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Patent Searching and Data


Title:
BLOCKS FOR WHEEL BRAKES
Document Type and Number:
WIPO Patent Application WO/2021/100011
Kind Code:
A1
Abstract:
A block (1; 11) for wheel brakes comprising a matrix (2; 12) made of a first sintered material and one or more inserts (3; 13) included inside the matrix and made of a second material having a hardness which is greater than the one of the first material. The inserts (3; 13) are arranged in a symmetrical manner relative to a transverse middle plane (X). The second material has a thermal diffusivity which is smaller by at least 1*10-6 m2/s than the one of the first material. The block has a friction surface (4; 14) made of said first material for 95 to 60% and of said second material for 5 to 40%.

Inventors:
DE SOCCIO VITTORIO (IT)
RICCI ANTONIO (IT)
Application Number:
PCT/IB2020/060971
Publication Date:
May 27, 2021
Filing Date:
November 20, 2020
Export Citation:
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Assignee:
COFREN SRL (IT)
International Classes:
F16D69/02
Foreign References:
US20160047016A12016-02-18
GB2219365A1989-12-06
Other References:
DATABASE WPI Week 201564, Derwent World Patents Index; AN 2015-548840, XP002799775
Attorney, Agent or Firm:
BOSMAN, Cesare et al. (IT)
Download PDF:
Claims:
C LA IM S

1. A block (1; 11) for wheel brakes comprising a matrix (2; 12) made of a first material and one or more inserts (3; 13) included inside said matrix and made of a second material having a hardness which is greater than that of said first material; said one or more inserts (3; 13) being arranged in a symmetrical manner relative to a transverse middle plane (X); said block being characterized in that said second material has a thermal diffusivity which is lower than that of said first material by at least a value equal to 1*10-6 m2/s than that of said first material; said block having a friction surface (4; 14) made of said first material for 95 to 60% and of said second material for 5 to 40%; said first material being a sintered material.

2. A block according to claim 1, characterized in that said second material has a hardness which is greater by at least 20 HRV than the one of said first material.

3. A block according to claim 2, characterized in that said first material has a hardness ranging from 40 to 130 HRV and said second material has a hardness ranging from 80 to 150 HRV.

4. A block according to one of the preceding claims, characterized in that said first material has a thermal diffusivity ranging from 2.0*10-6 m2/s to 4.0*10-6 m2/s and said second material has a thermal diffusivity ranging from

0.5*10-6 m2/s to 3.0*10-6 m2/s.

5. A block according to one of the preceding claims, characterized in that said second material is a sintered material.

Description:
"BLOCKS FOR WHEEL BRAKES" CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no. 102019000021795 filed on 21/11/2019, the entire disclosure of which is incorporated herein by reference. TECHNICAL FIELD

The invention relates to blocks for wheel brakes featuring better performances under ice or wet conditions.

BACKGROUND ART

In the railway industry, the aforesaid blocks for wheel brakes are usually used in trains with a medium/low speed (a maximum speed of 160 Km/h), with large masses and subjected to frequent braking, such as city trains.

As people skilled in the art know, extremely wet and, especially, extremely cold environments can create conditions that can cause the brake to lose efficiency due to the presence of water or ice between the wheel and the blocks. Indeed, the presence of water and, especially, of ice between the surface of the wheel and the friction surface of the block significantly decreases the friction between the block and the wheel and, hence, the effectiveness of the braking action of the block.

Obviously, this problem is particularly serious in Northern countries, where studies are being carried out in order to obtain an effective solution. The need was therefore felt to have a brake block for wheels whose technical characteristics were such as to guarantee the effectiveness of braking even in conditions of presence of water or ice.

The inventors of this invention unexpectedly found out that, if the block comprises inserts made of a material having a heat conductivity which is smaller than that of the material making up the remaining part of the block, the need discussed above can be fulfilled.

DISCLOSURE OF INVENTION The subject-matter of the invention is a block for wheel brakes comprising a matrix made of a first material and one or more inserts included inside said matrix and made of a second material having a hardness which is greater than the one of said first material; said one or more inserts being arranged in a symmetrical manner relative to a transverse middle plane; said block being characterized in that said second material has a thermal diffusivity which is lower than that of said first material by at least a value equal to 1*10 -6 m 2 /s than that of said first material; said block having a friction surface made of said first material for 95 to 60% and of said second material for 5 to 40%; said first material being a sintered material.

Experiments have shown that, if the friction surface consists of the first sintered material in a quantity smaller than 60%, the effectiveness of the braking does not meet the requirements set by specifications in case of extreme climate conditions .

Hereinafter by "friction surface" of the block we mean the surface of the block in contact with the wheel when the braking action is exerted.

Said second material preferably has a hardness which is greater by at least 20 HRV than that of said first material.

The first material preferably has a hardness ranging from 40 to 130 HRV and the second material has a hardness ranging from 80 to 150 HRV.

Said first sintered material preferably has a thermal diffusivity ranging from 2.0 to 4.0*10 -6 m 2 /s.

Said second material preferably has a thermal diffusivity ranging from 0.5 to 3.0*10 -6 m 2 /s. Said second material preferably is a sintered material.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter there is a description of embodiments of the invention, by mere way of explanatory and non-limiting example, with reference to the accompanying drawings, wherein: - figures 1 and 2 are a side view and a bottom view, respectively, of a first embodiment of a block for wheel brakes according to the invention;

- figures 3 and 4 are a side view and a bottom view, respectively, of a second embodiment of a block for wheel brakes according to the invention; figure 5 is a diagram showing the friction coefficients and the temperature changes of the friction surface detected for the block of figure 1 subjected to a plurality of braking operations; and figure 6 is a diagram showing the friction coefficients and the temperature changes of the friction surface detected for a comparison block subjected to the same plurality of braking operations as in figure 3.

BEST MODE FOR CARRYING OUT THE INVENTION In figures 1 and 2, number 1 generically indicates, as a whole, a block for wheel brakes according to the invention.

The block 1 comprises two side portions 2 made of a sintered material used in the prior art to manufacture the entire block. The block 1 further comprises a central insert 3 made of a material having a hardness, a heat conductivity and a heat capacity which are greater than the ones of the first material making up the side portions 2.

Table I shows the physical features of the first material and of the second material. Table

The block 1 comprises a friction surface 4, which is occupied by said first material for 90% and by said second material for 10%. The materials with a different thermal diffusivity and with a different hardness can also be obtained, besides from materials with a different chemical nature, by means of a different process of preparation of a same chemical type of material. For example, thermal diffusivity can be changed by acting upon the porosity of the resulting material.

The block 1 described above was subjected to a plurality of braking actions both under dry conditions and under wet conditions. For each one of said braking actions, the temperature change of the friction surface of the block and the block/wheel friction coefficient were measured. The results are shown in the diagram of figure 5.

In particular, in the diagram of figure 5, for each one of the braking actions, there are indicated the speed at which the braking was operated, the temperature change on the friction surface and the block/wheel friction coefficient .

A block entirely made of the sole first sintered material was manufactured as a comparison. The comparison block was subjected to the same braking action to which the block 1 was subjected and, for each one of the braking actions, the temperature of the friction surface and the block/wheel friction coefficient were measured. The results are shown in the diagram of figure 6.

A comparison of the two diagrams clearly shows how the temperature changes measured on the friction surface of the block 1 are, on average, 10% greater than the ones measured on the friction surface of the comparison block.

This temperature increase translates into a significant friction coefficient increase and, as a consequence, into a more effective braking action.

In particular, the effect described above is extremely important in the presence of water or ice between the friction surface and the wheel. Indeed, as one can clearly assume, the higher the temperature of the friction surface, the quicker water or ice is removed through evaporation, thus restoring the correct friction between the wheel and the friction surface of the block and, hence, the correct effectiveness of the braking.

To sum up, the inventors of the invention surprisingly found out that the presence, in the block, of inserts made of a material with a greater heat conductivity and capacity ensures a correct efficiency of the braking even in the presence of water or ice. This phenomenon is the result of the significant increase in the temperature of the friction surface, which is caused by the presence of the inserts during the braking phase.

This temperature increase can be explained by the ability of the inserts to spread heat to the rest of the friction surface, thanks to the heat conductivity and capacity properties thereof.

In figures 3 and 4, number 11 indicates, as a whole, a second embodiment of a block according to the invention.

The block 11 comprises four portions 12 made of a sintered material used in the prior art to manufacture the entire block and three inserts 13 arranged between the portions 12 and made of a material having a hardness, a heat conductivity and a heat capacity which are greater than the ones of the first material making up the portions 12. The features of the materials making up the portions 12 and the inserts 13 are the same as the ones discussed above for the portions 2 and the inserts 3 of the block 1.

The block 11 comprises a friction surface 4, which is occupied by said first material for 90% and by said second material for 10%.

The block 11 complies both with the feature concerning the portion of friction surface occupied by said first material and with the symmetry feature, according to which the portions 12 and the inserts 13 have to be arranged in a symmetric position relative to a transverse middle symmetry plane X.

Besides the embodiments shown in figures 1, 2 and 3, 4, the block according to the invention can also assume other configurations, provided that the requirement according to which the relative friction surface consists, for 95 to 60%, of the first material is fulfilled.

Finally, the solution according to the invention ensures, in general, a block for wheel brakes with a greater friction coefficient and, in particular, offers the great advantage of ensuring the effectiveness of the braking even in the presence of water or ice between the friction surface of the block and the wheel.