Pivotal heat exchanger with remote opener

Abstract

A cooling system for a machine is disclosed. The cooling system may have a heat exchanger pivotal between a first position and a second position. In addition, the cooling system may also have a positioning mechanism configured to move the heat exchanger between the first and second positions and retain the heat exchanger in at least one of the first and second positions.

Description

TECHNICAL FIELD

The present disclosure relates generally to a heat exchanger and, more particularly, to a pivotal heat exchanger having a remote opener.

BACKGROUND

Machines having a power source, such as an internal combustion engine, often include a cooling system that cools fluids directed into or out of the power source and/or other systems of the machine. For example, a machine power source may be fluidly connected to a liquid-to-air, air-to-air, or liquid-to-liquid heat exchanger to cool liquids circulated throughout the power source, or air directed into the power source. These heat exchangers may be located close together and/or close to the power source to conserve space on the machine. In some situations, it may be necessary to clean debris from between the heat exchangers and/or between the heat exchangers and the power source. However, because of the close mounting configuration, it may be difficult to access the area requiring the cleaning operation.

One method of providing service access to a cooling system is described in US Patent Application Publication No. 2006/0219451 (the '451 publication) by Schmitt published on Oct. 5, 2006. Specifically, the '451 publication discloses a heat exchanger having a guiding axle that is radially displaceable from an operating position to a servicing position. The guiding axle is moveable in a guide-way that has two indentations corresponding to the operating and servicing positions of the heat exchanger. That is, the heat exchanger may be lifted from the first indention, slid along the guide-way in a direction away from the engine, and dropped into the second indentation, thereby moving the heat exchanger from the operating position to the servicing position.

Furthermore, the top of the '451 publication's heat exchanger is pivotally moveable about the guiding axle, allowing the top of the heat exchanger to pivot down and away from the engine. The heat exchanger is secured in the servicing position by its weight holding the guiding axle in the servicing indentation, as well as by a support element mounted to a side of the heat exchanger. The heat exchanger is secured in the operating position by fasteners located in both a top-center area of the heat exchanger and in the support element. During service, the fasteners connecting the heat exchanger are removed, the heat exchanger's guiding axle is moved from the operating indention to the servicing indention, and then the heat exchanger may be pivoted away from the other exchanger to provide access to the space therebetween.

Although the '451 publication's configuration may improve access to and servicing of the space between heat exchangers, the access may still be difficult to attain. That is, significant time may be spent preparing for and reassembling after the pivoting of the heat exchanger, because of the fasteners. Servicing the heat exchanger may be awkward and difficult for an operator to perform because of the need to lift a large and heavy heat exchanger out of the operating and servicing indentations. This difficulty may increase service time and expense of a machine owner, especially when only an inspection is desired.

The disclosed heat exchanger and remote opener are directed to overcoming one or more of the problems set forth above.

SUMMARY

In one aspect, the present disclosure is directed to a cooling system, which may include a heat exchanger that is pivotal between a first position and a second position. The cooling system may also include a positioning mechanism configured to move the heat exchanger between the first and second positions, and retain the heat exchanger in at least one of the first and second positions.

In another aspect, the present disclosure is directed to a method of pivoting a heat exchanger. The method may include moving a handle to pivot the heat exchanger between a first position and a second position. The method may also include maintaining the heat exchanger in at least one of the first and second positions by way of the handle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosed machine;

FIG. 2 is an exploded view illustration of an exemplary disclosed positioning mechanism for use with the machine of FIG. 1;

FIG. 3 is pictorial illustration of the positioning mechanism of FIG. 2 in an operating position;

FIG. 4 is a pictorial illustration of the positioning mechanism of FIG. 2 in a servicing position; and

FIG. 5 is a pictorial illustration of another exemplary disclosed positioning mechanism for use with the machine of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates a machine 10 having an engine 12. Machine 10 may perform some type of operation associated with an industry such as mining, construction, farming, power generation, or any other industry known in the art. For example, machine 10 may embody a mobile machine such as a loader, a backhoe, an excavator, a motor grader, a dump truck, or another suitable mobile machine. Machine 10 may alternatively embody a generator set, a pump, or another stationary operation-performing machine.

Engine 12 may include multiple components that cooperate to produce a power output directed to move machine 10. In particular, engine 12 may include an engine block 14 that defines a plurality of cylinders 16, a piston 18 slidably disposed within each cylinder 16, and a cylinder head 19 associated with each cylinder 16. It is contemplated that engine 12 may include additional or different components such as, for example, a valve mechanism associated with cylinder head 19, one or more fuel injectors, and other components known in the art. For the purposes of this disclosure, engine 12 is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, that engine 12 may be any other type of internal combustion engine such as, for example, a gasoline or a gaseous fuel-powered engine.

Cylinder 16, piston 18, and the cylinder head 19 may form a combustion chamber 20. In the illustrated embodiment, engine 12 includes four combustion chambers 20. However, it is contemplated that engine 12 may include a greater or lesser number of combustion chambers 20 and that combustion chambers 20 may be disposed in an “in-line” configuration, a “V” configuration, or any other suitable configuration.

As also shown in FIG. 1, engine 12 may be associated with one or more systems that facilitate production of power. In particular, engine 12 may include a cooling system 24. Cooling system 24 may cool fluids (e.g. air, oil, and coolant) circulated throughout engine 12 and machine 10. It is contemplated that machine 10 may include additional systems such as, for example, an air induction system, a fuel system, a lubrication system, a transmission system, a control system, a hydraulic system, and other such engine or machine systems known in the art. Cooling system 24 may include a first heat exchanger 32 and a second heat exchanger 34, both being configured to cool a fluid circulated throughout machine 10. Heat exchanger 32 may be connected to a frame member 36 fixed to machine 10. A fan (not shown) configured to generate a flow of air across the heat exchangers may be included and disposed proximal to heat exchangers 32 and 34 (i.e. disposed in series with heat exchanger 32 and 34). Heat exchangers 32, 34 may be located adjacent each other such that an air flow generated by the fan passes first through one of the heat exchangers 32, 34 and then through the other. It is contemplated that the fan may be omitted, if desired, and replaced with a secondary fluid circuit (not shown) connected to heat exchanger 32 and/or heat exchanger 34 to transfer heat therewith.

As illustrated in FIG. 1, cooling system 24 may be located near a back-end of machine 10, forward of engine 12, and at an inclined angle for spatial constraints. It is contemplated that cooling system 24 may alternatively be located at a front-end of machine 10 and/or positioned in a substantially vertical manner with respect to gravity. It is further contemplated that other possible locations of heat exchangers 32, 34 may exist in the art.

Heat exchanger 32 and heat exchanger 34 may facilitate the transfer of heat to or from a heat transferring medium circulated through machine 10. For example, heat exchangers 32, 34 may include a tube and shell type heat exchanger, a plate type heat exchanger, or any other type of heat exchanger known in the art. Heat exchanger 32 may be a liquid-to-air exchanger connected to engine 12 via a top hose 30 and bottom hose 31 connected to corresponding upper and lower portions of heat exchanger 32. It is contemplated that heat exchanger 32 may function as the main radiator of engine 12 dedicated to conditioning only the heat-transferring medium supplied to engine block 14. It is further contemplated that heat exchanger 34 may function as the hydraulic cooler, conditioning fluids circulated throughout a hydraulic system. Alternatively, heat exchanger 32, 34 may condition a heat transferring medium supplied to a transmission oil cooler, a brake oil cooler, or any other cooling component of machine 10. It is contemplated that other fluid hoses, conduits, and lines may also be connected to heat exchanger 34 in various ways known in the art to facilitate its operation. All fluid connections to heat exchanger 34 may allow heat exchanger 34 to be pivoted with minimal, if any, disconnections thereof being necessary. The heat-transferring medium may be a low-pressure fluid. Exemplary low-pressures fluids may include, water, glycol, a water-glycol mixture, a blended air mixture, a power source oil such as transmission oil, engine oil, brake oil, or diesel fuel, or any other fluid known in the art for transferring heat.

Heat exchanger 34 may be connected and pivotal relative to heat exchanger 32. With reference to FIG. 2, heat exchanger 34 may be connected to frame member 36 by way of a boss 202 located at opposing lower corners of heat exchanger 34. Boss 202 may rest in a slot (not shown) configured slideably receive and hold boss 202 and allow pivotal movement. Boss 202 may alternatively be a hinge, a rod and bushing arrangement, or may embody another system that allows heat exchanger 34 to pivot about an exchanger pivot axis 210 at a lower edge of heat exchanger 34. In order to access a space between heat exchanger 34 and heat exchanger 32, an upper portion of heat exchanger 34 may be selectively pivoted at boss 202 about exchanger pivot axis 210 away from heat exchanger 32.

A positioning mechanism 204 may retain heat exchanger 34 in place and be used to pivot heat exchanger 34 about exchanger pivot axis 210. Specifically, positioning mechanism 204 may be movable from a first position 300 shown in FIG. 3 toward a second position 400 shown in FIG. 4. When in first position 300, heat exchanger 34 is firmly held in place near heat exchanger 32 with the top corners being supported by rubber mounts 212 and the bottom bosses 202 resting in their corresponding slots. When in second position 400, heat exchanger 34 is pivoted away from heat exchanger 32, being supported at the exchanger pivot axis 210 by bosses 202 and by positioning mechanism 204. Positioning mechanism 204 may be moveable within a horizontal plane 244 that may be generally orthogonal to a vertical plane 246 of heat exchanger motion (i.e. a plane orthogonal to exchanger pivot axis 210).

A plurality of resilient components such as rubber mounts 212 may be disposed between heat exchangers 32, 34 to support and separate heat exchangers 32, 34 when heat exchanger 34 is in the first position 300. That is, in one example, when heat exchanger 34 is in first position 300, positioning mechanism 204 may pull heat exchanger 34 against two rubber mounts 212 located in proximity of the top corners of heat exchanger 34. In another example, rubber mounts 212 may also dampen vibrations that may be induced during travel of machine 10 and/or operation of engine 12 being located in proximity of all four corners of heat exchanger 34. It is contemplated that additional or fewer rubber mounts 212 may be included and located as needed to support retaining heat exchanger 34 in the first position and, if desired, dampen vibrations.

Positioning mechanism 204 may include a handle 214 movable in horizontal plane 244 by an operator to mechanically pivot heat exchanger 34 in vertical plane 246, an inclined stud assembly 216 rigidly connected to heat exchanger 34, a linkage member 218 connecting handle 214 to stud assembly 216, and a resilient member 220 such as a spring configured to bias handle 214 toward the opposing first and second positions 300, 400 (referring to FIGS. 3 and 4). Handle 214 may be generally planar or plate like, with a portion shaped to be grasped by a hand for user operation. Handle 214 may have a mounting pivot hole 230 and a linkage pivot hole 232 therein. A boss 222 may be disposed within mounting pivot hole 230 to offset handle 214 from frame member 36 (referring to FIG. 1). A plurality of washers may be placed on the underside of handle 214 with a fastener 228 passing through boss 222, the washers, and mounting pivot hole 230 to engage frame member 36. Fastener 228 may pivotally connect handle 214 to frame member 36, allowing handle 214 to pivot about a positioning pivot axis 234 passing through mounting pivot hole 230 and generally orthogonal to the handle 214.

Linkage member 218, together with spring linkage 236, may be pivotally connected to handle 214 in a similar fashion as described with mounting pivot hole 230. That is, a fastener 228 may be passed through boss 222, linkage pivot hole 232 within handle 214, linkage member 218, spring linkage 236, and a washer to engage a nut. The connection through linkage pivot hole 232 may allow the pivotal movement of handle 214, linkage member 218, and spring linkage 236. Linkage member 218 may have a slot 242 disposed opposite the pivotal end connecting to handle 214.

Spring linkage 236 may be generally planar or plate like and include a curved portion to avoid contact with other components. Spring linkage 236 may be coupled to a first end of resilient member 220, which may be secured at a second end to frame member 36 by way of a fastener 228, a plurality of washers and a nut. A spacer 240 may be position between frame member 36 and resilient member 220 to offset resilient member 220 from frame member 36.

Referring to FIGS. 3 and 4, as handle 214 is moved within horizontal plane 244 about positioning pivot axis 234, linkage member 218 may be urged to translate linearly and in a direction substantially parallel to both horizontal plane 244 and vertical plane 246. As linkage member 218 translates, it may engage and move stud assembly 216 via slot 242. Stud assembly 216 may be fixedly connected to an upper surface of heat exchanger 34 and disposed at an angle relative to linkage member 218 and the upper surface. Stud assembly 216 may pivot with heat exchanger 34 in an arcuate manner about exchanger pivot axis 210. As stud assembly 216 pivots, linkage member 218 may slide along the shaft of stud assembly 216, thereby preventing binding as heat exchanger 34 is pivoted.

As handle 214 moves between the first and second positions 300, 400 shown in FIGS. 3 and 4, resilient member 220 may move from a first substantially neutral state (unstretched), through a substantially tensile stressed state (stretched), and then to a second substantially neutral state. That is, handle 214 may be an over-center device such that it may be retained in both the first and second positions 300, 400 by resilient member 220, resulting in heat exchanger 34 also being retained in an operating position (firmly held against heat exchanger 32) and in a servicing position (pivoted away from heat exchanger 32).

One or more guides may assist the operation positioning mechanism 204. Specifically, a front guide 248 may be fastened to frame member 36 and have a guiding slot 250 therein through which linkage member 218 may pass. Linkage member 218 may pass through guiding slot 250 as handle 214 is moved between first and second position 300, 400. Front guide 248 may help maintain linkage member 218 in a substantially orthogonal arrangement relative to heat exchanger 34 and parallel to both horizontal plane 244 and vertical plane 246. A rear guide 252 (shown in FIG. 2) may be positioned near linkage pivot hole 232 to provide additional support to the positioning mechanism's operation. That is, rear guide 252 may support handle 214, opposing any torque induced in handle 214 from resilient member 220. It is contemplated that additional guides may be included as needed.

Resilient member 220 may firmly hold heat exchanger 34 in both the operating and servicing positions, which correspond to the first and second positions 300, 400 of handle 214. Specifically, when in the first position 300, resilient member 220 may resist movement of the handle 214 toward the second position 400. By resisting movement of handle 214, resilient member 220 may firmly hold heat exchanger 34 against rubber mounts 212 and against heat exchanger 32. Likewise, resilient member 220 may resist the pivoting movement of heat exchanger 34 away from heat exchanger 32 by resisting the movement of handle 214 from the second position 400 toward the first position 300.

FIG. 5 shows an alternative embodiment, positioning mechanism 501, similar to positioning mechanism 204 of FIGS. 2, 3, and 4 may have a handle 500 and a linkage member 502. Handle 500 may include a mounting pivot hole 504 and a linkage pivot hole 506, as well as a portion shaped to be grasped by a hand. Mounting pivot hole 504 may facilitate the pivotal motion of handle 500 relative to frame member 36, while linkage pivot hole 506 may facilitate the pivotal connection of linkage member 502 to handle 500. Linkage member 502 may have a slot 508 similar to slot 242 of linkage member 218, thus allowing stud assembly 216 to slide through it as positioning mechanism 501 is operated. Positioning mechanism 501 may also include similar guides, and be connected to corresponding components similar to the fashion described above for positioning mechanism 204.

In contrast to the embodiment of FIGS. 2, 3, and 4, positioning mechanism 501 of FIG. 5 may include a resilient member 510 that is coupled to stud assembly 216 of heat exchanger 34, also, handle 500 may be generally L-shaped. Resilient member 510 may be fabricated from, for example, rubber, and may be connected to the slotted end of linkage member 502. In this embodiment, a bias generated by resilient member 510 may replace the bias of resilient member 220, if desired. Resilient member 510 may include a central slot 512 configured to grasp stud assembly 216 and, if desired, a gripping portion 514 that may help a technician secure and remove resilient member 510 to and from stud assembly 216 during initial assembly. Resilient member 510 may include one or more openings that facilitate compression and stretching, if desired. Resilient member 510 may be pivotally fixed to linkage member 502 such that resilient member 510 can pivot in a vertical manner to facilitate removal of heat exchanger 32 from machine 10, if needed. When handle 500 is in first position 300 (i.e. heat exchanger 34 is in the operating position), resilient member 510 may be stretched retaining heat exchanger 34 against rubber mounts 212 with a predetermined force. Specifically, resilient member 510 may always be in a tensile (stretched) state, pulling stud assembly 216 toward linkage pivot hole 506. A pin 516 may be placed through positioning mechanism 501 of FIG. 5 and frame member 36 to hold handle 500 in the first and second positions 300, 400 and heat exchanger 34 in the operating and servicing position.

INDUSTRIAL APPLICABILITY

The disclosed cooling system may be used in any machine where access to both sides of a heat exchanger is desired. In particular, the disclosed system provides a simple, reliable way to access the opposing faces of closely mounted heat exchangers for maintenance and servicing purposes. The pivoting and maintenance operation of heat exchanger 34 will now be described.

To access the space between heat exchanger 34 and heat exchanger 32, heat exchanger 34 may be pivoted away from heat exchanger 32 and retained in the pivoted position. Once heat exchanger 34 is retained in the pivoted position, the maintenance activity may be initiated. For example, a service technician may manually remove debris from between heat exchanger 34 and heat exchanger 32, direct a flow of fluid such as compressed air between heat exchanger 34 and heat exchanger 32. The service technician may also inspect the opposing surfaces of heat exchanger 34 and heat exchanger 32, or perform any other suitable maintenance/service activities known in the art. Following the maintenance/service activity, heat exchanger 34 may be returned and maintained in its operational position against heat exchanger 32. Additionally, if desired, heat exchanger 34 may be lifted from the slots receiving boss 202 after removing any connections, thereby making removal of heat exchanger 34 from machine 10 simple.

Specifically, a technician may remotely pivot heat exchanger 34 by moving handle 214 from first position 300 to second position 400 within horizontal plane 244. As handle 214 is pivoted about mounting pivot hole 230, it may engage linkage member 218, producing a fore/aft motion relative to heat exchanger 32. Linkage member 218 may pivot with respect to handle 214, moving in a generally linear direction through front and rear guides 248, 252. As linkage member 218 moves, it may engage stud assembly 216, causing stud assembly 216 to slide through slot 242 as heat exchanger 34 pivots away from heat exchanger 32. The sliding motion of stud assembly 216 may help maintain linkage member 218 within horizontal plane 244. As stud assembly 216 is engaged, the desired pivoting action of heat exchanger 34 may be produced. Heat exchanger 34 may be pivotally returned to the operating position by returning handle 214 to the first position 300.

During operation of engine 12, resilient member 220 may be first in a substantially neutral state (unstretched). During servicing, as handle 214 is moved from the first position 300 toward the second position 400, resilient member 220 may be stretched or transition to a substantially tensile stressed state and then transition to a second substantially neutral state (unstretched) as handle 214 reaches the second position 400. The cycle may be repeated as handle 214 is moved from the second position 400 back to the first position 300. Because resilient member 220 may resist the movement of handle 214 from both the first and the second positions 300, 400, heat exchanger 34 may be firmly held in the corresponding operating and servicing positions. That is, because of the over-center design of positioning mechanism 204, heat exchanger 34 may be both pivoted and firmly held into place by only moving handle 214.

In the embodiment of FIG. 5, similar to the embodiment of FIGS. 2, 3, and 4, a technician may remotely pivot heat exchanger 34 by moving handle 500 from first position 300 to second position 400 within horizontal plane 244. As handle 500 is moved it may pivot about a mounting pivot hole 504 and engage linkage member 502, producing a fore/aft motion relative to heat exchanger 32. Linkage member 502 may pivot with respect to handle 500, moving in a generally linear direction. As linkage member 502 moves, it may engage stud assembly 216, and stud assembly 216 may slide through slot 508 within linkage member 502. The sliding motion of stud assembly 216 may help maintain linkage member 502 within horizontal plane 244. As stud assembly 216 is engaged, the desired pivoting action of heat exchanger 34 may be produced. Heat exchanger 34 may be pivotally returned to the operating position by returning handle 500 to the first position 300.

In contrast to the embodiment of FIGS. 2, 3, and 4, the embodiment of FIG. 5 employs a different system for retaining heat exchanger 34 in the operating and servicing positions. That is, resilient member 510 may be the retention force needed to firmly hold heat exchanger 34 against rubber mounts 212 when handle 500 is locked in the first position by way of pin 516. Specifically, pin 516 may be removed from the first position 300, handle 500 pivoted to second position 400, and pin 516 inserted through frame member 36 and handle 500, thereby pivoting and retaining heat exchanger 34 in the servicing position. To return handle 500 to the first position 300 and heat exchanger 34 to the operating position pin 516 may be removed, handle 500 pivoted to first position 300, and pin 516 reinserted.

Positioning mechanisms 204 and 501 of both embodiments may benefit the operating technician and machine owner because they may be used to remotely pivot heat exchanger 34 from an operating position to a servicing position. The positioning mechanisms 204 and 501 of both embodiments may give a mechanical advantage to the technician, thereby making the pivoting of heat exchanger 34 less difficult. Substantial time may also be conserved with the use of positioning mechanisms 204, 501. That is, time may be conserved as the operation of positioning mechanisms 204, 501 may both pivot heat exchanger 34 between operating and servicing positions, and retain heat exchanger 34 in the operating and servicing positions (positioning mechanism 501 additionally using pin 516 for retention).

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed heat exchanger without departing from the scope of the disclosure. Other embodiments of the heat exchanger will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. A cooling system, comprising: a heat exchanger pivotal between a first position and a second position; anda positioning mechanism configured to move the heat exchanger between the first and second positions and retain the heat exchanger in at least one of the first and second positions.

2. The cooling system of claim 1, wherein the positioning mechanism includes a handle located remotely from the heat exchanger.

3. The cooling system of claim 1, wherein the positioning mechanism is an over-center positioning mechanism.

4. The cooling system of claim 3, further including a resilient member coupled to the positioning mechanism biasing the positioning mechanism toward the first and second positions.

5. The cooling system of claim 4, wherein the resilient member firmly holds the heat exchanger in both the first and second positions.

6. The cooling system of claim 2, wherein the positioning mechanism includes a linearly movable linkage member pivotally connected to the handle and slidingly coupled to the heat exchanger.

7. The cooling system of claim 6, wherein the linkage member is slidingly coupled to the heat exchanger by way of a stud assembly rigidly mounted to an upper surface of the heat exchanger.

8. The cooling system of claim 7, wherein the stud assembly is angled toward the positioning mechanism with respect to the upper surface of the heat exchanger.

9. The cooling system of claim 8, wherein the stud assembly passes through a slot in the linkage member during pivoting.

10. The cooling system of claim 1, wherein: the heat exchanger has an end movable in arcuate trajectory about a pivot axis; andthe positioning mechanism is coupled to an end of the heat exchanger and linearly translatable to move the heat exchanger.

11. The cooling system of claim 1, wherein the heat exchanger is locked in the first and second position by a resilient member and by a pin.

12. The cooling system of claim 1, wherein: the heat exchanger is pivotal in a first plane between the first and second position; andthe positioning mechanism is pivotal in a second plane substantially perpendicular to the first plane to move the heat exchanger between the first and second positions.

13. The cooling system of claim 1, wherein the heat exchanger is supported at four corner locations in the first position and retained by the positioning mechanism.

14. A method of pivoting a heat exchanger, comprising: moving a handle to pivot the heat exchanger between a first position and a second position; andmaintaining the heat exchanger in at least one of the first and second positions by way of the handle.

15. The method of claim 14, wherein maintaining the heat exchanger includes firmly holding the heat exchanger in the first position by a resilient member and in the second position by a pin.

16. The method of claim 14, wherein maintaining the heat exchanger includes creating a bias force toward both the first and second positions.

17. A machine, comprising: an engine configured to generate a supply of power that moves the machine;a cooling system configured to circulate fluids through the engine; anda heat exchanger configured to cool the fluids, the heat exchanger being pivotal between a first position and a second position; andan positioning mechanism configured to move the heat exchanger between the first and second positions and retain the heat exchanger in the first and second positions.

18. The machine of claim 17, wherein the positioning mechanism includes a handle located remotely from the heat exchanger and coupled to the heat exchanger by a linkage member that moves generally linearly.

19. The machine of claim 18, further including a stud assembly fixed to the heat exchanger and slidably moveable within a slot of the linkage member.

20. The machine of claim 19, wherein the positioning mechanism is an over-center positioning mechanism having a resilient member to bias the handle toward both the first and second positions.