Mechanism for dynamically varying blade load over a windshield wiper sweep cycle

A wiper arm assembly has a load member, a wiper arm, and a blade load cam with a cam slot. The load member mates with a joint disposed between first and second ends of the wiper arm. Changes in length of the load member impose a force in a lengthwise direction of the load member. The wiper arm is configured to rotate relative to the blade load cam about an axis proximate to the first end of the wiper arm. The cam slot is configured to vary the length of the load member as a function of a wiper angle in which the wiper angle is defined as the angle between the wiper arm and a starting position of the wiper arm.

BACKGROUND

The present invention relates generally to windshield wiper systems, and more particularly, to windshield wipers systems used on high-curvature windshields.

A windshield wiper system is responsible for clearing rain, snow, and other debris from a vehicle windshield, typically by movement of a rubber blade element across the windshield surface. Windshield wiper arms used in the automotive and aerospace industries generally apply a fixed blade load, which is set at the factory or during the installation of the wiper system on the vehicle. The method for applying this blade load can vary. For example, tension spring mechanisms, compression spring mechanisms, flexural cantilever loading, or conical spring washer assemblies are all methods for applying blade load. Although small blade load variation is inevitably caused by the wiper arm rotation that lengthens or shortens the load member as it traverses the wiper cycle, each method is fundamentally similar in that they are not designed to customize blade load as a function of wiper angle. As currently implemented, the connection point nearest to the hub is typically internal to the arm body itself, and there is no secondary attachment point on the drive mechanism. While this design is favorable from an installation and maintenance perspective, its independent nature of design essentially guarantees that the blade load cannot be a function of the angular sweep position.

During operation of a conventional windshield wiper on windshields with high curvature, the wiper arm rotates away from the drive mechanism as it traverses the high-curvature region. The wiper's rotation causes increased blade load and component stress within the wiper system. The additional blade load also increases the friction on the blade as it crosses the high-curvature region of the windshield. The result of increased blade load could be system lock-up, increased rating requirements of drive components, or reduced system reliability. Therefore, a need exists to customize the blade load of a wiper assembly to improve the operation of wiper systems.

SUMMARY

A wiper arm assembly has a load member, a wiper arm, and a blade load cam. The load member has a first end and a second end spaced in a lengthwise direction from the first end. Changes in length of the load member impose a force in a lengthwise direction of the load member. The wiper arm has a first end, a second end opposite the first end, and a joint disposed between the first and second ends. The joint is configured to mate with the load member. The blade load cam has a cam slot and an axis proximate to the first end of the wiper arm. The wiper arm is configured to rotate relative to the blade load cam about the axis. The cam slot is configured to vary the length of the load member as a function of a wiper angle in which the wiper angle is defined as the angle between the wiper arm and a starting position of the wiper arm.

A method of varying the blade load of a wiper arm assembly includes providing a load member, providing a wiper arm, providing a blade, providing a blade load cam, providing a cam follower, and configuring the cam slot to vary the blade load. The load member has a first end and a second end spaced in a lengthwise direction from the first end. Changes in length of the load member impose a force in a lengthwise direction of the load member. The wiper arm has a first end, a second end opposite the first end, and a joint disposed between the first and second ends. The joint is configured to mate with the load member, and the wiper arm is configured to rotate about an axis proximate to the first end. The blade is configured to mate with the second end of the wiper arm. The force transmitted through the load member causes the blade to contact a surface with a blade load. The blade load cam has a cam slot. The cam slot is configured to vary the length of the load member as a function of a wiper angle in which the wiper angle is defined as the angle between the wiper arm and a starting position of the wiper arm. The cam follower mates with the second end of the load member and the cam slot.

DETAILED DESCRIPTION

FIG. 1is a view of windshield wiper system10. Windshield wiper system10includes drive system12and wiper arm assembly14. Drive system12further includes a converter16, an output shaft sleeve18, and an output shaft20. Wiper arm assembly14further includes arm hub22, wiper arm24, blade26, load member28, cam follower30, and blade load cam32. Windshield wiper system10operates to remove water and other debris from a windshield surface by applying blade load L as drive system12actuates wiper arm assembly14across the windshield surface. Blade load L is the force exerted by blade26on the windshield surface (not shown).

Drive system12actuates wiper arm assembly14through a sweep cycle. A sweep cycle is a windshield operation in which blade26traverses from one end of the required vision clearing to the other and back again. Wiper angle is the angle between a starting position of wiper arm24and a present position of wiper arm24within a sweep cycle. A wiper angle range is a consecutive set of wiper angles within a sweep cycle. Generally, drive system12is incorporated into a vehicle such as an aircraft and is not designed to be removable without special tools.

Converter16is a component within drive system12that translates a rotatory input into an oscillatory motion at output shaft18. In one embodiment, converter16can include a motor and a linkage mechanism arranged such that the rotatory motion from the motor causes the linkage to oscillate. The oscillating end of the linkage is coupled to output shaft20, causing output shaft20to oscillate about its axis. Another embodiment of converter16can use a form of electronic actuation to oscillate output shaft20, for example a stepper motor. Another embodiment of converter16can use a form of hydraulic actuation. For example, a linear hydraulic actuator can be coupled to a rack-and-pinion arrangement, in which the linear hydraulic actuator causes the rack to oscillate and the pinion is coupled to output shaft20, which in turn, oscillates about its axis.

Output shaft20drives wiper arm assembly14in an oscillatory motion during a sweep cycle. In this embodiment, output shaft20is generally cylindrical and is concentric with output shaft sleeve18.

Output shaft sleeve18provides a fixed mounting point for wiper arm assembly14that facilitates varying blade load L and protects output shaft20from debris and mechanical damage. Output shaft sleeve18also provides output shaft20with lateral rigidity during normal operation by acting as a guide. Output shaft sleeve18is fixed relative to the vehicle structure while output shaft20is free to rotate within output shaft sleeve18. In this embodiment, output shaft sleeve18is cylindrical and has a length approximately equal to the length that output shaft20is exposed between converter16and arm hub22. The inner diameter of output shaft sleeve18is larger than the diameter of output shaft20such that output shaft20can be inserted concentrically within output shaft sleeve18. Another embodiment of output shaft sleeve18can include a rectangular block or other portion of converter16that extends to protect output shaft20.

Wiper arm assembly14is the portion of windshield wiper system10that is not incorporated into the vehicle and can be easily removed for maintenance. The configuration of wiper arm assembly14applies blade load L to the windshield. Blade load L has a normal component that acts perpendicularly to the windshield surface and a frictional component that acts tangentially to the windshield surface.

Arm hub22couples output shaft20to wiper arm24. Arm hub22is rigidly affixed to output shaft20. In this embodiment, arm hub22has a cylindrical bore for mating with output shaft20. To facilitate assembly and disassembly, arm hub22has a slot extending radially from the bore to an exterior surface of arm hub22. For clamping arm hub22to output shaft20, arm hub22can include a threaded hole for a fastener, the threaded hole being generally perpendicular to the slot. At the opposing end, arm hub22includes another bore for a pin joint that couples arm hub22to wiper arm24. Portions of arm hub22that interface with wiper arm24are sized such that arm hub22can be inserted into wiper arm24.

Wiper arm24is a fixed-length component that couples arm hub22to blade26and provides a mounting location for load member28at joint40. Wiper arm24and blade26can be customized to suit the particular windshield application. In this embodiment, wiper arm24has a generally straight portion extending from arm hub22to blade26. The mounting location for load member28on wiper arm24is located closer to arm hub22than to blade26and can be a cylindrical pin that is affixed to wiper arm24. The interface between wiper arm24and blade26can be adapted to suit a particular blade application.

Blade26is coupled to wiper arm24and holds a rubber blade element that clears the windshield of water or other debris.

Load member28couples wiper arm24to cam follower30and applies a force therebetween. When the length of load member28increases or decreases, load member28produces a corresponding force along its length. In this embodiment, load member28is a tension element, such as a coiled tension spring, and applies a tension force between cam follower30and wiper arm24. The tension force causes wiper arm24to rotate towards the windshield surface (not shown) and to press blade26into the windshield surface (not shown). The resulting interaction between blade26and the windshield surface (not shown) produces the normal component of blade load L. When drive system12actuates wiper arm assembly14, blade26traverses the windshield surface (not shown) and because the normal component of blade load L is greater than zero, produces a tangential component to blade load L or frictional force. Persons skilled in the art would appreciate that other load members are also applicable. For example, load member28can be configured for flexural cantilever loads, conical spring washer assemblies, compression members, or another conventional method.

Cam follower30couples load member28to blade load cam32and transmits the force produced by load member28to blade load cam32. Cam follower30couples to blade load cam32at cam slot36, which permits cam follower30to slide within cam slot36when drive system12actuates wiper arm assembly14. In this embodiment, cam follower30includes two plates that have pins affixed between the plates on opposing ends. The pins of cam follower30provide the mounting point for load member28on one end and for blade load cam32on the opposing end. To further improve the performance of wiper system10, the pins of cam follower30can also be bearings such as a roller bearing to reduce or eliminate sliding contact between cam follower30and blade load cam32.

Blade load cam32couples cam follower30to output shaft sleeve18and transmits the force produced by load member28therebetween. Blade load cam32includes cam slot32, and shaft mount38, and cam slot36includes inner face42and outer face44. Blade load cam32is affixed to output shaft sleeve18such that blade load cam32is stationary relative to drive system12. The geometry of cam slot36permits the length of load member28to increase or decrease, thereby varying blade load L as a function of wiper angle. The configuration of wiper arm assembly14is such that there is a small angle between cam follower30and blade load cam32to account for the angle between the two mounting points of load member28. To accommodate for this angle, inner face42of cam slot36is inclined with respect to a centerline axis of shaft mount38by acute angle A1. The inclination of inner face42is such that angle A1is substantially constant for radial sections passing through the centerline of shaft mount38and intersecting cam slot36. Outer face44is displaced outward from inner face42with respect to the centerline of shaft mount38such that the distance between the inner face42and outer face44is generally constant as measured within a radial section passing through the centerline of shaft mount38. In this embodiment, angle A1between cam follower30and blade load cam32is approximately 10 degrees.

FIG. 2is an enlarged longitudinal section of windshield wiper system10as depicted inFIG. 1, which further illustrates the relationship between wiper arm24, load member28, cam follower30, blade load cam32, and output shaft sleeve18.

Arm hub22can further include protrusion34for guiding cam follower30as it slides within cam slot36(seeFIGS. 4-6). In this embodiment, protrusion34includes two plates that extend from arm hub22and straddle cam follower30. The orientation of protrusion34restrains cam follower30such that the force from load member28remains aligned with the longitudinal axis of wiper arm24. Maintaining the alignment of cam follower30with respect to wiper arm24reduces stress in cam follower30and blade load cam32.

FIG. 3is an enlarged perspective view of windshield wiper system10, which further illustrates windshield wiper system10.

FIG. 4is a perspective view of blade load cam32.FIG. 5is a plan view of blade load cam32.FIG. 6is a section view of the blade load cam32ofFIGS. 4 and 5.FIGS. 4-6further illustrate blade load cam32, cam slot36, and shaft mount38.

The geometry of cam slot36can be customized to vary blade load L (FIG. 1) as a function of wiper angle. For example, the windshield surface (not shown) may have a region of high curvature. Generally, windshield wiper system10is positioned with respect to a windshield surface such that the gradients over which the wiper travels are minimized. Typically, the orientation of windshield wiper system10places the region of high curvature near the center of the windshield surface corresponding to a central portion of cam slot36. When cam slot36is designed to accommodate a high-curvature windshield, cam slot36can be generally concave, the concave opening facing the centerline of shaft mount38as depicted inFIGS. 4-6. Radius R1(shown inFIG. 5) between the centerline of shaft mount38and the center of cam slot36is approximately equal to corresponding radius R7on the opposite side of cam slot36while radius R2near the midpoint of cam slot36is generally greater than radius R1and radius R7at the ends of cam slot36. The resulting cam slot36reduces the tension spring length near the central portion of cam slot36thereby reducing blade load L through areas of high curvature. Similarly, if the region of high curvature was located closer to the start or end of the sweep cycle, cam slot36could be adjusted to reduce blade load L in a similar manner.

FIG. 7is a plan view of blade load cam32a. Blade load cam32aincludes cam slot36aand shaft mount38aand is similar to blade load cam32except that cam slot36ahas a different geometry. Cam slot36amay be designed to resist the lifting load on wiper arm assembly14. Generally blade26is orientated vertically or horizontally when parked so that blade arm24and blade26do not obscure the view of the vehicle operator. When blade26is generally parallel with the air flowing over the windshield, the lifting force on wiper arm assembly14is lower than when blade26is generally perpendicular to the air flow. Cam slot36acan be customized such that blade load L is proportionate to the lifting force on wiper arm assembly14as a function of wiper angle. For example, consider cam slot36athat is designed for a wiper arm assembly where blade26is parked vertically and parallel to the air flow. At the beginning of the sweep cycle, the lift force is low while the lift force is higher at the end of the sweep cycle. In this application, cam slot36awill have a sloped profile in which radius R3is greater than radius R4. The sloped profile causes the spring to lengthen as blade26approaches the midpoint of the sweep cycle, and thereby increases tension and blade load L as blade26traverses from the parked or vertical orientation to the horizontal orientation. Therefore, blade load L will be matched to the lifting force as a function of wiper angle.

FIG. 8is a plan view of blade load cam32b. Blade load cam32bincludes cam slot36band shaft mount38band is similar to blade load cam32except that cam slot36bhas a different geometry. Cam slot36ccan be designed to reduce blade load L when blade26traverses a small discontinuity between the windshield surface and the surrounding vehicle structure. For instance, some wiper systems are parked off the windshield such that view of the vehicle operator is completely unobstructed by components of windshield wiper system10. In this instance, cam slot36cwould have a corresponding region where radius R6between shaft mount38band the center of cam slot36cis greater than surrounding regions, such as radius R5located at the end of cam slot36c. This profile causes a corresponding decrease of blade load L over a wiper angle range near radius R6.

This invention strives to customize the blade load to a particular application by varying the blade load as a function of wiper angle. For example, a reduced blade load is advantageous when the blade traverses a high-curvature region on the windshield or when the blade transitions from the windshield to a parked position. Reducing the blade load is beneficial because it reduces system stress and torque requirements required to drive the blade through the sweep cycle. Reducing the blade load may also result in improved system reliability, reduced motor power required to drive the system, and reduced risk for system lock-up. Alternatively, this invention may also be used to increase the blade load to overcome aerodynamic forces that lift the wiper blade off the windshield surface during operation. Increasing the blade load proportionally with the aerodynamic force on the blade permits an increased blade load when the aerodynamic forces are high while maintaining a reduced blade load when the aerodynamic forces are low. Therefore, average blade load for a given sweep cycle will be reduced, improving system reliability.

Discussion of Embodiments

A wiper arm assembly can have a load member, a wiper arm, and a blade load cam. The load member can have a first end and a second end spaced in a lengthwise direction from the first end where changes in length of the load member impose a force in the lengthwise direction of the load member. The wiper arm can have a first end, and second end opposite the first end, and a joint disposed between the first and second ends. The joint can be configured to mate with the load member. The blade load cam can have a cam slot. The blade load cam can be configured to rotate about an axis proximate to the first end of the wiper arm. The cam slot can be configured to vary the length of the load member as a function of a wiper angle defined as the angle between the wiper arm and a starting position of the wiper arm.

A further embodiment of the foregoing wiper arm assembly can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components:

A further embodiment of any of the foregoing wiper arm assemblies can have a curved cam slot that is generally concave toward the axis of the blade load cam.

A further embodiment of any of the foregoing wiper arm assemblies can have a cam slot that has an inner face. The inner face of the cam slot can be inclined with respect to the axis of the blade load cam such that a radial section passing through the axis of the blade load cam and intersecting the cam slot defines an acute angle between an intersected edge of the inner face and the axis of the blade load cam.

A further embodiment of any of the foregoing wiper arm assemblies can have the second end of the wiper arm configured to connect to a blade that contacts a surface. The wiper arm assembly can be configured such that the load member causes the blade to impose a blade load on the surface.

A further embodiment of any of the foregoing wiper arm assemblies can have a radially outward portion of the cam slot with respect to the axis of the blade load cam corresponding to a wiper angle range through which the blade traverses a discontinuity on the surface.

A further embodiment of any of the foregoing wiper arm assemblies can also include an arm hub and a cam follower. The arm hub can be configured to mate with an output shaft of an actuator. The arm hub can be configured to mate with the wiper arm at a pin attachment end. The cam follower can mate with the second end of the load member and the cam slot.

A further embodiment of any of the foregoing wiper arm assemblies can have a cam follower that is substantially co-linear with the load member.

A further embodiment of any of the foregoing wiper arm assemblies can have an arm hub that also includes a first protrusion and a second protrusion. The second protrusion can be offset from the first protrusion. The first and second protrusions can restrain the cam follower such that the cam follower is co-planar with a plane defined by the axis of the blade load cam and the joint of the wiper arm.

A further embodiment of any of the foregoing wiper arm assemblies can also include a converter, an output sleeve, and an output shaft. The converter can be enclosed within a housing, and the converter can transform a rotatory input into an oscillatory output. The output sleeve can be defined by a cylindrical structure extending from the housing. The blade load cam can be affixed to the output sleeve. The output shaft can be disposed concentrically with the output sleeve. The output shaft can mate with the arm hub, and the output shaft can transmit the oscillatory output of the converter to the arm hub.

A method for varying the blade load of a wiper arm assembly can include providing a load member, providing a wiper arm, providing a blade, providing a blade load cam, providing a cam follower, and configuring the cam slot. The load member can have a first end and a second end spaced in a lengthwise direction from the first end where changes in length of the load member impose a force in the lengthwise direction of the load member. The wiper arm can have a first end, and second end opposite the first end, and a joint disposed between the first and second ends. The joint can be configured to mate with the load member. The blade can be configured to mate with the second end of the wiper arm, and the load member can be configured such that the force transmitted through it causes the blade to contact the surface. The blade load cam can have a cam slot. The blade load cam can be configured to rotate about an axis proximate to the first end of the wiper arm. The cam slot can be configured to vary the length of the load member as a function of a wiper angle defined as the angle between the wiper arm and a starting position of the wiper arm. The cam follower can mate with the second end of the load member and the cam slot. The cam slot can be configured to vary the blade load.

A further embodiment of the foregoing method can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components:

A further embodiment of any of the foregoing methods can have a cam slot configured to reduce the blade load of a wiper angle range through which the blade traverses a discontinuity in the surface.

A further embodiment of any of the foregoing methods can have a cam slot configured to increase the blade load or a wiper angle range through which aerodynamic forces on the wiper blade tend to decrease the blade load.

A further embodiment of any of the foregoing methods can also include actuating the wiper arm assembly such that the wiper arm and the blade oscillate about the axis proximate to the first end of the wiper arm.