Abstract:
The present invention concerns a brake system creating redundancy in electromechanical brakes. At least two drive units are provided at each single brake for activation of the brake. The at least two units may be controlled and/or energized separately. To safeguard the function the control and/or energy source systems are formed in two nets. The at least two units of each brake are connected to separate nets. The at least two units may be separate electrical motors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 11/388,564, filed Mar. 24, 2006, currently pending, which is a continuation of International Patent Application No. PCT/SE2004/001383 filed on Sep. 27, 2004, which designates the United States and claims priority of Swedish Patent Application No. 0302562-4 filed on Sep. 26, 2003. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to creating redundancy in an electromechanical brake by using at least two units giving actuating force in each separate brake. The solution can be used in an environment where electric energy is regarded as equally safe as mechanical energy (for example in the form of energy stored in a spring in a so called spring brake) in an application where safety is critical. In systems where safety is critical, the safety at catastrophic failures today most often depends on mechanical energy from application springs (spring braking). 
       BACKGROUND OF THE INVENTION 
       [0003]    According to one aspect of the present invention the safety is built up of two (or more) voltage sources and a redundancy in each single brake, where two or more cooperating units together can perform the duty required under normal circumstances. In this way the mechanical application springs may be removed from the design, leading to the advantage of reduced complexity and improved performance at catastrophic failures. 
         [0004]    The brakes may be of a self-energizing type but the invention is not restricted to that kind of brakes. Thus the invention may be used with any type of electromechanical brake. 
         [0005]    In each brake each separate unit of the two or more cooperating units is normally supplied by a separate voltage source. At a simple failure one of the two units can perform a possibly reduced function during a possibly reduced period of time. 
       SUMMARY OF THE INVENTION 
       [0006]    By the expression “two units” the following may be meant: 
         [0007]    a) Two separate motors with two separate shafts and a rotational speed reduction to a brake pad. The brake pad may be arranged slidably in relation to a ramp in a self-energizing disc brake as shown in WO 03/071150. In a self-energizing brake it is optimal to dimension the slope of the ramp so that the friction number is close to the number giving theoretical indefinite self-energization. A mechanical slack—together with the characteristics that a self-energizing brake has in this range—create control problems. By having the two motors working “against” each other at these occasions, the slack may be eliminated without costly mechanical solutions for slack minimizing. 
         [0008]    b) Two separate motors with two separate shafts and partly common mechanical transmission to the pad ramp. 
         [0009]    c) One motor package with thermally and electrically insulated winding packets in the stator portion and a common rotor on a common shaft. Each coil winding can per se perform the function of one motor with the drawback that the loss resistances increase with the decreasing copper volume and thus increase resistive losses, which may limit the time for keeping up the brake function or may limit the effect of the brake function during an indefinite time. 
         [0010]    A system for controlling the two or more cooperating units of each brake may be designed in one of the following ways: 
         [0011]    Each motor winding in the above configurations has its one driver supplied by separate voltage sources. The motor control can be performed by two separately supplied control units, each communicating with other parts of the brake system with separate interfaces to separate networks for brake system communication or a generally redundant, voltage supplied control unit communicating with the rest of the brake system by two separate interfaces to two separate networks with two smaller, separately voltage supplied emergency control units connected to each motor drive unit. 
         [0012]    According to one aspect of the present invention the power needed to actuate the brake is very low, meaning that the power may be produced in a simple manner giving advantages both regarding weight and cost. 
         [0013]    Further modifications and advantages of the present invention will be obvious to a person skilled in the art when reading the detailed description below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will be described more detailed below as way of an example and with reference to the enclosed drawings. In the drawings: 
           [0015]      FIG. 1  shows schematically one example of a network topology for both communication and voltage supply in a redundant network for brake control according to the present invention. 
           [0016]      FIG. 2  shows schematically one example of parts of a disc brake according to the present invention. 
           [0017]      FIG. 3  is a schematic top view of a disc brake arrangement for illustrating a principle of the invention. 
           [0018]      FIG. 4  shows schematically one example of parts of a disc brake according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    In  FIG. 1  one example of a network topology is shown. The shown embodiment is directed to the control function, but a person skilled in the art realizes that the voltage supply part has a similar design. 
         [0020]    In the shown embodiment six disc brakes  1  are shown, but a person skilled in the art realizes that any number of brakes may be used. Each disc brake  1  is actuated by means of a drive unit controlled by an electronic control unit  3 . The drive unit comprises at least two separate, cooperating drive units  2 . The electronic control unit  3  of each brake  1  is connected to a vehicle control unit  4 . As a safe guard the separate electronic control units  3  and the vehicle control unit  4  are connected by means of two separate nets  5 ,  6 . All control units  3 ,  4  are connected to both nets  5 ,  6  and thus, even if one net fails the control of the brakes  1  will function by means of the other net. 
         [0021]    For the voltage supply to the drive units  2  of each brake  1  two power supplies are provided, one for each of two nets. As stated above the main design of the nets is the same irrespectively of if it is for control or power supply. 
         [0022]    In normal use the brakes  1  are actuated by at least two cooperating units  2  for each brake, each unit  2  being capable of actuating the brake  1  on its own in an emergency situation. Thus, this redundancy may be used to safeguard the function of the brakes  1 . 
         [0023]    In existing brakes a mechanical energy in form of some kind of spring is required mainly due to the parking brake requirements. The mechanical energy is used to compensate for the force lowering effects caused by cooling mechanism and pads. Furthermore, the spring is considered to guarantee a last resort applying the brake if all primary and central energy supply would cease. A total elimination of the mechanical spring from the design would mean cost and above all weight savings. In order to eliminate the spring the parking brake and emergency brake has to be established in some other way. One possible way to achieve this is indicated in  FIG. 2 . 
         [0024]    The mechanism of  FIG. 2  is based on the mechanisms shown in WO 03/071150 being self-energizing (self-servo effect). One main difference being the way the wear of the brake pads is compensated. 
         [0025]    In the brake indicated in  FIG. 2  a brake disc  7  is in normal way received in a caliper or the like (not showed). On one side of the brake disc  7  a ramp plate  8  is provided with a brake pad  9  for braking engagement with the brake disc  7  at will. A further brake pad  9  is often provided on the opposite side of the brake disc  7 . The ramp plate  8  is movably connected to two ramp bridges  10 . 
         [0026]    At their surfaces facing each other, the ramp plate  8  and the ramp bridges  10  are provided with curved or straight ramps  8 ′ and  10 ′, respectively. Two rollers  11  are freely rotatable between the ramps  8 ′,  10 ′. 
         [0027]    In a rest position (or a position for a non-applied brake) the unit comprising the ramp plate  8  (with its brake pad  9 ), the rollers  11  and the ramp bridges  10  is held with the brake pads  9  at a small distance from the rotating brake disc  7  and with the rollers  11  at the “bottoms” of the ramps  8 ′,  10 ′. 
         [0028]    For brake application, a control force that is substantially transverse to the brake disc  7  (or in other words substantially axial) is applied on the ramp plate  8 . In the shown case the force is applied by means of a control rod  12  until contact between the brake pads  9  and the disc  7  is established. The force of the control rod  12  is normally given by the at least two units  2 , often being two separate electrical motors. By means of friction force, the ramp plate  8  is transferred to the left or right, depending on direction of rotation of the disc  7 , so that the rollers  11  roll up the relevant ramps  8 ′,  10 ′ and an application force is accomplished without applying any external brake force besides the control force. In other words the brake is self-energizing. 
         [0029]    In the shown embodiment the ramps  8 ′,  10 ′ are straight, but they can alternatively be curved. By having a certain curvature of the ramps  8 ′,  10 ′, a desired brake application characteristic can be obtained. 
         [0030]    The adjustment mechanism compensating for wear of the brake pads  9  is divided onto four screws  13 ,  14 ,  15 ,  16 . Two screws  13 ,  14  are provided for one ramp bridge  10  and two screws  15 ,  16  for the other ramp bridge  10 . The screws  13 - 16  are preferably ball screws. Screws being non self-locking are of advantage and give a larger freedom in use of the mechanism. By this arrangement the two ramps  8 ′,  10 ′ may be adjusted separately. The four screws  13 - 16  are to be controlled separately or in pairs in different configurations depending on the function to be brought about. For example the screws  13 - 16  may be controlled by an energized electromagnet mechanically coupling motion of a motor to the positions of the screws  13 - 16 . In a non-energized condition the positions of the screws  13 - 16  are locked. 
         [0031]    The screws  13 - 16  may be controlled separately but are often controlled in pairs. By controlling the screws  13 - 16  the angle of self-energizing may be controlled producing an optimal optimization of energy. With non self-locking screws this adjustment may be made during active braking and forming an optimal optimization of energy. 
         [0032]    In this description “angle of the ramp  8 ′,  10 ′” means the angle of the ramp plate  8  and ramp bridges  10 , respectively, in relation to the horizontal plane of the brake disc  7 . Thus, the roller  11  may have different angles in relation to the different parts of the ramps  8 ′,  10 ′ and will roll more easily in one direction. “Self-actuating angle” means an angle at which the brake will be actuated automatically if the friction between brake pads  9  and brake disc  8  is above a minimum value. 
         [0033]    The dimensions of the motor and its driving may be many times smaller than a design having a fixed angle of self-energizing. This will lead to lower weight and lower costs. 
         [0034]    The gear ratio between the driving force of the motors and the screws  13 - 16  should be high enough for the function of the screws to be slow and power efficient. This means that if the power supply fails the brake may be applied or loosened using little utilized power, as for example with the central generator or small local generators at the separate axles as power supply. 
         [0035]    For a self-energizing brake having a fixed angle of the ramps  8 ′,  10 ′ situations will arise that are hard to predict exactly and that demands extremely high powers at extreme values on the friction between pad  9  and disc  7 . With a design according to the present invention such extreme situations will be handled at a much lower power requirement. By having the double motors controlled and energized separately and adapted to a safe and double power supply system it will be possible to lower the costs, which is made possible by the substantially lowered power needs. 
         [0036]    For a parking brake and/or an emergency brake the angle of the ramps  8 ′,  10 ′ in relation to the disc  7  and the roller  11  may be modified in such a way that every second brake  1  will give a braking effect for travel forward, while the other brakes  1  will give a braking effect for travel backward. This may be done for non self-locking screws in that the angles of the ramps  8 ′,  10 ′ are controlled in pairs to a self-actuating angle, with the screws  13 ,  15  at the left (as seen in  FIG. 2 ) at the ramp bridges  10  synchronized and the screws  14 ,  16  at the right synchronized. Then the pad is applied by means of the screws  13 - 16  to a position which after cooling gives a minimum force &gt;0. By means of the self-actuating angle the brake  1  will apply in one direction of rotation. By setting this angle differently in pairs for the separate brake units half of the brakes  1  will jointly increase the braking power until standstill in the direction of rotation dictated by the slope of the ground. 
         [0037]    In an alternative embodiment the angles are varied in such a way that half the braking effect of each brake  1  is acting for brake of travel forward while the other half of the braking effect is used for braking travel backward. With non self-locking screws the angles of the ramps  8 ′,  10 ′ are controlled in pairs with the screws  13 ,  16  at the outer ends of the ramp bridges  10  synchronized and the screws  14 ,  15  at the inner ends synchronized. Outer and inner ends being in relation to the axis of rotation of the brake disc  7 . Hereby the left ramp (as seen in  FIG. 2 ), controlled by the two screws  13 ,  14  on the left, has a self-energizing effect in a forward direction of the vehicle and the right ramp, controlled by the two screws  15 ,  16  on the right, has a self-energizing effect in a backward direction of the vehicle. Thus, the brake pads  9  are applied by means of the screws  13 - 16  to a position that still after cooling gives a minimum force &gt;0. 
         [0038]    As an alternative the angles of the ramps  8 ′,  10 ′ are kept constant, even if the ramp plate  8  and ramp bridges  10  are inclined in relation to the brake disc  7 . By such an arrangement the parking and/or emergency brake will function irrespectively of direction of travel of the vehicle. 
         [0039]      FIG. 3  more specifically depicts a brake disc  37  rotating in the direction of an arrow  31 . A ramp plate  32  is provided with a brake pad  33  for braking engagement with the brake disc  31  at will. The ramp plate  32  is movably connected to a ramp bridge  34 , which for the purpose of this simple explanation can be regarded as fixed, by a connecting means  35 , here illustrated as a line. 
         [0040]    At their surfaces facing each other, the ramp plate  32  and the ramp bridge  34  are provided with curved or straight ramps  32 ′ and  34 ′, respectively. A roller  36  is freely rotatable between the ramps  32 ′ and  34 ″. 
         [0041]    In a rest position (or a position for a non-applied brake) the unit comprising the ramp plate  32  (with its brake pad  33 ), the roller  36  and the ramp bridge  34  is held with the brake pad  33  at a small distance from the rotating brake disc  31  and with the roller  36  in the “bottoms” of the ramps  32 ′ and  34 ′. 
         [0042]    For brake application, a control force which is substantially transverse to the brake disc  31  (or in other words substantially axial) is applied on the ramp plate  32 , in the shown case over the connecting means  35  as indicated by its upper arrow, until contact between the brake pad  33  and the disc  31  is established. By means of the friction force, the ramp plate  32  is transferred to the left in the drawing, so that the roller  36  rolls up the relevant ramps  32 ′ and  34 ′ and an application force is accomplished without applying any external brake force besides the control force. In other words the brake has a self-servo effect. 
         [0043]    The application force may be controlled by the control force, which can be positive or negative. This is indicated by the provision of also a lower arrow on the connecting means  35 , but is not further illustrated and described in connection with  FIG. 1 . 
         [0044]    If the brake disc  31  rotates in the opposite direction, the arrangement will function in a similar way due to the provision of the respective double ramps  32 ′ and  34 ′. 
         [0045]    In the shown case the ramps  32 ′ and  34 ′ are curved, but they can alternatively be straight. By having a certain curvature of the ramps, a desired brake application characteristic can be obtained. 
         [0046]    As mentioned above, the safety of the present invention is built up of two (or more) voltage sources and a redundancy in each single brake, where two or more cooperating units together can perform the duty required under normal circumstances. In this way the mechanical application springs may be removed from the design, leading to the advantage of reduced complexity and improved performance at catastrophic failures. 
         [0047]      FIG. 4  more specifically depicts one example of how such can be achieved, illustrating a particular example of the envisioned “two or more cooperating units.”  FIG. 4  thus illustrates one motor package  40  with thermally and electrically insulated winding packets  42 ,  42 ′ in the stator portion and a common rotor  44  on a common shaft  46 . Each coil winding  42  can per se perform the function of one motor.