referring to the drawings , fig1 shows an example embodiment of the improved rollover protection system 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 fig1 , improved rollover protection system 10 includes a roll bar assembly 12 , a raising and lowering mechanism 50 and an operator lever assembly 50 . roll bar assembly includes a bottom portion 14 which is fixed to the frame of vehicle 5 and a top portion 30 which is pivotably mounted to bottom portion 14 . as can be best seen by referring to fig3 , bottom 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 fig1 ) for fixing bottom members 16 a and 16 b to the frame of vehicle 5 . as can be seen in fig3 , top 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 top portion 30 . as can be best seen by referring to fig3 - 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 top portion 30 to pivot counterclockwise as viewed in fig3 - 8 between the raised position shown in fig1 , 3 , 4 , 5 and 6 to the lowered position shown in fig8 . in the alternative , relative movement between top portion 30 and bottom portion 12 as top 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 fig3 - 8 , in this example , bottom portion 14 and top portion 30 include a lock which is biased to secure top portion 30 in the raised position when top portion 30 is in the raised position . as can be seen in fig4 - 8 by viewing only one side of roll bar assembly 12 , the lock for securing top portion 30 in the raised position shown in fig4 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 fig6 , 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 top portion 30 . latch member 41 is biased by a spring 43 toward the latched position shown in fig4 and 5 . thus , latch member 41 is biased by spring 43 to secure top 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 fig4 ). bracket 35 is fixed to the lower end 34 a of side member 32 a of top 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 fig3 - 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 top portion 30 from bottom portion 14 and makes it possible for top portion 30 to fold down relative to bottom 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 top 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 top 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 bottom portion 14 and top portion 30 which align when top 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 top portion 30 when an operator applies a force to lower top 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 top portion 30 . we will first consider how raising and lowering mechanism 50 functions to lower top 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 fig3 - 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 fig3 , 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 fig4 , 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 fig3 , 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 top portion 30 are all able to rotate about an axis a shown in fig4 . axis a is fixed in relation to bottom portion 14 . as can be seen in fig4 , bracket 35 mounted to side member 32 a of top 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 fig5 , 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 top portion 30 ) cam 44 ceases its rotation relative to bracket 35 . since latch mechanism 40 is now unlatched , cam 44 , bracket 35 and top portion 30 are now free to rotate counterclockwise as seen in fig4 - 8 around the axis a ( shown in fig4 ) as cam 44 and bracket 35 are pulled by cable portion 102 a . top portion 30 continues to rotates until it reaches the lowered position shown in fig8 . 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 fig3 , the opposite side of roll bar assembly 12 includes a spring assembly 60 that biases top portion 30 toward the raised position . accordingly , when the operator releases pressure from operator lever 100 , top portion 30 rotates from the lowered position shown in fig7 back to the raised position shown in fig3 and 4 with the exception that slot 44 s and pin 35 a are in the relative positions shown in fig4 during the return stroke so that latch member 41 is in the position shown in fig4 before top portion 30 arrives in the position shown in fig4 . 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 fig2 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 fig2 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 fig3 . cable 102 is in tension because spring assembly 60 shown in fig3 pushes cam 144 in a clockwise direction as seen in fig3 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 fig2 , 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 fig3 which causes the release of latch mechanism 40 and the lowering of top 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 top 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 fig2 , so that when the operator ceases applying a force to lever 100 , the switch would open and the actuator would return top portion 30 to the raised position shown in fig1 , 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 . the structures described above merely provide an example embodiment for accomplishing the objectives of the invention . to accomplish the objectives of the invention , it is essential that a top portion of a roll bar assembly unlock and move to a lowered position in response to an operator input such as applying force to an operator lever , and then return to a raised position when the operator is no longer supplying an input such as applying force to the operator lever . 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 .
a rollover protection system unlocks and lowers from a raised position to a lowered position suitable for clearing a low hanging obstacle when an operator manually applies a force to an operator lever . the rollover protection system returns to the raised position when the operator ceases applying force to the operator lever .