Abstract:
A parking brake for a motor vehicle includes: a manual operating lever; a braking device designed to act on brake disks applied on a bevel pinion for transmission of the motion to the wheels of the motor vehicle; and a cable for transmission of the command imposed via the lever on the braking device. The brake is activated either automatically by a hydraulic actuator when the engine of the motor vehicle is turned off, or alternatively, by a manual command imposed by the operator through the lever whether or not the engine of the motor vehicle is running.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a parking brake for a motor vehicle, in particular for a tractor. 
   As is known, a parking brake, referred to commonly as “hand brake,” enables parking of the motor vehicle just by acting on the brake lever located in the cab. Consequently, the operator, even in the case where the engine of the motor vehicle is turned off, must engage the parking brake manually. 
   It has thus appeared desirable to provide a parking brake that may be activated automatically whenever the engine of the motor vehicle is turned off, and which, in any case, may be able to function as a traditional hand brake, and hence can be engaged manually by the operator, even when the engine of the motor vehicle is on. In the latter case, the motor vehicle should not have any gear engaged and, hence, be in neutral. 
   Consequently, a purpose of the present invention is to provide a parking brake that will carry out the aforesaid functions. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described further, by way of example, with reference to the accompanying drawings showing a non-limiting example of embodiment thereof, in which: 
       FIG. 1  illustrates, as a whole, a parking brake according to the invention; 
       FIG. 2  is a front view of a braking device used in the parking brake according to the invention; 
       FIG. 3  is a cross-sectional view according to the line A—A of the braking device of  FIG. 2 ; 
       FIG. 4  is a perspective view of the braking device of  FIGS. 2 and 3 ; 
       FIG. 5  is a perspective view of some elements belonging to the braking device shown in  FIGS. 2–4 ; 
       FIG. 6  is a perspective view, from another angle with respect to that of  FIG. 5 , of some elements belonging to the braking device shown in  FIGS. 2–5 ; 
       FIG. 7  is a perspective view of some elements used in the braking device of  FIGS. 2–6 ; 
       FIG. 8  is a perspective view of some elements used in the braking device of  FIGS. 2–7 ; and 
       FIG. 9  is a plan view of a cam used in the braking device illustrated in  FIGS. 2–8 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a parking brake  100  according to the preferred embodiment. The parking brake  100  comprises a manual operating lever  10  which is pivoted on a fulcrum  11  and is located in a control cab (not illustrated) of a motor vehicle (not illustrated). 
   The parking brake  100  has the purpose of braking a bevel pinion  12 , which meshes with a fitted crown wheel  13 , which transfers the motion to two axle shafts  14  ( FIG. 1  shows only one of them) on which are mounted two drive wheels W (only one shown in  FIG. 1 ) of the motor vehicle. 
   A spindle  15 , unitary connected with the pinion  12 , carries a plurality of brake disks  16  actuated by a braking device  50 , the constructional elements of which will be described in greater detail hereinafter with particular reference to the other annexed figures. In order to operate the braking device  50 , a cable  17  (preferably of a Bowden type, although other cables or even other types of linkages may be used) is disposed between the lever  10  and the braking device  50 . 
   More in particular, the cable  17  ( FIG. 1 ) is connected, on one side, to an eyelet  18  made on the lever  10 , whilst, on the other side, it is connected to an eyelet  51  provided on a relay lever  52 , which forms an integral part of the aforementioned braking device  50  (see further). 
   It is to be understood that in the ensuing description only the items present in the attached drawings that are essential for an understanding of the present invention will be numbered and described. 
   Referring now to  FIGS. 2 and 3 , the braking device  50  comprises a main body  53 , which provides, preferably as a single unit, a plate  53   a  for fixation to the frame (not shown) of the motor vehicle, a cylinder  53   b,  and projecting portions  53   c,  which are designed to support the brake disks  16  (visible only in  FIG. 1 ). Furthermore, the plate  53   a  comprises six through holes  54 , each of which is provided with a respective bolt  55  for fixing to the rear transmission case (not illustrated) of the motor vehicle. The cylinder  53   b  is closed at its bottom end by a disk  56  fixed thereto with means known and not described. 
   As shown in  FIG. 3 , defined within the cylinder  53   b  is a chamber  57  designed to house a piston  58 , on which an adjustment pin  59  rests. One end  59   a  of the adjustment pin  59  is in turn screwed to an internal threaded portion of a bushing  60  provided with a terminal flange  61 . The bushing  60  is housed partially in a through hole  60   a  made in the disk  56  and can slide freely in said through hole  60   a.    
   Between the terminal flange  61  and the disk  56 , a pack of Belleville washers  62  are tightly fitted; the washers  62  carrying out an indirect elastic action on the piston  58  via the bushing  60  and the adjustment pin  59  screwed thereto. Connected to the piston  58  on the other side of the adjustment pin  59  is a stem  64  terminating with a fork  65 . 
   Also the other end  59   b  of the adjustment pin  59  is threaded. Screwed to this end  59   b  is an adjustment detent  63   a  which is variably tightened for reasons that will be explained in greater detail hereinafter. As best shown in  FIGS. 2 and 3 , the aforesaid adjustment detent  63   a  is set between a nut  63  screwed onto the lower end of the adjustment pin  59  and the bottom surface of the disk  56 . 
   To return to the chamber  57 , it may be noted that a portion  57   a  is designed to receive pressurized oil coming from a hydraulic circuit (not shown) of the motor vehicle. More particularly, with reference to  FIGS. 2 and 3 , it will be seen that the pressurized oil is brought to the portion  57   a  by means of a hydraulic line  66 , inflow of oil being controlled by a solenoid valve  67  ( FIG. 2 ). In addition, the oil contained in the portion  57   a  is discharged, when needed (see later), through a port  68 , visible in  FIG. 3 , connected directly to the rear-transmission case (not illustrated) of the tractor. 
   The fork  65  connects the stem  64  via a pin  69  to a crank  70  provided with a circular cavity  71  ( FIG. 2 ) coupled to a shaft  72  (see  FIGS. 2 and 5 ). The coupling of the circular cavity  71  to the shaft  72  is such as to enable free rotation of the crank  70  with respect to the shaft  72 . Between the pin  69  and the shaft  72 , the crank  70  has a seat  73  designed to receive a pawl  74  for the purposes that will be described more fully hereinafter. The pawl  74  is idle with respect to its own seat  73 . 
   As shown in particular in  FIGS. 5–8 , the shaft  72  is coupled to a cam  76  ( FIG. 8 , and shown in greater detail in  FIG. 9 ) by means of splines  75  ( FIG. 7 ). In its central part, the cam  76  comprises a toothed seat  77  ( FIG. 9 ) that is coupled to the splines  75  provided on the shaft  72  in such a way that said cam  76  is angularly fixed with respect to the shaft  72 . Furthermore, on the periphery of the cam  76 , as shown again in  FIG. 9 , there are provided two shaped cavities  78 ,  79 , which have substantially the same shape and are obtained by removing part of the material constituting the periphery of the cam  76  or by casting the cam  76  with the shaped cavities  78 ,  79  formed in the periphery. 
   The shaped cavity  79  has a length L much greater than the diameter D 1  of the pawl  74  (see  FIG. 8 ). In fact, the pawl  74 , in use, is located within the shaped cavity  79 , as shown in  FIG. 9 . 
   The shaft  72  (see  FIGS. 7 and 8 ) is in turn elastically stressed, via the cavities of the cam  76 , by a spring  80  wound in a spiral about the longitudinal axis of symmetry (a) of the shaft  72 . A first end  80   a  of the spring  80  rests on an abutment element unitary provided on the main body  53  (not shown), whilst a second end  80   b  is fixed to a small pin  81  fitted into a seat  81   a  ( FIG. 9 ) made in the cam  76 . The reasons for the presence of the spring  80  will be explained hereinafter. 
   Provided at one end of the shaft  72  is a shaped element  82  (see  FIGS. 4–8 ), rotation of which, as will be seen more clearly hereinafter, packs together the brake disks  16  so as to brake the wheels W. 
   As regards the relay lever  52 , at the end opposite to the one where the eyelet  51  is located, there is provided a circular seat (not visible in the figures) engaged by the shaft  72 . More particularly, the relay lever  52  can rotate freely with respect to the shaft  72 . The cam  76  is thus located between the crank  70  and the relay lever  52 , as shown in  FIGS. 4 and 5 . 
   The relay lever  52  in turn has a pawl  83  (resting idle in its seat  83   a  in the lever  52 ), which, in use, is located within the shaped cavity  78 . The pawl  83  has a diameter D 2  ( FIG. 5 ) smaller than the length L of the shaped cavity  78  so as to enable its free displacement within the shaped cavity  78 . 
   Consequently, two commands can reach the cam  76 . 
   The first command can be imparted by the piston  58 , which, to all effects, forms an integral part of a hydraulic actuator  84  comprising, the elements already described in relation to the cylinder  53   b  (see above). 
   Conversely, the second command can reach the cam  76  via the relay lever  52  operated manually by the operator using, for this purpose, the lever  10  (see  FIG. 1 ). 
   In use, when the engine (not shown) of the motor vehicle is running, also the hydraulic circuit is pressurized. Consequently, from said circuit a certain amount of oil under pressure is deviated, which, through the hydraulic line  66  and the control of the solenoid valve  67  ( FIG. 2 ), fills the portion  57   a  of the chamber  57 . Consequently, the piston  58  moves down, compressing at the same time the pack of Belleville washers  62 . Driven by the stem  64 , by the fork  65  and by the crank  70 , the pawl  74  will be positioned closely to the side  79   a  of the shaped cavity  79  (see  FIGS. 5 ,  7 , and  9 ), so that the only way for the user to engage the parking brake remains the traditional one of acting manually on the relay lever  52  with the modalities referred to previously. Under the condition where the engine is running, the pawl  83  is located closely to the side  78   a  of the shaped cavity  78 . For simplicity reasons,  FIG. 9  shows both pawls  74  and  83  in a middle position of their respective cavities  78 ,  79  although this does not correspond to an operating position. 
   Consequently, in the case where the engine is on, the only way to apply the parking brake of the motor vehicle is to rotate the relay lever  52 , and hence the cam  76 , in the direction indicated by the arrow F 1  (see, for example,  FIG. 2 ). In this case, the pawl  83 , which is already in the proximity of the side portion  78   a  of the shaped cavity  78 , is immediately pushed against the wall  78   a  of the shaped cavity  78 , causing rotation in the direction of the arrow F 1  of the shaft  72  and of the shaped element  82 , which, as has been said, actuates the brake disks  16 . Such a rotation is enabled because pawl  74  is close to wall portion  79   a  and thus there is a considerable gap between said pawl  74  and the wall portion  79   b.    
   In other words, when the engine is on, each of the pawls  74  and  83  is located in an almost extreme upward position of its own shaped cavity  79  and  78 , respectively. In this condition, when the brake is operated manually, the pawl  83  will immediately contact the top portion  78   a  and will cause rotation of the cam  76  in the direction of the arrow F 1 . This is possible because there is a sufficient amount of space between the other pawl  74  and the bottom portion  79   b  of the shaped cavity  79 . When the engine is off and the handbrake is not operated, the pawl  74  will move upward and immediately contact the top portion  79   a  (on account of the pressure drop in the cylinder) and will set the cam  76  again in rotation in the direction of the arrow F 1 . This is again rendered possible by the fact that there is a sufficient space between the pawl  83  and the bottom portion  78   b  of the shaped cavity  78 , since at the instant when the engine is still on, the pawl  83  is located close to the wall portion  78   a.    
   If the operator so desires, he can have both systems active at the same time. With the engine off, and consequently the brake on by the action of the pawl  74 . the operator is still able to also put the handbrake on, by pulling the lever  51  lever  52  in the direction of an arrow F 1  and thereby moving pawl  83  towards and in contact with wall portion  78   a . At this instance, both pawls  74  and  83  are in contact with the respective wall portions  79   a  and  78   a  and braking is thus ensured both by the hydraulic system and the mechanical system. Should the engine be switched on again, the pawl  74  will release wall portion  79   a  and move in the direction of wall portion  79   b . the cam  76  however will not rotate because it is prevented from doing so by pawl  83  still pressing against wall portion  78   a . The brake therefore will remain on until the handbrake lever  10  also has been released. 
   As appears again from  FIG. 9 , the bottom ends of the shaped cavities  78 ,  79  are slightly curved because said cavities  78 ,  79  are preferably made with a ball-end two-fluted mill with a circular path. In so far as the path of the two pawls  83  and  74 , respectively, is circular, there consequently is no need for the bottom ends to be rectilinear, as long as the pawls  74  and  83  do not interfere with the slightly raised middle portion of the respective cavities  78  and  79  during their circular movement therethrough. 
   When the operator wants to disengage the hand brake (once again with the engine on) all he has to do is to release the lever  10  ( FIG. 1 ), and the system will return to the initial position thanks to the elastic action exerted by the spring  80  on the cam  76 . In this case, both the relay lever  52  and the cam  76  will rotate in the direction identified by the arrow F 2  (see for example  FIG. 2 ). 
   Conversely, in the case where the engine is turned off, the hydraulic circuit is connected to the discharge. Consequently, also the pressurized oil present in the portion  57   a  is discharged through the port  68 . Hence, the pack of Belleville washers  62  is allowed to push the bushing  60  upwards, as well as the adjustment pin  59 , the piston  58 , the stem  64 , the fork  65 , the crank  70 , and the pawl  74 , which will exert a thrust on the wall of the top portion  79   a  of the shaped cavity  79  ( FIG. 9 ). Also in this case, the cam  76  will turn in the direction of the arrow F 1  and will engage the brake according to what has been said previously. It is to be noted that the action of the Belleville washers  62  overcomes the oppositely directed action of the spring  80 . 
   A further function of the parking brake  100  is the park-lock function. Acting on the solenoid valve positioned in point  67 , it is possible to discharge the pressurized oil present in the portion  57   a  through the port  68  obtaining the same result as in the case described previously. This is a particular function that is required from the motor vehicle with the engine running when the driver wants to be certain that the vehicle will remain still in particular conditions of maneuver without having to operate the lever  10  in the cab. 
   In the park-lock situation, to disengage the parking brake, it is sufficient to re-supply the solenoid valve with electrical current in order to send pressurized oil again into the portion  57   a.    
   Consequently, it may be stated that, with the parking brake  100  forming the subject of the present invention, the system for blocking the wheels W will be activated automatically whenever the engine of the motor vehicle is turned off or else when the signal to the control solenoid valve of the device is intentionally interrupted, whilst there will always be the possibility of engaging the hand brake manually both with the engine off and with the engine on. In addition, it should be noted that, both when the actuator  84  goes into action and when the relay lever  52  is pulled manually, the same cam  76  provided with the two shaped cavities  78 ,  79  is used. 
   If there were a breakdown such as to cause the engine to be turned off, or some fault of the hydraulic circuit, or else a failure of a signal to arrive to the solenoid valve for control of the braking device, the oil would be discharged by the portion  57   a  through the port  68 , and the hand brake would remain engaged owing to the action of the actuator  84 . 
   However, in this case, to enable the towing of the motor vehicle, the hand brake can be disengaged by resorting to an emergency device  85 , which basically comprises the nut  63  and the adjustment detent  63   a  (see for example  FIG. 3 ). If the adjustment detent  63   a  is screwed on the threading provided on the end  59   b  until it presses against the bottom of the disk  56 , the emergency pin  59  will be pulled down, allowing the other elements connected thereto to move downwards, including the cam  76 , which will rotate in the direction of the arrow F 2 . In this connection, it should be noted that the permanent contact of the tip of the adjustment pin  59  with the bottom wall of the piston  58  is ensured by the presence of the return spring  80  which will cause a return action on respectively the cam  76 , the pawl  74 , the fork  65 , the stem  64 , and ultimately the piston  58 , which, consequently, will always remain pressed against the tip of the adjustment pin  59 . 
   Advantages of the present parking brake are the following: 
   assurance that, when the engine is off, the motor vehicle will, in all cases, have its parking brake automatically engaged; and 
   commands unified in a single cam, both in the case of automatic engagement of the parking brake and in the case of manual operation via a lever rotated by the operator in the cab.