Anti-skid device for motor vehicles

In an anti-skid device for motor vehicles with a plurality of resilient spreading arms (5) distributed over the circumference of a support (1) which can be set into a revolving motion for chain strands (3) forming anti-skid means, the spreading arms (5) are formed by compression springs (8) which are precompressed by connecting elements (13) which connect the chain strands (3) to the support (1).

BACKGROUND OF THE INVENTION 
The invention relates to an anti-skid device for motor vehicles with a 
plurality of resilient spreading arms distributed over the circumference 
of a support which can be pressed against the tire of a vehicle and can be 
set into a revolving motion, to which chain strands forming the anti-skid 
means are attached, of which the ends remote from the spreading arms are 
thrown away from the support by the effect of centrifugal force when the 
support revolves in the service position, and of which at least parts pass 
through the region of the ground contact surface of the tire when the 
vehicle tire rotates. 
An anti-skid device of the above-mentioned type is known from German 
Offenlegungsschrift No. 2,914,366, in which the spreading arms are 
constructed as cable sections or chain strand sections firmly enclosed by 
rubber envelopes. The rubber envelopes in this case exhibit at one end a 
head provided with an annular groove, which serves conjointly with a 
closing ring to anchor the spreading arms to the support, and the 
resilient properties of which should permit an easy exchange of the 
spreading arms and of the chain strand retained by them. The known 
solution cannot be satisfactory, if only because here the strength of the 
anchorage of the spreading arm and of the chain strand connected to them 
on the support is inadequate. Apart from this fact, the vulcanization 
process which is unavoidable in the case of the known construction 
represents an unfavorable burden on the production costs of the spreading 
arms. 
The object of the spreading arms is to transfer the chain strands, which 
form the anti-skid means, into a favorable position relative to the tire 
rolling surface and/or to the wedge gap between vehicle tires and road. 
Any entangling of the chain strands should also be counter-acted. The same 
purpose is served in an anti-skid device known from U.S. Pat. No. 
3,068,949 by traction springs interposed between the anti-skid elements 
and the support, one end of each of which exhibits an eye for a screwbolt 
serving for fastening the springs to the support. In the case of this 
second known device the traction springs, due to the fact that they have 
to transmit powerful centrifugal forces, must exhibit substantial torsion 
cross-sections, which impose narrow limits to their flexibility. 
Furthermore, substantial cyclic forces occur in the transition region 
between the fastening eye and the main part of the spring; these involve 
the danger of premature fatigue fractures. 
Lastly, French Pat. No. 409,260 discloses an anti-skid device in which 
chain strands forming anti-skid means are connected by springs to a 
support. However, in this device the support is not adapted to be pressed 
against the vehicle tire, and the springs serving to drive it are likewise 
exposed to not inconsiderable traction forces. 
SUMMARY OF THE INVENTION 
The underlying aim of the invention is to produce an anti-skid device of 
the type discussed, which can be produced at favorable cost, ensures 
reliable mounting of the chain strands forming the anti-skid means on the 
support, and in which the spreading arms move back into their initial 
position rapidly and without major vibratory movements. This aim is 
achieved according to the invention in that the spreading arms are formed 
by compression springs which are pre-tensioned by connecting elements 
which connect the chain strands to the support. 
The anti-skid device according to the invention presents the advantage 
that, due to the use of pre-tensioned compression springs as spreading 
arms, the entry and exit of the anti-skid means into and out of the region 
of the ground rolling surface of the tire is definitely improved, whilst a 
whiplash effect of the spreading arms which occurs in the case of the 
known constructions is avoided. Due to the facts that the chain strands 
forming the anti-skid means are connected to the support by connecting 
elements, and not by the spreading arms, their correct and secure 
anchorage to the support is ensured. It is furthermore possible, contrary 
to the case of constructions of the type first described, to combine one 
and the same connecting element with compression springs of different 
rigidity, so as to achieve an adaptation of the service behavior of the 
device to different conditions. 
In the anti-skid device according to the invention the compression springs 
are deformed maximally in the region of their ends near the support during 
service. Particularly if the connecting elements are formed by chain 
strand sections, it is then possible for contacts to occur between the 
connecting elements and the compression springs, which promote wear 
phenomena on the compression springs. In order to protect the compression 
springs in proximity of their ends near the support from a direct contact 
with parts of the connecting elements, particularly with members of chain 
links, as a further development of the invention sleeves are arranged 
between the connecting elements and the compression springs in the region 
of the ends of the compression springs facing the support. In this manner 
the service life of the compression springs and therefore of the anti-skid 
device generally can be prolonged.

BEST MODE FOR CARRYING OUT THE INVENTION 
In FIG. 1, 1 designates the support, constructed as a friction wheel, of an 
anti-skid device which is attached to a jib arm 2. The support 1 is 
equipped with six chain strand groups 4 distributed uniformly on its 
circumference and each consisting of four chain strands 3, only two of 
which have been illustrated in order to improve the clarity. The 
individual chain strand groups 4 are connected to the support 1 by 
resilient spreading arms 5. 
As FIG. 2 shows clearly, the axis of rotation 6 of the support 1 is placed 
obliquely to the road, and the spreading arms 5, to each of which only one 
chain strand is connected in the case of FIG. 2, are themselves placed 
obliquely to the axis of rotation 6, so that they are oriented obliquely 
to the rolling surface of the tire 7. 
Particulars of the construction of the spreading arms 5 are clear from 
FIGS. 3 and 4. 
In FIG. 3 the spreading arm 5 is formed by a cylindrical compression spring 
8, which is arranged between two abutments 9 and 10. The abutment 9 is 
connected firmly to the support and forms a bracing surface 11 oriented 
obliquely to the underside of the support for the one end of the 
compression spring 8. The end link of a chain strand section 13, which 
forms a connecting element, which connects the chain strands 3, which are 
combined by a ring 14 to form a chain strand group 4, to the support 1, 
projects through a recess 12 of the abutment. The end link is then secured 
to the support 1 by a locking member 15. 
The ring 14 forms a stop for the abutment 10. The interval between the 
abutments 9 and 10 is chosen so that the compression spring 8 is subjected 
to an adequate pre-tension, at the same time however it must be ensured 
that the turns of the spring 8 do not touch mutually. In the manner 
described, it is achieved that the spreading arm is adequately flexible on 
the one hand, but on the other hand does not tend to undesirably intense 
vibrating movements. It is found advantageous that the compression spring 
8 can be utilized simultaneously for the anchorage of the locking member 
15. 
The spreading arm according to FIG. 4 corresponds largely to the spreading 
arm according to FIG. 3. The same reference numerals have therefore been 
used for mutually corresponding parts, so that is is only necessary here 
to point out the differences between the two constructions. 
Whereas a cylindrical compression spring is used in the exemplary 
embodiment according to FIG. 3, the compression spring 16 forming the 
spreading arm 5 according to FIG. 4 is of conical construction. In 
addition, the abutment 17 remote from the support 1 has the form of a cap 
which guides the free spring end. 
In FIG. 5, 1 designates a support, to the underside of which a disc-shaped 
stamping 18 is screwed, and which serves for the mounting again of chain 
strands 3 combined into groups or bunches 4. In practice, six chain strand 
bunches are distributed uniformly over the circumference of the support. 
Spreading arms 5 are anchored to the support, each by an obliquely angled 
chain link 19. Sleeves 20, the external edge 21 of which is rounded or 
exhibits a chamfer, are present on the support ends of the spreading arms 
5. The sleeves 20 form centering means for compression springs 16 which 
are arranged between two abutments 9 and 17, of which abutments 9 are 
formed by bent tongues of the stamping 18. The chain link 22, which is 
guided in a recess 12 of the abutment 9, is used to fix the position of 
the sleeve 20 relative to the abutment 9. 13 designates a protecting 
element constructed as a chain strand section, which connects the chain 
strands 3 to the support. A ring 14, which combines the chain strands 3 to 
form a chain strand group, is arranged at the end of the connecting 
element 13. 
As indicated in FIG. 4, the compression spring 16 is of conical 
construction at least along part of its length. Its free end may however 
also be cylindrical. The spreading arms 5 become deformed during the 
service of the anti-skid device. The greatest deformation then occurs in 
the region of the link 23 of the chain strand section forming the 
connecting element 13. The sleeve 20 prevents frictional contacts, which 
promote wear, occurring between the link 23 and the turns of the 
compression spring 16 located in its proximity. For this purpose the 
sleeves 20 project into the compression springs 16 for a distance which 
corresponds to the height of 2 to 3 spring turns. 
In the exemplary embodiment according to FIG. 5 the sleeve 20 is of 
cylindrical construction. By contrast, a sleeve 24 with a conical external 
wall is illustrated in FIG. 6. An anti-wear ring 25, which is arranged on 
the end of the sleeve facing the chain strands 3, consists of a suitable 
material, particularly a plastic such as nylon or teflon. In both the 
cases illustrated, the sleeves 20 and 24 are retained in their desired 
position due to the conicity of the compression springs 16.