Abstract:
A hydraulic anti-lock braking system for a two-wheel vehicle includes: an inlet valve for connecting and disconnecting a hydraulic connection between a brake actuating device and a wheel brake; an accumulator for accommodating brake fluid from the hydraulic connection between the inlet valve and the wheel brake; and an outlet valve for connecting and disconnecting the accumulator to and from the wheel brake. The accumulator is designed to return brake fluid into the hydraulic connection between the inlet valve and the wheel brake.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a hydraulic anti-lock braking system for a two-wheeler and to a method for controlling a hydraulic anti-lock braking system. 
         [0003]    2. Description of the Related Art 
         [0004]    A bicycle anti-lock braking system is able to increase the safety of the bicyclist and the other road users. For example, bicycle anti-lock braking systems which control the braking force mechanically with the aid of cables are known. 
         [0005]    The growing market of electrically driven bicycles (so-called e-bikes) and the associated constant availability of electrical energy on the bicycle offer new possibilities for active bicyclist protection. The electric motor assistance of the bicyclist additionally, in principle, increases the average speed, and moreover also allows less experienced bicyclists to achieve destinations at higher altitudes. 
         [0006]    In the motorcycle field, anti-lock braking systems are known which operate analogously to motor vehicle anti-lock braking systems using a return principle. The brake fluid is delivered from the brake back in the direction of the brake lever with the aid of a pump and a motor. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    It is the object of the present invention to provide an energy-saving anti-lock braking system for a two-wheeler which has a simple design and is low-maintenance. 
         [0008]    One aspect of the present invention relates to a hydraulic anti-lock braking system for a two-wheeler, for example for an e-bike or a moped. 
         [0009]    According to one specific embodiment of the present invention, the anti-lock braking system includes an inlet valve for connecting and disconnecting a hydraulic connection between a brake actuating device and a wheel brake; an accumulator or intermediate accumulator for accommodating brake fluid from the hydraulic connection between the inlet valve and the wheel brake; and an outlet valve for connecting and disconnecting the accumulator to and from the wheel brake. 
         [0010]    The brake actuating device, which is attached to the handlebar of the two-wheeler, for example, may include a brake lever, which may be used to increase a pressure in a piston. The piston may be connected via a hydraulic connection to a wheel brake, in which a brake cylinder presses brake shoes against a brake disk or a wheel rim as a result of the hydraulic pressure, for example. An inlet valve is situated in the hydraulic connection (which may include one or multiple hydraulic lines) and may be used to prevent a pressure on the wheel brake from being increased further with the aid of the brake actuating device. The pressure on the wheel brake may be reduced via an outlet valve by being able to discharge brake fluid into an accumulator via the opened outlet valve. The accumulator may provide a variable volume, for example with the aid of a piston in a cylinder. 
         [0011]    The accumulator is designed to return brake fluid into the hydraulic connection between the inlet valve and the wheel brake, for example by reducing its variable volume. For example, the accumulator may be emptied again by pushing back the piston. 
         [0012]    In general, the accumulator may temporarily store the pressure present during filling and use it to automatically empty itself again. 
         [0013]    The brake fluid is thus not delivered into the hydraulic connection between the brake actuating device and the inlet valve, but is returned to where it was withdrawn from the hydraulic connection. In this way, additional lines may be dispensed with. 
         [0014]    A hydraulic anti-lock braking system may result in the advantages of shorter response times and lower maintenance compared to a cable-based mechanical anti-lock braking system. Moreover, a hydraulic anti-lock braking system may be adapted to existing hydraulic brakes. 
         [0015]    Compared to an anti-lock braking system using the return principle, less electrical energy is required since only the valves have to be switched. This may result in a lower box volume and a lower weight. Since a pump having an associated motor may be dispensed with, lower costs may result. 
         [0016]    The inlet valve, the outlet valve, and the accumulator may be combined to form a shared regulating module, which provides a shared housing for these components, the housing having ports and terminals for hydraulic and electrical lines, for example. A control circuit board having an electronic control device may also be situated in the regulating module. 
         [0017]    According to one specific embodiment of the present invention, the accumulator includes a spring element which is tensioned when the accumulator is filled, so that the spring element automatically empties the accumulator when the pressure in the accumulator drops. For example, the spring element may be a mechanical spring element, such as a helical spring or a leaf spring. The spring element may also be an elastically compressible body or a gas volume. 
         [0018]    According to one specific embodiment of the present invention, the inlet valve is an electrical inlet valve, which closes when energized, for example. As long as the inlet valve is not supplied with electric current, it is (completely) open, and brake fluid is able to flow unimpaired between the brake actuating device and the wheel brake. When it is supplied with electric current, the inlet valve closes (completely), and the hydraulic connection between the brake actuating device and the wheel brake is interrupted. 
         [0019]    According to one specific embodiment of the present invention, the outlet valve is an electrical outlet valve, which opens when energized, for example. As long as the outlet valve is not supplied with electric current, it is (completely) closed, and brake fluid is not able to flow out of or to the accumulator. When it is supplied with electric current, the outlet valve opens (completely), and (depending on the pressure gradient) brake fluid is able to flow out of the accumulator into the hydraulic connection, or out of the hydraulic connection into the accumulator. 
         [0020]    According to one specific embodiment of the present invention, the hydraulic anti-lock braking system further includes an electronic control device, which is designed to activate the inlet valve and the outlet valve and to open and close them as a function of an ascertained locked state of one wheel of the two-wheeler. When the wheel does not lock up, the two valves may remain non-energized. If the wheel locks up, initially the inlet valve may be closed, and if needed the outlet valve may be opened. 
         [0021]    According to one specific embodiment of the present invention, the control device is designed to receive signals from a position sensor of the brake actuating device and/or from a hydraulic pressure sensor in the hydraulic connection. These signals may be used to ascertain whether a rider of the two-wheeler intends to brake. For example, the rider may actuate a brake lever of the brake actuating device and change its position, which is then detected by the position sensor. As a result, a pressure of the brake fluid in the hydraulic connection increases, which is detectable by the pressure sensor. 
         [0022]    According to one specific embodiment of the present invention, the control device is designed to receive signals from a rotational speed sensor on a wheel and, based thereon, determine a locked state of the wheel of the two-wheeler. The rotational speed sensor may be used to ascertain a wheel circumferential speed. If the same deviates from a reference speed of the two-wheeler, this indicates the locking of the wheel. 
         [0023]    According to one specific embodiment of the present invention, the control device is designed to output signals to a signal lamp, which indicate whether the control device has identified a locked state. For example, the signal lamp may be switched off when the wheel does not lock up, and it may flash when the wheel locks up. 
         [0024]    According to one specific embodiment of the present invention, the inlet valve, the outlet valve, and the accumulator are connected to a first hydraulic brake circuit for a first wheel of the two-wheeler. The two-wheeler may have separate brake circuits for the two wheels. The hydraulic anti-lock braking system may include a second inlet valve, a second outlet valve, and a second accumulator, which are connected to a second hydraulic brake circuit for a second wheel of the two-wheeler. The hydraulic anti-lock braking system may be used for the front wheel and/or the rear wheel. When it is used for both wheels, two independent regulating modules, or also one shared regulating module, may be used. 
         [0025]    It is possible for the hydraulic anti-lock braking system to have an autonomous power supply unit (independently of a power supply unit of the two-wheeler). This power supply unit may be situated in the housing of the regulating module. The hydraulic anti-lock braking system may also be used in powered two-wheelers, which have an autonomous power supply unit directly in the hydraulic regulating module or outside thereof. 
         [0026]    A further aspect of the present invention relates to a two-wheeler having a hydraulic anti-lock braking system, as it is described above and below. In addition to electrically driven two-wheelers, the anti-lock braking system may also be used in powered two-wheelers having an internal combustion engine, in particular for lightly powered two-wheelers, for example up to a maximum speed of 40 km/h (such as motorized bicycles or mopeds). 
         [0027]    A further aspect of the present invention relates to a method for controlling a hydraulic anti-lock braking system for a two-wheeler. The method may be carried out using an anti-lock braking system as it is described above and below. For example, the method may be carried out by an electronic control device. 
         [0028]    According to one specific embodiment of the present invention, the method includes the following steps: ascertaining whether a wheel of the two-wheeler locks up after a pressure was built by a rider, with the aid of a brake actuating device, in a hydraulic connection which connects the brake actuating device and a wheel brake for the wheel; closing an inlet valve to disconnect the hydraulic connection when the wheel locks up; ascertaining whether the wheel of the two-wheeler locked up when the inlet valve was closed; opening an outlet valve to accommodate brake fluid in an accumulator from the hydraulic connection between the inlet valve and the wheel brake; and keeping the outlet valve open to return brake fluid into the hydraulic connection between the inlet valve and the wheel brake with the aid of the accumulator after the rider has released the brake actuating device. 
         [0029]    For example, based on the signals of the position sensor on the brake actuating device, the control device may identify that the rider has started to brake. It is also possible for the control device to ascertain this based on the signals of an alternative or additional pressure sensor, which ascertains the pressure in the hydraulic line between the brake actuating device and the inlet valve, for example. 
         [0030]    Based on the signals of a rotational speed sensor, the control device is then able to ascertain whether or not the wheel is locking up. If the wheel locks up, the control device closes the inlet valve (at least partially), so that the pressure on the wheel brake is not able to rise, and thus the braking force also does not increase further. 
         [0031]    If the wheel should still be locked up after the inlet valve has been closed, the control device may open the outlet valve (at least partially), and brake fluid may flow from the wheel brake into the accumulator, so that the pressure on the wheel brake decreases, and thus also the braking force is reduced. If the accumulator is full, the rider may further increase the braking force and thus trigger an intentional locking of the wheel. 
         [0032]    A spring element may be situated in the accumulator, for example, which is contracted when the accumulator is filled and thus absorbs energy. This energy, which was effectively introduced into the system with the aid of the brake actuating device, for example by the rider, may be used to empty the accumulator again. 
         [0033]    After the rider has released the brake actuating device, which may also be ascertained again by the control device with the aid of the position sensor and/or the pressure sensor, the outlet valve remains open until the accumulator has been emptied again, for example with the aid of the spring element. 
         [0034]    It shall be understood that features of the method, as described above and below, may also be features of the anti-lock braking system, and vice versa. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]      FIG. 1  shows a schematic diagram of an anti-lock braking system according to one specific embodiment of the present invention. 
           [0036]      FIG. 2  shows a schematic diagram of an anti-lock braking system according to a further specific embodiment of the present invention. 
           [0037]      FIG. 3  shows a schematic diagram of a control device of an anti-lock braking system according to one specific embodiment of the present invention. 
           [0038]      FIG. 4  shows a schematic diagram of a control device of an anti-lock braking system according to a further specific embodiment of the present invention. 
           [0039]      FIG. 5  shows a diagram of a chronological progression of speeds and brake pressure, which explains a method for controlling a hydraulic anti-lock braking system according to one specific embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    Identical or similar parts are denoted by the same reference numerals. 
         [0041]      FIG. 1  shows a two-wheeler  10  having a hydraulic anti-lock braking system  12 , which is designed to reduce a locking of the front wheel  14  of the two-wheeler. 
         [0042]    The hydraulic components of anti-lock braking system  12  include a brake actuating device  16 , which is connected via a first hydraulic line  18  to a regulating module  20 , which is connected via a second hydraulic line  22  to a wheel brake  24 . Wheel brake  24  includes a wheel brake cylinder, which presses brake shoes of the wheel brake against a brake disk or a wheel rim as a result of the hydraulic pressure. 
         [0043]    Brake actuating device  16  includes a brake lever  26 , a piston  28  having a seal  30 , and optionally a reservoir  32  for brake fluid. 
         [0044]    Regulating module  20 , which together with electrical components may be attached in a housing  34  to two-wheeler  10 , includes an inlet valve  36 , an outlet valve  38 , and an accumulator  40 . 
         [0045]    Inlet valve  36  is switched between first line  18  and second line  22  and connects or disconnects hydraulic connection  42 , which is formed of two lines  18  and  22  between brake actuating device  16  and wheel brake  24 . Inlet valve  36  may include a check valve, be open when de-energized, have filters on both sides and/or have a through-flow from both sides. 
         [0046]    Outlet valve  38  is hydraulically connected to second line  22  and accumulator  40 , i.e., is connected to hydraulic connection  42  between inlet valve  36  and wheel brake  24 . Outlet valve  38  may be closed when de-energized, have filters on both sides and/or have a through-flow from both sides. 
         [0047]    Accumulator  40  or intermediate accumulator  40  for brake fluid includes a spring element  44 , for example a return spring  44 , which tensions a piston  46  against the pressure of the brake fluid in line  22 . 
         [0048]    Brake actuating device  16  may [include] a path sensor  48  or a position sensor  48 , which may be used to ascertain the instantaneous position of lever  26 . Based on the position of lever  26 , it is also possible to derive a pressure in first hydraulic line  18  and/or in hydraulic connection  42 . As an alternative or in addition, it is also possible to use an internal hydraulic pressure sensor  50  or an external hydraulic pressure sensor  52  to ascertain the pressure in first hydraulic line  18  and/or in hydraulic connection  42 , and based thereon optionally to derive the position of lever  26 . 
         [0049]    Internal hydraulic pressure sensor  50  may be an integral part of regulating module  20 . External hydraulic pressure sensor  52  may be situated outside control module  20 . 
         [0050]    A rotational speed sensor  54  is attached to wheel  14  of two-wheeler  10  and may be used to ascertain the instantaneous rotational speed or the wheel circumferential speed of wheel  14 . Rotational speed sensor  54  may include a toothed disk, which may be designed together with the brake disk, but alternatively may also be present as a separate part. 
         [0051]    In addition to brake actuating device  16 , a signal lamp  56  may be attached to the handlebar of two-wheeler  10 , the signal lamp, as is described below, indicating to the rider of two-wheeler  10  when a control device of regulating module  20  identifies a locking of wheel  14 . 
         [0052]    When the rider of two-wheeler  10  actuates lever  26 , a volume  58  (in a cylinder) is reduced by piston  30 , so that brake fluid flows into first line  18  and from there (if inlet valve  36  is open) reaches second line  22  and wheel brake  24 . When wheel brake  24  brakes wheel  14 , the pressure in the lines increases. As is further described below, inlet valve  36  may be closed and outlet valve  38  may be opened when wheel  14  locks up. The pressurized brake fluid from second line  22  may then reach accumulator  40 . A volume  60  (in a cylinder) is increased by the brake fluid displacing piston  46  against the force of spring element  44 . In this way, the pressure on wheel brake  24  may be reduced, even though the rider actuates lever  26 . 
         [0053]      FIG. 2  shows a two-wheeler  10  having a hydraulic anti-lock braking system, which includes two brake circuits. The brake circuit for front wheel  14  is designed identically to the brake circuit shown in  FIG. 1 . 
         [0054]    A further brake circuit for a rear wheel  62  may also be identical to the brake circuit shown in  FIG. 1 . The two brake circuits may be implemented with independent regulating modules  20 , or with one shared control module (in a shared housing  34 ), for regulating wheel  14  and/or rear wheel  62 . 
         [0055]      FIG. 3  shows further electrical control components of hydraulic anti-lock braking system  12 . As is shown in  FIG. 3 , regulating module  20  may include an electronic control device  64 , which may include a logic circuit on a printed circuit board  66 , for example having a processor. 
         [0056]    Regulating module  20  may include terminals  68  for signal lamp  56 , rotational speed sensor  54 , position sensor  48 , and a power supply unit  65  (such as a battery of the two-wheeler). An autonomous power supply unit for regulating module  20  may be provided via an additional (internal) button cell. 
         [0057]    Terminals  68  for regulating module  20  include supply pins and signal pins (plugs having external contacts) for ground (GND) for position sensor  48 , voltage supply (U+) for position sensor  48  and for the signal from position sensor  48 , and ground (U BAT2− ) for signal lamp  56  and voltage supply (U BAT2+ ) for signal lamp  56 . 
         [0058]    An electrical connection or line from brake actuating device  16  to regulating module  20  may be connected to these terminals  68 . 
         [0059]    Terminals  68  for regulating module  20  further include supply pins and signal pins (plugs having external contacts), ground (GND) for rotational speed sensor  54 , voltage supply (U+) for rotational speed sensor  54  and for the signal from rotational speed sensor  54 . An electrical connection or line from rotational speed sensor  54  on wheel  14  to regulating module  20  may be connected to these terminals  68 . 
         [0060]    The regulating module further includes a terminal  68  for the ground (GN) of regulating module  20  and for power supply unit  65 . 
         [0061]    Printed circuit board  66  is moreover connected to inlet valve  36  and outlet valve  38  via internal lines in regulating module  20 . 
         [0062]      FIG. 4  shows an alternative specific embodiment for an electronic control device  64 , in which regulating module  20  includes an internal pressure sensor  50 . As an alternative or in addition, control device  64  may include a terminal  68  for an external pressure sensor  52 . 
         [0063]      FIG. 5  shows a diagram in which speeds V are plotted against time t in an upper portion. The upper portion shows velocity  70  of two-wheeler  10 , a reference speed  72  calculated by control device  64 , and a wheel circumferential speed  74 , which is ascertained by control device  64  based on the signal of rotational speed sensor  54 . 
         [0064]    Brake pressure  76  and fill volume  78  of accumulator  40  are plotted against time t in the lower portion. The upper portion and the lower portion show synchronous curves  70 ,  72 ,  74 ,  76 , and  78 . 
         [0065]    The braking process shown in  FIG. 5  begins by the rider actuating brake actuating device  16  (or lever  26 ) and building pressure in hydraulic connection  42  (point in time  100 ). Wheel brake  24  is thereby activated, and speed  70  of two-wheeler  10  is reduced. 
         [0066]    With the aid of rotational speed sensor  54 , control device  64  ascertains whether or not wheel  14  of the two-wheeler locks up. For this purpose, control device  64  calculates wheel circumferential speed  74  based on the signal of rotational speed sensor  54 , and reference speed  74  based on the signal of position sensor  58  and/or the signal of pressure sensors  50 ,  52 . The locked state of wheel  14  may be ascertained by comparing reference speed  74  to wheel circumferential speed  74 . 
         [0067]    During a braking process, during which wheel  14  continues to rotate or does not lock up (for example between point in time  100  and point in time  102 ), wheel circumferential speed  74  matches calculated reference speed  72 , and inlet valve  36  and outlet valve  28  are not energized. Inlet valve  36  is then open, and outlet valve  28  is then closed. The speed is reduced as a result of the brake pressure in wheel brake  24 . Since no locking of wheel  14  was ascertained, signal lamp  56  does not flash between points in time  100  and  102 . 
         [0068]    If the rider releases brake actuating device  16 , the braking process is completed at this point. This may then be detected via position sensor  48 , for example, and processed in regulating module  20 . 
         [0069]    When wheel  14  locks up, for example due to the high pressure or the low friction, control device  64  initially closes inlet valve  36  to disconnect hydraulic connection  42  (point in time  102 ). Signal lamp  56  flashes and visually indicates the regulation to the rider. The slip increases and the brake pressure is maintained between points in time  102  and  103 . 
         [0070]    When wheel  14  then continues to rotate (differently from the case shown) and wheel circumferential speed  74  again matches calculated reference speed  72 , inlet valve  36  is no longer energized and opens again. Signal lamp  56  stops flashing and visually indicates to the rider that the regulation has ended. 
         [0071]    Even when inlet valve  36  is closed, the control device continues to ascertain whether wheel  14  of two-wheeler  12  locks up. If wheel  14  is still locked up after some time (point in time  103 ), or wheel circumferential speed  74  does not yet match reference speed  72  of wheel  14 , control device  64  opens outlet valve  48  to accommodate brake fluid in accumulator  40  from hydraulic connection  42  between inlet valve  36  and wheel brake  24 . A pressure reduction takes place in wheel brake  24 , and brake fluid from the brake circuit is accommodated in accumulator  40 . Fill volume  78  of accumulator  40  increases. 
         [0072]    A pressure reduction thus takes place in wheel brake  24  between points in time  103  and  104 . 
         [0073]    At point in time  104 , control device  64  closes outlet valve  38  again. Since the inlet valve is still closed, the pressure is maintained. Wheel  14  accelerates again between points in time  104  and  196 . 
         [0074]    When wheel circumferential speed  74  again approaches reference speed  72 , control device  64  may briefly open inlet valve  36  to enable a pressure buildup on wheel brake  24 . This may be carried out in a gradual pressure buildup, for example as shown between points in time  106  and  108 . 
         [0075]    A renewed pressure reduction is shown between points in time  108  and  110 , during which volume  60  of accumulator  40  is filled completely up to a maximal volume  80 . Since wheel  14  locks up again, even though inlet valve  36  is closed, control device  64  opens outlet valve  38  again. The regulation continues until volume  60  in accumulator  40  has been completely filled. 
         [0076]    The hydraulic circuit is designed in such a way that volume  58  in brake actuating device  16  is greater than volume  60  in accumulator  40 . It is thus ensured that braking continues to be possible with a completely filled accumulator  40  after a pressure reduction. Wheel  14  may then lock up when a corresponding rider input and friction (for example in the event of ice or stone chips) occur. 
         [0077]    The pressure is then maintained between points in time  110  and  112 , and the braking process is ended after the rider has released brake actuating device  16 . 
         [0078]    After the rider has released brake actuating device  16  (point in time  112 ), control device  64  keeps outlet valve  48  open in order to return brake fluid into hydraulic connection  42  between inlet valve  36  and wheel brake  24 . Accumulator  40  accomplishes this automatically with the aid of spring element  44  tensioned by the pressure. The spring force of accumulator  40  pushes the volume accommodated during the regulation back into the brake circuit via energized outlet valve  38 . Accumulator  40  is completely emptied between points in time  114  and  166 , during which the pressure in the hydraulic line has dropped below the pressure in accumulator  40 . The level in optionally present brake fluid container  32  rises. 
         [0079]    In the event of a fault, for example when the rechargeable battery or power supply unit  65 , control device  64  and/or regulating module  20  (a valve  26 ,  38 , for example) is/are defective, signal lamp  56  is permanently illuminated and indicates to the rider that one of the above-described defects has occurred. 
         [0080]    In addition, it shall be pointed out that “including” does not exclude other elements or steps, and that “a” or “an” does not exclude a plurality. It shall moreover be pointed out that features or steps which were described with reference to one of the above-mentioned exemplary embodiments may also be used in combination with other features or steps of other above-described exemplary embodiments. Reference numerals in the claims shall not be regarded as limiting.