Variable pressure windshield wiper system

A variable force windshield wiper system for an automobile has a rod which is slidably received within a bore of the drive shaft of the wiper system. The end of the rod contacts a lever arm when the rod extends out from the drive shaft. The lever arm is connected to a spring. The other end of the spring is connected to the windshield wiper arm. As the distance of the rod outside the drive shaft increases, the lever arm rotates about a fulcrum and extends the spring thereby increasing the downward force of the wiper arm toward the windshield. To move the rod, a cam having a threaded exterior surface is mounted on the drive shaft and is attached to the rod. A nut having a threaded interior surface engages the threads of the cam. The nut and cam rotate together if no wiper force change is desired The exterior surface of the nut has ratchet teeth. A pawl is used to selectively engage the ratchet teeth of the nut. When an increase or decrease in force for the wiper arm is desired, the pawl is used to engage the ratchet surface to prevent the nut from rotating. The cam will travel up or down the drive shaft when the nut is prevented from rotating. As the cam moves relative to the drive shaft, the rod moves the lever arm.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates generally to a windshield wiper system, and 
more particularly, to a windshield wiper system that is adjustable to 
compensate for wind force particularly at high speeds. 
2. Discussion of the Related Art 
As the speed of a vehicle increases, the air impinging on the windshield 
increases the tendency for the wiper blades to lift from the windshield. A 
wiper blade that has lifted from the windshield does not effectively clear 
the windshield. 
Several solutions have been proposed to solve the above-stated problem. One 
solution is to provide an air deflector that connects directly to the 
wiper arm. The position, however, of an air deflector on the windshield 
wiper system is fixed. As the windshield wiper blade sweeps across the 
windshield, the position of the air deflector changes relative to the 
airflow. Therefore, a constant amount of force is not placed by the wiper 
blade on the surface of the windshield. As a result of the varying force, 
the windshield may not be cleared effectively. 
Other solutions include manually varying the amount of force of the blade 
against the windshield applied by the windshield wiper arm. Several 
problems are present in existing solutions. One problem is that a manually 
adjusted arm force does not account for varying vehicle speeds. If the 
wiper blade arm force is improperly adjusted, i.e., if too much force is 
provided to the wiper blade during low speed operation, the wiper blade 
may experience premature wear. Likewise, if too little force is provided 
by the wiper arm, the wiper blade may lift off the windshield at high 
speeds and not properly clear the windshield. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a method for 
varying the force on the windshield wiper blade to compensate for 
different load requirements. 
One advantage of the present invention is that since a variety of operating 
parameters of the vehicle and the wiper system are monitored, the 
operating force of the wiper blade arm can be continuously varied during 
vehicle operation, responsive to the operating parameters, providing an 
optimum windshield wiper blade force against the windshield. 
The present invention generally has a drive shaft, rotatable about a first 
axis, has a drive arm and a wiper arm connected to the drive shaft for 
unitary rotation therewith. The wiper arm has a portion pivotable about a 
second axis substantially perpendicular to the first axis. A wiper blade 
is disposed at an end of the wiper arm for movement therewith. A spring 
has a first end engaging the wiper arm and biases the wiper blade against 
the windshield. An adjustment mechanism disposed between the drive shaft 
and a second end of the spring controls the length of the spring and thus 
the force provided by the spring. 
The adjustment mechanism includes a lever arm rotatably connected to the 
wiper arm. One end of the lever arm is connected to the spring. The other 
end of the lever arm contacts a rod slidably received within a bore of the 
drive shaft. As the rod extends out from the drive shaft, the rod rotates 
one end of the lever arm and the other end of the lever arm stretches the 
spring. Because the spring is connected to the windshield wiper arm, the 
force of the wiper blade on the windshield increases. As the distance of 
the rod outside the drive shaft increases, the lever arm rotates and 
increases the biasing force of the wiper blade against the windshield. 
To move the rod, a screw having a threaded exterior surface is mounted on 
the drive shaft and attached to the rod by a pin connected through an 
elongated slot in the drive shaft so that the shaft rotates the screw. The 
screw and pin assembly can move axially on the drive shaft along the slot. 
The pin engages the rod to move the rod out of the end of the drive shaft. 
The maximum distance of the rod from the shaft corresponds to the length 
of the elongated slot. A nut having a threaded interior surface engages 
the threads of the screw. The nut stays in a fixed axial position with 
respect to the drive shaft but can rotate. The exterior surface of the nut 
has a ratchet tooth defining a ratchet surface. A pawl connected to a 
miniature motor is used to selectively engage the ratchet surface of the 
nut. If no change in the wiper blade force is desired, the pawl does not 
engage the ratchet surface. In this situation, the nut and screw move 
together around the drive shaft. When an increase or decrease in force of 
the wiper blade is desired, the pawl is used to engage the ratchet surface 
to prevent the rotation of the nut. In such a situation, the nut is 
prevented from rotating while the screw is allowed to rotate with the 
drive shaft. The screw and pin will then travel axially with the drive 
shaft. As the screw and pin move relative to the drive shaft, the pin 
pushes against the rod to either extend the rod from the drive shaft or 
retract the rod into the drive shaft. The biasing force on the wiper arm 
on the windshield is thereby either decreased or increased. 
In one aspect of the invention, the pawl movement is controlled by a 
microprocessor. The microprocessor determines the optimum amount of force 
to be applied to the windshield. Various parameters may be factored into 
the considerations such as speed of the wiper system, the rotational 
position of the drive shaft, the speed of the vehicle and the position of 
the nut and screw.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, an automotive vehicle 10 is shown having a windshield 
12 and windshield wipers 14. Windshield wipers 14 are controlled by a 
variable pressure wiper control system 16. Windshield wipers 14 include a 
conventional wiper blade 17 attached thereto. A speed sensor 18 is 
connected between variable force wiper control system 16 and a 
speed-measuring position such as a wheel 20. A wheel 20 is used for 
illustrative purposes only. One skilled in the art would recognize various 
positions in the vehicle for obtaining vehicle speed including directly 
from the engine control module. 
Referring to FIGS. 2 and 3, a drive shaft 26 is coupled to a windshield 
wiper arm 82 and to a drive arm 34. A wiper motor 27, shown in FIG. 7 in 
schematic form and selectively energized by a voltage source 29 acting 
through a relay 31, connects to drive arm 34 to rotate drive shaft 26 in 
both clockwise and counter clockwise directions to provide the back and 
forth movement of wipers in a conventional manner. Windshield wiper arm 82 
and windshield wiper blade 17 attached thereto moves with drive shaft 26. 
Windshield wiper arm 82 includes a cast head portion or head casting 74 
and an extension portion 85 pivotally connected to the head casting 74 by 
a pivot pin 84. 
The force biasing the wiper arm 82 toward the windshield is provided by 
steel coil tension spring 86 with one end connected to an adjustment 
mechanism 87 and with the other end connected to an attachment point 88 on 
extension portion 85. The adjustment mechanism 87 is coupled to drive 
shaft 26 and controls the elongation of spring 86. As spring 86 stretches, 
the force of wiper blade 17 against the windshield 12 is increased. 
Drive shaft 26 has an axial bore 28, preferably through its center. The 
adjustment mechanism has a rod 72 housed within bore 28 of drive shaft 26, 
a lever arm 76 connected to windshield wiper arm 82 and a means to move 
rod 72. Movement of rod 72 displaces one end of lever arm 76, causing 
lever arm 76 to rotate about a fulcrum defined by a pin 80. The other end 
of lever arm 76 is connected to spring 86 by a spring catch 78. In FIG. 2 
spring catch 78 is shown integrated into lever arm 76. Rotation of lever 
arm 76 varies the length of spring 86 and the force induced by spring 86. 
A lower housing 40 and an upper housing 44 are used to enclose the means 
for axially displacing rod 22 within bore 28. A spring washer 36 between 
housing 40 and drive arm 34 maintains an axial bias on shaft 26. A lower 
bearing 38 rotatably supports shaft 26 within lower housing 40. Similarly, 
upper bearing 42 rotatably supports shaft 26 within upper housing 44. A 
spring clip 46 fits in groove 48 to axially retain drive shaft 26 within 
housing 40 and 44. 
Lower housing 40 and upper housing 44 also enclose a threaded cam 50, a nut 
52 and a thrust washer 54. A pin 56 extends transversely through an 
axially elongated slot 30 in drive shaft 26. As can be seen in FIG. 2, pin 
56 has a square cross section. Ends of pin 56 are disposed in notches 57 
in an upper of surface of cam 50, rotatably fixing cam 50 to drive shaft 
26. Pin 56 is engaged near its middle by an end of rod 72. Cam 50, pin 56 
and rod 72 all move together in an axial direction with respect to drive 
shaft 26. 
Axial movement of cam 50 is the result of relative rotation between cam 50 
and nut 52. The outer surface of cam 50 has outer acme threads 58. Nut 52 
has inner acme threads 60 that mesh with threads 58 of cam 50. Nut 52 is 
axially fixed within housing 40 and 44 between thrust washer 54 and upper 
housing 44. Cam 50 is free to move within a predetermined axial range in 
the housing. This combination produces the desired axial displacement of 
cam 50, pin 56 and rod 72 with relative cam 50 to nut 52 rotation. Because 
the acme thread configuration resists being back-driven by the force from 
spring 86 applied through rod 72, nut 50 rotates with cam 50 as long as no 
significant torsional resistance is applied to nut 52. Cam 50, rotatively 
fixed to shaft 26 by pin 56, therefore rotates with shaft 26 when the 
windshield wipers are reciprocating. If nut 52 is prevented from rotating 
with cam 50, cam 50 will travel in an axial direction along drive shaft 26 
on threads 58 and 60. Engagement projections or ratchet teeth 62, 
extending from the outer surface of nut 52, are used to restrict the 
movement of nut 52. As shown, six teeth 62 are provided, however a greater 
or lesser number may be employed. A pawl 66 is used to selectively engage 
teeth 62 to prevent nut 52 from rotating. 
Also housed within lower housing 40 and upper housing 44 are a motor 64 and 
a release spring 68 which are used to control engagement and disengagement 
of pawl 66 with ratchet teeth 62 on nut 52. Pawl 66 has two arms 70 to 
engage ratchet teeth 62, one arm 70 for resisting nut rotation in each 
direction. Spring 68 biases pawl 66 to a disengaged position shown in 
solid lines in FIG. 5. Motor 64 is used to overcome the force of spring 68 
to alternatively rotate the pawl 66 in either a clockwise or counter 
clockwise direction, causing nut 52 to remain stationary while cam 50 
rotates with drive shaft 26, thereby increasing or decreasing wiper force 
against the windshield. 
Motor 64 is operated by a relay 67 in turn operated by a controller 65 that 
includes a microprocessor. Controller 65 has various inputs and outputs to 
determine the proper force of the windshield wipers against the windshield 
of the vehicle. Inputs may include, for example, the speed at which the 
wiper system is operating, the rotational position of the drive shaft and 
the position of the screw with respect to the nut. Each input is sensed in 
a conventional manner. In response to these inputs, pawl 66 is controlled 
by motor 64. 
Head casting 74 is secured to drive shaft 26 at shaft end 32. Shaft end 32 
includes an anti-rotation feature, such as splines, serrations, or 
knurling to help prevent relative rotation between drive shaft 26 and head 
casting 74. Fulcrum 80, about which lever arm 76 pivots, is fixed in head 
casting 74 substantially in parallel with pivot pin 84. 
FIG. 3 shows cam 50 in a lowermost position, and FIG. 4 shows cam 50 in an 
uppermost position with respect to nut 52. Nut 52 must be axially sized to 
permit the travel of cam 50 fully for the desired range within nut 52. 
When rod 72 extends out of drive shaft 26 responsive to an upward 
displacement of cam 50, as shown in FIG. 4, lever arm 76 rotates about 
fulcrum 80 in a clockwise direction to the position shown. The clockwise 
movement causes spring 86 to increase in length, thereby increasing the 
force at attachment point 88 and also shifting the location of the end of 
spring 86 at spring catch 78 downward, away from pivot point 84. The 
resultant force at attachment point 88 has an increased downward vector 
component normal to the direction of windshield 12, increasing the force 
of wiper blade 17 against windshield 12. 
We now refer to FIG. 5 to consider the operation of pawl 66. Pawl 66 is 
shown in a released position in solid lines. In the released position, nut 
52 and cam 50 rotate as a unit on drive shaft 26, and lever arm 76 does 
not change its position. As shown in phantom lines in the counter 
clockwise-most position indicated by letter A, pawl arm 70 is engaged with 
one of ratchet teeth 62, preventing nut 52 from rotating in a clockwise 
direction corresponding to downward wiper motion for the mounting 
arrangement shown. Therefore, with threads 58 and 60 being right-hand 
threads, wiper motion in the downward direction will cause a decrease in 
force when pawl 66 engages ratchet tooth 62 in position A. Of course, if 
threads 58 and 60 were left-hand threads, wiper motion in the downward 
direction would cause an increase in force. As shown by the phantom lines 
in the clockwise-most direction indicated by the letter B, pawl arm 70 is 
engaged with a ratchet tooth 62 to prevent nut 52 from rotating in a 
counter clockwise direction corresponding to upward wipe motion. This 
produces an increase in force with upward wiper motion when pawl 66 
engages tooth 62 in position B. If threads 58 and 60 are left-hand 
threads, instead of right hand threads, wiper motion in the upward 
direction will produce a decrease in force. Because drive shaft 26 moves 
only during a wipe operation, the windshield wiper blade force is only 
adjusted during a wipe cycle. 
Referring to FIGS. 6(a) and 6(b), the operation of the variable force wiper 
control system by controller 65 is illustrated in flow-chart form. For 
shorthand purposes, V represents instantaneous, real time vehicle 
velocity, V.sub.p represents the most recent velocity measurement of the 
vehicle, V.sub.max is the maximum vehicle velocity and V.sub.p-1 is the 
previous velocity measurement. 
In general, controller 65 monitors the velocity of the vehicle provided by 
vehicle speed sensor 18. A change in velocity is monitored by comparing 
the present vehicle velocity V.sub.p and the previous velocity V.sub.p-1. 
If the vehicle velocity has changed, the wiper force is adjusted 
accordingly. Controller 65 also monitors a wiper arm position sensor 92, a 
wiper direction sensor 94, an ignition condition senor 96 and a cam 
position sensor 98 as shown in FIG. 7. 
The controller 65 initiates at step 100. Vehicle velocity V is zero when 
the vehicle is first started as shown in step 102. Step 104 checks to see 
whether the wiper switch within the vehicle is on, and is set to activate 
the wiper. If the wiper switch is not on, step 104 is repeated. If the 
wiper switch is on, the position of the drive shaft is sensed in step 106. 
The present vehicle velocity V.sub.p is sensed in step 108 with sensor 18 
or another appropriate velocity sensor. 
The controller 65 is programmed to apply one of three different force 
levels to wiper blades 17: a high force, a medium force and a low force 
associated with a low, medium, and high vehicle speed range respectively. 
Each of the force levels corresponds to an axial position of cam 50 within 
housing 40, 44. Of course, three is an arbitrary number and any number of 
levels may be employed, or the controller can alternatively be programmed 
to vary the force continuously with vehicle velocity. Step 110 checks 
whether the vehicle is operating in the low speed range with the present 
vehicle velocity V.sub.p being between 0.33V.sub.max and zero. If the 
velocity is within that range, step 112 obtains the value of the previous 
velocity reading V.sub.p-1. Step 114 checks if the previous velocity 
V.sub.p-1 is also between 0.33V.sub.max and zero. If the previous velocity 
V.sub.p-1 is within that range, indicating the vehicle was previously 
operating in the low speed range, step 116 is executed which does not 
change the blade force against the windshield. Therefore, pawl 66 does not 
engage ratchets 62 of nut 52 to move cam 50 from the low force position. 
When the previous velocity of the vehicle V.sub.p-1 is not between zero and 
0.33 V.sub.max in step 114, step 118 is executed to determine whether the 
previous vehicle velocity V.sub.p-1 is within the medium speed range 
between 0.33 V.sub.max and 0.67 V.sub.max. If the previous vehicle 
velocity V.sub.p-1 falls within that range, step 120 is executed to 
decrease the blade force by moving cam 50 from a mid-force position to a 
low-force position at the next in or downward wipe. 
When the previous vehicle velocity V.sub.p-1 is not between 0.67 V.sub.max 
and V.sub.max in step 118, it can be concluded that V.sub.p-1 is in the 
high speed range between V.sub.max and 0.67 V.sub.max, and step 124 
therefore is executed to decrease the blade force by moving cam 50 from 
the high-force position to the low-force position in the next in or 
downward wipe interval. 
When the velocity of the vehicle V.sub.p is not between zero and 
0.33V.sub.max in step 110, step 126 is executed to evaluate whether the 
vehicle velocity is between 0.33V.sub.max and 0.67V.sub.max. If the 
vehicle velocity V.sub.p falls within that range, step 128 is executed to 
obtain the previous vehicle velocity V.sub.p-1. 
Step 130 is executed to determine if the previous vehicle velocity 
V.sub.p-1 is in the range between zero and 0.33V.sub.max. If so, step 132 
is executed to increase the blade force at the next out wipe by moving cam 
50 from a low-force position to a mid-force position. When previous 
vehicle velocity V.sub.p-1 is not between zero and 0.33V.sub.max, step 134 
is executed in which previous vehicle velocity V.sub.p-1 is compared to 
the range between 0.33V.sub.max and 0.67V.sub.max. If previous vehicle 
velocity V.sub.p-1 falls within that range, step 135 is executed in which 
the blade force is not changed by not moving cam 50, which should be in 
the mid-force position. If the previous vehicle velocity is not in that 
range, it is presumed that previous vehicle velocity V.sub.p-1 is in the 
range 0.67V.sub.max and V.sub.max. With V.sub.p-1 in that range, step 137 
is executed in which the blade force is decreased by moving cam 50 from 
the high-force position to the mid-force position at the next in or 
downward wipe. 
When the vehicle velocity is not between 0.33V.sub.ax and 0.67V.sub.max in 
step 126, vehicle velocity V.sub.p is presumed to be between 
0.67V.sub.max, and V.sub.max. When the vehicle velocity V.sub.p is within 
that range, the previous vehicle velocity V.sub.p-1, is obtained in step 
140. Step 142 is then executed to compare previous vehicle velocity 
V.sub.p-1 with the range of 0 and 0.33V.sub.max. If the previous vehicle 
velocity is in that range, step 144 is executed in which the blade force 
is increased by moving cam 50 from the low-force position to the 
high-force position at the next out or upward cycle. If previous vehicle 
velocity V.sub.p-1 is not between zero and 0.33V.sub.max, step 146 is 
executed to determine whether the previous velocity is between 
0.33V.sub.max and 0.67V.sub.max. If the previous vehicle velocity falls in 
that range, step 148 is executed. Step 148 increases the force by moving 
cam 50 from the mid-force position to the high-force position at the next 
out or upward cycle. 
When previous vehicle velocity V.sub.p-1 is not between 0.33V.sub.max and 
0.67V.sub.max in step 146, previous vehicle velocity V.sub.p-1 is presumed 
within the range between 0.67V.sub.max and V.sub.max. When previous 
vehicle velocity V.sub.p-1 falls within that range, step 152 is executed 
in which the blade force is not changed. 
After the blade force of the wiper arm is either increased, decreased or 
kept the same, step 160 is executed in which the wiper switch is checked 
to see whether it is still on. When the wiper switch is on, step 106 is 
executed and the sequence started again. When the wiper switch is not on 
in step 160, the position of cam 50 is checked in step 162. It is 
desirable to reduce the blade force to the low-force level if the cam 50 
is not already in the low force reduced position. Step 164 determines 
whether the cam 50 is in the low force position. If the cam 50 is in the 
low-force position, step 104 is executed to determine whether this wiper 
switch is on. If cam 50 is not in the low-force position in step 164, step 
166 checks whether the screw is in the medium force position. If cam 50 is 
in the mid-force position, step 168 is executed in which cam 50 is 
returned to the low-force position. Step 104 is then executed to determine 
whether the wiper switch is still on. 
When the screw is not in the mid-force position in step 166, cam 50 is 
presumed to be in the high-force position. When cam 50 is in the 
high-force position, step 172 is executed to move cam 50 to the low-force 
position. After step 172, step 104 is executed to determine whether the 
wiper switch is still on. 
Steps 162 through 172 are executed to decrease the force on the wiper blade 
so that the wiper blade does wear excessively or become permanently 
deformed under the force. 
It should be appreciated that one method of checking the range into which 
V.sub.p-1 falls, in addition to storing and recalling a value in 
controller 65, is to determine the axial position of cam 50, or the 
corresponding position of the nut 52, pin 56 or rod 72, since they will 
correspond to the previous vehicle velocity V.sub.p-1. 
While the best mode for carrying out the present invention has 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.