[0001] This invention relates to rotary electric switches, such as those used as ignition
switches in motor vehicles. In particular, the invention relates to a rotary electric
switch comprising a rotor carrying a sliding contact member which, on rotation of
the rotor, moves between a closed position, in which it bridges a stationary feed
contact member and a stationary output contact member, and an open position in which
such bridging does not occur. Such a switch will be referred to hereinafter as "a
rotary switch of the type described". When the switch is a vehicle ignition switch
there are usually a number of output contact members which are bridged in turn by
the sliding contact member.
[0002] Where the rotary switch is to supply an electronic circuit, it is important that
the supply should be continuous while the sliding contact member is moving over the
stationary contact members. In practice it is found that the supply is interrupted
for periods which, although very short, may result in the electronic circuits malfunctioning.
An object of the present invention is to avoid or minimise that malfunctioning in
a rotary electric switch of the type described.
[0003] According to the present invention, an auxiliary butting contact member is arranged
to be operated by rotation of the rotor and to provide a secondary connection, with
butting contact, between the stationary contact members. Advantageously, the secondary
connection is made and broken respectively after and before the connection through
the sliding contact member is made and broken, so that the auxiliary contact member
never switches the current; the connection through the auxiliary contact member then
ensures that no breaking of the circuit occurs during movement of the sliding contact
over the stationary contacts.
[0004] Preferably, the auxiliary contact member is spring-biased towards a closed position
in which that contact member makes butting engagement with the stationary contact
members, and the rotor has a camform, which is operative on the auxiliary contact
member, on rotation of the rotor, to cause movement of the auxiliary contact member
between a closed position in which said butting engagement occurs and an open position
in which it is out of engagement with at least one of the stationary contact members.
[0005] The invention will be more readily understood by way of example from the following
description of a rotary electric ignition switch in accordance therewith, reference
being made to the accompanying drawings, in which
Figures 1 and 2 show the switch in radial section, with the switch contacts closed
and open respectively, and
Figures 3 and 4 show the contact members of the switch in plan view and correspond
to Figures 1 and 2 respectively.
[0006] The vehicle ignition switch shown in the drawing comprises a rotor 1 carrying a sliding
contact- member 2, a ..' a base 3 on which the rotor 1 is mounted for rotation about
the central axis A. Contact member 2 is made of electrically conducting material and
has parts 2A which are pressed out of the metal to engage with the stationary contact
as required. A number of stationary output contact members are mounted in the base
3, but only that for the ignition contact member is shown at 4, while the feed stationary
contact member is indicated at 6. As the rotor 1 is turned, sliding contact member
2 bridges the feed contact member 6 successively with the stationary contact members.
Connection between the feed contact member and the ignition contact member 4 is made
over an arc of travel of the rotor 1, so that the ignition circuit is completed between
the IGNITION location and the START location.
[0007] During the travel of the sliding contact member 2 over the ignition contact member
4, short term interruptions in the connection may occur due to slight imperfections
in the feed contact member 6. Those interruptions are so short that the operation
of the ignition is unaffected, but they may affect any electronic circuit supplied
through the same contact members and may cause the electronic circuit to malfunction.
To avoid that possibility, the switch has an auxiliary butting contact member 5, which
is designed to connect between the feed contact member 6 and the ignition contact
member 4 in parallel with the sliding contact member 2. Auxiliary contact member 5
is located beneath the feed and ignition contact members and is biased towards them
by a spring 7 so that end 8 of the contact member 5 is permanently abutted against
the ignition contact member 4 in the IGNITION and START positions. The other end of
contact member 5 has an upwardly turned leg 10 which is biased by spring 7 against
a camform 9 on the underside of the rotor 1, and which serves to move the auxiliary
contact member 5 between the open position shown in Figure 2 and the closed position
of Figure 1, in which contact member 5 additionally engages the feed contact member
6. While the rotor 1 is in the OFF position or the ACCESSORY position, cam 9 retains
the auxiliary contact member 5 in the OFF position shown in Figure 2. As the rotor
is progressively turned to the IGNITION position, the camform allows the contact member
5 to pivot into the closed position of Figure 1, contact with the feed contact member
6 being made at a small angular position beyond that at which the connection to the
ignition contact member 4 is made by the sliding contact member 2. The secondary circuit
is thus completed by butting contact of auxiliary contact member 5 with contact members
4 and 6.
[0008] During subsequent movement of the rotor towards the START position and the return
to the IGNITION position, auxiliary contact member 5 remains stationary with the circuit
through it uninterrupted. Thus, the supply to the ignition contact member 4 is maintained,
regardless of short term interruptions in the connection through the sliding contact
member 2. Further, as the connection through the auxiliary contact member is made
after that through the sliding contact member 2, and similarly the connection through
the former is broken before that through sliding contact member 2 is broken, the auxiliary
contact member 5 never switches the current. Should the connection through the sliding
contact member 2 fail for any reason, while the auxiliary contact member is closed,
and welding of the latter occurs, the camform 9 on the rotor 1 will break the weld
on the rotor being returned to the ACCESSORY position.
1. A rotary electric switch comprising a rotor (1) carrying a sliding contact member
(2) which, on rotation of the rotor, moves between a closed position (Figure 1), in
which it bridges a stationary feed contact member (6) and a stationary output contact
member (4); and an open position (Figure 2), in which such bridging does not occur;
characterised in an auxiliary butting contact member (5) which is arranged to be operated
by rotation of the rotor (1) and to provide a secondary connection, with butting contact,
between the two stationary contact members (4, 6).
2. A rotary electric switch according to claim 1, in which the secondary connection
is made and broken respectively after and before the connection through the sliding
contact member (2) is made and broken, so that the auxiliary contact member (5) never
switches the current to the output contact member (4).
3. A rotary electric switch according to claim 2, in which the auxiliary contact member
(5) is spring-biased towards a closed position in which that contact member (5) makes
butting engagement with the stationary contact members (4, 6), and the rotor (1) has
a camform (9), which is operative on the auxiliary contact member (5), on rotation
of the rotor, to cause movement of the auxiliary contact member (5) between a closed
position in which said butting engagement occurs and an open position in which it
is out of engagement with at least one of the stationary contact members (4, 6).
