Patent Application
20230243393
This application is based on and claims priority under 35 U.S.C. § 119 to German Patent Application No. 102022200960.6, filed on Jan. 28, 2022 in the German Patent and Trade Mark Office, the disclosures of which are incorporated herein by reference.
The present application is in the field of mechanical engineering, in particular vehicle technology. The application relates to a piston for a brake system. It also discloses a brake system comprising such a piston as well as a method for manufacturing the piston.
According to the state of the art, disk brake systems typically comprise a housing holding a piston. The piston is pressed against a brake pad for braking. To this end, hydraulic pressure is exerted onto one side of the piston by way of a brake fluid present in a cavity of the housing.
The fluid volume of the brake fluid within this cavity and, in particular, the increase of fluid volume during braking, influence the pedal travel and pedal feel.
Moreover, as the piston engages with the brake pad, vibrations and noise can be transmitted to or generated within the piston.
It is thus an object of the present invention to improve pedal feel and/or to avoid noise and vibrations.
This is achieved by a piston according to claim 1. It is also achieved by a method for making a piston, or a brake system, as recited in claims 17 and 18. Advantageous embodiments can be found in the dependent claims and in the following description and the figures.
According to the invention, a piston for a brake system has a first end configured to engage with a brake fluid and a second end configured to engage with a brake pad, and a piston wall surrounding a cavity of the piston between the first end and the second end. The piston wall comprises a plastic portion. A piston base is provided at the first end of the piston, which piston base closes the piston at the first end, the piston base comprising a metallic portion which is configured to contact the brake fluid.
The metallic portion of the piston base plate may thus form an outer surface of the piston base, which constitutes a main pressing surface for the brake fluid.
A hydraulic brake system for a vehicle may comprise a housing, a brake pad and the piston according to any of the variants shown or described herein. The piston is movable along a longitudinal axis by hydraulic pressure acting on the piston base, for pressing the second end of the piston against the brake pad. To exert hydraulic pressure on the piston, brake fluid contained in a cavity of the housing may be pressurized.
During braking, as the brake system and in particular the piston heats up, the metallic portion of the piston base is subject to thermal expansion. As the metallic portion of the piston base expands, it reduces the volume available for the brake fluid in the cavity of the housing. In other words, expansion of the piston base may add to the pressure effected by the brake fluid. As a consequence, the amount of brake fluid that has to be displaced is reduced, which may inter alia result in improved pedal travel and pedal feel. The sizes and design features can advantageously be selected so that the expansion of the piston in axial direction is prioritized. This may in particular be achieved by the various embodiments shown herein.
In an embodiment, a thickness of the metallic portion of the piston base at room temperature may be at least 3 mm and/or at most 5 mm or at most 8 mm. In particular the thickness may be approximately 4 mm. The thickness is measured in the longitudinal direction in which the piston is configured to move. An increase in thickness Δx due to thermal expansion during braking may then be between 0.02 mm and 0.1 mm. Correspondingly, if a surface area of the metallic portion of the piston base, normal to the longitudinal direction, is denominated by A, an increase in volume is given by ΔV=Δx·A. Given typical piston dimensions, ΔV may for instance be between 0.1 and 0.3 cubic centimeters. The inventor has realized that the volume increase and increase in thickness associated with thermal expansion can thus be in the same order of magnitude as the brake fluid absorption and piston travel, respectively. Namely, in an example, approximately 0.7 to 1.2 cubic centimeters of brake fluid absorption within the cavity of the housing are envisioned during braking. For instance, this may lead to a displacement of the piston by as little as 0.01 to 0.03 mm, whereas the housing may be displaced by between 0.35 and 0.5 mm, or by between 0.38 and 0.4 mm. A sum of these two movements typically does not exceed 0.5 mm. The piston described herein is thus capable of impacting brake fluid absorption and pedal feel, based on thermal expansion of the metallic portion of the piston base.
Moreover, the metal portion of the piston base advantageously resists deformation by the brake fluid. I.e., inserting the metal portion facing the brake fluid pressure may improve the strength of the piston and reduce the axial deflection of the piston base.
The piston comprises the metal portion of the piston base, on the one hand, and the plastic portion of the piston wall, on the other hand, and thus it comprises at least two portions made of different materials. This may advantageously dampen vibrations or noise, for instance due to a joint damping effect.
The hybrid setup, wherein the piston comprises at least the two above-mentioned portions of different materials also helps to achieve a target mass for the piston, or even decrease the mass of the piston compared to known pistons.
In particular, the piston may be a piston for a front axle of a vehicle, such as a car or a truck. Therein, the piston may be open at the second end, while it is closed at the first end as described above.
The metallic portion of the piston base may for instance be disk-shaped.
The piston base may comprise a plastic portion which is arranged at an inner side of the metallic portion of the base plate, facing the cavity.
For example, a total thickness of the piston base, in particular including the metallic portion of the piston base and the plastic portion of the piston base, may be at least 4 mm and/or at most 8 mm.
In possible embodiments of the piston, the piston wall may comprise a metallic portion. This metallic portion of the piston wall may advantageously reduce compressibility of the piston in the axial direction. It may also enable heat transfer to the metallic portion of the piston base.
In either case, with or without the metallic portion, the piston wall may comprise a bent portion at the second end, for increasing a contact area with the brake pad.
The plastic portion of the piston wall may extend to the second end of the piston and may be configured to engage with the brake pad, in particular with a back plate of the brake pad. It may be envisioned that the metallic portion of the piston wall is configured not to contact the brake pad. Instead, only the plastic portion of the piston wall engages with the brake pad. This may be envisioned for reducing noise and vibration.
Alternatively, the metallic portion of the piston wall may extend to the second end of the piston and be configured to engage with the brake pad, in particular with the back plate of the brake pad. Then, the metallic portion of the piston wall may act as a heat conductor for transferring heat from the brake pad into the piston.
Additionally or alternatively, the metallic portion of the piston wall may contact the metallic portion of the piston base. If the metallic portion of the piston wall both contacts the metallic portion of the piston base and is configured to engage with the brake pad, it may conduct heat from the brake pad to the metallic portion of the piston base.
The metallic portion of the piston wall may for instance be formed integrally with the metallic portion of the piston base. Alternatively, it is possible to have the metallic portion of the piston wall and the metallic portion of the piston base as separate parts. A geometric connection feature may be provided between the metallic portion of the piston wall and the metallic portion of the piston base, for connecting them to each other. In particular this may be a protrusion-recess-connection. This may add to a joint damping effect.
In possible embodiments, the piston wall may comprise one or more plastic portions and one or more metallic portions. They may form shells that are arranged in layers. In particular, the plastic portions and the metallic portions may be arranged in an alternating fashion. This provides additional joinings which may add to a joint damping effect. For instance, an inner shell, facing the cavity of the piston, may be a plastic layer, followed by a metallic layer. This may be followed again by a further plastic layer. Alternatively, an inner shell, facing the cavity of the piston, may be a metallic layer, followed by a plastic layer. This may be followed again by a further metallic layer. It is also possible to have more than 3 layers, such as, for instance 4 layers.
Each of these layers may for instance have a thickness of at least 1 mm and/or of at most 4 mm.
A geometric feature may be provided between the metallic portion of the piston wall and the plastic portion of the piston wall. In particular, a step or a protrusion-recess-connection may be provided between them. For instance, if the metallic portion of the piston wall and the plastic portion of the piston wall are arranged in layers, a step-feature may be envisioned, which is designed such that the thickness of the metallic layer decreases from the second end towards the first end, and the thickness of the plastic layer increases from the second end towards the first end.
It may be envisioned that the metallic portion of the piston wall is made of a different metal than the metallic portion of the piston base. Alternatively or additionally, they may have a different thermal expansion coefficient from each other.
The metallic portion of the piston base and/or the metallic portion of the piston wall may comprise a sheet metal and/or a cast metal.
The metallic portion of the piston base and/or the metallic portion of the piston wall may comprise copper and/or aluminum and/or steel.
The metallic portion of the piston base may have a coefficient of thermal expansion α of at least 35E-6 1/K and/or at most 70E-6 1/K at room temperature. In particular, it may comprise steel and exhibit a coefficient of thermal expansion α=35E-6 1/K. It may comprise copper and exhibit α=50E-6 1/K. It may comprise Aluminum and exhibit α=70E-6 1/K.
The plastic portion of the piston base and/or the plastic portion of the piston wall may be made of a thermoplastic.
A method for making the piston shown and described herein, may comprise a casting process and/or an injection molding process and/or additive manufacturing. In particular, the method may comprise both a casting process for forming one or more of the metallic portions and an injection molding process for forming one or more of the plastic portions.
It should be understood that the aspects explained herein with the method of making the piston may be claimed for the piston itself, and vice versa.
The invention will now be explained with reference to the appended figures.
Therein,
The piston 100 is at the focus of the present application and various designs are shown in the following figures. The piston 100 has a first end configured to engage with the brake fluid. A piston base 101 closes the piston 100 at the first end. The piston 100 has a second end which is designed as an open end and configured to engage with the brake pad 2. A piston wall 110 surrounds a cavity 119 of the piston 100 between the first end and the second end.
For braking, brake fluid is injected into a cavity 4 of the housing 1 to exert pressure on the piston base 101, as indicated by an arrow. As pressure builds within the cavity 4 of the housing 1, the cavity volume increases and the piston 100 is displaced towards the brake pad 2 by typically between 0.01 to 0.03 mm, and the housing 1 is displaced towards the further brake pad 2′ by typically between 0.38 and 0.4 mm. Thereby, the volume of the cavity 4 increases for instance by approximately 0.7 cubic centimeters. It is an object of the present invention to limit this increase in volume, which corresponds to an amount of brake fluid displaced.
In the case of each of
The piston wall 110 comprises a first plastic portion 112 facing the cavity, and a second plastic portion 112 forming an outer hull of the piston wall 110, and a metallic portion 111 that is designed as a metal sheet interposed between the two plastic portions 112, 112′. The three portions 111, 112, 112′ are thus arranged as layered shells. A thickness of each of the layers or portions of the piston wall 110 is between 1 and 4 mm. In particular, a thickness of the metallic portion 111 may be chosen to be 3 mm.
The metallic portion 111 of the piston wall 110 extends to the second end of the piston 100 and is configured to engage with the brake pad 2. There is a bent section 115 formed by the metallic portion 111 of the piston wall 110, which increases the area that engages with the brake pad. A width of the bent portion is between 5 and 10 mm, in particularly it may be chosen to be 8 mm.
At the first end, the metallic portion 111 of the piston wall 110 contacts the metallic portion 102 of the piston base 101. The metallic portion 102 of the piston base 101 is in the shape of a disk, as can best be seen in
On the inside of the metallic portion 102 of the piston base 101, i.e., facing the cavity 119 of the piston 100, a plastic portion 103 is provided, which pertains to the piston base 101. This plastic portion 103 of the piston base 101 is formed integrally with the second plastic portion 112 of the piston wall 110. It has a thickness of between 2 and 4 mm, wherein it may be envisioned that a total thickness of the piston base 101 does not exceed 8 mm.
A seal groove 113 is provided on the outside of the piston wall 110.
The metallic portion 102 of the piston base 102 is a sheet metal or a cast metal.
The metallic portion 102 of the piston base 102 and the metallic portion 111, 111′ of the piston wall 110 comprise at least one of copper, aluminum and steel.
The plastic portion 103 of the piston base 101 and the plastic portion 112, 112′ of the piston wall are made of a thermoplastic.
The piston is made by at least one of a casting process and an injection molding process and additive manufacturing.
The portions of the piston wall 110 form shells that are arranged in layers. A first metallic portion 111 of the piston wall 110 forms an outer layer and has a thickness of 3 to 4 mm. It is followed by the plastic portion 112, which forms a central layer and has a thickness of 1 to 2 mm. Finally, there is the second metallic portion 111′, which forms the innermost layer, facing the cavity 119 of the piston 100. The second metallic portion 111′ has a thickness of 1 to 2 mm.
There is a step between an first metallic portion 111 and the remaining two portions 112, 111′ of the piston wall 110, for receiving the metallic portion 102 of the piston base 101.
There is a protruding feature 116, protruding from the piston wall 110 at the second end of the piston 100 towards a central axis of the cylindrical piston, for increasing a contact area for contacting the brake pad 2. It is made of plastic. It is between 3 and 4 mm wide. A total width of a ring-shaped contact area for contacting the brake pad 2 is for instance between 8 and 12 mm.
In the initial non-braking state (
During braking (
In the case shown in
In the case shown in
Exemplarily,
In the setup shown in
In the setup shown in
Exemplarily,
The metallic portion 111 of the piston wall 110 is thereby configured not to contact the brake pad 2. To maintain a gap between the metallic portion 111 of the piston wall 110 and the brake pad 2, the plastic portion 112 extends by between 0.5 mm and 1 mm beyond the metallic portion at the second end. A metal-metal contact between the piston and the brake pad 2 can thus be avoided, and noise or damage of the brake pad 2 is reduced.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102022200960.6 | Jan 2022 | DE | national |
