Head-up display device for vehicle

A HUD device includes a stepper motor, which rotates a reflection mirror for adjusting a display position of a virtual image. The stepper motor has an electric stabilization point and a mechanical stabilization point. A control system controls a drive signal for the stepper motor to change by a step angle at every predetermined period Ts in response to an adjustment instruction inputted from an adjustment switch. The control system continues to apply the drive signal until the electric stabilization point is attained even after the adjustment instruction is stopped to operate the stepper motor in a powered rotation mode. The stepper motor then operates in an inertia rotation mode toward the mechanical stabilization point is attained.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese patent application No. 2012-22169 filed on Feb. 3, 2012.

TECHNICAL FIELD

The present disclosure relates to a head-up display device for a vehicle.

BACKGROUND

In a conventional head-up display (HUD) device for a vehicle, a light-emitted image such as vehicle information, which is displayed by a display unit, is projected onto a projection target such as a windshield of a vehicle so that the displayed image may be displayed as a virtual image. JP 2011-207431A (US 2011/0241596 A1) discloses one example of such a HUD device, in which a display image provided by a display unit is reflected by a reflection mirror such as a concave mirror and projected onto a projection target. By using the reflection mirror, the HUD device can be mounted in a limited space in a vehicle.

In this HUD device, a stepper motor is used to rotate the reflection mirror in response to a drive signal corresponding to an adjustment instruction from an external side so that a display position of virtual image may be adjusted. According to this configuration, a passenger (driver) in a vehicle is enabled to adjust a position of a virtual image of vehicle information to a position, which is more readily viewable, by inputting a position adjustment instruction to the HUD device.

In addition, in the HUD device, the stepper motor is continued to be driven by the drive signal until it is stabilized electrically, when the input of the adjustment instruction is stopped. If the drive signal is stopped at a point, which is not at the electrically stabilization point, the stepper motor tends to step out of phase in response to an impact of external force or vibration. The drive signal is continued to be applied for a while to avoid this out-of-phase problem.

In the HUD device, it is assumed that plural electric stabilization points, at which the stepper motor is electrically stabilized by holding torque generated when powered, and plural mechanical stabilization points, at which the stepper motor is mechanically stabilized by detent torque provided when not powered, match each other. Under this assumption, the stepper motor is stabilized by continuously applying the drive signal until the electric stabilization point is attained, even when the drive signal is stopped after the electric stabilization point. In this case, the stepper motor is assumed to be stabilized by the detent torque generated at the electric stabilization point.

In actual products, however, the electric stabilization points and the mechanical stabilization points are different in phase due to manufacturing tolerance and the like. As a result, in a case that the drive signal is continued to be applied at the electric stabilization point and thereafter stopped, the stepper motor temporarily stops and then starts rotation toward the mechanical stabilization point. This causes the display position of the virtual image to move again after being stopped once. Passengers in the vehicle will thus feel discomfort and even unreliability of the vehicle information displayed as the virtual image.

SUMMARY

It is an object therefore to provide a head-up display device for a vehicle, which increases reliability of a virtual image display of vehicle information.

According to one aspect, a head-up display device for a vehicle includes a display unit, an optical system, a stepper motor and a control system. The display unit displays a light-emitted image of vehicle information. The optical system includes a reflection mirror, which is provided rotatably to reflect the light-emitted image and project a reflected image toward a projection target so that a virtual image of the light-emitted image is displayed. The stepper motor drives, when powered by a drive signal, the reflection mirror to rotate for adjusting a display position of the virtual image. The stepper motor has plural electric stabilization points, at which a motor operation is electrically stabilized by a holding torque generated when powered, and plural mechanical stabilization points, at which the motor operation is stabilized by a detent torque generated when not powered. The control system controls the drive signal for the stepper motor in response to an adjustment instruction inputted from an external side. The control system is configured to continue to apply the drive signal even after the adjustment instruction is stopped until the electric stabilization point is attained so that the stepper motor performs powered rotation, and immediately stop applying the drive signal when the electric stabilization point is attained so that the stepper motor performs inertia rotation toward the mechanical stabilization point after the powered rotation. Preferably, the control system is configured to change an electric angle of the drive signal applied to the stepper motor by a step angle at every predetermined time period until application of the adjustment instruction is stopped. The step angle is smaller than an interval between two electric stabilization points. The control system is configured to continue applying the drive signal to change the electric angle of the drive signal by the step angle after the application of the adjustment instruction is stopped until the electric stabilization point is attained by the powered rotation. It is possible to determine that the electric stabilization point is attained when not only the electric stabilization point is actually attained but also an electric stabilization point, which is slightly different from but just before the electric stabilization point, is attained.

DETAILED DESCRIPTION OF THE EMBODIMENT

Configuration

Referring first toFIG. 1, a head-up display (HUD) device1for a vehicle includes a housing10, a display unit20, an optical system30, a stepper motor40, a reduction gear mechanism50, an adjustment switch60and a control system70.

The housing10is formed in a hollow shape, which accommodates the other devices20,30,40,50and the like of the HUD device1, and mounted in an instrument panel2of a vehicle. The housing10has a translucent light projection window14at a position facing a windshield4, which is fixed to a front side of a driver's seat of the vehicle as a projection target, in an up-down direction.

The display unit20is a trans-illumination type liquid crystal panel (LCD) and has a screen22for displaying an image. The display unit20emits light of a display image of the screen22by illuminating the screen22by a built-in backlight (not shown). The light image displayed by the display unit20is for providing vehicle information related to vehicle driving or vehicle conditions. The light image provides, for example, navigation information such as a vehicle travel direction or the like (for example,FIG. 2). The display image of the display unit20may be a physical quantity data, which includes a vehicle speed, a residual fuel quantity, a coolant temperature or the like, and vehicle exterior condition information, which includes a traffic condition, a safety condition or the like, other than the navigation information.

The optical system30includes a number of optical parts including a reflection mirror32(other parts are not shown inFIG. 1), and projects the display image of the display unit20to the projection window14. The reflection mirror32is formed of a concave mirror having a smooth reflection surface34, which is curved in a concave shape. The reflection mirror32expands and reflects toward the projection window14side the display image, which is directly or indirectly incident as an optical image from the display unit20to the reflection surface34. The reflection image of the reflection mirror32is projected to the windshield4through the projection window14and is image-formed at a forward side of the windshield4. As a result, the vehicle information indicated by the display image of the display unit20is displayed at a driver's seat side in the vehicle as a virtual image36exemplarily shown inFIG. 2.

The reflection mirror32has a rotary shaft38supported rotatably in the housing10. When the rotary shaft38is driven to rotate, the reflection mirror32moves a display position of the virtual image36in the up-down direction relative to the windshield4as exemplified inFIG. 2. The display of the virtual image36is realized between a lower limit display position DI shown by solid lines inFIG. 2and an upper limit display position Du shown by dotted lines inFIG. 2in correspondence to optical characteristics of the optical system30and the windshield4.

As shown inFIG. 3, the stepper motor40is a claw-pole permanent magnet type and has a magnetic casing46, a rotor41and stators44,45. The magnetic casing46is formed of magnetic material and in a hollow shape. The rotor41is formed of a motor shaft42and rotor magnets43attached to the outer peripheral surface of the motor shaft42. The motor shaft42is supported rotatably by the magnetic casing46. The rotor magnets43are permanent magnets and are arranged to provide magnetic poles N and S alternately in a circumferential direction (rotation direction) of the rotor41.

The stators44and45are provided for two phases and firmly fixed to the magnetic casing46at a radially outside part relative to the rotor41. As shown inFIG. 3andFIG. 4, the stator44for one phase (A-phase) has magnetic yokes441,442and a coil443, and the stator45for the other phase (B-phase) has magnetic yokes451,452and a coil453. The magnetic yokes441,442,451,452have a plurality of nail-shaped pole teeth (claw poles)441a,442a,451a,452a, respectively, as shown inFIG. 5in the expanded manner. The pole teeth441a,442aof the magnetic yokes441,442for the A-phase are interleaved to be alternately arranged in the circumferential or rotation direction of the rotor41. Similarly, the pole teeth451a,452aof the magnetic yokes451,452for the B-phase are interleaved to be alternately arranged in the circumferential or rotation direction of the rotor41. The magnetic yokes441,442,451,452are arranged such that the pole teeth441a,451a,442a,452aare shifted by ½ pitch each other in this order in the rotation direction of the rotor41.

As shown inFIG. 3, the phase coil443is arranged coaxially with the magnetic yokes441,442for the A-phase, and the phase coil453is arranged coaxially with the magnetic yokes451,452for the B-phase. The coil443and the phase coil453are shifted from each in position in the axial direction. In the stepper motor40configured as described above, when the phase coil443of the A-phase and the phase coil453of the B-phase are energized by being powered by drive signals, respectively, the rotor magnets43and the motor shaft42are rotated.

The reduction gear mechanism50has plural gears52to59meshed in series in the magnetic casing46. The gear52of the first stage is provided on the motor shaft42and the gear59of the last stage is provided on the rotary shaft38of the reflection mirror32. Thus the rotary motion of the motor shaft42is reduced in accordance with gear ratios among the gears52to59and transferred to the rotary shaft38so that the reflection mirror32is driven to rotate. When the stepper motor40rotates in the normal rotation direction, the reflection mirror32is driven to rotate in the normal rotation direction so that the display position of the virtual image36is shifted upward, for example. When the stepper motor40rotates in the reverse rotation direction, the reflection mirror32is driven to rotate in the reverse rotation direction so that the display position of the virtual image36is shifted downward, for example.

The adjustment switch60shown inFIG. 1andFIG. 4is provided to be operable by the passenger on the driver's seat in the vehicle. The adjustment switch60has, for example, two push-type manipulation members62and63so that the passenger may selectively input an upward adjustment instruction for moving the display position of the virtual image36upward and a downward adjustment instruction for moving the display position of the virtual image36downward, respectively. The adjustment switch60is thus configured to output different instruction signals, one for instructing the upward adjustment and the other for instructing the downward adjustment.

The control system70includes a display control circuit72and plural switching elements74and is provided inside or outside the housing10. The display control circuit72is an electronic circuit including a microcomputer as a main part and electrically connected to the display unit20and the adjustment switch60. As shown inFIG. 4, each switching element74is a transistor, the collector of which is electrically connected to the phase coil443or453. The emitter and the base of each switching element74are connected electrically to a grounding terminal (not shown) and the display control circuit72. The switching element74varies amplitude of the drive signal applied to the phase coil443of the A-phase or the phase coil453of the B-phase in response to base signals inputted from the display control circuit72. Thus, by controlling the base signal for the switching element74by the display control circuit72, the drive signal applied to the phase coil443or453is controlled.

In the control system70configured as described above, the display control circuit72controls the image display of the display unit20. The display control circuit72further controls the drive signals applied to the phase coils443and453in response to the instruction signals inputted from the adjustment switch60. Specifically, the display control circuit72controls electric angles of the drive signals applied to the phase coils443and453to electric angles for driving the reflection mirror32in the normal rotation direction in response to the upward adjustment instruction generated by the operation member62so that the display position of the virtual image36is moved upward. Further, the display control circuit72controls an electric angles of the drive signals applied to the phase coils443and453to electric angles for driving the reflection mirror32in the reverse rotation direction in response to the downward adjustment instruction generated by the operation member63so that the display position of the virtual image36is moved downward.

According to the HUD device1configured as described above, the voltage amplitudes of the drive signals, which are applied to the phase coils443and453of the A-phase and the B-phase to supply electric power to the stepper motor40, are controlled to vary corresponding to the electric angles, respectively, for energizing the rotors44and45in two different phases. The drive signals for the phase coils443and453are controlled to be a maximum amplitude (Vmax, −Vmax) or a minimum amplitude (0) at every electric stabilization point θe, at which a holding torque for holding the motor shaft42is generated when the power is supplied. As exemplified inFIG. 6, the electric stabilization point ideally appears at every fixed angular interval of 90 degrees. However, the pole teeth441a,442a,451aand452ahave tolerable differences in shape, position and the like thereamong. As a result, the actual interval between the electric stabilization points becomes longer or shorter than 90 degrees as exemplified inFIG. 7.

When no drive signal is applied to the phase coils443and453, that is, in the non-energization period, plural mechanical stabilization points θm, at which a detent torque for holding the motor shaft42is generated, appear. The mechanical stabilization point θm is identical with the electric stabilization point θe ideally. However, as schematically exemplified inFIG. 7, it is likely in actual motor products that the mechanical stabilization point θm appears at a point, which is deviated from the electric stabilization point θe in phase in the rotation direction of the rotor41. This deviation results from a difference in magnetic attraction forces, which are generated relative to the rotor magnets43when the motor is not energized by the pole teeth (pole teeth451aand452ain the example ofFIG. 7) at the electric stabilization point θe in the energization phase and by the pole teeth (pole teeth441aand442ain the example ofFIG. 7) adjacent to the pole teeth in the energization phase in the rotation direction.

For the stepper motor40having the stabilization points θe and θm, the display control circuit72controls the drive signals applied to the phase coils443and453in response to the instruction signal inputted from the adjustment switch60so that the display position of the virtual image36is adjusted. The display control circuit72is therefore configured to perform drive signal control processing based on a computer program as shown in a flowchart ofFIG. 8. The drive signal control processing shown inFIG. 8is started and finished, when an engine switch of the vehicle is turned on and off, respectively.

At S101in the drive signal control processing, it is checked whether the instruction signal indicating the upward or downward adjustment instruction is inputted from the adjustment switch60. If no instruction signal is inputted (S101: NO), S101is repeated and no drive signal is applied to any of the phase coils443and453. If the instruction signal of either instruction is, applied (S101: YES), S102is executed.

At S102following the upward adjustment instruction or the downward adjustment instruction, it is checked whether the manipulation member62or63corresponding to the inputted adjustment instruction is continuously operated for more than a threshold time period Tth based on the instruction signal inputted from the adjustment switch60. The threshold time period Tth is set to, for example, about 0.5 seconds or other time periods, so that the passenger will not feel bored or uneasy because of a long period from the start of manipulation on the adjustment switch60to the actual change in the display position of the virtual image36.

If the instruction signal indicating the operation of the manipulation member62or63is temporary and not continued more than the threshold time period Tth (S102: NO), it is determined that the instruction of the upward adjustment or the downward adjustment indicates a fine adjustment of the display position of the virtual image36. In this case, S103is executed following S102. At S103, the drive signal applied to the phase coil443,453is controlled as shown inFIG. 9Aso that the stepper motor40is driven to make a full step rotation. That is, the drive signal is changed 90 degrees, which is a full step angle of one full step in the upward or the downward direction, from the present electric angle, that is, the electric stabilization point θe, to the next electric stabilization point θe. As a result, the reflection mirror32is driven to rotate in correspondence to a change in the electric angle of the stepper motor40so that the display position of the virtual image36is finely adjusted in accordance with a short-time manipulation of the manipulation member62or63.

If the instruction signal indicating the operation of the manipulation member62or63is long and continued more than the threshold time period Tth (S102: YES), it is determined that the instruction of the upward adjustment or the downward adjustment indicates a continuous adjustment of the display position of the virtual image36. In this case, S104is executed following S102. At S104, the drive signal applied to the phase coil443,453is controlled as shown inFIG. 9B, so that the stepper motor40is driven to make a micro-step rotation. That is, the drive signal is changed continuously for a predetermined period Ts in the upward or the downward direction, from the present electric angle to the next electric angle, which is different by a step angle Δθ for a micro-step driving. The step angle Δθ in the micro-step driving is predetermined to be, for example 18 degrees, which is far less than the interval of 90 degrees between the adjacent electric stability angles θe. The step angle Δθ may be determined as 90/N with N being an integer greater than two.

At S105following S104, it is checked based on the instruction signal inputted from the adjustment switch60whether the input of the adjustment instruction by the manipulation member62or63stopped. If the manipulation member62or63is continuously operated (S105: NO), S104is repeated. In each execution of S104, one micro-step driving of step angle Δθ is performed for the period Ts. Thus, the display position of the virtual image36is continuously adjusted. If the adjustment instruction by the manipulation member62or63is stopped (S105: YES), S106is executed. At S106it is further checked whether the present electric angle is at the electric stabilization point θe.

If the present electric angle does not equal the electric stabilization point Be yet (S106: NO), S107is executed in the similar manner as at S104. That is, the micro-step driving is performed so that the electric angle is changed by one step angle Δθ per the period Ts. Subsequently, S108is executed to check whether the present electric angle equals the electric stabilization point θe. If the present electric angle is not equal to the electric stabilization point θe yet (S108: NO), S107is repeated to make the micro-step driving of the step angle Δθ per period Ts. Thus, as the micro-step driving is performed as indicated as an energized or powered rotation mode Me shown inFIG. 9B, the display position of the virtual image36is continuously adjusted. If the present electric angle equals the electric stabilization point θe (S108: YES), S109is executed. At S109, the driving signals for the phase coils443and453are stopped.

If the present electric angle is at a point, which is prior to the electric stabilization point θe by one step angle Δθ (that is, at angle position θb inFIG. 9B), when S106is executed, the time interval from S107of micro-step driving to S109through S108substantially equals the predetermined period Ts. That is, after the electric angle reaches a point, which is prior to the electric stabilization point Be by one step angle Δθ, the drive signal is continued to be applied for one more period Is and then stopped at the electric stabilization point θe. By thus stopping the application of the drive signal, the rotor41of the stepper motor40rotates by inertia in the inertia rotation mode Mm toward the mechanical stabilization point θm, which is nearest to the electric stabilization point θe of the application stop time as shown inFIG. 7. The rotor41thus stops at or near the mechanical stabilization point θm.

If the present electric angle reaches the target stabilization point Bet after S103or at S106as shown inFIG. 8, S109is executed. After S109, the drive signal control processing is repeated from S101until the engine switch is turned off.

Operation

In the HUD device1, when inputting the adjustment instruction by the continuous operation (for example, pushing) on the manipulation member62or63is stopped, the energized rotation mode Me is generated. In this mode Me, the drive signal is continued to be applied to the stepper motor40by the control system70until the electric stabilization point θe is attained by the holding torque. When the electric angle θe is attained, the inertia rotation mode Mm appears following the energization rotation mode Me, in which the control system70stops the application of the drive signal. The stepper motor40rotates by inertia toward the mechanical stabilization point θm by the detent torque. By thus changing the rotation mode from the energization rotation mode Me to the inertia rotation mode Mm in sequence, the stepper motor40rotated by the continued application of the drive signal to the electric stabilization point θe can be rotated continuously toward the mechanical stabilization point θm without being stopped at the electric stabilization point θe. The display position of the virtual image36, which is adjusted by the stepper motor40rotating continuously in accordance with the rotation of the reflection mirror32, is continuously adjusted crossing the point corresponding to the electric stabilization point θe. For this reason, the reliability of the virtual image36of the vehicle information is improved.

In the HUD device1, in particular, when the electric angle reaches the angle, which is before the electric stability angle θe by one step angle Δθ, in the energized rotation mode Me at the time of stopping the input of the adjustment instruction, the application of the drive signal to the stepper motor40by the control system70is stopped after being continued for the predetermined period Ts. The predetermined period Ts is set to be a period, which changes the electric angle of the drive signal by the step angle Δθ smaller than the interval of the electric stabilization points Be while the adjustment instruction is being inputted. This period substantially equals the time period, in which the stepper motor40rotates by the application of the drive signal from the electric angle, which is one step angle Δθ prior to the electric stabilization point θe to the electric stabilization point Be. The application of the drive signal in the energized rotation mode Me is surely stopped at the time of arrival at the electric stabilization point θe after an elapse of the predetermined period Ts. As a result, in the subsequent inertia rotation mode Mm, the stepper motor40can be rotated by inertia toward the mechanical stabilization point θm without being stopped at the electric stabilization point θe. It is thus surely prevented that the display position of the virtual image36moves again after stopping at the position corresponding to the electric stabilization point Be. The virtual image36of the vehicle information can be displayed with high reliability.

Other Embodiment

The HUD device1described above is not limited to the above-described embodiment but may be implemented in many other embodiments.

For example, S102and S103may be omitted and the drive signal control processing may be performed without full step driving. The full step driving may be performed at S104and S107. The stepper motor40may be other than the permanent magnet type, for example a motor of a variable reluctance type, a hybrid type or the like, as far as the motor has a difference in phase between the electric stabilization point θe determined by the holding torque and the mechanical stabilization point θm determined by the detent torque. The display unit20may be other than the liquid crystal panel. For example, it may be an EL (electroluminescence) panel or a unit, which provides a light emission image by indicators or the like. The projection target, to which the reflection image of the reflection mirror is projected, is not limited to the windshield. It may be a combiner or the like, which is provided exclusively in the HUD device.

In addition, it is possible to execute S106, S108to check whether the present electric angle is just before the electric stabilization point θe. That is, S106is executed to check whether the electric stabilization point θe is attained including a case that the present electric angle is just before attaining the electric stabilization point θe.