FIELD OF THE INVENTION

This invention relates to a motor drive assembly for an electronic lock and, more particularly, to an arrangement for coupling a drive shaft to a gear within an electronic lock.

BACKGROUND OF THE INVENTION

Electronic deadbolt locks sometimes use a drive gear connected to the drive shaft of a DC motor to control movement of a deadbolt latch between extended and retracted positions. Although the motors used in a typical electronic lock does not supply a great deal of torque, the drive gear must nonetheless be connected to the drive shaft so as to prevent relative slippage therebetween under the torque levels expected for the particular application. A common problem is finding a reliable, cost-effective means of eliminating the relative slippage that can occur between these two components.

As will be described below in connection with

Fig. 1, it is known in the art to make a motor drive assembly for an electronic lock using an annular brass sleeve between the drive shaft and gear. However, there are problems with this type of prior art motor drive assembly. First, to eliminate relative slippage, glue is needed between the shaft and the sleeve and between the sleeve and the gear. Second, this type of coupler assembly is unreliable and costly to manufacture.

Another type of coupling technique involves keying the gear onto the drive shaft. In particular, the coupling utilizes either slots or protrusions to interact with similar mating structures in the shaft and/or gear to prevent relative slippage. An example of such a coupling is disclosed in United States Patent No. 4,774,852 to Matt. The Matt patent shows a coupling ring with an axial slot interconnected to a cam by way of a protrusion from the cam that extends into the slot in the ring. This type of design relies on the protrusion - slot interconnection to prevent relative slippage. However, these types of coupler and gear connections are more expensive to use because they are specially machined and require special alignment during assembly. Thus it is desirable to have a coupling ring that does not require special projections on either the coupling ring, the shaft, nor the gear to reduce relative slippage.

Some prior art assemblies have attempted to eliminate such projection-type interconnection by using elements in the coupler that need to be aligned to a mating structure in the gear or shaft. This type of coupling is shown in U.S. Patent No. 4,376,254 to Hellmann. The ring coupler has a standard axial slot, but includes a plurality of barbs and ribs that embed themselves into the inner surface of the gear body. Relative slippage is therefore prevented by the embedded interconnection of the coupler and the gear. Even though this design removes the necessity of coupler and gear alignment, such a coupler is complex and expensive to make.

Further improvements have appeared by way of merely using a coupler shaped like a double-conical ring

instead of a cylindrical ring. This design is shown in Italian Patent No. 597036. It eliminates the need for costly projections and modifications to the couplers and relies on its shape to prevent relative slippage. However, this invention requires the rotary gear to be wedged onto the conical surfaces with a locking disk and clamping screws. Such accessories increase the cost and size of the coupler assembly.

Due to economic consideration, it is desirable to utilize commercially available motors and gears. However, the other techniques described briefly above (i.e., keying, barbs, and double-conical ring) all require either numerous additional components or specially designed motors or gears. None of the prior art discloses a simple and effective low-cost coupler ring that does not require special modifications to the gear or shaft.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an arrangement for coupling the drive shaft of a small electric motor to a plastic gear in an electronically controlled, motorized, deadbolt locking system.

The invention is carried out by using a split- spring pin that couples the drive shaft to the plastic gear. Preferably, the split-spring pin comprises a cylindrical band of metal having an axial split that forms two abutments extending the length of the pin. The split-spring pin is disposed onto the distal end of a drive shaft and the plastic gear is press-fit over the split-spring pin.

The advantages of the present invention is that relative slippage between the drive shaft and the gear is eliminated in a simple and cost-effective manner. This advantage is achieved by the two abutment surfaces embedding themselves into the gear in combination with the friction between the drive shaft and the pin. Another advantage is the relative inexpensiveness of the split-spring pin design while requiring no modification of the gear or drive shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred exemplary embodiment of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and:

Figure 1 is a diagrammatic view of a prior art electronic lock that utilizes a motor drive assembly to move a deadbolt latch between retracted and extended positions;

Figure 2 is a cross section of the bull gear of the prior art electronic lock of Fig. 1;

Figure 3 is a cross section of the thumbturn and thumbturn shaft of the prior art electronic lock of Fig. 1;

Figure 4 is a partially exploded view of a preferred embodiment of the motor drive assembly of the present invention as it would be incorporated into the electronic lock of Fig. 1; and

Figure 5 is an end view of the motor drive assembly of Fig. 4.

PRIOR ART STATEMENT

A prior art electronic lock is generally shown at 10 in Fig. 1. The electronic lock 10 has a motor drive assembly 12 that includes a DC electric motor 14, a plastic worm gear 16, and an annular metal sleeve 18. Electric motor 14 has a drive shaft 20 that has a circular cross section and is coupled to worm gear 16 by way of metal sleeve 18. During assembly, sleeve 18 is placed over the distal end of drive shaft 20 and glued to the drive shaft 20. Worm gear 16 has a cylindrical bore and is press-fit and glued onto the sleeve 18.

Electronic lock 10 also includes a thumbturn 26 having a shaft 28 that drives a standard tailpiece (not shown) which in turn drives a deadbolt latch 30 between an extended (locked) and a retracted (unlocked) position. As is known, thumbturn 26 permits deadbolt latch 30 to be manually moved between the retracted and extended positions.

Worm gear 16 is coupled to shaft 28 and therefore to deadbolt latch 30 by way of a spur gear 32, a bull gear 34, and a slip clutch 36. As can be seen by reference to Figs. 2 and 3, slip clutch 36 comprises an O-ring 38 that is seated within complementary, annular grooves 28a and 34a that extend about the outer circumference of shaft 28 and about the inner cylindrical surface of bull gear 34, respectively. Slip clutch 36 allows slippage between shaft 28 of thumbturn 26 and bull gear 34 when sufficient torque is applied to thumbturn 26. Gears 16, 32, and 34, slip clutch 36,

shaft 28, and the tailpiece all define a drive train extending between motor 14 and deadbolt latch 30.

Referring again to Fig. 1, electronic lock 10 also includes an electronic control circuit 40 that provides operating power to motor 14. As will be known to those skilled in the art, circuit 40 can be operated to cause rotation of drive shaft 20 in either the clockwise or counterclockwise direction. In this way, circuit 40 can provide automatic control of the movement of deadbolt latch 30 between its extended and retracted positions.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the preferred embodiment shown in Figs. 4 and 5, an electric motor 14' has a drive shaft 20' that has a circular cross section and is coupled to a worm gear 16' by way of a split-spring 18. Split-spring pin 18 is a cylindrical band of metal having an axial split that forms two abutments 22,24 extending the length of the pin. This gives it a generally C-shaped cross section. In its unflexed state, split-spring pin 18 has an inner diameter that is less than the outer diameter of drive shaft 20'.

Worm gear 16' has a cylindrical bore 16a' and is press-fit onto the split-spring pin 18. Prior to assembly of the worm gear onto split-spring pin 18, the inner diameter of the worm gear 16' is less than the outer diameter of the split-spring pin and drive shaft combination. Thus, gear 16' provides a radially inward force on split-spring pin 18 and drive shaft 20' once it is press-fit onto pin 18.

Split-spring pin 18 provides a simple and cost effective coupling between drive shaft 20' and worm gear 16'. Although not wishing to be limited to any specific theory of operation, it is believed that the radially inward pressure exerted by gear 16' on pin 18 and by pin 18 on shaft 20' provides sufficient friction to permit shaft 20' to drive gear 16' without relative slippage therebetween. It is also believed that when gear 16' is press-fit onto pin 18 at least a portion of abutments 22 ',24' embed themselves into the inner surface of gear 16'.

As will be appreciated, motor 14', its drive shaft 20', worm gear 16', and split spring pin 18 can be incorporated into lock 10 of Fig. 1 in lieu of motor drive assembly 12.

Preferably, motor 14' is an SSK280SA-5V, manufactured by Mabuchi Motors of New York, N.Y. Worm gear 16' is a nylon worm gear, such as a N8100, manufactured by Nylomatic of Fallsington, Pennsylvania. Split-spring pin 42 is a 912-C ('/s" ^b Y V ₂ ") _/ manufactured by Hillman Fastener of Cincinnati, Ohio.

It will thus be apparent that there has been provided in accordance with the present invention an electronic lock and associated motor drive assembly which achieves the aims and advantages specified herein. It will of course be understood that the foregoing description is of a preferred exemplary embodiment of the invention and that the invention is not limited to the specific embodiment shown. Various changes and modifications will become apparent to those skilled in the art and all such variations and modifications are

intended to come within the scope of the appended claims.