This invention relates to rotary switch mechanisms, and particularly, although not exclusively, to switch mechanisms adapted for use in motor vehicles, such as ignition switches.

A particular problem encountered with ignition switches in modern motor vehicles, arises from the necessity to conduct and switch large currents, which are required for various electrical components of the vehicle such as starter solenoids, wiper motors, heater motors and window dβmisterε. The switching of these loads can cause arcing at the contacts, reducing their life, unless the contacts can be arranged to open and close quickly, even when the input shaft of the switch is rotated slowly.

Accordingly _/ the present invention provides a rotary switch mechanism comprising first and second rotary members, the first member being adapted for manual rotation, upon actuation of the switch, and the second member being drivably connected to the first member, via spring means; stop means adapted to act between the second member and a fixed member, so as to temporarily restrain rotation of the said second member and thereby load the spring; and override means which enables the second member to move past the stop means after a predetermined degree of rotation of the first member and thus allows the second member to be rapidly rotated, by means of the stored energy in the spring.

Preferably, the arrangement is such that the spring can be tenεioned in either direction, so as to enable the contacts of the switch to be actuated rapidly in both of its closing and opening actions.

Preferably, the second member carries a camming device which co-operates with spring loaded lever means, forming a cam follower, which co-operates with the switch contacts, so that the speed of movement of the contacts is

π.ultiplied by the leverage ratio of the cam follower.

Preferably, the spring in the rotary mechanism comprises a torsion spring having a central coiled portion, whose axis is parallel to the axis of rotation of the switch mechanism, and the two ends of which project on either side of the coil, to form "wings", each wing being engageable by a corresponding abutment on the first rotary member, so that the spring can be "loaded" in either direction.

Preferably, the stop means comprises a retractable spring loaded plunger mounted for radial movement on the second member, and a fixed, radially inwardly projecting abutment on the fixed member, the arrangement being such that the spring loaded plunger can "ride over" the fixed abutment, when sufficient force is applied to rotate the second member past it.

Preferably the override means comprises co¬ operating abutment means on the said first and second members which come into direct engagement with one another after a predetermined degree of rotation so as to positively drive the second member past the stop, forcing it to retract.

The invention also extends to an assembly of a ^~ number of such rotary switches mechanisms mounted on a common actuating shaft which are arranged to make and break their switch contacts at different rotational positions, so as to control a plurality of different electrical circuits. According to another aspect of the invention there is provided a switch contact mechanism comprising at least two spaced apart fixed contacts, at least two co-operating movable contacts, correspondingly spaced apart on a contact carrier, said carrier being resiliently biased to engage said movable contacts with said fixed contacts; and actuating means for engaging said contact carrier, so as to urge said carrier in opposition to said resilient bias, said actuating means engaging said contact carrier nearer to one

rovsble ccritact than the other so as to open said nearer contact first.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is an axial view of a rotary switch mechanism in accordance with the invention;

Figure 2 is a corresponding view of a first part of the mechanism of Figure 1, comprising a first rotary drive member; and

Figure 3 is a corresponding view of a second part of the mechanism of Figure 1, comprising a second rotary drive member.

Referring to the drawings, the illustrated mechanism comprises a housing 1 which encloses a movable contact assembly 3 mounted on a spring assembly 4 in the base of the housing. The other end of the housing has a generally semi-circular shape, to enclose the rotor mechanism, and carries radially inwardly extending tapered projection la.

A central drive shaft 8 is keyed into a first rotary member 10, Figure 2, comprising a disk which carries two sets of axial extending projections 12a, 12b and 14a, 14b. Projections 12a and 12b are respectively positioned at the circumference of the disk, at approximately the "1 O'clock" and "11 O'clock" positions, as seen in the drawing, whilst projections 14a and 14b are spaced inwardly from the circumference of the disk, at approximately the "3 '0 Clock" and "9 O'clock" positions.

Positioned beneath the disk 10, as seen in Figure 1, is a torsion spring 6 which comprises a central coiled portion 16, with its outer ends 18a and 18b extending in a "V", around the central shaft 8.

The central coil portion 16 of the torsion spring is located between a pair of facing arcuate projections 22

=nd 24 on the face of a second disk 20, positioned below the first disk, and shown in Figure 3, which has an axial hole 26 so as to be freely rotatable on the shaft 8. The second disk also carries a pair of circu ferentially spaced upstanding projections 28a and 28b against which the outer ends 18a and 18b of the torsion spring are located, in the rest position of the switch, by virtue of the tension in the spring material.

On the opposite side of the disk 20 to the coil of the spring 16, there is a radially extending tubular housing 30, containing a sprung plunger 32 which is urged into a position which it will abut against the projection la on the internal surface of the housing, as illustrated in Figure 1. The sides 34a and 34b of the housing 30 are tapered along radial lines, as indicated in the Figure, so as to coact vith respective abutments 12a and 12b of the first disk, in a manner to be described below.

A cam surface 7 is formed on the outer circumference of the driven disk 20, and co-operates with a cam follower 5, pivoted at 5a, whose other end 5b engages against the moving contact assembly 3 of the switch, so that the cam follower 5 is urged into engagement with the periphery of the disk 20, by the spring 4 of the contact assembly while the contacts are open.

The operation of the switch mechanism will now be described starting from the position illustrated in Figure 1, in which the contacts are shown as closed. It will thus be appreciated that in order to open the contacts, the second disk 20 must be rotated in a counter clockwise direction, so as to engage the cam surface 7 with the cam follower 5 and thus urge the movable contacts 3 away from the fixed contacts 2 of the switch.

When rotation of the first disk begins, the abutment 14a urges the spring arm 18a away from the abutment 28a of the second disk, against which it normally rests, but

the second disk itself does not rotate, because the outer end of the plunger 32 is engaged against the projection la on the internal surface of the switch housing. Instead, the spring begins to be tensioned, and this continues until the abutment 12a of the first disk engages against the tapered side 34a of the plunger housing 30, so that the second disk is now positively driven by the first disk. Because of the tapered formation of the outer end of the plunger, and the correspondingly tapered formation of the projection la, the plunger is then forced to retract so that it rides over the projection, so that the second disk 20 is allowed to move freely under the influence of the tensioned spring, in the counter clockwise direction, rapidly moving the cam follower and thus opening the switch contacts.

When the switch contacts have been opened, it will be appreciated that the symmetrical configuration of the spring and its associated abutment stops (28a, 28b) will cause the mechanism to "self centre", and the plunger 32 will be able to rotate anti-clockwise as far as the switch mechanism will allow. This allows additional mechanisms to be added which operate at different rotational positions of the drive 8.

For example Posn. 1 off-no contacts made

Posn. 2 accessory contacts made Posn. 3 ignition contacts made Posn. 4 start contacts made or combinations of the above.

In some instances more than one projection la may be required, for instance to enable an accessory circuit to switch off while start circuit is made.

When the operator subsequently rotates the mechanism in a clockwise direction, an identical sequence of operations will take place, but in the opposite direction to that described above, with the abutment 14b of the first disk tensioning the arm 18b of the torsion spring, and the

abutment 12b of the first disk engaging against the side 34b of the plunger housing so as to push it back over the projection la, allowing the second disk to rotate in a clockwise direction and thus move the cam surface 7, out of engagement with the cam follower 5, allowing the contacts to re-engage.

The contact arrangement illustrated in Figure 1, as described above, includes a movable contact carrier 3 which is mounted on a spring plunger 4 so that the contacts 40, 42 on the ends of the carrier are urged into engagement with the corresponding fixed contacts 44, 46. The outer end of the cam follower 5 is arranged to engage the contact 3 slightly to the right (as seen in the drawing) of the midpoint between contacts 40 and 42, i.e. slightly nearer to contact 40, and thus ensures that when the switch is opened, contacts 40 and 44 separate from one another a little before contacts 42 and 46, providing a slight wiping action which improves operating performance and particularly, aids in keeping the contacts clean.