EXTENDED SPINDLE ELECTRIC GAUGE MECHANISM

Abstract: An electric gauge (20) driving a pointer (26) has an extended spindle (22) so that the gauge movement can be substantially spaced from the pointer (26). The gauge (20) includes a spindle (22), an armature (48) driving the spindle (22), a bobbin (38) supporting a bearing (58) for the spindle (22) and electrical coils (46) around the bobbin (38). An outrigger support (18) remote from the bobbin (38) and adjacent the pointer (26) holds another spindle bearing (24) which may be mis-aligned with the bobbin (38). The bearing (58) on the bobbin (38) accommodates for the mis-aligned spindle (22).

Description: Field of the Invention This invention relates to an electric gauge and in particular to such a gauge having an extended spindle for driving a pointer at a location remote from the gauge movement as specified in the preamble of claim 1, for example as disclosed in US-A-3,460,038. Background of the Invention It is commonplace in automotive vehicle instrumentation to use electric gauges driving pointers mounted near the gauge movement. Preferably such gauges are of the air-core type shown in US-A-3,168,689 and have a plastics bobbin supporting an outer winding, a spindle journalled in two opposite walls of the bobbin, and a permanent magnet armature within the bobbin and secured to the spindle between the journal points. There are some applications where there is not enough room to locate the bobbin assembly adjacent the pointer and it is then required to use a very long spindle to span the distance between the pointer and the bobbin. Such an alteration to the conventional gauge structure is unworkable because the mass of the pointer is the greatest mass in the system and the bearings will not withstand the loads imposed on them. A stronger structure of the same general design can be made but only at a significant cost penalty. US-A-2,901,703 discloses an improved frictionless suspension means for the spindle of a delicate, sensitive electrical gauge in which the centre portion of the spindle is supported by a complex mechanism incorporating radial springs that are interconnected with one another by means of an encircling spring band, so as to prevent potential misalignment of the spindle during operation of the gauge. Summary of the Invention An electric gauge mechanism according to the present invention is characterised by the features specified in the characterising portion of claim 1. The invention therefore provides a gauge structure accommodating an extended spindle and having a reliable operation and low cost. Dependent claim 2 concerns a particular embodiment of the electric gauge mechanism specified in claim 1. Brief Description of the Drawings The above and other advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings wherein like reference numerals refer to like parts and wherein: Figure 1 is an isometric view of a speedometer and odometer assembly incorporating a gauge according to the invention; Figure 2 is a cross-sectional view through the assembly of Figure 1; Figure 3 is a detailed cross-sectional view of the gauge according to the invention, and Figure 4 is an enlarged view of the bearing of the gauge of Figure 3. Description of the Preferred Embodiment The speedometer and odometer assembly 10 of Figures 1 and 2 includes a frame 12 which has a rear plate 14, a pair of side members 16, and a front outrigger 18. The rear plate 14 carries a spacer 15 which, in turn, supports a speedometer gauge 20 having an elongated, extended spindle 22 that extends through an opening in the rear plate 14 and an opening in the outrigger 18 where a jewel bearing 24 journals the front end of the spindle 22. A pointer 26 is secured to one end of the spindle 22 for movement across the face of a dial 28. An odometer 30 and a tripmeter 32 are supported by the side members 16 and are driven by a stepper motor 34 that is secured to the rear plate 14. The odometer 30 and the tripmeter 32 are located respectively just above and below the spindle 22. The gauge 20 is enclosed in a metal case 36 which is mounted to the spacer 15. The internal details of the gauge 20 movement are best shown in Figure 3. A plastics bobbin 38 is moulded in separate front and rear portions 40 and 42 which mate to form a cavity 44. Electrical coils 46 are wound on the outside of the bobbin 38. Terminals 47 extend through peripheral portions of the bobbin 38 and are connected to the coils 46 for carrying energizing current to the coils. A permanent magnet armature 48 in the form of a disc resides in the cavity 44 and is operatively attached to the spindle 22 by a die-cast Babbitt metal hub 50. The hub 50 is shown as generally spherical with a flat forward face but may have other shapes. A large surface area at its point of contact with the cavity wall is preferred so that thrust forces applied by the spindle will be distributed over a large area. The cavity contains a viscous damping fluid to retard rapid changes in armature position. The front portion 40 has an outwardly extending hub 52 defining a bobbin axis. The hub 52 has a central aperture 54 accommodating the spindle 22 in a manner which seals the cavity yet allows the spindle to rotate about its axis. The aperture also allows the spindle to assume a small angle with respect to the bobbin axis so that some mis-alignment upon assembly will be tolerated. As shown in Figure 4, the aperture is moulded in the shape of a venturi which has a forward wall 56 tapering outwardly at about 5° from the bobbin axis to limit the off-axis movement of the spindle 22. The rounded venturi throat serves as the bearing 58 for the spindle and makes a sealing line contact with the spindle even when it is disposed off-axis. It will thus be seen that the structure of the gauge allows support of the front of the spindle 22 by the outrigger 18 through a bearing 24, and support of the rear of the spindle 22 by the bearing 58 in the front portion 40 of the bobbin 38. The front bearing 24 does not have to be accurately aligned with the rear bearing 58 due to the special rear bearing shape, thus facilitating assembly of the gauge. The structure further permits the gauge movement to be located remotely from the pointer via a long spindle which can pass through a narrow space.

Claims: An electric gauge mechanism (20) comprising: a gauge movement having a bobbin (38), an armature (48) within the bobbin (38), a pointer (26) located remotely from the armature (48), and a spindle (22) for driving the pointer (26) which has sufficient length to extend from the armature (48) to the pointer (26), characterised in that the spindle is an extended spindle (22); there are first (24) and second (58) bearings located between the pointer (26) and the armature (48); there is an outrigger (18) adjacent the pointer (26); the first bearing (24) is located in the outrigger (18) for rotatably supporting the spindle (22), the first bearing (24) being subject to mis-alignment with the bobbin (38); the second bearing (58) is located in the bobbin (38) for supporting the spindle (22) for rotary movement; the front portion (40) of the bobbin (38) has an outwardly-extending hub (52) defining a bobbin axis; and the hub (52) has a central aperture (54) accommodating the spindle (22), said aperture (54) being moulded approximately in the shape of a venturi which has a forward wall (56) tapering towards its proximal end at about 5° from the bobbin axis, having a rounded throat at the proximal end, which serves as said second bearing (58) for the spindle. An electric gauge mechanism (20) according to claim 1, in which the armature (48) is a permanent magnet armature; the bobbin (38) defines a cavity (44) containing a damping fluid; and the rounded throat of the aperture (54) sealingly engages the spindle (22).

Inventors: MACMANUS, DANIEL C.
Applicants: GENERAL MOTORS CORPORATION
Application year: 1988
Main classification: G01R5
IPC codes: G01D11, G01R1