Lawn mower

Abstract: An electro-mechanical interlock and module system for an electrically powered device such as a cordless, electric lawn mower that includes a normally open interlock switch for controlling the enabling of the power circuit for the lawn mower. A key member (20) is adapted for insertion into a specially configured opening (56) in the mower housing (14) to actuate and close the interlock switch (32). With the interlock switch (32) closed, energization of the motor is controlled by a separate handle-mounted ON/OFF switch (18) in a conventional manner. In addition, a modular assembly technique is disclosed which facilitates ease of manufacturing while assuring proper alignment between the various components of the interlock system.

Description: The present invention relates to an electro-mechanical interlock and module system for an electrical device, such as an electric lawn mower, that controls the operative state of the device. In various types of power equipment, such as electric lawn mowers, it is desirable to prevent inadvertent or unauthorized operation of the power switch and hence of the equipment controlled thereby. Various means for accomplishing this have been proposed, typically comprising mechanisms which selectively present a mechanical interference to the operation of the power switch. However, the primary disadvantage of these interlock mechanisms is that they are not "user friendly". In other words, the inconvenience caused by such mechanisms is frequently a source of user complaint and can even lead to users devising ways of defeating the interlock feature altogether, thereby eliminating the safety benefits of the mechanism. U.S. Patent No. 4,670,701 describes a rechargeable cordless vacuum cleaner apparatus includes a hand-held cordless vacuum cleaner containing rechargeable batteries, a motor, a fan driven by the motor and a dust-collection filter, and a charging unit containing a power transformer and rectifier diode, with the charging unit being formed with a pocket to removably retain the vacuum cleaner with charging terminals of the charging unit engaged in an electrical receptacle of the vacuum cleaner. Ribs or grooves are formed on an end of the vacuum cleaner which is inserted in the charging unit pocket, and these slidably engage with corresponding grooves or ribs formed on the charging unit, for accurate engagement. A micro-switch on the vacuum cleaner acts to disconnect the batteries from a motor drive circuit and connect them to a charging circuit when the vacuum cleaner is inserted in the charging unit. It is an object of the present invention to provide an interlock system for an electrically powered device, such as an electric lawn mower, in which the above disadvantages are reduced or substantially obviated. It is a further object of the present invention to provide an interlock system that is particularly adapted for use with a cordless, rechargeable, electrically powered device, such that when the interlock system is in a first position the device is disabled and the charging system is operable, and in a second position the device is enabled and the charging system is inoperable. Furthermore, it is an object of the present invention to provide an improved interlock and module system that is designed to provide ease of assembly and ensure proper alignment between the interactive components of the system. In general, the present invention, which is preferably incorporated into a cordless, rechargeable lawn mower, employs a mechanical "key" member that is adapted for insertion into a specially configured opening in the top of the motor shroud. The key member includes a cam surface that engages and actuates the plunger of a normally open interlock switch when the key member is fully inserted into the opening, thereby closing the switch and enabling the lawn mower power circuit. Simultaneously, an integral tab portion on the key member blocks the charging port so that the operator cannot connect the male plug from an outlet mounted charging transformer to the charger circuit when the power circuit is enabled. Conversely, when the key member is removed from the shroud, the normally open interlock switch returns to its OFF position and the power circuit of the lawn mower is disabled. In addition, with the key member removed, the charging port is exposed, thereby permitting connection of the charger circuit to a charging transformer. Significantly, the power circuit of the lawn mower also includes a conventional handle-mounted ON/OFF switch that controls the application of power to the motor when the power circuit is enabled. However, when the power circuit is disabled by the interlock switch, power cannot be applied to the motor, regardless of the position of the handle-mounted ON/OFF switch. Thus, unauthorized operation of the lawn mower, by children for example, is prevented. The preferred embodiment of the present invention also incorporates means for enhancing ease of assembly while at the same time ensuring proper alignment between the various interactive components of the interlock system. The configuration of the key member and the corresponding opening in the shroud are also designed to discourage the intentional insertion of foreign objects into the opening to defeat the purpose of the interlock system. While the present invention is described herein in combination with an electric lawn mower, it will be appreciated that is is equally applicable to other electrically powered devices such as other gardening tools or power tools such as a table saw or drill press. A preferred embodiment of a lawn mower according to the invention will now be further described with reference to the accompanying drawings, in which Fig. 1 is a perspective view of a cordless electric lawn mower incorporating the interlock system; Fig. 2 is an exploded view of the rear portion of the lawn mower with the shroud removed to illustrate the module subassembly of the interlock system; Fig. 3 is a plan view of the support bracket with the interlock switch mounted thereon; Fig. 4 is a rear view of the support bracket; Fig. 5 is a front view of the key member; Fig. 6 is a section view of the key member taken along line 6-6 in Fig. 5; Fig. 7 is a bottom view of the key member; Fig. 8 is a partial sectional view of the key member as it is inserted into the opening in the shroud; Fig. 9 is a partial sectional view of the key member fully inserted into the opening in the shroud; and Fig. 10 is a circuit diagram of the power circuit of the lawn mower shown in Fig. 1. In Figure 1 a pictorial view of an electric lawn mower incorporating the electro-mechanical interlock system of the present invention is shown. The cordless electric lawn mower 10 illustrated in Figure 1 comprises a mower deck 12 having mounted thereon, under shroud 14, a battery that is adapted to power an electric motor for driving a cutting blade located beneath the mower deck 12. Grass clippings are blown out through the discharge chute 13 on the side of the mower deck 12. A handle 16 that is removably attached to the mower deck 12 has mounted thereon a switch mechanism 18 for controlling the application of power from the battery to the motor via a cable 17. The switch mechanism 18 preferably includes an actuating lever 19 that require two physically distinct movements to actuate the switch between the OFF and ON positions. A switch of this type is described in U.S. Patent No. 4,044,532. In addition, the switching lever 19 is normally biased into the OFF position so that when the operator releases the handle, power to the motor is automatically interrupted. Also illustrated in Figure 1 in its installed or "RUN" position is a mechanical "key" member 20 that is adapted to be inserted into a specially configured opening in the shroud 14. As will subsequently be explained in greater detail, when the key member 20 is installed as shown, an interlock switch located inside the shroud 14 is actuated, thereby enabling the power circuit so that energization of the motor is controlled by the handle switch 18. Referring to Figure 10, a schematic diagram of the power circuit 70 of the present cordless electric lawn mower 10 is shown. The normally open interlock switch S2 is connected in the power circuit 70 in series between the battery 24 and the motor 72. Also connected in series between the battery 24 and the motor 72 are the switch contacts 78 of a relay 76. The relay coil 75 is connected to switch contact 80 of switch S1 which is located in the housing 18 on the handle 16 of the mower 10. Switch S1 is normally in the OFF position illustrated in Fig. 10 with switch contact 82 closed and switch contact 80 open. Actuation of lever 19 on the handle 16 of the mower turns the switch S1 to its ON position which closes switch contact 80 and opens switch contact 82. The power circuit 70 operates in the following manner. When the interlock switch S2 is open, the relay coil 75 cannot be energized regardless of the position of the handle switch S1. Thus, the relay contacts 78 remain open and no power is applied to the motor 72. However, when the interlock switch S2 is closed, actuation of the handle switch S1 to its ON position will energize the relay coil 75 and thereby close relay contacts 78 and provide power to the motor 72. In other words, the motor 72 cannot be operated unless both the interlock switch S2 is closed and the handle switch S1 is in the ON position. In addition, it will be appreciated that by connecting the handle switch S1 across the motor 72 in the OFF position of the switch S1, the motor 72 is dynamically braked when the operator releases the actuating lever 19 of the handle switch S1. In addition, a charger circuit 74 is provided that is connected across the battery 24 to recharge the battery after use of the mower. Charging current is supplied to the charger circuit 74 typically from a step-down transformer that is plugged into a standard wall outlet and connected to the charger circuit 74 via the connector 36. Turning now to Figure 2, an exploded view of the rear portion of the lawn mower 10 is shown. Mounted directly beneath the rear portion of the shroud 14 in the preferred embodiment is the rechargeable battery 24. Battery 24 is secured to the mower deck 12 via a metal strap 26. Additionally coupled to the strap 26 is a module subassembly 22 comprised of a plastic support bracket 30, an interlock switch 32, and a printed circuit board 28 containing the power circuit and the charger circuit for the cordless electric lawn mower 10. The printed circuit board 28 is mounted to the support bracket 30 via a pair of integrally formed posts 34 on the support bracket 30. The interlock switch 32 is of the normally open type and contains a plunger 35 that is spring biased to normally extend from the switch body. The interlock switch 32 is electrically connected to the power circuit on the PC board 28 and is also mounted to the support bracket 30. As best shown in Figure 3, the interlock switch 32 contains a pair of laterally extending terminals 33 that are used to mount the interlock switch 32 to the posts 34 on the support bracket 30. By mounting the PC board 28 over the switch 32 and bolting both the switch and PC board to the posts 34, printed conductive pads (not shown) on the PC board 28 serve to automatically make electrical contact between the terminals 33 of the switch 32 and the power circuit on the PC board. The charger circuit on the PC board 28 is adapted for electrical connection to an external source of charging current, typically from a transformer plugged into a wall outlet, via a connector 36 that is mounted to a first integrally formed mounting structure 37 on the support bracket 30. In addition, a pair of LEDs 38, one red and one green for providing visual indications of the battery charging condition and of the fully charged battery condition, respectively, is also mounted to a second integrally formed structure 39 on the support bracket 30. The rear portion of the support bracket 30 contains an integrally formed spring tab 62 that is adapted to be inserted under a raised stepped portion of the battery strap 26, as shown in phantom in Fig. 2 to loosely mount the module subassembly 22 to the battery 24. The rear portion of the shroud 14 contains a recessed area 60 that is configured to receive the key member 20 so that when the key member 20 is installed in the mower, the top of the key member 20 will be flush with the top surface 15 of the shroud. This provides the operator with a convenient visual indication of the proper installation of the key member 20. A charger port 50 is formed in a rearward-facing wall on one side of the recess 60 for providing access to the charger circuit connector 36, and a pair of smaller ports 52 is formed in a rearward-facing wall on the other side of the recess 60 for exposing the two LEDs 38. The key member 20 includes a central depending stem portion 44 that is adapted to fit into an opening 56 formed in the floor of the recessed area 60 of the shroud 14. The opening 56 is generally defined by the front wall 57 of the recess 60 and a U-shaped ridge 59. The opening 56 is partially obstructed by a pair of parallel fins 58 that project into the opening 56 from the front wall 57 of the recess 60, as shown. The fins 58 serve to specially configure the opening 56 as well as discourage the insertion of foreign objects, such as screwdrivers, into the opening 56 to improperly actuate the interlock switch 32 and defeat the interlock system. With additional reference to Figs. 5 - 7, the depending stem portion 44 of the key member 20 is correspondingly configured to fit into the opening 56 in the shroud 14. As best shown in Fig. 7, this results in the stem portion 44 having the general cross-sectional shape similar to the letter "M". Accordingly, the stem portion 44 of the key 20 defines two outer ribs 65 and a center rib 64, which interleave with the parallel fins 58 on the shroud 14 when the key member 20 is inserted into the opening 56 in the shroud 14. As best shown in Figs. 6, 8, and 9, the center rib 64 of the stem 44 has a cam surface 66 formed toward the lower end of the rib that is adapted to engage the plunger 35 of the interlock switch 32 when the key member 20 is inserted into the opening 56 in the shroud 14. In particular, as the key member 20 is inserted downwardly, the cam surface 66 on the center rib 64 will contact the plunger 35 (Fig. 8), causing the plunger 35 to retract into the switch body (Fig. 9), thereby electrically closing the interlock switch 32. To prevent the cam surface 66 on the center rib 64 from binding on the plunger 35, a chamfer 68 is formed on the upper surface of the plunger 35 to facilitate initial axial motion of the plunger 35. Preferably, the angle of the chamfer 68 formed on the plunger 35 corresponds to the angle of the cam surface 66 on the key member 20 so that full surface contact between the two components is achieved. With particular reference to Fig. 6, it will be noted that the leading edge 67 of the center rib 64 above the cam surface 66 is formed with a slight back taper and a small nib 69 is formed at the juncture between the two surfaces 66 and 67. In this manner, when the key member 20 is inserted into the opening 56 in the shroud 14, the nib 69 on the center rib 64 will snap over the plunger 35 providing tactile feedback upon complete installation of the key member. In addition, the presence of the nib 69 together with the back taper of surface 67 ensures that the force of the internal spring in the interlock switch 32 urging the plunger 35 into its extended position does not dislodge the key member 20 from its installed position during operation of the mower. In view of the relatively fragile nature of the PC board 28, it is important that the relatively large mechanical forces applied to actuate the plunger 35 of the interlock switch 32 not be transferred to the PC board 28. In this regard, it will be noted that the support bracket 30 is provided with an integrally formed loop 42 (Figs. 2 and 4) that extends over the top of the plunger 35 of the switch 32 to prevent the plunger 35 from being pulled upward when the key member 20 is extracted. In addition, as best shown in Figs. 3 and 4, the support bracket 30 also has integrally formed thereon an upstanding wall 92 that is adapted to abut the rear surface of the interlock switch 32 opposite the plunger 35 when the switch 32 is mounted in position on the support bracket 30. In this manner, the wall 92 of the support bracket 30 absorbs the force acting on the body of the switch 32 when the plunger 35 is depressed by insertion of the key member 20. Returning to Fig. 2, the key member 20 is also provided with a pair of integrally formed depending tabs 46 and 48 that are adapted to cover the LED ports 52 and the charger connector port 50, respectively, when the key member 20 is in the installed position. Accordingly, it will be appreciated that insertion of the key member 20 not only serves to close interlock switch 32 to thereby enable the power circuit of the lawn mower, but also to mechanically cover the charger connector port 50 so that the lawn mower cannot be charged when enabled for operation. Conversely, when the key member 20 is removed from the mower, allowing the interlock switch 32 to return to its normally open position and thereby disable the power circuit of the lawn mower, the charger connector 36 is exposed and therefore accessible to connection to a plug from a charging transformer. In addition, the removal of the key member 20 also exposes the two LEDs 38 which as previously noted provide visual indications of the operating state of the charger circuit. To ensure proper alignment between the opening 56 in the shroud 14 and the plunger 35 of the interlock switch 32 during assembly of the mower 10, the support bracket 30 to which the switch is mounted contains a pair of alignment holes 40 adapted to receive a corresponding pair of locator posts 54 integrally formed on the underside of the shroud 14 (Fig. 2). Thus, when the shroud 14 is placed over the battery 24 and module 22 during assembly, the locator posts 54 extend into and snugly engage the alignment holes 40 in the support bracket 30, thereby establishing the proper orientation between the shroud 14 and the module subassembly 22. The shroud 14 and battery 24 are then secured to the mower deck 12 via bolts 84 which extend through holes 86 and 88 in the shroud 14 and battery strap 26, respectively. Accordingly, it will be appreciated that the connection between the spring tab 62 of the support bracket 30 and the battery strap 26 generally locates the position of the module subassembly 22, and that upon installation of the shroud 14 to the mower deck 12, the position of the module subassembly 22 relative to the shroud 14 is precisely located by the interengagement of the locating posts 54 with the alignment holes 40. In addition, it will further be appreciated that the present construction technique allows the module subassembly 22 to essentially "float" between the battery 24 and the shroud 14, while at the same time maintaining the proper alignment with the shroud 14. To additionally ensure that the key member 20 is aligned properly when installed, a hole 90 (Fig. 3) is formed in the support bracket 32 which is configured to conform to the external shape of the stem 44 of the key member 20. Moreover, it will be noted that by locating the cam surface 66 on the center rib 64 an appropriate distance from the distal end of the stem (Fig. 6), it is further ensured that the distal end of the stem 44 will enter the hole 90 before the cam surface 66 contacts the plunger 35 of the switch 32. Thus, proper alignment between the cam surface 66 on the key member 20 and the plunger 35 of the switch 32 is assured. Moreover, due to the correspondence between the configuration of the hole 90 and the external shape of the stem 44, possible canting or twisting of the key member 20 during installation is substantially avoided. Finally, it will be noted that the support bracket 30 also has integrally formed thereon an upstanding wall 92 that is adapted to abut the back surface of the interlock switch 32 opposite the plunger 35. In this manner, the wall 92 of the support bracket 30 absorbs the force acting on the body of the switch 32 when the plunger 35 is depressed by insertion of the key member 20.

Claims: An electrically powered device having an electric motor (72), a housing (14) for said electric motor, a power circuit (7) including a rechargeable battery (24) for providing electrical power to the motor (72), and an electrical connector (36) adapted for connection to an external source of electrical current for charging the battery (24), and a first manually operable electric switch (S1) connected in said power circuit (70) and having ON and OFF positions for controlling the application of electrical power to the motor (72), further comprising : an interlock (32) connected in said power circuit (70), and having an actuator (35) for controlling the state of said interlock (32), said interlock (32) having a first normal state for disabling said power circuit (70) and a second state for enabling said power circuit, such that when said interlock (32) is in said first state the electric motor (72) cannot be energised by said power circuit (70) regardless of the position of said first electric switch (S1), and when said interlock (32) is in said second state the electric motor (72) is energisable by said power circuit (70) in accordance with the position of said first electric switch (S1); characterised by: means (30) for mounting said interlock (32) within said housing (14) adjacent an opening (56) in said housing (14) such that the actuator (35) of said interlock (32) is accessible through said opening (56); a key member (20) configured for insertion into said opening (56) in said housing (14) and including actuating means (44) for engaging said actuator (35) of said interlock (32) and causing said interlock to switch from said first state to said second state to thereby enable said power circuit (70); and blocking means (48) for blocking access to said electrical connector (36) when said key member (20) is fully inserted into said opening (56) in said housing (14) to thereby prevent said battery (24) from being charged when said interlock (32) is in said second state. An electrically powered device according to claim 1 characterised in that said interlock switch (32) is mounted to a bracket member (30) that is joined to said housing (14) by alignment means for aligning the actuator (35) of said interlock switch (32) with said opening (56) in said housing (14). An electrically powered device according to claim 2 characterised in that said power circuit (70) is contained on a printed circuit board (28) that is also mounted to said bracket member (30). An electrically powered device according to claim 2 or claim 3 characterised in that said key member actuating means (44) comprises a stem portion (44) having a cam surface (64) thereon for engaging the actuator (35) of said interlock switch (32). An electrically powered device according to any of claims 2 to 4 characterised in that said bracket member (30) has a second opening formed therein that is aligned with said opening (56) in said housing (14) and configured to conform to the shape of said stem portion (44) for receiving said stem portion (44) said second opening being located adjacent said actuator (35) when said interlock switch (32) is mounted on said bracket member (30) for aligning said cam surface (64) with said actuator (35) when said stem portion (44) is inserted into said second opening. An electrically powered device according to claim 5 characterised in that said stem portion (44) has a distal end and said cam surface (64) is positioned on said stem portion (44) such that the distal end of said stem portion (44) enters said second opening in said bracket member (30) before said cam surface (64) engages said actuator (35). An electrically powered device according to any of claims 1 to 6 characterised in that said key member (20) is further configured to be flush with the surface of said housing (14) when fully inserted into said opening (56) in said housing (14). An electrically powered device according to any of claims 1 to 7 characterised in that it includes means for retaining said key member (20) in said fully inserted position. An electrically powered device according to claim 8, characterised in that said bracket member (30) is located between said battery (24) and said housing (14) and further includes coupling means for loosely connecting said bracket member (30) to said battery (24). An electrically powered device according to any of claims 1 to 9 characterised in that the device is a cordless electric lawn mower comprising a mower deck (12), a handle (16) connected to the mower deck (12), and an electric motor (72) mounted to the mower deck (12) for rotatably driving a cutting blade located beneath the mower deck (12).

Inventors: DYKE COLIN, HESS KRISTOFFER A, SHAVER DAVID M, DYKE, COLIN, HESS, KRISTOFFER A., SHAVER, DAVID M.
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1991
Main classification: A01D34
IPC codes: A01D69, H01H27, H01H9, A01D34