Wheel substitutes for land vehicles – With means for tensioning track by moving at least one endwheel – Having hydraulic adjusting means
Reexamination Certificate
1998-03-20
2001-05-01
Morano, S. Joseph (Department: 3612)
Wheel substitutes for land vehicles
With means for tensioning track by moving at least one endwheel
Having hydraulic adjusting means
C305S143000
Reexamination Certificate
active
06224172
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a tensioning device for maintaining the proper tension on the track of a flexible belt driven vehicle.
BACKGROUND OF THE INVENTION
Flexible tracked vehicles are generally well known in the art, and are well-suited for many applications in which more conventional wheeled vehicles are unsatisfactory. For example, conventional wheeled vehicles traditionally do not have enough traction to operate in and around most construction sites, and thus a tracked vehicle, which spreads its load over a much greater area, is much more capable of traversing the rough and often muddy terrain at such construction sites. Bulldozers and certain types of paving machines are two examples of commonly used flexible tracked vehicles.
Most heavy tracked vehicles, such as bulldozers, use a flexible metal belt made go of a plurality of connected links, and are driven by a positive drive system in which a drive wheel engages teeth or cogs on the inside of the metal belt. On the other hand, many lighter duty flexible tracked vehicles use a flexible continuous rubber track incorporating a friction drive system. In contrast to a positive drive system, a friction drive system relies on the friction between the drive wheel and the track or belt in order to transmit motive force to the belt and hence the ground. The flexible track extends between a drive wheel and a free wheel, and an idler assembly is used to apply pressure to the free wheel in order to maintain the proper tension on the drive belt. The free wheel is slidably or adjustably mounted in a carriage assembly, and a compression spring or a gas charged cylinder applies outward force to the carriage assembly, thereby applying tension to the belt.
On friction drive systems, proper belt tension is critical to the operation of the vehicle. Unfortunately, when the drive system of the vehicle is reversed, the force applied against the free wheel, and hence the idler assembly, increases significantly. In such a state, a much greater force is required in order to maintain the proper belt tension. If not enough force is applied to the idler assembly and the belt tension decreases significantly, the carriage assembly and the free wheel will be drawn toward the drive wheel, and the belt will begin to bunch and/or slip. In some instances, the belt may even become untracked.
Consequently, the typical approach is to maintain a high level of force against the carriage assembly at all times. Unfortunately, this approach significantly increases the load on the drive components of the vehicle during normal forward operation. Many system components are thus subjected to increased wear and tear, which leads to premature system failure. Accordingly, there exists a need for an improved tensioning device or idler assembly that will automatically adjust to different operating conditions in order to prolong the life of the drive system and its components.
SUMMARY OF THE INVENTION
The present invention uses a two sided hydraulic cylinder connected to a control circuit to control the amount of force exerted by the hydraulic cylinder against a carriage supporting the free wheel of the tracked vehicle. During normal forward operating conditions, when the required force on the carriage is low, both sides of the hydraulic cylinder are charged and the cylinder exerts a constant force against the carriage. When the vehicle is shifted to reverse, the required force against the carriage increases significantly. Accordingly, a valve drains the second side of the hydraulic cylinder, while the force exerted against the first side of the cylinder remains essentially constant. Thus, the force against the carriage increases to the required level. An accumulator helps to maintain adequate pressure on the first side of the hydraulic cylinder.
According to one aspect of the invention, a tensioning device for dynamically adjusting the belt tension on a tracked vehicle includes a drive wheel mounted to a frame, a carriage slidably mounted to the frame and supporting a free wheel, a hydraulic cylinder mounted to the frame and engaging the carriage for applying a force to the carriage, a hydraulic circuit operatively connected to the hydraulic cylinder, and a sensor, a detector, or other similar devices for detecting the operating condition of the vehicle. The control circuit is adapted to adjust the pressure in the hydraulic cylinder to apply a first force against the carriage in response to a first detected condition, such as a forward drive condition, and is further adapted to apply a second, greater force against the carriage in response to a second detected condition, such as reverse, in order to maintain proper belt tension. A sensor is provided for detecting the operating condition of the vehicle and is operatively connected to the hydraulic circuit.
Preferably, the hydraulic cylinder is a two sided double acting cylinder, and an accumulator maintains a constant pressure against a first side of the hydraulic cylinder. The hydraulic circuit includes a valve operatively connected to a second side of the hydraulic cylinder, and the valve is shiftable between a pressurizing position for charging the second side in response to the first detected condition, such as a forward condition, and a drain position draining the second side in response to the second detected condition, such as reverse. Accordingly, during normal forward operation of the vehicle, the forces on the two sides of the cylinder are essentially balanced. When the vehicle is shifted to reverse, the force on the second side of the cylinder is dropped significantly by virtue of the valve shifting to a drain position, while the accumulator maintains a constant force on the first side of the cylinder. Accordingly, a greater force is applied against the carriage and additional belt tension is applied to counteract the increased tension demands of the reverse condition. A check valve is provided for maintaining the pressure in the accumulator and hence the force against the carriage, at a predetermined level.
According to another aspect of the invention, an idler device for a tracked vehicle having a flexible drive belt includes a drive wheel mounted to a frame, a carriage slidably mounted to the frame and supporting a free wheel, and a hydraulic cylinder mounted to the frame and engaging the carriage for applying a force to the carriage. A hydraulic control circuit controls the operation of the hydraulic cylinder. The control circuit includes a sensor, and is adapted to adjust the pressure in the hydraulic cylinder to thereby apply a first force against the carriage in response to the detection of a first condition, and further to apply a second force against the carriage in response to the detection of a second condition.
According to yet another aspect of the invention, a tensioning device for adjusting the tension on the drive belt of a tracked vehicle having a frame, a drive wheel mounted to the frame, and a free wheel mounted to a carriage and slidably supported on the frame, includes a sensor for detecting the operating condition of the vehicle and an idler assembly mounted to the frame. The idler assembly is positioned to apply a force to the carriage. A controller, such as a control valve, serves to control the force applied by the idler assembly against the carriage, whereby a first force is applied against the carriage in response to the detection of a first condition and a second, greater force is applied against the carriage in response to the detection of the second condition.
Further objects, features and advantages of the present invention will become readily apparent to those skilled in the art upon a reading of the following description and the appended claims.
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patent: 5316381 (1994-05-01), Isaacson et al.
patent: 5334106 (1994-08-01), Purcell
Bellinger Jason P.
Cedarapids
Marshall O'Toole Gerstein Murray & Borun
Morano S. Joseph
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