Patent Description:
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. This means that although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as buses, construction equipment, military vehicles and so on.

Air brakes or, more formally, compressed air brake systems, are a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle.

Air brakes are typically used on heavy trucks and buses. On this type of vehicle, the brake system consists of a service brake, a parking brake, a control pedal and an air storage tank. For the parking brake, there is a disc or drum brake arrangement, which is designed to be held in the "applied" position by spring pressure. Air pressure must be produced to release these "spring brake" parking brakes. For the service brake (i.e. the one used while driving for slowing or stopping) to be applied, the brake pedal is pushed, routing the air under pressure to the brake chamber, causing the brake to be engaged. Most types of truck air brakes are drum brakes, though there is an increasing trend towards the use of disc brakes.

A drum brake is a wheel brake that is applied by brake shoes being pressed against a brake drum. There are a number of different types of drum brakes, where the difference lies in the mechanism that transmits the braking force from the brake cylinder to the brake lining. In particular, drum brakes include cam brakes and wedge brakes.

In a cam brake, the brake cylinder converts the energy of compressed air to mechanical operation. It consists of two chambers separated by a rubber diaphragm. When the brake pedal is depressed, air flows into the cylinder and pushes the diaphragm against a push rod. This causes the push rod to move out from the cylinder and to push on a rotating lever (also known as "brake lever" or "brake arm"). The rotating lever transforms the force of the push rod into a torque that is applied to a brake shaft. A cam, e.g. a S-shaped cam, is arranged at the end of the brake shaft. As the cam rotates, it forces two symmetrical brake pads against the brake drum until the pressure is released and the brake pads return to their resting position. The brake shoe carries the brake lining, which is riveted or glued to the shoe. When the brake is applied, the shoe moves and presses the lining against the inside of the drum. The friction between lining and drum provides the braking effort. Energy is dissipated as heat.

As the brake linings wear, the shoes must travel a greater distance to reach the drum. Therefore, it is known to equip the cam brake arrangements with a mechanism that enables to adjust the rest position of the shoes when the distance between the drum and shoes reaches a certain point. Precisely, the brake shoes are moved radially outwards so as to be closer to the drum. Such mechanism, which is also known as "slack adjuster", can be manual or automatic (self-adjusting) and is built into the brake lever connecting the push rod to the brake shaft.

<CIT> discloses an example of an automatic slack adjuster for vehicle brakes. <CIT> discloses an example of an operating arm for a brake adjusting device.

In order to overcome some packaging constraints in the vehicle architecture, the brake lever is not straight, but includes angled parts. This means that there is an angle between the line extending between the two connection points of the brake lever and the plane perpendicular to the axis of rotation of the brake shaft. The greater the offset, the greater the angle.

The offset usually ranges from <NUM> to <NUM>. However, when the offset is high, e.g. about <NUM>, significant lateral loads are induced on the brake shaft during actuation of the brake, causing wear and tear on the brake shaft splines and accelerating the damage on the slack adjuster itself.

An object of the invention is to provide a new brake lever design that allows better withstanding to lateral stress.

The object is achieved by a brake lever according to claim <NUM>.

By the provision of a brake lever which comprises a stiffening member, the advantage is that the stiffening member absorbs at least a part of the lateral efforts to which the brake shaft is exposed in the connection area with the brake shaft.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims <NUM> to <NUM>.

The invention also concerns a drum brake according to claim <NUM> and a heavy-duty vehicle according to claim <NUM>.

With reference to the appended drawings, below follows a more detailed description of three embodiments of the invention cited as examples.

<FIG> represents a heavy-duty vehicle <NUM>, which, in the example, is a truck.

The truck <NUM> includes a front axle <NUM> and a rear axle <NUM>. In the example, the truck is a <NUM> by <NUM> truck, i.e. a truck with four wheels in which torque is delivered to only two wheels. Obviously, the invention is applicable to other truck configurations, such as <NUM> by <NUM> trucks and <NUM> by <NUM> trucks.

The rear axle <NUM> is better represented on <FIG>. For the clarity of the drawings, the wheels are not represented.

In known manner, rear axle <NUM> includes an axle housing <NUM> inside which a differential (not visible) is arranged. The differential includes an orifice for receiving one end of a propeller shaft <NUM>.

The axle <NUM> further includes two wheel brakes <NUM> provided each at one longitudinal end of the axle <NUM>.

Each wheel brake <NUM> is an air brake or, more formally, a compressed air brake system, which is a type of friction brake in which compressed air pressing on a piston is used to apply the pressure to the brake pad (not shown) needed to stop the vehicle <NUM>. In this respect, the vehicle <NUM> includes an air tank and a compressor (not represented).

In the example, each wheel brake <NUM> is a drum brake that is applied by brake shoes (not shown) being pressed against a brake drum <NUM>. There are a number of different types of drum brakes, where the difference lies in the mechanism that transmits the braking force from the brake cylinder to the brake lining. In particular, drum brakes include cam brakes and wedge brakes.

Typically, each wheel brake <NUM> includes a cam actuation mechanism, in which a brake cylinder <NUM>, also known as an "air cylinder", converts the energy of compressed air to mechanical operation. In the example, each wheel brake <NUM> has its own brake cylinder <NUM>, which means that there are two brake cylinders <NUM> fitted on the axle.

Each brake cylinder <NUM> consists of two chambers (not shown) separated by a rubber diaphragm (not shown either). When the brake pedal is depressed, air flows into the cylinder <NUM> and pushes the diaphragm against a push rod <NUM> (also known as "piston"). This causes the push rod <NUM> to move out from the cylinder <NUM> and to push on a rotating lever <NUM> (also known as "brake lever" or "brake arm"). The rotating lever <NUM> transforms the force of the push rod <NUM> into a torque that is applied to a brake shaft <NUM>. Therefore, brake lever <NUM> is designed for transmitting the movement of cylinder rod <NUM> to brake shaft <NUM>.

Preferably, brake lever <NUM> is made of metal or an alloy.

To be clear, <FIG> show a traditional drum brake. The claimed invention specifically concerns the brake lever <NUM> as represented on the <FIG>. In other words, the brake lever that is represented on <FIG> is a brake lever of prior art. The brake lever <NUM> according to the claimed invention is represented on <FIG>.

A cam (not shown), e.g. a S-shaped cam, is arranged at the end of the brake shaft <NUM>. As the cam rotates, it forces two symmetrical brake pads (not shown) against the brake drum <NUM> until the pressure is released and the brake pads return to their resting position. The brake shoe carries the brake lining, which is riveted or glued to the shoe. When the brake is applied, the shoe moves and presses the lining against the inside of the drum <NUM>. The friction between lining and drum provides the braking effort. Energy is dissipated as heat.

In the example, brake lever <NUM> comprises a first portion 20a delimiting a hole <NUM> for fitting the brake shaft <NUM>. Accordingly, hole <NUM> comprises a central axis X24 that is confounded with the axis of rotation of the brake shaft <NUM>.

Basically, the brake shaft <NUM> extends longitudinally parallel to the rotation axis of the wheels (in neutral configuration obviously, i.e. when steering angle is of <NUM>°).

In the embodiment of the figures, brake lever <NUM> further comprises a second portion 20b, which is configured to be pivotally connected to the cylinder rod <NUM>. In this respect, the second portion 20b includes a circular bore <NUM> for receiving a pin (not shown) attached to one end of the push rod <NUM>. Bore <NUM> defines a central axis X30 that represents the axis of rotation of the brake lever <NUM> relative to the push rod <NUM>. Axes X24 and X30 are parallel one with the other.

In the example, bore <NUM> is a through hole.

As the brake linings wear, the shoes must travel a greater distance to reach the drum <NUM>. Therefore, brake lever <NUM> includes a mechanism (not shown) that enables to adjust the rest position of the shoes when the distance between the drum and shoes reaches a certain point. Precisely, the brake shoes are moved radially outwards so as to be closer to the drum. Such mechanism, which is known as "slack adjuster", can be manual or automatic (self-adjusting) and is built into the brake lever <NUM> connecting the push rod <NUM> to the brake shaft <NUM>.

Typically, the slack adjuster is housed inside the first portion 20a of the brake lever <NUM>. In known manner, brake lever <NUM> and brake shaft <NUM> are coupled using a dog gear mechanism: The hole <NUM> is part of a crown wheel (that is partially visible on <FIG>), which is itself part of the slack adjuster and the crown wheel comprises, on the inside, a succession of teeth that engage into complementary splines provided on the brake shaft <NUM>. This enables to rigidly secure the crown wheel of the brake lever <NUM> in rotation with the brake shaft <NUM>.

A plane P1 is defined as the plane, perpendicular to the central axis X24, passing by a connection point A between the rotating lever <NUM> and the push rod <NUM> and. A plane P2 is defined as the plane, perpendicular to that of <FIG>, extending between point A and a connection point B between brake lever <NUM> and brake shaft <NUM>. A plane P3 is defined as the plane passing by point B and perpendicular to the central axis X24 of the hole <NUM>.

Preferably, the first and second portions 20a, 20b are end portions of the brake lever <NUM>. Portion 20b is flat, which means that it extends parallel to plane P1.

In order to overcome some packaging constraints in the vehicle architecture, the first portion 20a and the second portion 20b are offset from each other with respect to the central axis X24 of the hole <NUM>. In other words, planes P1 and P3 are spaced one from the other by a distance (or "offset") d1.

In this respect, the brake lever <NUM> is not straight, but includes angled parts. Precisely, brake lever <NUM> further includes a central portion 20c extending between the first and second portions 20a, 20b. The central portion 20c extends obliquely with respect to the second portion 20b. This means that there is an angle θ between the planes P1 and P2. The greater the offset d1, the greater the angle θ. Therefore, the first portion 20a of brake lever <NUM> is offset with respect to the second portion 20b.

The offset d1 ranges from <NUM> to <NUM>. In the example of the figures, the offset d1 is high, e.g. about <NUM>. Accordingly, significant lateral loads are induced on the brake shaft <NUM> during actuation of the brake, causing wear and tear on the brake shaft splines and accelerating the damage on the slack adjuster mechanism.

More precisely, and referring to <FIG> and <FIG>, as an angle θ exists between planes P1 and P2, the force F1 applied by the push rod <NUM> can be decomposed into a first force F2 corresponding to the projection of the force F1 into plane P2 and a second force F3 corresponding to the projection of the force F1 into a plane P4 corresponding to the plane of <FIG>, perpendicular to planes P1 and P3. Plane P4 includes axes X30 and X24.

As there is no displacement of the brake lever <NUM> along axis X24, i.e. no degree of freedom in that direction, the brake shaft <NUM> exerts on brake lever <NUM> a force F4 that balances force F3. This force F4, known as "lateral load", can cause wear and tear on the brake shaft splines (not shown) and accelerate the damage on the slack adjuster mechanism.

In order to absorb that lateral effort F4, and to avoid premature wear of the brake lever <NUM>, the brake lever <NUM> further includes a stiffening member <NUM> that extends along a direction L1 contained inside the plane P1 and that includes an orifice <NUM> for fitting the brake shaft <NUM>.

In the embodiment of <FIG>, the stiffening member <NUM> extends from the second portion 20b, which means that it forms an extension of the second portion 20b.

In the alternative embodiment of <FIG>, the stiffening member <NUM> extends from the central portion 20c. Accordingly, the stiffening member <NUM> is offset from the second portion 20b with respect to the central axis X24 of the hole <NUM>. In other words, stiffening member <NUM> extends along a direction contained inside a plane P5 that is perpendicular to the central axis X24 of the hole and that is spaced from plane P3 by a distance (or "offset") d2 that is inferior to d1.

In the example, orifice <NUM> is a through hole of circular shape.

Obviously, the orifice <NUM> is preferably coaxially aligned with the hole <NUM>.

The stiffening member <NUM> is not designed for transmitting any torque to the brake shaft <NUM>: The diameter of the orifice <NUM> is large enough to fit the end of the brake shaft <NUM>, with a radial clearance that allows the brake shaft <NUM> to rotate inside the orifice <NUM>. As a matter of fact, the orifice <NUM> acts as a bearing that supports the rotation of the brake shaft <NUM>. Accordingly, the stiffening member <NUM> acts as a support leg.

Basically, the diameter of orifice <NUM> is inferior to that of hole <NUM>. Therefore, in the example, the brake shaft <NUM> is a stepped shaft, provided with at least one radial shoulder (not shown) allowing to have a reduced outer diameter at the end.

In the non-claimed example of <FIG>, the stiffening member <NUM> extends perpendicular to the central axis X24 of hole <NUM>, which means that direction L1 is a straight line.

<FIG> represent a second embodiment of a brake lever <NUM>. For the purpose of clarity, the numeral references used herein are the same than that of the first embodiment.

In this second embodiment, the stiffening member <NUM> extends in a curved manner. More precisely, the stiffening member <NUM> is in the form of a curl (or comma-shaped). The advantage of having this curved stiffening member <NUM> is that it can match with the shape of the axle housing <NUM>.

In other words, the direction L1 along which extends the stiffening member <NUM> is a curved line contained inside the plane P1.

In this example, the orifice <NUM> delimited at the end of the stiffening member <NUM>, which is of circular shape, has a diameter similar to that of the brake shaft <NUM>, which means that there is no need to modify the brake shaft <NUM>.

In this example, orifice <NUM> is a through hole of circular shape.

Advantageously, the orifice <NUM> is delimited inside a casing <NUM> extending parallel to axis X24 between the stiffening member <NUM> and portion 20a. In other words, casing <NUM> makes the junction between stiffening member <NUM> and portion 20a of brake lever <NUM>. The casing <NUM>, of cylindrical shape, is arranged around the end of the brake shaft <NUM>. This enables to increase the robustness of the brake lever <NUM>, to offer a better protection against dust and to provide a better axial support of the brake shaft <NUM>.

Claim 1:
A brake lever (<NUM>) for a drum brake arrangement (<NUM>), said brake lever being designed for transmitting the movement of a cylinder rod (<NUM>) to a brake shaft (<NUM>), wherein the brake lever (<NUM>) comprises a first portion (20a) delimiting a hole (<NUM>) for fitting the brake shaft (<NUM>) and a second portion (20b), which is configured to be pivotally connected to the cylinder rod (<NUM>) and wherein the first portion and the second portion are offset from each other with respect to a central axis (X24) of the hole (<NUM>),
characterized in that:
- the brake lever further includes a stiffening member (<NUM>) that extends in a curved manner along a direction (L1) contained inside a plane (P1) perpendicular to the central axis (X24) of the hole and that includes an orifice (<NUM>) for fitting the brake shaft (<NUM>).