Patent Application
20100300776
1. Field of the Invention
The present invention relates to powertrains of work machines, and, more specifically, to integrated braking systems for such machines.
2. Description of the Related Art
For many years, work machines have incorporated brake assemblies within their powertrain and, more specifically, adjacent the torque-carrying shafts spaced from the wheels for such vehicles. Typically, these brake assemblies comprise a series of interdigitated annular plates that are respectively connected to a housing in which they are positioned and to a torque-carrying power shaft. The brake assemblies are activated by an external piston that forces the brake disc plates together to provide a retarding force between the housing and the torque-carrying shaft. Because the friction plates are positioned within the housing, a system for lubricating the plates and for dissipating excess heat must be employed. Typically, such cooling system includes a pump recirculating powertrain lubricant through a heat exchanger and through the friction plates for the unit.
In recent years, there has been an increased emphasis on minimizing parasitic losses within the entire system of a work machine. For such a machine, it has been proposed to vary the amount of coolant and lubricant flowing through the friction plates so as to minimize heat generated by the assembly.
In the past, it has been proposed to control the flow through the friction plates by means of a valve and a control system with logic sensing when the clutch plates are disengaged to minimize the lubricant flow through the assembly. While this is one attempt to minimize the expenditure of energy, it requires a complicated set of hardware and of control logic to achieve the end.
What is needed in the art, therefore, is a cooling system for the brake assembly of a powertrain that minimizes and simplifies the function of reducing lubricant flow during disengaged operation.
In one form, the invention includes a powertrain assembly with an integral brake assembly, the powertrain assembly including a housing and a torque-carrying power shaft. A brake assembly includes interdigitated annular friction plates respectively connected to the housing and to the torque-carrying power shaft. A liquid lubricant and cooling circuit provides liquid between the annular friction plates for distributing liquid between the annular friction plates when the plates are engaged with one another and around and through the annular friction plates when the plates are disengaged as a function of the displacement of said friction plates relative to one another and to said housing for reducing parasitic losses when the brake assembly is not engaged.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one embodiment of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
The housing 24 contains a central housing 26, generally annular in form, which provides a support and journaling for all of the interior elements and right and left extensions 28 for journaling and housing axles 20 and 22. The central housing 26 encompasses a chamber 19 for the differential 18 and provides a sump for lubrication and cooling fluid to be described later.
Each of the axles 20 and 22 are selectively braked by brake assemblies 30 and 32, respectively. Brake assemblies 30 and 32 are substantially identical so that only brake assembly 30 will be discussed to simply the description of the present invention.
Brake assemblies 30 and 32 are a wet plate design so that they are fed with lubricant for cooling and lubricant purposes from a pump (not shown) through passages 34 and 36 in central housing 26, leading to a chamber 38 in which a plurality of interdigitated annular friction plates are positioned. The friction plates are annular plates 42 and 40 respectively secured to the housing 26 and to the shaft 20. Annular plates 42 are connected to the housing 26 by appropriate interconnections (not shown to simplify the understanding of the present invention) that keep the plates 42 from rotating within housing 26 but permit axial movement within chamber 38. Annular friction plates 40 are appropriately connected to torque-carrying power shaft 20 by means of a splined connection on shaft 20 to cause the plates 40 to rotate with shaft 20 but permit limited axial movement with chamber 38. Friction plates 40 and 42 may be formed with appropriate materials and configuration to produce maximum braking effect when engaged while at the same time providing extended service life.
The interdigitated annular friction plates 40 and 42 have annular end plates 44 and 46, also contained within housing 38. Plate 44 is adjacent a wall 48 of chamber 38 and end plate 46 is adjacent an annular pusher plate 50 received within housing extension 28 and displaceable in an axial direction to press against the end plate 46 and cause the friction plates 40, 42, and end plate 44 to engage one another and for end plate 44 to abut wall 48.
Annular pusher plate 50 is received within bores 52 and 54 of housing extension 28, separated by a shoulder 56. Pusher plate has a corresponding shoulder 58 that abuts shoulder 56 when the pusher plate 50 is in its right most position. Appropriate seals 62 seal the chamber and pressurized fluid is introduced to the chamber to expand the axial distance between the shoulders 56 and 58 to move pusher plate 50 in a direction to the left as shown in
The flow of lubricant through port 36 passes from the exterior of the annular friction plates 40 and 42 and through appropriate recesses in the plates (not shown) to flow radially inward to finally exit the pack of friction plates adjacent shaft 20 and into the chamber 19 for differential 18.
In accordance with the present invention, the plates 40 and 42 and corresponding end plates 44 and 46, when in the disengaged position, are displaced so as to provide a gap between end face 48 and the interdigitated friction plates, specifically with end plate 44. This gap permits flow of lubricant from passage 34 and port 36 preferentially through a port 64 extending into the chamber 19 for the differential 18. The flow from port 36 may also flow through the interdigitated friction plates 40 and 42 to exit into the chamber for differential 18 adjacent shaft 20, but the path of least resistance is from port 36, past end plate 44 through port 64. This preferential path during disengagement of the brake assembly 30 greatly minimizes the parasitic pumping losses when the brake assemblies are disengaged. It has been found that a gap of at least as small as approximately 1 mm between end wall 48 and end plate 44 produces enhanced flow conditions for minimizing parasitic losses.
The mechanism in
Referring to
The arrangement described above permits an extremely simplified and effective way in which lubricant can be bypassed around a brake assembly during disengagement so as to significantly minimize the parasitic losses caused by pumping fluid to a high pressure and passing it through the flow resistance of abutting friction plates. This function is achieved without the need for complicated valve control and control logic to determine when the brakes are engaged or disengaged. As such, the reliability of this system is enhanced significantly relative to prior art devices and, at the same time, reduces cost of the overall system.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
