Motor vehicles – Power – Including traction motor of kind driven by noncompressible...
Reexamination Certificate
1997-06-27
2001-08-07
Vanaman, Frank (Department: 3611)
Motor vehicles
Power
Including traction motor of kind driven by noncompressible...
C180S212000
Reexamination Certificate
active
06269901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydraulic drive system for three wheeled vehicles.
Typically such three wheeled vehicles have three independent wheel drive shaft assemblies in an essentially triangular configuration namely one transversely in-line pair of drive shaft assemblies and a single wheel drive shaft assembly longitudinally spaced from the in-line pair. While there may be more than one wheel on each drive shaft whether side by side or spaced some distance apart such arrangements are still considered as three wheeled vehicles; the shafts and wheels being considered to be one wheel. Generally speaking the hydraulic drive system comprises a hydraulic pump and a drive unit directly coupled to each of the drive shaft assemblies namely a single drive unit and a pair of transverse drive units.
The invention is particularly directed to hydraulic drive systems for forklift trucks and the like vehicles and in particular for forklift trucks such as are sold under our Trade Mark MOUNTY which can be carried from site to site on the back of vehicles, in what is known as a “piggy back” fashion.
2. Background Information
Our Irish Patent No. 65, 047 discloses a forklift truck having a hydraulic fluid supply divider for controlling the supply of hydraulic fluid delivered between an hydraulic pump and the front and rear wheel drive motors of the forklift truck. Essentially in this system the front wheel drive motors form the in-line pair of drive units and the rear wheel drive motor forms the single drive unit. This hydraulic drive system ensures positive drive to all wheels such as desirable in many off-road situations for example on building sites. In operation, the fluid delivery from the pump is split by a fluid divider between the front and rear wheels of the forklift truck. This fluid divider works well and is effective. In some conditions, it is difficult to ensure exactly the same fluid supply to each of the wheels and some slippage can occur.
For example a somewhat similar system is described in U.S. Pat. No. 5,201,570 which describes what is suggested is a wheeled vehicle equipped with a simple and efficient anti-skid system for its wheels where restriction is placed on the supply conduit of each hydraulic motor coupled to the rear wheels and a restriction is placed on the exhaust conduit of each motor coupled to the front wheels. This while reasonably effective does not overcome the basic problems in operating such vehicles and this U.S. patent together with our Irish Patent Specification No. 65, 047 describe one particular way of solving this problem.
Many other elaborate systems of control and operation of hydraulic drive systems have been devised and the inventions of U.S. Pat. Nos. 3,952,511, 4,236,595 and 4,635,743 typify the complex and costly arrangements.
European Patent Specification No. 547, 947 describes an arrangement of an hydraulic drive system for a three wheel vehicle. In this hydraulic drive system there is the single drive unit formed from a drive provided by one hydraulic motor and the transverse drive units are provided by what are in effect two hydraulic motors. In fact the hydraulic motors are not separate hydraulic motors but indeed are the one hydraulic motor. Such hydraulic motors are generally of the radial piston type where all of the cylinders can be fed periodically with fluid under pressure or else the feed of the fluid under pressure can be interrupted to some or all of the pistons which correspond to an intermediate capacity. Still further the cylinders can be separated to effectively form two separate motors a good example of this is described in U.K. Patent Specification No. 2,281,944.
In the hydraulic system of European Patent Specification No. 547,947 the single drive unit as mentioned above is formed from one hydraulic motor and the in-line drive units are provided by two hydraulic motors such as those described in U.K. Patent Specification No. 2,281,944. In this hydraulic system the hydraulic pump feeds one of the drives forming each of the transverse drive units through a shut off valve and also feed directly the single drive unit namely the single hydraulic motor. The single hydraulic motor in turn feeds the other drives of the transverse drive units and all the outputs of the transverse drive units are fed directly back to the hydraulic pump. There is a permanent series arrangement of the drives.
This while a relatively efficient arrangement does not overcome all the problems inherent in the use of hydraulic motors with three wheeled vehicles and in particular with three wheeled vehicles such as forklift trucks and in particular forklift trucks of the “piggy back” type which forklift trucks have relatively short wheel bases: thus, any variations between torques or speed applied to any of the wheels causes considerable difficulties in operation. Indeed an arrangement such as described in this European Patent Specification No. 547,947 does not operate particularly efficiently with such hydraulic drive systems and indeed requires an elaborate steering system to compensate for the turning of the vehicle and to prevent slippage between the various drive wheels. While it is an efficient system it is still somewhat complicated and causes difficulties in use.
OBJECTS
The present invention is directed towards overcoming the problems inherent in the use of hydraulic motors with three wheeled vehicles and in particular with three wheeled vehicles such as forklift trucks which are mounted on the rear of truck or trailer bodies in “piggy back” fashion.
SUMMARY OF THE INVENTION
According to the invention there is provided a hydraulic drive system for a vehicle having three independent wheel drive shaft assemblies in an essentially triangular configuration namely a transversely in-line pair of drive shaft assemblies and a single wheel drive shaft assembly longitudinally spaced from the in-line pair of drive shaft assemblies comprising:
a hydraulic pump;
a single drive unit, forming part of the single wheel drive shaft assembly;
at least a pair of mechanically coupled drives each having separate hydraulic input and output and forming the single drive unit;
a pair of transverse drive units forming part of the transversely in-line pair of drive shaft assemblies;
two sets of at least a pair of mechanically coupled drives each having separate hydraulic input and output each set forming one of the pairs of transverse drive units;
hydraulic fluid pipelines connecting the drive units to the hydraulic pump and to each other; and
valving in the hydraulic fluid pipelines to control the flow of hydraulic fluid between the individual drives and each other and the pump so as to operate the drive units in series or parallel.
The main advantage of this system is that it eliminates all the difficulties of skidding, wheel spin and the like: because of the arrangement there will always be sufficient torque transmitted to those wheels which are not slipping or tending to slip. By using a series arrangement a simple and effective drive system is provided. Ideally there are two separate drives in each drive unit. This particular configuration is extremely effective in that it allows different speeds to be provided and in particular when operating in parallel the hydraulic system allows the forklift truck for example to be driven at sufficient speed over good ground.
Ideally each drive unit comprises a pair of drives. This is a particularly simple construction.
Ideally in this latter embodiment each drive unit is a hydraulic motor which comprises:
a plurality of cylinders housing pistons;
input ports defining an input for each drive;
a separate supply line connecting each input port with a number of cylinders;
an output port defining an output for each drive; and
a return line connecting all the cylinders to the output port.
Further the invention comprises a hydraulic system in which each drive unit is a hydraulic motor which comprises:
a pair of input ports defining an input for each drive;
an even number of cylinders of
Cadden Thomas
Harte Gerard
McAdam James
McHugh Gerard
McVicar Martin
Jacobson & Holman PLLC
Moffett Research and Development Limited
Vanaman Frank
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