Abstract:
Provided is a lifting device, lifting system and method for lifting a vehicle. The lifting device according to the invention includes a frame with a carrier configured for carrying the vehicle; a drive which acts on the carrier, wherein the drive includes an integrated hydraulic cylinder drive unit configured for raising the carrier with the integrated hydraulic cylinder drive unit including: a housing of a cylinder; a piston rod movable in the housing; a height measuring system configured for measuring the displacement of the piston rod; and an integrated hydraulic fluid tank and motor unit that is configured for driving the piston rod.

Description:
[0001]    This application claims priority to Netherlands Patent Application No. 2013123 filed Jul. 4, 2014, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a vehicle lifting device that is used for lifting trucks and busses, or other vehicles and may involve lifting columns of the two-post lift type with pivoting support arms, the four-post lift type with runways, the mobile type, in-ground lifts, etc. 
         [0004]    2. Description of the Related Art 
         [0005]    Lifting devices embodied as a lifting column are known from practice and comprise a frame with a carrier that is connected to a drive for moving the carrier upwards and downwards. In the ascent mode, hydraulic oil is pumped to a cylinder for lifting the carrier and, therefore, the vehicle. In the descent mode, the carrier with the vehicle is lowered and hydraulic oil returns to the reservoir. Such prior art lifting system is disclosed in U.S. Patent Application Publication No. 2006/0182563, which is incorporated herein by reference. 
         [0006]    Known lifting devices utilize hydraulic lifting circuits that are rather complex and utilize a combination of check valves and pressure compensation flow control (PCFC) valves or proportional valves. Also, these hydraulic lifting circuits require the use of a number or hoses and connections. This involves a high risk of failure leading to high maintenance costs and downtime. 
       SUMMARY OF THE INVENTION 
       [0007]    An object of the invention is to obviate or at least reduce the above problems. 
         [0008]    This object is achieved with a lifting device for lifting a vehicle according to the invention, the vehicle lifting device comprising:
       a frame with a carrier configured for carrying the vehicle;   a drive which acts on the carrier,   wherein the drive comprises an integrated hydraulic cylinder drive unit configured for raising the carrier, the integrated hydraulic cylinder drive unit comprising:   a housing of a cylinder;   a piston rod movable in the housing;   a height measuring system configured for measuring the displacement of the piston rod; and   an integrated hydraulic fluid tank and motor unit that is configured for driving the piston rod.       
 
         [0016]    The carrier of the lifting device is capable of carrying the vehicle that needs to be lifted. The carrier is moved upward and/or downward with a drive. According to the invention, the drive comprises an integrated hydraulic cylinder drive unit that is configured for raising the carrier. This unit comprises, in an integrated manner, a housing, a piston rod that is movable in the housing of the cylinder, and a height measuring system that is configured for measuring the displacement of the piston rod. The use of this height measuring system enables the direct measurement of the piston rod that is directly related to the height of the carrier. This provides a direct measurement enabling a direct feedback on the actual displacement of the carrier that in a presently preferred embodiment is performed contactless, i.e. without physical contact between the height measurement system and piston rod. This obviates the need for separate sensor systems, thereby reducing the complexity of the lifting device, and reducing the risk of additional noise or disturbances on measurement signals and/or communication between the different components of the lifting device. Furthermore, as the height measurement can be performed directly on the displacement of the piston rod the feedback of the displacement is directly available such that there is no time delay and, if necessary, appropriate control actions can be taken directly. This improves the safety of the lifting device according to the present invention. 
         [0017]    Furthermore, the lifting device according to the present invention comprises an integrated hydraulic fluid tank and motor unit, as part of the integrated cylinder drive unit, that is configured for driving the piston rod. Integrating the hydraulic fluid tank and motor in one unit reduces the need for space required for these components in&#39;the lifting device and enables a relatively compact construction. Such compact construction significantly reduces the number and/or length of hoses and other connections between the individual units or components of the lifting device according to the present invention. This renders the lifting device according to the invention more cost effective and, in addition, reduces the risk of failure of components and/or connections. In particular, the risk of hydraulic fluid leaking from a connection is reduced significantly. 
         [0018]    Lifting devices according to the invention include lifting columns of the two-post lift type with pivoting support arms, the four-post lift type with runways, the mobile type lifting columns, in-ground lifts etc. As an example, a number of lifting devices can be grouped together as a lifting system. In an embodiment of such a lifting system according to the invention, when lifting a vehicle at least two lifting columns are being used. In fact, often four lifting columns are being used. During such lifting operation, the timing of these separate lifting columns including the moving speed of the carrier that carries (part of) the vehicle when lifting a vehicle, requires synchronization. The control of the lifting system preferably comprises a system controller that synchronizes the height of the separate carriers in the ascent mode using, for example, a measurement signal generated by a height sensor, for example a potentiometer and/or more preferably the height measurement system according to a presently preferred embodiment of the present invention. Of course, other sensors can also be used. In case one of the carriers has moved too fast in the ascent mode and is too high as compared to the other carriers of the other lifting columns, for example the power supply to this carrier is either directly or indirectly lowered so that the other carriers can catch up or, alternatively, the power supply to the other carriers is either directly or indirectly increased so that the other carriers can catch up. In the descent mode, it is also important that the height of the carriers between the several lifting columns is synchronized. Therefore, in case one of these carriers has moved too slowly, for example its power supply is increased in order for this carrier to catch up with the other carriers or, alternatively, the power supply to the other carriers is either directly or indirectly lowered so that the other carriers can catch up. 
         [0019]    In a presently preferred embodiment according to the present invention, the height measuring system comprises a sensor code that is provided on the piston rod, and a sensing element configured for reading the sensor code to determine the extension of the displacement of the piston rod. 
         [0020]    Providing a sensor code directly on the piston rod enables a direct measurement of the displacement of this piston rod by providing a sensing element. This sensing element is configured for reading the sensor code to determine the displacement. This enables a direct measurement of the displacement of the piston rod and, therefore, the location of the carrier of the lifting device. 
         [0021]    In a presently preferred embodiment the sensor code is a magnetic code. The piston rod acts as host for the sensor code and is preferably of a steel material. The sensing element is preferably a row of magnetic field sensors which are located in the proximity of the sensor code. The use of such configuration enables measuring changes in the magnetic field(s) caused by displacement of the piston rod such that the sensing element, for example embodied as coils, respond to the magnetic field changes. This provides a measurement of the actual displacement of the piston rod and therefore of the height of the carrier of the lifting device. The measurement signal can be supplied to a lifting device controller that monitors and controls the height of the carrier. If required, the lifting device controller may compare the height of an individual carrier with heights of other carriers and determine corrective action, if necessary. Such corrective action may involve raising or lowering individual carriers in addition to the original steering command. 
         [0022]    In a further preferred embodiment according to the present invention the height measuring system of the lifting device comprises a locking system that is configured for locking the piston rod in response to an indication, such as a signal, of the height measuring system that the piston rod has reached a desired position. 
         [0023]    By providing a locking system in cooperation with the height measuring system of the lifting device according to the present invention a direct command for locking and/or unlocking the piston rod can be achieved. This lock/unlock signal can be supplied by the measuring system directly, or alternatively by a lifting device controller, to the locking system. Having the locking system acting directly on the piston rod, provides a direct locking means that provides a (direct) possibility to maintain the piston rod, and the carrier, at the desired height with improved accuracy. 
         [0024]    Preferably, the locking system comprises a number of rod clamps. This number of rod clamps can be one, two, four or any other number of clamps. In a presently preferred embodiment the locking system comprises two rod clamps that directly engage the piston rod. More preferably, the rod clamps are hydraulically de-activated such that locking system is capable of holding the piston rod at the desired height. This provides a locking system that is both robust, stable and can be operated with high accuracy. In addition, by the preferred combination of height measuring system and locking system, the actual locking position can be determined efficiently and with high accuracy thereby contributing to the overall safety of the lifting device according to the present invention. 
         [0025]    In a presently preferred embodiment according to the invention the locking system is configured to provide a continuously adjustable locking of the piston rod. This enables locking at any desired position of the piston rod, and therefore at any desired height of the carrier. Conventional lifting devices have a pitch between locking positions due to the functioning of the pawl or latch in the locking system provided on the mast of the lifting column. In case in one of such conventional lifting columns the locking does not function properly this introduces height differences equal to the pitch, for example in the range of 35-100 mm. It will be understood that this introduces a safety risk. In addition, in such case remaining conventional columns are confronted with additional loads that may add to the safety risk. This problem is solved with the continuously adjustable locking system according to the invention, wherein preferably rod clamps directly act on the piston rod. This provides a direct and continuously adjustable locking without requiring a pitch. 
         [0026]    In a further preferred embodiment according to the present invention the integrated fluid hydraulic tank and motor unit comprises a hydraulic fluid reservoir with a submerged pump. 
         [0027]    By providing the hydraulic fluid tank and motor unit with a hydraulic fluid reservoir and a submerged pump therein, a compact and effective hydraulic fluid circuit is achieved with a significant reduction of the number of hoses and connections. This reduces the risk of hydraulic fluid, such as hydraulic oil, leaking from the lifting device. In addition, the amount of hydraulic fluid that is required in a lifting device is further reduced. 
         [0028]    Preferably the reservoir comprises a direct valve connection between the reservoir and the housing of the cylinder. This enables a direct interaction between a chamber of the hydraulic cylinder and the reservoir thereby further reducing the need for additional hoses and connections. This further reduces the number of components in the lifting device according to the present invention and even further reduces the risk of hydraulic fluid leaking from the lifting device. 
         [0029]    The present invention also relates to a lifting system comprising one or more of the aforementioned lifting devices. 
         [0030]    The lifting system provides the same effects and advantages as those stated for the lifting device. For example, the lifting system may comprise a number of lifting columns acting as lifting device. The individual lifting devices/columns can be controlled by a central controller of the lifting system, for example. This enables an effective and efficient comparison of the actual height of the individual carriers of the lifting devices. Performing the direct measurement and the preferred direct locking/unlocking of the piston rod at a desired position provides additional accuracy and safety to the lifting system. 
         [0031]    The present invention further also relates to a method for lifting a vehicle, the method comprising the step of providing an aforementioned lifting device and/or lifting system. 
         [0032]    The method provides the same advantages and effects as those stated with reference to the lifting device and lifting system. In particular, the use of the lifting device(s) according to the present invention increases the overall safety and robustness of the lifting operation, and in addition, reduces the risk of failure including hydraulic fluid leaking from a lifting device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    An exemplary embodiment of a lifting device and lifting system according to the present invention is described herein below on the basis of a non-limitative exemplary embodiment thereof shown in the accompanying drawings, wherein: 
           [0034]      FIG. 1  shows a schematic overview of a vehicle lifted by lifting columns of a lifting system according to the invention; 
           [0035]      FIG. 2A-B  shows a drive for the hydraulic cylinder of the system of  FIG. 1 ; 
           [0036]      FIG. 3  shows an alternative embodiment for the drive according to the invention; 
           [0037]      FIG. 4  shows a schematic overview of the hydraulic scheme of the drive of  FIG. 2 ; 
           [0038]      FIGS. 5-7  show alternative embodiments of lifting columns of lifting systems according to the invention; and 
           [0039]      FIGS. 8A-B  and  9  show further alternative in-ground embodiments of lifting devices of a lifting system according to the invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0040]    A system  2  for efficient lifting and lowering a load ( FIG. 1 ) comprises four mobile lifting columns  4  in the illustrated embodiment. Lifting columns  4  lift a passenger car  6  from the ground  8 . Lifting columns  4  are connected to each other and/or a control system by wireless communication means or alternatively by cables. Lifting columns  4  comprise a foot  10  which can travel on running wheels  12  over ground surface  8  of for instance a floor of a garage or workshop. In the forks of foot  10  is provided an additional running wheel (not shown). Lifting column  4  furthermore comprises a mast  14 . A carrier  16  is moveable upward and downward along mast  14 . Carrier  16  is driven by a motor  18  of the drive of the lifting column that is provided in a housing of lifting column  4 . Motor  18  is supplied with power from the electrical grid or by a battery that is provided on lifting column  4  in the same housing as motor  18 , or alternatively on foot  10  (not shown). Control with control panel  20  is provided to allow the user of system  2  to control the system, for example by setting the speed for the carrier  16 . In one embodiment, motor  18  is a 3-phase low voltage motor controlled by a separate controller. In another embodiment, motor  18  is a 3-phase low voltage motor with integrated controller. Such motor with integrated controller can also be used in combination with conventional lifting devices with conventional height measurement systems. 
         [0041]    Lifting system  2  includes at least two lifting columns  4 . Each of the lifting columns has at least one ascent mode and one descent mode, and is under the influence of a control  20 . Control  20  can be designed for each lifting column  4  individually, or for the lifting columns  4  together. A pressure or load sensor may be used for monitoring, control and indication of the load that is lifted with lifting system  2 . 
         [0042]    Integrated hydraulic cylinder drive unit  22  ( FIG. 2A ) comprises a cylinder housing  24  wherein piston rod  26  can be displaced. Height measuring system  28  measures sensor code  30  that is provided on piston rod  26  using sensor system  32  comprising a number of sensor coils  34 . In the illustrated embodiment sensor code  30  is a magnetic code. Displacement of piston rod  26  changes the magnetic field that is measured with sensor coils  34 . 
         [0043]    In the illustrated embodiment locking system  36  is integrated in height measuring system  28  ( FIG. 2A ). Locking system  36  ( FIG. 2B ) comprises a spring element  36   a,  clamp block  36   b , hydraulic fluid supply  36   c  and rod clamp  36   d.    
         [0044]    Without oil or hydraulic fluid pressure spring element  36   a  forces clamp block  36   b  upwards thereby forcing rod clamps  36   d  inward into contact with piston rod  26 . This locks piston rod  26  and prevents displacement thereof ( FIG. 2A ). 
         [0045]    When supplying fluid pressure through supply  36   c  clamp, block  36   b  is forced downward against the spring force of spring element  36   a.  This enables rod clamp  36   d  to move outward away from piston rod  26  thereby unlocking piston rod  26  and enabling displacement thereof ( FIG. 2B ). 
         [0046]    The advantage of the illustrated embodiment is that when hydraulic fluid pressure is accidentally removed from the system, piston rod  26  is locked and maintained in a safe position. This provides additional safety to the lifting device  2  according to the present invention. It will be understood that alternative configurations of lock system  36  would also be possible in accordance with the present invention. In the illustrated embodiment the two rod clamps  36   b  are embodied as semi-circular bodies to increase the contact area between rod clamp  36   d  and piston rod  26 . It will be understood that another number of rod clamps  36   d  can also be applied in accordance with the invention. 
         [0047]    Integrated hydraulic fluid tank and motor unit  38  ( FIG. 2A ) comprises motor  40 , pump  42  with suction pipe  44  ( FIG. 2A ). Valve block  46  directs hydraulic fluid  54  from reservoir  52  towards supply pipe  48  towards connection  50  between reservoir  52  and cylinder housing  24  and vice versa depending on the direction of displacement of piston rod  26 . An inlet/outlet opening  56  is provided to reservoir  52 . 
         [0048]    In the illustrated embodiment, when carrier  16  needs to be raised, piston rod  26  will displace. In the illustrated embodiment piston rod  26  will move in an upward direction by providing hydraulic fluid  54  to cylinder housing  24  with pump  42  that is driven by motor  40 . After sensing with height measurement system  28  that piston rod  26  has reached the desired height or the desired position, and therefore carrier  16  has reached its desired height, locking system  36  locks piston rod  26 . In case carrier  16  needs to be lowered, locking system  36  unlocks piston rod  26  and piston rod  26  will displace in a downward direction thereby forcing hydraulic fluid  54  back into reservoir  52 . 
         [0049]    In an alternative embodiment of an integrated hydraulic fluid tank and motor unit  58  ( FIG. 3 ), pump  60  is submerged in hydraulic fluid  54  in reservoir  52  together with valve block  66 , pump  62 , suction pipe  64 , supply pipe  68  and connection  70 . It will be understood that this results in an increased compactness of the integrated hydraulic fluid tank and motor unit. 
         [0050]    Hydraulic scheme  72  ( FIG. 4 ) illustrates the hydraulic connection between individual components of lifting device  2 . Hydraulic scheme  72  illustrates the reduction of components, hoses and connections in lifting device  2  in comparison with conventional lifting devices. In the illustrated embodiment valve block  46 ,  66  comprises a safety/recirculation pipe  74  with valve  76  enabling recirculation of hydraulic fluid in reservoir  52 . Supply pipe  48 ,  68  is provided with valve  78  and valve  80 . It will be understood that alternative embodiments of hydraulic scheme  72  can be envisaged in accordance with the present invention. 
         [0051]    An alternative height measurement that can be used in addition, or as an alternative, to other height measurements, is measurement of the level of hydraulic fluid in reservoir  52 , for example with a level sensor using ultrasound or induction. This measurement is also capable of detecting leakage of hydraulic fluid. 
         [0052]    The present invention can be applied to the (wireless) lifting columns illustrated in  FIG. 1 . Alternatively the invention can also be applied to other types of lifting columns and lifting systems that will be described next. 
         [0053]    For example, a four-post lifting system  102  ( FIG. 5 ) comprises four columns  106  carrying runways  106 . Optionally, columns  104  comprise sensor  108 . In the illustrated embodiment an indicator  110  with a green light  112  and a red light  114  is provided. Indicator  110  can be used for load sensing. Light  110  signals to the driver when vehicle  6  is positioned correctly relative to columns  104  and the vehicle  6  can be lifted. In case each column  104  is provided with sensor  108  the position of the carrier  106  can be double checked in relation to height measurement system  28 . This contributes to the overall safety of the lifting operation. In addition thereto, or as an alternative therefor, indicator  110  can be used for position or speed control to indicate to a user that the system is operating correctly with carriers/runways  106  being at the same height, or indicate that there is some safety concern, for example. 
         [0054]    As a further example, lifting system  202  ( FIG. 6 ) comprises a so-called sky-lift configuration with four posts  204  carrying runways  206 . In the illustrated embodiment, optionally, additional sensor  208  is provided for every post  204 . This enables an additional safety check in addition to that of height measuring system  28  on positioning  206  of the carrier as described earlier. A light  210  with green  212  and red  214  lights can be provided on wall  216  to indicate to the driver of vehicle  6  that the vehicle is positioned correctly or needs to be repositioned and/or to indicate the controller status and/or indicate correct positions of carriers  206 . 
         [0055]    As an even further example, lifting system  302  ( FIG. 7 ) comprises a so-called two-post configuration with two posts  304  that are provided with carrier arms  306 . In the illustrated embodiment to measure position and speed of carrier arms  306 , optionally, additional sensor  308  is provided. This enables an additional check on positioning of carriers/arms  306  as described earlier. A light  310  with green  312  and red  314  lights can be provided to indicate to the driver of vehicle  6  that the vehicle is positioned correctly or needs to be repositioned and/or to indicate the controller status. 
         [0056]    In a further alternative embodiment lifting system  402  ( FIG. 8A-B ) is of the in-ground lift type comprising stationary lifting column/device  404  and a moveable lifting column/device  406  that are located on or in floor  408 . The front lifting column/device  404  is provided in cassette or box  410  with a telescopic lifting cylinder  412 . On top of cylinder  412  there is provided carrier  414  with axle carriers  416 . In the illustrated embodiment wheel edges or wheel recesses  418  are provided. Recesses  418  define the position of the front wheels of the vehicle. Furthermore, in the illustrated embodiment a hatch  420  is provided in front of the front lifting column/device  404  for maintenance, for example. 
         [0057]    The moveable lifting column/device  406  moves in cassette or box  422  comprising a telescopic lifting cylinder  430 . Box  422  provides a pit with a slot or recess  424  for guiding the moveable lifting column/device  406 . Moveable lifting column/device  406  is provided with carrier  426  whereon axle carriers  428  are mounted. Depending on the type of vehicle  432  additional adapters can be provided that cooperate with carriers  414 ,  426  to enable engagement with different axle dimensions. 
         [0058]    In an alternative lifting system  502  of the in-ground type ( FIG. 9 ) the telescopic lifting cylinders  412 ,  430  of lifting system  402  are replaced by scissor type lifts  504 ,  506 . It will be understood that operation of lifting systems  402 ,  502  of the in-ground type is similar. 
         [0059]    It will be understood that the invention can be applied to a range of lifting systems such as described above, including but not limited to four-post and two-post lifting columns, such as the Stertil-Koni one post lifts ST1075, the Stertil-Koni two post lifts SK 2070, and the Stertil-Koni four post lifts ST 4120, skylift, mobile columns, and in-ground lifts, such as the Stertil in-ground Ecolift and the Stertil in-ground Diamond lift. Also, it will be understood that additional embodiments of the invention can be envisaged combining and/or switching features from the described and/or illustrated embodiments. For example, instead of light  110 ,  210 , or in addition thereto, sound signals, indications on a control system etc. can be applied. 
         [0060]    The present invention is by no means limited to the above described preferred embodiments. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged. The present invention is described using a lifting device such as a lifting column and more specifically a mobile lifting column. The invention can also be applied to other type of lifting columns such as so-called boom-lifts, scissor-lifts and loading platforms. Such lifting equipment can be provided with the measures illustrated above according to the invention.