THERMALLY INSULATED PISTON ASSEMBLY FEATURING A SPACER FORMING A THERMAL BARRIER

Abstract

The invention relates to a brake caliper (2) for a disc brake device (4), comprising a brake control chamber (21) adapted to be open towards the brake disc (4), in which a piston (5) is slidably mounted, said piston (5) comprising an internal chamber (51) adapted to be open towards the brake disc (4), said internal chamber (51) comprising a spacer (6) made of a thermally insulating material, said spacer (6) comprising a portion extending projecting from the internal chamber (51) of the piston (5), towards the brake disc (4), over a length (Ld) of between 1 and 3 mm. Figure for the abstract: Fig. 2

Description

Title of the invention: THERMALLY INSULATED PISTON ASSEMBLY COMPRISING A SPACER FORMING A THERMAL BARRIER

[0001] The present invention relates to an improved cooling braking device.

[0002] The present invention relates to a thermally insulated piston assembly for a brake caliper of a brake disc braking device, comprising a piston which has an internal chamber adapted to be open towards the brake disc when said piston is positioned in the brake caliper, said internal chamber comprising a spacer which is made of a thermally insulating material, said spacer comprising a portion which projects from the internal chamber of the piston, towards the brake disc.

[0003] The aerodynamics of a vehicle are strongly impacted by the openings which are formed in the wheel web to cool the braking device, the fact of closing the wheel web further increases the temperature of the braking device in the event of high stresses and in particular the temperature of the hydraulic fluid.

[0004] Thus, during steep descents of mountain passes, the brakes are under heavy stress, the discs and the hydraulic braking fluid can reach very high temperatures which can cause the braking device to malfunction and in particular cause air bubbles to appear in the hydraulic fluid if it exceeds the maximum operating temperature, causing it to boil.

[0005] The main problem which risks boiling the hydraulic braking fluid comes from the temperature of the brake disc which is undersupplied with fresh air due to a wheel veil promoting aerodynamics, causing the disc to risk rising to a temperature of 700°C, transmitting part of this heat to the brake pads which will raise the temperature of the brake caliper and the hydraulic fluid contained in the caliper.

[0006] Document FR3114134 discloses a brake caliper which comprises a spacer which is made of a thermally insulating material and which is positioned between the piston of the brake caliper and the first of the two brake pads.

[0007] However, in this document, different embodiments are disclosed which are difficult to implement and which present safety problems in the event of breakage of the spacer during operation of the braking device.

[0008] The device according to the invention makes it possible to overcome these drawbacks.

[0009] It in fact comprises a thermally insulated piston assembly for a brake caliper of a brake disc braking device, comprising a piston which comprises an internal chamber adapted to be open towards the brake disc when said piston is positioned in the brake caliper, said internal chamber comprising a spacer which is made of a thermally insulating material, said spacer comprising a part which extends in projection from the internal chamber of the piston, towards the brake disc, over a length which is between 1 and 3 mm, the part of the spacer projecting from the internal chamber of the piston preferably extending over a length of 2 mm.

[0010] According to a first characteristic of the invention, the spacer extends to the bottom of the internal chamber of the piston.

[0011] According to a second characteristic of the invention, the spacer comprises, along the external wall of its bottom, a cavity bordered by a peripheral part of the external wall of the bottom of the spacer which bears against the bottom of the internal chamber of the piston.

[0012] According to a third characteristic of the invention, the spacer comprises along its external lateral wall a circular cavity delimiting two parts of the spacer which bear against the internal lateral wall of the piston.

[0013] According to a fourth characteristic of the invention, the piston (5) is made of steel, the spacer being made of bakelite.

[0014] The present invention also relates to a brake caliper for a brake disc braking device, which comprises a brake control chamber adapted to be open towards the brake disc, in which is slidably mounted a thermally insulated piston assembly which comprises at least one of the preceding characteristics.

[0015] Such a brake caliper comprises a friction pad positioned between the free end of the spacer and the brake disc, the friction pad comprising a rivet head projecting from the bearing surface of the spacer against said friction pad, the free end of the spacer comprising a cavity in which said rivet head is positioned.

[0016] The present invention finally relates to a vehicle comprising such a brake caliper.

[0017] The attached drawings illustrate the invention:

[0018] [Fig-1] represents a perspective view of a braking device which comprises a thermally insulated piston according to the invention.

[0019] [Fig.2] represents a partial sectional view, along a vertical sectional axis, of the braking device comprising the thermally insulated piston according to the invention.

[0020] With reference to Figures 1 and 2, the braking device 1 comprises a brake caliper 2 equipped with two friction pads 3 and a brake disc 4.

[0021] The brake caliper 2 comprises clamping means adapted to, during a braking command, move a first friction pad 31 against a first friction track 41 of a first face of the brake disc 4, this first friction causing the brake caliper 2 to move in the opposite direction and consequently, moving it by a second friction pad 32 against a second friction track 42 of a second face of the brake disc 4 and this as known from the state of the art for a so-called floating brake caliper 2.

[0022] The clamping means comprise a piston 5 slidably mounted in a braking control chamber 21 formed in the caliper 2.

[0023] The caliper 2 comprises conduits which make it possible to supply the braking control chamber 21 with hydraulic fluid to actuate the movement of the friction pads 3 against the friction tracks of the brake disc 4 during said braking control.

[0024] The piston 5 comprises an internal chamber 51 adapted to be open in the direction of the friction pads 3 and which is adapted to contain a spacer 6 made of a thermal insulating material.

[0025] The spacer 6 projects from the internal chamber 51 of the piston 5 by a length Ld of 2 mm, so as to exert pressure on the first friction pad 31 when braking is controlled, without the piston 5 being too close to the first friction pad 31 to limit the thermal transfer of the temperature of the friction pads 31 to the piston 5.

[0026] The spacer 6 is present to thermally insulate the first friction pad 31 from the piston 5 and consequently limit thermal heating of the hydraulic fluid.

[0027] The slight protrusion of a length Ld of 2 mm projecting from the internal chamber 51 of the piston 5 of the spacer 6 makes it possible to secure the operation of the braking device, because in the event of breakage or any other damage to the spacer 6, the piston 5 is able to resume its function of pressing against the first friction pad 31 when braking is commanded without the driver finding himself at the end of the depression of the brake pedal, requiring him to release and then re-depress the brake pedal so that the piston 5 cannot again exert pressure against the first friction pad 31.

[0028] The length Ld projecting from the internal chamber 51 of the piston 5 of the spacer 6 can vary between 1 mm and 3 mm while allowing both good insulation of the piston 5 and safe operation of the braking device in the event of breakage of the spacer 6.

[0029] Of course, with a length Ld of 1 mm, the thermal insulation of the piston is less effective, but remains acceptable and the operational safety in the event of breakage of spacer 6 is maximum, the driver will only slightly feel the change in the brake pedal travel.

[0030] With a length Ld of 3 mm, the thermal insulation of the piston is more effective, but the operational safety in the event of breakage of the spacer 6 is at least acceptable, the driver will strongly feel the modification of the travel of the brake pedal which still remains operational.

[0031] For a length Ld of 4 mm and more, the thermal insulation of the piston is increasingly effective, but the operational safety in the event of breakage of the spacer 6 is unacceptable, the driver, even when fully depressing the brake pedal, no longer has the piston 5 which will push against the first friction pad 31, to regain braking, he must completely release the brake pedal and brake again.

[0032] The spacer 6, in addition to having thermal insulation qualities, with a very low conductivity coefficient, must also play a role as a vibration insulator so as not to amplify braking noises.

[0033] Different materials can be considered such as a titanium alloy, stainless steel, bakelite.

[0034] The term bakelite designates a material formulated by a laminate consisting of layers of high-strength cotton fabric, impregnated with phenolic resin, hot-bonded under high pressure, offering both low thermal conduction and high heat resistance.

[0035] Bakelite is well suited for such use, but has a fragility which makes it important to have a length Ld which is between 1 and 3 mm.

[0036] The first friction plate 31 comprises a rivet 7 which serves to hold braking anti-noise means (not shown in these figures) and the spacer 6 comprises a first cavity 64 opposite this rivet 7 so as not to be in abutment against the rivet 7 during braking; the bakelite of the spacer 6 in abutment against the rivet 7 would have a stress point which could create a crack in the spacer 6 which could propagate throughout the spacer 6, increasing the risk of breakage of the spacer 6.

[0037] On the periphery of the external lateral wall of the spacer 6 is formed a second circular cavity 65 which, by limiting the contact zone between the spacer 6 and the internal lateral wall of the internal chamber 51 of the piston 5, reduces the heat transfer between the spacer 6 and the piston 5.

[0038] The second cavity 65 also facilitates the adjustment of the spacer 6 in the internal chamber of the piston 5 by limiting the contact area only to the upper and lower parts of the spacer 6.

[0039] The spacer 6 also comprises a third cavity 66 at the bottom of the internal chamber of the piston 5 to also reduce the heat transfer between the spacer 6 and the piston 5 without weakening the spacer 6, to reduce the weight of the spacer 6 and to reduce the manufacturing cost by reducing the quantity of material necessary for the manufacture of the spacer 6.

[0040] The spacer 6 must maintain around the first cavity 64 a sufficient contact surface so as not to create excessive stresses in the bakelite which could also create cracks which could propagate throughout the spacer 6 and end up breaking it; to do this, a circular strip is maintained at the periphery of the bearing surface of the spacer 6 against the friction plate 31 of at least 5 mm in width.

[0041] A piston 5 is always present which receives only small adjustments which makes the installation of such a spacer 6 very simple, without modifying the overall design of the caliper 2.

[0042] The dimensioning and geometry of the spacer 6 forms a good thermal insulator for the hydraulic fluid, making it possible without too much difficulty to achieve the objective of maintaining the fluid below 150°C, while ensuring safe operation of the braking device in the event of breakage of the spacer during a braking phase.

Claims

Claims

1. Thermally insulated piston assembly for a brake caliper (2) of a braking device (1) with a brake disc (4), comprising a piston (5) which has an internal chamber (51) adapted to be open towards the brake disc (4) when said piston (2) is positioned in the brake caliper (2), said internal chamber (51) comprising a spacer (6) which is made of a thermally insulating material, said spacer (6) comprising a portion which projects from the internal chamber (51) of the piston (5), towards the brake disc (4), the portion of the spacer (6) projecting from the internal chamber (51) of the piston (5) extending over a length (Ld) which is between 1 and 3 mm, characterized in that the spacer (6) comprises along its external side wall a circular cavity (65) delimiting two parts of the spacer (6) which are resting against the internal side wall of the piston (5).

2. Thermally insulated piston assembly according to claim 1, characterized in that the part of the spacer (6) projecting from the internal chamber of the piston (5) extends over a length (Ld) of 2 mm.

3. Thermally insulated piston assembly according to claim 1 or 2, characterized in that the spacer (6) extends to the bottom of the internal chamber (51) of the piston (5).

4. Thermally insulated piston assembly according to the preceding claim, characterized in that the spacer (6) comprises, along the external wall of its bottom, a cavity (66) bordered by a peripheral part of the external wall of the bottom of the spacer (6) which bears against the bottom of the internal chamber (51) of the piston (5).

5. Thermally insulated piston assembly according to any one of the preceding claims, characterized in that the piston (5) is made of steel.

6. Thermally insulated piston assembly according to any one of the preceding claims, characterized in that the spacer (6) is made of bakelite.

7. Brake caliper (2) for a braking device (1) with a brake disc (4), comprising a brake control chamber (21) adapted to be open towards the brake disc (4), in which is slidably mounted a thermally insulated piston assembly according to any one of the preceding claims.

8. Brake caliper (2) according to the preceding claim, characterized in that it comprises a friction pad (31) positioned between the free end of the spacer (6) and the brake disc (4), the friction pad (31) comprising a rivet head (7) projecting from the bearing surface of the spacer (6) against said friction pad (31), the free end of the spacer (6) comprises a cavity (64) in which said rivet head (7) is positioned.

9. Vehicle comprising a brake caliper (1) according to claim 7 or 8.

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