Composite operational display unit for vehicle instrument panel

A combination meter for a vehicle has a speedometer, a tachometer, a gauge and a warning light disposed in a casing. A holding panel having an annular wall and a rear wall is attached to the casing so that the speedometer, the tachometer, the gauge and the warning light are exposed through openings formed in the rear wall. The speedometer analog-displays a speed of the vehicle using a dial and a pointer and digital-displays a speed of the vehicle using an EL panel disposed at a front side of the dial and attached to the holding panel. An EL drive circuit for driving the EL panel is mounted on an outer surface of the annular wall of the holding panel. As a result, the EL panel and the EL drive circuit are readily attached to the casing simultaneously when the holding panel is attached to the casing, thereby improving an efficiency in attachment and replacement of the EL panel and the EL drive circuit.

CROSS REFERENCE TO RELATED APPLICATIONS
 This application relates to and claims priority from Japanese Patent
 Application No. 11-200676 filed on Jul. 14, 1999, the contents of which
 are hereby incorporated by reference.
 BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates generally to displays, and particularly to a
 composite operational display unit of a vehicle instrument panel having
 plural operational displays.
 2. Related Art
 JP-A-10-91076 discloses a composite operational display unit having a first
 operational display and a second operational display. The second
 operational display is a transparent electroluminescent (EL) display and
 is disposed at a front side of the first operational display. However, in
 addition to the first and second operational displays, the composite
 operational display unit needs to have two drive circuits for respectively
 driving the first and second operational displays, while a mounting space
 of the composite operational display unit in a vehicle has been demanded
 to be reduced. Therefore, it is required to improve an efficiency in
 attachment and replacement of the first and second operational displays
 and the drive circuits in the display unit.
 SUMMARY OF THE INVENTION
 In view of the foregoing problems, it is an object of the present invention
 to provide a composite operational display unit in which an efficiency in
 attachment and replacement of plural operational displays and drive units
 is improved.
 According to the present invention, a composite operational display unit
 has a first operational display and a second operational display disposed
 at a front side of the first operational display. An annular holding panel
 having a rear opening is attached to the second operational display from a
 front side of the second operational display so that the second
 operational display is disposed opposite the rear opening. A drive unit
 which drives the second operational display is mounted on an outer surface
 of the holding panel. The first operational display is visible through the
 second operational display. Since the drive unit is mounted on the outer
 surface of the holding panel, the drive unit is readily attached to the
 display unit simultaneously when the holding panel is attached to the
 display unit. Therefore, an efficiency in attachment and replacement of
 the drive unit is improved.
 Preferably, the holding panel has a front end forming a front opening, and
 the front end is formed to extend obliquely with respect to the rear
 opening so that the holding panel has a larger-width portion having a
 larger width in a front-rear direction. The drive unit is mounted on an
 outer surface of the larger-width portion. As a result, the drive unit is
 efficiently attached to the display unit while making good use of a shape
 of the holding panel. Therefore, a mounting space of the display unit is
 restricted from largely increasing.
 More preferably, the second operational display is attached to the holding
 panel, and the drive unit is mounted to the outer surface of the holding
 panel, before the holding panel is attached to a casing which accommodates
 the first and second operational displays therein. As a result, the drive
 unit and the second operational display are readily attached to the casing
 simultaneously when the holding panel is attached to the casing.
 Therefore, an efficiency in attachment and replacement of the drive unit
 and the second operational display is improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 A preferred embodiment of the present invention is described hereinafter
 with reference to the accompanying drawings. In the present embodiment,
 the present invention is applied to a combination meter for a vehicle as a
 composite operational display unit having plural operational displays.
 As shown in FIG. 1, the combination meter has a speedometer S, a tachometer
 R, a gauge G and a warning light W all of which are disposed in a casing
 10 in FIG. 3. As shown in FIG. 2, the speedometer S has a drive unit 20.
 As shown in FIG. 3, the drive unit 20 has a unit body 21 attached to a
 panel P and a pointer shaft 22. The pointer shaft 22 protrudes from a
 front surface of the unit body 21 and is rotatably held by the unit body
 21. The speedometer S also has a dial 30 and a pointer 40. The dial 30 is
 held in the casing 10 at an immediately front side of the unit body 21. As
 shown in FIG. 1, the dial 30 has an arc-shaped scale portion 31 and a
 center portion 32. As shown in FIG. 3, the scale portion 31 is formed to
 obliquely extend from the center portion 32 toward a front side. Light
 emitted from a cold cathode tube (not shown) held in the casing 10 enters
 the dial 30 through a light transmitting plate (not shown) disposed along
 a rear side of the dial 30 so that the dial 30 is illuminated.
 The pointer shaft 22 extends through a hole formed in the dial 30 so that
 an end of the pointer shaft 22 is disposed at a front side of the dial 30.
 A rotational base portion of the pointer 40 is coaxially connected to the
 end of the pointer shaft 22. The pointer 40 is rotated along a front
 surface of the dial 30 by the drive unit 20 while being illuminated by
 light emitted from the cold-cathode tube and transmitted by the light
 transmitting plate. As a result, the illuminated pointer 40 points a value
 on the illuminated scale portion 31 to indicate a speed of the vehicle.
 Thus, the speedometer S analog-displays a speed of the vehicle using the
 dial 30 and the pointer 40.
 Further, as shown in to FIG. 3, the speedometer S has an EL panel 50. The
 EL panel 50 is disposed at a rear side of an annular holding panel 60 and
 at an immediately front side of the dial 30 in parallel with the dial 30.
 The EL panel 50 is matrix-driven to digital-display a speed of the vehicle
 thereon at an inner circumferential side of the scale portion 31 of the
 dial 30. When the EL panel 50 is turned off, the EL panel 50 becomes
 transparent.
 The tachometer R is disposed at a left side of the speedometer S in FIG. 1.
 As shown in FIG. 2, the tachometer R has a drive unit 70 having a unit
 body 71 attached to the panel P and a pointer shaft (not shown). The
 pointer shaft is rotatably held by the unit body 71 and protrudes from a
 front surface of the unit body 71. The tachometer R has a dial 80 and a
 pointer 90. The dial 80 is held in the casing 10 at an immediately front
 side of the unit body 71. The dial 80 is formed similarly to the dial 30
 of the speedometer S and is illuminated by light emitted from the cold
 cathode tube and transmitted by the light transmitting plate.
 The pointer shaft of the drive unit 70 extends through a hole formed in the
 dial 80 so that an end of the pointer shaft is disposed at a front side of
 the dial 80. A rotational base portion of the pointer 90 is coaxially
 connected to the end of the pointer shaft. The pointer 90 is rotated along
 a front surface of the dial 80 by the drive unit 70 while being
 illuminated by light emitted from the cold-cathode tube and transmitted by
 the light transmitting plate. As a result, the illuminated pointer 80
 points a value on an illuminated scale portion of the dial 90 to
 analog-display a rotational speed of an engine of the vehicle.
 The gauge G is disposed at a right side of the speedometer S in FIG. 1. As
 shown in FIG. 2, The gauge G has a pair of drive units 100. Each of the
 drive units 100 has a unit body 101 attached to the panel P and a pointer
 shaft (not shown) protruding from a front surface of the unit body 101 and
 rotatably held by the unit body 101. The gauge G also has a dial 110 and
 pointers 120a, 120b. The dial 110 is held in the casing 10 at an
 immediately front side of the unit bodies 101.
 As shown in FIG. 1, the dial 110 has an arc-shaped scale portion 111 at a
 left side for showing an amount of fuel in a fuel tank of the vehicle. The
 dial 110 also has an arc-shaped scale portion 112 at a right side for
 showing a temperature of engine coolant flowing through an engine cooling
 unit of the vehicle. Light emitted from the cold-cathode tube enters the
 dial 110 through the light transmitting plate so that the dial 110 is
 illuminated.
 Each of the pointer shaft of the drive units 100 extends through a hole
 formed in the dial 110 so that each end of the pointer shafts is disposed
 at a front side of the dial 110. Each rotational base portion of the
 pointers 120a, 120b is coaxially connected to each end of the pointer
 shafts. Each of the pointers 120a, 120b is rotated along a front surface
 of the dial 110 by each of the drive units 100 while being illuminated by
 light emitted from the cold-cathode tube and transmitted by the light
 transmitting plate. As a result, the illuminated pointers 120a, 120b
 respectively points values on the illuminated scale portions 111, 112 to
 analog-display an amount of fuel and a temperature of engine coolant.
 The warning light W is disposed below the speedometer S in FIG. 1. The
 warning light W has a pattern display panel 130a and a warning lamp group
 130b. The pattern display panel 130a has plural display patterns to be
 projected such as a brake display pattern 131. The warning lamp group 130b
 is disposed at an immediately rear side of the pattern display panel 130a.
 The warning lamp group 130b includes plural lamps each of which is
 disposed opposite each of the display patterns of the pattern display
 panel 130a. For example, a brake lamp of the warning lamp group 130b,
 which is turned on when a parking brake of the vehicle is stepped, is
 disposed opposite the brake display pattern 131. As a result, when the
 brake lamp is turned on, the brake display pattern 131 is illuminated.
 As shown in FIGS. 1-3, the holding panel 60 has an annular wall 60a and a
 rear wall 60b. The rear wall 60b is disposed in a rear opening 61 of the
 annular wall 60a and is integrally formed with the annular wall 60a. As
 shown in FIG. 3, a front end of the annular wall 60a is formed to be
 curved so that a width of the annular wall 60a in a front-rear direction
 becomes largest at an upper end thereof and is decreased toward a lower
 end thereof in FIG. 3. The annular wall 60a is attached to the casing 10
 so that the rear opening 61 of the annular wall 60a is disposed opposite
 an opening of the casing 10 with the EL panel 50 being disposed
 therebetween. As a result, the rear wall 60b is disposed at an immediately
 front side of the EL panel 50 in parallel with the dials 30, 80 and 110.
 The rear wall 60b has three openings 62 each of which is disposed opposite
 each of the EL panel 50 and the dials 80, 100, and an opening 63 disposed
 opposite the pattern display panel 130a. In the present embodiment, as
 shown in FIG. 3, an outer peripheral portion 62a of the rear wall 60b
 formed along a periphery of the opening 62 for the EL panel 50 is disposed
 opposite an outer peripheral portion 51 of the EL panel 50. Similarly, an
 outer peripheral portion 62a of the rear wall 60b formed along a periphery
 of the opening 62 for the dial 80/110 is disposed opposite an outer
 peripheral portion of the dial 80/110.
 Still referring to FIG. 3, the front panel 140 is attached to the annular
 wall 60a to cover a front opening (i.e., right end opening in FIG. 3) of
 the annular wall 60a. The front panel 140 has a frame 141 and a
 "black-face" smoke glass 142 fitted into the frame 141. A translucent rate
 of the smoke glass 142 is set to approximately 25%, for example, so that
 the dial 30 is not seen through the smoke glass 142 when the cold-cathode
 tube is turned off.
 Next, a control system of the combination meter will be described with
 reference to FIG. 4. A sensor group 150 includes plural sensors and
 detects a speed of the vehicle, a rotation speed of the engine, a
 temperature of engine coolant and an amount of fuel in the fuel tank. An
 analog-digital switch 160 is for switching among analog display of the
 speedometer S by the dial 30, digital display of the speedometer S by the
 EL panel 50 and analog-and-digital display of the speedometer S by the
 dial 30 and the EL panel 50. The analog-digital switch 160 is set to
 either a first, second or third position. In the present embodiment, when
 the analog-digital switch 160 is set to the first position, the
 speedometer S analog-and-digital-displays a speed of the vehicle. When the
 analog-digital switch 160 is set to the second position, the speedometer S
 digital-displays a speed of the vehicle. When the analog-digital switch
 160 is set to the third position, the speedometer S analog-displays a
 speed of the vehicle.
 A micro-computer 190 executes a computer program according to a flow chart
 (not shown) for controlling the combination meter. During the program, at
 least one of the cold-cathode tube, the drive units 20, 70 and 100 and an
 EL drive circuit 170 for driving the EL panel 50 is driven according to
 detection output of the sensor group 150 and a set position of the
 analog-digital switch 160. Further, the warning light W outputs a warning,
 and if any abnormality of the gauge G and the warning light W is detected,
 the abnormality is corrected. As shown in FIG. 2, the EL drive circuit 170
 is connected to the EL panel 50 through a flexible print-circuit board
 180a. The EL drive circuit 170 is accommodated in a circuit casing 180,
 which is mounted on an upper surface of the annular wall 60a.
 While the micro-computer 190 executes the program, the drive unit 20
 rotates the pointer 40 according to a speed of the vehicle detected by the
 sensor group 150. The drive unit 70 rotates the pointer 90 according to a
 rotation speed of the engine detected by the sensor group 150. The drive
 units 100 respectively rotate the pointers 120a, 120b according to an
 amount of fuel in the fuel tank and a temperature of engine coolant
 detected by the sensor group 150.
 When the analog-digital switch 160 is set to either the first or third
 position, the cold-cathode tube is turned on. When the analog-digital
 switch 160 is set to either the first or second position, the EL drive
 circuit 170 matrix-drives the EL panel 50 so that a speed of the vehicle
 is digital-displayed on the El panel 50. When the switch 160 is set to the
 third position, the EL drive circuit 170 makes the EL panel 50
 transparent. Further, a corresponding lamp in the warning lamp group 130
 is turned on according to various operation of the vehicle such as
 operation of the parking brake.
 According to the present embodiment, the EL panel 50 is attached to the
 rear wall 60b of the holding panel 60 to be exposed through the opening 62
 of the rear wall 60b, and the EL drive circuit 170 accommodated in the
 circuit casing 180 is mounted on an upper surface of the annular wall 60a
 of the holding panel 60. Therefore, the EL drive circuit 170 and the EL
 panel 50 are readily attached to the casing 10 simultaneously when the
 holding panel 60 is attached to the casing 10. As a result, an efficiency
 in attachment of the holding panel 60, the EL panel 50, the EL drive
 circuit 170 to the casing 10 is improved. The circuit casing 180 is
 attached to the annular wall 60a by a fastening member such as a screw or
 a claw integrally formed on the circuit casing 180.
 Further, in the present embodiment, the annular wall 60a is formed to curve
 as shown in FIG. 3 to have a largest width in a front-rear direction at an
 upper end thereof. The EL drive circuit 170 accommodated in the circuit
 casing 180 is mounted on the relatively wide upper surface of the annular
 wall 60a. Therefore, the EL drive circuit 170 is efficiently attached to
 the casing 10 while making good use of a shape of the holding panel 60,
 thereby restricting a mounting space of the combination meter in the
 vehicle from largely increasing. Also, the EL drive circuit 170 and the EL
 panel 50 are readily replaced by detaching the holding panel 60 from the
 casing 10. Therefore, an efficiency in replacement of the EL drive circuit
 170 and the EL panel 50 is improved.
 Moreover, since the outer peripheral portion of the EL panel 50 is disposed
 opposite the outer peripheral portion 62a of the rear wall 60b formed
 along the periphery of the opening 62, the outer peripheral portion of the
 EL panel 50 is concealed by the outer peripheral portion 62a when viewed
 from a front side of the EL panel 50. The outer peripheral portion of the
 dial 30 is also concealed by the outer peripheral portion 62a. Therefore,
 when the EL panel 50 is viewed by the driver through the front panel 140,
 the outer peripheral portions of the EL panel 50 and the dial 30 are not
 seen by the driver. Therefore, when wiring of the speedometer S is
 disposed in the outer peripheral portions of the EL panel 50 and the dial
 30, the wiring can be concealed. Similarly, wiring of the tachometer R and
 the gauge G can be concealed when disposed in the outer peripheral
 portions of the dials 80, 110.
 In FIG. 5, the analog-digital switch 160 is set to the first position. As a
 result, the cold-cathode tube is turned on, and the dial 30 and the
 pointer 40 are illuminated by light emitted from the cold-cathode tube and
 transmitted by the light transmitting panel. The pointer 40 is rotated by
 the drive unit 20 along the front surface of the dial 30 to analog-display
 a speed of the vehicle. At the same time, the EL panel 50 is matrix-driven
 by the EL drive circuit 170 to digital-display a speed of the vehicle at
 an inner circumferential side of the scale portion 31 of the dial 30.
 In FIG. 6, the analog-digital switch 160 is set to the second position. As
 a result, the cold-cathode tube is turned off, and the dial 30 and the
 pointer 40 becomes invisible. At the same time, the EL panel 50 is
 matrix-driven by the EL drive circuit 170 to digital-display a speed of
 the vehicle.
 In FIG. 7, the analog-digital switch 160 is set to the third position. As a
 result, the cold-cathode tube is turned on and the EL panel 50 becomes
 transparent. The dial 30 and the pointer 40 are illuminated by light
 emitted from the cold-cathode tube and transmitted by the
 light-transmitting plate. The pointer 40 is rotated by the drive unit 20
 along the front surface of the dial 30 to analog-display a speed of the
 vehicle.
 A first modification of the present embodiment will be described with
 reference to FIG. 8. As shown in FIG. 8, the smoke glass 142 of the front
 panel 140 has a thinned portion 142a having a decreased thickness and
 disposed opposite the EL panel 50. Further, the rear wall 60b has a
 cylindrical portion 63. The cylindrical portion 63 is integrally formed
 with the rear wall 60b to coaxially surround the EL panel 50, the pointer
 40 and the dial 30. The cylindrical portion 63 is disposed opposite the
 thinned portion 142a.
 According to the first modification of the embodiment, even when a
 translucent rate of the EL panel 50 is relatively low, a brightness of the
 dial 30, the pointer 40 and the El panel 50 through the smoke glass 142 is
 increased due to the thinned portion 142a. As a result, a difference
 between a brightness of the dial 30, the pointer 40 and the EL panel 50
 through the thinned portion 142a and a brightness of the dials 80, 110
 through the smoke glass 142 is eliminated. Further, an end of the
 cylindrical portion 63 is disposed opposite a step portion of the smoke
 glass 142 formed along a periphery of the thinned portion 142a. Therefore,
 the step portion is restricted from being prominent when viewed from a
 front side of the front panel 140.
 A second modification of the present embodiment will be described with
 reference to FIG. 9. As shown in FIG. 9, three front panels 240 are used
 instead of the front panel 140. A thickness of the front panel 240 for the
 EL panel 50 is set larger than those of the front panels 240 for the dials
 80, 110. In FIG. 9, only the front panels 240 for the EL panel 50 and the
 dial 80 are shown. Further, the rear wall 60b has three tapered
 cylindrical portions 64 each of which is disposed opposite each of the
 front panels 240. An annular shielding wall 65 is disposed between the EL
 panel 50 and the dial 30. According to the second modification of the
 embodiment, the same effect as in the first modification is obtained.
 The present invention is not limited to the combination meter for the
 vehicle, but may be applied to any composite operational display unit for
 a ship or a general industrial device. The present invention may be
 applied to a single speedometer S instead of a composite display unit.
 Further, any other display panel such as a liquid crystal panel, which is
 turned on to conduct matrix display and is turned off to become
 transparent, may be used in stead of the EL panel 50.
 The EL panel 50 may not be matrix-driven, but may have plural seven-segment
 electrode patterns. Further, the speedometer S which analog-displays a
 speed of the vehicle may be replaced with a liquid crystal panel, an EL
 panel or a vacuum fluorescent display (VFD) panel which digital-displays a
 speed of the vehicle.
 While a speed of the vehicle is analog-displayed by the dial 30 and the
 pointer 40, the EL panel 50 may digital-display a speed of the vehicle in
 a part of or a whole area of the EL panel 50. In this case, a speed of the
 vehicle is preferably digital-displayed not to interfere the scale pattern
 31 of the dial 30. This is effective especially when the EL panel 50 is
 applied with diffusion treatment on both sides thereof to restrict noise
 image from being generated when the EL panel 50 is turned on. The noise
 image includes reflection image generated by glass of front and rear
 surfaces of the dial 30.
 Further, the EL panel 50 may be also disposed opposite the dials 80, 110.
 Also, when the annular wall 60a is curved in an opposite direction to that
 in FIG. 3, a mounting position of the circuit casing 180 is changed
 correspondingly, that is, the circuit casing 180 is mounted on a lower end
 surface of the annular wall 60a.
 Although the present invention has been fully described in connection with
 a preferred embodiment thereof with reference to the accompanying
 drawings, it is to be noted that various changes and modifications will
 become apparent to those skilled in the art. Such changes and
 modifications are to be understood as being within the scope of the
 present invention as defined by the appended claims.