Patent Description:
In general, it is known to provide an active restraint system comprising a seat belt retractor with an electric motor for facilitating different functions. For example from <CIT>, it is known to provide a seat belt retractor with electric motor for adjusting the force of the retraction spring, for facilitating a comfort function. An electric motor which is relatively flat in its dimensions is disclosed in <CIT> is mounted against the frame of the seat belt retractor such that a rotor of the electric motor is coupled with an radial outer end of the retraction spring, and thus is able to adjust the force acting on the belt reel. When the rotor is rotated such that the spring is unwound, the force acting on the belt webbing is lowered and thus, comfort is increased. <CIT> moreover discloses that a switchable clutch can be provided between the rotor of the electric motor and the belt reel, such that in a pre-crash situation the torque of the electric motor may be directly supplied to the belt reel for pretensioning the belt webbing. A drawback of this seat belt retractor is that only two functions (comfort function and pretensioning function) can be carried out.

A further active restraint system is known from <CIT>, in which a seat belt retractor is provided with an electric motor as well. Again the electric motor may be designed according to <CIT>. According to <CIT> the electric motor is connected to a shiftable transmission gear. Depending on how the transmission gear is shifted, the torque of the electric motor can be supplied for adjusting the force of the retraction spring, or supplied to a mechanism for adjusting a load limiter, or supplied directly on the belt reel for pretensioning a belt webbing in pre-crash situation.

However, a drawback of the arrangement disclosed in <CIT> is that the construction is rather complex and also space consuming leading to a cost intensive manufacturing and also error susceptibility.

The document <CIT> discloses an active restraint system according to the preamble of claim <NUM>.

Therefore, an object of the present invention is to further improve an active restraint system comprising a seat belt retractor having an electric motor attached thereto to even further increase comfort and safety for the passenger.

According to the first aspect of the invention, this problem is solved by an active restraint system comprising a seat belt retractor with an electric disc motor comprising a rotor and a stator, the rotor being directly attached to the belt reel, and a control unit connected to the disc motor and adapted to control the disc motor to drive the belt reel in accordance with a determined belt motion profile. Said seat belt retractor comprises a frame and a belt reel with a belt webbing wound thereon which is rotatably supported by the frame for allowing winding and unwinding the belt webbing.

Such a disc motor is a specific type of a motor having a disc shaped rotor and a stator having a corresponding disc shaped slot in which the disc shaped rotor is received. The rotor comprises a rotor shaft which may be directly coupled to the belt reel. The rotor may be coupled to the body of the belt reel itself, in particular to an extension of the belt reel. Alternatively the rotor may be coupled to a torsion bar provided within the belt reel. Preferably, the disc motor comprises a rotor with a plurality, e.g. two, three or four rotor discs. Preferably, the disc motor is formed by the torque disc motor and adapted to supply a relatively large torque. While the prior art electric motor, as e.g. disclosed in <CIT> is connected to the belt reel via a planet gear, according to the present invention, the rotor is directly attached to the belt reel and thus, it is preferred to supply a high torque with a lower speed.

Such a disc motor may comprise at least one air-core coil. The motor in general may be formed as disclosed in <CIT> or <CIT>. The rotor discs preferably are provided with a meander winding, which preferably is provided as a printed conductor path on a substrate of the rotor discs. Since the rotor does not comprise a coiled winding, the response time of the motor is short and safety can be improved. Preferably the air gap between the rotor and the stator is in the range of <NUM> or less.

The term directly attached in this instance means that no gearing or switchable clutch is provided between the rotor and the belt reel. The rotor may be formed integrally with the belt reel or connected the belt reel by means of a fixed clutch.

The control unit preferably comprises determination means for determining the belt motion profile. Such determination means may be formed of or comprise a software module carried out by a micro controller. The belt motion profiles define a time-traverse graph for the belt webbing.

According to a first preferred embodiment the active restraint system comprises a belt reel position sensor for measuring the rotational position of the belt reel, wherein the control unit is connected to the belt reel position sensor and adapted to determine the belt motion profile based on the measured belt reel position. The belt reel position sensor may be formed as a separate sensor element, e.g. a sensor measuring the thickness of the webbing wound on the belt reel, or also may be provided as a software module in the control unit and adapted to determine the belt reel position based on current induced by rotating the rotor of the disc motor. Such a belt reel position sensor is helpful for determining out-of-position of the passenger, a passenger size or child seat detection. Based on the determined belt reel position it is known how much webbing is on the belt reel and how much webbing is taken off. Thus, the size of the passenger can be inferred, and out-of-position position of the passenger, or the presence of a child seat can be inferred.

When the respective seat to which the seat belt retractor is assigned, is an adjustable seat e.g. adjustable in a longitudinal direction of the respective vehicle, the control unit of the seat belt retractor preferably is provided with seat position data, so that the relative position of the belt retractor and the respective seat can be taken into account when determining the passenger size, out of position, and/or a child seat. Based on these determined positions the respective belt motion profile can be determined. when an out-of-position position of the passenger is determined, it is preferred that the belt motion profile is chosen such that the passenger is moved back to the desired position. When e.g. a child seat is determined the belt motion profile is determined such that no pretensioning is performed in a pre-crash situation since this would be vulnerable for the child seat.

Preferably the active restraint system comprises a velocity sensor for measuring the rotational velocity of the belt reel, wherein the control unit is connected to the belt reel velocity sensor and adapted to determine the belt motion profile based on the measured belt reel velocity. Such a belt reel velocity sensor in particular is useful in view of a comfort function to support the passenger and permit the webbing to unreel with a desired velocity or to wind up the belt reel with a desired velocity. Also such a belt reel velocity sensor is beneficial in crash situation to determine the velocity of the displacement of the passenger. When the passenger is relatively light, e.g. a five percentile female passenger, a load limiter might be not optimal constructed for such a person and the deceleration of the person is too high, which may result in injuries. The belt reel velocity sensor detects such a velocity, which is too low, and the control unit is adapted to determine a respective belt motion profile to support this displacement of the person in the crash situation. The electric motor is accordingly controlled, such that it acts to unwind belt webbing to permit the person to displace in the desired manner. In the other way around, when it is determined that the displacement velocity of the person in a crash situation is too high, the electric motor acts on the belt reel to reduce the velocity. This improves safety of the safety restraint system and provides an actively controlled seat belt retractor.

Moreover, it is preferred the active restraint system comprises a belt reel torque sensor for measuring a torque applied on the belt reel by means of the belt webbing, wherein the control unit is connected to the belt reel torque sensor and adapted to determine the belt motion profile based on the measured belt reel torque. This can be in alternative or in addition to the before-mentioned preferred embodiment comprising the belt reel velocity sensor.

According to a further preferred embodiment, the control unit is connected to a vehicle control system and adapted to determine the belt motion profile based on at least one sensor value received from the vehicle control system. Such sensor values may be values provided by a pre-crash sensor, accelerometers, passenger sensors, as e.g. sleep detection, ACC (Adaptive Cruise Control)-sensors, ESE (Electronic Stability Control)-sensors and the like. For example, when a passenger sensor detects a passenger is under the risk of sleep, the control unit preferably is adapted to control the electric motor such that the belt webbing is tighten for a short period, for giving the passenger a signal to wake up again. This improves safety of the safety restraint system and provides an actively controlled seat belt retractor.

Furthermore, preferably the control unit comprises a memory unit in which a plurality of pre-defined belt motion profiles is stored, and wherein the control unit is adapted to determine the belt motion profile by electing the belt motion profile from the stored plurality of pre-defined belt motion profiles. The control unit may be provided with information from a vehicle control system and receives passenger identity data, e.g. via an interior camera, a key associated with the person, a card reader reading a personal card, e.g. as a driving license, or the like. Such pre-stored and pre-defined belt motion profile may be defined by the passenger itself, e.g. in view of comfort aspects. Additionally or alternatively, such pre-defined belt motion profiles for specific groups of persons, as e.g. age, weight, gender, body dimensions and the like.

Moreover, preferably the control unit comprises a memory unit in which a plurality of pre-defined parameters are stored, and a calculating unit for calculating the belt motion profile based on at least of the stored parameters. Each parameter may be associated with specific belt motion profiles or calculating rules for belt motion profile. Based on this parameter the respective belt motion profile can be calculated. Examples for parameters include but are not limited to passenger ID and passenger weight.

According to a further preferred embodiment, the seat belt retractor may optionally comprise a load limiter for limiting the belt webbing load in a crash situation, wherein the control unit is adapted to control the disc motor such that substantially the whole range of the load limiter is consumed or used. This is preferably done according to a pre-defined belt motion profile. The belt motion profile is determined such that in a crash situation the load limiter is substantially fully consumed or used in an optimal manner (i.e. fully twisted) and the control unit controls the electric motor such that the belt webbing is moved in accordance with this belt motion profile. This includes acting in addition, and/or against (subtractive to) the load limiter, dependent on the crash situation and dependent on passenger characteristics. Preferably the load limiter is formed as a torsion bar. Such torsion bars in general are not adjustable and usually designed to suit the <NUM> percentile male person. The motor thus can act in an additive or a subtractive manner to the load limiter, in particular torsion bar, to enable an increase in safety.

Furthermore, it is preferred that in a crash situation the control unit is adapted to control the electric motor after a first impact to tighten the belt webbing. In seat belt retractors as known in the state of the art, the belt webbing is relatively loose after the first impact, since the passenger has displaced to the front and consumed the load limiter. When a second impact occurs, the passenger is not held in place by the belt webbing which may result in severe injuries. According to the invention, the control unit is adapted to control the motor to tighten the belt webbing after the first impact and to pull the passenger back in the normal position. Thus, safety can be increased.

In a further preferred embodiment, the seat belt retractor comprises a mechanical blocking unit with a mechanical vehicle sensor, and a de-activation device for deactivating the vehicle sensor. Preferably the de-activation device is only active for deactivating the vehicle sensor, when the electric disc motor is active. The control unit preferably is adapted to receive acceleration signals from a vehicle control system and to supply a respective torque to the belt reel for fixing the belt reel, when the acceleration exceeds a predetermined threshold. Thus, the control unit substitutes the function of the mechanical vehicle sensor, and thus it is possible to de-activate the mechanical vehicle sensor. This may increase the comfort for passenger, since the mechanical noise generated by the sensor mass of the mechanical vehicle sensor is suppressed.

Moreover, in this embodiment preferably the de-activation device comprises a solenoid for engaging a moving member of the vehicle sensor. The moving member preferably is a sensor mass e.g. a ball of the vehicle sensor, as it is generally known in the prior art. Such a solenoid has the benefit that when no electric energy is delivered (the solenoid is de-activated) and the mechanical vehicle sensor is activated again. This increases safety. In case the energy supply system of the vehicle experiences an error and the electric disc motor is not active, the mechanical vehicle sensor automatically is activated again. This leads to a fail safe system. Alternatively, also an electric motor with an eccentric output shaft can be used. The eccentric output shaft engages the moving member to fix it and when no current is supplied to the motor, the rotor of the motor can be moved by the sensor mass so that the sensor mass is in a movable state again.

According to a second aspect of the invention a method for controlling an active restraint system of at least one of the beforehand described preferred embodiments of an active restraint system is provided, the method comprising the steps: receiving at the control unit a signal representing a first condition; determining a first belt motion profile; and controlling the disc motor such that the belt reel is moved according to the first belt motion profile. It shall be understood that the active restraint system according to the first aspect and the method for controlling an active restraint system according to the second aspect of the invention comprise similar and identical preferred embodiments as in particular defined in the dependent claims. Insofar reference is made to the above description of the active restraint system according to the first aspect of the invention.

According to a preferred embodiment of the method, the first condition is or comprises a vehicle condition. A vehicle condition in particular is an acceleration of the vehicle, a crash situation of the vehicle or the like. One possible belt motion profile according to such an embodiment is that the disc motor is controlled to rotate the belt reel in the wind-up direction to tighten the belt webbing for a short time after a latching signal is received, indicating that a tongue attached to the belt webbing has been latched in the respective seat belt buckle. Belt slack is removed and the belt webbing subsequently brought into a comfort position. The latching signal is a signal indicating a vehicle condition.

Alternatively or additionally, when the control unit receives a signal that the vehicle should be driven to a service garage, the disc motor is controlled to move the belt reel in an oscillating manner for reminding the passenger that a problem exists in the car. A further belt motion profile would be tensioning the belt webbing, when a crash signal is received.

According to a further preferred embodiment of the method, the first condition is or comprises a passenger condition. In such an embodiment for example, when the control unit receives a signal indicating that the passenger is in an out-of-position position, the disc motor is controlled to pull the passenger back into a normal position.

Furthermore, it is preferred that the method comprises the steps: receiving at the control unit a signal representing a second condition; determining a second belt motion profile; and controlling the disc motor such that the belt reel is moved according to the second belt motion profile.

Particularly preferred the method comprises the steps: detecting a first impact in a crash situation; and controlling the disc motor such that the belt is tightened after the first impact.

For more complete understanding of the invention, the invention will now be described in detail with reference to the companying drawings. The detailed description will illustrate and describe what is considered as a preferred embodiment of the invention. It should of course be understood that various modifications and changes in form or detail could readily be made without departing from the scope of the invention. It is therefore intended that the invention may not be limited to the exact form and detail shown and described herein, nor to anything less than the whole of the invention disclosed herein and is claimed hereinafter. In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The word "comprising" does not exclude other elements or steps. The wording "a" or "an" does not exclude a plurality. The wording "a number of items", comprises also the number <NUM>, i.e. a single item, and further numbers like <NUM>, <NUM>, <NUM> and so far.

According to an aspect of the invention an active restraint system <NUM>, comprises a seat belt retractor <NUM> with a frame <NUM> and a belt reel <NUM> with a belt webbing <NUM> wound thereon and rotatably supported by the frame <NUM> for allowing winding and unwinding the belt webbing <NUM>, an electric disc motor <NUM> comprising a rotor <NUM> and a stator <NUM>, the rotor <NUM> being directly attached to the belt reel <NUM>, and a control unit <NUM> connected to the disc motor <NUM> and adapted to control the disc motor <NUM> to drive the belt reel <NUM> in accordance with a determined belt motion profile. The frame <NUM> comprises two side walls <NUM>, <NUM>, in which the belt reel <NUM> is rotatable received, the side walls connected by a common wall or backwall <NUM>.

On the left hand side of <FIG> in a casing <NUM> the so called mechanical part of the seat belt retractor <NUM> is provided comprising a retraction spring <NUM>. The retraction spring <NUM> is supported with its radial outer end at the outer end <NUM> at the housing <NUM> and with its radial inner end <NUM> at an extension <NUM> of the belt reel <NUM> for biasing the belt reel <NUM> to retract the webbing <NUM>.

In the casing <NUM> moreover a web sensor <NUM> and a vehicle sensor <NUM> are provided, as it is known in the prior art. The web sensor <NUM> acts to block the belt reel <NUM> when the belt webbing <NUM> is unwound with an excess acceleration or excess speed. In the same manner, the vehicle sensor <NUM> blocks the belt reel <NUM> when the vehicle experiences an excess acceleration. Both sensors, the web sensor <NUM> and the vehicle sensor <NUM>, act on a mechanical basis, such that they are able to block the belt reel <NUM> even if the vehicle control system <NUM> (see <FIG>) experiences a failure.

Within an inner hollow portion <NUM> of the belt reel <NUM> is a load limiter. In this embodiment, the load limiter is in the form of a torsion bar <NUM>. The torsion bar <NUM> is attached via a fixed bearing <NUM> to the belt reel <NUM> on the right hand side of <FIG>. On the left hand side at <NUM> the torsion bar <NUM> is not attached to the belt reel <NUM>; the only portion of attachment to the belt reel <NUM> is at <NUM>.

The illustrated active restraint system <NUM> in particular is useful for electric vehicles having a <NUM> Volt board network <NUM> instead of a <NUM> Volt board network as usual gasoline or diesel cars have.

As mentioned above (<FIG>) the active restraint system <NUM> is provided with an electric disc motor <NUM> having a rotor <NUM> and a stator <NUM>. The rotor <NUM> is in the form of a disc and directly attached at <NUM> to an axial extension <NUM> of the belt reel <NUM> and thus in torque transmitting relationship with the belt reel <NUM>. It shall be noted that there is no clutch or transmission gear provided between the rotor <NUM> and the belt reel <NUM>. The rotor <NUM> may be attached to the extension <NUM> by known shaft and hub connecting means <NUM>, or by a weld line or the like. The rotor <NUM> may also be attached to the extension <NUM> by a clamping mechanism using a screw and a respective screw threaded bore in the extension <NUM>. In so far, the extension <NUM> form a rotor shaft of the electric disc motor <NUM>.

Two different embodiments of the connection between the rotor <NUM> and the extension <NUM> are shown in the details of <FIG> illustrates an embodiment in which the extension <NUM> is formed at the load limiter <NUM>. The load limiter <NUM> again is connected to the belt reel <NUM> via the fixed bearing <NUM> however extends in this embodiment (<FIG>) through an opening <NUM> of the belt reel <NUM>. The extension <NUM> carries a first positive engagement section <NUM> in the form of a toothed outer circumferential surface <NUM> and the rotor <NUM> (in <FIG> simply shown as a block) comprises a second positive engagement section <NUM> in the form of a toothed inner circumferential surface <NUM>. Rotor <NUM> engages the extension <NUM> by means of the corresponding inner and outer toothed circumferential surfaces <NUM>, <NUM>. This engagement inhibits a relative rotation of the rotor <NUM> to the extension <NUM>. The cooperation of the two surfaces <NUM>, <NUM> forms an attachment <NUM> of the rotor <NUM> to the extension <NUM>.

An axial fixation is provided by a clamp <NUM> which is tightened against the rotor <NUM> by a screw <NUM> extending through said clamp <NUM> and being received in a screw threaded bore <NUM> of the extension <NUM>.

According to the embodiment illustrated in <FIG> the extension <NUM> is directly formed with the belt reel <NUM>. The belt reel <NUM> comprises an inner axial recess <NUM> in which the load limiter <NUM> is received and connected to belt reel <NUM> by said fixed bearing <NUM>. Again, the rotor <NUM> is seated on the extension <NUM>. According to this second embodiment (<FIG>) the rotor <NUM> is attached to the extension <NUM> via an attachment <NUM> which is a press fit <NUM> in this embodiment (<FIG>).

It shall be understood that the embodiments of <FIG> also can be combined, in that e.g. the rotor <NUM> is attached to the extension <NUM> via a press fit in <FIG>, while in <FIG> the rotor <NUM> is attached to the extension <NUM> via the first and second positive engagement sections as described with reference to <FIG>.

The stator <NUM> according to the embodiment of <FIG> is comprised of two stator plates <NUM>, <NUM> which are connected to an energy supply <NUM> (see <FIG> and <FIG>) and comprise an electrical winding <NUM> (see <FIG>). A corresponding winding <NUM> is provided on the disc <NUM> (see <FIG>). When the stator <NUM> is supplied with energy, it produces an electric magnetic field inducing a corresponding current in the winding <NUM>, which is preferably printed as a printed conductor path on the disc <NUM>, thus again inducing an electric magnetic field. The two electric magnetic fields generate a magnetic force forcing the rotor disc <NUM> into rotation. This will be described in more detail based on <FIG> below.

Between the disc <NUM> and the two stator plates <NUM>, <NUM> gaps G1, G2 are provided which are relatively small, in particular in the range of <NUM> or less and might be that small that the stator plates <NUM>, <NUM> contact the disc <NUM>, when the motor <NUM> is not supplied with electrical energy. When the motor <NUM> is supplied with electrical energy, the electromagnetic fields causes the stator plates <NUM>, <NUM> to move away from each other and thus form the gaps G1, G2.

The active restraint system <NUM> moreover comprises a control unit <NUM> (see <FIG> and <FIG>). The control unit <NUM> is adapted to control the disc motor <NUM> to drive the belt reel <NUM> in accordance with a determined belt motion profile (see also <FIG> below).

The active restraint system <NUM> also comprises a connector <NUM> for connecting the active restraint system <NUM> to a vehicle control system <NUM> for supplying the active restraint system <NUM> with electrical energy from the board network <NUM> and also with signals from the vehicle control system <NUM>, such as passenger ID data, vehicle data and the like.

In the housing <NUM> of the mechanical side of the belt retractor <NUM> a de-activation device <NUM> is provided. The de-activation device <NUM> comprises a solenoid <NUM>, which acts on a housing portion <NUM> of the vehicle <NUM> to clamp the sensor mass <NUM>. This movement of the solenoid <NUM> is indicated in <FIG> by means of the arrow. The sensor mass <NUM> is formed as a ball, as known in the prior art. When the solenoid <NUM> is active, it pushes down the housing part <NUM> which engages the sensor mass <NUM>. The sensor mass <NUM> is held fixed and the vehicle sensor <NUM> is de-activated. At the same time also noise generated by the sensor mass <NUM> is suppressed when the housing is depressed. This can be done, since the electric disc motor <NUM> can be used to block rotation of the belt reel <NUM>, in that it provides a holding torque to the belt reel, which is high enough to block the belt reel <NUM> against unwinding of belt webbing <NUM>.

As mentioned within the belt reel <NUM> a basic load limiter <NUM> in the form of a torsion bar is provided. This torsion bar <NUM> is designed to suit a <NUM> percentile male passenger. When it is determined that the passenger is on the respective seat is a lighter person, for example a <NUM> percentile male person or even a <NUM> percentile female passenger, a respective belt motion profile for a crash situation is determined by the control unit <NUM>. Such a belt motion profile <NUM>, <NUM>, <NUM> is shown in <FIG> and described below.

<FIG> shows a second embodiment of an electric disc motor <NUM>, having a rotor <NUM> and a stator <NUM>. The rotor <NUM> according to this embodiment (<FIG>) comprises three rotor discs <NUM>, <NUM>, <NUM>, which are arranged sequentially with four stator discs <NUM>, <NUM>, <NUM>, <NUM> of the stator <NUM>. Between the single discs again gaps G1, G2, G3, G4, G5, G6 are provided. The rotor discs <NUM>, <NUM>, <NUM> are all arranged on a common axis A and attached to an axial extension <NUM> (see <FIG>) for driving the belt reel <NUM> by an attachment <NUM> (see <FIG>). It shall be understood that the disc motor <NUM> according to this embodiment (<FIG>) can also be used with the active restraint system <NUM> as shown in <FIG>. Using two or more rotor discs <NUM>, <NUM>, <NUM> enables the disc motor <NUM> to provide a higher torque. The number of discs can be chosen dependent on the respective type of use.

With respect to <FIG>, the meander winding on <NUM> the discs <NUM>, <NUM>, <NUM>, <NUM> is described. <FIG> shows a partially exploded view of the active restraint system <NUM> with the extension <NUM> protruding to the right hand side. For illustrative reasons, only one stator disc <NUM> and one rotor disc <NUM> are shown, even though it shall be understood that additional discs <NUM>, <NUM>, <NUM> (cf. <FIG> above) can be added and are provided with similar windings <NUM>. The stator disc <NUM> comprises a fixing portion <NUM> for fixing, e.g. screwing, the stator disc <NUM> against a housing portion <NUM> of the seat belt retractor <NUM>. The rotor disc <NUM> is provided with a meander winding <NUM> (see <FIG>). The meander winding <NUM> (<FIG>) runs in a meander shape from a radial inner portion <NUM> to a radial outer portion <NUM> to resemble the meander shape. The meander winding <NUM> comprises three phases Pa, Pb, Pc (see <FIG>), which are slightly offset to each other by offset O1, O2. Even though, the meander winding <NUM> is shown arranged in a straight way in <FIG>, this meander winding is provided on the rotor disc <NUM> in a circular manner, as can be seen in <FIG>. The meander winding <NUM> is provided by means of etching or printing on the rotor disc <NUM>. All other rotor discs, <NUM>, <NUM>, <NUM> are formed in the same manner.

The stator disc <NUM> (see <FIG>) is provided with a winding <NUM>, which comprises the same three phases Pa, Pb, Pc, which are sequentially supplied with current to induce a moving electromagnetic field. This electromagnetic field induces a corresponding electromagnetic field in the meander winding <NUM> and thus, the rotor disc <NUM> is forced in rotation.

<FIG> shows a schematic block diagram of the active restraint system <NUM> connected to a vehicle control system <NUM>.

The control unit <NUM> preferably comprises determination means <NUM> for determining the belt motion profile. Such determination means may be formed of or comprise a software module <NUM> carried out by a micro controller <NUM>. The determination means <NUM> can be adapted to determine the belt motion profile by selecting a pre-stored belt motion profile (as it is described below), and/or to determine the belt motion profile by calculating a belt motion profile based on a plurality of parameters (as it is described below).

According to an embodiment the active restraint system <NUM> comprises a belt reel position sensor <NUM> for measuring the rotational position of the belt reel <NUM>, wherein the control unit <NUM> is connected to the belt reel position sensor <NUM> via signal line 308a and adapted to determine the belt motion profile based on the measured belt reel position. The belt reel position sensor <NUM> in this embodiment (<FIG>) is formed as a separate sensor element, e.g. a sensor measuring the thickness of the webbing <NUM> wound on the belt reel <NUM>. Such a belt reel position sensor <NUM> is helpful for inferring out-of-position of the passenger, a passenger size or child seat detection. Based on the determined belt reel position, it is known how much webbing <NUM> is on the belt reel <NUM> and how much webbing is taken off i.e. unwound. Thus, the size of the passenger can be estimated and out-of-position position of the passenger, or the presence of a child seat can be inferred.

In case the respective seat to which the active restraint system <NUM> is assigned, is an adjustable seat e.g. adjustable in a longitudinal direction of the respective vehicle, the control unit <NUM> preferably is provided with seat position data, so that the relative position of the belt retractor and the respective seat can be taken into account when determining the passenger the above information as in particular passenger size, out of position, and/or a child seat. Preferably such information is taken into account when determining the belt motion profile.

Preferably the active restraint system <NUM> comprises a velocity sensor <NUM> for measuring the rotational velocity of the belt reel <NUM>, wherein the control unit <NUM> is connected to the belt reel velocity sensor <NUM> via a signal line 310a and adapted to determine the belt motion profile based on the measured belt reel velocity. Such a belt reel velocity sensor <NUM> in particular is useful in view of a comfort function to support the passenger and permit the webbing <NUM> to unreel with a desired velocity or permit the webbing <NUM> to wind up with a desired velocity. Also such a belt reel velocity sensor <NUM> is beneficial in crash situation to determine the velocity of the displacement of the passenger. When the passenger is relatively light, e.g. a five percentile female passenger, a load limiter <NUM> might be not optimal designed for such a person and the deceleration of the person is too high, which may result in injuries. The belt reel velocity sensor <NUM> detects such a velocity, which is too low, and the control unit <NUM> is adapted to determine a respective belt motion profile to support this displacement of the person in the crash situation. The electric motor <NUM> is accordingly controlled, such that it acts to unwind belt webbing <NUM> to permit the person to displace in the desired manner. In the other way around, when it is determined that the displacement velocity of the person in a crash situation is too high, the electric motor <NUM> is controlled by controller <NUM> to act on the belt reel <NUM> to reduce the velocity. This may improve safety of the safety restraint system <NUM> and provides an actively controlled seat belt retractor <NUM>.

Moreover, it is preferred the active restraint system <NUM> comprises a belt reel torque sensor <NUM> for measuring a torque applied on the belt reel <NUM> by means of the belt webbing <NUM>, wherein the control unit <NUM> is connected to the belt reel torque sensor <NUM> via signal line 312a and adapted to determine the belt motion profile based on the measured belt reel torque. Also the torque sensor <NUM> can be used to measure displacement of a person in a crash situation and the control unit <NUM> is adapted to determine the belt motion profile for controlling the electric motor <NUM> based on the measured torque. This can be done by calculating the forward displacement based on a twist of the load limiter <NUM>. The preferences of the load limiter <NUM> are known, and thus it is known how much the load limiter <NUM> will twist when a given torque is applied.

The control unit <NUM> is connected to the vehicle control system <NUM> and adapted to determine the belt motion profile based on at least one sensor value received from the vehicle control system <NUM>. Such sensor values may be values provided by a pre-crash sensor <NUM>, accelerometers <NUM>, passenger sensors <NUM>, as e.g. sleep detection <NUM>, ACC (Adaptive Cruise Control)-sensors <NUM>, ESE (Electronic Stability Control)-sensors <NUM> and the like. For example, when a passenger sensor <NUM> detects a passenger is under the risk of sleep, the control unit <NUM> preferably is adapted to control the electric motor <NUM> such that the belt webbing <NUM> is tensioned for a short period, for giving the passenger a signal to wake up again.

The control unit <NUM> comprises a memory unit <NUM> in which a plurality of pre-defined belt motion profiles P1, P2, etc. is stored. The control unit <NUM> is adapted to determine the belt motion profile P1, P2, etc. by selecting the belt motion profile P1, P2, etc. from the stored plurality of pre-defined belt motion profiles P1, P2, etc. The control unit <NUM> may be provided with information from a vehicle control system <NUM> and receives passenger identity data, e.g. via an interior camera, a key associated with the person, a card reader reading a personal card, e.g. as a driving license, or the like. Such pre-stored and pre-defined belt motion profiles P1, P2, etc. may be defined by the passenger itself, e.g. in view of comfort aspects. Additionally or alternatively, such pre-defined belt motion profiles P1, P2, etc. for specific groups of persons, as e.g. age, weight, gender, body dimensions and the like.

Preferably in the memory unit <NUM> a plurality of pre-defined parameters X1, X2, etc. are stored. The controller <NUM> comprises a calculating unit <NUM> for calculating the belt motion profile based on at least of the stored parameters X1, X2, etc. Each parameter X1, X2, etc. may be associated with specific belt motion profiles or calculating rules for belt motion profile. Based on the parameter X1, X2, etc. the respective belt motion profile can be calculated by means of the calculating unit <NUM>. The processor <NUM> will then process the calculated belt motion profile and the controller <NUM> will control the disc motor <NUM> accordingly. Examples for parameters include but are not limited to passenger ID and passenger weight. The parameter may be pre-known or the parameter is being determined by the control unit <NUM>.

<FIG> now shows a schematic diagram of an active restraint system <NUM> according to another embodiment of the invention. Identical and similar elements are provided with identical reference signs of the previously described embodiments, and insofar reference is made to the above description. In the following it is rather focused on the differences. If nothing is said regarding a specific element, the element is designed as defined above.

According to an embodiment the active restraint system <NUM> comprises a belt reel position sensor <NUM> for measuring the rotational position of the belt reel <NUM>. The belt reel position sensor <NUM> is provided as a software module in the control unit <NUM> and adapted to determine the belt reel position based on current induced by rotating the rotor <NUM> of the disc motor <NUM>. When the rotor <NUM> is rotated by means of pulling the webbing <NUM> causing a rotation of the belt reel <NUM>, a current is induced in the stator winding <NUM>, which can be measured. The current is indicative for the revolutions of the belt reel <NUM>, and thus, based on this current, the belt reel position can be calculated. The controller <NUM> in this embodiment is adapted to calculate this position.

Moreover, in this embodiment (<FIG>) the belt reel velocity sensor <NUM> is designed as a software module in the control unit <NUM> and adapted to determine the belt reel velocity based on current induced by rotating the rotor <NUM> of the disc motor <NUM>. The principle of function is the same as it has been described with respect to the belt reel position sensor <NUM>. Also the belt reel torque sensor <NUM> is designed as a software module in the control unit <NUM>. Again, the same principles as above apply here.

With respect to <FIG>, three different embodiments of belt motion profiles are described. It shall be understood that a plurality of further belt motion profiles can be implemented, depending on the use case of the seat belt retractor.

According to <FIG>, a force diagram is shown, wherein the force (F) in kilo Newton is shown on the ordinate axis and the time (t) in milliseconds is shown on the abscissa axis.

In <FIG>, three graphs <NUM>, <NUM>, <NUM> are shown, which indicate the force acting on the seat belt or belt webbing <NUM> i.e. the retraction force for three different persons. Thus, each graph <NUM>, <NUM>, <NUM> define a specific belt motion profile. The graph <NUM> is dedicated for a <NUM> percentile male person, the graph <NUM> for a <NUM> percentile average person and the graph <NUM> for a <NUM> percentile female person. In this embodiment, it is assumed that the torsion bar <NUM> is an average torsion bar limiting the belt force to <NUM> kN. This might not be enough for tall persons and too much for short and light persons. When a crash situation occurs at t=<NUM>, in a first portion <NUM> of the load limiting operation, which is a belt pre-tightening only carried out by the disc motor <NUM> is provided. This pre-tightening is done until a force F1 is reached. At t=<NUM>, the load limiting operation twisting the torsion bar starts. Now, the three different graphs <NUM>, <NUM>, <NUM> indicate the respective force levels F2, F3, F4. For an average person (graph <NUM>) no additional torque supply of the disc motor <NUM> is needed. The load limiting operation for force F3 is only carried out by means of the torsion bar without addition of force provided by the disc motor <NUM>. When a <NUM> percentile male person is detected on the seat, the disc motor <NUM> is controlled to add torque to the belt reel <NUM> causing the belt reel to rewind and thus adds force to the belt webbing. According to the present embodiment the disc motor <NUM> adds a torque resulting in additional <NUM>,<NUM> kN acting on the belt and thus force F4 in the diagram is obtained. In the same manner, when a <NUM> percentile female person is detected on the seat, the disc motor <NUM> is controlled so as to subtract force from the load limiter <NUM>, in this case -<NUM>,<NUM> kN.

The respective belt motion profile represented by one of the graphs <NUM>, <NUM>, <NUM> is determined by the controller <NUM>, in particular by the determination means <NUM>, by selecting a suitable belt motion profile from the memory <NUM>. The selection is carried out by using data from the belt reel position sensor <NUM> and optionally a weight sensor mounted within the respective passenger seat and also connected to the controller <NUM> or the vehicle control system <NUM>.

Thus, in summary, when in the crash situation, the passenger is displaced by a forward force caused by the experienced deceleration. Due to the force acting on the blocked belt reel <NUM> via the belt <NUM>, the torsion bar <NUM> is twisted for limiting the force acting between the belt and a passenger's body. When the passenger is lighter than a <NUM> percentile male person, the torsion bar <NUM> is dimensioned too stiff and thus as a consequence he torsion bar is not twisted enough and the forward displacement of the passenger is too short. For obtaining an optimal displacement and optimal twisting of the torsion bar <NUM>, and in consequence an optimal load limiting result, the disc motor <NUM> is controlled by the control unit <NUM> such that it supports the forward displacement of the passenger, in that it adds torque to the belt reel <NUM>, such that the torsion bar <NUM> is fully twisted. This may result in an improved forward displacement of the passenger which may increase safety and may reduce injuries.

<FIG> illustrates that the active restraint system <NUM> having the belt retractor <NUM> and the disc motor <NUM> according to the present invention can be used to carry out a full tensioning of the belt webbing <NUM> in a crash situation. The bold lined graph <NUM> illustrates the pulled-in belt webbing <NUM> on the ordinate in mm of webbing and the time scale in milliseconds on the abscissa axis. The dashed line illustrates a standard pyrotechnic belt tensioning mechanism, for comparison. Graph <NUM> in contrast indicates the movement of the belt <NUM> when only the disc motor <NUM> according to the invention is used in the active restraint system <NUM> without an additional pyrotechnical belt tensioning mechanism, as it is used in the state of the art. Graph <NUM> therefore represents a belt motion profile, which is selected by determination means <NUM>, upon the controller <NUM> receiving a corresponding signal of a pre-crash-sensor <NUM> via the connection <NUM> to the vehicle control system <NUM>.

It can be seen that the gradient of the graph <NUM> is lower than the gradient of the graph <NUM>, however, it can also be seen that the tensioning operation using the disc motor <NUM> starts earlier at about <NUM> millisec, while the tension operation of the pyrotechnic belt tensioning apparatus starts at about <NUM> millisec. This is due to the fact that the disc motor <NUM> can react much faster than a pyrotechnic belt tensioning apparatus, which needs to be ignited first. Having a lower gradient is more comfortable for the person and thus also adds to the safety aspect of the active restraint system <NUM>. Using the active restraint system according to the present invention makes it possible that no pyrotechnic belt tensioning device is needed anymore.

<FIG> shows a graph of a second impact control of the seatbelt retractor. The ordinate axis shows the length of the belt webbing <NUM> in mm, wherein values above zero show that belt webbing <NUM> is unreeled, i.e. the belt <NUM> is loosened, and values below zero show that belt webbing is retracted, i.e. tensioned. The abscissa axis shows the time T in milliseconds.

At t=<NUM>, a crash is detected and from t=<NUM> until t=<NUM> belt webbing is retracted (cf. Section <NUM> of the graph), such that a pretension operation is carried out. From t=<NUM> on, belt webbing is unwound to allow the passenger being displaced to the front to be decelerated accordingly. In this section <NUM> also, the load limiter is twisted. At t=<NUM>, a second impact of the crash is detected. With normal state of the art seatbelt retractors, no additional action is possible now, since the load limiter <NUM> is already twisted. However, according to the present invention, the disc motor <NUM> is controlled again to carry out a belt tensioning operation; this is shown by section <NUM> of the graph <NUM>. Belt webbing again is wound on the belt real and tensioned at t=<NUM>. A subsequent load limiting operation, similar to the graph section <NUM> can be carried out and supported by the disc motor <NUM> in a similar manner as described above. The disc motor <NUM> will be controlled to provide a respective torque, such that the passenger can be displaced forwards in a load limiting operation.

This belt motion profile according to <FIG> is stored in the memory <NUM> of the control unit <NUM> and is selected by the determination means <NUM> when the vehicle is in a crash situation and a respective signal is received from the vehicle control system <NUM>.

Now <FIG> illustrated a method for controlling an active restraint system <NUM> of at least one of the beforehand described preferred embodiments of an active restraint system <NUM>.

The method comprises the steps: receiving S100 at the control unit <NUM> a signal S1 representing a first condition; determining S102 a first belt motion profile P1; and controlling S108 the disc motor <NUM> such that the belt reel <NUM> is moved according to the first belt motion profile P1.

The first condition may be or may comprise a vehicle condition. A vehicle condition in particular is an acceleration of the vehicle, a crash situation of the vehicle or the like. One possible belt motion profile P1, P2, etc. according to such an embodiment is that the disc motor <NUM> is controlled to rotate the belt reel <NUM> in the wind-up direction to tension the belt webbing <NUM> for a short time after a latching signal of a seat belt buckle is received, indicating that a tongue attached to the belt webbing <NUM> has been latched in the respective seat belt buckle. Belt slack is removed and the belt webbing <NUM> subsequently brought into a comfort position. The latching signal is a signal indicating a vehicle condition.

Alternatively or additionally, when the control unit <NUM> receives a signal that the vehicle should be driven to a service garage, the disc motor <NUM> is controlled to move the belt reel <NUM> in an oscillating manner for reminding the passenger that a problem exists in the car. A further belt motion profile P1, P2, etc. would be tensioning the belt webbing <NUM>, when a crash signal is received.

The first condition may also be or comprise a passenger condition. In such an embodiment for example, when the control unit <NUM> receives a signal indicating that the passenger is in an out-of-position position, the disc motor <NUM> is controlled to pull the passenger back into a normal position.

According to <FIG>, the step of determining S102 a belt motion profile comprises accessing S104 a memory <NUM> of the control unit, and selecting S106 from a plurality of pre-stored belt motions profiles P1, P2, etc. a suitable belt motion profile P1 based on the received S100 signal S1.

Claim 1:
Active restraint system (<NUM>), comprising:
a seat belt retractor (<NUM>), having
a frame (<NUM>) and a belt reel (<NUM>) with a belt webbing (<NUM>) wound thereon and rotatable supported by the frame (<NUM>) for allowing winding and unwinding the belt webbing (<NUM>), an electric disc motor (<NUM>) comprising a rotor (<NUM>) and a stator (<NUM>), and
a control unit (<NUM>) connected to the disc motor (<NUM>) and adapted to control the disc motor (<NUM>) to drive the belt reel (<NUM>) in accordance with a determined belt motion profile, characterised in that the rotor (<NUM>) is directly attached to the belt reel (<NUM>).