Abstract:
A vehicle wiper system includes a wiper arm, a motor including a motor shaft, and a drive connection through which torque is transmitted from the motor shaft to the wiper arm when the motor is energized, and at least partially releasing a connection between the motor shaft and the wiper arm when the motor is deenergized.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to a rear wiper arm assembly for the lift gate of a motor vehicle. 
     In the automobile industry today, a detachable rear wiper arm system may be used on sport utility vehicles (SUV) and other such vehicles that have a hatch glass able to open separately from a lift gate. When the vehicle moves through a car wash, it is possible for wiper arm to become tangled with the car wash equipment resulting in the wiper arm being bent or broken. 
     In current practice, plastic rear wiper arms used on SUVs have much higher warranty costs as compared to the use of steel wiper arms, limiting the desire to use plastic rear wiper arms. 
     A need exists in the industry for an improved vehicle rear wiper system whose hatch glass is able to open separately from the lift gate. The wiper system should prevent permanent damage to the rear wiper arm during car wash usage and provide the opportunity to use plastic material for rear wiper arms. 
     SUMMARY OF INVENTION 
     A vehicle wiper system includes a wiper arm, a motor including a motor shaft, and a drive connection through which torque is transmitted from the motor shaft to the wiper arm when the motor is energized, and at least partially releasing a connection between the motor shaft and the wiper arm when the motor is deenergized. 
     The assembly lowers the potential damage to vehicle wiper arms caused by car wash equipment. By minimizing the current spring loaded latch pin engagement feature and using a non-conductive plate and electromagnet or solenoid to more fully engage the coupling pin during wiper system usage, the potential for rear wiper arm damage is reduced. 
     The assembly prevents permanent damage to the wiper arm during car wash usage and improves the opportunity to use plastic rear wiper arms having a warranty cost equal to or lower than that of steel rear wiper arms. 
     Use of a plastic rear wiper arm reduces weight and parts costs and enhances styling and design of the wiper arm. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a top perspective view of a rear wiper system for a vehicle lift gate; 
         FIG. 2  is perspective front view of the motor assembly and gear wheel of  FIG. 1 ; 
         FIG. 3  is a perspective top view showing the drive pin, lever, gear wheel and actuator; and 
         FIG. 4  is a perspective rear view showing the lever and wiper shaft. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-4  illustrate a rear wiper system  10  having a wiper arm  12  and wiper blade  14 , which oscillates across the exterior surface  16  of a rear glass pane  18  located on a lift gate of a vehicle. The hatch glass  18  swings upward to provide access to the cargo area and is able generally to open separately from the lift gate. 
     The system  10  further includes a plate  22 , which is secured to the glass pane  18  so that the plate  22  and glass pane  18  move as a unit. The rear wiper arm  12  is attached by a shaft  23  to the glass  18  and plate  22 . The wiper arm  12  oscillates about axis  27 . 
     A drive pin  24  enters and exits a hole  26  formed eccentric of axis  27  in a drive lever  28 , which is secured to shaft  23 . 
     A rear wiper motor  30  is secured to the lift gate by a bracket  32 , which is attached to the lift gate by mechanical attachments secured to bosses  34 ,  35 ,  36 . As shown in  FIG. 3 , the surface  37  along a length of the drive pin  24  extending toward its tip is conical. The conical surface  37  facilitates passing the drive pin  24  through hole  26  when producing a drive connection between the motor  30  and the wiper arm  12 . The conical surface  37  also allows the drive pin  24  to disengage readily from hole  26  when the wiper arm  12  is rotated externally after having partially retracted the drive pin  24  from hole  26 . When the drive pin  24  disengages from hole  26 , the wiper arm  12  is disengaged from the motor and drive assembly. 
     A gear wheel  38 , driven by motor  30 , supports an actuator  40  for drive pin  24 . Actuator  40  contains a compression spring  42 , which urges drive pin  24  to retract into the actuator  40  and to, at least partially, disengage from hole  26  in the drive lever  28 . Actuator  40  includes an electromagnet or solenoid  44 , which when energized forces drive pin  24  to enter hole  26  against the bias of the spring  42 , thereby driveably engaging the drive lever  28 . 
     The spring loaded drive pin  24  couples the wiper arm  12  to the drive motor shaft  46 . 
     In operation, when motor  30  is off and solenoid  44  deactivated, the spring loaded drive pin  24  retracts within actuator  40  to a less engaged position in hole  26 , thereby allowing the drive pin  24  to slip out of the drive plate hole  26 , to disengage the drive lever  28 , and to allow the rear wiper arm  12  to move if arm  12  encounters rotational force other than that produced by the motor  30 . A force applied to the wiper arm  12  by car wash equipment would cause the wiper arm to move free from the motor  30 , gear wheel  38 , and drive pin  24 . 
     When solenoid  44  is energized, the drive pin  24  extends deeper into the hole  26  of the drive lever  28 , thereby engaging the wiper arm  12  without slipping as the motor shaft  46  oscillates. 
     Preferably either the drive lever  28  or drive pin  24  is coated with a low friction material to facilitate the spring loaded drive pin  24 , which may be out of position due to abuse or movement of the wiper arm  12  during glass operation, to move on the drive lever face until it engages the hole  26  in the drive lever  28 . 
     While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.