The present invention relates generally to a disk brake system in a moving vehicle. More specifically, it relates to a hydraulic disk brake retractor system.
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 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 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. Ideally, a very small running clearance between brake disks is desired to allow for fast brake engagement and a short pedal throw. However, if the clearance is too small, windage effect 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.
In most of today's brake system design, there is usually a compromise between having as much running clearance as possible to reduce drag, and improve system efficiency, while at the same time, keeping this running clearance small to meet manual braking stopping distance versus time requirement per regulation.
To minimize windage loss through brake disks, it is therefore desirable to maximize the running clearance between brake disks. Alternatively, it is also desirable to minimize running clearance between brake disks in order to maximize braking performance, especially in the power-down condition, where hydraulic power to brake valve is lost, and the operator must make an emergency brake stop with only the limited available flow volume from the brake valve.
For the reasons listed above, it has been a challenge for the industry to provide a brake design with more running clearance for improved efficiency, and yet, still be able to meet the regulated requirement for manual brake stopping distance versus time.
In light of the above background information, an improved spring-loaded brake retractor system is proposed. This spring-loaded brake retractor system uses the system's hydraulic power to retract the brake piston to provide desired running clearance between disks. In the power-down condition, the spring will provide the force to position the brake piston against brake disk pack to eliminate the piston “travel” that is normally required to bring brake piston and brake disks to a near contact position.
The proposed invention improves brake system efficiency by allowing increased running clearance between brake disks. Additionally, the invention minimizes the distance the piston has to travel, and the corresponding volume of oil required from brake valve, to engage the brake in power-down condition.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
In general, the present invention is directed to a spring-loaded brake retractor system 36,
Reference is made to
As shown in
As shown in
When brake is deenergized, as shown in
The actual running clearance of the brake assembly 10 equals the distance the brake piston 20 must travel in order to clamp the at least first and second friction disks 26 equal to the sum of the running clearances 30. The desired running clearance is based on various factors including at least a first and second friction disk 26, separator plates 28, the required response time of the brake assembly 10, the brake retractor system 36 and the cooling requirements for a particular application. In addition, windage effects may generate additional heat and prevent sufficient hydraulic pressure from flowing between the at least first and second friction disks 26. These factors may cause damage to brake assembly 10 having very small running clearance 30. Thus, running clearance 30 utilizing a brake retractor system 36 eliminates the risk of the damage, while still keeping the response time and pedal throw to a minimum.
The invention is carried out when the system 36 is in a power on condition, pressurized hydraulic pressure or fluid in a passage 24 to cavity 54 is used to retract the brake piston 20 in a second direction opposite the first, and apply a disengagement force against a brake spring 22. This retraction then provides a desired running clearance 30 between disks 26 and separator plate 28,
In the power down condition, as shown in
This invention is being shown and claimed with one brake retractor. However, a preferred alternative embodiment can be designed to accommodate three brake retractors. The three brake retractors are positioned on the outer edge of the brake piston. By locating the brake retractors on the outer edge of the brake piston, the entire system has a tendency to be more balanced than a system that positions its brake retractors near the center of axis of the brake piston. Passage 60 is used to supply oil pressure to all three brake retractors. Additionally, the further away each brake retractor is from the center of axis of the brake piston the more torque carrying capacity.
As the person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles of 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.