Patent Publication Number: US-2011072811-A1

Title: Engine driven lift gate power system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to lift gates, and in particular, to a system for powering lift gates. 
     2. Description of Related Art 
     Lifts such as lift gates are typically mounted at a structure such as the rear of a vehicle to lift payloads on a platform from one level (e.g., ground level) up to another level (e.g., the bed of the vehicle), or vice versa. 
     One type of lift gate employs linkages to maintain the lift platform in a horizontal plane through the lifting range. The lift platform is attached to linkages by pivot members, which allow the lift platform to be pivoted. Operation of the lifting mechanism may also rotate the lift platform into an inverted, stowed position beneath the vehicle body. Hydraulic actuators and electric actuators are used to provide lifting force for moving the lift. 
     Electrical power to electric motors for such actuators is provided by batteries. The batteries are charged/recharged by an alternator that is coupled to the vehicle engine to convert mechanical energy from the running vehicle engine to electrical energy. 
     In between recharges from the vehicle engine alternator, the batteries are used to provide electrical energy to the actuators in repeated cycles of lift operations. This drains the batteries to low voltages (e.g., below stated charge acceptable to run an electrical motor), causing problems with the electric solenoids and pump electric motors used in the actuators. Low battery voltage leads to inefficiencies and premature failures. The electric actuator motors run hot when voltage is low. Further, electric motors that energize hydraulic pumps run slower due to low battery voltage, slowing operation of the lift. 
     Further, the batteries require frequent running of the vehicle engine to recharge them. The vehicle engines are large, and designed to move an entire vehicle and its load. Idling the vehicle engine to recharge the batteries consumes extra fuel, causes wear on the engine, pollutes the environment, etc. In many areas where local laws prevent engine idling, the batteries cannot be recharged by idling the vehicle engine. There is often insufficient time between uses of the lift gate to fully recharge the batteries. Battery charging is time consuming. 
     Conventional approaches to address such problems involve using a charging device in addition to the vehicle engine alternator, to charge the batteries that energize the lift actuators. However, the batteries continue to run down on high cycle uses of the lift, requiring recharging. Further, such additional charging devices require long wiring between various electrical components, causing large voltage drops and energy waste. 
     BRIEF SUMMARY OF THE INVENTION 
     A power system for a lift gate is provided. In one embodiment, the power system includes an actuator system including an actuator for a lift gate, and a lift gate engine coupled to the actuator system. The lift gate engine is configured for generating kinetic energy from a fuel source to power the actuator system for operating the lift gate. 
     The actuator may comprise a hydraulic actuator and the actuator system may further include a hydraulic pump for pumping hydraulic fluid to the hydraulic actuator. The lift gate engine is coupled to the hydraulic pump for directly driving the hydraulic pump to pump hydraulic fluid to the hydraulic actuator for operating the lift gate. The lift gate may comprise a platform coupled to a support frame via a lift linkage, the platform capable of being moved by the actuator via the lift linkage. 
     The power system may further include a controller module configured for monitoring a condition, and based on the condition controlling at least one of: the lift gate engine and the actuator system for operating the lift gate. The controller may further comprise a feedback loop configured for dynamically monitoring the lift gate engine and generating a signal to control the operation of the lift gate engine for operation of the lift gate. The controller module may further be configured for dynamically monitoring the actuator system and the lift gate engine to generate a signal for controlling operation of the lift gate engine. In so doing, the actuator system operation satisfies a predefined condition. 
     The power may further comprise a sensor system including an engine sensor for sensing operation of the lift gate engine. The controller is further configured for receiving engine sensor information and generating a control signal to maintain the lift gate engine within an operation range in powering the actuator system for proper operation of the actuator system for the lift gate. 
     The sensor system may further comprise an actuator sensor for sensing operation of the actuator system. The controller is further configured for receiving actuator sensor information and generating a control signal to the lift gate engine for maintaining the actuator system within an operation range for proper operation of the lift gate. 
     The sensor system may further comprise a lift gate sensor for sensing status of the lift gate. The controller is further configured for receiving lift gate sensor information and generating a control signal for proper operation of the lift gate to at least one of the following: the lift gate engine, the actuator system, the lift gate control module. 
     In another embodiment, the invention provides a lift gate system, comprising a lift gate, an actuator system including an actuator for the lift gate, and a lift gate engine coupled to the actuator system. The lift gate engine is configured for generating kinetic energy from a fuel source to power the actuator system for operating the lift gate. The lift gate system may further include a sensor system for sensing status of the system, a controller module configured for monitoring sensed status, and a lift gate engine or the actuator system for operating the lift gate depending on the sensed status. 
     The controller module may further be configured for dynamically monitoring sensed status of the actuator system and the lift gate engine, and generating a signal for controlling operation of the lift gate engine such that the actuator system operation satisfies a predefined condition. 
     The sensor system may include an engine sensor for sensing operation status of the lift gate engine, an actuator sensor for sensing operation status of the actuator system, and a lift gate sensor for sensing status of the lift gate. The controller may further be configured for receiving engine sensor information and generating a control signal to maintain the lift gate engine within an operation range in powering the actuator system for proper operation of the actuator system for the lift gate. The controller may further be configured for receiving actuator sensor information and generating a control signal to the lift gate engine for maintaining the actuator system within an operation range for proper operation of the lift gate. The controller may further be configured for receiving lift gate sensor information and generating a control signal to at least one of the following: the lift gate engine, the actuator system, the lift gate control module, for proper operation of the lift gate. 
     The controller module may further be configured for dynamically monitoring sensed hydraulic fluid pressure in the actuator system and sensed engine speed of the lift gate engine, and generating a signal for controlling operation of the lift gate engine such that hydraulic fluid pressure in the actuator system operation satisfies a predefined condition. The lift gate engine comprises an internal combustion engine. 
     In another embodiment, the invention provides a method of powering a lift gate by providing an actuator system including an actuator for a lift gate, and coupling a lift gate engine to the actuator system, wherein the lift gate engine is configured for generating kinetic energy from a fuel source to power the actuator system for operating the lift gate. 
     The lift gate may comprise a platform coupled to a support frame via a lift linkage, the platform capable of being moved by the actuator via the lift linkage. The method may further comprise dynamically sensing status of at least one of the following: the lift gate engine, the actuator system and the lift gate, a dynamically monitoring sensed status, and at least one of the following based on the sensed status controlling: the lift gate engine, the actuator system for operating the lift gate. 
     Controlling at least one of the following: the lift gate engine and the actuator system for operating the lift gate, may further comprise: if the lift gate engine is not running, then starting the lift gate engine using a starter; based on the sensed status, check if conditions for proper operation of the lift gate are satisfied; if the conditions are satisfied, then allowing operation of the lift gate; and monitoring the actuator system, and controlling lift gate engine RPM to maintain the actuator system in an operating range for proper operations of the lift gate. 
     The actuator may comprise a hydraulic actuator and the actuator system further includes a hydraulic pump for pumping hydraulic fluid to the hydraulic actuator, wherein coupling a lift gate engine to the actuator system further includes coupling the lift gate engine to the hydraulic pump for directly driving the hydraulic pump to pump hydraulic fluid to the hydraulic actuator for operating the lift gate. 
     The method may further comprise monitoring hydraulic fluid pressure in the actuator system, and controlling the lift gate engine RPM to maintain the hydraulic fluid pressure actuator system in a range for proper operations of the lift gate. 
     The method may further comprise dynamically monitoring sensed hydraulic fluid pressure in the actuator system and upon the hydraulic fluid pressure in the actuator system reaching a predefined level, generating a signal for opening a valve in the actuator system to allow hydraulic fluid to flow to the hydraulic actuator for moving the lift gate linkage. 
     These and other features, aspects and advantages of the present invention will become understood with reference to the following description, appended claims and accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a functional block diagram of a system for powering a lift gate, according to an embodiment of the invention. 
         FIG. 2  shows a functional block diagram of a lift gate and power system for powering a lift gate, according to an embodiment of the invention. 
         FIG. 3  shows a more detailed functional block diagram of a lift gate and power system for powering a lift gate, according to an embodiment of the invention. 
         FIG. 4  shows a flowchart of a process for powering a lift gate using a power system, according to an embodiment of the invention. 
         FIG. 5  shows an example schematic of a lift gate and power system, according to an embodiment of the invention. 
         FIG. 6  shows a flowchart of a process for lift gate power system, and lift gate operation, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is made for the purpose of illustrating the general principles of the invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations. Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc. 
     In one embodiment, the power system includes an actuator system including an actuator for a lift gate, and a lift gate engine coupled to the actuator system. The lift gate engine is configured for generating kinetic energy from a fuel source to power the actuator system for operating the lift gate. 
     The actuator may comprise a hydraulic actuator and the actuator system may further include a hydraulic pump for pumping hydraulic fluid to the hydraulic actuator. The lift gate engine is coupled to the hydraulic pump for directly driving the hydraulic pump to pump hydraulic fluid to the hydraulic actuator for operating the lift gate. The lift gate may comprise a platform coupled to a support frame via a lift linkage, the platform capable of being moved by the actuator via the lift linkage. 
     The power system may further include a controller module configured for monitoring a condition, and based on the condition controlling at least one of: the lift gate engine and the actuator system for operating the lift gate. The controller may further comprise a feedback loop configured for dynamically monitoring the lift gate engine and generating a signal to control the operation of the lift gate engine for operation of the lift gate. The controller module may further be configured for dynamically monitoring the actuator system and the lift gate engine, and generating a signal for controlling operation of the lift gate engine such that the actuator system operation satisfies a predefined condition. 
     The power may further comprise a sensor system including an engine sensor for sensing operation of the lift gate engine. The controller is further configured for receiving engine sensor information and generating a control signal to maintain the lift gate engine within an operation range in powering the actuator system for proper operation of the actuator system for the lift gate. 
     The sensor system may further comprise an actuator sensor for sensing operation of the actuator system. The controller is further configured for receiving actuator sensor information and generating a control signal to the lift gate engine for maintaining the actuator system within an operation range for proper operation of the lift gate. 
     The sensor system may further comprise a lift gate sensor for sensing status of the lift gate. The controller is further configured for receiving lift gate sensor information and generating a control signal to at least one of: the lift gate engine, the actuator system and a lift gate control module, for proper operation of the lift gate. 
     In another embodiment, the invention provides a lift gate system, comprising a lift gate, an actuator system including an actuator for the lift gate, and a lift gate engine coupled to the actuator system. The lift gate engine is configured for generating kinetic energy from a fuel source to power the actuator system for operating the lift gate. The lift gate system may further include a sensor system for sensing status of the system, and a controller module configured for monitoring sensed status, and based on the sensed status controlling at least one of: the lift gate engine and the actuator system for operating the lift gate. 
     The controller module may further be configured for dynamically monitoring sensed status of the actuator system and the lift gate engine, and generating a signal for controlling operation of the lift gate engine such that the actuator system operation satisfies a predefined condition. 
     The sensor system includes an engine sensor for sensing operation status of the lift gate engine, an actuator sensor for sensing operation status of the actuator system, and a lift gate sensor for sensing status of the lift gate. The controller may further be configured for receiving engine sensor information and generating a control signal to maintain the lift gate engine within an operation range in powering the actuator system for proper operation of the actuator system for the lift gate. The controller may further be configured for receiving actuator sensor information and generating a control signal to the lift gate engine for maintaining the actuator system within an operation range for proper operation of the lift gate. The controller may further be configured for receiving lift gate sensor information and generating a control signal to at least one of: the lift gate engine, the actuator system and a lift gate control module, for proper operation of the lift gate. 
     The controller module may further be configured for dynamically monitoring sensed hydraulic fluid pressure in the actuator system and sensed engine speed of the lift gate engine, and generating a signal for controlling operation of the lift gate engine such that hydraulic fluid pressure in the actuator system operation satisfies a predefined condition. The lift gate engine comprises an internal combustion engine. 
     Although the power system herein is described in relation to an example lift gate, the invention is also useful for powering other types of lift gates, and powering other systems such as wheel chair lifts and other systems that use actuation systems. 
     Referring to the example functional block diagram in  FIG. 1 , one embodiment of the invention comprises a power system  1  including a lift gate engine  2  that directly powers a lift gate actuator system  3  of a lift gate assembly  4 . The power system  1  further includes a controller  5  and one or more sensors  6 , wherein using information from the sensors  6  (and other sources as needed), the controller  5  controls operation of the lift gate engine  2  in providing power to the actuator system  3 . The power system  1  alleviates the need for batteries to power the actuator system  3 . 
     In one example, the lift gate engine is coupled to a hydraulic pump of an actuator for powering the pump for moving hydraulic fluid to operate a lift gate. The coupling may comprise, for example, a mechanical coupling, a viscous coupling, etc. 
     The lift gate engine is preferably a small engine such as a known small displacement internal combustion engine (e.g., gasoline, diesel). The lift gate engine is operable independent of the vehicle engine, and is of substantially lower displacement than the vehicle engine. For example the lift gate engine can comprise about a 2 to 10 horse power engine (e.g., single-cylinder 2-stroke air-cooled gasoline engine, displacement of 42.7 cc, bore and stroke of 40×34 mm and speed up to 6,500 rpm). Generally, the horse power required for the lift gate engine is based on the lift gate load lifting capacity, wherein the higher the lifting capacity of the lift gate (e.g., in pounds), the higher the lift gate engine horsepower to enable sufficient hydraulic fluid pressure in the hydraulic manifold. An example operating range for a desired hydraulic fluid pressure in the hydraulic manifold of a lift gate may be about 500 pounds per square inch (PSI) to 4000 PSI depending on whether the lift gate is loaded or unloaded. 
       FIG. 2  shows a block diagram of an example implementation of the system of  FIG. 1  for a lift gate with a hydraulic pump. Specifically,  FIG. 2  shows a system  10  including a power system for a lift gate  11  for a vehicle  12 , according to an embodiment of the invention. The power system includes a lift gate engine  13 , a controller  14  and one or more sensors  15 . 
     Using information from at least the sensors  15 , the controller  14  controls operation of the lift gate engine  13  in providing power to a lift gate actuator system comprising a hydraulic pump  16  and hydraulic manifold  17 . The power system alleviates the need for batteries to power the hydraulic pump  16 . 
     The lift gate engine  13  drives the hydraulic pump  16  which moves hydraulic fluid in the hydraulic manifold  17 . Hydraulic fluid is distributed from the manifold  17  to hydraulic actuators of the lift gate  11  that provide force for moving components of the lift gate. The lift gate actuator system may be of a conventional type. 
     The system  10  further includes a starter  18  for starting the engine  13 , wherein the starter  18  can be powered by a battery such as the vehicle engine battery  12 A (i.e., the same battery that starts the vehicle engine). 
     The engine  13  is started by the starter  18  when the lift control switch  19  is closed by an operator, indicating that the operator wishes to operate the lift gate (such as raise/lower the lift platform). 
     In one embodiment, the controller  14  can be shut off or eliminated wherein the engine  13  is started by the starter  18  when the lift control switch  19  is closed by an operator, indicating that the operator wishes to operate the lift gate (such as raise/lower the lift platform). 
     In a preferred embodiment, the engine  13  is started by the starter  18  when the lift control switch  19  is closed by an operator, wherein the controller  14  manages operation of the engine  13 , such as by controlling the engine speed (RPM) based on sensed information as described in more detail below. The engine  13  may include an engine management module (EMM) that provides engine status information to the controller  14 , and the EMM can receive signals from the controller  14  to control operation of the engine  13 . The vehicle  11  may include a management module that provides vehicle status (e.g., vehicle transmission in park mode, etc). Further, the vehicle engine may include engine management module that provide vehicle engine information (e.g., vehicle engine running/off). 
     The controller  14  receives sensor information from one or more components of the system  10  using the sensors  15 , and processes the sensed information using control logic  14 A to provide management control signals to one or more components of the system  10 . 
     In one example, the control logic  14 A of the controller  14  implements a feedback processing loop that senses hydraulic fluid pressure in the manifold  17  and controls speed of the engine  13  and/or operation of the hydraulic pump  16 , such that fluid pressure in the manifold  17  is maintained at a desirable level for proper operation of the lift gate actuator system. The desirable level of fluid pressure in the manifold may be a predetermined value provided by the manufacturer of the hydraulic components such as the hydraulic actuators. 
     The controller  14  may also provide control signals to other components of the system  10  such as the lift gate  11  and vehicle  12 . For example, the controller  14  may signal the lift gate  11  to prevent raising/lowering the lift platform while fluid pressure in the manifold  17  is below a desirable level for proper operation of the lift gate. 
     The controller  14  uses sensor information (e.g., from sensor on the engine  13 , from sensor on the hydraulic manifold  17 ) to determine status, and allows operation of the lift gate when certain conditions are met. For example, the controller  14  senses if the engine  13  is running, and if there is sufficient hydraulic fluid pressure available to operate the lift gate. If so, then the controller  14  activates valves that control movement of hydraulic fluid for operation of the lift gate  11 . If the engine  13  is off, and the lift control switch  19  is closed by an operator, the controller  14  causes the starter motor  18  to start the engine  13 , and allows the engine revolutions to come up to a certain speed (as sensed by a sensor) for driving the hydraulic pump  16  such that sufficient fluid pressure is generated in the manifold  17  (as sensed by a sensor) to properly operate the lift gate (such as lower/raise the platform). 
       FIG. 3  shows a block diagram of another example implementation of powering a lift gate with a hydraulic pump, according to the invention. Specifically  FIG. 3  shows a system  20  including a power system for a lift gate  11  on a vehicle  12 , wherein power system  11  includes a lift gate engine  13 , a controller  14  and one or more sensors  15 . The controller  14  monitors and controls the lift gate engine  13  along with a hydraulic circuit powered by the lift gate engine  13 , for proper operation of the lift gate  11 . 
     Due to action of the pump  16  (as powered by the engine  13 ), the hydraulic fluid flows to the actuator  11 A then returns to a reservoir  16 A. The fluid is then re-pumped by the pump  16 . The path of the hydraulic fluid is called a hydraulic circuit, as is known to those skilled in the art. The controller  14  starts the engine  13  to run the hydraulic pump  16  directly, waits for the engine  13  to reach a threshold revolutions per minute (RPM) as sensed by a sensor, then the controller  14  shifts a two-way valve  16 B that allows fluid to enter the manifold  17  from the reservoir  16 A. The controller  14  senses pressure build up in the manifold  17  to be above a threshold, before it sends a signal to allow operation of the lift gate such as raising the platform via a hydraulic actuator  11 A. 
     The controller  14  may also sense fuel level for the engine  13  and generate a signal alerting an operator if the fuel level is too low and/or prevent operation of the lift gate since if the engine  13  may run out of fuel (leading to loss of hydraulic fluid pressure) in mid cycle of lift gate operation. 
     The controller  14  may also monitor pressure of the hydraulic fluid circuit (e.g., from the reservoir to the hydraulic actuator and back) when control switch  19  is engaged (e.g., to raise the lift gate platform). The pump  16  may comprise a regenerative pump in the hydraulic circuit, including a circulating valve system (i.e., inlet and outlet valves). 
     In one embodiment, the controller  14  monitors pressure sensors to sense pressure in the manifold  17 , and when that pressure reaches a desired level, the control signals a valve to allow hydraulic fluid to flow from the manifold  17  to the lift gate actuator, for proper operation of the lift gate (e.g., to hold the lift platform up). In one embodiment, the controller  14  starts the engine  13  to run the hydraulic pump directly, then waits for the engine  13  to reach a threshold RPM as sensed by a sensor, then the controller  14  shifts a two-way valve that allows fluid to enter the manifold  17 . The controller senses pressure build up in the manifold  17  to reach a desired level, before it allows operation of the lift gate such as raising the platform. 
     Using sensors, the controller  14  senses condition of the lift gate, such as if the platform is down or lift gate is stowed in the proper position, etc., before it allows shut down of the engine  13 . The controller  14  may employ a feedback loop to control RPM speed of the engine  13  to maintain the engine RPM within a desired range for driving the pump  16 , to allow sufficient hydraulic fluid pressure for proper operation of the lift gate, such as based on sensed pressure in the pump manifold. The controller  14  may receive input from the vehicle chassis indicating condition of the chassis (e.g., parked vehicle, not moving, level ground, etc.) before it allows the engine  13  to be started and/or the lift gate to be operated. 
     The controller  14  and sensors  15  form a system that automatically monitors various parameters in the system  10  (e.g., lift gate engine RPM, pump speed, fluid pressure in manifold  17 , lift gate state/condition), and sends control commands to various components in the system  10  to enable proper operation of the lift gate by an operator. 
     The standalone engine  13  can be turned on to run the hydraulic pump  16  to operate the lift gate, and then turned off when the lift gate operation is completed. The vehicle engine need not be running to operate the lift gate or to charge batteries for running the lift gate. 
       FIG. 4  shows a flowchart of a sense and control process  30  implemented by control logic  14 A of the controller  14 , according to an embodiment of the invention. The controller  14  receives notification that an operator desires to operate the lift gate  11  using the lift gate switch  19  (e.g., lower/raise the lift gate platform, fold/unfold the lift gate, etc.). This requires use of the actuator system including the hydraulic system. The control process  30  includes:
         Block  31 : If lift gate engine  13  is not running, then start the engine  13 .   Block  32 : Sense status of the lift gate engine  13  (e.g., RPM).   Block  33 : Sense status of the hydraulic system (e.g., hydraulic pressure in the system).   Block  34 : Sense status of lift gate  11  (e.g., platform up/down).   Block  35 : Based on the sensed information, check if conditions for proper operation of the lift gate are satisfied.   Block  36 : If the conditions are satisfied, then proceed to block  37 , otherwise disable lift control switch  19  and repeat blocks  32 - 35  until the conditions are satisfied.   Block  37 : Enable lift control switch  19  to allow operation of the lift gate. Monitor fluid pressure, and control engine RPM (i.e., send control signal to engine governor) to maintain fluid pressure at desired level for proper operation of the lift gate (e.g., increase engine RPM when demand for fluid pressure increases based on lift gate operation).       

     If the conditions are not satisfied, the controller may attempt to remedy the situation to satisfy the conditions. For example, if after waiting for a time period the fluid pressure remains below a threshold, the controller  14  may signal the engine  13  to increase RPM to raise the fluid pressure to the threshold. 
       FIG. 5  shows an example system  40  comprising a lift gate  11  and power system  41 , according to an embodiment of the invention. The lift gate  11  is attached to a vehicle (bed of truck, partially shown) and includes a platform  42  (shown in unfolded and lowered position) coupled to a support frame  43  via a lift linkage  44 , wherein the platform  42  is capable of being moved (lowered/raised) by the actuator  11 A via the lift linkage  44 . 
     In this embodiment, the power system  41  comprises the above-described lift gate engine  13  and controller  14 , wherein the lift gate engine  13  is coupled to the hydraulic pump  16  by a coupler  16 B to directly drive the pump  16 . The coupler  16 A may comprise a rotating axle connected between crank shaft of the lift gate engine  13  and the pump  16 , or may comprise a viscous coupling, etc. The pumping action of the pump  16  directs hydraulic fluid from the reservoir  16 A to the manifold  17 , and hydraulic fluid from the manifold  17  flows to the hydraulic actuator  11 A using pipes/tubes. 
     The lift control switch  19  may comprise user operable interface such as buttons, levers, etc., for receiving operator commands for operating the lift gate (e.g., lower/raise platform, stow/unstow lift gate). The switch  19  may also include display/audio devices for providing the operator with information about one or more of the lift gate, the actuator system, the power system, etc. 
     The operator commands from the switch  19  are processed by a lift gate control module  45 . The lift gate control module  45  maintains information (status) about certain operational parameters of the various components of the lift gate  11  (e.g., platform up/down, lift gate stowed/unstowed, actuator condition, temperature). The lift gate control module  45  can provide this information to the controller  14  as needed. 
     As described above, the power system controller  14  functions to ensure that the power system (e.g., lift gate engine and the actuator system) operates in a way to provide proper level of power to the lift gate as demanded by operation of the lift gate  11  from an operator. The control module  45  functions to ensure that the lift gate  11  itself is operated properly by an operator, and the controller  14  ensures proper operation of the power system in powering the lift gate  11 . 
     The lift gate control module  45  controls operation of the lift gate based on certain operational parameters of the lift gate  11 . For example, after powering on the control module  45 , sensor data are obtained by the controller. Sensor data may include, for example, power supply voltages, electric current, cycle of the operation of the lift, and load on the lift, etc. The obtained sensor data are correlated/compared with parameters pre-stored in a memory of the control module  45 . 
     Inputs received by the control module  45  from the operator switch  19  are processed and a determination is made as to whether the required conditions are satisfied. The determination may include, for example, comparing the operator input sequence with the stored sequence to determine whether the input sequence is correct, and the lift gate is within operation limits. If the conditions are satisfied, the operation of the lift gate is enabled. If one or more of the conditions are not satisfied, a warning message may be provided to the operator and the control module  45  further awaits instructions without enabling the motion of the lift gate. 
     In one example, the lift gate engine  13  may be installed in a housing mounted on a frame of the vehicle (e.g., under the vehicle bed) near the hydraulic system and coupled to the pump  16  to drive the pump  16  (e.g., via an axle, viscous coupling, etc.). The controller  14  may also be placed in said housing, or placed elsewhere on the vehicle, and connected to the various sensors  15 , the engine  13 , the lift gate control module  34 , the lift gate control switch  19 , the pump  16 , etc., in a wired or wireless manner. The controller  14  may be powered by the vehicle electrical power system or have a dedicated power system. 
     In another embodiment, the invention provides a method of powering a lift gate by providing an actuator system including an actuator for a lift gate, and coupling a lift gate engine to the actuator system, wherein the lift gate engine is configured for generating kinetic energy from a fuel source to power the actuator system for operating the lift gate. 
     The lift gate may comprise a platform coupled to a support frame via a lift linkage, the platform capable of being moved by the actuator via the lift linkage. The method may further comprise dynamically sensing status of at least one of: the lift gate engine, the actuator system and the lift gate, and dynamically monitoring sensed status, and based on the sensed status controlling at least one of: the lift gate engine and the actuator system for operating the lift gate. 
     Controlling at least one of the lift gate engine and the actuator system for operating the lift gate, may further comprise: if the lift gate engine is not running, then starting the lift gate engine using a starter; based on the sensed status, check if conditions for proper operation of the lift gate are satisfied; if the conditions are satisfied, then allowing operation of the lift gate; and monitoring the actuator system, and controlling lift gate engine RPM to maintain the actuator system in an operating range for proper operations of the lift gate. 
     The actuator may comprise a hydraulic actuator and the actuator system further includes a hydraulic pump for pumping hydraulic fluid to the hydraulic actuator, wherein coupling a lift gate engine to the actuator system further includes coupling the lift gate engine to the hydraulic pump for directly driving the hydraulic pump to pump hydraulic fluid to the hydraulic actuator for operating the lift gate. 
     The method my further comprise monitoring hydraulic fluid pressure in the actuator system, and controlling lift gate engine RPM to maintain the hydraulic fluid pressure actuator system in a range for proper operations of the lift gate. 
     The method may further comprise dynamically monitoring sensed hydraulic fluid pressure in the actuator system and upon the hydraulic fluid pressure in the actuator system reaching a predefined level, generating a signal for opening a valve in the actuator system to allow hydraulic fluid to flow to the hydraulic actuator for moving the lift gate linkage. 
       FIG. 6  shows a flowchart of a process  50  for operation of the lift gate power system and the lift gate, according to an embodiment of the invention, comprising the following process blocks:
         Block  51 : Receive operator command to enable lift gate for operation.   Block  52 : Receive (gather) input from sources including lift gate sensors and/or vehicle components (e.g., vehicle parked status, parking brake status, vehicle transmission status, vehicle engine status).   Block  53 : Determine if based on the received inputs primary lift gate operation conditions are satisfied (e.g., vehicle parked and parking brake set and vehicle transmission in park mode). If the primary lift gate operation conditions are satisfied, then proceed to block  54 , otherwise, disable lift gate operation, generate alert to indicating lift gate is disabled.   Block  54 : Begin lift gate engine operation (e.g., start the lift gate engine).   Block  55 : Monitor lift gate power system via inputs from sources including sensors (e.g., hydraulic system status, hydraulic fluid pressure in manifold, engine speed, pump state).   Block  56 : Determine if secondary conditions for operation of the lift gate are satisfied (e.g., hydraulic system operational, hydraulic fluid pressure in manifold at acceptable level, engine speed at desired level). If yes, proceed to block  58 , otherwise proceed to block  57 .   Block  57 : Send control signals to the lift gate engine power system (e.g., lift gate engine) to adjust the lift gate power system to meet the secondary conditions for operation of the lift gate. Proceed back to block  55 .   Block  58 : Determine if operator wishes to disable lift gate or operate lift gate. If the operator wishes to disable lift gate, then proceed to block  59 . If the operator wishes to operate the lift gate, then proceed to operation block  60 .   Block  59 : Disable lift gate (e.g., such lift gate engine off) and generate alert message.   Block  60 : Perform lift gate operations based on operator commands, with the controller monitoring sensor information and making adjustments to lift gate power system (i.e., repeat process blocks  55 - 60 ).       

     The processing block  60  includes receiving operator commands for lift gate operation (e.g., unfold lift platform, fold lift platform, raise lift platform, lower lift platform). In response to each command, the controller determines if relevant lift gate operation conditions/parameters are satisfied. If so, then the controller allows execution of the received command, otherwise an alert may be generated. Process blocks  55 - 60  are repeated for the controller to ensure that the lift gate engine power system provides adequate and proper power output for proper lift gate operation, discussed above. The controller  14  may implement the above process  60  in conjunction with other controllers such as the lift gate control module  45 , etc. 
     The present invention has been described in considerable detail with reference to certain preferred versions thereof; however, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 
     The embodiments of the controller  14 , control module  45  and other controllers can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In a preferred embodiment, the invention is implemented in software, which includes but is not limited to firmware, resident software, microcode, etc. 
     Furthermore, the embodiments of the controllers of the invention can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer, processing device, or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can contain, store, communicate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The medium can be electronic, magnetic, optical, or a semiconductor system (or apparatus or device). Examples of a computer-readable medium include, but are not limited to, a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a RAM, a read-only memory (ROM), a rigid magnetic disk, an optical disk, etc. Current examples of optical disks include compact disk-read-only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD. 
     I/O devices (including but not limited to keyboards, displays, pointing devices, etc.) can be connected to the system either directly or through intervening controllers. Network adapters may also be connected to the system to enable the data processing system to become connected to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modem and Ethernet cards are just a few of the currently available types of network adapters. In the description above, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. For example, well-known equivalent components and elements may be substituted in place of those described herein, and similarly, well-known equivalent techniques may be substituted in place of the particular techniques disclosed. In other instances, well-known structures and techniques have not been shown in detail to avoid obscuring the understanding of this description. 
     The terms “computer program medium,” “computer usable medium,” “computer readable medium,” and “computer program product,” are used to generally refer to media such as main memory, secondary memory, removable storage drive, a hard disk installed in hard disk drive, and signals. These computer program products are means for providing software to the computer system. The computer readable medium allows the computer system to read data, instructions, messages or message packets, and other computer readable information, from the computer readable medium. The computer readable medium, for example, may include non-volatile memory, such as a floppy disk, ROM, flash memory, disk drive memory, a CD-ROM, and other permanent storage. It is useful, for example, for transporting information, such as data and computer instructions, between computer systems. Furthermore, the computer readable medium may comprise computer readable information in a transitory state medium such as a network link and/or a network interface, including a wired network or a wireless network that allow a computer to read such computer readable information. Computer programs (also called computer control logic) are stored in main memory and/or secondary memory. Computer programs may also be received via a communications interface. Such computer programs, when executed, enable the computer system to perform the features of the present invention as discussed herein. In particular, the computer programs, when executed, enable the processor or multi-core processor to perform the features of the computer system. Accordingly, such computer programs represent controllers of the computer system. The wireless protocol for communication between the various modules may comprise protocols such as IEEE 802.11, Bluetooth, Personal Area Network, control signals at different frequencies reflecting different tunable signals, FM, AM, packet communication, TCP/IP and other technologies which those skilled in the art recognize. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.