Abstract:
A switch device including a first switch, a first push-button assembly having a push surface and disposed to alternately turn on and off the first switch in response to a push force, a first spring for urging the first push-button assembly in a direction opposite the push force, a locking device including a spring and a cam for locking said first push-button assembly in a pushed-in position, a second switch, a second push-button assembly having a push surface and disposed to turn on the second switch-in response to a push force, a second spring for urging the second push-button assembly in a direction opposite the second push force, and a lug for preventing the locking device from unlocking in response to an inadvertent push force.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a switch device in which two switches are manipulated by two push-buttons, and the push surface of one of the push-buttons extends through an opening in the push-surface of the other button. 
     2. Description of the Prior Art 
     A conventional switch device of the type described above was disclosed in Japanese Utility Model Application (OPI) No. 153040/81. In this type of switch device, a first push-button is urged in a direction opposite to the pushing force by a helical spring. A push locking mechanism acts to hold the button in a pushed-down position after a first push and to release the button in response to a second push. A second push-button projects through an opening in the first push-button and is urged in a direction opposite to the pushing force by a second helical spring. A switch corresponding to each of the push-buttons is disposed within the switch device, each of which is operated by pushing the respective button. 
     An inherent problem with prior art devices is that when the second button is pushed after the first button is already in the pushed-in position, the first button is likely to be pushed by mistake, releasing the first button. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to resolve the above-mentioned problem by providing an improved switch device. 
     This and other objects are accomplished by a switch device comprising a first switch, a first push-button assembly having a push-surface and disposed to alternately turn on and off said switch in response to a push force, first urging means for urging said first push-button assembly in a direction opposite said push force, locking means for locking said first push-button assembly in a pushed-in position, a second switch, a second push-button assembly having a push-surface and disposed to turn on said second switch in response to a push force, second urging means for urging said push-button assembly in a direction opposite said second push force, and preventing means for preventing said locking means from unlocking in response to an inadvertant push-force. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constituted a part of the specification, illustrate one embodiment of the invention, and together with the description, serve to explain the principles of the invention. 
     FIG. 1 is a perspective view of an embodiment of a switch device in accordance with the present invention; 
     FIG. 2 is a longitudinal cross-sectional front view of the switching device of FIG. 1; 
     FIG. 3 is a longitudinal cross-sectional side view of the switch device of FIG. 1; 
     FIG. 4 is a cutaway perspective view of the switch device of FIG. 1; 
     FIG. 5 shows a cross-sectional view of the switch device along a section line V--V shown of FIG. 1; 
     FIG. 6 is a perspective view of the cam of the switch device; and 
     FIGS. 7(a), 7(b), and 7(c) are schematic diagrams showing the operation of the cam and the locking pin. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the present preferred embodiment of the invention, examples of which are illustrated in the accompanying drawings. 
     The switch device comprises a box-shaped body 1, a first push-button assembly 4, compressed helical springs 7 and 14, movable contacts 9 and 15, a second push-button assembly 11, a locking pin 17, and a cam 18. The box-shaped body 1 is composed of a case 2 having a substantially U-shaped cross-section. First push-button assembly 4 is movable relative to the case 2 and includes a push-button shaft 5 extending through an opening in the top of the case 2, and a button portion 6 having a relatively large surface area and formed on the top of the push-button shaft 5. 
     A compressed helical spring 7 is provided in the rectangular opening 5a of the push-button shaft 5 and is held in place by a support boss 5b that extends down from the top of the opening 5a and is fitted in to the spring 7. A spring support 8 is provided at the bottom of the rectangular opening 5a beneath the spring 7. The compressed helical spring 7 urges the first push-button assembly 4 in an upward direction opposite the push force. A movable contact 9 is provided on the first push-button assembly 4 and is disposed to contact a fixed contact (not shown) provided on the inside surface of the case cover 3. These contacts constitute a first switch 10, that is activated depending on the position of the first push-botton assembly 4. When the first push-button assembly 4 is in a protruding position as shown in FIG. 2, the first switch 10 is turned off. When the first push-button assembly 4 is pushed-in, the switch 10 is turned on. 
     The second push-button assembly 11 is composed of a push-button shaft 12 and a contact support shaft 13 engaged therewith. The push-button shaft 12 has a push-button portion 12a that extends through an opening in the first push-surface 6a so that a push-surface 12b of the second push-button assembly 11 projects over the push-surface 6a of the first push-button 6. A compressed helical spring 14 is provided between the bottom of the contact support shaft 13 and a shelf 2a formed within the case 2. A boss 13a, formed on the bottom of the contact support shaft 13, is fitted in the spring 14 to support it. The compressed helical spring 14 urges the second push-button assembly 11 in an upward direction opposite the push force. 
     A movable contact 15 is provided on the contact support shaft 13 so as to contact a fixed contact (not shown) provided on the inside surface of the case cover 3. These contacts constitute a second switch 16, that is actuated depending upon the position of the second push-button assembly 11. When the second push-button assembly 11 is in a protruding position as shown in FIG. 2, the switch 16 is turned off. When the push-button 11 is pushed-in, the switch 16 is turned on. 
     The switch device also includes a locking pin 17 that is made of spring wire and includes a locking portion 17a having a bent tip, a helical torsion spring portion 17b, and an engaging portion 17c. The spring support 8 has a groove 8b adapted to receive the engaging portion 17c of the locking pin 17. The boss 8 also has a spring support portion 8a adapted to support the helical torsion spring portion 17b of the locking pin 17. 
     As shown in FIG. 6, a heart-shaped cam 18 is disposed at the lower end of the first push-button assembly 4, to engage the locking portion 17a of the locking pin 17. The spring force of the locking pin 17 urges the locking portion 17a leftward. Every time the first push-button assembly 4 is pushed, the cam 18 is moved in a downward direction relative to the locking portion 17a of the locking pin 17 as shown in FIGS. 7(a), 7(b) and 7(c). When the cam 18 and the locking portion 17a are in the position shown in FIG. 7(b), the first push-button assembly 4 is locked in the pushed-in position. When the cam 18 and the locking portion 17a are in the position shown in FIG. 7(a), the push-button assembly 4 is in a protruding position. The push-button assembly 4 is alternately locked and released every time the push-button is pressed. 
     As depicted in FIG. 5, the push-button portion 12a of the push shaft 12 has button 12c. When the second push-button assembly 11 is depressed, the bottom 12c of the push-botton portion 12a is engaged with the step 6b of the first push-button assembly 4. Therefore, depressing the second push-button assembly 11 also depresses the first push-button assembly 6. As depicted in FIG. 2, the contact support shaft 13 and the push-button shaft 12 are connected at their upper and lower portions, respectively. Contact support shaft 13 has a preventive lug 13b disposed to selectively block cam groove 18c. When the second push-button assembly 11 is depressed while the first push-button assembly 4 is in the locked position, the preventive lug 13b blocks the cam groove 18c depicted by a dotted line in FIG. 7(b). This prevents the locking portion 17a of the locking pin 17 from entering the cam groove 18c, and therefore prevents the push-button assembly from being released from the pushed-in position. 
     The following is a description of the operation of the switch device described above. When the first and the second push-button assemblies 4 and 11 are both in their protruded positions and the first push-button assembly 4 is then depressed, the cam 18 of the first push-button assembly 4 is moved downward. This causes the locking portion 17a of the locking pin 17 to move relative to the cam 18. The locking portion 17a is moved along slope 18a, from a position shown in FIG. 7(a), to a position shown in FIG. 7(b) so that the locking portion 17a is moved into the notch 18b of the cam 18. Since locking pin 17 is urged to the left side of the notch as shown in FIG. 7b, even when the push force is removed from the push-button assembly 4, the assembly 4 is locked in the pushed-in position. When the push-button assembly 4 is depressed a second time, the cam 18 is moved from the locked position shown in FIG. 7(b) to the released position shown in FIG. 7(c) and finally to the unlocked position as shown in FIG. 7(a). As shown in FIG. 7(c), when the push-button assembly 4 is depressed a second time the locking portion 17a of the locking pin 17 goes out of the notch 18b of the cam 18, so that the cam 18 and the locking pin 17 are disengaged from each other. When the push-button assembly 4 is then released, the cam 18 is moved upward by the pressure of helical spring 7, and the locking portion 17a of the pin 17 passes through the cam groove 18c. The locking portion 17a is thereby returned to the bottom portion 18d of cam 18 as shown in FIGS. 6 and 7a. Consequently, the first push-button assembly 4 is returned to the protruded position and the first switch 10 is turned off. The first push-button assembly 4 is thereby alternately locked and unlocked every time the button is depressed. 
     As described earlier, when the first push-button assembly 4 is in the protruded position and the second push-button assembly 11 is pushed, the bottom 12c of the push-button portion 12a is engaged with the step 6b of the first push-button assembly 4, so that both the push-buttons are moved together in a downward direction. 
     When both push-button assemblies 4 and 11 are moved to the pushed-in positions, the first and the second switches 10 and 16 are turned on. However, when the second push-button 12b is released, the first push-button assembly 4 remains locked in the pushed-in position and the second push-button assembly 11 is returned to the protruded position by the force of the compressed helical spring 14. As a result, the first switch 10 remains turned on, and the second switch 16 is turned off. 
     When the second push-button assembly 11 is pushed while the first push-button assembly 4 remains locked in the pushed-in position, the second switch 16 is turned on and the first switch remains on. When the second push-button assembly 11 is depressed, the lug 13b of the contact support portion 13 blocks the cam groove 18c as shown by the dotted line in FIG. 7(b). This assures that even if the first push-button assembly 4 is accidentally pushed together with the second push-button assembly 11, locking portion 17a of the locking pin 17 is prevented from entering groove 18c and therefore remains in the locked position. When pressure is removed from the second push-button assembly 11, the first push-button assembly 4 remains locked in the pushed-in position, and the second push-button assembly 11 returns to the protruded position.