Abstract:
A permeameter including a fluid control chamber, a permeability specimen area, and a first outlet from the specimen area measuring fluid as a function of a normal permeability of at least one specimen in the specimen area and a second outlet from the specimen area receiving and measuring further fluid as a function of a radial permeability of the at least one specimen in the specimen area.

Description:
Priority to U.S. Provisional Patent Application Ser. No. 61/003,106, filed Nov. 14, 2007, is claimed, the entire disclosure of which is hereby incorporated by reference herein. 
    
    
     The present invention relates generally to the permeability measurements of wet friction materials for wet clutch applications. 
     BACKGROUND 
     U.S. Pat. No. 6,655,192, hereby incorporated by reference herein, describes a permeameter providing both normal and lateral permeability measurements on porous materials. The prior art permeameter has a base, a fluid chamber housing and a compression ring. The base has a recess. The recess is defined by a transverse wall and a cylindrical upper sidewall. The fluid chamber housing has an upper axially extending tubular section and an enlarged lower section. A piston is positioned within the upper tubular section which is axially moveable within the upper tubular section. A seal is provided between the head of the piston and the upper tubular section with an o-ring. 
     SUMMARY OF THE INVENTION 
     An object of the present invention provides a permeameter including a fluid control chamber, a permeability specimen area, and a first outlet from the specimen area measuring fluid as a function of a normal permeability of at least one specimen in the specimen area and a second outlet from the specimen area receiving and measuring further fluid as a function of a radial permeability of the at least one specimen in the specimen area. 
     An object of the present invention includes the simultaneous measurement of normal permeability and lateral permeability of porous materials with equal flow path and equal cross-sectional flow area in each test direction with the same test fluid using a stand alone permeameter with constant compression force on the test specimen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  illustrates one embodiment of a permeameter according to the present invention. 
         FIG. 2  illustrates a perspective view of the present invention. 
         FIG. 3  illustrates a geometrically optimized disk and ring specimen used in a permeameter of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Fluid flow through a porous media can be measured using a permeameter. However, the pore structure of paper based wet friction materials is anisotropic, hence permeability depends on the direction in which fluid flows through the material. The liquid permeability of wet friction materials needs to be measured in normal and radial directions with oil. The normal and radial permeability measurements are done sequentially in the current state of the art. Comparison of normal and radial permeability measurements with sequential measurements is inadvertently affected by the change in room temperature which affects the viscosity of fluid and by the repeatability of the loading mechanism of the test machine from test to test in the current state of the art. 
     The fluid flow paths through a normal permeability test specimen and a radial permeability test specimen are not equal in the current state of the art. Typically, the flow path is 10 to 20 times shorter in a normal permeability test than in a radial permeability test in the current state of the art. Therefore a radial permeability test lasts 10 to 20 times longer than a normal permeability test when the tests are run with the same fluid. In order to shorten the test time, radial permeability tests are typically run with water (low viscosity fluids) while normal permeability tests are run with oil (high viscosity fluid) in the current state of the art with an assumption that permeability measurements will not be affected by the chemistry of fluids, which may not always be true. 
     The specimens cross sectional area perpendicular to the fluid flow is also different in the normal permeability test and in the radial permeability test in the current state of the art. Cross sectional area is 8.6 times larger in the normal permeability test than in the radial permeability tests in the current state of the art. Hence, normal permeability test results are averaged over a larger area than the radial permeability test results in the current state of the art causing different levels of accuracies in each measurement due to the inherent inhomogeneity of most wet friction materials. 
     Comparison of normal and radial permeability values becomes difficult if the measurements are done at two different lengths of flow path, on two different cross sectional areas and two different fluid systems in the current state of the art. 
     Furthermore, the current state of the art is not a stand alone unit and requires a universal testing machine to compress the test specimen and to force the fluid flow through the specimen. Compression of the test specimen and compression of the test fluid are done sequentially with increased test setup time and added complexity. The current state of the art performs compression of the test specimen as follows: after the test specimen is compressed by the apply shaft of the universal test machine, the compression displacement is fixed by a compression ring and the apply shaft of the universal test machine is freed for the next task which is compression of the test fluid. However, due to viscoelasticity, the test specimen goes through relaxation, meaning that the compression force does not stay constant while the compression displacement stays constant on the test specimen. The universal testing machines are typically much more expensive than the permeameter itself and require a substantial capital investment. 
       FIG. 1  shows one embodiment of a permeameter according to the present invention. Permeameter  100  has a holey block  50  and a fluid chamber  52  with a piston  32 . Fluid chamber  52  supplies pressurized test fluid for both the normal and radial permeability measurements simultaneously. Piston  32  is enclosed by a cylinder and upper platen  34 . Mounted on cylinder and upper platen  34  is a bearing  30 . Attached to bearing  30  is a diaphragm spring  36 . Diaphragm spring  36  and a frictionless loading mechanism provide constant compression force to normal and radial test specimens simultaneously. Spring  36  may be a Belleville spring. Attached to holey block  50  is an outlet  46  used to drain the fluid into a graduated cylinder or flowmeter  58  to measure the normal fluid flow. An outlet  44  is attached to another graduated cylinder or flowmeter  60  used to measure the radial fluid flow independently of the normal fluid flow. Connected to fluid chamber  52  is a plug  56 . In between fluid chamber  52  and holey block  48  are a ring  62  and a disk  54 . In between ring  62  and disk  54  is a seal  48 , which separates the normal permeability test specimen compartment from the radial permeability test specimen compartment. Cylinder and upper platen  34  is connected to a lower platen  42  by a cap  38 . In between cylinder and upper platen  34  and lower platen  42  can be an o-ring seal groove. Handles  40  are engaged to cap  38 . 
     Permeameter  100  also can have on/off valves  64 ,  66 , for example, enabling the running of the normal and radial permeability tests individually. If both valves are open, simultaneous testing can occur. If valve  64  is closed and  66  open, a normal test can be run individually. If valve  64  is open and  66  closed, the radial test may be run individually. On/off valves and/or seals can also be located so that the normal and radial permeability tests can be run on the same disk specimen sequentially. Attachments may be added to the permeameter to measure the Joseph and Beaver slip coefficients of the porous test specimen. 
     Permeameter  100  can also be configured without piston  32  and piston cylinder  34 . A pressurized oil source can be used to introduce fluid into the fluid chamber, in place of the piston and piston cylinder, with all other aspects of the apparatus remaining the same. 
       FIG. 2  shows the enlarged view of the present invention. Piston  32  is enclosed by cylinder and upper platen  34  and deadweight  68 . Deadweight  68  loads integrated with piston  32  of the stand alone permeameter to apply constant pressure on the test fluid. At the end of piston  32  is fluid chamber  52 . Below fluid chamber  52  are disk  54  and ring  62 . Mounted on cylinder and upper platen  34  are bearings  30 . Attached to bearing  30  is diaphragm spring  36 . Cylinder and upper platen  34  connects with cylinder and lower platen  42  via cap  38 . Engaged with cap  38  are handles  40 . Permeameter  100  is mounted via mounting  70 . 
       FIG. 3  shows a perspective view of a geometrically optimized ring and disk specimen used in the permeameter according to the present invention. Ring  62  surrounds disk  54 . r 1  is the radius of disk  54  and r 2  is the inner radius of ring  62 . Geometrically optimized disk  54  and ring  62  test specimens can be comparable if the following relations are satisfied:
 
A1=A2  (1)
 
L1=L2  (2)
 
r1&lt;r2  (3)
 
     where A is the specimen area perpendicular to the fluid flow. L 1  is the thickness of disk  54  and ring  62  and L 2  is the width of annulus of ring  62 . 
     For example, assuming the friction material is 1 mm thick and the width of the annulus of ring  62  is 5 mm. Then if 5 layers of material are stacked in for disk  54  and ring  62  in one test, the equation (2) is satisfied:
 
L1=L2=5 mm
 
     Equation (2) requires:
 
π* r 1 2 =2 *π*r 2* L 1
 
     Since L 1 =5 mm
 
 r 1 *r 1=10* r 2
 
     Finally, the inequality of (3) provides final dimensions: 
     if r 1 =15 mm, then r 2 =22.5 mm 
     or if r 1 =17 mm, then r 2 =28.9 mm, etc. 
     In the above example, disk  54  and ring  62  specimens are created by stacking up 5 layers of 1 mm thick friction material. If the thickness of one layer of friction material is 5 mm, then only one layer of material is needed to make disk  54  and ring  62  specimens. In the above example, the dimensions were selected to be reasonable with the current state of manufacturing processes. However, the dimensions of disk  54  and ring  62  specimens are not limited to the dimensions used in the example, provided the mathematical relationships are used. 
     Interactions of normal and radial permeability of wet friction materials affect the friction performance of wet friction materials. Formulation and development of superior wet friction materials is possible if the normal and radial permeability are measured simultaneously. Simultaneous measurement of normal and radial permeability values with the same test fluid is needed for accurate comparison of normal and radial permeability of wet friction materials. A stand alone permeameter with dead weights negates the need for a universal testing machine to actuate the permeameter and provides an economical solution. Hence, the current invention provides a unique solution to simultaneous measurement of normal and radial permeability. Furthermore, the application of simultaneous normal and radial liquid permeametry is not limited to wet friction material but can be applied to any porous materials which have three dimensional structural integrity.