Parking brake device for vehicles

Abstract

Parking brake device (1) comprising a brake device (2) and a linear actuator (3) configured to actuate the brake device by means of a pull rod (4), wherein a motion transmission mechanism (5) is mechanically inserted in series on the pull rod (4) to divide it into a first section (6) connected to the linear actuator (3) and a second section (7) connected to the brake device (2); wherein the motion transmission mechanism (5) is configured to connect the second section (7) to the first section (6) with a variable transmission ratio, such that when the first section (6) moves at a first velocity (V1), this reconfigures the motion transmission mechanism (5) to move the second section (7) at a second velocity (V2) which is a function of a reaction force (R) exerted by the brake device (2).

Description

Technical field of the invention

[0001] The present invention relates to a device for braking vehicles in a parking mode, which is suitable for ensuring a high braking torque / force and a rapid activation. State of the art

[0002] It is well known that when a vehicle is parked, it is important to ensure that the vehicle does not move accidentally, for example as a result of external forces or, when parked on an incline or sloped ramp, the force of gravity.

[0003] This function is performed by the parking brake, formerly also called "handbrake" because it was usually a lever with a harpoon mechanism, manually operated by a user who tightened a cable that mechanically activated the respective brake shoes on the wheels of a vehicle's axle, locking them to prevent them from rotating.

[0004] In current vehicles, the function of the parking brake is increasingly taken over by a mechatronic device, which is generally activated automatically when the vehicle is stationary with the engine switched off.

[0005] A first type of parking brake device, called a MOC (Motor On Caliper), consists of an electric actuator mounted directly on the caliper that acts on the brake pads, placing them in a braking position. This device is generally expensive and can be relatively bulky, sometimes even excessively so.

[0006] A second type of parking brake device, known as a "cable-actuated" parking brake, comprises a linear electric actuator, such as a worm-screw type, which actuates a pull rod, which in turn mechanically actuates a braking device (brake shoes or caliper) acting on the vehicle's wheels.

[0007] The braking device, whether it is normally present on the wheels of the vehicle and is actuated by the vehicle braking system while the vehicle is moving, or it is an additional braking device used exclusively for braking in parking mode, necessarily has a two-stage activation stroke: • In a first phase, the linear movement of the tie rod takes up the play necessarily present at rest (i.e. in the disengaged state) between the braking element (e.g. brake shoe or brake pad) and the element to be braked (e.g. brake disc or brake drum), in such a way that the former abuts the latter; in this phase, the actuator only has to exert a limited force in relation to a relatively long linear stroke; • In a second phase, the actuator must press the braking element against the element to be braked with increasing force, so that the rotation of the element to be braked is blocked by friction over a limited stroke (5-20 mm). The braking torque thus exerted is converted into a linear force acting on the pull rod, which the actuator must counteract and overcome.

[0008] This type of actuation results, on the one hand, in a relatively long time for the parking brake to engage due to a relatively long "rest" stroke, and, on the other hand, requires the use of actuators dimensioned for the maximum force exerted on the drawbar and thus the maximum torque acting on the braking element. This results in a relatively long waiting time (up to approximately ten seconds) before the user can exit the vehicle, as well as higher structural costs, greater volume, and lower efficiency of the entire parking brake device. Summary of the invention

[0009] The aim of the present invention is to provide a mechatronic-type parking brake device for vehicles that can be automatically engaged but does not have the disadvantages of the prior art. In particular, the invention aims to create a "cable-type" parking brake device that allows for rapid application of the braking torque to the vehicle wheels, while at the same time being relatively simple in design and limited in cost and volume.

[0010] The invention therefore provides a parking brake device for vehicles having the features specified in the appended claims. Short description of the drawings

[0011] The invention will now be described with reference to the accompanying drawings, which show a number of non-limiting embodiments of the invention, in which: - Fig. Figure 1 schematically shows a parking brake device according to the invention, comprising a reconfigurable transmission mechanism arranged between a braking device and an actuator for that device, the reconfigurable transmission mechanism being shown in a first configuration in which the parking brake device is released; - Fig. 2 and Fig. 3 schematically shows the reconfigurable transmission mechanism of the parking brake device of the Fig. 1, each shown in a second and third operating configuration in which the parking brake device of the Fig. 1 is gradually engaged; - Fig. 4, Fig. 5 and Fig. 6 schematically show a first alternative of the reconfigurable transmission mechanism of the parking brake device of the invention, in the same operating configurations as in the Fig. 1, Fig. 2 and Fig. 3 is shown; - Fig. 7 schematically shows in simplified form a first embodiment of a force amplification mechanism which is applied to the reconfigurable transmission mechanism of the Fig. 1 to 6 and is usable in the parking brake device according to the invention; - Fig. 8 and Fig. 9 schematically show a second alternative of the reconfigurable transmission mechanism of the parking brake device of the invention, in the same operating configurations as in the Fig. 2 and 3 respectively; - Fig. 10 and Fig. 11 respectively show schematically and in simplified form a second and a third embodiment of a force amplifying mechanism applicable to the reconfigurable transmission mechanism provided in the parking brake device according to the invention; - Fig. 12 and Fig. 13 schematically show the components of two further alternatives of the reconfigurable transmission mechanism of the parking brake device of the invention; and - Fig. 14 and Fig. 15 show, by means of respective (locking) force / movement (stroke) diagrams, the operating performance that can be achieved with the parking brake device according to the invention. Detailed description

[0012] With reference to the Fig. 1 to 3, the reference numeral 1 generally designates a device known per se and not shown for the sake of simplicity for braking a vehicle in a parking mode.

[0013] The parking brake device 1 is of the type comprising a braking device 2 for braking the vehicle, which is known, e.g. a brake caliper, and a linear actuator 3, of the generally known type, e.g. electric, which is designed to actuate the braking device 2 by means of a tie rod 4 inserted between the braking device 2 and the linear actuator 3.

[0014] According to one aspect of the invention, the parking brake device 1 further comprises a motion transmission mechanism 5 which is mechanically mounted in series on the pull rod 4 in order to divide it into a first section 6 which is connected to the linear actuator 3 and a second section 7 which is opposite the first section 6 which is connected to the braking device 2.

[0015] According to one aspect of the invention, the motion transmission mechanism 5 is designed to connect the second section 7 to the first section 6 with a variable transmission ratio, so that a translational movement at a first speed V1 of the first section 6 after actuation of the linear actuator 3 automatically reconfigures the motion transmission mechanism 5, as shown below, to change its transmission ratio and cause a translational movement of the second section 7 at a second speed V2, which is a function of a reaction force R (in Fig. 1 by the arrow next to the section 7 of the pull rod 4 and also on the section 7 itself) which is exerted by the braking device 2 on the second section 7 when the braking device 2 is engaged or released.

[0016] According to one aspect of the invention, the speed V1 during the engagement phase of the braking device 2 is identical to the speed V2 (and thus the gear ratio of the mechanism 5 is equal to 1) until the reaction force R reaches a predetermined value. When the reaction force R exceeds this predetermined value or threshold, the motion transmission mechanism 5 is reconfigured, as shown below, gradually changing its gear ratio so that it is always less than 1, so that the speed V2 gradually decreases below V1, while in parallel, based on known physical laws, the force exerted on the portion 7 of the tie rod 4 by the linear actuator 3 increases, counteracting and overcoming the reaction force R.

[0017] According to a non-secondary aspect of the invention, to achieve this result, the motion transmission mechanism 5 comprises: a support 8 stationary with respect to the first and second sections 6, 7 of the drawbar 4; a frame 9 supported by the support 8 and slidably movable parallel to the drawbar 4; a force amplification mechanism 10 supported by the frame 9 and mechanically connecting the first section and the second section 7 of the drawbar 4 with a selectively variable transmission ratio to move the second section 7 as a result of a linear movement of the first section 6; a trigger system 11 configured to selectively activate the force amplification mechanism 10 to vary its transmission ratio when the reaction force R exceeds the predetermined value;and a force exchange system 12 between the stationary support 8 and the movable frame 9, which is designed to block the sliding of the movable frame 9 and make it integrally rigid with the support 8;

[0018] According to one aspect of the invention, the force amplification mechanism 10 is designed to actuate the force exchange system 12 after activation of the force amplification mechanism 10 itself by the triggering system 11 and to apply to the second portion 7 of the pull rod 4 a force F2 which increases progressively and is always greater than the reaction force R, always after activation by the triggering system 11.

[0019] Furthermore, the force amplification mechanism 10 and the force exchange system 12, when activated, are designed to deliver a portion of the reaction force R to the support 8, so that while the linear actuator 3 applies a first force F1, which is substantially constant, to the first portion 6, the force amplification mechanism 10 applies a second force F2, which is always greater than the first force F1 and the reaction force R, to the second portion 7 of the tie rod 4 (F2 and R are reactions relating to the same portion of the tie rod, and therefore F2=R).

[0020] According to the many alternative embodiments shown, which will now be described in detail, the force amplification mechanism 10 comprises one or more levers or connecting rods 18 hingedly attached to the frame 9 and pivotally connected to each other and / or to at least one pair of carriages 13, 14, which, in the non-limiting example shown, are slidably housed in corresponding guides 15, 16 received on / supported by the frame 9; wherein the first and second portions 6, 7 of the tie rod 4 are attached to at least one or more levers or connecting rods 18 and / or to the carriages 13, 14.

[0021] In a manner obvious to those skilled in the art, it is clear that the guides 15, 16 can be replaced by equivalent elements, for example, the sliding coupling can take the form of a bushing (or sleeve) sliding on the cylindrical element (in any case of limited length).

[0022] In the first non-limiting embodiment of the invention, which is shown in the Fig. 1-3 in three different operating positions, the motion transmission mechanism 10 comprises a triangular lever or element 18a pivotally mounted at a first end 19 thereof, forming the apex of a triangle, on a pin 20 rigidly supported by the frame 9. An opposite end 21 of the lever or element 18a forms one side of a triangle opposite the apex 19 and is pivotally mounted to the corresponding adjacent apex of the triangle formed by the lever 18a by two connecting rods 18b and 18c pivotally mounted on the carriage 13 and carriage 14, respectively. The portion 6 of the tie rod 4 is integrally rigidly connected to the carriage 13, while the portion 7 of the tie rod 4 is integrally rigidly connected to the carriage 14.

[0023] According to a further aspect of the invention, the triggering system 11 is designed to lock the force amplification mechanism 10 by preventing any relative rotation between the at least one or more levers or connecting rods 18 and the frame 9 until the reaction force R exceeds the predetermined value; below the predetermined value, the linear actuator 3 ( Fig. 1) consequently, the frame 9 by means of the section 6 of the connecting rod 4; the frame 9, sliding relative to the support 8, in turn drives the second section 7 of the connecting rod 4 by means of the locked force amplification mechanism 10, locked by the triggering system 11 (the articulated mechanism 10, when locked, acts as a rigid connection system between the sections 6 and 7 of the connecting rod 4), and thus with a transmission ratio equal to 1. The carriages 13 and 14 do not move along the respective guides 15, 16 (or equivalent elements).

[0024] Above the predetermined value of the reaction force R exerted by the braking device 2 on the section 7 of the drawbar 4, the sliding movement of the frame 9 with respect to the support 8 is blocked, as can be seen below ( Fig. 2), and the linear actuator 3 thus takes the second section 7 of the pull rod 4 by a relative movement of the force amplification mechanism 10 with respect to the frame 9 ( Fig. 3) with a transmission ratio which is less than 1 and (due to the geometry given to the lever 18a and the connecting rods 18b and 18c) decreases progressively with increasing reaction force R.

[0025] In the Fig. 1-3, the triggering system 11 consists of a calibrated spring 22 with a predetermined stiffness, which is inserted in the guide 16 so as to oppose the movement of the carriage 14 towards the guide 15 in order to keep the carriage 14 normally in the position of Fig. 1 to keep.

[0026] When the reaction force R exceeds the predetermined value, the force F2 that the mechanism 10 is required to exert on the section 7 of the tie rod 4 exceeds the biasing force of the spring 22, which begins to compress, allowing the carriage 14 to move inside the guide 16 and approach the guide 15. This movement is accompanied by a similar sliding movement in the same direction of the carriage 13 within the guide 15, with the carriage 13 sliding toward the linear actuator 3.

[0027] This initial movement of the slides 13, 14 generates the initial rotation of the lever 18a around the pin 20, which activates the power transmission system 12, which blocks the sliding of the frame 9 ( Fig. 2). At this point ( Fig. 3) the linear actuator 3 can drive the section 7 of the tie rod 4 only by the movement of the motion transmission mechanism 10, which is precisely designed (by giving the lever 18a and the connecting rods 18b and 18c the appropriate dimensions) to progressively reduce the transmission ratio in such a way that a progressively increasing force F2 is exerted on the section 7, while the force F1 remains substantially constant.

[0028] In the Fig. 1-3, the force exchange system 12 consists of a harpoon 23 comprising a toothing 24 obtained integrally with the support 8 and a lock 250 urged by a spring 25 and mounted on a pin 26 with the frame 9 in a pivotable manner to cooperate with or depend on the force amplification mechanism 10 to be prevented by the latter from engaging the toothing 24 until the reaction force R exceeds the predetermined value.

[0029] In particular, in the embodiment of the Fig. 1 to 3, the harpoon 23 cooperates with the lever 18a of the mechanism 10 by means of an arm 27 integral with the end 19 and projecting radially from the pin 20 on the side opposite the end 21, and by means of a corresponding rib 28 integral with the lock 250 and projecting radially from the pin 26 on the side opposite the toothing 24.

[0030] In a parking brake device 1 which is deactivated and / or in the first initial phase of its activation ( Fig. 1), the arm 27 rests against the rib 28 and counteracts the action of the spring 25, which in turn urges the lock 250 in a direction that engages it with the toothing 24. Therefore, the lock 250 cannot engage with the toothing 24, as it is immobilized by the arm 27, and the frame 9 can thus slide freely with respect to the support 8, parallel to the tie rod 4.

[0031] As soon as the reaction force R exceeds the predetermined value, the lever 18a begins to rotate towards the guide 16 and the arm 27 gradually loses contact with the rib 28; consequently, the spring 25 can push the lock 250 to engage the toothing 24 ( Fig. 2).

[0032] At this point, the frame 9 is locked and can no longer slide on the support 8, and the motion transmission mechanism 10 comes into play in the manner described above. The difference between the forces F1 (which remains constant) and F2 (which increases progressively with the increasing action of the linear actuator 3 and is proportional to the reaction force R exerted by the braking device 2 on the section 7 of the tie rod 4) is transmitted from the support 8, via the frame 9 and the harpoon 23 in the engaged position ( Fig. 3) recorded / derived.

[0033] It should be noted that the carriage 13 moves as the engagement / activation stroke of the braking device 2 progresses over the Fig. 3 and reaches the end of the stroke towards the end of the guide 15, away from the guide 16. During this movement, the connecting rod 18b gradually rotates towards the guide 16, passing (as can be clearly seen in the drawings) a dead center (not shown for simplicity) corresponding to a position of the connecting rod 18b transverse (substantially perpendicular) to the tie rod 4. Therefore, at the end of the stroke, the motion transmission mechanism 10 is in an irreversible position in which the braking device 2 remains engaged (i.e., a force F1 equal to and opposite to the reaction force R remains exerted on the portion 7 of the tie rod 4), without it being any longer necessary to have the linear actuator 3 in operation and activated, i.e. also with a force F1 equal to zero.

[0034] The Fig. 4, Fig. 5 and Fig. 6 schematically show a second embodiment 1b of the parking brake device of the invention. Details similar or identical to those already described are indicated by the same reference numerals for simplicity.

[0035] The device 1b is substantially identical to the parking brake device 1 just described, with the exception that the triggering system 11 is replaced by a triggering system 11b and the force transmission system 12 consists of a harpunism 23b which differs slightly from the harpunism 23 described above.

[0036] More precisely, the harpoon mechanism 23b is identical to the harpoon mechanism 23, except that, in addition to the toothing 24, the locking mechanism 250 with its rib 28, the spring 25 and the connecting pin 26, it further comprises a second spring 29 inserted between the rib 28, to which it is rigidly attached, and the arm 27. This configuration has the advantage that the arm 27 does not "press" on the rib 28 directly, but via the spring 29, which allows the correct functioning of the harpoon mechanism 23b even during negative strokes of the "user" slide 14 (i.e., when the slide is moved towards the end of the guide 16, away from the guide 15).

[0037] Conversely, the trigger system 11b differs slightly from the trigger system 11 described above in that it includes a calibrated spring 22b arranged in the guide 16 at the end opposite the spring 22 and cooperating with a sliding carriage 30 connected to the carriage 14 by a snap coupling 31. In all other respects, the operation of the device 1b is identical to that of the device 1 described above.

[0038] More precisely, the snap coupling 31 is the device responsible for releasing the slide 14 when the predetermined value R is reached. The spring 22b therefore has a dual function: • ensure the correct balance of internal forces to release the 250 harpoon when the brake is released; • return the carriage 14 to its initial configuration when the brake release stroke is over.

[0039] As soon as the spring 22b allows the movement of the carriage 14, the lock 250 can engage the toothing 24; in the meantime, the movement of the carriage 30 is stopped by a stroke end carried by the guide 16 and the snap coupling 31 is consequently released, while the carriage 14, which is carried by the carriage 13 via the connecting rod 18c, continues its stroke towards the guide 15, which allows the articulated device consisting of the lever 18a and the connecting rods 18b and 18c to gradually reach the stroke end ( Fig. 4 and Fig. 5), which causes the connecting rod 18 to pass through a point of kinematic singularity (dead center - connecting rod 18b perpendicular to the tie rod 4), which ensures the kinematic irreversibility of the mechanism 10.

[0040] In both described embodiments, the mechanism 10 with the support 8 and the frame 9 forms a kinematic system with two links, which in Fig. 7 is shown even more clearly.

[0041] The Fig. 8 and Fig. 9 schematically show a third possible embodiment 1c of the parking brake device of the invention. Details similar or identical to those already described are identified by the same reference numerals for simplicity.

[0042] The device 1c is identical to the device 1 described above, except that the trigger system 11 is replaced by a trigger system 11b which, in addition to the spring 22, further comprises a calibrated trigger spring 32 with a predetermined stiffness, which is connected at a first end thereof to the frame 9 and at the opposite end to the end 19 of the lever, but eccentrically with respect to the pin 20. The spring 22 is therefore not indispensable for all embodiments according to this alternative.

[0043] In the position of the beginning of the release of the braking device 2, the device 1c is in the Fig. 8, and the spring 32 prevents the rotation of the lever or element 18a by generating a resisting torque or moment that is resistant with respect to the pivot pin 20. When the force F1 exceeds the preload of the spring 32, the resisting torque generated thereby is overcome and the mechanism 10 "snaps" into the position of Fig. 9, in which the spring 32 rotates slightly and passes a dead center or singularity point. The arm 27 is separated / removed from the rib 28, thereby releasing the latter, and the lock 250 engages the toothing 24 ( Fig. 9). At this point, device 1c functions in the same way as devices 1 and 1b described above.

[0044] In all the devices 1, 1b and 1c described so far, to release the braking device 2 it is sufficient to reverse the translation direction of the linear actuator 3; more precisely, F2 or R are the forces acting on the carriage 14, exclusively as a function of the clamping of the brake, not of the direction of movement.

[0045] With reference to the Fig. 10 and Fig. 11 schematically show two different possible embodiments of the force amplification mechanism 10.

[0046] Fig. Figure 10 shows a force amplification mechanism 10b in which the frame 9 is provided with guides 15 and 16 arranged side by side, not as in the devices of the Fig. 1-9 in series or "one after the other." Within the guides 15, 16, the carriages 13 and 14 are slidably arranged and connected, respectively, to section 6 and section 7 of the drawbar 4, which are therefore also arranged laterally next to one another rather than being aligned along the same direction or axis. The carriages 13 and 14 are interconnected by a lever 33 having a longitudinal slot 34 into which two pins 35 and 36, integral with the carriage 13 and the carriage 14, respectively, slidably engage. The lever 33 is also pivotally connected at one end thereof to a pin 37 integral with the support 8.

[0047] Fig. Figure 11 shows a force amplification mechanism 10c in which the frame 9 is provided with two guides 38 arranged obliquely to each other so as to converge towards the braking device 2 and slidingly receive a pair of identical carriages 39. The carriages 39 are pivotally connected to each other by an articulated quadrilateral consisting of two pairs of levers or connecting rods 40b and 40c, the levers or connecting rods 40b, c being pivotally connected to each other at opposite ends. The pair of connecting rods 40b is connected to the section 6 of the pull rod 4 and thus to the force F1 applied by the actuator 3, while the pair of connecting rods 40c is connected to the section 7 of the pull rod 4 and thus to the braking device 2 to be activated. The sections 6 and 7 are aligned with each other.

[0048] Further embodiments of the described force amplification mechanism 10 are possible and obvious to those skilled in the art and are therefore not described in detail here, although they are included in the invention.

[0049] With reference to the Fig. 12 and Fig. 13, these schematically show two different possible embodiments of the force exchange system 12. Details that are similar or identical to those already described are marked with the same reference numerals for the sake of simplicity.

[0050] Fig. Figure 12 schematically shows a force exchange system 12b comprising a block or wedge 42 supported relatively movably by the frame 9 against the action of a spring 43; the block or wedge 42 can engage with the support 8 by a form coupling, for example, as in Fig. 12, by means of an inclined plane 44 integrally supported by / attached to the support 8. The block or wedge 42 is further connected to the force amplification mechanism 10 via a rigid angle 45 integrally supported by the carriage 13.

[0051] During the initial engagement phases of the parking brake device of the invention, the wedge 42 moves integrally with the frame 9 until it wedges against the inclined plane 44, thereby blocking the sliding of the frame 9; the stop is cushioned by the spring 43. During the release phase of the braking device 2, when the mechanism 10 reverses its kinematic rotation, the rigid bracket 45 abuts the wedge 42, thereby releasing it from the inclined plane 44.

[0052] Fig. Figure 13 schematically shows a force exchange system 12c similar to the system 12 described above, in which the harpoon 23 is replaced by a cam element or "resistance brake" 41 having an elliptical profile, pivotally mounted on the frame 9, and cooperating with the force amplification mechanism 10 (by means of an arm 27 integral with the lever or element 18a and a rib 28 integral with the cam 41) against the action of a spring 25 to prevent interaction by friction or other force coupling with the support 8 until the reaction force R exceeds the predetermined value. When the predetermined value is exceeded, the cam element or resistance brake 41 rotates and "wedges" itself against the support 8, thereby blocking the relative sliding of the frame 9 with respect to the support 8.During the initial engagement phases of the parking brake device of the invention, the wedge 42 moves integrally with the frame 9 until it wedges against the inclined plane 44, thereby blocking the sliding of the frame 9; the stop is cushioned by the spring 43. During the release phase of the braking device 2, when the mechanism 10 reverses its kinematic rotation, the rigid bracket 45 abuts the wedge 42, thereby releasing it from the inclined plane 44.

[0053] From the above, it follows that the triggering system 11 consists of, or at least comprises, a calibrated element selected from the group consisting of one or more elastic elements 22, 32 with a predetermined stiffness, a locking / unlocking element 31 with a snap action, and combinations thereof.

[0054] The calibrated element must also be connected to or part of the force amplification mechanism 12.

[0055] Likewise, the force exchange system 12 is selected from the group consisting of: a harpunism 23 or 23b; a cam 41; a block or wedge 42 capable of engaging with the support 8 by a force coupling; all as described above.

[0056] From the above explanations it is also clear that the force amplification mechanism 10 must always be kinematically coupled to the force exchange system 12 in order to release the latter from the support 8 when the first section 6 of the tie rod 4 is moved by the linear actuator 3 towards the braking device 2 in order to release it gradually.

[0057] It is also clear that the booster mechanism 10 always comprises at least one articulated element (such as the connecting rod 18b, the connecting rods 40b or the lever 33) designed to exceed a dead center immediately before a final stroke position of the linear actuator 3 (and the carriage 13 or the two carriages 39) in which the braking device 2 is fully engaged, in order to ensure kinematic irreversibility of the booster mechanism 10, so that the braking device 2 remains engaged even when the linear actuator 3 is inactive.

[0058] Finally, according to a further feature of the invention, the force amplification mechanism 10 may include a replaceable calibration spring 46 ( Fig. 12) which is arranged on the load, ie on the section 7, and has a predetermined stiffness and can be designed so that, for the same stroke of the linear actuator 3, the same motion transmission mechanism 5, which has a variable transmission ratio, can work with a braking device 2 having reaction forces of different magnitude, simply by replacing the calibration spring 46. This property is illustrated by the diagram in Fig. 15, which shows two curves of force F (the force F2 or the reaction force R) / stroke Y (the available stroke of the carriages or of the section 7 of the tie rod 4), designated K1 and K2 respectively, where K is the stiffness of the spring 46.

[0059] As can be seen, the left segment of the two curves is identical and represents the approach stroke, which is essentially performed at rest, except for the opposing resistances of the mutual interactions between the mechanisms (mainly caused by friction). During this stroke, the braking elements 2 move until contact is established, absorbing the play resulting from brake wear.

[0060] The right-hand segment of the curves represents the clamping stroke, which follows the approach stroke during which the device 1 must exert the required force to ensure the vehicle's parking. As can be seen, by using a calibration spring 46, it is possible to vary the overall stiffness of the mechanism 10 so that the inclination of this part of the curve can be modified without modifying the entire device 1. In other words, the device 1 can be designed to support any load with a stiffness greater than the design stiffness. In the example shown, curve K1 represents the behavior of the mechanism 10 in the absence of the spring 46, while curve K2 represents the behavior of the mechanism 10 in the presence of a spring 46 with a predetermined stiffness K.

[0061] Likewise, the curves of the Fig.14, how it is possible to obtain identical clamping strokes (ΔY) even if the total strokes required to activate the braking device 2 are substantially different, remaining within a predetermined interval.

[0062] The advantages associated with the device described are clear: • The approach stroke, in which lies the ability to adapt to the play of the mechanism, varies as a function of the operating condition; • The behavior of the force curve before the start of the clamping phase makes it possible to carry out this phase at high speed, i.e. without relatively long waiting times for the automatic engagement of the braking device 2, as in known electronic braking devices; • The maximum force F1 max required by the activation device 3 is substantially lower than the maximum force F2max exerted, allowing the use of smaller, less powerful and cheaper actuators; • The clamping stroke section ΔY is of constant length.

[0063] The most important feature of the described devices is the ability to change their operating mode, with different behavior during the approach phase and the clamping phase. The clamping phase, in which it is advantageous to have variable force transmission ratios, is carried out by a mechanism with predetermined kinematic properties. The applicable motion transmission mechanisms can differ only with regard to the transition from one operating mode to the other.

[0064] Thus, all the objectives of the invention are achieved.

Claims

[1] Device (1; 1b; 1c) for braking a vehicle in a parking mode, which is of the type comprising a braking device (2) of the vehicle and a linear actuator (3) designed to actuate the braking device by means of a tie rod (4) inserted between the braking device and the linear actuator; characterized byin that it further comprises a motion transmission mechanism (5) mechanically inserted in series on the tie rod (4) to divide it into a first section (6) connected to the linear actuator (3) and a second section (7) opposite the first section and connected to the braking device (2);wherein the motion transmission mechanism (5) is designed to connect the second section (7) to the first section (6) with a variable transmission ratio, so that a translational movement at a first speed (V1) of the first section (6) following the actuation of the linear actuator (3) reconfigures the motion transmission mechanism (5) to change its transmission ratio and cause a translational movement of the second section (7) at a second speed (V2) which is a function of a reaction force (R) exerted by the braking device (2) on the second section (7) when the braking device is engaged or released; [2] Parking brake device according to claim 1, characterized byin that the motion transmission mechanism (5) comprises: a carrier (8) which is stationary with respect to the first and second sections of the drawbar (4); a frame (9) which is carried by the carrier for sliding movement parallel to the drawbar (4); a force amplification mechanism (10; 10b; 10c) which is carried by the frame (9) and mechanically connects the first and second sections (6, 7) of the drawbar with a selectively variable transmission ratio in order to move the second section (7) as a result of a linear movement of the first section (6); a trigger system (11; 11b) which is designed to selectively activate the force amplification mechanism in order to change its transmission ratio when the reaction force (R) exceeds a predetermined value; and a force exchange system (12; 12b;12c) between the stationary support (8) and the movable frame (9), designed to block the sliding of the movable frame (9) and make it integrally rigid with the support (8); wherein the force amplification mechanism (10; 10b; 10c) is designed to actuate the force exchange system (12; 12b; 12c) following the activation of the force amplification mechanism itself by the triggering system (11; 11b) and to exert on the second portion (7) of the tie rod a force (F2) which increases progressively and is always greater than the reaction force (R), always following the activation by the triggering system; [3] Parking brake device according to claim 2, characterized bythat the force amplification mechanism (10; 10b; 10c) and the force exchange system (12; 12b; 12c), when activated, are designed to deliver a portion of the reaction force (R) to the support (8) so that, while the linear actuator (3) exerts a first force (F1) on the first portion (6) which is substantially constant, the force amplification mechanism exerts a second force (F2) on the second portion (7) of the pull rod which is always greater than the first force and the reaction force. [4] Parking brake device according to claim 2 or 3, characterized byin that the force amplification mechanism (10; 10b; 10c) comprises one or more levers or connecting rods (18) which are articulated to the frame (9) and pivotally connected to one another and / or to at least one pair of carriages (13, 14; 39) which are slidably housed in corresponding guides (15, 16; 38) provided on the frame (9); wherein the first and second portions (6, 7) of the pull rod are held on the at least one or more levers or connecting rods and / or on the carriages. [5] Parking brake device according to claim 4, characterized byin that the triggering system (11; 11b) is designed to lock the force amplification mechanism (10; 10b; 10c) by preventing any relative rotation between the at least one or more levers or connecting rods (18) and the frame (9) until the reaction force (R) exceeds the predetermined value; wherein below the predetermined value, the linear actuator (3) drives the frame (9), which drives the second rod portion (7) by means of the locked force amplification mechanism and therefore with a transmission ratio equal to 1; and wherein above the predetermined value, the linear actuator (3) drives the second rod portion (7), when the frame is locked, by means of a relative movement of the force amplification mechanism (10; 10b, 10c) with respect to the frame, with a transmission ratio that is less than 1 and is progressively reduced as the reaction force increases. [6] Parking brake device according to claim 5, characterized by in that the triggering system (11, 11b) consists of a calibrated element selected from the group consisting of: one or more elastic elements (22, 32) having a predetermined stiffness; a locking / unlocking element (31) with a snap action; wherein the calibrated element is bonded to the force amplification mechanism or is part thereof. [7] Parking brake device according to one of claims 2 to 6, characterized byin that the force exchange system (12; 12b; 12c) is selected from the group consisting of: a harpoon mechanism (23; 23b) comprising a toothing (24) integral with the support (8) and a lock (250) fixed to the frame (9) with limited pivoting capability to cooperate with or be bound to the force amplifying mechanism (10; 10b; 10c) in order to be prevented from engaging the toothing (24) until the reaction force (R) exceeds the predetermined value; a cam element (41) pivotally mounted by the frame (9) and cooperating with the force amplifying mechanism against the action of a spring (25) in order to be prevented from interacting with the support (8) by friction or other force coupling until the reaction force exceeds the predetermined value;a block or wedge (42) movably supported by the frame (9) against the action of a spring (43) and capable of engaging with the support by a form coupling, for example by means of an inclined plane (44), the block or wedge being further connected to the force amplification mechanism by means of a rigid angle (45); [8] Parking brake device according to one of claims 2 to 7, characterized by in that the force amplification mechanism (10; 1b; 10c) is kinematically coupled to the force exchange system in order to release the latter from the support (8) when the first section (6) of the drawbar is moved by the linear actuator (3) towards the braking device (2) in order to release it step by step. [9] Parking brake device according to one of claims 2 to 8, characterized byin that the force amplification mechanism (10; 10b; 10c) comprises at least one joint element (18b) which is designed to exceed a dead center immediately before a final stroke position of the linear actuator (3) in which the braking device (2) is fully engaged, in order to ensure kinematic irreversibility of the force amplification mechanism, so that the braking device (2) remains engaged even when the linear actuator is inactive. [10] Parking brake device according to one of claims 2 to 9, characterized byin that the force amplification mechanism comprises a replaceable calibration spring (46) which has a predetermined stiffness and is designed such that, for the same stroke of the linear actuator (3), the same motion transmission mechanism (5) which has a variable transmission ratio can work with a braking device (2) which has reaction forces of different magnitudes, simply by replacing the calibration spring.

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