(12) United States Patent
`Bilz et al.
`
`US006480806B1
`US 6,480,806 B1
`Nov. 12, 2002
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`(54) AUTOMATIC HEADLIGHT LEVELING
`SYSTEM FOR MOTOR VEHICLES
`
`FR
`JP
`
`2738193
`10181426
`
`3/1997
`7/1998
`
`(75) Inventors: Frank Bilz, Munich (DE); Peter
`Lehnert, Munich (DE)
`
`(73) Assigneez Bayerische Motoren Werke
`Aktiengesellschaft, Munich (DE)
`_
`_
`_
`_
`Sub]ect to any dlsclalmer, the term of thls
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 69 days.
`
`_
`( * ) Notlce?
`
`OTHER PUBLICATIONS
`_
`_
`_
`Toop, “Dynamische LeuchtWe1teregulung” (Dynamic Head
`lamp Levelling Control), ATZ Automobiletechnische
`Zeitschri? 95 (1993) PP- 466469
`TietZe et al., "Halbleiter—Schaltungstechnik” (Semiconduc
`tor Circuitry) (Chapter title: LoW Pass as Mean Value
`Generator), 1986,
`
`* cited by examiner
`
`(21) Appl. No.: 09/676,214
`.
`_
`Sep' 29’ 2000
`(22) Flled'
`(30)
`Foreign Application Priority Data
`
`Primary Examiner—John S. Hilten
`Assistant Examiner—Stephen J. Cherry
`(74) Attorney, Agent, or Firm—CroWell & Moring LLP
`
`Oct. 1, 1999
`
`(DE) ....................................... .. 199 47 40s
`
`(57)
`
`ABSTRACT
`
`(51) Int. Cl.7 .............................................. .. G06F 15/00
`(52) US. Cl. ..................... .. 702/154; 362/460; 362/464;
`362/465
`(58) Field of Search ............................... .. 362/460, 464,
`362/465; 702/154
`
`(56)
`
`References Cited
`
`U'S' PATENT DOCUMENTS
`6,183,118 B1 * 2/2OO1 Toda et a1_ _______________ __ 315/360
`
`FOREIGN PATENT DOCUMENTS
`
`Asystem for automatic headlight leveling control in a motor
`vehicle has tWo level sensors Which are offset in the longi
`tudinal direction for measuring the vehicle body pitch angle
`in the form of a level difference- An electronic Control unit
`determines a desired value for the headlight adjustment as a
`function of the ?rst derivative of the directly measured or
`further processed level difference. In one embodiment of the
`invention, electronic control unit determines a static level
`difference and a dynamic level difference, and the desired
`value is determined as a function of the ?rst derivative or the
`second derivative of the dynamic level difference.
`
`EP
`
`0899156
`
`3/1999
`
`9 Claims, 1 Drawing Sheet
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`Page 1 of 5
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`

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`U.S. Patent
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`Nov. 12, 2002
`
`US 6,480,806 B1
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`Illl'lllllllllllll
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`Page 2 of 5
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`

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`US 6,480,806 B1
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`1
`AUTOMATIC HEADLIGHT LEVELING
`SYSTEM FOR MOTOR VEHICLES
`
`BACKGROUND AND SUMMARY OF THE
`INVENTION
`This application claims the priority German patent docu
`ment 199 47 408.7, ?led Oct. 1, 1999, the disclosure of
`Which is expressly incorporated by reference herein.
`The invention relates to an automatic headlight leveling
`system for a motor vehicle.
`Dynamic headlight leveling helps to improve traf?c
`safety, since it eliminates the need for the driver to carry out
`a manual operation, Which Would have to take place as a
`function of the vehicle load. When headlights With an
`improved luminous poWer are used, for eXample, by means
`of electric discharge lamps, the dynamic headlight leveling
`additionally prevents the projection of glare onto oncoming
`traf?c. This applies also to dynamic operations, as, for
`eXample, considerable acceleration.
`An automatic headlight leveling system of this type is
`described, for eXample, in the AT Z article “Dynamic Auto
`matic Headlight Leveling”, 9/1992, Page 466, and on, in
`Which compression of the vehicle springs (Which has the
`effect of a longitudinal inclination or pitch of the vehicle
`body), is detected by tWo ultrasonic level sensors Which are
`offset in the longitudinal direction. After measurement, the
`pitch angle of the vehicle body Will be manifested in the
`form of a level difference. (In this case, the level sensors
`measure the levels or distances betWeen the vehicle body
`and the road in the front and in the rear on the vehicle body
`?oor. Level sensors are also used in the form of aXle sensors
`Which each measure the level or the distance betWeen the
`vehicle body and the front and rear vehicle axles). In an
`electronic control unit having a microcomputer, the desired
`value for the headlight adjustment, such as the position of a
`stepping motor to be adjusted, is computed as a function of
`the measured level difference. The level difference is aver
`aged over a time period Which is a function of the vehicle
`speed.
`The knoWn dynamic automatic leveling system differen
`tiates betWeen a sloW (static) and a fast (dynamic) control
`mode. In the sloW automatic control mode, the compara
`tively long-lasting or static pitch angles (longitudinal
`inclinations) Which are generated particularly by the loading
`of the vehicle, the emptying of the tank and/or the change of
`the aerodynamic drag are taken into account. In the fast
`automatic control mode, the changes of the pitch angle as a
`result of driving-dynamics-related in?uences (particularly,
`acceleration or deceleration operations) are taken into
`account.
`In order to avoid stressing the stepping motor in the
`headlights too long, rapid automatic control mode Will be
`sWitched on only When a considerable pitch angle change
`due to driving-dynamics-related in?uences is to be eXpected.
`For this purpose, the ?rst derivative of the vehicle speed
`signal and/or the brake light signal are analyZed. In vieW of
`the actual pitch angle changes, these signals supply only
`limited information. Furthermore, a control as a function of
`these signals takes place only in a delayed manner.
`One object of the invention is to provide an improved
`system for an automatic leveling control of the type
`described above, Which avoids the disadvantages of the prior
`art, under dynamic driving conditions, and at the same time
`achieves an optimal illumination of the road.
`Another object of the invention is to provide a headlight
`control system that minimiZes glare that is directed at the
`oncoming traf?c.
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`These and other objects and advantages are achieved by
`automatic headlight leveling system according to the
`invention, Which has tWo level sensors that are offset in the
`longitudinal direction for measuring the vehicle body pitch
`angle in the form of a level difference, and an electronic
`control unit for determining the desired value for the head
`light adjustment as a function of the measured level differ
`ence. The control unit determines the desired value as a
`function of the ?rst derivative of either the directly measured
`level difference or a further processed level difference. The
`term “directly measured level difference” indicates particu
`larly the difference of the level values measured by the level
`sensors and supplied in the form of measuring signals to the
`control unit. The term “further processed level difference”
`indicates particularly the difference of the measured level
`values and/or the level values further processed in the
`control unit and/or the further processed difference of the
`measured or further processed level values. Further process
`ing may be, for eXample, an averaging or another ?ltering,
`and may also be another elimination of interfering in?u
`ences.
`By analysis of the ?rst derivative of the level difference,
`it is determined Whether and to What eXtent a change of the
`pitch angle actually eXists. This permits a more direct
`automatic pitch angle control. Based on the magnitude of the
`?rst derivative, it can, for eXample, be decided Whether a
`sloW or fast automatic control mode is to be selected.
`In an advantageous embodiment of the invention, the time
`period for averaging of the measured level difference is
`de?ned as a function of the ?rst derivative of the measured
`level difference.
`In another embodiment of the invention, a static level
`difference value is determined at least by averaging the
`directly measured level difference for a ?rst time period; and
`a dynamic level difference value is determined at least by
`averaging the directly measured level difference for a second
`time period. The ?rst time period is de?ned to be signi?
`cantly longer than the second time period. The desired value
`is de?ned as a function of the ?rst derivative of the dynamic
`level difference value as the further processed level differ
`ence. As a result, the pitch angle deviation due to both static
`and dynamic in?uences can be carried out simultaneously.
`The pitch angle changes due to static and dynamic in?u
`ences are considered separately, and their mutual interaction
`can also be taken into account.
`The desired value is preferably determined also a function
`of the second derivative of the dynamic level difference
`value. By adding vehicle-relevant quantities (such as the
`position of the center of gravity, moments of inertia, spring
`rates, etc.), automatic control can be carried out as a function
`of a predictable pitching movement. This permits a further
`acceleration and improvement of the control.
`In another advantageous embodiment of the invention, the
`desired value is determined also as a function of additional
`information transmitted to the control unit (Which informa
`tion is preferably already available from other systems in the
`vehicle). Such information may, for eXample, be road infor
`mation from a navigation system, distance from a preceding
`vehicle from a ranging system, accelerator pedal position,
`brake pressure, vehicle speed and/or the visual range of a fog
`sensor. As a result, a very good situation-adapted intelligent
`control of the headlight inclination can be carried out.
`GPS data, for eXample, can be used in conjunction With a
`navigation system in the motor vehicle concerning the type
`of road (for eXample, turnpike or city street). The control
`unit can thereby alWays implement a comparatively more
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`Page 3 of 5
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`US 6,480,806 B1
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`3
`raised headlight adjustment for turnpikes than for city
`streets. By means of the level course information of the GPS
`data and of the navigation system, humps and troughs can be
`better illuminated.
`Furthermore, the current distance from a preceding or an
`oncoming vehicle can be transmitted, for example, by an
`ACC system (adaptive cruise control) in the motor vehicle
`to the control unit. In this case, a loWering of the headlights
`can alWays take place for limiting glare.
`The position of accelerator pedal or of the throttle valve
`can be taken into account in order for example, to carry out
`a preventive loWering of the headlights in the event of an
`expected elevation of the front Wheels as a result of an
`acceleration operation.
`Likewise, the brake pressure or the speed of the change
`from the accelerator pedal to the brake pedal can be analyZed
`in order to preventively raise the headlights, for example, in
`the event of an emergency braking, for improving the
`visibility.
`Finally, the signal of a range-of-vision sensor or fog
`sensor can also be analyZed in order to preventively loWer
`the headlights in dense fog for minimiZing the scattered
`light density.
`The invention permits more direct, more precise and
`faster control of the headlight inclination than the prior art.
`Other objects, advantages and novel features of the
`present invention Will become apparent from the folloWing
`detailed description of the invention When considered in
`conjunction With the accompanying draWings.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic vieW of a ?rst automatic headlight
`leveling system according to the invention; and
`FIG. 2 is a schematic vieW of a second, very precisely
`Working, automatic headlight leveling system according to
`the invention.
`
`35
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`DETAILED DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates tWo level sensors offset in the longitu
`dinal direction on a vehicle (not shoWn); speci?cally a
`forWard sensor Sv and a rearWard sensor Sh. As knoWn from
`the prior art, the sensors Sv and Sh are, for example,
`ultrasonic sensors in the front and rear on the vehicle body
`?oor or axle sensors at the front and at the rear axle. To
`measure the vehicle body pitch angle in the form of a level
`difference D, the output signals of the sensors Sv and Sh are
`connected With a level difference detector 1 of an electronic
`control unit 4a, Which in turn is connected With a ?lter 2. In
`the control unit 4a, the ?rst time derivative dD/dt of the
`directly measured level difference D is calculated. The ?lter
`2, Which averages the level difference, may be for example,
`a loW-pass ?lter Whose time constant can be adjusted as a
`function of dD/dt. The averaged value of the level difference
`is transmitted from the ?lter to a desired-value detector 3a
`of the control unit 4a.
`The desired value S for the adjustment of the headlight
`arrangement 5, Which is shoWn here only schematically, is
`computed in the desired-value detector 3a as a function of
`the averaged value of the level difference and optionally of
`other signals a, b and c. The signals a, b and c are, for
`example, the vehicle speed signal, the brake light signal and
`the accelerator pedal position signal.
`It is alWays checked in the control unit 4a Whether the ?rst
`derivative dD/dt of the level difference exceeds a de?ned
`threshold. If so, the pitch angle has changed such that a
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`folloW-up of the headlights may be necessary. By determin
`ing the time constant of the ?lter 2, as a function of the value
`of the ?rst derivative or of the frequency of the change of the
`value of the ?rst derivative dD/dt, a sloW or fast automatic
`control can be initiated. In the simple control unit 4a
`illustrated in FIG. 1, the sWitch-over function of the speed
`signal knoWn from the prior art based on the value of the ?rst
`derivative dD/dt of the level difference can therefore be
`taken over. In this manner, a control is achieved Which is
`more responsive to the actual vehicle pitch angle change
`than in the prior art.
`By taking into account the additional signals, the control
`can be better adapted to the respective situation. For
`example, the loWering of the headlights in response to
`vehicle body pitch (amount of the desired value S) can
`alWays be reduced at a high speed because here no high
`forces Which de?ect the vehicle can act upon the chassis.
`The brake light signal and the accelerator pedal signal
`indicate an imminent deceleration or acceleration operation.
`As in FIG. 1, in FIG. 2, the tWo level sensors Sv and Sh
`offset in the longitudinal direction are connected With a level
`difference detector 1 for measuring the vehicle body pitch
`angle in the form of a level difference D. The level difference
`detector 1 is arranged in a control unit 4b. The level
`difference D formed in the level difference detector 1 is, on
`the one hand, provided to ?lters 2a and 2b in the control unit
`4b. Filter 2a is a loW-pass ?lter With a large time constant;
`?lter 2b is a loW-pass ?lter With a small time constant. By
`means of ?lters 2a and 2b, a static level difference value D1
`is formed by averaging the directly measured level differ
`ence D for a ?rst de?ned time period, and a dynamic level
`difference value D2 is formed by averaging the directly
`measured level difference D for a second de?ned time
`period. As a result of the selection of the time constants, the
`?rst time period is signi?cantly longer than the second time
`period. The level difference values D1 and D2 are therefore
`further processed level difference values.
`The desired value S is determined by the desired-value
`detector 3b at least as a function of the ?rst derivative dD2/dt
`of the dynamic level difference value. Preferably, the desired
`value S is also determined as a function of the second
`derivative d2D2/dt2 of the dynamic level difference value D2
`in conjunction With vehicle-speci?c quantities, and of addi
`tional information transmitted to the control unit as Well.
`Quantities or information of this type are, for example, the
`road information a from a navigation system, the distance b
`to a preceding vehicle from a ranging system, the accelerator
`pedal position c, the brake pressure d, the vehicle speed e
`and/or the visual range of a fog sensor. Possible effects of the
`additional information a to f on the detection of the desired
`value S Were described above.
`This embodiment of the invention permits fast control,
`because it is also foresighted; as Well as a highly precise
`control of the headlight adjustment as a function of actual
`pitch angle changes.
`The foregoing disclosure has been set forth merely to
`illustrate the invention and is not intended to be limiting.
`Since modi?cations of the disclosed embodiments incorpo
`rating the spirit and substance of the invention may occur to
`persons skilled in the art, the invention should be construed
`to include everything Within the scope of the appended
`claims and equivalents thereof.
`What is claimed is:
`1. An automatic leveling system for vehicle headlights
`comprising:
`at least tWo level sensors Which are offset in a longitudinal
`direction of the vehicle body for measuring vehicle
`body pitch angle in the form of a level difference; and
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`US 6,480,806 B1
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`5
`an electronic control unit for determining a target value
`for headlight adjustment as a function of the measured
`level difference;
`Wherein the control unit determines the target value as a
`function of the ?rst derivative of at least one of the
`measured level difference and a further processed level
`difference.
`2. The automatic headlight leveling system according to
`claim 1, further comprising a ?lter Which averages said level
`difference over a determinable time period, said time period
`being a function of the ?rst derivative of measured level
`difference.
`3. The automatic headlight leveling system according to
`claim 1, Wherein:
`said electronic control unit determines a static level
`difference value by averaging at least the measured
`level difference over a ?rst de?ned time period, and a
`dynamic level difference value by averaging at least the
`measured level difference over a second de?ned time
`period, the ?rst time period being substantially longer
`than the second time period; and
`the target value is determined as a function of the ?rst
`derivative of the dynamic level difference value as a
`further processed level difference.
`4. The automatic headlight leveling system according to
`claim 3, Wherein the target value is determined as a function
`of the second derivative of the dynamic level difference
`value.
`5. The automatic headlight leveling system according to
`claim 2, Wherein the target value is determined as a function
`of additional vehicle information transmitted to the control
`unit, said additional vehicle information comprising at least
`one of vehicle speed, a brake light signal and accelerator
`pedal position.
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`6. A method of controlling an inclination angle of vehicle
`headlights, comprising:
`measuring time varying vehicle pitch;
`calculating a ?rst derivative, With respect to time, of
`measured vehicle pitch;
`averaging said vehicle pitch over a ?rst time period,
`Wherein said ?rst time period is determined as a func
`tion of said calculated ?rst derivative; and
`generating a headlight adjustment control signal as a
`function of averaged vehicle pitch determined in said
`averaging step.
`7. The method according to claim 6 Wherein said step of
`averaging comprises ?ltering said vehicle pitch in a loWpass
`?lter having a time constant Which is adjustable based on
`said ?rst derivative.
`8. A method of controlling an inclination angle of vehicle
`headlights, comprising:
`measuring time varying vehicle pitch;
`determining a static vehicle pitch by averaging said time
`varying vehicle pitch over a ?rst time period;
`determining a dynamic vehicle pitch by averaging said
`time variable vehicle pitch over a second time period
`Which is signi?cantly shorter than said ?rst time period;
`calculating ?rst and second derivatives, With respect to
`time, of measured time variable vehicle pitch; and
`generating headlight adjustment control signals as a func
`tion of said static and dynamic averages and at least
`said ?rst derivative.
`9. The method according to claim 8, Wherein said head
`light control signal is generated as a function of said ?rst and
`second derivatives.
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