TECHNICAL FIELD

The present invention relates to a braking apparatus for an axle of an electric vehicle.

In particular, the present invention relates to a braking apparatus of an electric vehicle with an axle equipped with two wheels driven by two independent electric engines, one for each wheel.

BACKGROUND ART

It should be said, incidentally, that the teachings of the present invention can also be applied to an axle, or to a gear equipped with a single engine.

Electric vehicles of this kind can be, for example, a yard forklift, an overhead platform, a towing trolley, etc.

It is well known in the field of electric traction vehicles, such as, for example, forklift trucks, axles equipped with two independent electric motors, one for each hub and for each drive wheel. Each hub is equipped, furthermore, with a relevant planetary gear.

Axles of this kind further include a planetary gear for each wheel, a parking brake unit, common to the two drive wheels, and a service brake unit, which is also common to the two drive wheels.

As is known, while the service brake is of the "normally open" type, and must therefore be actuated directly by an operator, typically through hydraulic actuating means, the parking brake may, instead, be of the "normally closed" type and is actuated through hydraulic actuating ^' means, or electric means comprising a coil.

In other words, the parking brake is always on (for safety reasons) until the electric vehicle is set into motion by the operator. That is to say, when the operator commands the starting of the electric vehicle, an electronic control system generates a signal which, by making an electric current passes through the coils, generates an electromagnetic force that moves a piston, which releases the parking brake so that the vehicle moves.

One of the problems resulting from this kind of parking brake actuation consists in that, in order to remain in the released position and allow the vehicle to move, the coil must be continuously energized by the passage of an electric current; this clearly results in continuous power absorption with consequences in terms of overheating and reduced autonomy of the batteries and, thus, reduced productivity, especially in the case of heavy trucks on which very large parking brakes (and related coils) are mounted.

DISCLOSURE OF INVENTION

Therefore, the main aim of the present invention is to provide a braking apparatus provided with a parking brake, which overcomes the drawback described above and is, at the same time, easy and inexpensive to manufacture.

According to the present invention, there is thus provided a braking apparatus for an axle of an electric vehicle, as claimed in claim 1, or in anyone of the claims depending, directly or indirectly, on claim 1. BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, a preferred embodiment is now described, purely by way of non-limiting example and with reference to the accompanying drawings:

- Figure I illustrates an exploded view of an axle of an electric vehicle incorporating a braking apparatus according to the teachings of the present invention;

- Figure 2 shows an enlarged and partially sectioned portion of the axle illustrated in Figure 1; Figure 3 illustrates a first view of some details belonging to the braking apparatus object of the present invention; and

Figure 4 shows a second view of some details belonging to the braking apparatus object of the present invention .

BEST MODE FOR CARRYING OUT THE INVENTION

In Figures 1 and 2 number 1000 designates an axle of an electric vehicle (not illustrated in its entirety) ; said axle 1000 comprising a braking apparatus 100 according to the teachings of the present invention.

The axle 1000 has a longitudinal axis (X) of substantial symmetry.

The braking ^' apparatus 100, in turn, comprises a service brake 50 and an actuator for the parking brake 70.

Before describing the braking apparatus 100 in greater detail,. it is necessary to briefly mention the other component s of the ax1e 1000.

In principle, the axle 1000 comprises two side casings (CRTL) arranged symmetrically with respect to a central casing (CRTC) (Figure 1); each side casing (CRTL) containing in its interior a respective electric traction engine (not illustrated) , Each side casing (CRTL) is coupled, by means of a respective flange (FLG) , to a respective reduction box (not shown) , which is in tur connected by known means to a respective wheel (not illustrated) .

Each gear box contains in its interior a respective mechanical gear, for example, of the planetary type (not illustrated) , which is used, as is known, to reduce the number of output revolutions from the respective electric traction engine, and hence, consequently, to increase the active torque on the wheel.

As shown in Figures 1 and 2, each electric traction engine makes a respective grooved shaft (SHS) jutting out towards the central casing (CRTC) rotate.

In a known manner, each grooved shaft (SHS) is coupled with a respective rotating disc brake (not illustrated) bearing, on its interior, teeth which are coupled to the grooves of said grooved shaft (SHS) .

The two rotating disc brakes are contained in a disc brake holder 60 enclosed in the central casing (CRTC) , which is common to the service brake 50 and the parking brake 70.

The disc brake holder 60 comprises, for example, three fixed disc brakes that do not move with respect to the central casing (CRTC) . Note that, in this case, the fixed disc brakes must be three in number so that each rotating disc brake is included between two fixed disc brakes.

In a known manner, springs (not illustrated) are interposed between the disc brakes (rotating and fixed) , said springs being suitable to return the disc brake holder to the initial configuration once the braking action (both service and parking) is over.

One or more ears 61 (three can be seen in Figure 1, by way of example) jut out from the perimeter of the disc brake holder 60 to fix (by known means and not illustrated) said disc brake holder 60 to the central casing (CRTC) .

As shown, again in Figure 1, on the right of the central casing (CRTC) is located the service brake 50 mentioned above which, as stated previously, is of the "normally open" type.

The service brake 50 comprises, in a known manner, a piston 51 (substantially axi symmetrical in shape) suitable to act on the brake discs of the disc brake holder 60.

This piston 51 is activated by an actuating device 52, for example, of the hydraulic type (but it could also be electric, or of any other type) .

When the piston 51, by effect of the actuating device 52, moves in a parallel manner with respect to the axis (X) in a direction identified by an arrow (Fl), it closes the disc brake holder 60 by pressing the discs (mobile and fixed) against each, other. In such a way, an indirect braking action is achieved on the two shafts (SH) , thus achieving the desired braking of the axle 1000 and hence of the entire electric vehicle.

The piston 51 moves back once the "positive" signal, applied as a result of the force of separating springs and the viscous force which originates between the disc brakes, ceases.

As regards, instead, the parking brake 70 (of the normally closed type) , it comprises a piston 71 (made of a ferromagnetic material and substantially cylindrical in shape) , which normally presses the disc holder (mobile and fixed) so that the discs are pressed against each other, thus holding the axle 1000 braked due to the thrust of a plurality of springs 74 (in this embodiment the springs are of the coil type) .

When the operator starts the vehicle, a coil 72 (which acts as an electromagnet) , mounted on a flange 73, attracts the piston 71 towards it (in a direction identified by an arrow (F3) ) overcoming the elastic resistance exerted by the coil springs 74 having an axis parallel to the axis (X) ; said coil springs 74 being arranged, precisely, between the piston 71 and a front face 73A of the flange 73 on which the coil 72 is located.

Therefore, t e coil springs 74 are compressed, due to the crushing action of the piston 71 on the front face 73A.

At this point, in order to continue to hold the parking ^' brake 70 open, the system would need, to supply electric power continuously to the coil 72.

It is evident that all this would involve a considerable waste of electric power, and a really significant waste of power in the case of very large axles which hence require particularly sturdy brakes with large coils (electromagnets ) and involve the use of considerable electromagnetic forces .

Therefore, to overcome this problem, the outer circular edge 71A. of the piston 71 has been provided with a. circular frame 7 IB jutting outwards.

The circular frame 7 IB has a plurality of recesses 71C spaced, an equal distance apart from one another.

The solution chosen in the present case consists of four recesses 71C, each of which is arranged at 90° with respect to the two adjacent recesses.

Actually, the number of recesses 71C depends on project needs and, if necessary, a solution with only one recess 71C could be adopted. The parking brake 70 comprises a mechanical device for locking/unlocking 80 the piston 71 in the open position.

The mechanical device for locking/unlocking 80 comprises, in turn, a ring 81 provided with projections 82 that jut out internally and radially in the direction of the axis (Z) .

It should be noted that the number of projections 82 present on the ring 81 is equal to the number of the recesses 71C on. the protruding circular frame 7 IB.

Therefore, if the projections 82 face the recesses 71C with precision, when the attractive magnetic force is developed on the piston 71 by the coil 72, an axial- displacement of said piston 71 in the direction of the arrow (F3) becomes possible.

If, instead, the piston 71 needs to be kept detached from the discs of the disc brake holder 60, even in the absence of the magnetic force, it will therefore suffice to rotate the ring 81 about the axis (Z) in a direction identified by an arrow (F4) so that the projections 82 are no longer at the recesses 71C, but rest against a full side 71D of the circular frame 71B to hold the piston 71 in a detached position from the disc brake holder 60, the ring 81 being, in turn, held fixed in the axial direction by suitable projections present on the casing (CRTC) (Figure 2) .

The rotation of the ring 81 about the axis (Z) (arrow (F4)) is performed by an actuator 83 that acts tangential ly to said ring 81.

Advantageously, but not necessarily, the actuator 83 is also of the electric type.

Moreover, note that the actuator 83 overcomes the elastic resistance of a spring (not illustrated) , and that the mechanism is held fixed without any waste of electric power thanks to the thrust (and the friction) exerted by the piston 71 on the ring 81 through the coil springs 74.

Also note that to increase the security of the system, and to allow a manual insertion of the braking system in the absence of the electric current due to a fault, there may be two actuators (see the accompanying Figures) . All the elements are held together by means of a plurality of screws (SCR) , each of which is screwed into a respective threaded hole (HL) .

The next time the parking brake 70 has to be applied, it will suffice to send an electric command to the coil 72 so that after the thrust of the magnetic force there is no force of friction between the actuator 71 and the ring 81 and consequently the force of the spring present in the actuator 83 rotates the ring 81 in a direction identified by an arrow (F5) opposite to the direction of the arrow

At this poi t, when each projection 82 is facing exactly in front of the respective recess 71C, the piston 71 is thrust again (in the direction identified by an arrow (F6)) against the discs of the disc brake holder 60 owing to the thrust exerted by the coil springs 74, thereby applying the parking brake 70 again.

According to the present invention, the possibility of connecting the actuator 83 with a cable (not illustrated) is also envisaged, so that, in case of a failure, the ring 81 can be rotated manually from the outside to manually release the parking brake 70 after pushing the piston 71 back following the application of a manual control on the piston 51 of the service brake 50.

The main advantage of the braking apparatus according to the present invention consists in that, by using a simple mechanical device for locking/unlocking the piston, the amount of electric power needed to hold the parking brake open is almost zero.