Patent Publication Number: US-2018051786-A1

Title: Automated Differential Locking System

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit to U.S. Provisional Patent Application No. 62/377,862 filed on Aug. 22, 2016, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to an automated differential locking system for use in a motor vehicle. 
     BACKGROUND OF THE DISCLOSURE 
     A locking differential is a variation of a standard automotive differential (or open differential) which enables a vehicle to experience an increase in traction in comparison to the standard differential. This increase in vehicle traction is achieved by locking the wheels on an axle system together. By locking the wheels on the axle system together, the differential is prevented from allowing a differential action to occur. As a result, the wheels of the axle system of act as if they are mounted on a common shaft thereby restricting the wheels of the axle system to have the same rotational speed. In order to lock the differential(s) found in one or more axle assemblies of the vehicle, such as but not limited to tandem axle assemblies, the differential(s) may be fitted with a differential locking system that is able to selectively lock (engage) and unlock (disengage) the differential as needed. 
     One of the problems with incorporating the differential locking system into a vehicle is the availability of hardware resources within the existing infrastructure of the vehicle. Most vehicles have maxed out all of their available i/o pins (inputs and outputs) in the engine control unit making it hard to incorporate differential locking systems into the axle system(s) of the vehicle. Even though the complexity of the software needed to operate the differential locking system is low enough to be controlled by the engine control unit of the vehicle, there is typically not enough i/o pins (inputs and/or outputs) available that can be dedicated to the control of the differential locking system. As a result, additional components need to be added to the vehicle to be able to control the differential locking system. This increases the overall costs associated with the drive axle system of the vehicle. It would therefore be advantageous to develop a differential locking system that was able to engage and disengage a vehicle differential using the existing infrastructure that is already available in the vehicle. 
     Additionally, it is understood that automated differential locking systems are particularly useful in tandem rear axle vehicles (herein after referred to as “tandem axle vehicles”). Tandem axle vehicles driven in a 6×2 driving mode typically have a lower traction capability but have a higher fuel efficiency than tandem axle vehicles driven in a 6×4 driving mode. It would therefore also be advantageous to develop an automated differential locking system for a tandem axle vehicle that can be used to selectively transition the vehicle between the 6×2 and the 6×4 driving modes. 
     Furthermore, it would be advantageous to develop an automated differential locking system that is scalable and able to be used in a wide variety of vehicles and applications. 
     SUMMARY OF THE DISCLOSURE 
     An automated differential locking system. The system includes a differential locking system sliding collar that is selectively engageable with a differential case. An actuator disposed within a protruding portion of a housing is in driving engagement with the sliding collar of the differential locking system. In pneumatic communication with the actuator is a differential lock pneumatic solenoid valve that is in electrical communication with pneumatic solenoid valve slave controller. The solenoid valve and the slave controller are J-1939 and/or ISO-11898 compliant. At least a portion of an outer surface of the solenoid valve and the slave controller are integrally connected to at least a portion of an outer surface of the protruding portion of the housing. In response to an occurrence or absence of a predetermined vehicle operating condition, a second controller sends a signal over a vehicle communication bus to engage and/or disengage the sliding collar with the differential case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present disclosure, will become readily apparent to those skilled in the art from the following detailed description when considered in light of the accompanying drawings in which: 
         FIG. 1  is a schematic top-plan view of a vehicle having a differential locking system according to one embodiment of the disclosure; 
         FIG. 2  is a schematic top-plan view of a vehicle having a differential locking system according to another embodiment; 
         FIG. 3  is a schematic top-plan view of a vehicle having an inter-axle differential locking system according to yet another embodiment; 
         FIG. 4  is a partial cut-away schematic side view of an axle system having a differential locking system according to an embodiment of the disclosure where the differential locking system is in a first position; 
         FIG. 5  is a partial cut-away schematic side view of the axle system illustrated in  FIG. 4  where the differential locking system is in a second position; 
         FIG. 6  is a partial cut-away schematic side view of the differential locking system illustrated in  FIGS. 4 and 5  according to an alternative embodiment of the disclosure where the differential locking system is in a first position; 
         FIG. 7  is a partial cut-away schematic side view of the differential locking system illustrated in  FIG. 6  where the differential locking system is in a second position; 
         FIG. 8  is a partial cut-away schematic side view of the differential locking system illustrated in  FIGS. 4-7  according to another embodiment of the disclosure; 
         FIG. 9  is a partial cut-away schematic side view of the differential locking system illustrated in  FIGS. 4-8  according to an yet another embodiment of the disclosure; 
         FIG. 10  is a partial cut-away schematic side view of the differential locking system illustrated in  FIGS. 4-8  according to still yet another embodiment of the disclosure; 
         FIG. 11  is a partial cut-away schematic side view of the differential locking system illustrated in  FIGS. 4-7 and 9  according to still a further embodiment of the disclosure; 
         FIG. 12  is a schematic exploded view of a differential lock pneumatic solenoid valve and the pneumatic solenoid slave controller assembly according to an embodiment of the disclosure; 
         FIG. 13  is a diagram illustrating an electrical control system for the differential locking system illustrated in  FIGS. 4-12  according to an embodiment of the disclosure; 
         FIG. 14  is a diagram illustrating an electrical control system for the differential locking system illustrated in  FIGS. 4-12  according to an alternative embodiment of the disclosure; 
         FIG. 15  is a flow chart illustrating a method of operating the differential locking system illustrated in  FIGS. 4-12  according to an embodiment of the disclosure; and 
         FIG. 16  is a flow chart illustrating a sub-routine used to engage and/or disengage a differential locking system according to an embodiment of the disclosure with a differential case of a differential assembly of an axle system housing. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also understood that the specific devices and processes illustrated in the attached drawings, and described in the specification are simply exemplary embodiments of the inventive concepts disclosed and defined herein. Hence, specific dimensions, directions or other physical characteristics relating to the various embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. 
     It is within the scope of this disclosure, and as a non-limiting example, that the automated differential locking system disclosed herein may be used in automotive, off-road vehicle, all-terrain vehicle, construction, structural, marine, aerospace, locomotive, military, machinery, robotic and/or consumer product applications. Additionally, as a non-limiting example, the automated differential locking system disclosed herein may also be used in passenger vehicle, electric vehicle, hybrid vehicle, commercial vehicle and/or heavy vehicle applications. 
       FIG. 1  schematically illustrates a vehicle  2  having a differential locking system according to an embodiment of the disclosure. The vehicle  2  has an engine  4 , which is drivingly connected to a transmission  6 . A transmission output shaft  8  is then drivingly connected to the end of the transmission  6  opposite the engine  4 . The transmission  6  is a power management system which provides controlled application of the rotational power provided by the engine  4  by means of a gearbox. 
     A first propeller shaft  10  extends from the transmission output shaft  8  and drivingly connects the transmission  6  to a forward tandem axle system  12  of a tandem axle system  13  having an inter-axle differential  14 . The first propeller shaft  10  may be connected to the inter-axle differential  14  through one or more of the following components (not shown) a drive shaft, a stub shaft, a coupling shaft, a forward tandem axle system input shaft, a pinion gear shaft, an inter-axle differential pinion gear shaft and/or an inter-axle differential input shaft. The inter-axle differential  14  is a device that divides the rotational power generated by the engine  4  between the axles in the vehicle  2 . The rotational power is transmitted through the forward tandem axle system  12  as described in more detail below. 
     As illustrated in  FIG. 1 , the inter-axle differential  14  is drivingly connected to a forward tandem axle differential  16  and a forward tandem axle output shaft  18 . The forward tandem axle differential  16  is a set of gears that allows the outer drive wheel(s) of a wheeled vehicle  2  to rotate at a faster rate than the inner drive wheel(s). 
     The forward tandem axle system  12  further includes a first forward tandem axle half shaft  20  and a second forward tandem axle half shaft  22 . The first forward tandem axle half shaft  20  extends substantially perpendicular to the first propeller shaft  10 . A first end portion  24  of the first forward tandem axle half shaft  20  is drivingly connected to a first forward tandem axle wheel assembly  26  and a second end portion  28  of the first forward tandem axle half shaft  20  is drivingly connected to a side of the forward tandem axle differential  16 . As a non-limiting example, the second end portion  28  of the first forward tandem axle half shaft  20  is drivingly connected to a forward tandem axle differential side gear, a separate stub shaft, a separate coupling shaft, a first forward tandem axle differential output shaft and/or a shaft that is formed as part of a forward tandem axle differential side gear. 
     Extending substantially perpendicular to the first propeller shaft  10  is the second forward tandem axle half shaft  22 . A first end portion  30  of the second forward tandem axle half shaft  22  is drivingly connected to a second forward tandem axle wheel assembly  32 . A second end portion  34  of the second forward tandem axle half shaft  22  is drivingly connected to a side of the forward tandem axle differential  16  opposite the first forward tandem axle half shaft  20 . As a non-limiting example, the second end portion  34  of the second forward tandem axle half shaft  22  is drivingly connected to a forward tandem axle differential side gear, a separate stub shaft, a separate coupling shaft, a second forward tandem axle differential output shaft and/or a shaft that is formed as part of a forward tandem axle differential side gear. 
     One end of the forward tandem axle system output shaft  18  is drivingly connected to a side of the inter-axle differential  14  opposite the first propeller shaft  10 . Drivingly connected to an end of the forward tandem axle output shaft  18 , opposite the inter-axle differential  14 , is a second propeller shaft  35 . The second propeller shaft  35  extends from the forward tandem axle system  12  to a rear tandem axle system  36  of the tandem axle system  13  of the vehicle  2 . An end of the second propeller shaft  35 , opposite the forward tandem axle output shaft  18 , is drivingly connected to a rear tandem axle differential  38  of the rear tandem axle system  36 . It is within the scope of this disclosure and as a non-limiting example that the second propeller shaft  35  may be connected to the rear tandem axle differential  38  through one or more of the following (not shown) a drive shaft, a propeller shaft, a stub shaft, a coupling shaft, a rear tandem axle system input shaft, a pinion gear shaft and/or a rear tandem axle differential input shaft. The rear tandem axle differential  38  is a set of gears that allows the outer drive wheel(s) of a wheeled vehicle  2  to rotate at a faster rate than the inner drive wheel(s). The rotational power is transmitted through the rear tandem axle system  36  as described in more detail below. 
     The rear tandem axle system  36  further includes a first rear tandem axle half shaft  40  and a second rear tandem axle half shaft  42 . The first rear tandem axle half shaft  40  extends substantially perpendicular to the second propeller shaft  35 . A first end portion  44  of the first rear tandem axle half shaft  40  is drivingly connected to a first rear tandem axle wheel assembly  46  and a second end portion  48  of the first rear tandem axle half shaft  40  is drivingly connected to a side of the rear tandem axle differential  38 . As a non-limiting example, the second end portion  48  of the first rear tandem axle half shaft  40  is drivingly connected to a rear tandem axle differential side gear, a separate stub shaft, a separate coupling shaft, a first rear tandem axle differential output shaft and/or a shaft that is formed as part of a rear tandem axle differential side gear. 
     Extending substantially perpendicular to the second propeller shaft  35  is the second rear tandem axle half shaft  42 . A first end portion  50  of the second rear tandem axle half shaft  42  is drivingly connected to a second rear tandem axle wheel assembly  52 . A second end portion  54  of the second rear tandem axle half shaft  42  is drivingly connected to a side of the rear tandem axle differential  38  opposite the first rear tandem axle half shaft  40 . As a non-limiting example, the second end portion  54  of the second rear tandem axle half shaft  42  is drivingly connected to a rear tandem axle differential side gear, a separate stub shaft, a separate coupling shaft, a second rear tandem axle differential output shaft and/or a shaft that is formed as part of a rear tandem axle differential side gear. 
     As it can be seen by referencing  FIG. 1  of the disclosure, the vehicle  2  may further include a forward tandem axle differential locking system  56  and/or a rear tandem axle differential locking system  58 . The forward tandem axle differential locking system  56  includes a forward tandem axle differential locking system  60  that drivingly connects the second forward tandem axle half shaft  22  to the forward tandem axle differential  16 . The forward tandem axle differential locking system  60  allows the vehicle  2  to experience an increase in traction by locking the wheels  26  and  32  on the forward tandem axle system  12  together. This restricts the rotation of the wheels  26  and  32  to the same speed and prevents a differential action from occurring within the forward tandem axle differential  16  as if they were mounted on a common shaft. 
     In order to selectively transition the forward tandem axle differential locking system  60  between a first position (a disengaged position) and/or second position (an engaged position), a forward tandem axle pneumatic actuator  62  is used. The forward tandem axle pneumatic actuator  62  is drivingly engaged with the forward tandem axle differential locking system  60 . 
     Pneumatically connected to the forward tandem axle pneumatic actuator  62  is a forward tandem axle pneumatic solenoid valve  64  having a first position (not shown) and a second position (not shown). According to an embodiment of the disclosure and as a non-limiting example, the forward tandem axle pneumatic solenoid valve  64  complies with Society of Automotive Engineers (SAE) J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. SAE J-1939 is an internal vehicle communication network that interconnects the various components in the vehicle  2 . This will allow for communication and diagnostics among the various components of the vehicle. By making the forward tandem axle pneumatic solenoid valve  64  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the forward tandem axle pneumatic solenoid valve  64  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     In pneumatic communication with the forward tandem axle pneumatic solenoid valve  64  is a compressed air supply  66  via a forward tandem axle pneumatic solenoid air-line  68 . The compressed air supply  66  provides the energy necessary to selectively transition the forward tandem axle differential locking system  60  between the first disengaged position (not shown) and/or second engaged position (not shown). 
     When the forward tandem axle pneumatic solenoid valve  64  is in its first position (not shown), the forward tandem axle pneumatic solenoid valve  64  is closed. When the forward tandem axle pneumatic solenoid valve  64  is closed, the compressed air from the compressed air supply  66  is blocked thereby preventing the actuation of the forward tandem axle pneumatic actuator  62 . 
     When the forward tandem axle pneumatic solenoid valve  64  is in its second position (not shown), the forward tandem axle pneumatic solenoid valve  64  is open. Once open, compressed air is allowed to flow from the compressed air supply  66 , through the forward tandem axle pneumatic solenoid air-line  68 , to the forward tandem axle pneumatic actuator  62 . The compressed air then actuates the forward tandem axle pneumatic actuator  62  and engages the forward tandem axle differential locking system  60  with the forward tandem axle differential  16 . 
     In order to instruct the forward tandem axle pneumatic solenoid valve  64  to open or close, it is put into electrical communication with a forward tandem axle pneumatic solenoid slave controller  70 . According to an embodiment of the disclosure and as a non-limiting example, the forward tandem axle pneumatic solenoid slave controller  70  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the forward tandem axle pneumatic solenoid slave controller  70  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the forward tandem axle pneumatic solenoid slave controller  70  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     The forward tandem axle pneumatic solenoid slave controller  64  is then in electrical communication with a second controller  72  via a forward tandem axle pneumatic solenoid slave controller data-link  74 . In accordance with an embodiment of the disclosure and as a non-limiting example, the second controller  72  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the second controller  72  compliant with J-1939, J-1939-71, J-1939-82, J-1939-84 and/or ISO-11898 standards, it allows the second controller  72  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). As a non-limiting example, the second controller  72  may be a master controller, an instructing controller, a second slave controller or any other controller that is capable of sending, receiving and/or interpreting messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     Additionally, the second controller  72  is also in electrical communication with a vehicle communication bus  76  via a vehicle communication bus data-link  78 . The vehicle communication bus  76  is a specialized internal communications network that interconnects the various components found in the vehicle  2 . As a non-limiting example, the vehicle communication bus  76  may be a controller area network (CAN bus) that conforms to SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. The CAN bus is a type of vehicle communication bus  76  that is designed to allow the various micro-controllers and devices in the vehicle  2  to communicate with each other without the need for a host computer. By making the vehicle communication bus  76  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the vehicle communication bus  76  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     When a pre-determined vehicle operating condition is detected, the second controller  72  sends an instruction over the vehicle communication bus  76  to instruct the forward tandem axle pneumatic solenoid slave controller  70  to open the forward tandem axle pneumatic solenoid valve  64 . This allows the compressed air from the compressed air supply  66  to actuate the forward tandem axle pneumatic actuator  62  thereby engaging the forward tandem axle differential locking system  60  with the forward tandem axle differential  16 . 
     As discussed previously, the vehicle  2  may include the rear tandem axle differential locking system  58 . In accordance with the embodiment of the disclosure illustrated in  FIG. 1  and as a non-limiting example, the rear tandem axle differential locking system  58  includes a rear tandem axle differential locking system  80  that drivingly connects the second rear tandem axle half shaft  42  to the rear tandem axle differential  38 . The rear tandem axle differential locking system  80  allows the vehicle  2  to experience an increase in traction by locking the wheels  46  and  52  on the rear tandem axle system  36  together. This restricts the rotation of the wheels  46  and  52  to the same speed and prevents a differential action from occurring within the rear tandem axle differential  38  as if they were mounted on a common shaft. 
     In order to selectively transition the rear tandem axle differential locking system  80  between a first position (a disengaged position) and/or a second position (an engaged position), a rear tandem axle pneumatic actuator  82  is used. The rear tandem axle pneumatic actuator  82  is drivingly engaged with the rear tandem axle differential locking system  80 . 
     Pneumatically connected to the rear tandem axle pneumatic actuator  82  is a rear tandem axle pneumatic solenoid valve  84  having a first position (not shown) and a second position (not shown). In accordance with an embodiment of the disclosure and as a no-limiting example, the rear tandem axle pneumatic solenoid valve  84  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. SAE J-1939 is an internal vehicle communication network that interconnects the various components in the vehicle  2 . By making the rear tandem axle pneumatic solenoid valve  84  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the rear tandem axle pneumatic solenoid valve  84  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     In pneumatic communication with the rear tandem axle pneumatic solenoid valve  84  is the compressed air supply  66  via a rear tandem axle pneumatic solenoid air-line  86 . The compressed air supply  66  provides the energy necessary to selectively translate the rear tandem axle differential locking system between the first disengaged position (not shown) and/or second engaged position (not shown). 
     When the rear tandem axle pneumatic solenoid valve  84  is in its first position (not shown), the rear tandem axle pneumatic solenoid valve  84  is closed. When the rear tandem axle pneumatic solenoid valve  84  is closed, the compressed air from the compressed air supply  66  is blocked thereby preventing the actuation of the rear tandem axle pneumatic actuator  82 . 
     When the rear tandem axle pneumatic solenoid valve  84  is in its second position (not shown), the rear tandem axle pneumatic solenoid valve  84  is open. Once open, compressed air is allowed to flow from the compressed air supply  66 , through the rear tandem axle pneumatic solenoid air-line  86 , to the forward tandem axle pneumatic actuator  82 . The compressed air then actuates the rear tandem axle pneumatic actuator  82  and engages the rear tandem axle differential locking system  80  with the rear tandem axle differential  38 . 
     In order to instruct the rear tandem axle pneumatic solenoid valve  84  to open or close, it is put into electrical communication with a rear tandem axle pneumatic solenoid slave controller  88 . According to an embodiment of the disclosure and as a non-limiting example, the rear tandem axle pneumatic solenoid slave controller  88  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the rear tandem axle pneumatic solenoid slave controller  88  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the rear tandem axle pneumatic solenoid slave controller  88  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     The rear tandem axle pneumatic solenoid slave controller  88  is then in electrical communication with the second controller  72  via a rear tandem axle pneumatic solenoid slave controller data-link  90 . It is within the scope of this disclosure that the second controller  72  is also in electrical communication with the vehicle communication bus  76  via the vehicle communication bus data-link  78 . 
     When a pre-determined vehicle operating condition is detected, the second controller  72  sends an instruction over the vehicle communication bus  76  to instruct the rear tandem axle pneumatic solenoid slave controller  88  to open the rear tandem axle pneumatic solenoid valve  84 . This allows the compressed air from the compressed air supply  66  to actuate the rear tandem axle pneumatic actuator  82  thereby engaging the rear tandem axle differential locking system  80  with the rear tandem axle differential  38 . 
     According to an alternative embodiment of the disclosure (not shown), the rear tandem axle pneumatic solenoid slave controller  88  may be in electrical communication with a third controller (not shown) via a third controller data-link (not shown). In accordance with an embodiment of the disclosure and as a non-limiting example, the third controller (not shown) complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the third controller (not shown) compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the third controller (not shown) to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). As a non-limiting example, the third controller (not shown) may be a master controller, an instructing controller, a third slave controller or any other controller that is capable of sending, receiving and/or interpreting messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     In accordance with this embodiment (not shown), the third controller (not shown) is in electrical communication with the vehicle communication bus  76  via a vehicle communication bus data-link (not shown). 
     When a pre-determined vehicle operating condition is detected, the third controller (not shown) sends an instruction over the vehicle communication bus  76  to instruct the rear tandem axle pneumatic solenoid slave controller  88  to open the rear tandem axle pneumatic solenoid valve  84 . This allows the compressed air from the compressed air supply  66  to actuate the rear tandem axle pneumatic actuator  82  thereby engaging the rear tandem axle differential locking system  80  with the rear tandem axle differential  38 . 
     By making the forward tandem axle pneumatic solenoid valve  64 , the rear tandem axle pneumatic solenoid valve  84 , the forward tandem axle pneumatic solenoid slave controller  70 , the rear tandem axle pneumatic solenoid slave controller  88 , the second controller  72 , the third controller (not shown) and/or the vehicle communication bus  76  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, the forward tandem axle differential locking system  56  and/or the rear tandem axle differential locking system  58  are able to be installed using the existing infrastructure within the vehicle  2 . This means that the forward rear tandem axle differential locking system  56  and/or the rear tandem axle differential locking system  58  can be installed into the vehicle  2  without adding any additional or new components to the infrastructure of the vehicle  2 . This in turn makes the system more cost efficient. Additionally, this allows the forward and/or the rear tandem axle differential lock pneumatic solenoid valves  64  and/or  84  to be controlled by any controller in the data-link of the vehicle communication bus  76  that has adequate memory to accommodate the control logic needed to engage and/or disengage the differential locking systems  60  and/or  80 . Furthermore, this also gives the differential locking systems  56  and/or  58  standardization and scalability, allowing the systems  56  and/or  58  to be used across a wide range of platforms and allowing the differential locking systems  56  and/or  58  to be compatible with the standard diagnostic tools used by field service personnel. 
       FIG. 2  illustrates a schematic top-plan view of a vehicle  100  having a differential locking system according to another embodiment. In accordance with the embodiment of the disclosure illustrated in  FIG. 2 , the vehicle  100  has an engine  102  that is drivingly connected to a transmission  104 . A transmission output shaft  106  is then drivingly connected to the end of the transmission  104  opposite the engine  102 . 
     A first propeller shaft  108  extends from the transmission output shaft  106  and drivingly connects the transmission  104  to an axle system  110  having a differential  112 . The first propeller shaft  108  may be connected to the differential  112  through one or more of the following components (not shown) a drive shaft, a stub shaft, a coupling shaft, a differential input shaft and/or a pinion gear shaft. The rotational power is transmitted through the axle system  110  as described in more detail below. 
     The axle system  110  further includes a first axle half shaft  114  and a second axle half shaft  116 . The first axle half shaft  114  extends substantially perpendicular to the first propeller shaft  108 . A first end portion  118  of the first axle half shaft  114  is drivingly connected to a first axle wheel assembly  120  and a second end portion  122  of the first axle half shaft  114  is drivingly connected to a side of the differential  112 . As a non-limiting example, the second end portion  122  of the first axle half shaft  114  is drivingly connected to a differential side gear, a separate stub shaft, a separate coupling shaft, a first differential output shaft and/or a shaft that is formed as part of a differential side gear. 
     Extending substantially perpendicular to the first propeller shaft  108  is the second axle half shaft  116 . A first end portion  124  of the second axle half shaft  116  is drivingly connected to a second axle wheel assembly  126 . A second end portion  128  of the second axle half shaft  116  is drivingly then connected to a side of the differential  112  opposite the first axle half shaft  114 . As a non-limiting example, the second end portion  128  of the second axle half shaft  116  is drivingly connected to a differential side gear, a separate stub shaft, a separate coupling shaft, a second differential output shaft and/or a shaft that is formed as part of a differential side gear. 
     As it can be seen by referencing  FIG. 2  of the disclosure, the vehicle  100  may further include a differential locking system  130 . The differential locking system  130  includes a differential locking system  132  that drivingly connects the second axle half shaft  116  to the differential  112 . The differential locking system  132  allows the vehicle  100  to experience an increase in traction by locking the wheels  120  and  126  on the axle system  110  together. This restricts the rotation of the wheels  120  and  126  to the same speed and prevents a differential action from occurring within the differential  112  as if they were mounted on a common shaft. 
     In order to selectively transition the differential locking system  132  between a first position (a disengaged position) and/or a second position (an engaged position), a pneumatic actuator  134  is used. The pneumatic actuator  134  is drivingly engaged with the differential locking system  132 . 
     Pneumatically connected to the pneumatic actuator  134  is a differential lock pneumatic solenoid valve  136  having a first position (not shown) and a second position (not shown). According to an embodiment of the disclosure and as a non-limiting example, the differential lock pneumatic solenoid valve  136  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. SAE J-1939 is an internal vehicle communication network that interconnects the various components in the vehicle  100  allowing for communication and diagnostics among vehicle components. By making the differential lock pneumatic solenoid valve  136  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the differential lock pneumatic solenoid valve  136  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     In pneumatic communication with the differential lock pneumatic solenoid valve  136  is compressed air supply  138  via a pneumatic solenoid air-line  140 . The compressed air supply  138  provides the energy necessary to selectively transition the differential locking system  132  between a first disengaged position (not shown) and/or second engaged position (not shown). 
     When the differential lock pneumatic solenoid valve  136  is in its first position (not shown), the differential lock pneumatic solenoid valve  136  is closed. When the differential lock pneumatic solenoid valve  136  is closed, the compressed air from the compressed air supply  138  is blocked thereby preventing the actuation of the pneumatic actuator  134 . 
     When the differential lock pneumatic solenoid valve  136  is in its second position (not shown), the differential lock pneumatic solenoid valve  136  is open. Once open, compressed air is allowed to flow from the compressed air supply  138 , through the pneumatic solenoid air-line  140 , to the differential lock pneumatic actuator  134 . The compressed air then actuates the forward tandem axle pneumatic actuator  134  and engages the differential locking system  132  with the differential  112 . 
     In order to instruct the differential lock pneumatic solenoid valve  136  to open or close, it is put into electrical communication with a pneumatic solenoid slave controller  142 . According to one embodiment, the pneumatic solenoid slave controller  142  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the pneumatic solenoid slave controller  142  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the pneumatic solenoid slave controller  142  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     The pneumatic solenoid slave controller  142  is then in electrical communication with a second controller  144  via a pneumatic solenoid valve slave controller data-link  146 . According to one embodiment of the disclosure and as a non-limiting example, the second controller  144  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the second controller  144  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the second controller  144  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). As a non-limiting example, the second controller  144  may be a master controller, an instructing controller, a second slave controller or any other controller that is capable of sending, receiving and/or interpreting messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     Additionally, the second controller  144  is also in electrical communication with a vehicle communication bus  148  via a vehicle communication bus data-link  150 . The vehicle communication bus  148  is a specialized internal communications network that interconnects the various components found in the vehicle  100 . As a non-limiting example, the vehicle communication bus  148  may be a controller area network (CAN bus) that conforms to SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. The CAN bus is a type of vehicle communication bus  148  that is designed to allow the various micro-controllers and devices in the vehicle  100  to communicate with each other without the need for a host computer. By making the vehicle communication bus  148  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the vehicle communication bus  148  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     When a pre-determined vehicle operating condition is detected, the second controller  144  sends an instruction over the vehicle communication bus  148  to instruct the differential lock pneumatic solenoid slave controller  142  to open the differential lock pneumatic solenoid valve  136 . This allows the compressed air from the compressed air supply  138  to actuate the pneumatic actuator  134  thereby engaging the differential locking system  132  with the differential  112 . 
     As previously discussed, by making the differential lock pneumatic solenoid valve  136 , pneumatic solenoid slave controller  142 , the second controller  144  and/or the vehicle communication bus  148  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, the differential locking system  130  is able to be installed using the existing infrastructure within the vehicle  100 . This means that the differential locking system  130  can be installed into the vehicle  100  without adding any additional or new components to the infrastructure of the vehicle  100 . This in turn makes the system more cost efficient. Additionally, this allows the differential lock pneumatic solenoid valve  136  to be controlled by any controller in the data-link of the vehicle communication bus  148  that has adequate memory to accommodate the control logic to engage and disengage the differential locking system  132 . Furthermore, this also gives the differential locking system  132  standardization and scalability, allowing the system  132  to be used across a wide range of platforms and allowing the differential locking system  132  to be compatible with the standard diagnostic tools used by field service personnel. 
       FIG. 3  is a schematic top plan view of a vehicle  200  having an inter-axle differential locking system  202  according to yet another embodiment of the disclosure. It is within the scope of this disclosure to include the use of the inter-axle differential locking system  202  illustrated in  FIG. 3  in a vehicle (not shown) having the forward tandem axle differential locking system  56  and/or the rear tandem axle differential locking system  58  illustrated in  FIG. 1 . The vehicle  200  has an engine  204 , which is drivingly connected to a transmission  206 . A transmission output shaft  208  is then drivingly connected to the end of the transmission  206  opposite the engine  204 . The transmission  206  is a power management system which provides controlled application of the rotational power provided by the engine  204  by means of a gearbox. 
     A first propeller shaft  210  extends from the transmission output shaft  208  and drivingly connects the transmission  206  to a forward tandem axle system  212  of a rear tandem axle system  213  having an inter-axle differential  214 . The first propeller shaft  210  may be connected to the inter-axle differential  214  through one or more of the following components (not shown) a drive shaft, a stub shaft, a coupling shaft, a forward tandem axle system input shaft, a pinion gear shaft, an inter-axle differential pinion gear shaft and/or an inter-axle differential input shaft. The inter-axle differential  214  is device that divides the rotational power generated by the engine  204  between the axles in the vehicle  200 . The rotational power is transmitted through the forward tandem axle system  212  as described in more detail below. 
     As illustrated in  FIG. 3  of the disclosure, the inter-axle differential  214  is drivingly connected to a forward tandem axle differential  216  and a forward tandem axle output shaft  218 . The forward tandem axle differential  216  is a set of gears that allows the outer drive wheel(s) of a wheeled vehicle  200  to rotate at a faster rate than the inner drive wheel(s). 
     The forward tandem axle system  212  further includes a first forward tandem axle half shaft  220  and a second forward tandem axle half shaft  222 . The first forward tandem axle half shaft  220  extends substantially perpendicular to the first propeller shaft  210 . A first end portion  224  of the first forward tandem axle half shaft  220  is drivingly connected to a first forward tandem axle wheel assembly  226  and a second end portion  228  of the first forward tandem axle half shaft  220  is drivingly connected to a side of the forward tandem axle differential  216 . As a non-limiting example, the second end portion  228  of the first forward tandem axle half shaft  220  is drivingly connected to a forward tandem axle differential side gear, a separate stub shaft, a separate coupling shaft, a first forward tandem axle differential output shaft and/or a shaft that is formed as part of a forward tandem axle differential side gear. 
     Extending substantially perpendicular to the first propeller shaft  210  is the second forward tandem axle half shaft  222 . A first end portion  230  of the second forward tandem axle half shaft  222  is drivingly connected to a second forward tandem axle wheel assembly  232 . A second end  234  of the second forward tandem axle half shaft  222  is drivingly connected to a side of the forward tandem axle differential  216  opposite the first forward tandem axle half shaft  220 . As a non-limiting example, the second end portion  234  of the second forward tandem axle half shaft  222  is drivingly connected to a forward tandem axle differential side gear, a separate stub shaft, a separate coupling shaft, a second forward tandem axle differential output shaft and/or a shaft that is formed as part of a forward tandem axle differential side gear. 
     One end of the forward tandem axle system output shaft  218  is drivingly connected to a side of the inter-axle differential  214  opposite the first propeller shaft  210 . Drivingly connected to an end of the forward tandem axle output shaft  218 , opposite the inter-axle differential  214 , is a second propeller shaft  235 . The second propeller shaft  235  extends from the forward tandem axle system  212  to a rear tandem axle system  236  of the tandem axle system  213  of the vehicle  200 . An end of the second propeller shaft  235 , opposite the forward tandem axle output shaft  218 , is drivingly connected to a rear tandem axle differential  238  of the rear tandem axle system  236 . It is within the scope of this disclosure and as a non-limiting example that the second propeller shaft  235  may be connected to the rear tandem axle differential  238  through one or more of the following (not shown) a drive shaft, a propeller shaft, a stub shaft, a coupling shaft, a rear tandem axle system input shaft, a pinion gear shaft and/or a rear tandem axle differential input shaft. The rear tandem axle differential  238  is a set of gears that allows the outer drive wheel(s) of a wheeled vehicle  200  to rotate at a faster rate than the inner drive wheel(s). The rotational power is transmitted through the rear tandem axle system  236  as described in more detail below. 
     The rear tandem axle system  236  further includes a first rear tandem axle half shaft  240  and a second rear tandem axle half shaft  242 . The first rear tandem axle half shaft  240  extends substantially perpendicular to the second propeller shaft  235 . A first end portion  244  of the first rear tandem axle half shaft  240  is drivingly connected to a first rear tandem axle wheel assembly  246  and a second end portion  248  of the first rear tandem axle half shaft  240  is drivingly connected to a side of the rear tandem axle differential  238 . As a non-limiting example, the second end portion  248  of the first rear tandem axle half shaft  240  is drivingly connected to a rear tandem axle differential side gear, a separate stub shaft, a separate coupling shaft, a first rear tandem axle differential output shaft and/or a shaft that is formed as part of a rear tandem axle differential side gear. 
     Extending substantially perpendicular to the second propeller shaft  235  is the second rear tandem axle half shaft  242 . A first end portion  250  of the second rear tandem axle half shaft  242  is drivingly connected to a second rear tandem axle wheel assembly  252 . A second end portion  254  of the second rear tandem axle half shaft  242  is drivingly connected to a side of the rear tandem axle differential  238  opposite the first rear tandem axle half shaft  240 . As a non-limiting example, the second end portion  254  of the second rear tandem axle half shaft  242  is drivingly connected to a rear tandem axle differential side gear, a separate stub shaft, a separate coupling shaft, a second rear tandem axle differential output shaft and/or a shaft that is formed as part of a rear tandem axle differential side gear. 
     As it can be seen by referencing  FIG. 3  of the disclosure, the vehicle  200  may further include the inter-axle differential locking system  202 . The inter-axle differential locking system  202  includes an inter-axle differential locking system  256  that drivingly connects the forward tandem axle system  212  to the rear tandem axle system  236 . This prevents a differential action from occurring within the inter-axle differential  214 , which allows power to transferred be equally to both the forward tandem axle system  212  and the rear tandem axle system  236  which results in an increase in vehicle traction. 
     In order to selectively transition the inter-axle differential locking system  256  between a first position (a disengaged portion) and/or a second position (an engaged position), an inter-axle differential pneumatic actuator  258  is used. The inter-axle differential pneumatic actuator  258  is drivingly engaged with the inter-axle differential locking system  256 . 
     Pneumatically connected to the inter-axle differential pneumatic actuator  258  is a pneumatic solenoid valve  260  having a first position (not shown) and a second position (not shown). According to an embodiment of the disclosure and as a non-limiting example, the pneumatic solenoid valve  260  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. SAE J-1939 is an internal vehicle communication network that interconnects the various components in the vehicle  200  allowing for communication and diagnostics among vehicle components. By making the pneumatic solenoid valve  260  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the pneumatic solenoid valve  260  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     In pneumatic communication with the pneumatic solenoid valve  260  is a compressed air supply  262  via a pneumatic solenoid air-line  264 . The compressed air supply  262  provides the energy necessary to selectively transition the inter-axle differential locking system  256  between the first disengaged position (not shown) and/or the second engaged position (not shown). 
     When the pneumatic solenoid valve  260  is in a first position (not shown), the pneumatic solenoid valve  260  is closed. When the pneumatic solenoid valve  260  is closed, the compressed air from the compressed air supply  262  is blocked thereby preventing the actuation of the inter-axle differential pneumatic actuator  258 . 
     When the pneumatic solenoid valve  260  is in a second position (not shown), the pneumatic solenoid valve  260  is open. Once open, compressed air is allowed to flow from the compressed air supply  262 , through the pneumatic solenoid air-line  264 , to the inter-axle differential pneumatic actuator  258 . The compressed air then actuates the inter-axle differential pneumatic actuator  258  and engages the inter-axle differential locking system  256  with the inter-axle differential  214 . 
     In order to instruct the inter-axle differential pneumatic solenoid valve  260  to open or close, it is put into electrical communication with a pneumatic solenoid slave controller  266 . According to an embodiment of the disclosure and as a non-limiting example, the pneumatic solenoid slave controller  266  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the pneumatic solenoid slave controller  266  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the pneumatic solenoid slave controller  266  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     The pneumatic solenoid slave controller  266  is then in electrical communication with a second controller  268  via a pneumatic solenoid slave controller data-link  270 . In accordance with an embodiment of the disclosure and as a non-limiting example, the second controller  268  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the second controller  268  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the second controller  268  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). In a non-limiting example, the second controller  268  may be a master controller, an instructing controller, a second slave controller or any other controller that is capable of sending, receiving and/or interpreting messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     Additionally, the second controller  268  is also in electrical communication with a vehicle communication bus  272  via a vehicle communication bus data-link  274 . The vehicle communication bus  272  is a specialized internal communications network that interconnects the various components found in the vehicle  200 . As a non-limiting example, the vehicle communication bus  272  may be a controller area network (CAN bus) that conforms to SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. The CAN bus is a type of vehicle communication bus  272  that is designed to allow the various micro-controllers and devices in the vehicle  200  to communicate with each other without the need for a host computer. By making the vehicle communication bus  272  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the vehicle communication bus  272  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     When a pre-determined vehicle operating condition is detected, the second controller  268  sends an instruction over the vehicle communication bus  272  to instruct the pneumatic solenoid slave controller  266  to open the pneumatic solenoid valve  260 . This allows the compressed air from the compressed air supply  262  to actuate the inter-axle differential pneumatic actuator  258  thereby engaging the inter-axle differential locking system  256  with the inter-axle differential  214 . 
     As previously discussed, by making the pneumatic solenoid valve  260 , pneumatic solenoid slave controller  266 , the second controller  268  and/or the vehicle communication bus  272  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, the inter-axle differential locking system  202  is able to be installed using the existing infrastructure within the vehicle  200 . This means that the inter-axle differential locking system  202  can be installed into the vehicle  200  without adding any additional or new components to the infrastructure of the vehicle  200 . This in turn makes the system more cost efficient. Additionally, this allows the pneumatic solenoid valve  260  to be controlled by any controller in the data-link of the vehicle communication bus  272  that has adequate memory to accommodate the control logic to engage and disengage the inter-axle differential locking system  256 . Furthermore, this also gives the inter-axle differential locking system  256  standardization and scalability, allowing the system  256  to be used across a wide range of platforms and allowing the differential locking system  256  to be compatible with the standard diagnostic tools used by field service personnel. 
       FIGS. 4 and 5  are a partial cut-away schematic side view of an axle system  300  having a differential locking system  302  according to an embodiment of the disclosure. As illustrated in  FIGS. 4 and 5  of the disclosure the axle system  300  has a housing  304  having an inner surface  306  and an outer surface  308  defining a hollow portion  310  therein. It is within the scope of this disclosure that the housing  304  of the axle system  300  may be made of a single unitary piece or a plurality of pieces that are connected to one another by using one or more adhesives, one or more welds and/or one or more mechanical fasteners. 
     As best seen in  FIG. 4  of the disclose, an input shaft  312  having a first end portion  314 , a second end portion  316  and an outer surface  317  extends through an input shaft opening  318  extending from the inner surface  306  to an outer surface  308  of the housing  304  of the axle system  300 . In accordance with e embodiment of the disclosure illustrated in  FIG. 4  of the disclosure, at least a portion of the first end portion of the input shaft  312  is disposed outside the housing  304  of the axle system  300 . 
     Integrally connected to at least a portion of the outer surface  317  of the second end portion  316  of the input shaft  312  is a pinion gear  320  having a plurality of pinion gear teeth  322 . According to an embodiment of the disclosure and as a non-limiting example, the pinion gear  320  may be integrally formed as part of the second end portion of the input shaft  312 . In accordance with an alternative embodiment of the disclosure and as a non-limiting example the pinion gear  320  may be integrally connected to at least a portion of the outer surface  317  of the second end portion  316  of the input shaft  312  by using one or more adhesives, one or more welds and/or one or more mechanical fasteners. 
     The input shaft is rotationally supported within the housing  304  of the axle system  300  by using one or more input shaft bearings  324 . As best seen in  FIG. 4  of the disclosure, the one or more input shaft bearings  324  are interposed between the outer surface  317  of the input shaft  312  and the inner surface  306  of the housing  304  of the axle system  300 . 
     The pinion gear  320  is drivingly connected to a differential ring gear  326  of a differential assembly  327  having an inner surface  328 , an outer surface  330 , a first end portion  332 , a second end portion  334 , a first end  336  and a second end  338 . Circumferentially extending from at least a portion of outer surface  330  of the second end portion  334  of the differential ring gear  326  is a plurality of ring gear teeth  340 . The plurality of ring gear teeth  340  on the outer surface  330  of the differential ring gear  326  are complementary to and meshingly engaged with the plurality of pinion gear teeth  322  on the pinion gear  320 . 
     As best seen in  FIG. 4  of the disclosure, the inner surface  328  of the differential ring gear  326  has, in axial order, from the first end  336  to the second end  338  of the differential ring gear  326 , a first receiving portion  342 , a second receiving portion  344 , a third receiving portion  346  and a fourth receiving portion  348 . The first receiving portion  342  has an inner diameter D 1 , the second receiving portion  344  has an inner diameter ID 2 , the third receiving portion has an inner diameter ID 3  and the fourth receiving portion has an inner diameter ID 4 . In accordance with the embodiment of the disclosure illustrated in  FIG. 4  and as a non-limiting example, the inner diameter ID 1  of the first receiving portion  342  of the differential ring gear  326  is less than the inner diameter ID 2  of the second receiving portion  344  of the differential ring gear  326 . Additionally, in accordance with the embodiment of the disclosure illustrated in  FIG. 4  and as a non-limiting example, the inner diameter ID 2  of the second receiving portion  344  of the differential ring gear  326  is less than the inner diameter ID 3  of the third receiving portion  346  of the differential ring gear  326 . Furthermore, in accordance with the embodiment of the disclosure illustrated in  FIG. 4  and as a non-limiting example, the inner diameter ID 3  of the third receiving portion  346  of the differential ring gear  326  is less than the inner diameter ID 4  of the fourth receiving portion  348  of the differential ring gear  326 . It is within the scope of this disclosure and as a non-limiting example that the first, second, third and fourth receiving portions  342 ,  344 ,  346  and  348  are substantially cylindrical in shape. 
     Extending co-axially with and integrally connected to at least a portion of the differential ring gear  326  is a differential case  350  having an inner surface  352 , an outer surface  354 , a first end portion  356  and second end portion  358 . The inner surface  352  and the outer surface  354  of the differential case  350  defines a hollow portion  360  therein. As illustrated in  FIG. 4  of the disclosure, at least a portion of the first end portion  356  of the differential case  350  is received within the fourth receiving portion  348  of the differential ring gear  326 . It is within the scope of this disclosure and as a non-limiting example that the first end portion  356  of the differential case  350  may be integrally connected to at least a portion of the differential ring gear  326  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. 
     As illustrated in  FIG. 4  of the disclosure and as a non-limiting example, the differential assembly  327  includes one or more pinion gears  362  disposed on a shaft  364  secured to the differential case  350 . The one or more pinion gears  362  of the differential assembly  327  have a plurality of pinion gear teeth  366  circumferentially extending from at least a portion of an outer surface  368  of the one or more pinion gears  362 . 
     Drivingly engaged with the one or more pinion gears  362  of the differential assembly  327  is a first side gear  370  and a second side gear  372 . At least a portion of the one or more pinion gears  362 , the first side gear  370  and the second side gear  372  are disposed within the differential ring gear  326  and/or the differential case  350  of the differential assembly  327  of the axle system  300 . As best seen in  FIG. 5  of the disclosure, the first side gear  370  has a first end portion  374 , a second end portion  376 , an inner surface  378  and an outer surface  380 . Circumferentially extending along at least a portion of the inner surface  378  of the first side gear  370  is a plurality of axially extending first side gear splines  382 . 
     As best seen in  FIG. 5  of the disclosure, the second end portion  376  of the first side gear  370  has an increased diameter portion  384  circumferentially extending from at least a portion of the second end portion  376  of the first side gear  370  of the differential assembly  327 . The increased diameter portion  384  of the first side gear  370  has an outermost diameter OD 1  that is larger than an outermost diameter OD 2  of the first end portion  374  of the first differential side gear  370 . In accordance with the embodiment of the disclosure illustrated in  FIG. 5  and as a non-limiting example, at least a portion of the first end portion  374  of the first side gear  370  is disposed within the second receiving portion  344  of the differential ring gear  326 . Additionally, in accordance with the embodiment of the disclosure illustrated in  FIG. 5  and as a non-limiting example, at least a portion of the increased diameter portion  384  of the first side gear  370  is disposed within the third receiving portion  346  of the differential ring gear  326 . As a result, at least a portion of the first side gear  370  is disposed within the second and third receiving portions  344  and  346  of the differential ring gear  326  of the differential assembly  327 . 
     Circumferentially extending along at least a portion of the outer surface  380  of the increased diameter portion  384  of the first side gear  370  is a plurality of first side gear teeth  386 . The plurality of first side gear teeth  386  are complementary to and meshingly engaged with the plurality of pinion gear teeth  366  on the outer surface  368  of the one or more pinion gears  362 . 
     Extending co-axially with and drivingly connected to at least a portion of the first side gear  370  of the differential assembly  327  is a first stub shaft  388  having a first end portion  390 , a second end portion  392  and an outer surface  394 . In accordance with the embodiment of the disclosure illustrated in  FIGS. 4 and 5  and as a non-limiting example, at least a portion of the first stub shaft is disposed within the first receiving portion  342  of the differential ring gear  326 . 
     Circumferentially extending from at least a portion of the first end portion  390  of the first stub shaft  388  is an increased diameter portion  396 . A plurality of first shaft clutch teeth  398  circumferentially extend from at least a portion of the outer surface  394  of the increased diameter portion  396  of the first stub shaft  388 . As best seen in  FIG. 5  of the disclosure and as a non-limiting example, at least a portion of the increased diameter portion  396  of the first stub shaft  388  extends outside of the differential ring gear  326  of the differential assembly  327 . 
     In accordance with the embodiment of the disclosure illustrated in  FIG. 5  and as a non-limiting example, a plurality of axially extending first stub shaft splines  400  circumferentially extend along at least a portion of the outer surface  394  of the second end portion  392  of the first stub shaft  388 . The plurality of axially extending first stub shaft splines  400  are complementary to and meshingly engaged with the plurality of axially extending first side gear splines  382  on the inner surface  378  of the first side gear  370 . 
     Extending co-axially with the first stub shaft  388  is a first axle half shaft  402  having a first end portion (not shown), a second end portion  404  and an outer surface  406 . At least a portion of the second end portion  404  of the first axle half shaft  402  is rotationally connected to at least a portion of the first end portion  390  of the first stub shaft  388  of the axle system  300 . Circumferentially extending from at least a portion of the second end portion  404  of the first axle half shaft  402  is a plurality of first axle half shaft splines  408 . 
     As best seen in  FIG. 5  of the disclosure, at least a portion of the first axle half shaft  402  and the first stub shaft  388  is disposed within a first axle half shaft housing  403 . The first axle half shaft housing  403  extends axially outboard from at least a portion of the outer surface  308  of the housing  304  of the axle system  300 . According to an embodiment of the disclosure and as a non-limiting example, the first axle half shaft housing  403  is formed as part of the housing  304  of the axle system  300 . In accordance with an alternative embodiment of the disclosure and as a non-limiting example, an end of the first axle half shaft housing  403  is integrally connected to at least a portion of the outer surface  308  of the housing  304  of the axle system by using one or more adhesives, one or more mechanical fasteners, one or more welds and/or a threaded connection. 
     Disposed at least partially radially outboard from at least a portion of the second end portion  404  of the first axle half shaft  402  is an axle disconnect sliding collar  410  having a an inner surface  412 , an outer surface  414 , a first end portion  416  and a second end portion  418 . Circumferentially extending along at least a portion of the inner surface  412  of the axle disconnect sliding collar  410  is a plurality of axially extending axle disconnect sliding collar splines  420 . The plurality of axially extending axle disconnect sliding collar splines are complementary to and meshingly engaged with the plurality of first axle half shaft splines  408  on the outer surface  406  of the second end portion  404  of the first axle half shaft  402 . 
     As best seen in  FIG. 5  of the disclosure, circumferentially extending along at least a portion of the outer surface  414  of the second end portion  418  of the axle disconnect sliding collar  410  is a plurality of axle disconnect sliding collar clutch teeth  422 . As a non-limiting example, the plurality of axle disconnect sliding collar clutch teeth  422  and the plurality of first stub shaft clutch teeth  398  are a plurality of face clutch teeth, a plurality of dog clutch teeth, or a friction clutch. 
     The plurality of axle disconnect sliding collar clutch teeth  422  are selectively engageable and/or disengageable with the plurality of first stub shaft clutch teeth  398 . As a result, the axle disconnect sliding collar  410  is selectively engageable and/or disengageable with the first stub shaft  388  of the axle assembly  300 . This allows the first axle half shaft  402  to be selectively connected and/or disconnected from driving engagement with the differential assembly  327  of the axle system  300 . When the axle disconnect sliding collar  410  is in the first position  424  illustrated in  FIG. 5  of the disclosure, the plurality of axle disconnect sliding collar clutch teeth  422  are meshingly engaged with the plurality of first stub shaft clutch teeth  398  thereby drivingly connecting the first axle half shaft  402  to the differential assembly  327 . When the axle disconnect sliding collar  410  is in the second position  426  illustrated in  FIG. 4  of the disclosure, the plurality of axle disconnect sliding collar clutch teeth  422  are not meshingly engaged with the plurality of first stub shaft clutch teeth  398  thereby disconnecting the first axle half shaft from driving engagement with the differential assembly  327 . 
     In order to translate the axle disconnect sliding solar  410  between the first position  424  and the second position  426  an actuator assembly (not shown) is used to drive the axle disconnect sliding collar  410  into and out of engagement with the first stub shaft  388  of the axle system  300 . It is within the scope of this disclosure that the actuator assembly (not shown) may be an actuator assembly according to an embodiment of the disclosure. 
     As previously discussed, the second side gear  372  is drivingly engaged with the one or more pinion gears  362  of the differential assembly  327 . As best seen in  FIG. 5  of the disclosure, the second side gear  372  has an inner surface  428 , an outer surface  430 , a first end portion  432  and a second end portion  434 . Circumferentially extending along at least a portion of the inner surface  428  of the second side gear  372  is a plurality of axially extending second side gear splines  436 . 
     As best seen in  FIG. 5  of the disclosure, the first end portion  432  of the second side gear  372  has an increased diameter portion  438  circumferentially extending from at least a portion of the first end portion  432  of the second side gear  372  of the differential assembly  327 . The increased diameter portion  438  of the second side gear  372  has an outermost diameter OD 3  that is larger than an outermost diameter OD 4  of the second end portion  434  of the second differential side gear  372 . Circumferentially extending along at least a portion of the outer surface  430  of the increased diameter portion  438  of the second side gear  372  is a plurality of second side gear teeth  440 . The plurality of second side gear teeth  440  are complementary to and meshingly engaged with the plurality of pinion gear teeth  366  on the outer surface  368  of the one or more pinion gears  362 . 
     Extending co-axially with and drivingly connected to at least a portion of the second side gear  372  of the differential assembly  327  is a second stub shaft  442  having a first end portion  444 , a second end portion  446  and an outer surface  448 . Circumferentially extending along at least a portion of the first end portion  444  of the second stub shaft  442  is a plurality of axially extending second stub shaft splines  450 . The plurality of axially extending second stub shaft splines  450  are complementary to and meshingly engaged with the plurality of axially extending second side gear splines  436  on the inner surface  428  of the second side gear  472  of the differential assembly  427 . 
     A second axle half shaft  452  having a first end portion  454 , a second end portion (not shown) and an outer surface  456  extends co-axially with the second stub shaft  442  of the axle system  300 . In accordance with the embodiment of the disclosure illustrated in  FIG. 5  and as a non-limiting example, at least a portion of the first end portion  454  of the second axle half shaft  452  is rotatively connected to at least a portion of the second end portion  446  of the second stub shaft  442 . Circumferentially extending along at least a portion of the outer surface  456  of the first end portion  454  of the second axle half shaft  452  is a plurality of axially extending second axle half shaft splines  458 . 
     Extending co-axially with and slidingly engaged with the first axle half shaft  452  is a differential locking system sliding collar  460  having a first end portion  462 , a second end portion  464 , an inner surface  466  and an outer surface  468 . The inner surface  466  and the outer surface  468  of the differential locking system sliding collar  460  defines a hollow portion  470  therein. Circumferentially extending from the inner surface  466  of the differential locking system sliding collar  460  is a plurality of splines  472  that are complementary to and meshingly engaged with the plurality of second axle half shaft splines  458  on the outer surface  456  of the first end portion  454  of the first axle half shaft  452 . 
     Circumferentially extending from at least a portion of the outer surface  468  of the first end portion  462  of differential locking system sliding collar  460  is a plurality of differential locking system sliding collar clutch teeth  474 . The plurality of differential locking system sliding collar clutch teeth  474  are complementary to and selectively engageable and/or disengageable with a plurality of differential case clutch teeth  476  circumferentially extending from at least a portion of the outer surface  354  of the second end portion  358  of the differential case  350 . As a non-limiting example, the plurality of differential case clutch teeth  476  and the plurality of differential locking system sliding collar clutch teeth  474  are a plurality of face clutch teeth, a plurality of dog clutch teeth, or a friction clutch. 
     According to an embodiment of the disclosure illustrated in  FIG. 5  and as a non-limiting example, the differential locking system sliding collar  460  has a groove  478  circumferentially extending along at least a portion of the outer surface of the differential locking system sliding collar  460 . 
     In order to transition the differential locking system sliding collar  460  from a first position  480  illustrated in  FIG. 4  to a second position  482  illustrated in  FIG. 5 , an actuator  484  is used. The actuator  484  is disposed radially outward from the second axle half shaft  452  and has an axis that is substantially parallel to the second axle half shaft  452 . As a non-limiting example, the actuator  484  is a piston, a pneumatic piston or a pneumatic actuator. The actuator  484  is drivingly engaged with a shift shaft  485 , which in turn is drivingly engaged with an end of a shift fork  487 . An end of the shift fork  487  opposite the shift shaft  485  is in driving engagement with at least a portion of the differential locking system sliding collar  460 . It is within the scope of this disclosure that at least a portion of the end of the shift fork  487  opposite the shift shaft  485  may be disposed within the groove  478  on the outer surface  464  of the differential locking system sliding collar  460   
     According to the embodiment of the disclosure illustrated in  FIG. 4  and as a non-limiting example, at least a portion of the actuator  484  is housed within a protruding portion  486  extending from at least a portion of the outer surface  308  of the housing  304  of the axle system  300 . The protruding portion  486  of the housing  304  has an inner surface  488  and an outer surface  490  defining a hollow portion  492  therein. As illustrated in  FIG. 4  of the disclosure and as a non-limiting example, at least a portion of the actuator  484  is housed within the hollow portion  492  of the protruding portion  486  of the housing  304  of the axle system  300 . 
     As illustrated in  FIG. 4  of the disclosure, at least a portion of the protruding portion  486  is disposed proximate to an outer surface  494  of a second axle half shaft housing  496 . According to an embodiment of the disclosure and as a non-limiting example, at least a portion of the second axle half shaft housing  496  may form a portion of the protruding portion  486  of the housing  304  of the axle system  300 . In accordance with an alternative embodiment of the disclosure and as a non-limiting example, at least a portion of the protruding portion  486  may be integrally connected to at least a portion of the outer surface  494  of the second axle half shaft housing  496  by using one or more adhesives, one or more mechanical fasteners, one or more welds and/or a threaded connection. 
     As best seen in  FIG. 4  of the disclosure, at least a portion of the second axle half shaft  452  and the second stub shaft  442  is disposed within the second axle half shaft housing  496 . The second axle half shaft housing  496  extends axially outboard from at least a portion of the outer surface  308  of the housing  304  of the axle system  300 . According to an embodiment of the disclosure and as a non-limiting example, the second axle half shaft housing  496  is formed as part of the housing  304  of the axle system  300 . In accordance with an alternative embodiment of the disclosure and as a non-limiting example, an end of the first axle half shaft housing  496  is integrally connected to at least a portion of the outer surface  308  of the housing  304  opposite the first axle half shaft housing  403 . As a non-limiting example, the second axle half shaft housing  496  may be integrally connected to at least a portion of the outer surface of the housing  304  of the axle system  300  by using one or more adhesives, one or more mechanical fasteners, one or more welds and/or a threaded connection. 
     In order to activate the actuator  484  and drive the differential locking system sliding collar  460  from the first position  480  illustrated in  FIG. 4  to the second position  482  illustrated in  FIG. 5 , the actuator  484  is pneumatically connected to a differential lock pneumatic solenoid valve  498 . As best seen in  FIG. 4  and as a non-limiting example, the differential lock pneumatic solenoid valve  498  has an actuator aperture  500  that is in pneumatic communication with the actuator  484  via an opening  502  extending from the inner surface  488  to the outer surface  490  of the protruding portion  486  of the housing  304 . It is within the scope of this disclosure and as a non-limiting example that the differential lock pneumatic solenoid valve  484  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. SAE J-1939 is an internal vehicle communication network that interconnects the various components in the vehicle (not shown) allowing for communication and diagnostics among vehicle components. By making the differential lock pneumatic solenoid valve  484  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the differential lock pneumatic solenoid valve  338  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     According to the embodiment of the disclosure illustrated in  FIG. 4 , at least a portion of an outer surface  500  of the differential lock pneumatic solenoid valve  498  is integrally connected to at least a portion of the outer surface  490  of the protruding portion  486  of the housing  304  of the axle system  300 . It is within the scope of this disclosure and as a non-limiting example that the outer surface  500  of the differential lock pneumatic solenoid valve  498  may be integrally connected to the outer surface  490  of the protruding portion  486  of the housing  304  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. 
     In pneumatic communication with the differential lock pneumatic solenoid valve  484  is a compress air supply (not shown) via a pneumatic solenoid air-line  506 . The compressed air supply (not shown) provides the energy necessary to selectively engage and/or disengage the differential locking system sliding collar  460  of the differential locking system  302  with the plurality of differential case clutch teeth  476  on the second end portion  358  of the differential case  350 . 
     When the differential locking system sliding collar  460  is in the first position  480  illustrated in  FIG. 4 , the differential lock pneumatic solenoid valve  484  is in a closed position. When the differential lock pneumatic solenoid valve  484  is in the closed position, the compressed air from the compressed air supply (not shown) is blocked thereby preventing the actuator  484  from transitioning the differential locking system sliding collar  460  from the first position  480  illustrated in  FIG. 4  to the second position  482  illustrated in  FIG. 5  of the disclosure. 
     When the differential locking system sliding collar  460  is in the second position  482  illustrated in  FIG. 5 , the differential lock pneumatic solenoid valve  484  is in an open position. Once open, the compressed air from the compressed air supply (not shown) is allowed to flow through the differential lock pneumatic solenoid valve  484  to the actuator  484  thereby transitioning the differential locking system sliding collar  460  from the first position  480  illustrated in  FIG. 4  to the second position  482  illustrated in  FIG. 5  of the disclosure. 
     In accordance with the embodiment of the disclosure illustrated in  FIGS. 4 and 5  and as a non-limiting example, the differential locking system  302  further includes the use of a return spring  508  disposed radially outboard from at least a portion of the shift shaft  485 . As illustrated in  FIGS. 4 and 5  of the disclosure, the return spring  508  is interposed between the shift fork  487  and a flange portion  510  supporting an end of the shift shaft  485  opposite the actuator  484 . According to an embodiment of the disclosure and as a non-limiting example, the flange portion  510  may be integrally formed as part of the inner surface  306  of the housing  304  of the axle system  300 . In accordance with an alternative embodiment of the disclosure and as a non-limiting example, at least a portion of the flange portion  510  may be integrally connected to at least a portion of the inner surface  306  of the housing  304  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. 
     When the differential lock pneumatic solenoid valve  498  is open, the actuator  484  drives the shift fork  487  and transitions the differential locking system sliding collar  460  from the first position  480  illustrated in  FIG. 4  to the second position  482  illustrated in  FIG. 5  thereby loading the return spring  508  with energy. When the differential lock pneumatic solenoid valve  498  is closed, the compressed air from the compressed air supply (not shown) is prevented from acting on the actuator  484 . The energy loaded within the return spring  510  is then released driving the shift fork  487  and the differential locking system sliding collar  460  from the second position  482  illustrated in  FIG. 5  to the first position  480  illustrated in  FIG. 4  of the disclosure. 
     In order to instruct the differential lock pneumatic solenoid valve  498  to transition between the open and/or the closed position, the differential lock pneumatic solenoid valve  498  is put into electrical communication with a pneumatic solenoid valve slave controller  512 . As a non-limiting example, the pneumatic solenoid valve slave controller  512  complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the pneumatic solenoid valve slave controller  512  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the pneumatic solenoid valve slave controller  512  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     As illustrated in  FIG. 4  of the disclosure and as a non-limiting example, the pneumatic solenoid valve slave controller  512  is interposed between the differential lock pneumatic solenoid valve  498  and the outer surface  308  of the housing  304  of the axle system  300 . At least a portion of an outer surface  514  of the pneumatic solenoid valve slave controller  512  may be integrally connected to at least a portion of the outer surface  308  of the housing  304 , the outer surface  490  of the protruding portion  486  and/or the outer surface  504  of the differential lock pneumatic solenoid valve  498 . As a non-limiting example, the outer surface of the  514  of the pneumatic solenoid valve slave controller  512  may be integrally connected to the outer surfaces  308 ,  490  and/or  504  of the housing  304 , the protruding portion  486  and/or the differential lock pneumatic solenoid valve  498  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. It is within the scope of this disclosure that the differential lock pneumatic solenoid valve  498  and the pneumatic solenoid valve slave controller  512  may be connected as a single component within the axle system  300 . 
     According to an embodiment of the disclosure and as a non-limiting example, the pneumatic solenoid valve slave controller  512  may be a multi-layered board. It is within the scope of this disclosure that the pneumatic solenoid valve slave controller  512  may further include one or more sensors (not shown). As a non-limiting example, the one or more sensors (not shown) in electrical communication with the pneumatic solenoid valve slave controller  512  are one or more pressure sensors, one or more temperature sensors and/or one or more position sensors. The one or more temperature sensors (not shown) are configured to determine a temperature within the actuator  484  and/or the differential lock pneumatic solenoid valve  498 . The one or more pressure sensors (not shown) are configured to determine an amount of air pressure within the actuator  484  and/or the differential lock pneumatic solenoid valve  498 . The one or more position sensors (not shown) may be configured to determine whether the differential locking system  302  is in the first position  480  illustrated in  FIG. 4  or in the second position  482  illustrated in  FIG. 5  of the disclosure. Additionally, it is within the scope of this disclosure that the one or more pressure sensors (not shown) may be configured to determine whether the differential lock pneumatic solenoid valve  498  is open or closed. 
     The pneumatic solenoid valve slave controller  512  is then in electrical communication with a vehicle communication bus (not shown) through a second controller (not shown) via a pneumatic solenoid slave controller data-link  516 . As a non-limiting example, the second controller (not shown) complies with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the second controller (not shown) compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the second controller (not shown) to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). It is within the scope of this disclosure and as a non-limiting example that the second controller (not shown) may be a master controller, an instructing controller, a second slave controller or any other controller that is capable of sending, receiving and/or interpreting messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     As previously discussed, the vehicle communication bus (not shown) is a specialized internal communications network that interconnects the various components found in the vehicle (not shown). In a non-limiting example, the vehicle communication bus (not shown) may be a controller area network (CAN bus) that conforms to SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. As previously discussed, the CAN bus is a type of vehicle communication bus (not shown) that is designed to allow the various micro-controllers and devices in the vehicle (not shown) to communicate with each other without the need for a host computer. By making the vehicle communication bus (not shown) compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the vehicle communication bus (not shown) to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     Once a pre-determined vehicle operating condition is detected or an instruction is received from a user, the second controller (not shown) sends an instruction over the vehicle communication bus (not shown) to instruct the differential lock pneumatic solenoid valve slave controller  512  to open the differential lock pneumatic solenoid valve  498 . This allows the compressed air from the compressed air supply (not shown) to actuate the actuator  484  thereby engaging the differential locking system  302  with the plurality of differential case clutch teeth  476  on the outer surface  354  of the second end portion  358  of the differential case  350 . 
     By making the differential lock pneumatic solenoid valve  498 , pneumatic solenoid valve slave controller  512 , the second controller (not shown) and/or the vehicle communication bus (not shown) compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, the differential locking system  302  is able to be installed using the existing infrastructure within the vehicle (not shown). This means that the differential locking system  302  may be installed into the vehicle (not shown) without adding any additional or new components to the infrastructure of the vehicle (not shown). As a result, this makes the axle system  300  more cost efficient. Additionally, this has the advantage of allowing the differential lock pneumatic solenoid valve  498  to be controlled by any controller in the data-link of the vehicle communication bus (not shown) that has adequate memory to accommodate the control logic needed to transition the differential locking system  302  from the first position  480  to the second position  482 . Furthermore, this also gives the differential locking system  302  standardization and scalability, thereby allowing the differential locking system  302  to be used across a wide range of platforms and allowing the system  302  to be compatible with the standard diagnostic tools used by field service personnel. 
       FIGS. 6 and 7  are a partial cut-away schematic side view of a differential locking system  600  according to an alternative embodiment of the disclosure. The differential locking system  600  illustrated in  FIGS. 6 and 7  is the same as the differential locking system  302  illustrated in  FIGS. 4 and 5 , except where specifically noted below. As illustrated in  FIGS. 6 and 7  of the disclosure, the differential lock pneumatic solenoid valve  498  and the pneumatic solenoid valve slave controller  512  are not integrally connected to the outer surface  490  of the protruding portion  486  of the housing  304  of the axle system  300 . 
     In accordance with the embodiment of the disclosure illustrated in  FIGS. 6 and 7  of the disclosure and as a non-limiting example, the differential lock pneumatic solenoid valve  498  and the pneumatic solenoid valve slave controller  512  are packaged as a signal component and integrally connected to at least a portion of the outer surface  308  of the housing  304 . As illustrated in  FIGS. 6 and 7  of the disclosure, the differential lock pneumatic solenoid valve  498  and the pneumatic solenoid valve slave controller  512  are disposed outboard from the outer surface  490  of the protruding portion  486  of the housing  304  of the axle system  300 . It is within the scope of this disclosure and as a non-limiting example that the differential lock pneumatic solenoid valve  498  and the pneumatic solenoid valve slave controller  512  are connected to the outer surface  308  of the housing  304  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. 
     According to the embodiment of the disclosure illustrated in  FIGS. 6 and 7 , the differential lock pneumatic solenoid valve  498  is in pneumatic communication with the actuator  484  via an actuator input air-line  602 . An end of the actuator input air-line  602  is connected to and is in pneumatic communication with the actuator aperture  500  of the differential lock pneumatic solenoid valve  498 . An end of the actuator input air-line  602 , opposite the differential lock pneumatic solenoid valve  498 , is in pneumatic communication with the actuator  484  via the opening  502  in the protruding portion  486  of the housing  304  of the axle system  300 . 
     It is within the scope of this disclosure that the differential locking system  600  may further include the use of an indicator switch  604  in order to determine when the differential locking system  600  is in a first disengaged position  606  illustrated in  FIG. 6  or in a second engaged position  608  illustrated in  FIG. 7 . When the differential locking system sliding collar  460  is successfully engaged with the plurality of differential case clutch teeth  476 , the indicator switch  604  sends an electrical signal over an indicator switch data-link  610  to an indicator light (not shown) and/or an audible signaling device (not shown) in the cab of the vehicle (not shown). The indicator light (not shown) and/or the audible signaling device (not shown) informs the operator of the vehicle (not shown) that the differential locking system  600  is successfully engaged. 
       FIG. 8  is a partial cut-away schematic side view of a differential locking system  700  according to another embodiment of the disclosure. The differential locking system  700  illustrated in  FIG. 8  of the disclosure is the same as the differential locking systems  302  and  600  illustrated in  FIGS. 4-7 , except where specifically noted below. As illustrated in  FIG. 8  of the disclosure and as a non-limiting example, the axle system  300  includes a differential locking system flange portion  702  having a first side  704  and a second side  706 . The differential locking system flange portion  702  extends outboard from at least a portion of the outer surface  308  of the housing  304  at a location outboard from at least a portion of the protruding portion  486  of the housing  304  and the second axle half shaft housing  496  of the axle system  300 . According to an embodiment of the disclosure and as a non-limiting example, the differential locking system flange portion  702  may be integrally formed as part of the outer surface  308  of the housing  304  of the axle system  300 . In accordance with an alternative embodiment of the disclosure and as a non-limiting example, the differential locking system flange portion  702  may be integrally connected to at least a portion of the outer surface  308  of the housing  304  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. 
     As illustrated in  FIG. 8 , at least a portion of the outer surface  504  of the differential lock pneumatic solenoid valve  498  is integrally connected to at least a portion of the outer surface  308  of the housing  304  and/or to at least a portion of the first side  704  of the differential locking system flange portion  702 . It is within the scope of this disclosure and as a non-limiting example, that the differential lock pneumatic solenoid valve  498  may be integrally connected to the outer surface  308  of the housing  304  and/or to the first side  704  of the differential locking system flange portion  702  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. 
     In accordance with the embodiment of the disclosure illustrated in  FIG. 8  and as a non-limiting example, the differential locking system flange portion  702  of the housing  304  has an opening  708  extending from the first side  704  to the second side  706  of the differential locking system flange portion  702 . The opening  708  in the differential locking system flange portion  702  is of a size and shape to receive at least a portion of the actuator input air-line  602  of the differential locking system  700 . 
     At least a portion of the outer surface  514  of the pneumatic solenoid valve slave controller  512  is integrally connected to at least a portion of the outer surface  308  of the housing  304  and/or to at least a portion of the outer surface  504  of the differential lock pneumatic solenoid valve  498 . As a non-limiting example, that the outer surface  514  of the pneumatic solenoid valve slave controller  512  may be integrally connected to the outer surface  308  of the housing  304  and/or to the outer surface  504  of the differential lock pneumatic solenoid valve  498  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. 
       FIG. 9  is a partial cut-away schematic side view of a differential locking system  800  according to yet another embodiment of the disclosure. The differential locking system  800  illustrated in  FIG. 9  is the same as the differential locking systems  700  illustrated in  FIG. 8 , except where specifically noted below. As illustrated in  FIG. 9  of the disclosure, the differential locking system  800  includes a differential locking system housing  802  having an inner surface  804  an outer surface  806  defining a hollow portion  808  therein. The hollow portion  808  of the differential locking system housing  802  is of a size and shape to receive and/or retain at least a portion of the differential lock pneumatic solenoid valve  498  and the pneumatic solenoid valve slave controller  512 . 
     In accordance with the embodiment of the disclosure illustrated in  FIG. 9  and as a non-limiting example, the differential locking system housing  802  extends outboard from at least a portion of the outer surface  308  of the housing  304  of the axle system  300 . The differential locking system housing  802  is disposed outboard from at least a portion of the protruding portion  486  of the housing  304  and the second axle half shaft housing  496  of the axle system  300 . According to an embodiment of the disclosure and as a non-limiting example, the differential locking system housing  802  may be integrally formed as part of the housing  304  of the axle system  300 . In accordance with an alternative embodiment of the disclosure and as a non-limiting example, the outer surface  806  of the differential locking system housing  802  may be integrally connected to at least a portion of the outer surface  308  of the housing  304  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. 
     As illustrated in  FIG. 9  of the disclosure and as a non-limiting example, the differential locking system housing  802  has a first opening  810 , a second opening  812  and a third opening  814  extending from the inner surface  804  to the outer surface  806  of the differential locking system housing  802 . The first opening  810  in the differential locking system housing  802  is of a size and shape to receive at least a portion of the actuator input air-line  602  and the second opening  812  is of a size and shape to receive at least a portion of the pneumatic solenoid air-line  506 . The third opening  814  in the differential locking system housing  802  is of a size and shape to receive at least a portion of the pneumatic solenoid slave controller data-link  516 . 
       FIG. 10  is a partial cut-away schematic side view of a differential locking system  850  according to still yet another embodiment of the disclosure. The differential locking system  850  illustrated in  FIG. 10  is the same as the differential locking systems  302 ,  600  and  700 , except where specifically noted below. As illustrated in  FIG. 10  of the disclosure, the differential locking system  850  includes the differential locking system flange portion  702  illustrated in  FIG. 8 . In accordance with this embodiment of the disclosure and as a non-limiting example, at least a portion of the outer surface  514  of the pneumatic solenoid valve slave controller  512  and the outer surface  504  of the differential lock pneumatic solenoid valve  498  are integrally connected to at least a portion of the first side  704  of the differential locking system flange portion  702 . As a non-limiting example, the outer surfaces  504  and  514  of the differential lock pneumatic solenoid valve  498  and the pneumatic solenoid valve slave controller  512  may be integrally connected to the first side  704  of the differential locking system flange portion  702  by using one or more adhesives, one or more mechanical fasteners and/or one or more welds. 
       FIG. 11  is a partial cut-away schematic side view of a differential locking system  900  according to still a further embodiment of the disclosure. The differential locking system  900  illustrated in  FIG. 11  is the same as the differential locking systems  302 ,  600  and  800 , except where specifically noted below. In accordance with the embodiment of the disclosure illustrated in  FIG. 11  and as a non-limiting example, the differential locking system  900  includes the differential locking system housing  802 . 
       FIG. 12  is a schematic exploded view of a differential lock pneumatic solenoid valve and the pneumatic solenoid slave controller assembly  950  according to an embodiment of the disclosure. In accordance with the embodiment of the disclosure illustrated in  FIG. 12  and as a non-limiting example, the pneumatic solenoid valve slave controller  512  is a multi-layered board having a plurality of layers  952 . Additionally, in accordance with the embodiment of the disclosure illustrated in  FIG. 12  the pneumatic solenoid valve slave controller  512  has a hollow interior portion  954  extending from a first side  956  to a second side  958  of the pneumatic solenoid valve slave controller  512 . The hollow interior portion  954  of the pneumatic solenoid valve slave controller  512  is of a size and shape to receive and/or retain at least a portion of the pneumatic solenoid air-line  506 . 
     As illustrated in  FIG. 12  of the disclosure and as a non-limiting example, the pneumatic solenoid valve slave controller  512  may include one or more pressure sensors  960 , one or more temperature sensors  962  and/or one or more position sensors  964 . The one or more pressure sensors  960 , one or more temperature sensors  962  and/or one or more position sensors  964  are in electrical communication with and connected to at least a portion of the outer surface  514  of the pneumatic solenoid valve slave controller  512 . 
     It is within the scope of this disclosure that the embodiments of the disclosure illustrated in  FIGS. 4-12  may be combined with one another to form a differential locking system according to an embodiment of the disclosure. 
       FIG. 13  is a diagram illustrating an electrical control system  1000  for a vehicle according to an embodiment of the disclosure. One or more detection devices  1002  are used to detect the occurrence of one or more pre-determined vehicle operating conditions. As discussed previously, the one or more per-determined vehicle operating conditions may be an instruction from a user, a wheel slip condition, a loss of traction condition and/or a spin out condition. 
     When the one or more detection devices  1002  detects the occurrence of one or more of the one or more pre-determined vehicle operating conditions, one or more second controllers  1004  send an instruction over a vehicle communication bus  1006 . In accordance with an embodiment of the disclosure and as a non-limiting example, the one or more second controllers  1004  may comply with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the one or more second controllers  1004  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the one or more second controllers  1004  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). As a non-limiting example, the one or more second controllers  1004  may be a master controller, an instructing controller, a second slave controller or any other controller that is capable of sending, receiving and/or interpreting messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     As previously discussed, the vehicle communication bus  1006  is a specialized internal communications network that interconnects the various components found in the vehicle (not shown). In a non-limiting example, the vehicle communication bus  1006  may be a controller area network (CAN bus) that conforms to SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. The CAN bus is a type of vehicle communication bus  1006  that is designed to allow the various micro-controllers and devices in the vehicle (not shown) to communicate with each other without the need for a host computer. By making the vehicle communication bus  1006  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the vehicle communication bus  1006  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     Once the instruction sent by the one or more second controllers  1004  is received by one or more slave controllers  1008 , the one or more slave controllers  1008  instruct one or more solenoid valves  1010  to either open on close. According to one embodiment, the one or more solenoid valves  1010  may comply with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. SAE J-1939 is an internal vehicle communication network that interconnects the various components in the vehicle (not shown) allowing for communication and diagnostics among vehicle components. By making the one or more solenoid valves  1010  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the one or more solenoid valves  1010  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). In a non-limiting example, the one or more solenoid valves  1010  may be a pneumatic solenoid valve that is in pneumatic communication with the compressed air-supply (not shown) as previously discussed herein. 
     As previously discussed and according to an embodiment of the disclosure, the one or more slave controllers  1008  may comply with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the one or more slave controllers  1008  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the one or more slave controllers  1006  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     When the one or more second controllers  1004  instruct the one or more solenoid valves  1010  to open, a differential locking system sliding collar (not shown) engages a plurality of differential case clutch teeth (not shown) thereby locking the differential (not shown) and preventing a differential action from occurring within the differential (not shown). As a non-limiting example, the differential (not shown) may be an inter-axle differential, a forward tandem axle differential, a rear tandem axle differential, a front axle differential and/or a rear axle differential. 
     When the one or more second controllers  1004  instruct the one or more solenoid valves  1010  to close, the differential locking system sliding collar (not shown) disengages the plurality of differential case clutch teeth (not shown) thereby unlocking the differential (not shown) and allowing a differential action to occur within the differential (not shown). 
       FIG. 14  is a diagram illustrating an electrical control system  1100  for a vehicle (not shown) according to an alternative embodiment of the disclosure. One or more detection devices  1102  are used to detect the occurrence of one or more pre-determined vehicle conditions. As discussed previously, the one or more per-determined vehicle conditions may be an instruction from a user, a wheel slip condition, a loss of traction condition and/or a spin out condition. 
     When the one or more detection devices  1102  detect the occurrence of one or more of the one or more pre-determined vehicle operating conditions, one or more slave controllers  1104  send an instruction over a vehicle communication bus  1106  to instruct the one or more solenoid valves  1108  to either open or close. The one or more slave controllers  1108  may be any controller in the vehicle communication bus data-link that has adequate memory to accommodate the control logic to engage and disengage the differential locking system (not shown). According to one embodiment of the disclosure, the one or more slave controllers  1108  comply with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the one or more slave controllers  1108  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the one or more slave controllers  1108  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     As previously discussed, the vehicle communication bus  1106  is a specialized internal communications network that interconnects the various components found in the vehicle (not shown). In a non-limiting example, the vehicle communication bus  1106  may be a controller area network (CAN bus) that conforms to SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. The CAN bus is a type of vehicle communication bus  1106  that is designed to allow the various micro-controllers and devices in the vehicle (not shown) to communicate with each other without the need for a host computer. By making the vehicle communication bus  1106  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the vehicle communication bus  1106  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     In accordance with an embodiment of the disclosure and as a non-limiting example, the one or more solenoid valves  1108  may comply with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. SAE J-1939 is an internal vehicle communication network that interconnects the various components in the vehicle (not shown) allowing for communication and diagnostics among vehicle components. By making the one or more solenoid valves  1108  compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the one or more solenoid valves  1108  to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). As a non-limiting example, the one or more solenoid valves  1108  may be a pneumatic solenoid valve that is in pneumatic communication with the compressed air-supply (not shown). 
     When the one or more slave controllers  1104  instruct the one or more solenoid valves  506  to open, a differential locking system sliding collar (not shown) engages a plurality of differential case clutch teeth (not shown) thereby locking the differential (not shown) and preventing a differential action from occurring within the differential (not shown). As a non-limiting example, the differential (not shown) may be an inter-axle differential, a forward tandem axle differential, a rear tandem axle differential, a front axle differential and/or a rear axle differential. 
     When the one or more slave controllers  1104  instruct the one or more solenoid valves  1106  to close, the differential locking system sliding collar (not shown) disengages the plurality of differential case clutch teeth (not shown) thereby unlocking the differential (not shown) and allowing a differential action to occur within the differential (not shown). 
       FIG. 15  is a flow chart illustrating a method of operating a differential locking system  1200  according to an embodiment of the disclosure. As illustrated in  FIG. 15  of the disclosure, the first step in the method of operating the differential locking system  1200  is to provide a differential locking system sliding collar  1202 . Once the differential locking system sliding collar has been provided  1202 , an amount of travel needed to engage and/or disengage the differential locking system sliding collar with a differential case having a plurality of differential case clutch teeth  1206 . As illustrated in  FIG. 15  of the disclosure, the method of operating the differential locking system  1200  further includes the steps of determining an area and/or geometry of an aperture of a differential lock pneumatic solenoid valve  1208 , an actuator  1204  and/or an opening in the actuator  1210 . 
     The method of operating the differential locking system  1200  further includes identifying an amount of noise, vibration and harshness to be experienced by a differential locking system and/or identifying an amount of time needed to engage the differential locking system sliding collar with the differential case  1212 . Based on the information obtained in steps  1204 ,  1206 ,  1208 ,  1210  and/or  1212  an actuator and/or a differential lock pneumatic solenoid valve are identified  1214 . 
     Once the differential lock pneumatic solenoid valve has been identified  1214 , a pneumatic solenoid valve slave controller is provided and put into electrical communication with the differential lock pneumatic solenoid valve  1216 . The actuator, the differential lock pneumatic solenoid valve and the pneumatic solenoid valve slave controller are then attached to at least a portion of an outer surface of a housing of an axle system  1218 . Once the actuator, the differential lock pneumatic solenoid valve and the pneumatic solenoid valve slave controller are then attached have been attached to the housing of the axle system a differential locking system sub-routine is run  1220 . 
       FIG. 16  is a flow chart illustrating a sub-routine  1300  used to engage and/or disengage a differential locking system according to an embodiment of the disclosure with a differential case of a differential assembly of an axle system housing. If one or more detectors (not shown) detect a pre-determined vehicle operating condition  1302 ,  1304 ,  1306  or  1308 , then a signal is sent over a vehicle communication bus (not shown) to one or more slave controllers (not shown) to open one or more solenoid valves (not shown). As illustrated in  FIG. 16  and as a non-limiting example, the one or more pre-determined vehicle operating conditions may be a wheel slip condition  1304 , a loss of traction condition  1306 , a spin out condition  1308  and/or an instruction from an operator to lock and/or unlock the differential  1302 . 
     As previously discussed, the vehicle communication bus (not shown) is a specialized internal communications network that interconnects the various components found in the vehicle (not shown). In a non-limiting example, the vehicle communication bus (not shown) may be a controller area network (CAN bus) that conforms to SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. As previously discussed, the CAN bus is a type of vehicle communication bus (not shown) that is designed to allow the various micro-controllers and devices in the vehicle (not shown) to communicate with each other without the need for a host computer. By making the vehicle communication bus (not shown) compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the vehicle communication bus (not shown) to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     According to one embodiment of the disclosure, the one or more slave controllers (not shown) comply with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. By making the one or more slave controllers (not shown) compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the one or more slave controllers (not shown) to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). 
     Furthermore, as a non-limiting example, the one or more solenoid valves (not shown) may comply with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards. SAE J-1939 is an internal vehicle communication network that interconnects the various components in the vehicle (not shown) allowing for communication and diagnostics among vehicle components. By making the one or more solenoid valves (not shown) compliant with SAE J-1939, SAE J-1939-71, SAE J-1939-82, SAE J-1939-84 and/or ISO-11898 standards, it allows the one or more solenoid valves (not shown) to send, receive and/or interpret messages formatted according to SAE J-1939 and/or SAE J-1939-71 standard protocol(s). In a non-limiting example, the one or more solenoid valves (not shown) may be a pneumatic solenoid valve that is in pneumatic communication with the compressed air-supply (not shown). 
     Once the one or more solenoid valves (not shown) have been opened, an actuator (not shown) is able to actuate a differential locking system (not shown) and engage  1310  the differential (not shown). When the differential locking system sliding collar (not shown) is successfully engaged with the differential case (not shown), the differential (not shown) is locked thereby preventing a differential action from occurring within the differential (not shown). As a non-limiting example, the differential (not shown) may be an inter-axle differential, a forward tandem axle differential, a rear tandem axle differential, a front axle differential and/or a rear axle differential. 
     According to an embodiment of the disclosure and as a non-limiting example, the vehicle (not shown) may include an indicator light (not shown) and/or an audible alarm (not shown) within the cab of the vehicle (not shown). The indicator light (not shown) and/or the audible alarm (not shown) informs the user that the differential locking system sliding collar (not shown) is successfully engaged with the differential case (not shown) and that the differential (not shown) has been successfully locked. As illustrated in  FIG. 16 , once differential locking system sliding collar (not shown) has been successfully engaged  1312  with the differential case (not shown), a signal is sent to the cab of the vehicle (not shown) to turn on  1314  the indicator light (not shown) and/or sound  1314  the audible alarm (not shown). 
     Once the differential (not shown) has been successfully locked  1312 , the differential (not shown) will remain locked until the one or more detectors (not shown) no longer detect a wheel slip condition  1316 , loss of traction condition  1318 , spin-out condition  1320  or an instruction is sent from the user  1322  to unlock the differential (not shown). When the one or more detectors (not shown) no longer detect a wheel slip condition  1316 , loss of traction condition  1318 , spin-out condition  1320  or an instruction is sent from the user  1322  to unlock the differential (not shown), a signal is sent over the vehicle communication bus (not shown) to the one or more slave controllers (not shown) to close the one or more solenoid valves (not shown). 
     Once the one or more solenoid valves (not shown) have been closed, the differential locking system sliding collar (not shown) is disengaged  1324  from the differential case (not shown) thereby allowing a differential action to occur within the differential (not shown). 
     According to the embodiment when the indicator light (not shown) and/or the audible alarm (not shown) is used, when the differential (not shown) has been successfully unlocked  1326 , a signal is sent to the cab of the vehicle (not shown) to turn off  1328  the indicator light (not shown) and/or sound the audible alarm (not shown). In accordance with an alternative embodiment of the disclosure, the audible alarm (not shown) may remain on  1314  while the differential (not shown) is locked  1312  and once the differential (not shown) is successfully unlocked  1326 , the audible alarm (not shown) is turned off  1328 . 
     In accordance with the provisions of the patent statutes, the present invention has been described to represent what is considered to represent the preferred embodiments. However, it should be noted that this invention can be practiced in other ways than those specifically illustrated and described without departing from the spirit or scope of this invention.