Abstract:
A rollover protection apparatus unlocks and lowers from a raised position to a lowered position suitable for clearing a low hanging obstacle when an operator applies a force to an operator lever or pedal. The rollover protection apparatus returns to the raised position when the operator ceases applying force to the operator lever or pedal.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/655,014 filed on Oct. 18, 2012, which is incorporated herein by reference. 
     U.S. patent application Ser. No. 13/655,014 was a Continuation-in-Part of U.S. patent application Ser. No. 12/945,277 filed on Nov. 12, 2010 which is incorporated herein by reference. 
     U.S. patent application Ser. No. 12/945,277 claimed the benefit of U.S. Provisional Patent Application Ser. No. 61/281,059 filed on Nov. 12, 2009 which is incorporated herein by reference. 
    
    
     FIELD 
     This invention relates to a rollover protection apparatus which moves from a raised position to a lowered position suitable for clearing a low hanging obstacle. 
     BACKGROUND 
     Numerous rollover protection apparatuses may be found in the prior art. Various prior art rollover protection apparatuses teach various ways for folding down, retracting or telescoping a upper portion of a roll bar assembly usually in order to clear low hanging obstacles. Typically, the prior art teaches various types of joints that can be manually adjusted to lower the upper portion of a roll bar assembly. A problem that arises when using prior art retractable rollover protection apparatuses arises when an operator begins work in an area which includes low hanging obstacles. The potential exists for an operator to merely place the upper portion of a roll bar assembly in a lowered position prior to working in such an area. If the same area also includes a sloped surface and the operator fails to return the upper portion of the roll bar assembly to the raised position suitable for protecting the operator during a roll over, the operator will be exposed to a roll over hazard. What is needed is a rollover protection apparatus wherein an operator may quickly and temporarily lower the upper portion of a roll bar assembly to clear a low hanging obstacle and which automatically returns to a raised position when the operator is no longer acting to cause the upper portion to be lowered. With such a rollover protection apparatus, the upper portion of the roll bar assembly would lower only as needed to clear low hanging obstacles and would otherwise remain in a raised position suitable for protecting the operator during a roll over. 
     SUMMARY 
     In order to overcome the above stated problems and limitations there is provided an improved rollover protection apparatus for a vehicle which may be selectively lowered to clear low hanging obstacles. The improved rollover protection apparatus includes a roll bar assembly and a lowering and raising mechanism. The roll bar assembly includes a lower portion that is mounted to the vehicle frame and an upper portion that is mounted to the lower portion. The upper portion is movably mounted to the lower portion so that the upper portion may move between a raised position and a lowered position. A lock is associated with the upper portion and the lower portion such that when the upper portion is in the raised position, the lock secures the upper portion sufficiently to the lower portion so that the roll bar assembly will support the vehicle and protect the operator should the vehicle rollover. 
     The raising and lowering mechanism includes an operator lever. The operator lever may take the form of a handle, a foot pedal or any other movable element suitable for receiving a manually applied force from an operator. The raising and lowering mechanism is adapted so that when the operator of the vehicle applies sufficient force to the operator lever, the raising and lowering mechanism unlocks the upper portion of the roll bar assembly and urges the upper portion to move from the raised position to the lowered position. The raising and lowering mechanism is also adapted so that when the operator ceases applying force to the operator lever, the upper portion moves from the lowered position to the raised position at which point the lock re-engages. 
     Accordingly, an operator using the improved rollover protection apparatus may apply force to the operator lever to cause the upper portion of the roll bar assembly to move to the lowered position to clear an low hanging obstacle. When the vehicle has cleared the low hanging obstacle, the operator can stop applying force to the operator lever thereby allowing the upper portion of the roll bar assembly to return to the raised position where the lock re-engages to sufficiently secure the upper portion in the raised position to protect the operator should the vehicle roll over. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the improved rollover protection apparatus installed on a vehicle. 
         FIG. 2  is a side view showing an operator lever mounted to the vehicle. 
         FIG. 3  is a perspective view of a roll bar assembly. 
         FIG. 4  is a close up perspective view of one side of the roll bar assembly shown in  FIG. 3 . 
         FIG. 5  is a close up side view of the roll bar assembly showing the upper portion in the upright position with the lock engaged. 
         FIG. 6  is a close up side view of the roll bar assembly showing upper portion in the upright position and with the lock disengaged. 
         FIG. 7  is a close up side view of the roll bar assembly showing the upper portion in a position which is between the raised position and the lowered position and showing the lock disengaged. 
         FIG. 8  is a close up side view of the roll bar assembly showing the upper portion in the lowered position and the lock disengaged. 
         FIG. 9  is a perspective view of a second embodiment of a rollover protection apparatus showing the upper portion of the roll bar assembly in a raised position. 
         FIG. 10  is a rear view of the second embodiment of the rollover protection apparatus showing the upper portion of the roll bar assembly in the raised position with locking mechanism engaged. 
         FIG. 11  is a rear view of the second embodiment of the rollover protection apparatus showing the upper portion of the roll bar assembly in the raised position with locking mechanism disengaged. 
         FIG. 12  is a rear view of the second embodiment of the rollover protection apparatus showing the upper portion of the roll bar assembly in the lowered position and the upper portion actuator cable fully extended. 
         FIG. 13  is a perspective view of the second embodiment of the rollover protection apparatus showing the upper portion of the roll bar assembly in the lowered position. 
         FIG. 13A  is a magnified perspective view of the second embodiment of the rollover protection apparatus showing the details of the pivot joint between the lower portion and the upper portion of the roll bar assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings,  FIG. 1  shows an example embodiment of the improved rollover protection apparatus  10  installed on vehicle  5 . In this example, vehicle  5  may be any type of vehicle but will most typically be a riding lawn mower, tractor or other such vehicle which is likely to be exposed to a risk of a roll over. As can be seen in  FIG. 1 , improved rollover protection apparatus  10  includes a roll bar assembly  12 , a raising and lowering mechanism  50  and an operator lever assembly  50 . Roll bar assembly includes a lower portion  14  which is fixed to the frame of vehicle  5  and a upper portion  30  which is pivotably mounted to lower portion  14 . 
     As can be best seen by referring to  FIG. 3 , lower portion  14  of roll bar assembly  12 , in this example, includes two spaced bottom members  16 A and  16 B. Each of the two spaced bottom members  16 A and  16 B have upper ends  18 A and  18 B respectively and lower ends  19 A and  19 B respectively where, in this example, may be found bolt holes  19 H for receiving bolts (shown in  FIG. 1 ) for fixing bottom members  16 A and  16 B to the frame of vehicle  5 . As can be seen in  FIG. 3 , upper portion  30  includes two side members  32 A and  32 B. Each side member  32 A and  32 B includes lower ends  34 A and  34 B respectively and upper ends  36 A and  36 B respectively. A top transverse member  38  connects between upper ends  36 A and  36 B to complete a rigid upside down U shaped upper portion  30 . 
     As can be best seen by referring to  FIGS. 3-8 , lower ends  34 A and  34 B of side members  32 A and  32 B are pivotably mounted to the upper end  18 A and  18 B of bottom members  16 A and  16 B respectively. The joints between the lower ends of side members  32 A and  32 B and the upper ends of bottom members  16 A and  16 B are adapted to allow upper portion  30  to pivot counterclockwise as viewed in  FIGS. 3-8  between the raised position shown in  FIGS. 1, 3, 4, 5 and 6  to the lowered position shown in  FIG. 8 . In the alternative, relative movement between upper portion  30  and lower portion  12  as upper portion  30  moves between the raised position and a lowered position could be accomplished by a translation such as with a telescoping structure or by a pivoting parallelogram structure or the like. The pivoting structure shown and described in this example is merely one way of accomplishing movement between a raised position and a lowered position. The remaining elements of the raising and lowering mechanism which will be described in greater detail below, are, out of necessity, adapted to function with a pivoting structure. 
     As can be seen in  FIGS. 3-8 , in this example, lower portion  14  and upper portion  30  include a lock which is biased to secure upper portion  30  in the raised position when upper portion  30  is in the raised position. As can be seen in  FIGS. 4-8  by viewing only one side of roll bar assembly  12 , the lock for securing upper portion  30  in the raised position shown in  FIG. 4  is a latch mechanism  40  which includes a latch member  41  which is pivotably mounted to a bracket  20  to pivot about a shaft  41 A which is carried by bracket  20 . Bracket  20  is fixed to upper end  18 A of bottom member  16 A. As can be best seen in  FIG. 6 , latch member  41  includes a notch  41 B that is shaped to engage a rod  42 . Rod  42  is generally horizontal and oriented transversely and is fixed to a bracket  35  that is fixed to the lower end  34 A of side member  32 A of upper portion  30 . Latch member  41  is biased by a spring  43  toward the latched position shown in  FIGS. 4 and 5 . Thus, latch member  41  is biased by spring  43  to secure upper portion  30  in the raised position. Latch member  41  further presents a boss  41 C. A cam  44  is rotatably mounted to a bracket  35  for rotation about an axis passing through the center of shaft  36  (shown in  FIG. 4 ). Bracket  35  is fixed to the lower end  34 A of side member  32 A of upper portion  30 . Cam  44  engages boss  41 C with two portions: a first recessed cam portion  44 A and a second offset cam portion  44 B. As a downward movement of cable  102  rotates cam  44  counterclockwise as viewed in  FIGS. 3-8 , boss  41 C of latch member  41  is contacted by second offset cam portion  44 B of cam  44  which has a larger radius than first recessed cam portion  44 A. This urges latch member  41  out against spring  43  and disengages latch member  41  from rod  42 . This unlatches upper portion  30  from lower portion  14  and makes it possible for upper portion  30  to fold down relative to lower portion  14 . The skilled reader should understand that the same latch and cam mechanism is preferably identically repeated on the opposite side of roll bar assembly  14  between upper end  18 B of bottom member  16 B and the lower end  34 B of side member  32 B. The skilled reader should further consider that the latch mechanism described above is merely one way to provide a lock that is biased to lock upper portion  30  in the raised position. A multitude of other mechanisms well known in the art, may be selected for providing such a biased lock that can be selectively disengaged to allow upper portion  30  to move to a lowered position. Just one example of an alternate locking mechanism might include a spring biased pin which engages corresponding holes in lower portion  14  and upper portion  30  which align when upper portion  30  is in the raised position. The spring biased pin could be connected to the raising and lowering mechanism such that it is urged against its spring bias to unlock upper portion  30  when an operator applies a force to lower upper portion  30 . 
     Raising and lowering mechanism  50  includes an operator lever  100  and a spring assembly  60 . Raising and lowering mechanism  50  functions in combination with an operator lever  100  to cause the lowering and raising of upper portion  30 . 
     We will first consider how raising and lowering mechanism  50  functions to lower upper portion  30  from the raised position to the lowered position. In this example operator lever  100 , which may take the form of a handle or a pedal, is connected by cable  102  to cam  44 . In this example, cable  102  connects to a sliding bracket  22  shown in  FIGS. 3-8 . An upper cable portion  102 A connects between sliding bracket  22  and a pin  102 P that is mounted to cam  44 . As can be seen in  FIG. 3 , a shaft  64  extends between cam  44  and a cam  144  that is mounted to the opposite side of roll bar assembly  12 . As can be seen in  FIG. 4 , cam  44  includes two opposite, identical plates that are located on opposite sides of upper end  18 A of bottom member  16 A. As can be seen in  FIG. 3 , the same arrangement exists for cam  144  on the opposite side for bottom member  16 B. Shaft  64  is fixed to both side plates of cam  44  as well as both side plates of the cam  144  on the opposite side. Bracket  35  that is fixed to side member  32 A presents ears on both sides of side member  32 A which present co-axial bores for receiving shaft  64 . A bracket  21  is fixed to the upper end  18 A of side member  16 A supports a bushing  36  that, in turn, also receives shaft  64 . Thus cams  44 ,  144 , shaft  64  and upper portion  30  are all able to rotate about an axis A shown in  FIG. 4 . Axis A is fixed in relation to lower portion  14 . As can be seen in  FIG. 4 , bracket  35  mounted to side member  32 A of upper portion  30  includes a pin  35 A which rides in a constant radius slot  44 S. Also, a tension spring  44 S 2  connects between cam  44  and pin  35 A that biases cam  44  clockwise toward pin  35 A. Slot  44 S, first recessed cam portion  44 A and second offset cam portion  44 B are arranged so that, as cable portion  102 A pulls on cam  44 , cam  44  rotates counterclockwise as second offset cam portion  44 B rotates counterclockwise to encounter boss  41 C of latch member  41 . As is shown in  FIG. 5 , and as described above, this causes latch member  41  to release rod  42 . Latch member  41  releases rod  42  before the clockwise end of slot  44 S encounters pin  35 A. Once the clockwise end of slot  44 S of cam  44  encounters pin  35 A, (which is fixed to bracket  35  which is, in turn, fixed to upper portion  30 ) cam  44  ceases its rotation relative to bracket  35 . Since latch mechanism  40  is now unlatched, cam  44 , bracket  35  and upper portion  30  are now free to rotate counterclockwise as seen in  FIGS. 4-8  around the axis A (shown in  FIG. 4 ) as cam  44  and bracket  35  are pulled by cable portion  102 A. Upper portion  30  continues to rotates until it reaches the lowered position shown in  FIG. 8 . if cable  102  and cable portion  102 A continue to transmit sufficient force. 
     The operation described above occurs in reverse when the operator releases pressure from operator lever  100 . As can be seen in  FIG. 3 , the opposite side of roll bar assembly  12  includes a spring assembly  60  that biases upper portion  30  toward the raised position. Accordingly, when the operator releases pressure from operator lever  100 , upper portion  30  rotates from the lowered position shown in  FIG. 7  back to the raised position shown in  FIGS. 3 and 4  with the exception that slot  44 S and pin  35 A are in the relative positions shown in  FIG. 4  during the return stroke so that latch member  41  is in the position shown in  FIG. 4  before upper portion  30  arrives in the position shown in  FIG. 4 . Accordingly, during the return stroke, pin  42 A encounters a sloped upper surface of latch member  41  to cause latch member  41  to turn out to receive pin  42 A. Also because spring  44 S 2  biases cam  44  clockwise, boss  41 C of latch assembly  40  remains in contact with first recessed cam portion  44 A thereby maintaining latch assembly  40  in the latched position. 
     Operator lever  100  is shown in  FIG. 2  as a foot pedal but can also be a hand lever or other such member for receiving force from an operator. Operator lever  100  is connected to a cable  102 . Lever  100  is biased in the position shown in  FIG. 2  by tension which is applied by cable  102 . Cable  102  routed to connect to sliding member  22  mounted to bracket  20  of roll bar assembly  12  shown in  FIG. 3 . Cable  102  is in tension because spring assembly  60  shown in  FIG. 3  pushes cam  144  in a clockwise direction as seen in  FIG. 3  which in turn applies a torque to shaft  64  which further pushes cam  44  in a clockwise direction to apply to an upper cable portion  102 A which is connected to cable  102 . When operator lever  100  is up as shown in  FIG. 2 , cable  102  is not pulling down on cam  44 . When operator lever  100  is pressed forward by an operator, cable  102  pulls on cam  44  which rotates counterclockwise as seen from the perspective of  FIG. 3  which causes the release of latch mechanism  40  and the lowering of upper portion  30  as described above. 
     The skilled reader will appreciate that, for example, an actuator may be interposed between operator lever  100  and cam  44  so that the lowering and even the raising of upper portion  30  may be powered in response to a switch which is activated by the rotation of lever  100 . So, for example, in an embodiment having a powered actuator, lever  100  might close a switch for activating a powered actuator and might also be biased toward the position shown in  FIG. 2 , so that when the operator ceases applying a force to lever  100 , the switch would open and the actuator would return upper portion  30  to the raised position shown in  FIGS. 1, 3 and 4 . As is well known in the art, power may be supplied to an actuator in any one of a number of forms including, but by no means limited to, hydraulic power, electric power and pneumatic power. 
     Second Embodiment 
     A second embodiment of the improved rollover protection apparatus, namely rollover protection apparatus  410 , is shown in  FIGS. 9-13 . As can be seen in  FIG. 9 , rollover protection apparatus  410  includes a lower portion  420  and an upper portion  480 . In this example, lower portion  420  includes two upright supports  422  and  424  which are rigidly fixed to vehicle frame  402 . Upper portion  480 , in this example, is a generally upside down U shaped member  482  which is pivotably mounted at its lower ends  484  and  486  to the upper ends of upright supports  422  and  424  respectively. In this example, lower portion  420  also includes a releasable lock mechanism  490  which will be described in greater detail below. Releasable lock mechanism  490  is coupled to a lock releasing device, which in this example, includes a manually operable foot lever  406  pivotably mounted to frame  402  and a lock actuation cable  406 A. Foot lever  406  may be replaced by any one of a number of actuation devices which may even include electrically powered or hydraulically powered devices which may be activated by a small manual input such as the pushing of a button or the toggling of a switch. When, in this example, foot lever  406  is pivoted by an operator from the position shown in  FIG. 9  to the position shown in  FIG. 13 , cable  406 A is pulled. Cable  406 A is connected to releasable lock mechanism  490  so that, when cable  406 A is pulled, releasable lock mechanism  490  initially moves from a locked position shown in  FIG. 10  to a released position shown in  FIG. 11 . When releasable lock mechanism  490  is in the released position, it is possible for upper portion  480  to pivot from the raised position shown in  FIG. 9  toward the lowered position shown in  FIG. 13 . 
     As can be seen in  FIG. 9 , upper portion  480  is pivotably mounted to lower portion  420  for rotation about axis AA. In  FIGS. 9 and 13 , axis AA is shown to be offset behind the centerlines of the members of upper and lower portions  480  and  420 . As can be seen in  FIG. 9 , a bracket  484 A is fixed to and extends back from the lower end  484  of upper member  482 . Bracket  484 A attaches to an upper portion cable which is used associate the movement of upper portion  480  with releasable lock mechanism  490  as will be described in greater detail below. A second set of opposite brackets  484 A and  484 B extend from the opposite sides of the lower portions of upper portion  480  and connect to a pair of upper portion return springs  482 S 1  and  482 S 2 . Return springs  482 S 1  and  482 S 2  connect between brackets  484 A and  484 B and upright supports  422  and  424  respectively of lower portion  420  and bias upper portion  480  toward the upright position shown in  FIG. 9 . 
     Releasable lock mechanism  490  can be better understood by referring to  FIGS. 9-12 . In this example, lock mechanism  490  includes a cam plate  492  and a bell crank  496 . As can be best seen in  FIGS. 10 and 11 , cam plate  492  is pivotably mounted for rotation about axis A which is generally longitudinal and bell crank  496  is pivotably mounted for rotation about axis B which is also generally longitudinal. Cam plate  492  is spring biased in the counter-clockwise direction by spring  492 A. As can be best seen in  FIGS. 10 and 11 , bell crank  496  is connected at its opposite ends to two opposing rods  496 A and  496 B to which are pivotably jointed at their distal ends to two opposite latch pins  498 A and  498 B. Latch pins  498 A and  498 B are received by the co-axial bores of a clevis fittings  422 A and  424 A fixed to the upper ends of upright supports  422  and  424  respectively and also by the aligned co-axial bores of corresponding lug fittings  484 L and  486 L fixed to lower ends  484  and  486  respectively of upper portion  480 . Thus, when these corresponding clevis and lug fittings associated with the upper and lower portions of the roll bar assembly receive latch pins  498 A and  498 B, upper portion  480  of roll bar assembly  410  is locked in the upright position as shown in  FIG. 9 . The skilled reader should observe by referring to  FIGS. 9 and 13 , that axis AA, which is the axis of rotation of upper portion  480  with respect to lower portion  420 , is offset from the center line of latch pins  498 A and  498 B, so that the hinge structure for the pivot joint between upper and lower portions  480  and  420  and latch pins  498 A and  498 B secure upper portion  480  in the upright position as shown in  FIG. 9  when latch pins  498 A and  498 B are engaged as shown in  FIG. 10 . The skilled reader can also observe that, in this example, lug fittings  484 L and  486 L have extending portion  484 L 2  and  486 L 2  which are generally symmetrical and identical. Extending portion  484 L 2  may be best seen in  FIG. 13A . As can be seen in  FIG. 13A , extending portion  484 L 2  is shaped to block clevis  422 C so that it is not possible for latch pin  498 A to enter lug clevis  422 C when upper portion  480  is moved away from the upright position shown in  FIG. 9 . The same arrangement is repeated on the other side so that it is not possible for either latch pin  498 A or  498 B to enter either clevis  422 C or  424 C respectively when upper portion  480  is moved away from the upright position shown in  FIG. 9 . 
     As is noted above, in this example, cam plate  492  shown in  FIG. 10  is pivotably mounted for rotation about axis A and is spring biased in the counterclockwise direction. Bell crank  496  is pivotably mounted for rotation about axis B. As can be seen in  FIGS. 10 and 11 , bell crank  496  presents a cam follower  496 F which is normally received by a recess  492 R in the periphery of cam plate  492 . As can also be seen in  FIGS. 9 and 10 , the distal end of lock actuation cable  406 A is connected to cam plate  492 . Still further, the proximate end of upper portion actuation cable  402  is also connected to cam plate  492  but by means of a pin  502 A which is slidably received by a tangential slot  492 TS defined near the periphery of cam plate  492 . The result of this arrangement is that when lock actuation cable  406 A pulls on cam plate  492 , cam plate  492  rotates clockwise through angle A 1  from a first locked position shown in  FIG. 10  to a second unlocked position shown in  FIG. 11 . When this occurs, cam follower  496 F of bell crank  496  is forced out of recess  492 R which forces the counter clockwise rotation of bell crank  496 . All of this has been arranged so that as cam plate  492  rotates by angle A between the first locked position to the second unlocked position, sufficient rotation of bell crank  496  occurs in order to withdraw latch pins  498 A and  498 B sufficiently from the corresponding lugs of the lock structure common to upper portion  480  so that upper portion  480  can freely rotate from the raised position shown in  FIG. 9  toward the lowered position shown in  FIG. 13 . 
     Once the operator has depressed foot lever  406  sufficiently to withdraw latch pins  498 A and  498 B from the respective fittings, and in particular lug fittings  484 L 1  and  486 L 1  as described above, thus unlocking upper portion  480  from lower portion  420 , the operator may continue pressing foot lever  406 . When this occurs, lock actuation cable  406 A continues pulling on cam plate  492 . Recall that at this point, cam plate  492  is in the unlocked position shown in  FIG. 11  and the pin at the end of upper portion actuation cable  502  is at the extreme end of tangential slot  492 TS. Thus, now, cam plate  492  begins pulling on the proximate end of upper portion actuation cable  502  as it continues to rotate clockwise until cam plate  492  reaches a third upper portion fold down position shown in  FIG. 12 . Note that in  FIG. 12 , cam plate  492  is rotated as far as possible in the clockwise direction, yet bell crank  496  has not changed its position from  FIG. 11 . This is because the arc describing the outer edge of cam plate  492  extending counterclockwise from recess  492 R is centered on axis A. Thus, cam follower  496 F does not move even as cam plate  492  rotates from the second unlocked position shown in  FIG. 11  to the third upper portion fold down position shown in  FIG. 12 . As the proximate end of upper portion actuation cable  502  is pulled to the position shown in  FIG. 12 , the distal end of actuation cable  502  pulls on bracket  484 B shown in  FIGS. 9 and 13 . This causes upper portion  480  to rotate down to the lowered position shown in  FIG. 13 . 
     Once upper portion  480  has cleared the overhead obstacle, and once the operator has released pressure from foot lever  406 , upper portion  480  is free to return to the upright position shown in  FIG. 9 . Upper portion pivots back to the upright position at least in part because it is biased to do so by upper portion return springs  48251  and  482 S 2 . When this occurs, brackets  484 A attached to the fitting at the lower ends of member  484  pulls on cable  502 . Cable  502  then pulls on cam plate  492  (shown in  FIG. 12 ) to cause cam plate  492  to pivot in the counter clockwise direction from the position shown in  FIG. 12  to the position shown in  FIG. 11 . When cam plate  492  is in the position shown in  FIG. 11 , upper portion  480  (shown to include members  484  and  486  in  FIG. 11 ) is in the upright position (as is also shown in  FIG. 9 ), but latch pins  498 A and  498 B are still withdrawn from lugs  484 L 1  and  484 L 2  and at least the outboard portions of clevises  422 C and  424 C respectively. This is the case because cam follower  496 F is at the edge of recess  492 R but has not been received by recess  492 R. At this point cable  502  has no more travel remaining to cause further counterclockwise rotation of cam plate  492 . At this point, spring  492 A continues to pull cam plate  492  clockwise as cam follower  496 F rolls down into recess  492 R. When this occurs, bell crank  496  rapidly rotates clockwise thereby allowing the outwardly spring biased latch pins  498 A and  498 B to slide out to reengage lugs  484 L 1  and  484 L 2  and the outboard portions of clevises  422 C and  424 C respectively. This causes upper portion  480  to be locked and secured in the upright position shown in  FIG. 9 . 
     With the second embodiment apparatus  410  described above, it is possible for the operator to merely press lever  406  sufficiently to unlock upper portion  480  prior to encountering an overhead obstacle. With apparatus  410  it is possible the obstacle itself could provide a force to push upper portion  480  down while clearing the obstacle. Although this might not be a recommended way of using apparatus  410 , and although it might cause damage to either the obstacle or apparatus  410 , less damage would likely occur than would occur if an upright, fixed roll over protection bar or hoop were to simply collide with an overhead obstacle. The above described apparatus  410 , once unlocked as described above, is able to rotate down toward the lowered position shown in  FIG. 13  in response to pressure from an obstacle. In such as case cable  502  would buckle where it connects to bracket  484 A (see  FIG. 9 ). Extending portions  484 L 2  and  486 L 2  of lug fitting  484 L and  486 L would block the retracted latch pins  498 B and  498 A respectively from entering the space needed for lugs  484 L and  486 L until upper portion  480  was returned to the upright position shown in  FIG. 9 . 
     Thus, such an apparatus would accommodate a mode where upper portion  480  was merely unlocked to allow upper portion  480  to yield to an obstacle and wherein once the obstacle was cleared, upper portion  480  would return to the upright position and be secured and locked. Thus, the apparatus described above, provides a structure that can be folded down to avoid overhead obstacles, but which, as a default mode of operation, is locked in an upright position suitable for protecting an operator during a roll over, thus providing a more versatile and safer vehicle. 
     The structures described above merely provide example embodiments for accomplishing the objectives of the invention. To accomplish the objectives of the invention, it is essential that an upper portion of a roll bar assembly unlock in response to an operator input so that the upper portion can move to a lowered fold-down position. To accomplish the objectives of the invention, it is also essential that the upper portion of the roll bar assembly be biased to return to the upright raised position and to lock after the obstacle has been cleared. 
     It is to be understood that while certain forms of this invention have been illustrated and described, it is not limited thereto, except in so far as such limitations are included in the following claims and allowable equivalents thereof.