FR3080160A1 - REDUCTION DEVICE FOR A BRAKE SYSTEM FOR A VEHICLE - Google Patents

Abstract

This braking system (2) for a vehicle comprises: - a motor, - a screw (18) capable of being rotated by the motor, - at least one brake lining (6) able to be actuated by the screw (18 ), and - a transmission device coupling the motor with the screw (18) and having a transmission ratio between 230 and 280.

Description

The invention relates to a braking system for a vehicle. More particularly, the invention relates to drive means for a braking system for a vehicle.

[0002] A braking system, for example a disc braking system more commonly known as a "disc brake" or a drum braking system more commonly known as a "drum brake", generally comprises friction means connected to an actuating member capable of moving the friction means in the direction of a braking member fixed to a wheel of the vehicle. This is to bring the friction means, for example linings or brake pads, into contact with the braking member to brake the vehicle by friction or to move them away from the braking member in order to stop the braking. The actuator is generally coupled to transmission means intended to cause the displacement of the friction means by means of the energy supplied by the actuator. When the braking system is a disc brake, the braking member is formed by a disc integral in rotation with the wheel. In the case where the braking system is a drum brake, the braking member is formed by a drum integral in rotation with the wheel.

Transmission means are known which are formed by assembling a nut and a screw housed in the nut. The screw comprises on a external face a thread capable of cooperating with a threaded hole of the nut. The actuator, for example an electric motor coupled with a gear transmission device, rotates the screw, which generates a helical movement of the nut relative to the screw and a sliding of the nut relative to the actuator which allows the brake pads to come into contact with the vehicle wheel. In other words, the engine provides torque which is transmitted to the pads to effect braking.

In order to improve braking, it is desired to increase the torque supplied by the engine. This reduces the time it takes to apply the brakes and increases their effectiveness. One solution to this effect is to increase the speed of rotation of the motor because the torque supplied is an increasing function of the speed of rotation.

However, this solution is not satisfactory. The engine is generally controlled by a control member. When its rotational speed becomes too high, engine control becomes difficult and the quality of braking can be reduced.

To overcome this problem, it is possible to modify the transmission ratio of the transmission device. In standard braking systems, it is approximately equal to 136. Increasing this transmission ratio allows, at constant engine speed, to increase the torque supplied to the screw. However,

-2 the increase in this transmission ratio also has the consequence of increasing the size of the transmission device and the engine. These consequences have a dissuasive effect, so that it is generally not envisaged to modify the transmission ratio.

An object of the invention is to increase the torque supplied by the motor without increasing its speed of rotation.

To this end, a braking system for a vehicle is provided according to the invention, comprising:

- a motor,

- a screw capable of being rotated by the motor,

- at least one brake lining capable of being actuated by the screw, and a transmission device coupling the motor with the screw and having a transmission ratio of between 230 and 280.

It has been noted that with a transmission ratio included in this range, much greater than the value of 136 of the prior art, the space requirements of the engine and of the transmission device remain accommodative. We therefore roughly doubled the transmission ratio, which considerably increases the torque supplied to the screw without having to increase the engine speed. In other words, it is thus possible, thanks to the invention, to increase the torque supplied to the screw while allowing precise control of the motor.

Advantageously, the transmission ratio is between 245 and 265, preferably equal to 255.

This narrower range, and more particularly the value of 255, for the transmission ratio constitutes an optimal range for the balance of the various constraints of the braking system.

Advantageously, the motor is a brush motor.

This type of engine is relatively inexpensive and compatible with the invention. The choice of this type of engine therefore makes it possible to reduce the manufacturing cost of the braking system.

Advantageously, the motor comprises a rotor having a diameter between 35 and 45 mm.

These values of the diameter of the rotor of the motor make it possible to obtain a good compromise between the torque generated by the motor and its bulk, which are both increasing functions of the diameter of the rotor.

Advantageously, the motor is capable of turning a rotational speed between 8,500 rpm and 11,500 rpm, preferably between 9,500 rpm and 10,500 rpm.

These motor speed values are close to the limit for optimal operation of the motor control. These are therefore the ones that maximize the torque supplied to the screw while allowing precise control of the engine.

Advantageously, further comprising a current control system of the motor.

The engine is thus controlled in a controlled manner and simple to implement.

We will now present an embodiment of the invention given by way of nonlimiting example and with the support of the appended figures in which:

FIG. 1 is a diagram of a braking system according to the invention, and

- Figure 2 is a perspective view with partial cutaway of an engine and a reduction device of the braking system of Figure 1.

Illustrated in Figure 1 a braking system 2 according to the invention. This system 2 comprises a stirrup 4 mounted to slide relative to a chassis of a vehicle in which the system 2 is installed and friction means 6 mounted to slide relative to the stirrup 4. The friction means 6 are here formed by two brake linings or pads intended to come into contact with opposite faces of a disc 8 secured to a wheel of the vehicle (not shown), the disc 8 extending partially between the two friction means 6. We will describe more how far the braking system 2 slows down the vehicle.

The system 2 comprises an assembly 10 intended to convert a torque produced by a geared motor or motorized group 12 in a sliding of the plates 6 towards the disc 8 and a tightening of the latter. As shown in FIG. 2, the motorized group 12 comprises a motor 14 and a transmission device 16. The motor 14 is here a brush motor which is a relatively inexpensive type of motor and which is suitable for the invention. Alternatively, one could choose any other type of motor that would be suitable. The motor 16 comprises a rotor which has a diameter between 35 and 45 millimeters in order to allow the generation of a sufficiently large torque. The motorized group 12 further comprises a control system (not shown) capable of controlling the motor in current. The braking system 2 is thus of the type comprising a floating caliper disc brake of the hydraulic type (service brake) comprising an electric parking brake driven by the gear motor 12, the caliper being slidably mounted relative to a yoke which it is fixed to the chassis of the vehicle.

The transmission device 16 is of the gear type 17. The gears 17 are chosen so that the transmission device has a transmission ratio between 230 and 280, preferably between 245 and

-4255, for example around 255.

The assembly 10 includes a screw 18 coupled to the motor 14 by the transmission device 16 so that a torque produced by the motor 14 allows to drive the screw 18 in rotation relative to the caliper 4 around d a main axis 20 of the screw 18. The latter comprises a threaded rod 22 and a crown 24 attached to the threaded rod 22. The crown 24 forms a head of the screw 18.

The assembly 10 includes a nut 26 mounted fixed in rotation relative to the stirrup 4 and movable to slide relative to the latter along the axis 20. It is coupled with the screw 18 by virtue of their mutual threads. so that the screw 18 and the nut 26 form a helical connection. This helical connection is preferably irreversible. This means that a rotation of the screw 18 can cause the nut 26 to slide relative to the screw 18, but that a force acting on the nut 26 to make it slide cannot cause the screw 18 to rotate. in return. The irreversibility of this assembly prevents the parking brake from being released in the absence of power from the electric motor 14.

The assembly 8 includes a piston 28 slidably mounted parallel to the axis 20 relative to the bracket 4 and having a conduit or housing 30 in which extend the screw 18 and the nut 26. The piston 28 is rigidly fixed to one proximal of the two plates 6. The latter is thus slidably mounted parallel to the axis 20 relative to the stirrup 4.

We will now describe how the braking system 2 works.

We assume that the vehicle is moving. The head of the nut 26 is located in the vicinity of the motorized group 12, in a so-called rolling position, and the pads 6 are located at a distance from the disc 8. If the user wishes to slow down the vehicle, he actuates a braking (not shown), for example a vehicle brake pedal or a button located in a passenger compartment of the vehicle, which is connected to the steering system. The latter controls the motor 14 so that it rotates in a braking direction at a speed of between 8,500 and 11,500 rpm, preferably between 9,500 and 10,500 rpm, for example around 10,000 rpm.

The motor 14 thus drives the screw 18 in rotation with respect to the stirrup 4 around the axis 14 via the transmission device 16. The latter makes it possible to increase the torque supplied by the motor 14 to screw 18 in order to improve the application of braking. The screw 18 being engaged with the nut 26 and thanks to the shape of the conduit 30 of the piston 28, the nut 26 is slidably driven relative to the stirrup 4 parallel to the axis 20.

When it slides, the nut 26 ends up coming into contact with a

-5 axial end of the conduit 30. From this moment, if one continues to rotate the screw 18, the nut 26 drives with it the piston 28 in sliding parallel to the axis 20. The proximal plate 6 being rigidly fixed to the piston 28, it then moves towards the disc 8 until it comes into contact with it. The nut 26 then occupies a position remote from the motorized group 12, called the braking position. At that time, it is the other plate 6, distal, which begins to move towards the disc 8 in the opposite direction until coming into contact with it. Indeed, the braking system 2 having here a configuration in floating caliper, once the proximal pad 6, that is to say that fixed to the piston 28, comes into contact with the disc 8, if we continue to do turn the screw 18, it is the distal plate 6 that begins to slide parallel to the axis 20 relative to the chassis in the direction of the disc 8. In other words, the nut 26 ensures the application of the two plates 6 against the opposite faces of the disc 8.

Since the disc 8 is integral with the wheel, the friction between the pads 6 and the disc 8 converts the kinetic energy of the wheel into heat. This has the effect of reducing the speed of rotation of the wheel and therefore of slowing down the vehicle. Once the vehicle speed has decreased to a value desired by the driver, he stops applying the braking device. The control system then controls a rotation of the motor 14 in the direction opposite to the braking direction so that the nut 26 moves away from the disc 8. The contact between the pads 6 and the disc 8 ceases, so that it there is no more friction between these two elements. The vehicle is then no longer slowed down.

We can also predict that the braking system 2 is not intended to slow the vehicle but to keep it stationary. The braking system 2 would then be controlled by a locking member, such as a hand brake also known by the designation "parking brake". A vehicle is moreover generally equipped with first braking systems intended to cooperate with the braking member and second braking systems intended to cooperate with the locking member.

The invention is not limited to the embodiments presented and other embodiments will be apparent to those skilled in the art. In particular, it is possible to replace the braking system so that it has a drum configuration.

Nomenclature :

: braking system: caliper: pad: disc

10 together 12 motorized group 14 engine 16 transmission device 5 18 screw 20 main axis 22 threaded shaft 24 crowned 26 nut 10 28 piston 30 pipe

Claims (7)

claims 1. Braking system (2) for a vehicle, characterized in that it comprises: - a motor (14), - a screw (18) capable of being rotated by the motor (14), - at least one brake lining (6) capable of being actuated by the screw (18), and - a transmission device (16) coupling the motor (14) with the screw (18) and having a transmission ratio of between 230 and 280. 2. Braking system (2) according to the preceding claim, wherein the transmission ratio is between 245 and 265, preferably equal to 255. 3. Braking system (2) according to any one of the preceding claims, in which the motor (14) is a brush motor. 4. Braking system (2) according to any one of the preceding claims, in which the motor (14) comprises a rotor having a diameter between 35 and 45 mm. 5. Braking system (2) according to any one of the preceding claims, in which the motor (14) is capable of turning a rotational speed of between 8,500 rpm and 11,500 rpm, preferably between 9,500 rpm / min and 10500 rpm. 6. Braking system (2) according to any one of the preceding claims, in which the motor (14) is capable of turning a rotational speed of approximately 10,000 rpm. 7. Braking system (2) according to any one of the preceding claims, further comprising a motor control system (14) in current.