DE20119617U1 - Test roller for roller brake test bench - Google Patents

Description

The present invention relates to a roller brake test bench according to the preamble of claim 1.

Such test benches are used to test braking forces on motor vehicles to determine their roadworthiness. Such test benches usually have rollers arranged in pairs on which the vehicle to be tested is placed. Each pair of rollers is set horizontally in the floor of a test bench, with the rollers of each pair being spaced apart so that a vehicle tire can be placed above the rollers so that the vehicle tire rolls equally on both rollers and transfers its weight load to the pair of rollers.

To test the braking force of a motor vehicle, the vehicle to be tested is positioned on a pair of rollers with the vehicle tires to be braked. At least one of the two rollers in the pair of rollers is then driven, the rotating vehicle tire is braked by applying the vehicle brake, and the resistance to the rotational movement of the roller (braking force) transmitted to the pair of rollers is measured and evaluated.

In order to record the actual braking force of the vehicle as accurately as possible, it is necessary to ensure that the torque is transmitted from the vehicle tire to the driven roller with as little loss as possible.

In practice, steel rollers are usually used for this purpose, which form a relatively good coefficient of friction with the vehicle wheels to be tested. Nevertheless, these test benches still sometimes exhibit considerable slip, so that an exact measurement of the braking force range is not always satisfactorily possible.

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The object of the present invention is therefore to present a roller for a roller brake test bench, which enables an improved power transmission from the vehicle tire to be tested to the roller or vice versa and at the same time is subject to low wear.

The object is achieved by a test roller according to claim 1.

The invention is based on the fact that it is advantageous to provide at least one roller of a roller brake test stand with a coating which increases the friction between the roller and the vehicle tire and at the same time is subject to only minimal wear. The coating consists of two individual layers of a ceramic composite material lying one above the other, with silicon carbide elements embedded in the second and thus outer layer. These silicon carbide elements partially protrude through the outer surface of the second layer, resulting in an overall uneven to grainy surface profile of the test roller.

A test roller manufactured in this way offers the advantage of high wear resistance, which is guaranteed by the ceramic composite material compared to conventional coatings or "bare" metal surfaces. In addition, this coating also offers a higher coefficient of friction in interaction with the vehicle tires driven by the roller. This coefficient of friction reduces the slip between the roller and the tire and enables a more precise determination of the actual braking effect of the vehicle.

On the other hand, the uneven or grainy surface of the second layer not only provides the advantageously high coefficient of static or sliding friction but also a partial form fit between the silicon carbide elements, which protrude from the surface and interact with the tire or tire profile of the vehicle tire.

This form fit supports the desired slip-minimized force transmission between the roller and the tire through the force transmission principle of the form fit, which is applied in addition to the static friction. The inventive combination of the ceramic composite coating with the silicon carbide elements incorporated into it thus advantageously ensures extremely low abrasion and high frictional adhesion between the tires of the vehicles to be tested and the actual test roller.

The two layers can be applied in the following way:
The test roll to be coated, which is usually essentially a cylindrical steel tube, is first cleaned on its outer surface by sandblasting or a similar surface treatment and prepared for the application of the first layer. The first layer of the ceramic composite material is then applied to this prepared roll surface, which can be done for example by brushing or rolling on or by spraying or dipping etc. The aim is preferably to achieve a layer thickness of approx. 200 μm.

After this first layer has dried, the second layer made of a ceramic composite material is applied to its outer surface in a suitable manner. Before this second layer has hardened, silicon carbide elements are introduced into the layer, which can be done, for example, by sprinkling or rolling. After the second layer has hardened, the silicon carbide elements are then arranged in or on this layer in such a way that they partially protrude through the outer surface of the second layer.

The first layer, which is on the inside and has already dried, advantageously prevents the silicon carbide elements from coming into direct contact with the outer surface of the steel pipe and damaging it. The second layer, which is then applied, is partially penetrated by the silicon carbide elements and gives them the necessary hold.

Since silicon carbide is very hard and resistant, it forms an extremely robust and low-wear profile for the vehicle wheels running on it with the ceramic composite material of the second layer. The second, outer layer advantageously also has a thickness of around 200 μm, although, as mentioned, individual silicon carbide elements can protrude beyond this dimension through the surface of the second layer.

The view in terms of "two" layers is based on the fact that there is a radially outer area of the test roller which is provided with silicon carbide elements, while an inner area is provided without these elements. In a simple embodiment of the invention, however, the two layers basically consist of the same carrier material, which is a ceramic composite material. When viewed independently of the manufacturing process, the two layers applied one after the other can therefore also be seen as "one" layer, since they merge seamlessly into one another in terms of their carrier substance, and this "one" layer also has silicon carbide elements in its outer area.
A surface has the first layer in the sense that the second layer borders on the first layer via this surface. After both layers have hardened, this surface no longer needs to have a physical structure if the same carrier material is on both sides of the surface. It then serves only as an imaginary boundary between two layers.

In an advantageous embodiment of the invention, the two layers applied to the outer surface of the test roller consist of the same ceramic composite material. This simplifies production and minimizes costs.

In principle, however, different types of ceramic composite materials are conceivable, which can be used for one or the other layer. As described above, it is particularly important for the inner first layer that the

The silicon carbide elements embedded in the layer above cannot press through this first layer onto the steel surface of the test roller and damage it. For this purpose, the first layer could also be made from a ceramic composite material that is harder than the second layer, in which case this layer could then be made thinner than the second layer, for example.

Conversely, it is also conceivable to form the first layer with a softer composite material than is used for the second layer. The protection of the outer surface of the steel roller could then be ensured by increasing the layer thickness of the first layer to an appropriate extent.

In a further advantageous embodiment of the invention, the coating can also consist of a single layer applied in one operation. The silicon carbide elements are introduced into the not yet hardened outer area of this single layer in such a way that a sufficiently large distance is maintained from the surface of the test roll core. This prevents damage to the surface of the roll by the silicon carbide elements by selecting a sufficiently thick hardening and then protective layer between the silicon carbide elements and the roll.

In a further embodiment of the invention, more than two layers are provided, of which at least the outermost one is interspersed with silicon carbide elements. In this way, layers with different friction values, degrees of hardness, strengths or corrosion-inhibiting properties can be advantageously combined. This allows the absorption of the silicon carbide elements to be advantageously optimized.

For example, a first layer for protecting the roller is conceivable; a second holding layer to be applied on top for a particularly good absorption and fixation of the silicon carbide elements and a third, especially for a particularly good static friction with

Adhesive layer formed on a vehicle tire, wherein the silicon carbide elements from the holding layer can penetrate the adhesive layer and/or protrude beyond it.

In a further advantageous embodiment of the invention, the ceramic composite material of at least one - preferably the outermost - layer can be mixed with a suitable color. In this way, the test roller can advantageously be given a visually appealing appearance without limiting the technical properties of the particularly good static friction.

In an advantageous embodiment of the invention, the ceramic composite material of at least one layer consists at least partially of the product of a reaction of an epoxy resin with an aliphatic hardening agent, which imparts advantageous resistance and static friction to the layer.

In one embodiment, the ceramic composite material of at least one layer has a compressive strength of at least 82 N/mm ² and/or a tensile strength of at least 23 N/mm ² and/or a thermal expansion coefficient of at most 5 x 10 ⁵ 1/°C. These properties have an advantageous effect on the durability of the layer.

The coating of the test roller according to the invention can advantageously also be easily repaired locally, so that a complete replacement of a roller is not necessary in the event of damage or wear.

In an advantageous embodiment of the invention, the silicon carbide elements have a grain size between 200 μιη and 300 μιη. This size enables particularly advantageous good adhesion and wear properties of the coating.

The test roller with the coating is advantageously suitable for all common wheel loads. In an advantageous embodiment, the roller is designed for a wheel load of up to 10,000 kg. In a further advantageous embodiment, the roller is designed for a wheel load of 10 kg - 5000 kg. In a further preferred embodiment, the roller is designed for a wheel load of 100 kg - 1000 kg.

Further advantageous embodiments of the invention emerge from the subclaims.

An exemplary embodiment of the invention is explained below using an example figure. The figures show:

Fig. 1 is a schematic side view of a roller brake test bench;

Fig. 2 is a schematic sectional view of a test roll with coating.

As can be seen in Fig. 1, a motor vehicle 1 with a vehicle tire 3 is arranged on a roller brake test stand 5. The roller brake test stand 5 has two test rollers 7. At least one of the two test rollers 7 can be driven by a drive (not shown in detail), so that a rotational movement of the driven test roller 7 about its axis can cause a rotational movement of the vehicle tire 3 in contact with the test roller 7. A corresponding movement is illustrated by the direction of movement shown in Fig. 1 with two arrows. In order to transfer a torque from the vehicle tire 3 to a test roller 7 or vice versa, the best possible frictional adhesion between them is required.

Fig. 2 shows a schematic sectional view through a test roller 7. The test roller 7 has a cylindrical tube 9, the axis of which penetrates the plane of the drawing vertically. The tube 9 has a jacket surface 10 on its outside. A first layer 13 is applied to the jacket surface 10. The first layer 13 has a first thickness

11, in which it evenly surrounds the pipe 9. On its side facing away from the pipe, the first layer 13 forms a first surface 18. Due to the essentially constant first thickness 11, the first surface 18 essentially takes on the shape of a cylinder arranged concentrically around the pipe 9.

A second layer 14 is arranged on the first surface 18. The second layer 14 has a substantially constant second thickness 12 with which it completely envelops the first layer 13. On its side facing away from the first surface, the second layer 14 forms a second surface 19. Due to the substantially constant second thickness 12, the second surface 19 takes the form of a cylinder arranged substantially concentrically around the tube 9 and the first layer 13.

Silicon carbide elements 16 are incorporated into the second layer 14. As can be seen from Fig. 2, some of the silicon carbide elements are arranged entirely between the first surface 18 and the second surface 19; however, some silicon carbide elements 16 protrude outward from the second layer 14 through the second surface 19.

In particular, the first and second layer thicknesses 11 and 12 as well as the silicon carbide elements 16 are not shown to scale in the figures.

As can also be seen from Fig. 2, no silicon carbide elements are arranged in the first layer 13. Rather, this first layer 13 takes on the function of preventing the penetration of silicon carbide elements 16 from the second layer 14 into the first layer 13 in order to avoid possible subsequent contact and damage to the lateral surface 10 by the silicon carbide elements 16.

The first layer thickness 11 and the second layer thickness 12 are each 200 μm in the embodiment shown. The SiIi arranged in the second layer 14

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The silicon carbide elements 16 partially protrude beyond the second surface 19 defined by the second layer thickness 12 by approximately 60 pm.

Claims (6)

1. Test roller of a roller brake tester for motor vehicles, a) with at least one cylindrical tube for applying a braking force to a vehicle, wherein b) an outer surface of the at least one tube has a coating, characterized in that the coating a) a first layer of a ceramic composite material applied to the outer surface, which has a first layer thickness and has a first outer surface at a radial distance of this first layer thickness from the surface, and b) a second layer of a mixture of a ceramic composite material and silicon carbide elements applied to the first outer surface, which second layer has a second layer thickness and has a second outer surface at a radial distance of this second layer thickness from the first outer surface. 2. Test roller according to claim 1, characterized in that silicon carbide elements of the second layer protrude through the second surface by a certain amount. 3. Test roller according to one of the preceding claims, characterized in that the ceramic composite material of at least one layer consists at least partially of the product of a reaction of an epoxy resin with an aliphatic hardening agent. 4. Test roller according to one of the preceding claims, characterized in that the first and/or the second layer thickness is less than 250 µm. 5. Test roller according to one of the preceding claims, characterized in that the ceramic composite material of at least one layer has a compressive strength of at least 82 N/mm ² and/or a tensile strength of at least 23 N/mm ² and/or a thermal expansion coefficient of at most 5 × 10 ^-5 1/°C. 6. Test roller according to one of the preceding claims, characterized in that the grain size of the silicon carbide elements is substantially between 200 µm and 300 µm.