Abstract:
The issue is to show displayed items on a display device of a cargo-handling vehicle, where only a display device having a small display space can be used, so that operations accompanying the operating sequence of the cargo-handling vehicle can be performed. The device has a tilt angle sensor, which detects forward tilt or backward tilt by a mast provided at the front of the cargo handling vehicle, a hydraulic pressure sensor, which measures the supply hydraulic pressure to a lift cylinder that is provided on the mast and raises and lowers a fork, and a calculation unit, which converts the cylinder supply hydraulic pressure detected by said hydraulic pressure sensor to the weight of the cargo loaded on the aforementioned fork. A selection display area is also provided, which selectively displays the tilt angle and the weight in the same location outside of the vehicle speed display area. When the vehicle&#39;s power is turned on and the tilt angle sensor detects forward tilt or backward tilt continuing for a predetermined period of time when the aforementioned mast is tilting forward or tilting backward, the tilt angle is displayed. When the application of pressure in a direction to raise the fork is detected, continuing for a predetermined period of time, the weight of the loaded cargo calculated by the calculation unit is displayed, with priority given to display of the tilt angle.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a display device for cargo-handling vehicles, especially for vehicles with a small display device having a small display due to limited space for installing the display device, such as a forklift, in which0 the limited display space can be utilized and the display device displays items in an operation sequence of the cargo-handling vehicle. 
     2. Description of the Related Art/Background Art 
     A schematic structure of a forklift as a cargo-handling vehicle shown in  FIG. 4  has a vehicle body  72  equipped with front wheels  70  and rear wheels  71 , a fork  73  for loading a cargo  86 , and a mast consisting of an outer mast  74  and an inner mast  75  for raising and lowering the fork  73 , and being provided at the front of the vehicle body  72 . 
     The fork  73  is installed on the mast via lift brackets  76 , and the fork is constructed in such way that the outer mast  74  is capable of controlling a position of the cargo  86  forward and backward by tilting the fork  75  forward or backward (tilting operation), and the inner mast  75  being fixed to the top part of the outer mast  74  and being connected to the lift brackets  76  via rails, so as to move the fork  73  having the cargo  86  loaded thereon and the lift bracket  76  in the vertical direction along the rail (lifting operation) by the outer mast  74  and inner mast  75 . 
     The outer mast  74  is capable of controlling the tilt angle around a supporting axis of the outer mast  74  by a tilt cylinder  77 . The lift bracket  76  is constructed to move in the vertical direction on the rail of the inner mast  75  via a chain wheel  79  and a chain  80  with the vertical movement of a lift cylinder  78 . Thus, the fork  73  for loading the cargo  86  thereon connected to the tip of the lift bracket  76 , can be controlled to move forward and backward and up and down 
     A tilt angle sensor  81  such as a potentiometer, which detects change of the tilt cylinder  77 , is provided on the tilt cylinder  77 . And a lift sensor such as a wire-type displacement sensor  82 , which detects change of the lift cylinder  77  in the vertical direction, is provided on the lift cylinder  78 . A hydraulic pressure sensor  85  which measures the hydraulic pressure of the oil being supplied to the lift cylinder  78 , is provided on a hydraulic pipe  84  filled with oil  83   b  for pressurizing the lift cylinder  78 . With this structure, the hydraulic pressure in the direction to raise the fork  73  is converted to the weight of the cargo, so as to measure the weight of the cargo  86  loaded on the fork  73 . 
       FIG. 5  is a perspective view of a driving unit of a forklift as a cargo-handling vehicle. The figure shows a handle  90 , a display unit  91  for displaying speed, fuel gage, weight of the loaded cargo  86 , tilt angle of the mast and the like, a forward-backward lever  92  for shifting gears between forwarding and reversing, a parking-brake lever  93 , a lift lever  94  for raising and lowering the fork  73 , a tilt lever  95  for controlling the position of the cargo  86  loaded on the fork  73  forward and backward by tilting the mast forward or backward, a brake pedal  96  and an accelerator pedal  97 . 
       FIG. 6  is a diagram to explain an example of operation sequence for moving the cargo  86  by the forklift  72  as a cargo-handling vehicle. As shown in  FIG. 6(A)  which is a preparation state before loading the cargo  86 , the tilt lever  95  is pulled and the mast is tilted backward so as to raise the fork  73  by 15 to 20 cm from the ground. In the state, the forklift  72  drives to the location where the cargos  86  are placed. Next, as shown in  FIG. 6(B)  the forklift  72  stops where the distance between the front tip of the fork  73  and the cargos  86  is about 20 to 30 cm and the parking-brake lever  93  being pulled to a lock position. 
     As shown in  FIG. 6(C) , the mast tilted by operation of the tilt lever  95  is returned to an upright position and being lifted by operation of the lift lever  94  to the same height as an insertion gap of pallets. In the state, as shown in  FIG. 6(D) , the parking-brake lever  93  is released, the forward-backward lever  92  being moved so as to the forwarding position to move the forklift slowly forward, the fork  73  being inserted between the pallets, the forklift  72  stopping and the parking brake  93  being moved to the lock position. 
     Next, as shown in  FIG. 6(E) , the cargo  86  is lifted by about 10 cm with operation of the lift lever  94 , and as shown in  FIG. 6(F)  the tilt lever  95  is pulled so as to tilt the mast backward for a stable transportation of the cargo. In the state, the forward-backward lever  92  is moved to the reverse position, the parking-brake lever  93  being released, the forklift backing up to the location where the cargo  86  can be safely unloaded. 
     Then, the forklift stopping about 20 to 30 cm away from the stack of remaining cargos  86 , the parking-brake lever  93  being locked, and the lift lever  94  being operated as to lower the fork  73  so that the bottom of the fork  73  is about 15 to 20 cm off the ground as shown in  FIG. 6(G) . In the state, as shown in  FIG. 6(H)  the forward-backward lever  92  is moved to the reverse position, the parking-brake lever  93  being released so as to back up the forklift to the location where the forklift can safely change the direction, and then the forklift moving to a destination such as to a truck. 
     These are examples of the schematic structure of the forklift as a cargo-handling vehicle and operation examples of moving the cargos. With this type of forklift, in the case of loading the cargos  86  onto a truck it is preferable to display the weight of the cargo loaded on the forklift while lifting the cargo  86  so as to avoid the total weight of the cargos exceeding the maximum allowable weight of the truck. Moreover, when an entry-level operator operates the forklift, it is hard to visibly confirm a forward or backward tilt of the mast (tilt angle), and thus display of current state of the tilt angle is desired. 
     In this case, a passenger vehicle has a sufficient space for a display device displaying a variety of information such as vehicle speed, engine rotation, fuel gage, shift lever position, engine coolant temperature, a traveling distance, a light operation mode, an operation mode of a windshield wiper, turn-signal signs, an operation mode of air-conditionings, indoor temperature and the like. However, in a cargo-handling vehicle such as a forklift, visibility from the front is important and as shown in  FIG. 5 , the display device  91  can only be installed in a small space such as on a front side of the vehicle body with respect to a steering wheel  90 , and thus only a small display device with a small display can be installed. 
     In order to display essential pieces of information in a display device with limited space, Patent Reference 1 (JP5-260605A) proposes a monitor device with alert indications in which when any abnormality is detected in the vehicle, the display is automatically switched to a alarm display showing contents of the abnormality along with alarm, the alarm being turned off by pressing a confirmation key, and the display being returned to a normal display or switched to a detailed display of the abnormality so as to provide sufficient information. 
     Patent Reference 2 (JP6-67158A) discloses a display device for a vehicle in which for the purpose of easy confirmation of conditions of the vehicle, a multi-display is provided adjacent to a speed indicator which is always on and normally displays a rotation speed of the engine but switched to a warning indication upon receiving signals from a variety of warning sensors in the case of detecting any defects. In a similar manner, the display is changed when a shift lever, light switch or radio switch is turned on. 
     Furthermore, Patent Reference 3 (JP2003-173210A) proposes a display device in an operating machine such as a combine, in order to display plural types of abnormal information in a LCD display device provided in the combine for easy confirmation of the displayed information. The proposed display device has a CAN controller which shows each piece of the abnormal information sequentially on LCD display panel. 
     However, all of the display devices disclosed by the cited references have a limited space for a display. The display device of Patent Reference 1 switches the normal display to the alert display indicating details of the detected abnormality. The display device disclosed in Patent Reference 2 switches the display in the case of detecting defects of the parts or operation the shift lever, light switch and radio switch. The display device of Patent Reference 3 switches the display sequentially to show information of abnormality. However, there is no indication of displaying warnings in such a case that an entry-level operator operates the vehicle without following the operation sequence as described above such as driving the forklift while the fork  73  is upright or the mast is tilted forward and the tip of the fork  73  is barely off the ground. 
     Therefore, an object of the present invention is to provide a display device of a cargo-handling vehicle such as a forklift which can use only a display device with a small display due to a limited space to install the device, wherein the small display space is fully utilized and the operation steps of the cargo-handling vehicles are sequentially displayed in the order of the operation. 
     SUMMARY OF THE INVENTION 
     In order to achieve the object, the present invention proposes a display device for a cargo-handling vehicle which has a mast located at a front of the vehicle, the mast being capable of tilting a fork forward and backward around a support axis and moving the fork up and down, a tilt-angle detector detecting a tilt angle of the mast, and a cargo weight detector detecting weight of a cargo loaded on the fork, the display device comprising: 
     a display which displays speed of the cargo-handling vehicle, the tilt angle of the mast and the cargo weight; and 
     a control unit which controls the display, 
     wherein the display includes a speed display area displaying the speed of the cargo-handling vehicle and a selection display area which selectively displays the tilt angle and the weight outside the speed displaying area, 
     wherein the control unit controls the display so that contents of the selection display area are changed depending on driving states of the cargo-handling vehicle including an initial driving state from turning on the cargo-handling vehicle to starting the vehicle, a slow driving state from staring the vehicle to reaching a prescribed speed and a normal driving state when the vehicle drives at the prescribed speed or higher, and 
     wherein at least in the initial driving state, the selection display area displays the tilt angle detected when turning on the vehicle, and in the normal driving state, the selection display area displays only error indications. 
     In this manner, the tilt angle and the cargo weight are displayed in the same area, i.e. the selection display area, and the tilt angle is displayed in the initial driving state so that the display device displays the fork being upright or tilted with the tip thereof barely off the ground when the cargo-handling vehicle is turned on. This allows the operator to recognize any existing problem before driving the vehicle and prompts the operator to drive in the order of the operating sequence as shown in  FIG. 6 . 
     As the tilt angle and the cargo weight are selectively displayed in the selection display area, both of the tilt angle and the cargo weight can be displayed when only the display device with a small display can be used, which allows easy understanding of the total weight of the cargos loaded on the vehicle such as a truck by adding the cargo weights displayed in the selection display area. 
     Furthermore, in the slow driving state, the selection display area displays either the tilt angle being currently detected by the tilt-angle detector or the cargo weight being detected by the cargo weight detector, and 
     the control unit controls the selection display area so as to display the tilt angle in priority to the cargo weight, the selection display area switching from the tilt angle to the cargo weight only when the cargo-weight detector detects a change of the cargo weight not less than a prescribed value. 
     When using a cargo-handling vehicle such as a forklift which normally does not have suspension, vibration from the ground is directly passed to the fork and the change of the tilt angle or the cargo weight may be momentarily detected due to the vertical movement of the loaded cargo from the vibration. However, the selection display area displays the tilt angle or the cargo weight only in the slow driving state when the vibration is small, and displays the cargo weight only when the change of the cargo weight is not less than a prescribed value, and thus there is no displaying incorrect tilt angle or cargo weight in spite of influence of the vibration. 
     Furthermore, only the error indications are displayed in the normal driving state, and displaying of the tilt angle or the cargo weight is needed only in the initial driving state and when the cargo being loaded and not needed until the cargo being loaded onto a truck or being unloaded onto another location. Thus, when returning from the normal driving state to the slow driving state, if one of the tilt angle and the cargo weight changes, the control unit controls the selection display area so as to display the one of the tilt angle and the cargo weight. With this configuration, only the display of the changed one is needed when the cargo is loaded onto the truck or unloaded onto another location, when returning from the normal driving state to the slow driving state, or when the vehicle stops. The display device shows only essential information when needed. 
     Furthermore, the tilt angle displayed in the selection display area includes an image representing the tilt angle of the fork so as give the operator intuitive acknowledgement of the tilt angle (forward tilt or backward tilt). 
     And the error indications are given the priority in any case of the initial driving state, the slow driving state or the normal driving state so that error indications can be displayed in the cases of failure of the control unit such as CPU or failure of components such as the coolant temperature rising and hydraulic pressure drastically declining without providing a separate display area for the error indications. 
     Moreover, the tilt angle displayed in the selection display area during the slow driving state is updated when a change component of a tilt-angle signal from the tilt-angle detector exceeds a prescribed threshold, or the tilt angle displayed in the selection display area during the slow driving state is updated when the tilt-angle detector keeps detecting the tilt angle not less than a prescribed value for a predetermined period of time. When using a cargo-handling vehicle such as a forklift which normally does not have suspension, vibration from the ground is directly passed to the fork and the tilt angle may be momentarily changed due to the vertical movement of the loaded cargo from the vibration. However, the tilt angle is updated when a change component of a tilt-angle signal from the tilt-angle detector exceeds a prescribed threshold or when the tilt-angle detector keeps detecting the tilt angle not less than a prescribed value for a predetermined period of time. Thus, the change of the tilt angle when the operator operates the tilt lever can be distinguished from the change of the tilt angle due to the vibration from the ground, and it is possible to display a correct tilt angle. 
     And the cargo weight detector includes a hydraulic sensor which calculates the cargo weight from the hydraulic pressure moving the fork. The cargo-handling vehicle normally has a hydraulic cylinder controlled by the hydraulic pressure pump so as to move the fork, and the hydraulic pressure is monitored by the hydraulic pressure sensor. The cargo weight and the hydraulic pressure are in relation to each other and the cargo weight can be measured from the hydraulic pressure. Thus, the weight of the loaded cargo can be measured without providing a separate measuring device for measuring the cargo weight. 
     In the similar manner as determining the tilt angle, the cargo weight displayed in the selection display area is determined based on the hydraulic pressure detected for a predetermined period of time, the hydraulic pressure corresponding to a static load of the cargo received on the fork, and also the display is switched to the loaded cargo weight when the cargo-weight detector keeps detecting the change of the cargo weight not less than a prescribed threshold for a predetermined period of time. As the static load of the cargo received on the fork is determined when the change of the cargo weight not less than a prescribed threshold is detected, the change of the cargo weight when the operator operates the lift lever can be distinguished, and there is no error in displaying the cargo weight. 
     Accordingly, if only the display device with a small display can be installed due to the limited space, the display device for a cargo-handling vehicle of the present invention can display the tilt angle in the initial driving state when the cargo-handling vehicle is turned on, so as to prompt the operator to drive in the correct operation sequence if there is a problem with driving the vehicle in the indicated state of the fork. And the selection display area switches from the tilt angle to the cargo weight when the cargo is lifted so as to promote easy understanding of the total weight of the cargos being loaded onto a vehicle such as a truck. Additionally, the tilt angle or the cargo weight is displayed only in the initial driving state and the slow driving state so it is possible to display the correct tilt angle or the cargo weight in spite of influence of the vibration. 
     Furthermore, the tilt angle or the cargo weight is displayed when a change component of a tilt-angle signal from the tilt-angle detector exceeds a prescribed threshold, or the tilt angle displayed in the selection display area during the slow driving state is updated when the tilt-angle detector keeps detecting the tilt angle not less than a prescribed value for a predetermined period of time. Thus, the change of the tilt angle or the cargo weight when the operator operates the tilt lever or the lift lever can be distinguished from the change of the tilt angle or the cargo weight from the influence of the vibration directly passed to the fork so it becomes possible to display the tilt angle or the cargo weight without an error. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1(A)  is a front view of a display device for a cargo-handling vehicle of the present invention, and  FIG. 1(B)  shows a display displaying a tilt angle,  FIG. 1(C)  showing tilt symbols, and  FIG. 1(D)  showing a display displaying the weight of a loaded cargo. 
         FIG. 2  is a transition diagram of displaying tilt symbols, tilt angle, load symbols or load weight displayed in the display device for the cargo-handling vehicle of the present invention. 
         FIG. 3  is a control block diagram for displaying in the display device for the cargo-handling vehicle of the present invention. 
         FIG. 4  illustrates a schematic structure of a forklift as a cargo-handling vehicle as an example. 
         FIG. 5  shows an example of a driving device of the forklift as a cargo-handling vehicle. 
         FIG. 6  is a diagram to explain an example of the operation sequence for moving a cargo by the forklift as a cargo-handling-vehicle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereafter, the present invention will be described in detail with reference to the embodiments shown in the figures. However, the dimensions, materials, shape, the relative placement and so on of a component described in these embodiments shall not be construed as limiting the scope of the invention thereto, unless especially specific mention is made. 
     First Embodiment 
       FIG. 1  (A) is a front view of a display device for a cargo-handling vehicle of the present invention, and  FIG. 1  (B) shows a display displaying a tilt angle,  FIG. 1(C)  showing tilt symbols, and  FIG. 1  (D) showing a display displaying the weight of a loaded cargo. 
       FIG. 1  shows a display device  10 , a numerical display area  11  which uses liquid crystal display and displays numerical data, vehicle speed  12 , weight symbol  14  indicating the cargo is loaded, weight  15 , a display area  16  for displaying warning or caution symbols, a first indicator  17  for displaying marks such as fuel gage, and a second indicator  18  for displaying marks such as coolant temperature. The area in which the weight symbol  14  and the weight  15  are displayed is a selection display area which also selectively displays the tilt angle  20  and a tilt angle image  21  which indicates an angle change of a mast by predetermined angle as shown in  FIG. 1  (B). 
       FIG. 1  (B) illustrates an enlarged image of a mode when the tilt symbol is displayed next to the display area displaying the vehicle speed. Shown in the figure are the tilt angle  20  and the tilt symbol  21 , the tilt symbol  21  having three symbols, a forward tilt symbol  211 , backward tilt symbol  212  and neutral symbol  213  as shown in  FIG. 1(C) .  FIG. 1  (D) illustrates an enlarged image of a loaded symbol of the cargo, weight  15 , the weight symbol  14 , and the vehicle speed  12 . 
       FIG. 2  is a transition diagram of displaying the tilt symbols and the tilt angle as shown in  FIG. 1  (B) and  FIG. 1(C) , and the load symbols and the load weight as shown in  FIG. 1  (D).  FIG. 3  is a control block diagram for displaying on a display unit for a cargo-handling vehicle of the present invention. 
     The control block diagram of  FIG. 3  will be briefly explained before explaining the transition diagram of  FIG. 2 .  FIG. 3  shows a control unit  50  which controls the cargo-handling vehicle including display control of the display unit having CPU, memory and the like; a hydraulic pressure control unit  51  for cargos; I/O interface  52  which sends to the control unit  50  signals from a keyless switch  551 , an accelerator switch  552 , a brake switch  553 , and a forward-backward lever  554  (shown as  92  in  FIG. 5 ) constituting an operation unit  55 , and from a lift lever  561  and a tilt lever  562  constituting a cargo-handling device  56 , and from a speed sensor  57  for detecting the vehicle speed, various sensors  58 , a tilt angle sensor  81 , and a hydraulic pressure sensor  85 ; a driving unit  53  including front wheels  70  and rear wheels  71  (shown in  FIG. 4 ) as well as an engine, a gear case, and a brake those which are not shown in the drawings; an display part  54  shown in  FIG. 1 ; a calculation unit  59 ; a memory unit  60  which stores various data; a tilt cylinder  61  shown as  77  in  FIG. 4 ; and a lift cylinder  62 . 
     Next, the transition diagram of  FIG. 2  will be explained in reference to  FIG. 3 . When the key switch  551  of the operation unit  55  is turned on and the vehicle starts as indicated with  30  in  FIG. 2 , the selection display area of the display device  10  is cleared as indicated with  31  during an initial driving state. In  FIG. 1  (A), the selection display area displaying the weight symbol  14  and the weight  15  in the display device  10  is the selection display area for the tilt angle and weight where the weight symbol  14  and the weight  15  or the tilt angle  20  and the tilt symbol  21  are displayed. 
     Subsequently, the tilt angle sensor  81  detects an initial tilt-angle state of the tilt cylinder  61 , the detection signal being sent to the control unit  50  via I/O interface  52 . Then, the control unit  50  moves on as shown by arrow  35  of  FIG. 2  to display the tilt angle meter as shown by  32  in  FIG. 2 , and the initial tilt-angle  20  as shown in  FIG. 1  (B) as well as an appropriate tilt symbol  21  selected from the symbols shown in  FIG. 1(C)  are displayed in the display unit  54 . Thus, as the display unit  54  displays when the fork  73  is upright or the front tip of the fork  73  is barely off the ground while driving, the operator can view the display and recognize that there is a problem in driving the vehicle, and is prompted to drive according to the operation sequence explained in  FIG. 6 . 
     As illustrated in  FIG. 6  (A), in the preparation state before moving the cargo  86 , the tilt lever  562  (shown as  95  in  FIG. 5 ) is pulled and the mast is tilted backward causing the tilt angle to change from the initial state. When the tilt angle sensor  81  detects forward tilt or backward tilt of the mast over predetermined value, specifically detecting the change of the tilt angle continuing for a predetermined period of time, or when a differential value calculated from the detected value from the tilt angle sensor  81 , specifically the displacement value, is not less than a prescribed threshold, the tilt angle is displayed. And when a differential value calculated from the value detected by the tilt angle sensor  81 , specifically a displacement value, is not less than a prescribed threshold, the tilt angle is displayed in the selection display area which selectively displays the tilt angle and the cargo weight. 
     In this process, the tilt lever  562  (shown as  95  in  FIG. 5 ) of the cargo-handling device  56  is operated so that the control unit  50  sends the signal to the hydraulic pressure control unit  51  and the hydraulic pressure is applied to the tilt cylinder  61  so as to tilt the mast backwards. Then, the tilt angle sensor  81  detects the change of the tilt angle, sending the detection signal to the control unit  50  via the I/O interface  52 . The control unit  50  sends the detection signal to the calculation unit  59  so as to calculate a differential value, i.e. a displacement value, and compares the displacement value with a threshold stored in the memory unit  60 . If the displacement value is not less than the threshold, the control unit  50  further refers to the vehicle speed being sent from the speed sensor  57  and displays an appropriate mode on the display unit  54 . For example, the vehicle speed is below 4 km/hr and a main machine (engine or motor) is turned on, the control unit  50  determines the slow driving state, thereby displaying on the display  54  the tilt angle and the backward-tilt symbol which are shown as  20  and  212  in  FIG. 1  (B) and  FIG. 1(C)  respectively. 
     Now the fork  73  is about 15 to 20 cm off the ground, and the parking-brake lever  93  being released, the forward-backward lever  554  is moved to the forward position, the accelerator switch  552  being turned on by stepping on the accelerator pedal  97 , and the vehicle moving forward to the location of the cargos. In this process, once the speed sensor  57  indicates the vehicle speed being not less than a prescribed speed, e.g. 4 km/hr or above as indicated with arrow  39 , it is determined that the vehicle is back in the normal driving mode and the tilt angle is cleared as indicated as  31  in  FIG. 2 . The step of clearing the display is also performed in the case of displaying the weight as indicated with arrow  40 . 
     And as shown in  FIG. 6(B) , the vehicle stops temporarily with a distance of 20 to 30 cm between the cargo  86  and the front of the fork  73  facing each other, and the parking-brake lever  93  being moved to the lock position. Next, as shown in  FIG. 6(C) , the tilt lever  562  ( 95  in  FIG. 5 ) is operated so as to move the backward-tilted mast to an upright position, the tilt-angle sensor  81  detecting the change of the tilt angle, and the detection single being sent to the control unit  50  via the I/O interface  52 . The control unit  50  sends the detection signal to the calculation unit  59  so as to calculate a differential value, and comparing it with a threshold of a differential value of the tilt-angle change stored in the memory  60 . If the calculated differential value exceeds the threshold, the control unit  50  refers to the vehicle speed sent from the speed sensor  57  so as to check that the main machine (engine or motor) is currently operated and the vehicle is not moving, and controlling the display to selectively display the upright symbol  213  of  FIG. 1(C)  to update the tilt symbol  21  in  FIG. 1(B)  as indicated by  32  of  FIG. 2 . 
     Subsequently, the operator operates the lift lever  561  ( 94  in  FIG. 5 ) and thus the control unit  50  controls the hydraulic pressure control unit  51  as to apply hydraulic pressure to the lift cylinder  62 , thereby raising the fork  73 . The fork  73  is raised to the height of an insertion gap of the pallets, and the hydraulic pressure sensor  85  detects the change and sending the detection single to the control unit  50  via the I/O interface  52 . Therefore, the control unit  50  sends the detection signal to the calculation unit  59  so as to calculate a differential value, i.e. the change of the cargo weight not less than a prescribed value, and if the change of the cargo weight is detected for a predetermined period of time, the differential value is compared with a threshold of a lift differential value stored in the memory  60 . If the calculated differential value exceeds the threshold, the control unit  50  refers to the vehicle speed sent from the speed sensor  57  so as to check that the vehicle is not moving, and controlling the display to switch from the tilt angle ( 33  of  FIG. 2 ) to the cargo weight ( 33  of  FIG. 2 ), displaying the weight symbol  14  in the location shown as  21  in  FIG. 1  (B). Moreover, the calculation unit  59  converts the hydraulic pressure of the hydraulic pressure sensor  85  to the weight of the cargo  86 , and the converted cargo weight being displayed in the location indicated with  20  in  FIG. 1  (B). In  FIG. 1  (B), the cargo weight is zero as the cargo  86  is not lifted. 
     In the state, the parking-brake lever  93  is released and the forward-backward lever  92  being moved to the forward position so as to move forward slowly as shown in  FIG. 6  (D). In this process, the vehicle speed does not exceed 4 km/hr, thus the load meter display  33  is not cleared, the fork  73  being inserted between the pallets, and the parking brake  93  being moved to the lock position. The lift lever  561  ( 94  in  FIG. 5 ) is operated so as to lift the cargo  86  about 10 cm off the ground as shown in  FIG. 6  (E), the hydraulic pressure sensor  85  detecting the change, sending the detection signal to the control unit  50  via the I/O interface  52 . In a similar manner as the previous case, the control unit  50  sends the detection signal to the calculation unit  59  so as to calculate a differential value, and comparing it with a threshold of the lift differential value stored in the memory  60 . If the calculated differential value exceeds the threshold, the control unit  50  refers to the vehicle speed sent from the speed sensor  57  so as to check that the vehicle is not moving and the vehicle speed is less than 4 km/hr, and controlling the display to maintain the load meter display ( 33  of  FIG. 2 ), displaying the weight symbol  14  in the location shown as  21  in  FIG. 1  (B). Moreover, the calculation unit  59  converts the hydraulic pressure of the hydraulic pressure sensor  85  to the weight of the cargo  86 , and in this case as the cargo  86  being lifted, the calculated cargo weight is displayed in the area shown as  20 . 
     Then, the tilt lever  562  ( 95  in  FIG. 5 ) is pulled so as to tilt the mast backward as shown in  FIG. 6  (F), and stabilizing the cargo  86 . The tilt-angle sensor  81  detects the movement and the detection signal being sent to the control unit  50  via the I/O interface  52 . In a similar manner as the previous cases, the control unit  50  sends the detection signal to the calculation unit  59  so as to calculate a differential value, and comparing it with a threshold of a differential value of the tilt-angle change stored in the memory  60 . If the calculated differential value exceeds the threshold, the control unit  50  refers to the vehicle speed sent from the speed sensor  57  so as to check that the vehicle is not moving, and controlling the display  54  to display the tilt angle  20  of  FIG. 1  (B) and the backward-tilt symbol  212  of  FIG. 1(C)  to update the tilt angle  21 . 
     In this manner, the tilt angle and the load of the cargo (weight measurement from the lift movement) are measured. For example, when the various sensors  58  detects abnormalities including failure of the control unit such as CPU or failure of components such as the coolant temperature rising and hydraulic pressure drastically declining due to malfunction of the hydraulic pressure pump, the detection signal is sent to the control unit  50  via the I/O interface  52 . In the next step as explained as  34  in the transition diagram of  FIG. 2 , the control unit  50  retrieves error codes corresponding to the detected abnormality from the memory  60 , and controlling the display  54  to display the error indications in the area where the tilt angle  14  and the cargo weight  15  are shown in  FIG. 1  (A). The aforesaid error indications are given the priority in any case of the normal driving state when the vehicle speed is not less than 4 km/hr, the initial driving state and the slow driving state when the tilt angle or the cargo weight is displayed. Consequently, it is not necessary to provide a separate display area for the error indications, and in the case of detecting abnormalities, the display promptly display the error indications. 
     Moreover, According to the transition diagram of  FIG. 2 , the tilt angle or the cargo weight is cleared once the vehicle speed becomes not less than 4 km/hr. However, this predetermined speed is a mere example and can be arbitrarily set. In reference to  FIG. 2 , when the vehicle speed becomes not less than 4 km/hr, i.e. the normal driving state, the tilt angle display or the cargo weight display is cleared, and when the vehicle speed returns to slower than 4 km/hr, i.e. the slow driving state, the tilt angle or the cargo weight whichever changes. 
     As explained above, the display device of the present invention for the cargo-handling vehicle, initially displays the tilt angle when turning on the vehicle, which allows the operator to recognize any existing problem before driving the vehicle and prompts the operator to drive in the order of the operating sequence. And when lifting the cargo, the cargo weight is displayed instead of the tilt angle so as to promote easy understanding of the total weight of the cargos being loaded onto a vehicle such as a truck. The tilt angle or the weight of the loaded cargo is displayed when the speed sensor detects the vehicle speed being not more than a predetermined speed, i.e. in the initial driving state and the slow driving state. Therefore, there is not such an error as displaying a wrong tilt angle or cargo weight affected by the vibration. 
     Furthermore, the tilt angle or the cargo weight is displayed when the tilt-angle sensor or the hydraulic pressure sensor detects the change of the pressure for tilting the mast forward or backward or the pressure for raising the fork to be not less than a predetermined value, when the change is detected for a predetermined period of time, or when the differential value calculated from the outputs of tilt angle sensor or the hydraulic pressure sensor exceeds the prescribed threshold. Therefore, the change of the tilt angle or the cargo weight when the operator operates the tilt lever or lift lever can be distinguished from the change of the same affected by the vibration from the ground, and there is no such error as displaying wrong tilt angle or cargo weight. 
     INDUSTRIAL APPLICABILITIES 
     The cargo-handling vehicle described in the present invention comprises a display device which prompts the operator to drive in the correct operation sequence, thereby achieving a safe driving of the cargo-handling vehicle.