Mobile work platform

Abstract

A mobile work platform includes an operator platform ( 6 ), a base ( 2 ) and a lift mechanism ( 4 ) for lifting the operator platform relative to the base. A hydraulic drive system for the mobile work platform includes an internal combustion engine ( 14 ), an electric motor ( 24 ) and a hydraulic pump ( 26 ). The internal combustion engine ( 14 ) and the electric motor ( 24 ) are constructed and arranged so as to be capable of driving the hydraulic pump ( 26 ) either separately or together.

1 . A hydraulic drive system for a mobile work platform, the system
 including an internal combustion engine, an electric motor and a hydraulic pump, wherein the internal combustion engine and the electric motor are capable of driving the hydraulic pump either separately or together.   
   
   
       2 . A hydraulic drive system according to  claim 1 , including a clutch mechanism for disconnecting the internal combustion engine from the pump. 
   
   
       3 . A hydraulic drive system according to  claim 1 , further including a battery for powering the electric motor. 
   
   
       4 . A hydraulic drive system according to  claim 3 , wherein the electric motor is operable as a generator to charge the battery. 
   
   
       5 . A hydraulic drive system according  claim 1 , further including a control device for controlling the transfer of power between the internal combustion engine, the electric motor and the hydraulic pump. 
   
   
       6 . A hydraulic drive system according to  claim 5 , wherein the control device has a plurality of selectable operational modes, including at least one of a mode selected from the group consisting of an electric mode in which power is supplied to the pump exclusively from the electric motor, an IC engine mode in which power is supplied to the pump exclusively from the IC engine, and a boost mode in which power is supplied to the pump from both the electric motor and the IC engine. 
   
   
       7 . A hydraulic drive system according to  claim 6 , wherein the control device selects boost mode when the power requirement of the pump exceeds a predetermined value. 
   
   
       8 . A hydraulic drive system according to  claim 6 , wherein the control device has a regeneration mode in which the electric motor is driven by the IC engine and operates as a generator to charge a battery. 
   
   
       9 . A hydraulic drive system according to  claim 8 , in which the control device controls the transfer of electric power between the battery and the motor. 
   
   
       10 . A hydraulic drive system according to  claim 1 , wherein the internal combustion engine has a power in the range 5-50 kW. 
   
   
       11 . A hydraulic drive system according to  claim 1 , wherein the hydraulic pump is a variable displacement pump. 
   
   
       12 . A hydraulic drive system according to  claim 1 , wherein the internal combustion engine, the electric motor and the hydraulic pump are arranged co-axially. 
   
   
       13 . A hydraulic drive system according to  claim 1 , wherein the pump and the electric motor are mounted on a common drive shaft, which is offset from an output shaft of the internal combustion engine, wherein the drive shaft and the output shaft are connected by a drive transfer mechanism. 
   
   
       14 . A mobile work platform comprising an operator
 platform, a base and a lift mechanism for lifting the operator platform relative to the base, and a hydraulic drive system according to  claim 1  for operating the lift mechanism.   
   
   
       15 . A mobile work platform according to  claim 14 , wherein the operator platform has a working height of 10 m or more and a load capacity in the range 100-1000 kg.