Patent Publication Number: US-2004048095-A1

Title: Reinforced aluminum metal composite carrier

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001] This invention generally relates to a carrier in an axle assembly of a motor vehicle. More specifically, this invention relates to a carrier made of aluminum reinforced with ceramic particles installed in the axle assembly of a motor vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002] Most vehicles use at least one gearset to transfer torque between rotating shafts or other components that rotate around different axes. For example, the axle of a rear wheel drive vehicle includes a pinion gear rotating around a generally longitudinal axis and driven by torque from the transmission coupled to a ring gear which rotates around a generally transverse axis and drives torque into the differential. In the case of some four wheel drive vehicles with transverse-mounted engines, a perpendicular axis or skew axis gearset within a power take-off unit is used to transfer torque from the transverse axis of the engine and transmission to the longitudinal axis of a driveshaft  
       [0003] Typically, the carrier that supports the differential case and the gear set is made of magnesium, aluminum or cast iron. The gears themselves are made of steel. Typically, these gearsets are sensitive to changes or inaccuracies in the positions of the gears. Even small deflections can lead to noise and premature gear failure. Since the operating temperatures are relatively high, differences in thermal expansion between the carrier and the gears can lead to such deflections as the temperature of the axle assembly changes. Applications in which the temperature range is expected to be broad must then use in the carrier a material with low thermal expansion, such as cast iron. The use of cast iron makes the axle assembly heavy.  
       [0004] In the present invention, a carrier made of an aluminum reinforced with ceramic particles allows for a lower thermal expansion and for a stable carrier in the axle assembly. Further, the low thermal expansion of the carrier reduces the deflection and prevents noise and premature failure of the gearsets. In addition, the carrier made of aluminum matrix reinforced with ceramic particles is much lighter thereby reducing the overall weight of the motor vehicle. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0005] Further features and advantages of the invention will become apparent from the following discussion and the accompanying drawings in which:  
     [0006]FIG. 1 is a perspective representation of the axle assembly as installed in a motor vehicle in accordance with the teachings of the present invention;  
     [0007]FIG. 2 is an exploded view of the axle assembly having the carrier installed in a motor vehicle in accordance with the teachings of the present invention;  
     [0008]FIG. 3 is a top perspective view of the carrier in accordance with the teachings of the present invention; and  
     [0009]FIGS. 4 a  through  4   c  represent the processes of manufacturing the carrier in accordance with the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0010] The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention or its application or uses.  
     [0011] Referring in particular to the drawings, an axle assembly incorporating the reinforced aluminum carrier of the present invention in accordance with the teachings of the present invention is designated by reference  10 . As shown in FIG. 1, the axle assembly  10  is installed in the under body of a motor vehicle and serves to transmit the power from the engine  12  to the wheels  14 .  
     [0012] As shown in FIG. 2, the axle assembly  10  includes two tubes  16  and a carrier  18 , with the tubes  16  extending from each side of the carrier  18 . The carrier  18  preferably houses a differential case  20 . As shown in FIG. 3, the carrier  18  is preferably formed of a first portion  40  and a second portion  42 . The first portion  40  is made of aluminum with ceramic particles reinforced in the aluminum matrix. The first  40  is preferably coupled to a cover  36 . The cover  36  preferably holds the lubricants inside the carrier  18  and substantially prevents the lubricants from leaking the carrier  18 . It is also preferable that the thermal expansion properties of the first portion  40  are low compared to carrier formed of a pure aluminum or cast iron. The low thermal expansion properties of the carrier  18  will prevent or reduce relative displacement of the carrier with respect to the gears thereby reducing the premature failure of the gears. Further, the low thermal expansion properties of the carrier  18  will ensure that when the carrier  18  is subject to high heat and stress, the cover  36  is not displaced or dislodged from the carrier  18 . The second portion  42  of the carrier  18  is preferably made of unreinforced aluminum or substantially pure aluminum metal or an aluminum alloy. Preferably, the second portion  42  is present in the form of discrete pockets in the first portion  42 . The second portion  42  is capable of being machined, to facilitate assembly of the axle  10  and such that the carrier  18  is capable of being connected to other components in the motor vehicle.  
     [0013] Although in the drawings a rear axle assembly from a non-independent suspension is generally shown and described, it must be understood that this invention is not limited to a carrier having a differential case installed in a rear axle assembly. It incorporates a carrier installed in drive axle assembly either in a front wheel drive, a rear wheel drive or in all wheel drive vehicles. Further, the carrier incorporating a differential case is shown and explained in detail, it must be understood that the carrier  18  may incorporate a power take off unit and have more than one output shafts. In addition, the carrier as described may also be used to support a skew axis gearset installed within a power takeoff unit. In general, the carrier  18  in accordance with the teachings of the present invention may be used to support any gearsets necessary to transfer the torque from the transverse axis of the engine and transmission to the longitudinal axis of the driveshaft.  
     [0014] As shown in FIG. 2 the carrier  18  houses a differential case  20 , a first side gear  22 , a second side gear  24 . The differential case  20  is preferably coupled to an input shaft  30  (shown in FIG. 1), whereas the first side gear  22  and the second side gear  24  are coupled to an output shaft  32 . Typically, the input shaft  30  transmits torque to the carrier  18  from the engine  12  or the transmission (as shown in FIG. 1) and the output shaft  32  transmits torque from the carrier  18  to the wheels  14 . The carrier  18  also supports a ring gear  34  and a pinion gear  26 . The pinion gear  26  transfers the rotational movement of the input shaft  30  into the rotational movement of the ring gear  34  about a perpendicular axis. The ring gear  34  is fixed to the differential case  20 , and transfers rotational motion to the differential case  20 .  
     [0015] The carrier  18  is also adaptable to receive a cover  36 . The cover  36  preferably seals the carrier  18  and substantially prevents lubricants from leaking from the carrier  18 . Additionally, the carrier  18  is adaptable to provide attachment for axle bearings  28  (as shown in FIG. 3). Further, the carrier  18  also includes mounting holes  27  to mount the carrier  18  and the axle housing  16  in the motor vehicle (as shown in FIG. 3). The carrier  18  may include other components such as a second pinion gear, a hydraulic conduit etc. Typically the differential case  20 , the first side gear  22 , the second side gear  24 , the pinion gear  26  and the ring gear  34 , are preferably made with conventional structural material, such as steel, and from conventional method. The cover  36  is preferably made from aluminum or steel.  
     [0016] Referring in particular to FIG. 3, the carrier  18  in accordance with the teachings of this invention is formed of a first portion  40  and a second portion  42 . In the preferred embodiment, the second portion  42  is preferably integral with the first portion  40  such that the physical appearance of the first portion  40  and the second portion  42  are indistinguishable. Although in the drawing the second portion  42  is shown to be separate and distinct from the first portion, it must be understood this is only for illustration purposes.  
     [0017] The first portion  40  of the carrier  18  is formed of aluminum with ceramic particles reinforced in the aluminum matrix. The first portion  40  preferably forms from about 80% to 97% of the weight of the carrier  18 . In order to obtain the desired physical properties of the carrier  18  the total percentage of the ceramic particles are in the range of 10% to 50% of the volume of the first portion  40  and preferably about 20% of the total volume of the first portion  40 . Preferably, the ceramic particles used in forming the first portion  40  of the carrier  18  are selected from the group consisting of silicon carbide or aluminum oxide. In the preferred embodiment, the size of the ceramic particles is preferably in the range of about 4 microns to 30 microns. Preferably, the ceramic particles are in the range of 7 microns to 20 microns. The first portion  40  of the carrier  18  is adapted to receive the cover  36 , such that the cover  36  snugly fits over the opening  35  of the carrier  18 .  
     [0018] The second portion  42  of the carrier  18  is preferably formed of unreinforced aluminum. Preferably, the second portion  42  is formed of an aluminum alloy. Alternatively, the second portion  42  may also be formed of pure aluminum metal. The second portion  42  forms the remaining 20% to 3% of the weight of the carrier  18 . The second portion  42  is preferably located between or encapsulated within the first portion  40 , such that the first portion  40  has pockets of second portion  42 . Alternatively, it also possible that a part of the carrier  18  is formed of the first portion  40  and the remaining part of the carrier  18  is formed of the second portion  42 . In this case, it is preferred that the ceramic particles are uniformly distributed throughout the first portion  40 . As will be explained later, the second portion  42  can be formed by more than one method. Preferably, the second portion  42  is located in regions of the carrier  18  such that the carrier  18  is adapted to be welded or machined at the second portion  42 .  
     [0019]FIGS. 4 a  to  4   c  represent the processes of forming the first portion  40  and the second portion  42  of the carrier  18 . The first process of forming the first portion  40  and the second portion  42  is shown in FIG. 4 a . As shown the process starts at Step S 1 . In this step, the ceramic particles are added to molten aluminum. The process then shifts to step S 2  where unreinforced aluminum consisting of either substantially pure aluminum or an aluminum alloy, in the shape of the second portion  42  are placed in the casting mold or die. Typically the mold or die will have the desired shape of the carrier  18 . As represented in step S 3  the second portion  42  is preferably formed by placing the piece of unreinforced aluminum in the casting mold or die before the mixture of ceramic particles and aluminum is poured or injected into the casting mold or die.  
     [0020] As shown in FIG. 4 b  the carrier  18  may also be formed by mixing ceramic particles into the molten aluminum as disclosed above to form the first portion  40 , shown as step S 1 . Quenching certain surfaces in the casting mold or die, shown as step S 2 , forms the second portion  42 . The quenched surfaces tend to repel particles during the casting process, thereby leaving pockets of unreinforced aluminum in the first portion  40  (shown as step S 3 ). Another method of forming the carrier  18  is shown in FIG. 4 c . In this process at step S 1 , the ceramic particles are bonded together either by sintering to the shape of the first portion  40 , called the pre-form. The pre-form is then inserted into a casting mold or a die, where the casting mold or die is in the shape of the carrier  18 . When the pre-form is inserted in the mold or die, voids are formed in the areas where the pre-form is not present. At step S 3  molten aluminum is then poured or injected into the die, filling in spaces between the areas not otherwise filled by the pre-form.  
     [0021] The first portion  40  of the carrier  18  exhibits the following physical properties: yield strength in the range of 20 ksi to 52 ksi, preferably not less than 42 ksi; elastic modulus in the range of 13.2 to 16.5 Msi, preferably not less than 14.3 Msi; and a thermal expansion coefficient in the range of 6.5 ppm/F to 11.2, preferably not more than 9.7 ppm/F. The table below compares the physical properties of the first portion  40  of the carrier  18  of the present invention with other materials. The Al/SiC materials indicated in the table below are commercially available from Alcan Aluminum under the trade name of DURALCAN. The names indicated in the parenthesis in the table are different grades of DURALCAN that have been used to conduct the experiments. As can be seen from the chart below, the carrier  18  formed from reinforced aluminum (F3S.20S-T6) exhibits superior physical properties, in particular reduced thermal expansion compared to aluminum.  
                                              Thermal           Modulus Expansion Yield                                     Material   (Msi)   (ppm/F)   (ksi)                                                 Aluminum A356-T6   10.9   11.9   29           Aluminum A357-T6   10.9   11.9   36           Al/SiC Composite (F3S.10S-T6)   12.5   11.5   41           Al/SiC Composite (F3S.20S-0)   14.3   9.7   24           Al/SiC Composite (F3S.20S-T6)   14.3   9.7   43           Al/SiC Composite (F3S.20S-T71)   14.3   9.7   31           Cast Iron   22   6.3   40                      
 
     [0022] As any person skilled in the art will recognize from the previous description and from the figures and claims, modifications and changes can be made to the preferred embodiment of the invention without departing from the scope of the invention as defined in the following claims.