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Control system for a work machine and method for controlling a hydraulic cylinder in a work machineControl system for a work machine and method for controlling a hydraulic cylinder in a work machine description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070166168, Control system for a work machine and method for controlling a hydraulic cylinder in a work machine. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001]The present application claims the benefit of U.S. Application No. 60/759,996 filed 18 Jan. 2006 and claims priority to Swedish Application No. 0600087-1 filed 16 Jan. 2006. Said applications are expressly incorporated herein by reference in their entirety. FIELD AND BACKGROUND [0002]The present invention relates to a control system for a work machine and a method for controlling at least one hydraulic cylinder in a work machine. Herein, the work machine is described in terms of a wheel loader. This is a preferred but is in no way limiting to the invention as the he invention can also be used for other types of work machines (or work vehicles), such as an excavator loader (backhoe) and excavating machine. [0003]The invention relates, for example, to controlling lifting and/or tilting cylinders for operating an implement. [0004]More precisely, the invention relates to a control system which comprises a hydraulic machine that functions as both pump and motor. The hydraulic machine is connected in a driving manner to an electric machine which functions as both motor and generator. [0005]The hydraulic machine therefore functions as a pump in a first operating state and supplies pressurized hydraulic fluid to the hydraulic cylinder. The hydraulic machine also functions as a hydraulic motor in a second operating state and is driven by a hydraulic fluid flow from the hydraulic cylinder. The electric machine therefore functions as an electric motor in the first operating state and as a generator in the second operating state. [0006]The first operating state corresponds to a work operation, such as lifting or tilting, being carried out with the hydraulic cylinder. Hydraulic fluid is therefore directed to the hydraulic cylinder for movement of the piston of the cylinder. On the other hand, the second operating state is an energy recovery state. SUMMARY [0007]A first object of the invention is to provide a control system, preferably for a lifting and/or tilting function, which affords an opportunity for energy-efficient operation. [0008]This object is achieved with a control system for a work machine, which system comprises an electric machine, a hydraulic machine and at least one hydraulic cylinder, the electric machine being connected in a driving manner to the hydraulic machine, the hydraulic machine being connected to a piston side of the hydraulic cylinder via a first line and a piston-rod side of the hydraulic cylinder via a second line, the hydraulic machine being adapted to be driven by the electric machine and supply the hydraulic cylinder with pressurized hydraulic fluid from a tank in a first operating state and to be driven by a hydraulic fluid flow from the hydraulic cylinder and drive the electric machine in a second operating state. [0009]The hydraulic cylinder is preferably adapted to move an implement in order to perform a work function. According to a first example, the hydraulic cylinder comprises a lifting cylinder for moving a loading arm which is pivotably connected to a vehicle frame, the implement being arranged on the loading arm. According to a second example, the hydraulic cylinder comprises a tilting cylinder for moving the implement which is pivotably connected to the loading arm. [0010]The speed of the cylinder is preferably controlled directly by the electric machine, that is to say no control valves are required between the hydraulic machine and the cylinder for regulating direction and speed of the movement. In some cases, on/off valves which open and respectively close a communication for the hydraulic fluid flow are required. [0011]A second object of the invention is to provide a method for controlling a hydraulic cylinder, preferably for a lifting and/or tilting function, which provides smooth operation and reduces jerking/jolting of the driver. [0012]This object is achieved by a method according to claim 31. It is therefore achieved with a method comprising the steps of detecting that a lowering movement of the implement is initiated, of before the lowering movement takes place pressurizing a first side of the piston of the hydraulic cylinder, which side is opposite a second side on which said load acts, and then reducing the pressurization so that the lowering movement can start. [0013]A third object of the invention is to provide a method which takes account of the size of the load and provides energy-efficient operation. [0014]This object is achieved by a method according to claim 36. It is therefore achieved with a method comprising the steps of detecting a load acting on the implement, of comparing the size of the detected load with a predetermined load level, and of, if the detected load lies below the predetermined load level, bringing the piston-rod side of the hydraulic cylinder into flow communication with the piston side so that hydraulic fluid coming from the piston-rod side is brought to the piston side without passing through the hydraulic machine. [0015]A fourth object of the invention is to provide a method which provides energy-efficient operation during movement of the implement. [0016]This object is achieved by a method according to claim 38. It is therefore achieved with a method comprising the steps of delivering such a pressure to the hydraulic cylinder that the implement is brought into a basic position, of, in the event of a disturbance which results in a downward movement of the implement, allowing driving of a hydraulic machine by a hydraulic fluid flow from the hydraulic cylinder, and of regenerating the energy from the hydraulic machine in an electric machine connected to it in a driving manner. [0017]A fifth object of the invention is to provide a method which provides energy-efficient springing of the movement of the implement during transport. [0018]This object is achieved by a method according to claim 44. It is therefore achieved with a method comprising the steps of delivering such a pressure to the hydraulic cylinder that the implement is brought into a basic position, of bringing a first port of the hydraulic machine into flow communication with a piston side of the hydraulic cylinder via a first line and a second port of the hydraulic machine into flow communication with a piston-rod side of the hydraulic cylinder via a second line, and of, in the event of a disturbance which results in an upward movement of the implement, supplying a corresponding quantity of hydraulic fluid to the hydraulic cylinder and, in the event of a downward movement of the implement, draining a corresponding quantity of hydraulic fluid from the hydraulic cylinder. BRIEF DESCRIPTION OF THE DRAWINGS [0019]The invention will be described in greater detail below with reference to the embodiments shown in the accompanying drawings, in which: [0020]FIG. 1 shows a side view of a wheel loader; Continue reading about Control system for a work machine and method for controlling a hydraulic cylinder in a work machine... Full patent description for Control system for a work machine and method for controlling a hydraulic cylinder in a work machine Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Control system for a work machine and method for controlling a hydraulic cylinder in a work machine patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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