the vehicle through a drive transmission; a second, fluid-operated motor; means for selectively supplying pressurized fluid from the pump to the second motor to drive the second motor; and means coupling the second motor to the drive transmission to provide relative differential movement between the tracks on operation of the second motor.
2. A system according to claim 1, wherein the second motor is a reversible fluid motor, and wherein the means for selectively providing pressurized fluid from the pump to the second motor includes means for selectively directing pressurized fluid through the second motor in a first or a second direction.
3. A system according to claim 2, wherein the means for selectively providing pressurized fluid from the pump to the second motor includes valve means movable between a first position in which pressurized fluid is directed in the first direction to the second motor to drive the second motor in one direction and a second position in which pressurized fluid is directed in the second direction to the second motor to drive the second motor in the other direction.
4. A system according to claim 3, further comprising a pilot pressure system operatively coupled with the valve means, and a selector valve operatively coupled with the pilot pressure system to provide shifting of the valve means to the first and secoIlre positions thereof.
5. A system according to claim 1, substantially as described with reference to the accompanying drawing.
6. A vehicle having a pair of tracks and a drive and steering system according to any of claims 1 to 6.