Abstract:
A system for controlling gear shifting of an industrial vehicle having a transmission operable between at least two gear ratios by actuation of a transmission actuator. The system generally comprises a sensor configured to monitor one or more vehicle parameters and a controller associated with the sensor and the transmission actuator. The controller is configured to prevent actuation of the transmission actuator unless one or more vehicle parameters is in a predetermined condition.

Description:
BACKGROUND  
         [0001]    The present invention relates to industrial vehicles, and more particularly to devices for controlling the transmission of such vehicles.  
           [0002]    Many industrial vehicles include a tractor which is mobilized either by separate wheels or by tracks driven by wheel trains. In both cases, the wheels of the tractor are typically rotated by a drive system that includes one or more motors, each having a shaft connected to driven wheels by means of a transmission mechanism. Generally, such transmission mechanisms are adjustable between at least two operating conditions, for example, a “high speed/low torque”condition and a “low speed/high torque” condition, and may operate at three or more states to inversely vary the torque and speed.  
           [0003]    In many industrial vehicles, the transmission mechanisms are gear trains that are adjustable between different operating states or “gear ratios” by means of one or more actuators, for example, hydraulic clutches. The clutches function to alternatively engage with and disengage from certain gear train components in order to change gear ratios, and thus vary the speed and torque applied to the driven wheels. However, due to the mass of these vehicles, changing between gear ratios when the vehicle is moving above a given speed may damage the transmissions. As such, the operating manuals generally instruct the operator to stop the vehicle prior to changing of the gear ratio, which instruction may or may not be followed.  
         SUMMARY  
         [0004]    The present invention provides a system for controlling gear shifting of an industrial vehicle having a transmission operable between at least two gear ratios by actuation of a transmission actuator in response to a gear ratio command. The system generally comprises a sensor configured to monitor one or more vehicle parameters and a controller associated with the sensor, the gear ratio command and the transmission actuator. The controller is configured to prevent actuation of the transmission actuator unless one or more vehicle parameters is in a predetermined condition. In a first embodiment, the sensor monitors the speed of the vehicle and actuation of the transmission actuator is prevented unless the vehicle speed is less than or equal to a limit value. In a second preferred embodiment, the sensor monitors whether the vehicle drive system is in neutral or in drive and actuation of the transmission actuator is prevented unless the drive system is in neutral. By preventing actuation of the transmission actuator, the controller helps reduce the risk of damage to the transmission. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is an isometric view of an illustrative industrial vehicle.  
         [0006]    [0006]FIG. 2 is a bottom plan view illustrating the drive system of the vehicle of FIG. 1.  
         [0007]    [0007]FIG. 3 is a system diagram of a first embodiment of the transmission control system of the present invention.  
         [0008]    [0008]FIG. 4 is a flow diagram of a first control sequence of the controller of the first embodiment.  
         [0009]    [0009]FIG. 5 is a flow diagram of a second control sequence of the controller of the first embodiment.  
         [0010]    [0010]FIG. 6 is a system diagram of a second embodiment of the transmission control system of the present invention.  
         [0011]    [0011]FIG. 7 is a flow diagram of a first control sequence of the controller of the second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    The preferred embodiments of the present invention will be described with reference to the drawing figures with like numerals representing like elements throughout. Certain terminology, for example, “right”, “left”, “forward” and “reverse”, is used in the following description for clarity of relational description only and is not intended to be limiting.  
         [0013]    Referring to FIGS. 1 and 2, an illustrative industrial vehicle, a paver  10 , is shown. The illustrated paver  10  includes a tractor  12 , mounted on opposed drive tracks  14 , and various conveyors  36  and augers  38 . Power is provided by an engine  16  and delivered through a PTO clutch  18  and drive shaft  20  to a pump drive box  22 . Traction drive power is hydrostatically transmitted from independent left-hand and right-hand traction drive pumps  24   a ,  24   b  to left-hand and right-hand drive units  26   a ,  26   b  located inside the respective drive track assemblies  14 . In vehicles having separate wheels and a steering wheel, as opposed to independent drive tracks, a single drive unit may be used. Each drive unit  26   a ,  26   b  includes a motor  28  coupled to a planetary transmission hub  30  via an actuator  31 , in this case, a solenoid valve controlled hydraulic clutch. Mechanical levers  29   a ,  29   b  control the traction drive pumps  24   a ,  24   b  to operate the drive motors  28  between neutral and forward and reverse drive. The left and right-hand actuators  31  are controlled by an operator input device  32  on the operator&#39;s console  34 . The input device  32  provides an electrical signal indicative of the desired gear ratio. Preferably, a single device is utilized to send a common signal to both actuators  31  such that both transmissions  30  maintain the same gear ratio. While the illustrated vehicle is described with specific control levers, transmissions and actuators, other devices may also be used.  
         [0014]    In the present invention, a transmission control system  100  is positioned in the path of the gear input signal between the input device  32  and the actuators  31 . Preferably the control system  100  is self-contained such that it can be manufactured within a vehicle electrical system or spliced into the electrical system of an existing vehicle. Additionally, the self-contained system  100  can easily be removed from the electrical system, for example, for maintenance or replacement.  
         [0015]    Referring to FIGS. 3 and 4, a first embodiment of the control system  100  is illustrated. In this embodiment, the control system  100  includes a controller  110  which receives input from the gear inputs  32  and from a vehicle speed sensor  120 , for example, the vehicle&#39;s speedometer sensor. Based on the information received from the gear and speed inputs  32 ,  120 , the controller  110  determines the appropriate gear signal to be sent to the transmission actuators  31  which in turn control the gear ratios of the transmissions  30 .  
         [0016]    The controller  110  determines the appropriate gear signal in accordance with the flow diagram illustrated in FIG. 4. The controller  110  continuously monitors the gear input and determines if it is equivalent to the current gear. If it is, the controller  110  maintains the current gear signal being sent to the actuators  31 . As such, if the gear input is not changed, the controller  110  maintains a continuous loop of checking the input and maintaining the gear signal at the current value. If, on the other hand, the gear input is changed, the controller  110  then determines, based on the vehicle speed input  120 , if the vehicle speed is above a limit value. It is preferred that the limit value equal zero, however, for different vehicles and different transmission arrangements, it may be acceptable to change gears at speeds greater than zero. For example, with the illustrated paver, it may be acceptable to change gears when the vehicle speed is 10 feet-per-minute or less. The limit speed can be set to meet the criteria of a given application.  
         [0017]    If the vehicle speed is less than or equal to the limit value, the controller  110  sends the new gear input to the actuators  31  which in turn change the transmission gear ratios. If the vehicle speed is greater than the limit value, the controller  110  maintains the current gear signal being sent to the actuators  31 , i.e., the controller  110  prevents a gear change while the vehicle speed is greater than the limit value. The controller  110  then waits a given amount of time, for example, 5 seconds, and again determines if the vehicle speed is greater than the limit value and repeats the control sequence as described above. It is intended that the operator will recognize that the gear ratio has not changed, and thereby will be alerted to slow the vehicle to a speed at or below the limit value. The control system  100  may also include an indicator (not shown), for example, a light or sound, which alerts the operator that the gear change is being prevented due to vehicle speed. Once the vehicle speed has been slowed to or below the limit speed, the controller  110  sends the new gear input to the actuators  31  which in turn change the transmission gear ratios as described above.  
         [0018]    Referring to FIG. 5, an alternate control sequence is illustrated. In this sequence, if the speed is greater than the limit value, the controller  110  automatically places the vehicle drive into neutral to assist in slowing the vehicle and alerting the operator. If the vehicle has an electrically control drive mechanism, the controller  110  is configured to provide the drive mechanism with a neutral signal. If the drive mechanism is a mechanical system, as in the illustrated paver  10 , the vehicle is provided with a mechanical shift override, an electro-mechanical device configured to receive a signal from the controller  110  and mechanically override the vehicle mechanical system to place the drive in neutral. After the drive is in neutral, the controller  110  will wait a predetermined amount of time and repeat the control sequence described above.  
         [0019]    Referring to FIGS. 6 and 7, a second embodiment of the control system  200  is illustrated. The controller  110  receives input from the gear input  32  and a vehicle drive input  220 . The vehicle drive input  220  is configured to signal the controller  110  whether the respective traction drive motors  28  are in neutral, or alternatively, are in forward or reverse drive. In the preferred embodiment, the specific drive direction is not material, only the distinction between neutral and a drive condition. Based on the information received from the gear and vehicle drive inputs  32 ,  220 , the controller  110  determines the appropriate gear signal to be sent to the transmission actuators  31  which in turn control the gear ratios of the transmissions  30 .  
         [0020]    The controller  110  determines the appropriate gear signal in accordance with the flow diagram illustrated in FIG. 7. The controller  110  continuously monitors whether the drive motors  28  are in neutral. In the preferred embodiment, the drive signals for both motors are connected in series such that as either of the traction levers  29   a ,  29   b  is moved off of neutral, either forward or reverse, the signal from the vehicle drive input  220  drops from operating voltage, approximately 12 volts DC, to 0 volts DC. When the signal is 12 volts DC, the controller  110  recognizes both of the drive motors  28  are in neutral.  
         [0021]    If the drive motors  28  are not in neutral, the controller  110  maintains the current gear signal being sent to the actuators  31  and disregards any new gear input signals, i.e., the controller  110  prevents a gear change when the motors are not in neutral. It is intended that the operator will recognize that the gear ratio has not changed, and will thereby be alerted to shift the vehicle drives to neutral. The control system  200  may also include an indicator (not shown), for example, a light or sound, which alerts the operator that the gear change is being prevented due to the vehicle drive. Once the vehicle drives have been placed in neutral, the controller  110  proceeds with the control sequence as described below.  
         [0022]    Once a neutral signal is detected, the controller  110  determines if the transmissions  30  are currently operating in a “low”gear ratio, i.e., low speed, high torque. If the transmissions  30  are in a low gear ratio, the controller  110  sends a signal to apply the vehicle&#39;s parking brake. In the preferred embodiment, the vehicle parking brake is a function of the transmissions  30 , that is, a brake signal causes the actuators  31  to produce a gear ratio which stops the drive track drive units  26   a ,  26   b . However, the parking brake may also be configured to be independent of the transmission assembly. After the parking brake is applied, the controller  110  determines if a new gear ratio is selected by determining if the gear ratio input is equal to the current low gear operating condition or to a high gear ratio signal. If the gear ratio input signal is maintained at low while the vehicle is in neutral, the signal is not changed. If the gear ratio input signal is changed to high while the vehicle is in neutral, the controller  110  sends the new gear input to the actuators  31  which in turn change the transmission gear ratios. In the preferred embodiment in which the park brake is associated with the transmissions  30 , the controller  110  awaits shifting of the drive from neutral and then, simultaneously therewith, sends the new gear ratio signal to the actuators  31 , thereby avoiding premature deactivation of the parking brake. In embodiments wherein the parking brake is independent of the transmission signal, the signal can be sent immediately since it will not interfere with the parking brake.  
         [0023]    If a neutral signal is received when the vehicle transmission is in a high gear, i.e. high speed, low torque, the controller  110  checks the gear input signal. If the gear input signal is a high gear signal, i.e., no change in gear, the controller  110  maintains the current gear signal. If the gear input signal is a low gear signal, i.e., a gear shift, the controller  110  waits a given amount of time, for example, 2 seconds, and then applies the parking brake. The delay helps prevent the paver from lurching to a halt from a high speed. After application of the parking brake, the new gear signal will be transmitted. Again, if the parking brake is associated with the transmissions, the controller  110  awaits a shifting from neutral before sending the new signal.  
         [0024]    The automatic application of the parking brake is preferably included to prevent undesired rolling of the vehicle during working operation, for example, when the paver is paving. In the illustrated control sequence, the brake is not applied when the gear ratio is maintained in high gear since this is typically a travel gear condition as opposed to a working gear condition. If desired, the controller  110  can be configured to apply the brake in all conditions. Additionally, some vehicles have transmission ratios which are sufficient to independently prevent vehicle rolling when the motors are in neutral. In such cases, each of the “apply brake” steps of the control sequence can be eliminated.  
         [0025]    Another feature of many industrial vehicles is a destroking of the traction pump when the vehicle brake is applied. This feature is intended to prevent an operator from trying to “drive through” the braking condition. The controller  110  of the present invention can be configured to override this destroking feature when the brake is automatically applied. Since the brake is only automatically applied when the drive motors are in neutral, the potential for “drive through” is eliminated, thereby eliminating the need for destroking. To override the destroke feature, the controller  110  sends a signal overriding the destroke signal to the mechanism controlling destroking of the pumps. Since the pumps are not destroked, they will not have to “spool up” when the drives are moved from neutral, but will instead by ready for immediate operation. This prevents the vehicle from coasting forward or backwards on grades while the pumps spool up.  
         [0026]    It will be appreciated by those skilled in the art that changes can be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as generally and illustratively described herein.