Abstract:
An electric vehicle is provided with motor braking and includes a locking differential that provides positive braking on slippery surfaces so as to prevent relative movement of the first and second output shafts of the differential.

Description:
FIELD 
       [0001]    The present disclosure relates to electric vehicles, such as golf cars and utility vehicles, and more particularly, to a locking differential for an electric vehicle. 
       BACKGROUND AND SUMMARY 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    Electric vehicles have grown more and more popular for use as golf cars and utility vehicles. Electric vehicles are relatively low maintenance and emit zero environmentally harmful emissions. In addition, the electric vehicles are highly reliable. 
         [0004]    Although electric vehicles have proven to be very popular and efficient, the need to improve the vehicle&#39;s manufacture and assembly still exists. One area of recent development for electrical vehicles relates to the braking system. Examples of such inventions are disclosed in U.S. Pat. Nos. 6,457,568 and 6,686,719 which are commonly assigned. In U.S. Pat. No. 6,457,568, a disc brake system for use with electric vehicles is provided. Electric vehicle disc brake systems are specially designed due to the limited ground clearance of the electric vehicle which has smaller wheels than a standard automotive vehicle. Additionally, U.S. Pat. No. 6,686,719 provides for regenerative braking, wherein electric energy is generated during braking so as to aid in the charging of the vehicle batteries. 
         [0005]    The present invention utilizes the drive motor as a source of braking torque. Providing braking by the electric motor accomplishes two things: it returns energy back to the battery by using the electric motor  12  as a generator, and it reduces the cost and maintenance associated with a mechanical braking system. However, braking on slippery surfaces can be difficult when the drive motor is used for providing braking torque. In cases where one wheel loses traction, the other wheel is free to turn, resulting in no braking torque being applied to either of the wheels. This can also happen when an electro-mechanical brake on the motor shaft is used for emergency braking or for parking. To prevent this problem, the present disclosure provides a locking mechanism for locking both sides of the differential together so that both wheels will turn together, thus providing braking torque. In other words, when the first and second output shafts of the differential are locked together, and the input from the motor is braked, the differential is locked up and, therefore, the rear wheels are prevented from rotating. The locking differential can be actuated by a solenoid that will force the locking mechanism to lock. The lock signal is provided by a drive controller when a brake pedal is pressed a predetermined amount of its travel. The amount of the braking signal necessary to actuate the lock can be programmable. 
         [0006]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0007]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0008]      FIG. 1  is a schematic diagram of an electric vehicle drivetrain, according to the principles of the present disclosure; 
           [0009]      FIG. 2  is a perspective view of a locking differential, according to the principles of the present disclosure; and 
           [0010]      FIG. 3  is a plan view of the differential shown in  FIG. 2  with the differential cover removed. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0012]    With reference to  FIG. 1 , an electric vehicle  10  is provided including an electric motor  12  provided with an output shaft  14  which is drivingly connected to a differential  16 . The differential  16  includes first and second output axle shafts  18 ,  20  for driving the left and right rear wheels  22 ,  24 , respectively. The differential  16  is a locking differential which includes a locking mechanism  26  which is controlled by a vehicle central processor unit  28 . The vehicle central processing unit  28  also provides control to the electric motor  12  in response to signals received from the vehicle accelerator pedal  30  and brake pedal  32 . In response to braking signals received from the brake pedal  32 , the central processor unit  28  controls the electric motor to provide braking torque to the locking differential  16 . Upon receipt of a braking signal from the brake pedal  32  exceeding a predetermined value, the central processor unit activates the locking mechanism  26  in order to engage the output shafts  18 ,  20  to one another. 
         [0013]    As shown in  FIG. 2 , the locking mechanism  26  includes an electronic solenoid  40  including an axially extending plunger  42  which is connected to a linkage member  44  which, in turn, is connected to an actuating arm  46 . The actuating arm  46  is connected to a pivot shaft  48  which includes a shift fork  50 , as best shown in  FIG. 3 . The shift fork  50  engages a coupling sleeve  52  having internal splines which engage external splines  54  and  56  which are connected to first and second output shafts  18 ,  20 , respectively. When the coupling sleeve  52  straddles both sets of splined teeth  54 ,  56  of first and second output shafts  18 ,  20 , the output shafts  18 ,  20  are engaged to one another so as to prevent relative rotation therebetween. When the coupling sleeve  52  is moved into engagement with only one set of splined teeth  54 ,  56 , then the first and second output shafts are free to rotate relative to one another. 
         [0014]    The differential  16  includes the input shaft  14  which is connected to a drive gear  60 . Drive gear  60  drivingly engages input gear  62  which drives the casing  64 . As is typically known in a differential, the casing  64  supports a pair of beveled gears which rotate with the casing and drive a pair of output gears (only of which,  72 , is shown) which are mounted to the first and second output shafts  18 ,  20 , respectively. It should be understood that the locking mechanism can be utilized for locking any of the components of the differential  16  together. By locking any two components, the entire differential is locked-up to thereby engage the first and second output shafts together to prevent relative rotation therebetween. In particular, a locking mechanism may directly engage the first and second output shafts to one another, or may engage the differential housing  64  to one of the output shafts  18 ,  20  in order to engage the first and second output shafts together.