DE202020004103U1 - Brake lever for a brake of a motor vehicle - Google Patents

Abstract

Brake lever (1) for a brake of a motor vehicle for transmitting a braking force from an actuator to a brake actuation mechanism for frictional engagement of brake linings, the brake lever (1) having a housing (2,3) made of cast iron, characterized in that the cast iron is austenitic -Ferritic cast iron with spheroidal graphite (ADI) is.

Description

The present invention relates to a brake lever for a brake of a motor vehicle for transmitting a braking force from an actuator to a brake actuation mechanism for frictional engagement of the brake linings.

The invention relates in particular to a special material composition for such brake levers.

In heavy-duty vehicles, buses, trailers or the like, both drum brakes and disc brakes are used, each of which has a brake lever. Disc brakes with a corresponding lever arrangement are for example from the EP 0 553 105 B1 or the WO 2004/059187 A1 known to the applicant. However, the invention is preferably aimed at drum brakes in which the brake lever engages an S-cam spline shaft and has a housing in which an automatic adjustment device is received, as is the case, for example, in FIG EP 0 598 290 B1 and the EP 1 064 472 B1 the applicant or the U.S. 3,392,810 is revealed.

The brake lever for such drum brakes is used to convert the linear movement of a tappet from a pneumatic or hydraulic actuator into a rotational movement of a cam of such a drum brake arrangement in order to adjust the brake linings of the brake lining shoes when the brake is actuated. The brake lever itself is preferably designed in one piece and has a housing section in which an automatic adjustment device is received in order to enable compensation for the wear on the brake lining shoes of the drum brake. For the exact functioning of the automatic adjustment device and the brake lever in this context, for example, refer to EP 0 598 290 B1 be referred to the applicant.

With regard to the dynamic and static force loads prevailing in such a drum brake, the brake lever is consequently to be regarded as the essential and critical component of the overall arrangement. The brake lever is generally designed as an elongated component with a housing section in which the automatic adjustment device is inserted, and with a lever section which has a free end which is connected to the actuator.

So far, the brake lever and in particular the housing for receiving the adjustment device were usually made of a cast iron with spheroidal graphite, which was present with different ferritic and pearlitic proportions, that is, the base mass of the cast iron consists of ferrite to pearlite. In this context, spheroidal graphite means that the free carbon is embedded in the ferrite and / or pearlite matrix in a spherical, that is to say spherical or nodular form. This is a special form of precipitation of carbon in a spherical shape, i.e. in contrast to steel, the carbon is not directly embedded in the unit cell of iron, but forms differently shaped graphite phases within the alloy.

A larger proportion of pearlite in the matrix results in increased hardness and strength, while a larger proportion of ferrite is responsible for better elasticity or ductility and easier machinability.

As an alternative to cast iron, the housing of a brake lever according to the prior art can also be forged from steel.

The housing or the housing section of the brake lever, in which the adjustment device is arranged, has several inner surface sections that are exposed to great pressure contact and wear, since elements of the adjustment device are supported on these sections, these as abutments or as a corresponding bearing surface for movable ones Use components of the adjustment device.

For these reasons, it is necessary to subject these inner surfaces to a hardening heat treatment. Nitriding of these surfaces is also used here, for example. Such hardening processes are very costly. In addition, chemicals are used in such hardening treatments, which have a considerable negative impact on the environment and safety as well as the well-being of the workers during industrial production.

At the free end of the brake lever, the latter is connected to a tappet of a pneumatic or hydraulic actuator in that a bolt penetrates a recess in the upper lever section and a fork bracket of the actuator tappet. The recess in the upper lever section is often reinforced by the fact that a bearing sleeve is pressed in, which is able to counteract the frictional effects occurring during the brake actuation with better wear resistance. This additional work step with the additional component also has a negative effect on the overall costs of producing such a brake lever.

In general, it is an object of the present invention to provide a brake lever for a brake such as a drum brake or a Disc brake, available, which on the one hand can be produced more cost-effectively and on the other hand has significantly better material properties both in terms of machinability and in terms of service life and functional reliability.

Another object of the invention is to remedy the inadequacies for brake levers, which are known in particular for the drum brake sector.

These objects are achieved with a brake lever according to claim 1 and with a drum brake according to claim 10 or with a disc brake according to claim 11.

The core of the invention is therefore that the housing of the brake lever is made from an austenitic-ferritic or austenitic-ferritic or austenitic cast iron with spheroidal graphite, also called ADI (Austempered Ductile Iron). Ideally, the brake lever is made in one piece from such a cast iron.

ADI is a cast iron material in which the carbon is designed as a sphere and the microstructure matrix consists of ausferrite. This ausferrite is a fine-grained mixture of ferrite and stabilized austenite, which ensures the high strength and ductility of the ADI.

The austenitic structure is achieved in that the casting is heated to an austenitizing temperature and then immersed for a predetermined period of time in a bath which maintains a certain temperature.

Depending on the chemical composition and, consequently, depending on the design of the metallic matrix, the ADI material has good machinability, which results from the addition of mainly nickel (Ni) and also copper (Cu).

ADI is an alloyed nodular cast iron, which, combined with a special heat treatment, leads to corresponding material and therefore machining properties.

In a first embodiment of the brake lever according to the invention, the ADI cast iron has carbon (C) with a weight fraction of 3.5-3.75%.

In a second embodiment of the brake lever according to the invention, the ADI cast iron has silicon (Si) with a weight fraction of a maximum of 2.8%.

In a third embodiment of the brake lever according to the invention, the ADI cast iron has manganese (Mn) with a weight fraction of 0.25-0.35%.

In a fourth embodiment of the brake lever according to the invention, the cast iron (ADI) has copper (Cu) with a weight fraction of 0.20-1.00%, preferably with a weight fraction of 0.50-1.00%.

In a fifth embodiment of the brake lever according to the invention, the ADI cast iron has nickel (Ni) with a weight proportion of 0.20-1.00%, preferably with a weight proportion of 0.35-1.00% and particularly preferably with a weight proportion from 0.35 to 0.85%.

Depending on the selection of the above-mentioned material proportions and / or corresponding heat treatment processes, corresponding tensile strengths, hardnesses and 0.2% elongation limits can be achieved, whereby the machinability of such a brake lever can be influenced in a targeted manner.

The invention is characterized by the advantage that for a planned component, such as a brake lever for a drum brake or a disc brake, made of ADI cast iron, a better comparison between the machinability on the one hand and the strength on the other hand can be achieved.

The machinability is mainly determined by the hardness of the hardest points within the component to be machined. There are very hard areas in the cast iron where the material is harder than in the immediate vicinity (macro area) due to the cooling time etc. In addition, very small, locally limited hard spots in the micro range can occur, which are formed due to a non-homogeneous structure of the material of the spheroidal graphite cast iron. Since the proportion of these areas is influenced by the cooling time, etc., very large variations between the hardest and softest points are the rule with conventional cast iron. In contrast, ADI cast iron with spheroidal graphite shows a much more homogeneous structure than conventional types of cast iron, which have these points or sections with different hardnesses in the micro range.

There is also the disadvantage of conventional cast irons with the usual ferritic and pearlitic components that there is always a thin layer with a reduced percentage of pearlite in the area of the surface, which reduces the actually usable strength, because these are the areas with the softest Material that mainly determines the usable strength of a component.

For these reasons, it is a common practice of designers to set an upper limit for the hardness of a component to be cast in advance, with the proviso that problems, and the associated high costs, are avoided in subsequent machining. Based on this hardness, the designer then selects the appropriate material and then finally defines the actually possible usable strength for his strength calculations.

If the designer uses ADI cast iron with the aforementioned weight proportions of the individual components according to the invention, he will consequently arrive at a considerably higher usable strength for the component to be cast than would be the case for conventional spheroidal graphite cast iron.

It has been shown that by using ADI cast iron according to the invention for a brake lever, a significantly higher strength can be achieved, while at the same time the machinability moves in ideal ranges.

In addition, the invention relates to a drum brake, in particular for commercial vehicles, with an automatic slack adjuster, which has a brake lever according to one of the aforementioned embodiments, and a disc brake, in particular for commercial vehicles, with a brake actuation mechanism, which has a brake lever according to one of the aforementioned embodiments having.

• 1 eine Seitenansicht des Bremshebels im Teilschnitt und
• 2 eine Schnittdarstellung entlang A - A aus 1 wiedergibt.

The attached 1 and 2 show to illustrate the invention a brake lever for a drum brake, wherein

• 1 a side view of the brake lever in partial section and
• 2 a sectional view along A - A 1 reproduces.

The brake lever 1 is constructed in one piece and has an upper lever portion 2 and a lower housing section 3 to accommodate an automatic adjustment device 4th on.

A worm wheel 5 the adjustment device 4th is in a corresponding recess 6th in the housing section 3 rotatably received and cooperates with corresponding internal splines with an S-cam spline shaft not shown here for the brake linings. The worm wheel 5 combs with a worm spindle 7th that are in the housing section 3 perpendicular to the worm wheel 5 in a corresponding recess 8th is stored.

With regard to the type and function of the other components of the automatic adjustment device, which will not be discussed in detail here, is hereby referred to EP 0 598 290 B1 referred to the applicant.

As can be seen, the recess 6th for the worm wheel 5 corresponding inner storage areas 9 on, as well as the recess 8th for the worm spindle 7th appropriate storage space 10 having.

On these inner storage areas 9 , 10 There is a strong pressure contact, which is why these bearing surfaces had to be processed by appropriate hardening processes, such as nitriding, with the above-mentioned disadvantages of increased environmental pollution and the associated cost disadvantages.

The use of ADI cast iron, which compared to conventional ferritic or pearlitic grades for the same hardness, as mentioned above, has a higher usable strength, therefore offers increased resistance to very high pressure loads, especially in the point area, without becoming plastic to deform.

Especially with regard to the inner bearing surfaces 9 , 10 in the housing section 3 of the brake lever 1 For a drum brake, the use of ADI cast iron with the chemical compositions provided according to the invention has proven to be particularly advantageous, since the mentioned subsequent hardening processes can be completely dispensed with. Mechanical processing steps on the storage areas 9 , 10 can be carried out more easily overall.

In the upper area of the lever section 2 is a recess 11 provided, which is used to connect to a tappet of an actuator, not shown here. A bolt extends through this recess 11 . Due to the relative movements between the bolt of the plunger and the recess 11 of the lever section 2 when the brake lever is pivoted 1 the resulting friction must be countered with a corresponding resistance in order to keep the wear low, which is why the recess 11 This is often reinforced by pressing a corresponding hardened bearing sleeve into the recess in brake levers in the prior art.

Since the ADI cast iron has better usable strength with the same hardness, it is for the recess 11 no longer necessary to provide an additional bearing sleeve, since the inner surface of the recess 11 can even offer a sufficiently large resistance to the pressure contact of the bolt without deforming. As a result, the costs can be further reduced by shortened assembly time and by omitting an additional bearing sleeve.

It goes without saying that the brake lever, be it for a disc brake or a drum brake, represents an essential safety-critical component of the entire brake arrangement, since in the event of a failure, for example the brake lever breaking or breaking, the braking function for the corresponding wheel would fail completely.

Cast iron materials that have similar processing properties and are in the range of 0.2% yield strengths similar to those of the cast iron according to the invention are, however, as already mentioned several times above, less homogeneous and have more casting defects, which can then be the starting point for spreading cracks . However, such a risk of breakage is avoided by the much more homogeneous structure of the ausferritic cast iron with spheroidal graphite according to the invention, which makes its use particularly suitable for a brake lever.

The recesses 6th and 8th with their cylindrical surfaces have minimally larger dimensions than the worm wheel 5 and the worm spindle 7th , which is why the cylindrical surfaces are elastically and plastically deformed when high forces from the worm wheel during brake actuation 5 or the worm spindle 7th be exercised on these surfaces. When using conventional cast iron, due to the poor machinability, dimensional deviations or casting errors are often found. Due to the lower ductility in comparison to the ADI cast iron according to the invention, such defects show the risk of cracking during the deformation. In addition, the risk is increased as the corresponding bearing surfaces are hardened 9 , 10 further reduces the ductility.

When using the ADI cast iron according to the invention for the lever 1 are the deformations that result from being caused by the worm wheel 5 or the worm spindle 7th exerted pressure result, through a higher ductility of the surrounding material of the bearing surfaces 9 , 10 better tolerated, so that such cracking during the deformation can be excluded.

In addition, an advantage of the ausferritic cast iron with spheroidal graphite according to the invention is that the required proportion of carbon solidified in spheres or nodules is considerably reduced compared to the ferritic and pearlitic types in order to meet the minimum properties under tensile stress. In conventional spheroidal graphite cast irons, the manufacturing process causes the carbon to solidify in the form of spheres, rather than in the form of flakes as in gray cast iron. However, if this ball formation fails or cannot be completely completed for any reason, the cast iron is far more brittle and tends to crack easily, which increases the risk of breakage.

Such deficiencies in the production of the material of corresponding components are excluded by the use of ausferritic cast iron with spheroidal graphite according to the invention, which in particular increases the safety in use for a brake lever.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 0553105 B1 [0003]
• WO 2004/059187 A1 [0003]
• EP 0598290 B1 [0003, 0004, 0036]
• EP 1064472 B1 [0003]
• US 3392810 [0003]

Claims (11)

Brake lever (1) for a brake of a motor vehicle for transmitting a braking force from an actuator to a brake actuation mechanism for frictional engagement of brake linings, the brake lever (1) having a housing (2,3) made of cast iron, characterized in that the cast iron is austenitic -Ferritic cast iron with spheroidal graphite (ADI) is. Brake lever (1) Claim 1 , in which the cast iron (ADI) contains carbon (C) with a weight fraction of 3.5-3.75%. Brake lever (1) Claim 1 or 2 , in which the cast iron (ADI) has silicon (Si) with a weight fraction of a maximum of 2.8%. Brake lever (1) Claim 1 , 2 or 3 , in which the cast iron (ADI) contains manganese (Mn) with a weight fraction of 0.25-0.35%. Brake lever (1) after one of the Claims 1 to 4th , in which the cast iron (ADI) has copper (Cu) with a weight fraction of 0.20 - 1.00%. Brake lever (1) Claim 5 , in which the cast iron (ADI) has copper (Cu) with a weight proportion of 0.50 - 1.00%. Brake lever (1) after one of the Claims 1 to 6th , in which the cast iron (ADI) has nickel (Ni) with a weight fraction of 0.20 - 1.00%. Brake lever (1) Claim 7 , in which the cast iron (ADI) has nickel (Ni) with a weight fraction of 0.35 - 1.00%. Brake lever (1) Claim 8 , in which the cast iron (ADI) has nickel (Ni) with a weight fraction of 0.35-0.85%. Drum brake, especially for commercial vehicles, with an automatic slack adjuster that has a brake lever (1) according to one of the Claims 1 to 9 having. Disc brake, in particular for commercial vehicles, with a brake actuation mechanism which has a brake lever (1) according to one of the Claims 1 to 9 having.

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