A LATCH MECHANISM FOR SAFETY BELTS

Abstract: A latch mechanism for safety belts of the roller belt type, intended preferably for vehicles and comprising a strap (3) which can be withdrawn from a roll-up mechanism (1) against spring bias. This roll-up mechanism includes a strap roller (2) rotatable about a roll-up shaft, a latch mechanism (8) including a ratchet (11) and a latch (10) which can be adjusted, in dependence on unnormal speed changes, between a position releasing the strap roller, and a latching position. The latch mechanism comprises a latch plate (13) provided with an engagement portion (25) which can be adjusted between a latching position in engagement with latch teeth (26) of a stationary latch ring (27) and a releasing position dependent on unnormal speed changes of the vehicle as well as unnormal acceleration in the withdrawal of the strap. A second latch (29) is pivotally mounted to the latch plate (13) and is biased with a force tending to keep the latch in releasing position. An adjustment element (35) adjusts the latch on the latch plate from releasing position to latching position at a relative movement of the ratchet (11) and the latch plate (13). This latch is arranged to guide, by the adjustment thereof to latching position, the latch teeth (25) of the engagement portion of the latch plate to complete engagement with the latch teeth (26) of the latch ring.

Description: A LATCH .MECHANISM FOR SAFETY BELTS The present invention relates to a latch mechanism of the kind referred to in the preamble of the accom- panying claim 1. The Swedish patent specification 7315301-7 describes a latch mechanism with a latch plate pivotably suspended on an edged portion of the roll-up shaft. This solution presents the drawback that the latch teeth of the latch plate can .get caught on the crests of the stationary latch teeth, no complete latch engagement thus being obtained. As a consequence thereof the un¬ completed latch engagement may be released by a heavy load and the safety belt may yield over a distance before latch engagement is again obtained, which may cause body injuries to the belt user. Moreover, such a latch engagement may cause deformation of the tooth crests resulting in an ever increasing tendency of un¬ completed engagement. The purpose of the present invention is to provide a latch mechanism which secures a complete latch engage¬ ment. Said purpose is achieved by means of a latch mechanism according to the present invention the characteristics of which appear from the accompanying claim 1. The invention will be described in more detail below by means of an illustrative embodiment reference being made to the accompanying drawings in which FIG. 1 shows, partly in sectional view, a roll-up mechanism for safety belts, FIG. 2 is a cross-sectional view of the roll-up mechanism with a latch mechanism according to the present invention in releasing position, and FIG. 3 is a corresponding cross-sectional view of the latch mechanism in latching position. OMPI Λ, WIPO In -FIG. 1 there is shown a roll-up mechanism 1 for safety belts. This mecha-nism comprises substantially a strap roller 2 to which one end of the strap 3 -of the safety belt is connected. The strap roller * is rotatably 5 mounted in two end pieces 4, 5 and is adapted to roll up and roll off, respect vely, the belt strap under the influence of a roll-up spring δ incorporated into one end piece 4. Incorporated into the other end piece 5 is a latch mechanism according to the invention, the • 10 construction of which will be ' seen from FIGS. 2 and 3. The latch mechanism comprises substantially an activat¬ ing means 7 and a latch mechanism 8 to be actuated by said activating means, v/hich is adapted to latch the strap roller against withdrawal of the belt strap under 15 specific conditions. The activating means according to the invention is an automatically operating mechanism .actuated by inertia forces, which will be described, in more detail below. The latch mechanism 8 comprises a latch 10 mounted for pivotal movemeπ-t in a joint 9, and 20 a ratchet 11 which is fragmentar ly indicated by dot and dash lines in FIG. 2. The ratchet 11 is circular and rotationally symmetric and has a plurality of latch teeth 12 distributed over the entire periphery. The latch is adapted to co-operate with the ratchet 11 so as to latch 25 the ratchet against rotation in one direction at unnormal speed changes of the vehicle, al ernatively to release the ratchet, the strap roller 2 as a consequence thereof being latched against rotation in one direction and being released, respectively. The latch mechanism 8 is 30 constructed such that the ratchet 12 shown is arranged to initiate a second mechanism, relieving the latch 10, which is adapted to take up stresses in the belt strap. Such, a mechanism can be arranged e.g. in such a way that it is initiated also by the acceleration forces in the 35 belt strap occurring at a rapid withdrawal of the belt OMH " strap by the arrangement of a latch plate 13 eccentrically suspended on a portion 15 of the shaft of the strap roller. The activating means 7 according to the invention thus is arranged to sense the speed change of the vehicle and to adjust the latch 10 from releasing position to latching position at unnormal changes. However, the construction of said means is known and the description thereof has been excluded for the sake of clar ty. The latch plate 13 forms an opening 14 through which said portion 15 of the roll-up shaft of the roll-up mechanism extends. This portion 15 of the roll-up shaft accordingly projects beyond one mounting position of the strap roller 2 in the end piece 5. The shaft portion 15 has two flat parallel edge surfaces 15, 17 which are each intended to co-operate wfth one 'straight edge portion 18, 19 of -.the opening 14 in the latch plate 13. These two edge portions 18, 19 include an acute angle. The opening 14 has two further opposite edge portions 20, 21 which in the embodiment shown are parallel with each other but of different lengths such that the opening has the shape of a trapezoid. The shaft portion 15 has two curved portions 22, 23 one of which is intended for co-operation with the edge portion 20 by rolling contact while the other portion is intended for co-operation with the edge portion 21 by sliding. Some small play is maintained in practice between the shaft portion and said edge portions 20, 21 such that there is obtained in practice contact with one of the curved portions of the shaft portion namely; the .. port on which for the ti e being is turned upwards. The latch plate 13 thus is pivotally mounted on the shaft portion 15 and is suspended therefrom by means of the opening 14 and is arranged to oscillate between two positions, one releasing position shown in FIG. 2 with the. edge portion 18 engaging, the edge surface 16 of the shaft portion, and a latching portion according to FIG. 3 with the edge portion 19 of the opening " engaging the edge surface 17 of the shaft portion. Moreover, the opening 14 is eccentrically located in the latch plate 13 in order that a major mass of the latch plate shall be located at one side of the opening, facing a portion of the latch plate which forms an engagement portion 24 with four latch teeth 25. These teeth, are adapted to engage, in the latch position of the mech¬ anism, stationary inwardly facing latch teeth 26 of a stationary latch ring 27 which is fixedly mounted to the end piece 5. The latch plate 13 is made of a relatively heavy material, e.g. metal with no tendency of deformation, by stamping from a sheet blank. The latch plate 13 is mounted by contact with a sheet metal end wall in the end piece 5, the latch ring 27 also being made of a metal material preferably by stamping from a sheet blank. A countersink is thus formed inwardly of the latch ring 27 in a substantially circular space 28 with flat bottom wherein the latch plate 13 is allowed to rotate together with the shaft portion 15 and to oscillate between releasing position and latching position. According to the invention, the latch plate 13 has a latch 29 pivotally connected therevnth, which is biased by means of a spring 30 such that the latch tends to take the releasing position according to FIG. 2. The spring 30 in the embodiment shown comprises a wire spring which is attached at one end thereof to a pin 31 on the shaft portion .15 and at the other end thereof at an angled portion 32 in a bore in the latch 29. The spring - is attached to the latch 29 spaced from the bearing pin 33 of the latch, said bearing pin projecting into a Λ m WO semi -ci r . cul ar opening 34 in the latch plate 13. The latch 29 can be made of a folded metal sheet which thus extends with two portions one on each side of the latch plate. The .ratchet 11 described above which co-operates with the latch 10 of the activating means 7, is made e.g of plastics as is the. atch 10, because these two elements as well as the latch 29 need not take up heavy loads occurring in the belt strap 3 at great speed changes of the vehicle. However, the ratchet 11 as well as the latch plate 13 also must- have some inertia and therefore the ratchet preferably is provi-ded with a weight-increasing metal plate or the like, not shown, which can be mounted to the ratchet. Furthermore, the ratchet 11 has a stud 35 which projects inwardly into the space 28 for the latch plate 13, said stud being shown in cros.s section taken such that the ratchet 11 is not shown in the views of FIGS. 2 and 3 ' ; for the ' sake of clarity the ratchet is indicated f agmentari ly only by dot and dash lines. The ratchet 11 can be rotatably mounted to the shaft pin 31 or on a pin projecting in the opposite direction from a wall of a cap on the end piece 5. The extension of the strap 3 is indicated in FIGS. 2 and 3 by a dot and dash line. The direction for withdrawal of the strap is indicated in FIG. 2 by an arrow 40. Accordingly, the withdrawal takes place against the bias of the roll-up spring which provides a rota¬ tional force in counter-clockwise direction on the shaft portion 15. The latch plate also forms a recess 36 with an abutment edge 37, the adjustment stud 35 being arranged to co-operate with said edge at rotation of the strap roller and thus of the latch plate 13 in a direction opposite to the arrow 38 according to FIG. 2, i.e. in the roll-up direction and also under ordinary driving OMPI conditions. Moreover, the latch 29 has a guide edge 39 which is angled and is adapted to co-operate with the adjustment stud 35 in order to adjust the latch to the latching position in a manner which will be described in more detail below. The latch mechanism also preferably includes a spring which acts on the latch plate 13 and is engaged e.g. between the ratchet 11 and the latch plate 13 in order to keep the latch plate in the releas¬ ing pos . ition of FIG. 2 when the strap roller is at rest or is moving slowly. When the vehicle is at rest in a normal position and when normal speed changes of the vehicle occur, the activating means 7 is in the position shown in FIG. 2, wherein the latch 10 is pivoted to a lower releasing position spaced from the latch teeth 12 of the ratchet 11. Then, said ratchet is allowed " to follow the rota¬ tion of the latch plate in a direction opposite to the arrow 38 by the engagement of the adjustment stud 35 with the abutment edge 37 of the latch plate. Moreover, ' the ratchet 11 will follow the rotational movements of the latch plate also in the direction of the arrow 38 at normal acceleration movements of the belt strap 3. This is achieved e.g. by the ratchet 11 and the latch plate 13 being interconnected by means of a spring as mentioned above. Thus, the belt strap 3 is allowed to be pulled out from the roll-up πechanism 1 and to be pulled in by being rolled up, respectively. At a relative movement of the ratchet 11 and thus the adjustment stud 35 on the one hand and the latch plate 13 on the other hand such that the latch plate 13 rotates in the direc¬ tion of the arrow 38 with a speed which is higher than the speed of the ratchet 11, the adjustment stud 37 will leave the position shown in FIG. 2 and will engage the guide edge 39 of the latch 29, said latch being displaced outwards against the bias of the spring 30 thereof to OMPI WIPO engage one of the latch teeth 26 of the latch ring 27. At the same time the latch p-late 13 oscillates from the releasing position shown in FIG. 2 to the latching posi¬ tion shown in FIG. 3 with the engagement pOrtion 24 thereof engaging the latch teeth 26 of the latch ring 27, the strap roller being prevented from rotation in the direction of the arrow 38 and the belt strap thus being prevented from withdrawal. The relative movements descri bed above according to the invention take - place due to two prerequisites, viz. that either the activating means 7 is being activated and thus the latch 10 is being brought to block the ratchet 11 against rotation in the direction of the arrow 38, o r that the belt strap 3 is being withdrawn with a strap acceleration exceeding a pre¬ determined value. T-he activating means 7 is activated at unnormal speed changes of the vehicle, the ratchet thus being stopped and the adjustment stud 35 being held stationary which provides said relative movement when the latch plate 13 rotates together with the shaft portion 15 in the direction of the arrow 38. When the acceleration of the strap 3 exceeds a predetermined value which most often occurs due to an unnormal speed change of the vehicle, said relative movement will be obtained by the mass inertia of the ratchet 11. the speed change of which does not follow the speed change of the shaft portion 15 and thus the rotational movement of the latch plate 13, which means that the adjustment stud displaces the latch 29 to the latching position. At unnormal strap acceleration the oscillation of the latch plate 13 will be brought about substantially by the mass inertia of the ratchet. Thus, in this case the latch 29 does not provide the adjustment operation proper but guarantees according to the invention, which is also the case at activation by means of the activating means 7, that the OMPI adjustment of the latch plate takes place in a proper manner such that the latch -teeth 25 of the engagement portion 24 penetrate completely into the spaces between the latch teeth 26 of the latch rtng 27 so that the latch teeth of the latch plate do not get caught on the crests of the latch teeth of the latch ring. This provides an uncompleted latch engagement and at heavy load the risk that the engagement is lost and that the belt strap is withdrawn further over a distance before a proper engagement is obtained. This is guaranteed by the fact that the other end of the latch 29 in the latching position is located in a position in relation to the latch teeth 25 of the engagement portion, which is chosen geometrically such that the latch plate is guided to the proper position. This proper positioning comprises a spacing along the periphery of the latch ring 27 between the tooth crests of the latch teeth 25 of the engagement portion- 24 and the outer end of the latch 29 which is a multiple of the spacing of the latch teeth. When the latch plate is adjusted to the latching position according to FIG. 3, there is thus obtained a pendelum movement in relation to the shaft portion 15, the latch 29 as will be seen from the figure, immediately after engagement with a latch tooth 26 being returned slightly to be somewhat spaced from the related latch tooth. As will be seen from the figures, the latch 29 has no fixed bearing. The bearing pin 33 thereof is allowed to be dis¬ placed in the semi-circular opening 34 providing some mobility of the latch and some yielding effect at the moment of engagement, which reduces the stresses in the elements involved. However, due to the bias of the spring 30 the bearing pin 33 tends to take a position in the outer corner of the opening 34. Thus, due to the fact that the latch plate 13 is stopped in definite positions with the latch teeth 25 of the engagement OMPI portion 24 in "phase" with the latch teeth 26 of the latch ring 27 a complete latch engagement is secured. Although according to the description above, the adjustment to latching position takes place at high strap acceleration as well as unnormal speed changes of the vehicle it is obvious that FIG. 3 is intended to show particularly the case wherein activation takes place due to unnormal speed changes of the vehicle, because the activating means 7 is activated and the latch 10 .of the activating means is adjusted to latching position in engagement with the ratchet 11. In practice, this occurs most often at the same occasion but with a time delay such that the activating means reacts first. When the tension load in the belt strap is relieved and the latch 10 of the activating means has been adjusted to the releasing position due to a reduced velocity change or a redu.ced strap acceleration, respecti ely, to a normal condition the adjustment stud ' 35 is allowed to be returned to the position shown in FIG. 2 e.g. under the bias of said spring enαaπed between the latch plate 13 and the ratchet. Then, the latch 29 will be changed over and the latch plate 13 will be allowed to return to the releasing position e.g. under the bias of said spring. The strap 3 thus can be freely withdrawn in the direction of the arrow 40. The invention is not limited to the illustrative embodiment described above and shown in the drawings but can be modified within the scope of the following claims. E.g. the change of movement of the ratchet 11 in relation to the latch plate 13 can be communicated in another way such that the latch 29 is activated. Moreover, the opening 14 and the shaft portion 15 can be formed in several different ways in order to allow said oscillating movement of the latch plate and simulta- neously initiate that the latch plate is carried on by the rotational movement of the strap roller. .OMPI

Claims: CLAIMS 1. A latch mechanism tor safety belts of the roller belt type, intended preferably for vehicles and comprising a strap (3) which can be withdrawn from a roll-up mechanism (1) against spring bias, including a belt roller (2) rotatable about a roll-up shaft, a latch mechanism (8) including a ratchet (11) and a ■ latch (10) which can be adjusted in dependence on un¬ normal speed changes between a position releasing the strap roller, and a latching position wherein the strap roller is latched against rotation in one direction, and an activating means (7) for adjusting the latch mechanism to the latching position when the vehicle is exposed to said unnormal speed changes, said latch mechanism also comprising a latch plate (13) provided with an engagement portion (24), which can be adjusted between a latching position in engagement with latch teeth (26) of a stationary latch ring (27) and a releasing position in dependence on said unnormal speed changes of the vehicle as well as unnormal acceleration in the withdrawal of the strap, said latch plate forming an opening (14) by means of which the latch plate is suspended on a portion (15) of the roll-up shaft and which has two engagement edges (18, 19) facing each other, flat edge surfaces (16, 17) of said shaft portion being arranged to engage the abutment edges in releasing position and latching position, respectively, c h a r a c t e r i z e d in that the mechanism comprises a second latch (29) which is pivotally mounted to the latch plate (13) and. is biased by a force tending to keep the latch in releasing position, and an adjust¬ ment element (35) arranged to adjust the latch of the latch plate from releasing position to latching position at a relative movement of the ratchet (11) and the latch plate (13), and that the latch of the latch plate is W arranged.. to guide, by the displacement thereof, the latch teeth (25) of the engagement- portion of the latch plate to complete engagement with the latch teeth of the latch ring. 2. latch mechanism as claimed in claim 1, c h a r a c t e r i z e d in that the ratchet (11) as well as the latch plate (13) has such a mass inertia that the ratchet at a normal acceleration in the with¬ drawal of the strap is imparted said movement in relation to the latch plate. 3. A latch mechanism as claimed in claim 1, c h a r a c t e r i z e d in that said adjustment element (35) comprises a stud located on the ratchet (11), which is directed towards the latch plate (13) and is arranged to engage, under normal driving con¬ ditions, an abutment edge (37) on the latch plate and to co-operate at said relative movement with a guide sur¬ face (39) on said second, latch (29) so as to adjust this latch to the latching position. 4. A latch mechanism as claimed in any of the preceding claims, c h a r a c t e r z e d in that said second latch (29) in the latching position has the catching portion thereof spaced from the tooth crests of the latch teeth (25) of the engagement portion (24), said spacing along the periphery of the latch ring (27) forms a multiple of the spacing of the latch. teeth (26) of the latch ring.

Inventors: LINDBLAD STIG KARL GUNNAR
Applicants: LINDBLAD STIG KARL GUNNAR, SAFETY TRANSPORT INT DEV, SAFETY TRANSPORT INTER DEV AB
Application year: 1982
Main classification: A62B35
IPC codes: B60R22