Abstract:
The present invention concerns a parking lock for combination with a service brake actuator for a vehicle, preferably a heavy road vehicle. The service brake actuator comprises a fluid actuated piston having a piston rod. The parking lock surrounds the piston rod of the service brake. The parking comprises a pneumatically or hydraulically actuated locking means. The parking lock has a locking mechanism and an actuating mechanism. The piston rod is free to move in axial, radial and angular directions in relation to the locking mechanism.

Description:
[0001]     This application is a continuation of pending International Patent Application PCT/SE2003/001093 filed on Jun. 26, 2003 which designates the United States and claims priority from Swedish Patent Application No. 0202095-6 filed on Jul. 4, 2002. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention concerns a parking lock for combination with a service brake actuator for a vehicle, preferably a heavy road vehicle. The service brake actuator comprises a fluid actuated piston having a piston rod.  
       BACKGROUND OF THE INVENTION  
       [0003]     A parking braking of a vehicle may be performed by means of a parking lock, integrated in the service brake actuator to form a unit therewith. Such a unit is known for use on trucks and buses. As is well known in the art, the parking brake may for example be a so-called spring brake actuator or an actuator with fluid actuation. The fluid normally used on heavy road vehicles is compressed air, but hydraulic fluid may equally well be utilized.  
         [0004]     A special type of parking lock is the so-called lock actuator, with which the present invention is concerned. The function of a lock actuator is to lock the service brake actuator or parts thereof in an applied condition, in such a way that the service brake actuator will stay locked even in the absence of any fluid pressure. Thus, a parking brake is obtained.  
       SUMMARY OF THE INVENTION  
       [0005]     The parking lock according to the present invention fulfils different requirements with regard to simple and reliable design, space requirement and excellent manoeuvrability. This is achieved according to the invention by a parking lock surrounding a piston rod of a service brake actuator. The parking lock comprises a number of jaws or other locking means moveable in a radial direction.  
         [0006]     The locking means of the parking lock are moved in and out of engagement with the piston rod by means of fluidly activated parts, i.e. pneumatically or hydraulically activated parts, and a number of springs acting in a direction to urge the locking means away from or towards the piston rod.  
         [0007]     By means of the parking lock the brakes of the vehicle may be locked in an actuated position, e.g. in that grooves of the piston rod and jaws are engaged with each other. The reaction force of the brake keeps up said engagement even when the service brake actuator is deactivated. Thus, it could be said that the parking lock includes a self-locking locking means. A spring, a pressurised chamber or the like in the brake actuator urges the brake actuator piston to resume a start position. To release the parking lock the service brake actuator has to apply a force on the piston rod, having a magnitude being enough to unload the self-locking engagement between the piston rod and the jaws or other locking means.  
         [0008]     The parking lock comprises in principal a locking mechanism and an actuating mechanism. The piston rod for brake actuation is free to move in axial, radial and angular directions in relation to the locking mechanism. The locking mechanism is formed of a locking sleeve and further parts received on or in connection with the locking sleeve.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The invention will be described further below by way of an example and with reference to the drawings below. In the drawings:  
         [0010]      FIG. 1  is a cross-sectional view of a service brake including a parking lock according to the present invention in an inactivated position;  
         [0011]      FIG. 1   a  is an enlarged cross-sectional view of the part marked A in  FIG. 1 ;  
         [0012]      FIGS. 2 and 2   a  are cross-sectional views corresponding to  FIGS. 1 and 1   a  with the parking lock in a locking position;  
         [0013]      FIG. 3  is a plan view of the parking lock;  
         [0014]      FIGS. 4 and 4   a  are cross sectional views corresponding to  FIGS. 1 and 1   a  of an alternative embodiment of the present invention with the parking lock in an inactivated position;  
         [0015]      FIGS. 5 and 5   a  are cross sectional views of the embodiment of  FIGS. 4 and 4   a  with the parking lock in a locking position; and  
         [0016]      FIGS. 6 and 7  are cross-sectional views of a further embodiment of a parking lock, using the same type of service brake as in the embodiment of  FIGS. 1 and 2  and showing an inactivated and locking position, respectively. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]     In this description, expressions like “right”, “left”, “upper”, “lower” and other expressions concerning directions are with reference to the Figs. being referred to. A person skilled in the art realises that in use the different parts may have other orientations. The expressions “axial”, “radial” and similar expressions are with reference to a central axis of the parking lock. The parking lock according to the invention is received on a brake caliper (not shown). The parking lock is fixed to the caliper by means of screws, or any other suitable fastening means. As indicated in  FIGS. 1, 2 ,  4  and  5  the parking lock is also fixed to a service brake actuator  18 .  
         [0018]     The service brake actuator  18  is conventional and is only briefly described here. The exact design of the service brake actuator forms no part of the present invention. In a housing comprising a lower part  19  and a cover part  20  there is a piston  22  and a piston rod  2 , from which a pushing brake force may be delivered to further, not shown brake elements. Such brake elements may be part of a compressed air brake system for a heavy road vehicle, such as a truck or a bus. Normally, the piston rod  2  acts on a lever (not shown).  
         [0019]     In the shown case the service brake actuator  18  is of the diaphragm type, which means that a diaphragm  21  in contact with the piston  22  is clamped between the two housing parts  19 ,  20 . Compressed air can be admitted to a service brake chamber at the diaphragm  21  through an inlet (not shown).  
         [0020]     A piston return spring  23  is arranged between the piston  22  and the lower housing part  19 . The main purpose of said piston return spring  23  is to bring the diaphragm  21  back to its starting position. A bellows  24  may be arranged between the piston rod  2  and the lower housing part  19  protecting the interior of the parking lock.  
         [0021]     At the admission of compressed air through the inlet the diaphragm  21 , the piston  22  and thus the piston rod  2  will be pushed to the right as shown in  FIG. 1  for accomplishing a brake actuation in a way well known in the art. A return stroke, when the compressed air pressure is again decreased, is brought about by the reaction force of the brake.  
         [0022]     The parking lock of  FIGS. 1, 1   a ,  2  and  2   a  comprises an outer housing  1 , a locking sleeve  5 , two springs  4 ,  9 , an operating body  6 , a number of jaws  35 , an operating sleeve  14 , an operating washer  16 , a piston  7 , a cap  12 , bearings  17 , a chamber A and a number of further washers. The jaws  35  are received in the locking sleeve  5 , with the operating sleeve  14  placed over the jaws  35 . One of the springs is an inner spring  4  placed between two locking washers received on the locking sleeve  5  and the housing  1 , respectively. The other, outer spring  9  is placed between a flange of the operating body  6  and the cap  12 .  
         [0023]     The parking lock is formed of a locking mechanism and an actuation means  6 ,  7 ,  9 . The locking mechanism comprises the locking sleeve  5  and different parts received on or in connection with the locking sleeve  5 . The piston rod  2  is free to move in axial, radial and angular directions in relation to the locking mechanism.  
         [0024]     The outer spring  9  will be compressed in that the piston  7  and the operating body  6  are pressed to the right (as seen in the FIGS.), when the chamber A is exposed to a pressure sufficient to overcome the force of the spring  9 . The chamber A is defined by an annular recess, formed in the housing  1  and the piston  7 . The piston  7  is received in the recess with seals  8  in contact with the walls of the recess. The piston  7  is free to move axially in the recess.  
         [0025]     The locking sleeve  5 , which is received on the piston rod  2  by means of plain bearings  17 , is pressed against the housing  1  by the inner spring  4 , via a washer  13 . Said washer  13  has a spherical connection with the locking sleeve  5  and may move in a radial direction in relation to the housing  1 . The operating sleeve  14  may be displaced in an axial direction on the locking sleeve  5  and is spherically connected to the operating washer  16 . The function of the spherical connections is to assist in taking up any radial and angular movement caused by the lever (not shown) of the brake. The movement of the lever is rotational and this movement is transformed to a radial movement for the locking sleeve  5 . The operating sleeve  14  acts on the jaws  35  by means of the outer end of the sleeve  14  forming a flange. Said outer end of the locking sleeve  14  covers part of the jaws  35 .  
         [0026]     The function of the embodiment of FIGS.  1  to  2   a  is as follows. During normal operation the chamber A is constantly exposed to a positive pressure, which keeps the parking lock inactive. Normal service braking may be performed without influence of the parking lock mechanism. This operational position of the parking lock is shown in  FIG. 1   a.    
         [0027]     When the parking lock is to be applied, the service brake is first drawn to the desired parking lock force. The positive pressure in chamber A is then relived, whereby the piston  7  and the operating body  6  are pressed to the left, by means of the outer spring  9 . After a short distance also the operating sleeve  14  is brought along by means of the operating washer  16 , whereby the jaws  35  are forced into contact with the piston rod  2 . When the pressure of the service brake is relived the braking force is kept by the parking lock mechanism. When the pressure is relived the piston  22  of the service brake mechanism will be pressed to the left by the spring  23 , at the same time as the piston rod  2  is locked by the parking lock mechanism. This operation position of the parking lock is shown in  FIG. 2   a . As shown in  FIG. 2   a  the locking of the piston rod  2  is accomplished by means of contact between grooves  3  and  10  of the piston rod  2  and jaws  35 , respectively. The engagement between the grooves  3 ,  10  of the piston rod  2  and the jaws  35  is a self-locking engagement supported by the reaction force of the brake. In one embodiment (not shown) the grooves  3 ,  10  have the form of threads.  
         [0028]     To inactivate the parking lock the service brake actuator  18  is actuated with a braking force exceeding the braking force of the parking lock and the chamber A is pressurised. Hereby, the grooves  10  of the jaws  35  will be released from the grooves  3  of the piston rod  2 . The jaws  35  will then be urged radially outwards by means of the return springs  11  arranged between adjacent jaws  35 .  
         [0029]     In  FIG. 3  the function of the jaws  35  is shown schematically. The jaws  35  are received between the locking sleeve  5  and the operating sleeve  14  in the embodiment of  FIGS. 1 and 2 . The piston rod  2  from the service brake actuator  18  goes centrally through the parking lock. The jaws  35  encircle the piston rod  2  in the parking lock.  
         [0030]     The parking lock is slidably received on the piston rod  2  by means of plain bearings  17  or the like. In another embodiment (not shown) there are no bearings but the parking lock is slidably received directly on the piston rod  2 . In this case the material and surfaces of the parking lock and the piston rod may be adapted to make the sliding possible.  
         [0031]     In the shown embodiment the parking lock comprises three jaws  35 , which are equally distributed to together form a ring in plan view. In other embodiments the number of jaws  35  vary. Preferably 3 to 6 jaws  35  are used. The jaws  35  are urged radially outwards by means of jaw return springs  11  placed between adjacent jaws  35 . In an alternative embodiment one single, annular pressure spring placed in a groove (not shown) urges the jaws  35  outwardly. The jaws  35  together form a conical surface  15 , which is in contact with a conical surface  32  of the locking sleeve  5 . Movement between the jaws  35  and the locking sleeve  5  follows said conical surfaces  15 ,  32 .  
         [0032]     A person skilled in the art realises that the jaws  35  may be replaced by any other locking means capable of fulfilling the same function. Such other locking means may include but are not limited to balls or rollers wedged between the locking sleeve  5  and the piston rod  2 .  
         [0033]     The embodiment of  FIGS. 4, 4   a ,  5  and  5   a  will now be described briefly. In this embodiment the service brake actuator  18  is slightly modified, compared to the other shown embodiments. Thus, in this embodiment a diaphragm  28  is acting on a piston  26 . A cup spring  27 , urging the piston  26  to the right, is kept compressed in that the piston  26  and a piston washer  25  are pressed to the left, by a positive pressure in a chamber C. The piston  26  acts on the cup spring  27  by means of a surface  26   a . When the cup spring  27  is fully compressed the piston  26  will abut the cup spring  27  at a surface  26   b . The cup spring  27  is fixed to the housing  19  of the service brake actuator  18  by means of a locking ring  41 . In other respects the service brake actuator  18  of FIGS.  4  to  5   a  functions in the same way as described above for the previous embodiment.  
         [0034]     The parking lock is formed of a locking mechanism and an actuation means  6 ,  25 ,  26 ,  27 . The locking mechanism comprises the locking sleeve  5  and different parts received on or in connection with the locking sleeve  5 . The piston rod  2  is free to move in axial, radial and angular directions in relation to the locking mechanism.  
         [0035]     The locking sleeve  5  is received on the piston rod  2  by means of plain bearings  17 . The locking sleeve  5  is pressed against the piston washer  25 , by means of a washer  13 . The washer  13  has a spherical connection to the locking sleeve  5  and may be displaced radially in relation to the piston washer  25 . An operating body  6  receives two springs, one inner spring  4  and one operating spring  29 . The inner spring  4  is received between an inner end of the operating body  6  and a locking washer  36 . An operating sleeve  30  is received axially displaceable on the locking sleeve  5 . The operating sleeve  30  acts on the jaws  35  by means of the outer end of the operating sleeve  30  forming a flange. Said flange covers parts of the jaws  35 . The operating sleeve  30  is furnished with two locking rings  31 , between which the biased operating spring  29  and a washer  33  act.  
         [0036]     One end of a diaphragm  28  is fixed to the outside of the operating body  6 , by means of a cap  37 . The end of the diaphragm  28  is fixed to the operating body  6  at the outer (right according to the FIGS.) end of the park lock, between the operating body  6  and the cap  37 . The other end of the diaphragm  28  is fixed at the service brake actuator  18  by means of the cap  37 . The chamber C is formed in the space between the diaphragm  28  and the cap  37 .  
         [0037]     During normal operation, i.e. when the parking lock is not to be applied, the chamber C is exposed to a constant positive pressure. The positive pressure of chamber C keeps the parking lock inactive and the service brake may be used without influence of the parking lock mechanism.  
         [0038]     To activate the parking lock the service brake is first drawn to a desired parking lock force. Then the positive pressure of chamber C is relived, which means that the piston  26  and piston washer  25  are pressed to the right by means of the cup spring  27 . The locking sleeve  5  is brought along in said movement to the right. After a short distance the washer  33  will abut the operating body  6 , forcing the jaws  35  into contact with the piston rod  2 , by means of the operating spring  29 . This operating position is indicated in  FIG. 5   a . When the service brake pressure is relived, the brake force is kept by means of the parking lock mechanism and the cup spring  27 . In this case the cup spring  27  will be in series with the parking lock force and will reduce variations of the parking lock force. Such variations are caused e.g. by the cooling of the brake disc.  
         [0039]     To inactivate the parking lock the service brake actuator  18  is actuated with a braking force exceeding the braking force of the parking lock and chamber C is pressurised. Hereby, the grooves  10  of the jaws  35  will be released from the grooves  3  of the piston rod  2 . The jaws  35  will then be urged radially outwards by means of the return springs  11  arranged between adjacent jaws  35 , as indicated in  FIG. 4   a.    
         [0040]     In the embodiment of  FIGS. 6 and 7  the service brake actuator  18  has the same general design as for the embodiment of  FIGS. 1, 1   a ,  2  and  2   a . Thus, the service brake actuator  18  will not be described once again here.  
         [0041]     The parking lock of  FIGS. 6 and 7  comprises an outer housing  39 , a mounting ring  38 , a locking sleeve  5 , a spring  4 , a number of jaws  35 , an operating sleeve  14 , an operating washer  16 , a piston  39 , a locking washer  36 , a further washer  13  and a chamber B.  
         [0042]     The parking lock is formed of a locking mechanism and an actuation means  39 . The locking mechanism comprises the locking sleeve  5  and different parts received on or in connection with the locking sleeve  5 . The piston rod  2  is free to move in axial, radial and angular directions in relation to the locking mechanism.  
         [0043]     The parking lock is received in an outer housing  40 , which housing  40  is attached to the service brake actuator  18  by means of a mounting ring  38 . The jaws  35  are received in the locking sleeve  5 , with the operating sleeve  14  placed over the jaws  35 . The spring  4  is placed between the piston  39  and the locking washer  36 . The locking washer  36  is held at a recess on the outer side of the locking sleeve  5 .  
         [0044]     When a pressure, of a magnitude to overcome the force of the spring  4 , is introduced into the chamber B, the piston  39  will go to the left as viewed in  FIGS. 6 and 7 . The chamber B is defined by the inner (left as viewed in the Figs.) end of the piston  39  and the outer housing  40 , to the right of said inner end of the piston  39 . The outer end of the piston  39  is received in a central opening of the outer housing  40 . The piston  39  is free to move axially in the opening of the outer housing  40 . Normally, a seal is placed between the opening of the outer housing  40  and the piston  39 . The inner spring  4  urges the piston  39  against the outer housing  40 .  
         [0045]     The operating washer  16  is received axially slideable on a spherical surface of the operating sleeve  14 . The inclination of the contact surfaces of the operating washer  16  and the operating sleeve  14  is such that washer  16  is free to move to the right in relation to the operating sleeve  14 , as viewed in the Figs. A washer  13  is placed between the mounting ring  38  and the locking sleeve  5 . The washer  13  has a spherical connection with the locking sleeve  5  and may move in a radial direction in relation to the mounting ring  38 .  
         [0046]     The function of the embodiment of  FIGS. 6 and 7  is as follows. During normal operation the chamber B is not pressurised, i.e. the spring  4  will hold the piston  39  against the inner housing  40 . The spring  4  constantly keeps the locking sleeve  5  in contact with the washer  13  and said washer  13  in contact with the mounting ring  38 . The washer  13  and the operating washer  16  are spherically pivoted. This will keep the parking lock inactivated, as indicated in  FIG. 6 . Normal service braking may be performed without influence of the parking lock mechanism.  
         [0047]     When the parking lock is to be applied, the service brake is first drawn to the desired parking lock force. The chamber B is then pressurised to a pressure high enough to overcome the force of the inner spring  4 . The piston  39  is moved to the left by the pressure of the chamber B. After a short distance the piston  39  will go into contact with the operating washer  16 . The operating washer  16  will move the operating sleeve  14  to the left. When the operating sleeve  14  goes to the left, the jaws  35  will be forced into contact with the piston rod  2 . It is grooves  3  and  10  of the piston rod  2  and the jaws  35 , respectively, which will go into contact. The jaws  35  are forced into contact with the rod  2  in that the conical surfaces  15  of the jaws  35  will glide on the conical surface  32  of the locking sleeve  5 , in the same way as indicated above for the other embodiments. The engagement between the grooves  3 ,  10  of the piston rod  2  and the jaws  35  is a self-locking engagement supported by the reaction force of the brake. This operating position of the park lock is shown in  FIG. 7 .  
         [0048]     To inactivate the parking lock the service brake actuator  18  is actuated with a braking force exceeding the braking force of the parking lock and the chamber B is depressurised. Hereby, the grooves  10  of the jaws  35  will be released from the grooves  3  of the piston rod  2 . The jaws  35  will then be urged radially outwards by means of the return springs  11  arranged between adjacent jaws  35 . 
     1 . outer housing      2 . piston rod      3 . groove      4 . inner spring      5 . locking sleeve      6 . operating body      7 . piston      8 . seal      9 . outer spring      10 . groove      11 . return spring      12 . cap      13 . washer      14 . operating sleeve      15 . conical surface      16 . operating washer      17 . plain bearing      18 . service brake actuator      19 . housing part      20 . housing part      21 . diaphragm      22 . piston      23 . return spring      24 . bellows      25 . piston washer      26 . piston      26   a . surface      26   b . surface      27 . cup spring      28 . diaphragm      29 . operating spring      30 . operating sleeve      31 . locking ring      32 . conical surface      33 . washer      34 . locking washer      35 . jaw      36 . locking washer      37 . cap      38 . mounting ring      39 . piston      40 . outer housing     A. chamber     B. chamber     C. chamber