Abstract:
In a parking brake arrangement in an electrically operated brake, a rotary movement of an electric motor is transformed into a translational brake applying movement. An engageable or disengageable elasticity spring for providing a parking brake force when engaged is so arranged in the force transmitting chain that its elasticity is in series with the elasticity of the brake.

Description:
[0001]     This application is a continuation of pending International Patent Application No. PCT/SE02/02363 filed Dec. 16, 2002 which designates the United States and claims priority of pending Swedish Patent Application No. 0104279-5 filed Dec. 18, 2001. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a parking brake arrangement in an electrically operated brake, in which a rotary movement of an electric motor is transformed into a translational brake applying movement.  
       BACKGROUND OF THE INVENTION  
       [0003]     There is a tendency to employ an electric drive motor as the means for operating a brake actuator for a vehicle. In the present case this electric motor is used for operating a disc brake, especially but not exclusively for a heavy road vehicle, such as a truck, trailer, or bus. This disc brake contains means for transforming the rotational movement of the electric motor into a translational movement of a brake pad.  
         [0004]     The electric motor can be used not only for service braking but also for parking braking. In the latter case the brake is applied by the electric motor to a force which is suitable for safely holding the vehicle in the parked position and is held in this applied condition.  
         [0005]     A problem may, however, be encountered in that the brake disc and certain portions of the disc brake may have been heated to considerable temperatures during the preceding service braking. When the heated members gradually cool off and return to normal size after their heat expansion, the parking brake force may decrease to such a level that the safe parking braking may be jeopardized.  
       SUMMARY OF THE INVENTION  
       [0006]     The problem of ensuring a satisfactory parking braking when the heated members cool off may according to the invention be solved by an elasticity spring, which is so arranged in the force transmitting chain that its elasticity is in series with the elasticity of the brake and is adapted to provide a rotary parking brake force.  
         [0007]     The elasticity spring is preferably loaded at a service brake application of the brake and then locked until released for parking brake application.  
         [0008]     A practical embodiment is characterized in that a transmission sleeve rotatably biased by the elasticity spring is rotatably arranged in the rotary force transmitting chain in the housing of the brake and is held to the housing at service braking but is disengaged therefrom at parking braking.  
         [0009]     Hereby, the force of the elasticity spring is transmitted via the transmission sleeve to the brake pad only at parking braking. The elasticity spring may provide a force which is suitable for parking braking.  
         [0010]     For practically accomplishing the engagement and disengagement of the transmission sleeve there is a locking rod, which is arranged in the housing for engagement with the transmission sleeve by means of an electromagnet and disengagement therefrom by means of a compression spring.  
         [0011]     The elasticity spring may either be a compression spring connected to the transmission sleeve by means of a sleeve arm or a clock spring or spiral spring arranged in the housing with its outer end attached to the housing and its inner end attached to the transmission sleeve. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The invention will de described in further detail below under reference to the accompanying drawings, in which  
         [0013]      FIG. 1  is a sectional side-view and  FIG. 2  is a section along the line II-II in  FIG. 1  of a first embodiment of an electric disc brake according to the invention,  
         [0014]      FIG. 3  is a sectional side-view and  FIG. 4  is a section along the line IV-IV in  FIG. 3  of a second embodiment of an electric disc brake according to the invention, and  
         [0015]      FIG. 5  is a sectional side-view and  FIG. 6  is a section along the line VI-VI in  FIG. 5  of a third embodiment of an electric disc brake according to the invention. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0016]     The first embodiment according to  FIGS. 1 and 2   
         [0017]     A disc brake according to the invention is very schematically shown in  FIG. 1 . A disc brake caliper or housing  1  is to be mounted astraddle of a brake disc  2  on a vehicle axle. The vehicle is preferably but not exclusively a heavy road vehicle, such as a bus, a truck, or a trailer.  
         [0018]     An electric motor  3  is attached to the caliper  1 . Its drive shaft  4 , which may be rotated in either direction by the motor  3 , is connected to a coupling  5  of the kind that keeps its outgoing coupling shaft  6  non-rotatable or braked, in a brake release direction, when no current is supplied to the motor  3 .  
         [0019]     The coupling shaft  6  is provided with a gear  7  in gear engagement with a planet gear  8 , which is also in gear engagement with a transmission sleeve  9  to be described below. The planet gear  8  is rotatably arranged on an intermediate gear  10 , rotatably arranged in the caliper  1 . By this exemplary arrangement the rotational speed of the intermediate gear  10  is reduced in relation to that of the coupling shaft  6 . Other reduction arrangements, for example in more than one stage, are possible.  
         [0020]     The intermediate gear  10  is in gear engagement with a thrust rod gear  11  of each of two thrust rods  12 . The thrust rods  12  have the general function of transforming the ingoing rotational movement of the gear  11  into an outgoing linear movement of a part connected to a first disc brake pad  13  at one side of the brake disc  2 . At the other side of the brake disc  2  there is a second disc brake pad  14  connected to the caliper  1 , which in this case is of the so called floating type, i.e. it is mounted for certain movements perpendicularly to the disc  2 . The caliper may, however, equally well be of the fixed type.  
         [0021]     With the briefly described design the first disc brake pad  13  will be applied against the brake disc  2 , when the motor  3  is rotated in its application direction. At a motor rotation in the opposite direction the disc brake pad  13  will be withdrawn from the brake disc  2 .  
         [0022]     The transmission sleeve  9  is rotatable in the caliper  1  and is provided with a sleeve arm  9 ′ extending out of the caliper  1  trough a slot  1 ′ having an end shoulder  1 ″, against which the sleeve arm  9 ′ is shown to be resting in  FIG. 2 .  
         [0023]     An elasticity spring  15  fixedly supported to the left in  FIG. 2  (in a way not shown) exerts a bias to the right on the sleeve arm  9 ′.  
         [0024]     A locking rod  16  axially movably arranged in the caliper  1  is arranged for locking cooperation with a corresponding opening  9 ″ in the transmission sleeve  9 . The locking rod  16  is brought into engagement with the opening  9 ″ by an electromagnet  17  when energized and biased by a compression spring  18  in the return direction.  
       First Service Brake Application  
       [0025]     Initially, for example after the installation of new brake pads  13  and  14 , the locking rod  16  is out of engagement with the transmission sleeve  9  and the elasticity spring  15  is released, so that the transmission sleeve is rotatably biased to the right in  FIG. 2 .  
         [0026]     The disc brake is applied in a normal way by rotation of the electric motor  3  in its application direction. During this application the electromagnet  17  is energized, so that the locking rod  16  strives for getting into engagement with the transmission sleeve  9 .  
         [0027]     When the brake force reaches a level corresponding to the bias of the elasticity spring  15 , the spring is compressed, and the transmission sleeve  9  is rotated, until the sleeve arm  9 ′ engages the slot shoulder  1 ″ and the locking rod  16  engages the transmission sleeve  9 .  
         [0028]     At a subsequent release of the brake to a force below the bias of the elasticity spring  15 , the locking rod  16  will be clamped in an engaged position in the transmission sleeve  9 , which means that the engaged, shown position will remain even at a current loss for the brake system.  
       Normal Brake Operation  
       [0029]     In normal operation the different parts are in the positions shown in  FIGS. 1 and 2  with the electromagnet  17  energized and the locking rod  16  in locking engagement with the transmission sleeve  9 . Also, the elasticity spring  15  is in a compressed state.  
         [0030]     The disc brake is applied and released by rotating the electric motor  3  in either direction (without any influence from the elasticity spring  15 , as the transmission sleeve  9  is held stationary).  
       Parking Brake Application  
       [0031]     The disc brake is applied by the electric motor  3  to a force which is somewhat higher than the bias of the elasticity spring  15 , and the electromagnet  17  is de-energized.  
         [0032]     In this situation the compression spring  18  is able to withdraw the locking rod  16  from engagement with the transmission sleeve  9 .  
         [0033]     The elasticity spring  15  is now in the force transmitting chain. If the parking brake force decreases under the force of the elasticity spring  15 , only the elasticity spring will provide the braking force.  
         [0034]     The movement of the locking rod  16  can be monitored by the electronics of the brake system, so that it can be verified that the correct force has been attained and that extra elasticity is available. Differently stated, the fact that the locking rod  16  is withdrawn or pulled out (under the bias of the compression spring  18 ) is verification that the parking brake functions and that a brake force is available.  
       Parking Brake Release  
       [0035]     When the parking brake is to be released the electromagnet  17  is energized. The brake is applied to a force which is somewhat higher than the bias of the elasticity spring  15 , and the locking rod  16  engages the the transmission sleeve  9 .  
       The Second Embodiment According to FIGS.  3  and  4   
       [0036]     The main difference between the second and the first embodiments is that the former has an elasticity spring in the form of a clock spring or spiral spring instead of a compression spring.  
         [0037]     Parts that are similar in the two embodiments have the same reference numerals. This is true for the disc brake caliper  1 , the brake disc  2 , the electric motor  3 , the drive shaft  4 , the coupling  5 , the coupling shaft  6 , the intermediate gear  10 , the trust rod gears  11 , the thrust rods  12 , the disc brake pads  13  and  14 , the locking rod  16 , the electromagnet  17 , and the compression spring  18 .  
         [0038]     A modified transmission sleeve is given the reference numeral  9 A, and the modified elasticity spring is given the reference numeral  15 A.  
         [0039]     In this embodiment the rotational speed reduction from the coupling shaft  7  to the intermediate gear  10  is performed by a gear box  19 , preferably a planetary gear box, in the transmission sleeve  9 A.  
         [0040]     The transmission sleeve  9 A has a protrusion  9 A′, extending into a caliper slot  1 A′ having an end shoulder  1 A″, and an opening  9 A″ for the locking pin  16 .  
         [0041]     The outer end of the elasticity spring  15 A is attached to the caliper  1  and the inner end to the transmission sleeve  9 A.  
         [0042]     The function of the brake according to the second embodiment is the same as that of the first embodiment, and the description thereof is not repeated.  
       The Third Embodiment According to FIGS.  5  and  6   
       [0043]     The third embodiment according to  FIGS. 5 and 6  has closest similarities with the first embodiment. The principal difference in relation thereto is that the third embodiment has only one thrust rod instead of two.  
         [0044]     Again, parts that are similar in these two embodiments have the same numerals. This is true for the brake caliper  1 , the brake disc  2 , the electric motor  3 , the drive shaft  4 , the coupling  5 , the gear  7 , the planet gear  8 , the disc brake pads  13  and  14 , the elasticity spring  15 , the locking pin  16 , the electromagnet  17 , and the compression spring  18 .  
         [0045]     The planet gear  8  is rotatably arranged on a thust rod ring  11 B (journalled in the caliper  1 ) of the single thrust rod  12 B. The coupling shaft  6 B with the gear  7  is sleeve-shaped in order to accomodate the thrust rod  12 B.  
         [0046]     The function of this embodiment is the same as that of the first embodiment.  
         [0047]     An alternative function of the arrangement is to have the elasticity spring  15 ;  15 A locked in unloaded state at service brake application of the brake. At a parking brake application the unlocked elasticity spring is loaded by the electric motor  3  and used for parking brake application.  
         [0048]     Modifications are possible within the scope of the appended claims. It would for example be possible to make use of the basic thought behind the invention not only for a disc brake but also for a drum or block brake, and the invention is not limited to brakes for heavy road vehicles.