AU2004101046A4 - A Hydraulic Drive System for Multi-Speed Vehicle - Google Patents

Description

0 0 A HYDRAULIC DRIVE SYSTEM FOR MULTI-SPEED VEHICLE o Field of the Invention.

The present invention relates to hydraulic drive systems and, in Oparticular, to hydraulic drive systems for driving vehicles with wheels or tracks at a variety of speeds and torques.

Background Art.

Various types of hydraulic drive systems for propelling wheeled or O tracked vehicles are commercially available. Drive systems for wheeled vehicles generally include a hydraulic pump connected to a drive unit directly coupled to one 0 O 10 or more drive shaft assemblies. These drive systems enable the vehicles to operate in either two- or four-wheel mode by varying the speed of the pump.

Conventional four-wheel drive working vehicles may be provided with a hydraulic transmission including a hydraulic pump driven by an engine and a hydraulic motor fluidly connected with the pump for driving either a pair of front or rear wheels (usually rear wheels). Such conventional four-wheel hydraulic drive vehicles have been provided under the bottom of the midsection thereof with a transmission shaft for transmitting power from the hydraulic transmission to the other pair of wheels (usually, front wheels).

As compared to a two-wheel drive vehicle, a four-wheel drive vehicle has greater traction and is therefore more effective in climbing a hill.

During normal travel of a four-wheel drive vehicle on a flat road, such as asphalt pavement or the like, a problem arises in that the differences in peripheral speeds between the front wheels and the rear wheels causes the front wheels to slip or be dragged and to wear, even if the vehicle travels in a substantially straight direction.

The tendency for the front wheels to drag increases in proportion to the travelling speed of the vehicle. Furthermore, unnecessary driving of all four wheels wastes fuel.

Therefore, on a flat road it is common to shut-off power transmission to the front wheels, so as to drive only the rear wheels.

Many drive systems that provide a four-wheel drive mode and a twowheel drive mode use a variable displacement hydraulic pump. As the mode of the drive is switched from two-wheel drive to four-wheel drive, the pump increases its displacement to maintain the same speed. Systems such as these therefore use more fuel when operating in the four-wheel drive mode as the hydraulic pump is operating 2

O

0 at greater displacement and therefore requires more input energy.

oVariable displacement hydraulic pumps tend to be bigger, and hence more expensive, than fixed displacement pumps. Hence, they are generally unsuitable ofor compact vehicles, such as skid steer mini-loaders where issues of space and weight are paramount.

IThe present invention may offer a substantial contribution to the state o of the art by providing a hydraulic drive assembly requiring less space and having o lower weight than the prior art systems, but still providing the two-wheel and fourwheel drive functionality for the vehicle.

0 S 10 Summary of the Invention.

In one form, the invention comprises a hydraulic drive system for a multi-speed vehicle having a front drive assembly, a first hydraulic motor for rotating the front drive assembly, a rear drive assembly, a second hydraulic motor for rotating the rear drive assembly, and a pump for driving the motors, characterised in that the hydraulic drive system includes control means for selectively disconnecting one of the motors from the pump, such that the hydraulic drive system can be operated in first high speed, low torque mode wherein one motor is driven, and a second low speed, high torque mode wherein both motors are driven.

In use, the innovative drive system allows a vehicle to operate in either mode dependent upon the load placed on the vehicle or the torque or traction required.

In the high torque mode, the hydraulic fluid drives both first and second motors, and thereby provides driving force at each of the pair of axle assemblies. In the high speed mode, one of the drive assemblies is disconnected or isolated from the pump and all of the drive force is transferred to the other drive assembly. The motor associated with the isolated drive assembly continues to operate in a closed loop which is not in fluid communication with the pump so that the motor is lubricated, but the motor of the isolated assembly is not driven by the pump through the hydraulic circuit.

The isolation of one of the motors from the pump results in an increase in hydraulic fluid velocity or pressure available to the driven motor due to the decreased hydraulic load on the hydraulic circuit. The first and second hydraulic motors may have different displacements. For example, a particularly preferred embodiment of the invention may include a rear motor with a 29 in 3 displacement and 3 0 a front motor with a 21 in 3 displacement. In this form, the motor which is isolated O when the two-wheel drive mode is engaged is the front motor.

The front and rear drive assemblies will typically be linked so that they Orotate in unison. When one of the pair of motors is isolated from the hydraulic circuit, it will still rotate and move hydraulic fluid about the isolated section of the hydraulic Icircuit. This will prevent the motor from running dry and possibly being damaged.

oThe multi-speed vehicle is typically a skid steer vehicle, such as a or the like. In particular, the present invention is adapted to be used with miniloaders, as the fixed displacement pump can be accommodated in such small vehicles.

0 O 10 The multi-speed vehicle is typically capable of travelling in either twowheel or four-wheel drive modes, and of swapping between the two modes at the discretion, or under the control of, the user.

The two-wheel drive mode is a high speed, low torque mode. This mode may be used for travelling longer distances or in straight lines between two points. It could also be used where the torque required is not great, for instance where light loads are being carried by the vehicle.

The four-wheel drive mode is a low speed, high torque mode. This mode will typically be used in situations where a higher torque is required such as where heavier loads are to be carried or greater forces are applied. It may also be used where a tighter or smaller radius of turn is needed as an increased force can be transmitted to the ground surface.

In a preferred form, each drive assembly will include an output shaft or axle extending from the respective hydraulic motors and a wheel or other ground engaging member or assembly thereon. There may be one or more linkages in between the output shaft of the motor and the axles of the respective wheel assembly.

The vehicle will suitably have at least four wheels for locomotion and these wheels may be divided into a pair of front wheels and a pair of rear wheels, one of each pair of wheels on each side of the vehicle.

Each drive assembly may comprise a wheel. The front and rear wheels may be linked by an endless track, and constrained to rotate at the same speed.

Alternatively, each drive assembly may comprise a sprocket, the sprockets being linked by an endless chain.

4 0 o A motor will generally be provided for each wheel. A mirror image O hydraulic drive system may be provided on the left and the right of the vehicle. There may be a single controller controlling the mode of operation, or two controllers, each Ocontrolling a side of the vehicle.

The pump is suitably a fixed displacement hydraulic pump. The I, hydraulic motors are both suitably fixed displacement hydraulic motors but they may obe of different displacements.

oAs stated above, the selective change between the high torque and the low torque conditions may preferably isolate one of the motors of the pair in its own 0 S 10 hydraulic circuit, separate to the hydraulic circuit in fluid communication with the pump. There may be multiple hydraulic circuits provided in the same vehicle and depending upon the number of motors, multiple isolated circuits may be created when a motor is isolated from the hydraulic circuit in fluid communication with the pump.

Generally, the hydraulic motors of the assembly are connected in parallel with the control means interposed between one of the motors and the pump.

Alternatively, the motors may be connected in series, although this configuration is less preferred.

Each hydraulic motor provided in the drive assembly is suitably operable at the discretion of the user in either direction, that is forward and reverse.

In a second form, the invention comprises in a skid-steer mini-loader having hydraulically driven front and rear drive assemblies driven by a fixed displacement hydraulic pump, wherein the vehicle is selectively operable in either one of a first high speed, low torque mode wherein one motor is driven, and a second low speed, high torque mode wherein both motors are driven.

Brief Description of the Drawings.

An embodiment of the invention will be described with reference to the following drawings, in which: Figure 1 is a schematic illustration of a preferred embodiment of the present invention in a low speed, high torque condition.

Figure 2 is a schematic illustration of a preferred embodiment of the present invention in a high speed, low torque condition.

Figure 3 is a schematic illustration of the hydraulic circuit of a preferred embodiment of the present invention.

0 Detailed Description of the Preferred Embodiment.

oAs illustrated in schematic form in Figures 1 and 2, a multi-speed hydraulic drive system is provided. The system illustrated in Figures 1 and 2 is Oparticularly adapted to use in a skid steer vehicle and as such, a multi-speed hydraulic drive system is generally provided on each side of the vehicle in order to provide the O vehicle's skid-steer capability. According to the preferred embodiment of the Oinvention, the multi-speed hydraulic drive system provided on each side of the vehicle owill be identical.

The multi-speed hydraulic drive system includes a fixed displacement 0 S 10 hydraulic pump 20 which is in fluid communication with a first hydraulic motor A directional valve and/or transmission pump (not shown) may suitably be interposed between the pump 20 and the motors to provide directional control.

The first hydraulic motor 10 drives a first axle 11. The first axle 11 has a wheel (not shown) connected to the axle, and the wheel is rotated by the first hydraulic motor The multi-speed hydraulic drive system also includes a second hydraulic motor 12 which is also in fluid communication with the hydraulic pump The second hydraulic motor 12 drives a second axle 13. The second axle 13 has a wheel (not shown) connected to the axle, and the wheel is rotated by the second hydraulic motor 12.

The motors in the hydraulic circuit are of fixed displacement but will generally be of different displacements. For example, in a particularly preferred embodiment of the invention, the first motor is located at the rear of the vehicle, and has a 29 in displacement, and the second motor is located at the front of the vehicle, with a 21 in 3 displacement.

The wheels (not shown) of the vehicle have pneumatic tyres and are encircled by an endless track 15 or similar arrangement for ground engagement. The track 15 also constrains the wheels of the vehicle to rotate at the same speed.

A control valve 14 is interposed in the system between the second hydraulic motor 12 and the hydraulic pump When the hydraulic drive system is operating in a first mode as illustrated in Figure 1, the control valve 14 is open. In the first mode, the second hydraulic motor 12 is in fluid communication with the pump 20. The hydraulic fluid 6 0 o from the pump 20 is split between the two motors 10 and 12 and thereby provides driving force to each of axles 11 and 13. This mode is a low speed, high torque mode.

This mode will typically be used in situations where a higher torque is required such Oas where heavier loads are to be carried or greater forces are applied. It may also be used where a tighter or smaller radius of turn is needed as an increased force can be Itransmitted to the ground surface.

OThe hydraulic drive system also has a second mode in which the control valve 14 is closed, so that the second hydraulic motor 12 is no longer in fluid communication with the pump 20. With the second motor 12 isolated from the pump 0 S 10 20, the first motor 10 will experience an increase in hydraulic fluid velocity or pressure due to the decreased hydraulic volume in the hydraulic circuit. This mode is a high speed, low torque mode (Figure 2) in which only the first (typically rear) hydraulic motor 10 is driven by the pump.

There are therefore two hydraulic circuits present in this mode as illustrated in Figure 2. The second motor 12 in the isolated circuit 22 is rotated by the track 15 and is lubricated as it circulates hydraulic fluid in circuit 22.

In the present specification and claims, the word "comprising" and its derivatives including "comprises" and "comprise" include each of the stated integers but does not exclude the inclusion of one or more further integers.

In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.

Claims (2)

1. 3. A hydraulic drive system according to either claim 1 or claim 2 wherein the front drive assembly and rear drive assembly are linked to thereby constrain the assemblies to rotate at the same speed.
2. 4. A hydraulic drive system according to any one of the preceding claims wherein the multi-speed vehicle is a skid steer vehicle. A skid-steer mini-loader having hydraulically driven front and rear drive assemblies driven by a fixed displacement hydraulic pump, wherein the vehicle is selectively operable in either one of a first high speed, low torque mode wherein one motor is driven, and a second low speed, high torque mode wherein both motors are driven. Dated this 10 th day of December 2004 Jaden Charters Pty Ltd By its patent attorneys CULLEN CO.