Patent Application
20080116019
1. Field of the Invention
The present invention generally relates to a brake assembly for a motor vehicle. More specifically, it relates to a device that provides running clearances in the brake disks used in the brake assembly of an agricultural vehicle, such as a tractor.
2. Description of Related Technology
Brake assemblies are generally used to stop the movement of motor vehicles, such as an agricultural tractor. As shown in U.S. Pat. No. 6,002,976, the driveline of a typical agricultural tractor, for example a tractor in the John Deere 6000 series, includes an engine, a shifted multi-speed transmission, a reversing unit, a drive clutch, an optional creeper transmission, a shifted range transmission, and a rear axle differential gear which the drives the rear wheels. As shown in U.S. Pat. No. 5,197,574, a brake may also be provided between the transmission housing and the rear axle differential gear. Due to the low operating speeds, large mass and high torque under which agricultural tractors operate, these brakes are often configured so the brake disks are submerged in oil. The oil serves to lubricate and carry heat away from the brake disks when the brakes are applied by a tractor operator.
When the brakes are initially assembled, an optimal running clearance is set between a brake piston, the brake disks, separator plates (if applicable) and a brake cover. The optimal running clearance is carefully calibrated, depending on the geometry of a particular application, to minimize the response time and pedal throw required to engage the brake piston against the brake disks, while also minimizing the effects of windage (the frictional force acting on the oil caused by the relative motion of the brake disks to the brake piston separator plates and cover).
Ideally, a very small running clearance is desired to allow for fast brake engagement and a short pedal throw. However, if the clearance is too small, windage effects may prevent sufficient oil flow between the braking surfaces, interfering with the lubrication and cooling of the brake disks. In addition, the small amount of oil between the braking surfaces may become entrapped. As a result, even when the brake is not engaged, significant heat may be generated between the braking surfaces and the entrapped oil, causing damage to the brake assembly.
Once the optimal clearance has been established for a particular application, it is desirable to maintain that clearance over the lifetime of the components. However, as the brakes are applied during operation of the tractor, the braking surfaces of the brake disks, brake piston, brake cover and separator plates (if applicable) experience wear. After a number of hours of operation, which varies from application to application, the wear may result in an actual running clearance significantly greater than the optimal clearance. This has the undesirable effect of increasing both the response time and pedal throw of the brake assembly. Currently, any increased running clearance is periodically compensated for by manually adjusting the brake assembly. This is a time consuming process, however, and increases the maintenance costs of the vehicle. In addition, there is the risk that the running clearance may be incorrectly adjusted.
In view of the above, it is apparent that there exists a need for a brake assembly for a motor vehicle that that automatically adjusts the running clearance of the brake discs to compensate for wear of the braking surfaces.
In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, the present invention provides a brake assembly that maintains an optimal running clearance between braking surfaces of the assembly, without the need for periodic manual adjustment. This is accomplished by providing at least one bolt includes a sleeve coaxially installed with a slip fit around a head of the bolt. A spring, bearing against the brake cover, acts to bias the sleeve against a shoulder of the bolt head and acts to return a brake piston to a start position when the brake is disengaged. The sleeve is installed using a frictional press fit within a bore in the brake piston. The brake piston is actuated hydraulically by pressurized brake fluid applied against a brake piston area. The pressurized brake fluid causes the piston assembly to move axially, closing the running clearance, and engaging the braking surfaces of the assembly.
When the brake is engaged the sleeve translates with the brake piston and the bolt head slides within the sleeve a distance equal to the running clearance of the brake assembly. When the actual running clearance is equal to the optimal running clearance, the bolt head will just come into contact with a retainer ring as the brake piston engages the braking surfaces. If the running clearance exceeds the optimal running clearance, the bolt head will contact the retainer before the piston engages the braking surfaces. In this case, the sleeve stops moving while the hydraulic fluid continues to move the brake piston. Since the hydraulic force exceeds the frictional fit of the sleeve, the sleeve will slip slightly within the bore and compensate for the increased running clearance by repositioning the brake piston so the actual running clearance equals the optimal running clearance.
Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification.
Referring now to the drawings,
The actuation system 34 may be any conventional system including, but not limited to, hydraulic, pneumatic, or electrical systems. The present embodiment presumes a hydraulic system. When the actuation system 34 is activated, for example by an operator depressing a brake pedal (not shown), pressurized hydraulic fluid is provided to a brake piston area 36. The fluid is contained within the brake piston area 36 by o-rings 38 and applies a brake engagement force to the brake piston 18 causing it to move axially and engage the brake disk 22. When the actuation system 34 is deactivated, the hydraulic fluid is depressurized and at least one spring 42 returns the brake piston 18 to its initial position, disengaging it from the brake disk 22.
The brake disk 22 may be coupled to the rotating shaft 20 by means of a disk spline 23, or a similar arrangement, that allows the brake disk 22 to float axially along the shaft while still transferring torque between the disk 22 and the shaft 20. In the present example, the rotating shaft 20 is further coupled to wheels of the motor vehicle (not shown) by, for example, a differential and to an engine by, for example, a transmission. When the vehicle (not shown) is in operation, the brake disk 22, being coupled to the rotating shaft 20, rotate within the friction chamber 16. Stopping the rotation of the brake disk 22 stops rotation of the shaft 20 and, accordingly, stops rotation of the wheels and brings the vehicle to a halt. This is but one exemplary use of the brake assembly 10. Another example may locate two brake assemblies 10 between the differential and the wheels.
Turning to
Referring to
While the above description is one embodiment, the number of brake disks 22 may vary significantly between applications. Depending on the weight and performance of a particular tractor it may have as few as one brake disk 22 (see
The actual running clearance of the brake assembly 10 equals the distance the brake piston 18 must travel in order to clamp the brake disks 22 equal to the sum of the running clearances 24a, 24b, 24c, and 24d. (See
The brake piston 18 is coupled to the brake cover 14 by at least one bolt 40, with an exemplary embodiment using three bolts 40. As best shown in
The sleeve 44 is dimensioned to be substantially restrained from radial movement around the bolt head 46, while permitting axial motion along the length of the bolt 40. The amount of axial motion is determined by the axial separation between the retainer 48 and the shoulder 50, wherein the axial separation exceeds the axial height of the bolt head 46 by an amount equal to an optimal running clearance, as reflected by a gap 52 shown in
The optimal running clearance is calculated based on various factors including the number of brake disks 22, separator plates 26, the required response time of the brake assembly 10, the brake pedal throw (not shown) of the actuation system 34 and the cooling requirements for a particular application. Since most applications desire a quick response time and a short pedal throw, it is desirable for the gap 52 to be as small as possible. However, at a certain point gap 52 will be too small and incidental contact may result between the brake disks 22, brake cover 14, brake piston 18, and the separator plates 26 when the brake is not engaged due to the tolerance stack up between these components. In addition, windage effects may generate additional heat and prevent sufficient cooling oil from flowing between the brake disks 22. These factors may cause damage to brake assemblies 10 having very small running clearances 24. Thus, the optimal running clearance is calculated to eliminate the risk of damage, while still keeping the response time and pedal throw to a minimum.
In a brake assembly 10 experiencing little or no wear, the gap 52 equals the actual running clearance and the brake piston 18 will fully engage the brake disks 22, stopping their rotation. On the other hand, when the braking surfaces 28 and 30 of the brake disks 22, along with the opposing surfaces of the brake cover 14, the brake piston 18 and separator plates 26, experience wear from operation, the running clearances 24 will increase. This undesirably increases the response time and pedal throw required to engage the brake assembly 10.
As constructed, the frictional fit between the sleeve 44 and the brake piston 18 allows the brake assembly 10 to compensate for such wear. As can be seen in
As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.
