Abstract:
A brake for a work machine includes a brake rotor, a hydraulically operated device for actuating the brake by clamping the brake rotor, and an arrangement for damping jerks resulting from a sudden brake actuation. The brake rotor includes a pair of brake force transmitting discs and the damping arrangement is formed by a damping layer positioned between the discs and secured to each of the discs.

Description:
BACKGROUND AND SUMMARY 
       [0001]    The present invention relates to a brake for a work machine, wherein the brake comprises a brake rotor, a hydraulically operated device for actuating the brake by clamping the brake rotor, and means for damping jerks resulting from a sudden brake actuation. The invention further relates to a wheel hub unit comprising the brake and a work machine comprising the wheel hub unit. 
         [0002]    The invention can be applied in vehicles or work machines which are intended to be driven on a relatively flat surface, such as a road, and/or on uneven ground off road. The invention is—especially applicable for a relatively slow moving work machine, such as a wheel loader. By the term “relatively slow moving” is meant a vehicle/work machine with a maximum speed of about 50 km/h. 
         [0003]    A wheel loader must be equipped with brakes that are suited for the varying characteristics of the machine. In one extreme case, a fully loaded machine must be powerfully retarded and in another extreme case the same machine without any load must be gently braked. In order to enable the driver of the machine to handle the machine, the retardation must feel controllable and manageable under all conditions. 
         [0004]    According to a known solution, wet brakes are arranged at each wheel. More specifically, a reduction gear in the form of a planetary gear is operatively connected between an end of a drive shaft extending from a central gear (differential gear) in an axle and a wheel hub. The planetary gear is adapted for a downshift of rotational speed from the drive shaft to the wheel hub. The wet brake is arranged for braking the drive shaft. Especially, a brake rotor is rotationally rigidly connected to the drive shaft. A moveable piston is operatively connected to brake pads for clamping a brake rotor between the brake pads for brake actuation. The piston is moved under the pressure of a hydraulic oil. 
         [0005]    When the brake is actuated (initiated via depression of a brake pedal) it takes a certain time to move the brake piston from an initial position to the position when the brake pads are in contact with the brake rotor. Once the brake piston has reached the latter position, the pressurization of the hydraulic oil against the brake piston commences, which leads to a powerful excess pressure surge in the form of a pressure pulse in the hydraulic oil. This excess pressure surge gives rise to a brake shock (a powerful retardation of the machine), which the driver experiences as a jerk. Such a jerk results in that the driver is exposed to vibrations. The excess pressure surge also results in that the components of the brake being exposed to heavy stresses, which among other things generates noise. The noise is experienced by the driver and persons near the machine as an irritation. 
         [0006]    According to a known solution to said problem of jerks in the actuation phase of the brake, the hydraulic circuit is provided with damping means in the form of an accumulator for accumulating the excess energy in the hydraulic oil. 
         [0007]    It is desirable to provide a hydraulically operated brake which is adapted to at least reduce the jerks resulting from brake actuation and which creates conditions for a more cost-efficient brake system. Further, the brake should provide good controllability. 
         [0008]    According to an aspect of the present invention, a brake rotor comprises a pair of brake force transmitting discs and that the damping means is formed by a damping layer positioned between the brake force transmitting discs and secured to each of the discs. 
         [0009]    The brake rotor design reduces the sensitivity of the brake at the initiation in that the damping layer is adapted to absorb energy. In other words, the damping layer functions as a cushioning means. 
         [0010]    A secondary effect is that the noise from the actuation of the brake is eliminated. 
         [0011]    The brake force transmitting discs are configured for a rotationally rigid connection with a drive member (preferably a drive shaft). Due to the fact that the damping layer is interposed between the discs, the brake function is preserved even if the damping layer and/or the attachment of the damping layer to the metallic discs is damaged. 
         [0012]    Accordingly, the inventive design of the brake creates conditions for eliminating the accumulator in the hydraulic system according to prior art. 
         [0013]    According to a preferred embodiment of the invention, the damping layer comprises cork material. 
         [0014]    Further preferred embodiments and advantages of these emerge from the description below and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0015]    The invention will be described in greater detail below with reference to the embodiments shown in the accompanying drawings, in which 
           [0016]      FIG. 1  shows side view of a wheel loader, 
           [0017]      FIG. 2  shows a diagrammatic, partly cut side view of a wheel hub unit of the wheel loader according to a first embodiment, 
           [0018]      FIG. 3  shows a cross sectional view of a brake rotor in a brake provided in the wheel hub unit in  FIG. 2 , and 
           [0019]      FIG. 4  is a side view of the brake rotor in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  shows a frame-steered work machine constituting a wheel loader  101 . The body of the wheel loader  101  comprises a front body section  102  and a rear body section  103 , which sections each has an axle  112 , 113  for driving a pair of wheels. The rear body section  103  comprises a cab  114 . The body sections  102 , 103  are connected to each other in such a way that they can pivot in relation to each other around a vertical axis by means of two first actuators in the form of hydraulic cylinders  104 , 105  arranged between the two sections. The hydraulic cylinders  104 , 105  are thus arranged one on each side of a horizontal centerline of the vehicle in a vehicle traveling direction in order to turn the wheel loader  101 . 
         [0021]    The wheel loader  101  comprises an equipment  111  for handling an external load, such as objects or material. The equipment  111  comprises a load-arm unit  106  and an implement  107  in the form of a bucket fitted on the load-arm unit. A first end of the load-arm unit  106  is pivotally connected to the front vehicle section  102 . 
         [0022]    The bucket  107  is pivotally connected to a second end of the load-arm unit  106 . 
         [0023]    The load-arm unit  106  can be raised and lowered relative to the front section  102  of the vehicle by means of two second actuators in the form of two hydraulic cylinders  108 , 109 , each of which is connected at one end to the front vehicle section  102  and at the other end to the load-arm unit  106 . The bucket  107  can be tilted relative to the load-arm unit  106  by means of a third actuator in the form of a hydraulic cylinder  110 , which is connected at one end to the front vehicle section  102  and at the other end to the bucket  107  via a link-arm system  115 . 
         [0024]      FIG. 2  shows a first embodiment of a wheel hub unit  201  in a diagrammatic, partly cut side view. The wheel hub unit  201  is arranged at one end of an axle case  203  of a wheel axle  205 . A drive shaft  207  extends inside the axle case  203  in a transverse direction of the work machine. The drive shaft  207  is, at one  209  of its ends, provided with a hub reduction gear  211  in the form of a planetary gear transmission. At its other end, the drive shaft  207  is operationally connected to a central gear (not shown) which in turn is driven by the power unit of the vehicle via a gearbox and a drive shaft extending in a longitudinal direction of the work machine. 
         [0025]    The planetary gear transmission  211  comprises a sun gear  213 , which is rotationally rigidly connected to the drive shaft  207 . Thus, the sun gear  213  forms an input to the reduction gear. The planetary gear transmission  211  further comprises a number of circumferentially spaced planet gears  215  in driving interconnection with the sun gear and with a ring gear  217  via teeth. The planetary gear transmission  211  is of a type with a stationary ring gear. 
         [0026]    A planet carrier  221 , also known as a planet gear holder, is adapted so as to hold the planet gears  215 . 
         [0027]    To be precise, each of the planet gears  215  is journalled on an axially extending shaft pivot  219 . The number of planet gears  215  can be one, two, three, four or more. The planet carrier  221  forms an output from the reduction gear. 
         [0028]    A brake  223  consisting of or comprising a wet brake is adapted to brake the drive shaft  207 . Thus, the brake  223  is arranged between the reduction gear  211  and the central gear (not shown) in the axle. The brake comprises a single brake rotor  225 . The sun gear  213  has guide surfaces, in the form of a number of parallel ridges, or teeth, for engagement with and guidance in the axial direction of the brake rotor  225  when the brake  223  is activated. The connection consists of or comprises a spline joint  250 . Thus, the brake rotor  225  is connected to the sun gear  213  and therefore to the drive shaft  207  in a rotationally fixed manner and is displaceable in the axial direction on said spline joint  250 . 
         [0029]    The single brake rotor  225  is arranged between a pair of brake pads  237 , 239 . The brake further comprises a hydraulically operated device  240  for actuating the brake by clamping the brake rotor  225 . The brake device  240  comprises a brake piston  241  for applying the brake by pressing the brake rotor between the brake pads  237 , 239  and thus increasing the friction force between them. Thus, one of the brake pads  239  is moveable by means of the brake piston  241  and the other brake pad  237  on an opposite side of the brake rotor relative to the brake piston forms a pressure surface, or stay, against which the brake rotor is brought when the brake is applied. 
         [0030]    By means of this type of brake, the drive shaft  207  is braked directly. The drive shaft  207  usually has a speed which is approximately six times higher than that of the wheel. 
         [0031]    A wheel hub  242  is connected firmly to the planet carrier  221 . More specifically, the wheel hub  242  is rotationally rigidly connected to the planet carrier  221  via a splined connection  246 . The wheel is fastened by a conventional fastening device on the hub, usually a bolt joint  244 . 
         [0032]    The brake rotor  225  is shown in more detail in  FIGS. 3-4 . The brake rotor  225  comprises a pair of brake force transmitting discs  227 , 229  and a damping layer  231  positioned between the discs  227 , 229  and secured to each of the discs. The brake force transmitting discs  227 , 229  are preferably of metallic material. The damping layer is configured for absorbing energy in order to provide the brake with a soft actuation. Preferably, the damping layer comprises a cork material. However, according to an alternative, complement, the damping layer may comprise other materials, such as organic material and/or polymeric material. Each of the brake force transmitting discs  227 , 229  is configured for a rotationally rigid connection to a the drive shaft  207 . More specifically, each of the brake force transmitting discs  227 , 229  comprises a central hole  248  with a cross sectional pattern complimentary to the outer pattern of the sun gear  213  for engagement therewith. The brake force transmitting discs  227 , 229  are connected to the drive shaft  207  via the splined connection  250 , see  FIG. 2 . 
         [0033]    Further, the brake rotor  225  comprises a layer  233 , 235  of friction material on an outer side of each of the brake force transmitting discs  227 , 229 . Thus, the brake pads  237 , 239  are disposed adjacent each friction layer  233 , 235  such that a smooth surface of the pads is forced against the friction surfaces of the brake rotor. 
         [0034]    Turning now to  FIG. 4 , the brake rotor  225  comprises a plurality of circumferentially spaced elongated openings  303  extending in a radial direction of the brake rotor. The opening configuration is configured for providing the brake rotor with a pumping effect for transporting a coolant during rotation in order to cool the brake rotor. The elongated openings  303  extend through the brake rotor in an axial direction and are open radially outwards. The friction layer  233  is provided with a groove pattern  305  adapted to transport coolant during operation. More specifically, the pattern  305  comprises a channel configuration comprises a plurality of straight channels  307  extending over the friction layer. The straight channels have a substantially radial direction. More specifically, the straight channels  307  are arranged in parallel with each other in each sector of the brake rotor  225  between two adjacent openings  303 . The channel configuration contributes to said pumping effect. 
         [0035]    The invention is not to be regarded as being limited to the illustrative embodiments described above, but a number of further variants and modifications are conceivable within the scope of the patent claims which follow. For example, the application may differ, or the power unit of the vehicle may be arranged so as to drive the drive shaft  207  directly, that is to say without an intermediate drive shaft and central gear. 
         [0036]    Further, the invention is not limited to a brake with a single brake rotor. Thus, the brake may be provided with a plurality of brake rotors of the design described above.