Seat belt retractor

Abstract: A seat belt retractor with a belt reel (3) for the seat belt webbing, a load limiter which is designed as a hydraulic pump (7) allows limited extraction of belt webbing with energy absorption when the belt reel is blocked, the absorption of energy being adjustable as a function of crash-related data.

Description: The invention relates to a seat belt retractor according to the preamble of claim 1. Such a seat belt retractor is disclosed in DE-A-22 15 892. The known retractor comprises a belt reel for the seat belt webbing and a load limiter which allows limited extraction of the belt webbing with absorption of energy. An adjusting device adjusts the load limiter as a function of crash-related data. The load limiter can be a friction brake or any other braking system. The earlier EP-A-911229 describes a seat belt retractor with a belt reel for the seat belt webbing and a load limiter which is designed as a hydraulic pump. The load limiter allows limited extraction of the belt webbing with absorption of energy when the belt reel is blocked, wherein the hydraulic pump forces a fluid through a restrictor which could be programmable. The load limiter can be connected by means of a clutch selectively only in crash conditions to the belt reel. DE 196 04 483 C1 teaches a seat belt retractor provided with a load limiter which allows limited extraction of belt webbing with absorption of energy when the belt reel is blocked. The absorption of energy can be adjusted as a function of crash-related data detected by sensors. This crash-related data can be data about the vehicle occupant's body, seat position data, crash condition data such as severity of the crash and the like. This data is determined by sensors arranged outside the seat belt retractor and is evaluated for adjusting the energy absorption of the load limiter. This should allow the restraint characteristic of the seat belt to be influenced in a controlled manner when the seat belt is blocked, in particular after the tightening of the seat belt, optionally in conjunction with the restraint function of an airbag. It is an object of the invention to provide a seat belt retractor of the type mentioned at the outset with which limited extraction of belt webbing with crash-related energy absorption is achieved at reduced cost when the belt reel is blocked. This object is achieved according to the invention by the characterising features of claim 1. The load limiter is designed as a hydraulic pump. Preferably an energy absorber with variable energy absorption operates by the principle of a hydraulic pump in which the rotor of the hydraulic pump is coupled to the belt reel, for example by actuation of a coupling, and the rotor conveys a hydraulic medium through a throttle device adjusted as a function of the measurement signal or the measurement signals. The hydraulic pump alone can form the adjustable load limiter. However, it is also possible to combine the hydraulic pump with an energy absorber having a predetermined energy absorption characteristic, for example with a torsion bar. The hydraulic pump then forms the variable part of the load limiter. DE 44 26 621 A1 discloses a hydraulic pump as tightener drive for tightening a seat belt. With the present invention, however, the hydraulic pump is used for the consumption of energy, hydraulic medium being conveyed through a butterfly valve controlled by the measurement signal or the measurement signals by the rotation caused by the winding shaft. The hydraulic pump can therefore be used if limited extraction of belt webbing with energy absorption that can be adjusted to the respective incidence of a crash is to be achieved when the belt reel is blocked. The information required for obtaining the restraint characteristic required for decelerated extraction of belt webbing can be obtained from the behavior, in particular rotating behavior, of the belt reel. The severity of the crash, the weight and the size of the vehicle occupant are indicated directly by the rotating movement of the belt shaft. A direct relationship between the crash sequence and the adjustment of load limitation is therefore obtained. Brief Description of the Drawings The invention will be explained in more detail hereinafter with reference to the figures in which: Fig. 1 shows a first embodiment of the invention with a hydraulic pump for adjusting the desired absorption of energy; and Fig. 2 is a force diagram showing various energy absorption steps as a function of the band extraction velocity. Detailed Description of the Invention In the embodiment shown in Fig. 1, only the components of the seat belt retractor required for understanding the invention are shown. The seat belt retractor has a belt reel 3 onto which the seat belt webbing, not shown in detail, is coiled. Blocking discs that have sets of blocking teeth 4 at their periphery are connected to the end flanges of the belt reel 3 by shearing pins 15. To block the belt reel 3 against further rotation, a blocking pawl 14 associated with each set of blocking teeth 4 is brought into engagement with the set of blocking teeth. Blocking of this type optionally takes place after the tightening of the seat belt, for example in the event of a crash. To reduce the load transmitted from the belt webbing to a vehicle occupant's body during the forward displacement of the vehicle occupant, a limited extraction of belt webbing with braking effect or energy absorption is provided which comes into effect between the vehicle body or a seat belt retractor frame 28 and the belt reel 3. This limited extraction of belt webbing with energy absorption is ensured in the respective embodiments by a load limiter 5. In the embodiments illustrated, adjustment of the absorption of energy to a desired restraint characteristic predetermined by a belt force characteristic curve is possible as a function of the severity of the crash and/or the body weight of the vehicle occupant. For this purpose, the rotational movement of the belt reel is scanned after blocking (blocking engagement of the pawl 14 in the set of blocking teeth 4) and the energy absorption of the load limiter 5 adjusted as a function thereof. In the embodiment shown in Fig. 1, the rotation of the belt reel is scanned by a scanner 2. For example, a marking 16 representing rotational angle increments can be scanned using the scanner. By scanning the rotational angle increments of the marking, the scanner delivers a signal proportional to the length of extracted belt webbing. A measurement signal proportional to the angular velocity (speed of rotation) can be obtained by differentiation of this signal in a differentiator 17. A measurement signal proportional to the rotational acceleration is obtained by further differentiation of this velocity signal over time in a second differentiator 18. This signal proportional to the rotational acceleration is proportional to the force that comes into effect on the belt webbing or on the belt reel 3 during the forward displacement of the vehicle occupant's body. The described arrangement forms a sensor device 1 with which the above-mentioned measurement signals can be obtained. Measurement signals containing information about the severity of the crash and about the body weight of the vehicle occupant can therefore be obtained by scanning the rotating movement of the belt reel 3. The load limiter 5 can then be adjusted optionally as a function of a predetermined belt force characteristic curve as a function of one or more of these signals. In the described embodiment, the blocking pawl 14 is brought into engagement with the set of blocking teeth 4 after tightening of the belt on both sides or on one side of the winding shaft. During the forward displacement of the vehicle occupant's body, a force acts on the belt reel 3 such that the shearing pins 15 are sheared off and the belt reel is able to rotate relative to the blocking disc 19 secured by the blocking pawl 14. A coupling 20 is engaged by this relative rotation of the belt reel 3 with respect to the blocked blocking disc 19 so the belt reel 3 is coupled to a drive member 21 of an energy absorber designed as a hydraulic pump 7. Couplings that are engaged owing to the relative rotation of two parts are known. The hydraulic pump that is capable of operating, for example, by the Eaton principle conveys an incompressible medium, for example oil, into a closed circuit 23. This circuit comprises a controllable valve 24. The cross section of flow can be adjusted by the valve 24 for producing losses of flow and therefore for achieving the desired energy consumption. The hydraulic pump 7 and the attached circuit 23 with an adjustable cross section of flow therefore bring about an adjustable limitation of load during the limited extraction of belt webbing. The cross section of flow can be adjusted as a function of a belt force characteristic curve filed in a memory 25. This belt force characteristic curve which is plotted in relation to the extracted length of belt webbing is compared with the force trend of the measurement signal obtained from the second differentiator 18 and the signal proportional to the extracted length of belt webbing from the scanner 2. The two signals are evaluated in an evaluating device 26 which generates a signal representing the force exerted on the belt webbing as a function of the extracted length of belt webbing. This signal is compared in the comparator 22 with the belt force set characteristic curve stored in the memory 25. The actuating signal with which the valve 24 is adjusted is derived from the comparison signal. Adjustment takes place in such a way that the curve evaluated in the evaluating device 26 for the force variation corresponds to the belt force characteristic curve stored in the memory 25. The hydraulic pump 7 together with the closed circuit 23 can form the load limiter 5. However, it is also possible to combine the hydraulic pump and the circuit 23 with the adjustable cross section of flow (valve 24) with an energy absorber having predetermined energy absorption, for example with a torsion bar which acts on the winding shaft 3. Activation of the valve 24 in the embodiment of Fig. 1 can also be effected as a function of the velocity of extraction of belt webbing. For this purpose, the signals from the two differentiators 17, 18 are evaluated in the evaluating device 26. A stepwise increase in energy absorption or in the load limiter force of the type shown, for example, in the embodiment of Fig. 2 and stored in a memory 37 can be achieved. Fig. 2 is a force diagram showing various energy absorption steps as a function of the belt extraction velocity (reel speed). Energy absorption steps of this type dependent on the belt extraction velocity determined by the scanning of the belt reel can be achieved in the embodiments illustrated. The dependency of the individual steps on the belt extraction velocity and the step height can obviously be modified. With the embodiment illustrated, the necessary restraint characteristics can be produced by the load limiter, as a function of the crash event, in the range of a 5th percentile woman to a 95th percentile man.

Claims: Seat belt retractor with a belt reel (3) for the seat belt webbing, a load limiter which allows limited extraction of belt webbing with absorption of energy when during a forward displacement of vehicle occupant's body the belt reel (3) is able to rotate relative to a blocking disc (19) secured by a blocking pawl (14) and an adjusting device which adjusts the load limiter as a function of crash-related data, characterised in that the load limiter is designed as a hydraulic pump (7), which displaces a fluid through a cross section of flow which is adjusted by means of a controllable valve (24) as a function of the crash-related data and a coupling (20) is designed to be engaged by the relative rotation of the belt reel (3) with respect to the secured blocking disc (19) so that the belt reel (3) is coupled to a drive member (21) of the hydraulic pump (7). Seat belt retractor according to claim 1, characterised in that the fluid displaced by the hydraulic pump (7) is displaced in a closed circuit (23) containing the valve (24).

Inventors: KILIAN THOMAS, KRAUSS WALTER, SPECHT MARTIN, KILIAN, THOMAS, KRAUSS, WALTER, SPECHT, MARTIN
Applicants: KEY SAFETY SYSTEMS INC, KEY SAFETY SYSTEMS, INC.
Application year: 1999
Main classification: B60R22
IPC codes: B60R22