SE543709C2 - Mobile energy supply unit for hand-held hydraulic tools and method for operating a hand-held hydraulic tool - Google Patents

Abstract

A mobile energy supply unit for hand-held hydraulic tools is provided. The unit comprises at least one electric motor, at least one hydraulic pump, each being driveably coupled to at least one of the electric motor(s), one or more hydraulic connectors for connecting at least one hand-held hydraulic tool to at least one of said hydraulic pump(s), and an electrical storage arrangement being electrically coupled to the at least one electric motor as the sole source of energy. A corresponding method is also provided.

Description

MOBILE ENERGY SUPPLY UNIT FOR HAND-HELD HYDRAULIC TOOLS ANDMETHOD FOR OPERATING A HAND-HELD HYDRAULIC TOOL TECHNICAL FIELD The invention relates to a mobile energy supply unit for hand-held hydraulic tools,hydraulic railway track maintenance tools in particular. The invention further relates toa method for operating a hand-held hydraulic (railway track maintenance) tool usingsuch a mobile energy supply unit.

BACKGROUND When performing maintenance of railway tracks, hydraulic hand-held tools such as railsaws, grinders, tampers, drills, impacts, spike drivers and spike pullers are frequentlyused. Since maintenance is often performed at remote locations, mobile power unitsproviding pressurized hydraulic fluid, and optionally electric power, are used. Thepower units of today are powered by internal combustion engines. Such power unitsare usually noisy and cause exhaust gas pollutants. This may be disadvantageouswhen working in for example densely populated areas and tunnels, and does not allowmaintenance work to be performed at night or during weekends. Furthermore, thepower units of today are, due to the use of an internal combustion engine, usually quite inefficient and suffer from poor environmental performance.

SUMMARY An object of the invention is to at least partly solve one or more of the problems of theprior art identified above. This and other objects are achieved by the present inventionby means of a mobile energy supply unit and a method according to the independent claims.

According to a first aspect of the invention, a mobile energy supply unit for hand-heldhydraulic tools is provided, which hand-held hydraulic tools may be hand-heldhydraulic railway track maintenance tools. The unit comprises at least one electricmotor, at least one hydraulic pump, each being driveably coupled to at least one ofthe electric motor(s), one or more hydraulic connectors for connecting at least onehand-held hydraulic tool to at least one of said hydraulic pump(s), and an electrical storage arrangement being electrically coupled to the at least one electric motor asthe sole source of energy. ln other words, a mobile energy supply unit configured to provide pressurizedhydraulic fluid is provided. The supply unit is adapted for use with hand-heldhydraulic tools, for example hand-held hydraulic railway track maintenance tools of astandard type presently available on the market. Such tools typically have a rating(hydraulic fluid flow rate) of for example 5 or 10 US gallons per minute (GPM). Thesupply unit is provided with one or more hydraulic pumps (typically one pump), eachbeing driven by at least one of the electric motor(s). The at least one electric motor ispowered solely from the electrical storage arrangement, i.e. the electric motor(s) aresolely connected to the electrical storage arrangement to provide electric powerthereto, and no other sources of power (such as an internal combustion engine) arecomprised in the supply unit. The electrical storage arrangement may comprise alithium-ion battery pack, but may alternatively, or additionally comprise storagemeans such as capacitors or other types of batteries.

The inventive energy supply unit provides the advantage that noise and localpollutants are substantially reduced. Furthermore, the use of a highly efficient electricmotor substantially increases energy efficiency. This is particularly the case whenoperating at lower hydraulic fluid flows such as 5 GPM, where the use of an electricmotor allows the flow to be easily reduced, rather than short-circuiting half of the flow back to the tank (as in present internal combustion powered units).

The invention is based on the insight that the hand-held hydraulic railway trackmaintenance tools are used for only brief periods of time during a typical work shift,and that when powered by an efficient electrically driven hydraulic pump, a relativelysmall electrical storage arrangement is sufficient to last for an entire work shift, thusallowing the electrical storage arrangement to be the sole source of power. This isparticularly the case when the supply unit is using energy saving means, asdescribed in embodiments below. lt is understood in this context that a mobile energy supply unit refers to a unit which is of such a size and weight that it may be easily transported for example on a light truck and lifted by a crane or a group of people. Such units typically have a weight of100-250 kilograms.

According to the invention, the unit further comprises a motor control systemconfigured to determine a target oil flow which is equal to or less than a rated oil flow.The target oil flow, which may also be referred to as set oil flow, corresponds to thecurrently desired output oil flow from the unit, which at all times should be lower thanor equal to the rated oil flow of the hydraulic tool connected thereto. The motorcontrol system is electrically coupled to the electric motor and is configured to controlthe speed and torque of the electric motor to achieve the target oil flow. This istypically achieved by controlling the speed and torque of the electric motor based onknown characteristics of the electric motor and hydraulic pump. During normaloperation, the target oil flow equals the rated oil flow. The motor control system maycomprise two or more physical units, for example an electronic control unit (ECU) anda separate power electronics device, such as a variable frequency drive (VFD) orinverter. ln other embodiments, the motor control system may be formed by a singleunit comprising both ECU functionality and the power electronics.

According to the invention, the motor control system is configured to measure voltageand current over the electric motor, and to calculate torque based on data comprisingthe measured voltage and current. Typically, the data also comprises characteristicsof the electric motor, and may also comprise measured temperature of the motor.The motor control system is further configured to determine if the calculated torque isbelow a predetermined torque idle level, and/or if the measured current is below apredetermined current idle level, and if either of this is the case, activate an idle statein which the motor is controlled to operate at a predetermined idle speed orpredetermined idle oil flow. The latter may alternatively be described in that the targetoil flow is set to a predetermined oil flow. The motor control system may furthermorebe configured to activate the idle state only if the calculated torque and/or measuredcurrent is below the corresponding idle level for a predetermined period of time, forexample 1-60 seconds. This embodiment provides several important advantages.Firstly, energy consumption is substantially decreased since the motor speed isdecreased when the hydraulic tools are not used. Secondly, the temperature of thehydraulic oil is decreased, as well as heat generation in the electric motor, the battery and the motor control system. Thirdly, noise is reduced since the electric motor and hydraulic pump operates at much lower speed when the hydraulic tools are not used.

According to the invention, the motor control system, during the idle state, isconfigured to determine if the calculated torque is above a predetermined level,and/or determine if the measured current is above a predetermined level, and if eitherof this is the case, activate an operating state in which target oil flow is set to therated oil flow. ln other words, when operating in the idle state, the motor controlsystem is configured to detect if the user starts using the hydraulic tool by monitoringthe torque and/or current. An important, and surprising, insight of this embodiment isthat an increase in torque and/or current may be accurately detected even if thepredetermined idle speed is set to a very low value (typically less than 50 RPM, oreven as low as 10 RPM). This results in a very low energy consumption in the idlestate, consequently greatly prolonging battery operating time, while reducing heat generation and noise.

According to the invention, the motor control system is configured to determine therated oil flow based on received tool data. The unit comprises a Human MachineInterface (HMl) configured to supply the motor control system with the tool databased on user input comprising said tool data or comprising information regarding aselection of tool data from a predetermined set of tool data. The HMl may be in theform of a simple switch allowing the user to select between 5 and 10 GPM.Alternatively, the HMl may comprise a touch-screen on which the user can enter thetool data directly, or select predefined tool data. The HMl may be integrated with themotor control system, or may be an external device such as a computer or hand helddevice, such as a cellular phone or a portable computer, connected to the motor control system via wired or wireless communication means.

According to the invention, the motor control system is configured to determine arated torque based on received tool data. The motor control system in thisembodiment is configured to determine if the calculated torque exceeds the ratedtorque, and if so control the motor such that the torque decreases to the rated torque.This is particularily advantageous for certain types of tools, for example stonegrinders where the wear of the grinding stone can be greatly reduced by limiting the maximum torque, i.e. even if the user pushes the stone grinder with great forcetowards the rail, the maximum torque is limited by the energy supply unit to spare thegrinding stone. ln embodiments, the electrical storage arrangement comprises a set of batteries, i.e.a plurality of battery cells, and the mobile energy supply unit further comprises aBattery Management System (BMS) configured to provide the motor control systemwith a battery status signal comprising information regarding a state of the set ofbatteries. The BMS may either be a separate unit, typically located in close vicinity tothe set of batteries, or form a part of the motor control system. The motor controlsystem is configured to, in response to a battery status signal indicating that a stateof charge (SOC) and/or individual cell capacity is below a respective predeterminedlevel, activate a power saving state in which the motor is controlled such that thetorque is limited to below a torque limit level. The torque limit level may calculatedbased on data comprising the present SOC and/or individual cell capacity. This mayalternatively be expressed in the sense that maximum allowable torque is reduced orthat a target torque is reduced (to said torque limit level). Since the maximum torque is reduced, the power drawn from the battery to the motor is reduced. ln embodiments, a charging arrangement is electrically coupled with the set ofbatteries, wherein the charging arrangement is configured to communicate with themotor control system and BMS. The motor control system is configured, during saidpower saving state, to increase the torque limit level, i.e. increase maximumallowable torque or target torque, based on power supplied from said chargingarrangement during operation of the hand held tool(s). ln other words, when themotor control system is operating in the power saving state, and the chargingarrangement is activated, the motor control system receives a signal from thecharging arrangement indicating the power supplied therefrom, and in response tothis signal increases the torque limit level or target torque, i.e. uses the powersupplied from the charging arrangement to compensate for the insufficient SOC orlow individual cell capacity of the set of batteries.

According to a second aspect of the invention, a method for operating a hand-heldhydraulic tool is provided, which hand-held hydraulic tool may be a hand-held hydraulic railway track maintenance tool. The method comprises providing at leastone hydraulic pump, at least one electric motor and an electrical storagearrangement as a mobile unit, wherein each hydraulic pump is driveably coupled to atleast one of the electric motor(s). The method further comprises powering the electricmotor solely by said electrical storage arrangement, and connecting the hand-heldhydraulic tool to the hydraulic pump to receive pressurized hydraulic fluid therefrom. ln embodiments, the method further comprises determining a target oil flow which isequal to or less than a rated oil flow, controlling the speed and torque of the electricmotor based on the target oil flow.

According to the invention, the method furthermore comprises repeatedly measuringthe voltage and current over the electric motor, repeatedly calculating the torquebased on data comprising the measured voltage and current, and identifying an idlestate by checking if the calculated torque and/or measured current is below apredetermined level, and if so controlling the motor to operate at a predetermined idle speed.

According to the invention, the method further comprises, when in said idle state,identifying an operating state by checking if the calculated torque is above apredetermined level, or if the measured current is above a predetermined level, and ifso controlling the motor to operate at a speed corresponding to a rated oil flow. lnother words, the method comprises activating an operating state in which the targetoil flow is set to the rated oil flow.

According to the invention, the method further comprises, receiving user input using aHuman Machine Interface (HMI) regarding the hand held tool which is connected tothe unit, the user input comprising tool data or comprising information regarding aselection of tool data from a predetermined set of tool data, and determining therated oil flow based on said tool data.

According to the invention, the tool data further comprises data from which a ratedtorque is determined. Further according to the invention, the method comprises determining if said calculated torque exceeds said rated torque, and if so controllingthe electric motor such that the torque decreases to said rated torque.

The HMI may be in the form of a simple physical switch allowing the user to selectbetween 5 and 10 GPM. Alternatively, the HMI may comprise a touch-screen on which the user can enter the tool data directly, or select predefined tool data. ln embodiments, the method further comprises, in response to a battery status signalfrom a Battery Management System (BMS), indicating that a state of charge (SOC)and/or individual cell capacity is below a respective predetermined level, activate apower saving state in which the motor is controlled such that the torque is limited tobelow a torque limit level. The torque limit level may be calculated based on datacomprising the present SOC and/or individual cell capacity. The method may furthercomprise, during said power saving state, increasing the torque limit level, i.e.increase maximum allowable torque or target torque based on power supplied from a charging arrangement during operation of the hand held tool(s).

According to a third aspect of the invention, a method for providing pressurizedhydraulic fluid to a hand-held hydraulic tool is provided, which hand-held hydraulic toolmay be a hand-held hydraulic railway track maintenance tool. This methodcorresponds to the above described method according to the second aspect, exceptthat it does not comprise the step of connecting a hand-held tool to the mobile unit.

The features of the embodiments described above are combinable in any practicallyrealizable way to form embodiments having combinations of these features. Further,all features and advantages of embodiments described above relating to the firstaspect of the invention may be applied in corresponding embodiments of the secondand third aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGSAbove discussed and other aspects of the present invention will now be described inmore detail using the appended drawings, which show presently preferred embodiments of the invention, wherein: fig. 1 is a schematic illustration of an embodiment of a mobile energysupply unit according to the first aspect of the invention, along with a hand heldhydraulic tool connected thereto; fig. 2 is a schematic illustration of another embodiment of a mobile energysupply unit according to the second aspect of the invention, along with a hand heldhydraulic tool connected thereto, and fig. 3 is a flow chart ofan embodiment ofa method according to the secondaspect of the invention.

DETAILED DESCRIPTION Figure 1 is a schematic illustration of an embodiment of a mobile energy supply unitaccording to the first aspect of the invention, along with a hand held hydraulic railwaytrack maintenance tool connected thereto. ln the figure, the thick arrows indicate a flowof electric power to/from the electrical storage and to the electric motor, and the thinarrows indicate a flow of control signals. The supply unit 1 comprises one electric motor3, one hydraulic pump 4 being driveably coupled to the electric motor, one hydraulicconnector 5 (in the figure shown as a hose, but could refer to a hydraulic socket) forconnecting a hand-held hydraulic tool 2 (in the figure exemplified by a drill) to thehydraulic pump, and an electrical storage arrangement 6 being electrically coupled tothe electric motor (as the sole source of energy) via the motor control device (MCD)7b. lt is understood that the energy supply unit also comprises a hydraulic fluid tankfrom which the hydraulic pump 4 sources its hydraulic fluid, and to which the returnhose from the hand-held hydraulic tool is connected (not shown in the figure). Thesupply unit also comprises an air-to-hydraulic fluid heat exchanger for cooling thehydraulic fluid. The electrical storage arrangement is a lithium-ion battery pack, whichin this embodiment is formed of 16 cells having a total capacity ofabout 5 kWh. ln other embodiments, the capacity may be about 10 kWh.

The MCD 7b and the electronic control unit (ECU) 7a together form the motor controlsystem which serves to control the motor to provide the desired hydraulic fluid flow tothe hydraulic tool 2. ln this embodiment, the MCD is an inverter, which converts theDC from the battery to 3 phase AC to control the speed and torque of the electric motor3. As feedback from the motor, the inverter measures the speed/rpm, voltage, currentand temperature. Based on measured data comprising at least the voltage and current, and other predefined data such as characteristics data of the electric motor, torque iscalculated.

The ECU is configured to determine a target oil flow which is equal to or less than arated oil flow of the hydraulic tool connected thereto. Based on the target oil flow, atarget speed is calculated, which is communicated to the MCD/inverter as a targetspeed control signal. Thus, the inverter controls the speed of the electric motor inresponse to a target speed control signal from the ECU. Depending on the presentload of the hydraulic tool, the inverter determines the required current, and supplies itto the electric motor 3.

The ECU receives feedback signals from the inverter comprising a torque feedbacksignal corresponding to the calculated torque, and a current feedback signalcorresponding to the measured current. During operation of the supply unit, the ECUis configured to determine if the calculated torque is below a predetermined torque idlelevel, and/or if the measured current is below a predetermined current idle level, and ifeither of this is the case, activate an idle state in which the motor is controlled to operateat a predetermined idle speed or predetermined idle oil flow, i.e. the target oil flow isset to a predetermined oil flow. The predetermined idle speed is typically 10 RPM.The ECU is further configured, during the idle state, to determine if the calculatedtorque is above a predetermined level, and/or determine if the measured current isabove a predetermined level, and if either of this is the case, activate an operating state in which target oil flow is set to the rated oil flow.

The ECU 7a comprises a Human Machine Interface (HMI) 8 configured to supply theECU with tool data based on user input regarding a selection of tool data from apredetermined set of tool data. As shown in fig. 1, the HMI has a touch-screenshowing different tools, allowing the user to select which tool is connected to thesupply unit. By selecting a tool on the screen, the ECU determines the rated oil flowand optionally also a rated torque based on received data from the HMI. ln additionto this selection, the HMI may comprise the possibility to manually enter the tool data.ln other embodiments, the HMI may be in the form of a physical switch allowing theuser to select between 5 and 10 GPM.

The ECU 7a is configured to determine if the calculated torque exceeds the ratedtorque, and if so control the motor such that the torque decreases to the rated torque.This is achieved by reducing the maximum allowable torque or current, whichtranslates into a torque or current limitation control signal from the ECU 7a to the inverter 7b.

The supply unit further 1 comprises a Battery Management System (BMS) 9configured to provide the motor control system with a battery status signal comprisinginformation regarding a state of the set of batteries. The BMS is located in closevicinity to the set of batteries 6. The ECU 7a is configured to, in response to a batterystatus signal indicating that a state of charge (SOC) and/or individual cell capacity isbelow a respective predetermined level, activate a power saving state in which thetarget oil flow is reduced to a lower level than the rated oil flow, and to communicate a corresponding target speed control signal to the inverter 7b.

A charging arrangement 10 is electrically coupled with the set of batteries 6, whereinthe charging arrangement is configured to communicate with the motor controlsystem and BMS.

Figure 2 is a schematic illustration of another embodiment of a mobile energy supplyunit 11 according to the first aspect of the invention, along with a hand held hydraulicrailway track maintenance tool 12 connected thereto. This embodiment correspondsto the embodiment in figure 1, except that the motor control system 17 is formed as asingle unit comprising both an ECU and a MCD/inverter with correspondingfunctionality as described above with reference to figure 1. Another difference is thatthe HMI 18 is formed separately from the ECU and communicates wirelesslytherewith. ln figure 2, the HMI 18 is illustrated identically with the integrated HMI 8 infigure 1, but in other embodiments, the HMI may for example be a cellular phone orlaptop provided with customized HMI software. The hydraulic tool 12, electric motor13, hydraulic pump 14, the hydraulic connector 15, the battery set 16, the BMS 19and the charging arrangement 110 corresponds exactly to the corresponding parts ofthe embodiment in figure 1, and will not be further described here. 11 Figure 3 is a flow chart of an embodiment of the method according to the secondaspect of the invention. The method comprises providing 21 at least one hydraulicpump, at least one electric motor and an electrical storage arrangement as a mobileunit, wherein each hydraulic pump is driveably coupled to at least one of the electricmotor(s), i.e. providing a mobile energy supply unit according to the first aspect of theinvention. The method further comprises powering 22 the electric motor solely by theelectrical storage arrangement, and connecting 23 the hand-held hydraulic tool to thehydraulic pump to receive pressurized hydraulic fluid therefrom. A rated oil flow isdetermined 24 based on received user input regarding the hand held tool which isconnected to the unit, the user input comprising tool data or comprising informationregarding a selection of tool data from a predetermined set of tool data. The userinput is preferably received using an HMI as described above with reference tofigures 1 and 2. The method further comprises operating 25 the hydraulic tool at adetermined target oil flow which is equal to or less than a rated oil flow by controllingthe speed and torque of the electric motor based on the target oil flow. Voltage andcurrent are repeatedly measured over the electric motor, and torque is repeatedlycalculated based on data comprising the measured voltage and current. An idle stateis identified 26 by checking if the calculated torque and/or measured current is belowrespective predetermined levels, and if so controlling the motor to operate at apredetermined idle speed. When in the idle state, an operating state is identified 27by checking if the calculated torque is above a predetermined level, or if themeasured current is above a predetermined level, and if so controlling the motor to operate 25 at a speed corresponding to the rated oil flow.

The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that severalchanges and modifications may be made within the scope of the invention. Forexample, the charging arrangement may be any charger available on the market, anddoes not necessarily need to be communicating with the BMS and ECU.Furthermore, different types of electrical storage arrangement are possible.Furthermore, the MCD and electrical motor do not need to be of the above described inverter and 3-phase types described above.

Claims (1)

1. A mobile energy supply unit (1; 11) for hand-held hydraulic tools (2; 12), comprising: - at least one electric motor (3; 13); - at least one hydraulic pump (4; 14), each being driveably coupled to atleast one of said electric motor(s); - one or more hydraulic connectors (5; 15) for connecting at least one hand-held hydraulic tool to at least one of said hydraulic pump(s); - an electrical storage arrangement (6; 16) being electrically coupled to theat least one electric motor as the sole source of energy, and - a motor control system (7a-b; 17) being electrically coupled to said electricmotor (3; 13) and being configured to control speed and torque of theelectric motor, wherein said motor control system (7a-b; 17) is configuredto measure current over the electric motor (3; 13), characterized in that said motor control system (7a-b; 17) is configured to determine a target oil flow which is equal to or less than a rated oil flow, and is configured to control the speed and torque of the electric motor based on said target oil flow, wherein said motor control system (7a-b; 17) is further configured to measure voltage over the electric motor (3; 13), and to calculate torque based on data comprising the measured voltage and current, and is further configured to determine if the calculated torque is below a predetermined idle level, and/or determine if the measured current is below a predetermined idle level, and if so activate an idle state in which the electric motor is controlled to operate at a predetermined idle speed, and wherein said motor control system (7a-b; 17), during said idle state, is configured to check if said calculated torque is above a predetermined level, and/or check if said measured current is above a predetermined level, and if so activate an operating state in which the target oil flow is set to said rated oil flow, said mobile energy supply unit further comprising a Human Machine Interface, HMI, (8; 18) configured to supply said motor control system (7a-b; 17) with tool data based on user input comprising said tool data or comprising information regarding a selection of tool data from a predetermined set of tool 13 data, wherein said motor control system (7a-b; 17) is configured to determinesaid rated oil flow based on said tool data, wherein said motor control system(7a-b; 17) is furthermore configured to determine a rated torque based on saidtool data, and wherein said motor control system (7a-b; 17) is configured todetermine if said calculated torque exceeds said rated torque, and if so controlthe electric motor such that the torque decreases to said rated torque. _ Mobile energy supply unit according to claim 1, wherein said HMI (8) is integrated with the motor control system. _ Mobile energy supply unit according to claim 1, wherein said HMI (18) is an external device such as a computer or hand held device connected to the motor control system via wired or wireless communication means. _ Mobile energy supply unit according to any of claims 1-3, wherein said electrical storage arrangement (6; 16) comprises a set of batteries, said mobileenergy supply unit further comprising a Battery Management System, BMS, (9; 19) configured to provide the motor control system (7a-b; 17) with a batterystatus signal comprising information regarding a state of said set of batteries,wherein said motor control system, in response to a battery status signalindicating that a state of charge, SOC, and/or individual cell capacity is belowa respective predetermined level, is configured to activate a power savingstate in which the electric motor is controlled such that the torque is below a torque limit level. _ Mobile energy supply unit according to claim 4, further comprising a charging arrangement (10; 110) being electrically coupled with said set of batteries,wherein said charging arrangement is configured to communicate with themotor control system (7a-b; 17) and the BMS (9; 19), and wherein said motorcontrol system is configured, during said power saving state, to increase thetorque limit level based on power supplied from said charging arrangement during operation of said hand held tool(s)_ _ Method for operating a hand-held hydraulic tool, said method comprising: 14 providing (21) at least one hydraulic pump, at least one electric motor andan electrical storage arrangement as a mobile unit, wherein each hydraulicpump is driveably coupled to at least one of said electric motor(s);powering (22) the electric motor solely by said electrical storagearrangement; connecting (23) the hand-held hydraulic tool to said hydraulic pump toreceive pressurized hydraulic fluid therefrom, repeatedly measuring current over the electric motor; the method being characterized by: repeatedly measuring voltage over the electric motor; repeatedly calculating torque based on data comprising the measuredvoltage and current; identifying (26) an idle state by checking if the calculated torque and/ormeasured current is below a predetermined level, and if so controlling themotor to operate at a predetermined idle speed; when in said idle state, identifying (27) an operating state by checking if thecalculated torque is above a predetermined level, or if the measuredcurrent is above a predetermined level, and if so controlling the motor tooperate (25) at a speed corresponding to a rated oil flow; receiving user input using a Human Machine Interface (HMI) regarding thehand held tool which is connected to the unit, said user input comprisingtool data or comprising information regarding a selection of tool data from apredetermined set of tool data; determining (24) said rated oil flow based on said tool data; determining a rated torque based on said tool data, determining if said calculated torque exceeds said rated torque, and if socontrolling the electric motor such that the torque decreases to said rated torque.