Method for operating a hydraulic system of an industrial truck

Abstract

The invention relates to a method for operating a hydraulic system (1) of a forklift truck, which has a hydraulic pump (3) driven by a drive motor (2) and has at least one consumer (4) driven by the volume flow (Q) of the hydraulic pump (3), wherein when controlling the consumer (4) the volume flow (Q) of the hydraulic pump (3) is controlled depending on the control signal of an actuator (11), in particular a joystick or a hand control lever.When controlling the consumer (4), the volume flow rate (Q) of the hydraulic pump (3) is controlled as a function of the temperature (T) of the hydraulic fluid in such a way that the influences of the temperature (T) of the hydraulic fluid on the volume flow rate (Q) delivered by the hydraulic pump (3) are compensated, thereby providing a constant volume flow rate (Q) for the consumer (4) over the entire temperature operating range of the hydraulic fluid for the control signal of the actuator (11).

Description

[0001] The invention relates to a method for operating a hydraulic system of an industrial truck, which has a hydraulic pump driven by a drive motor and at least one consumer driven by the volume flow of the hydraulic pump, wherein when the consumer is activated the volume flow of the hydraulic pump is controlled as a function of the actuating signal of an actuator, in particular a joystick or a hand control lever, wherein the hydraulic pump is designed as a constant pump with a constant delivery volume and when the consumer is activated the volume flow of the hydraulic pump is controlled as a function of the actuating signal of the actuator, in particular a joystick or a hand control lever, by a speed specification of the drive motor.

[0002] From DE 101 28 583 A1 and US 6 005 360 A1 generic methods for operating a hydraulic system of an industrial truck are known.

[0003] JP 2010 255780 A discloses a hydraulic system in which the maximum flow rate of the hydraulic pump is to be kept constant regardless of the temperature of the pressure medium. To this end, a temperature sensor measures the temperature of the pressure medium in the tank. As the temperature of the pressure medium decreases, the speed of the pump motor increases. This allows the hydraulic pump to deliver the maximum flow rate even at low temperatures and thus high pressure fluid viscosity, while the intake volume of the hydraulic pump is reduced.

[0004] In battery-electric industrial trucks, the hydraulic system typically features a fixed-displacement pump with a constant flow rate. The hydraulic pump typically supplies multiple consumers, such as a lifting drive for raising and lowering a load-handling device, a tilt drive for tilting a mast on which the load-handling device is mounted so that it can be raised and lowered, and, if necessary, one or more additional consumers, such as a sideshift for the load-handling device. To control a consumer, the driver of the industrial truck operates an actuator, such as a joystick or hand control lever, and, depending on the actuator's deflection, a specific target speed is specified, at which a drive motor driving the hydraulic pump operates.The target speed and the delivery volume of the hydraulic pump result in a specific volume flow (discharge rate) delivered by the hydraulic pump, which is then supplied to the consumer. When controlling a consumer, the hydraulic pump, designed as a fixed-displacement pump, is thus operated at a controlled speed that depends solely on the deflection of the actuator. Depending on the deflection of the actuator, a target speed is generated at which the hydraulic pump, designed as a fixed-displacement pump, is operated. This means that different target speeds are generated for different deflections of the actuator.

[0005] The disadvantage here is that when these target speeds are generated and therefore specified, the load pressure of the consumer and the viscosity-dependent and speed-dependent volumetric efficiency of the hydraulic pump are not taken into account. This means that for the same deflection of the actuator, i.e. a specific deflection point of the actuator, with different viscosities of the pressure medium, different volume flows and thus a varying volume flow are made available to the consumer. This effect is based on the fact that in a hydraulic pump designed as a fixed displacement pump, the volume flow varies with fluctuating viscosity of the pressure medium at the same load pressure. For the driver of the industrial truck, this means that for a specific deflection of the actuator and therefore a specific constant speed of the constant displacement pump assigned to the deflection of the actuator, a fluctuating orA varying volume flow of the fixed-displacement pump results, and thus, for a given actuator displacement (i.e., equal actuator displacements), varying actuation speeds of the consumer are set depending on the prevailing pressure medium temperature. Furthermore, the hydraulic pump is not operated at its functionally correct and optimal operating point.

[0006] If varying actuation speeds of the consumer occur for a specific actuator deflection (i.e., identical actuator deflections), this leads to a loss of comfort for the industrial truck driver, as consumer movements are not executed optimally, as well as to non-reproducible actuation speeds of the controlled consumer across the entire operating range. The industrial truck driver may then be forced to readjust the actuator deflection in order to achieve the expected actuation speed of the controlled consumer.

[0007] The present invention is based on the object of providing a method for operating a hydraulic system of an industrial truck of the type mentioned at the outset, which avoids the disadvantages mentioned.

[0008] This object is achieved according to the invention in that the temperature of the pressure medium is measured with a temperature sensor and, when controlling the consumer, the volume flow of the hydraulic pump is controlled as a function of the temperature of the pressure medium in such a way that, when controlling the volume flow of the hydraulic pump, the influences of the temperature of the pressure medium on the volume flow delivered by the hydraulic pump are compensated, whereby a constant volume flow is provided for the consumer over the entire temperature operating range of the pressure medium for the control signal of the actuator.To compensate for the influence of the pressure medium temperature on the volume flow delivered by the hydraulic pump, a temperature-dependent adjustment of the drive motor's speed setting is performed. The temperature-dependent adjustment of the speed setting is carried out in such a way that the drive motor's speed setting increases as the pressure medium temperature increases. The temperature-dependent adjustment of the speed setting is achieved by factoring with a viscosity-dependent factor. This makes it easy to increase the drive motor's speed setting as the pressure medium temperature increases.

[0009] With the invention, a constant volume flow is thus made available to the hydraulic pump for a specific deflection of the actuator and thus a specific actuating signal from the actuator, regardless of the temperature of the pressure medium and thus across the entire temperature operating range of the pressure medium. For a specific deflection of the actuator, i.e., identical deflections of the actuator, the same actuation speed of the consumer is thus established at different temperatures of the pressure medium. This leads to increased comfort for the driver of the industrial truck, as consumer movements are carried out optimally, as well as to reproducible actuation speeds of the controlled consumer across the entire operating range.Furthermore, with the invention, the driver of the industrial truck is no longer forced to readjust the deflection of the actuator in order to achieve an expected actuation speed of the controlled consumer.

[0010] In the invention, the hydraulic pump is designed as a fixed-displacement pump with a constant displacement. When controlling the consumer, the volume flow of the hydraulic pump is controlled by a speed specification of the drive motor as a function of the control signal of the actuator, in particular a joystick or a manual control lever. In a hydraulic pump designed as a fixed-displacement pump, the volume flow delivered by the fixed-displacement pump can be easily controlled by specifying a speed of the fixed-displacement pump.

[0011] According to the invention, a temperature-dependent adjustment of the drive motor's speed setting is performed to compensate for the influence of the pressure medium temperature on the volume flow delivered by the hydraulic pump. This allows the volume flow delivered by a hydraulic pump designed as a fixed-displacement pump to be easily controlled in such a way that the influence of the pressure medium temperature on the volume flow delivered by the hydraulic pump is compensated, thus providing a constant volume flow for the consumer across the entire temperature operating range of the pressure medium for the control signal of the actuator.

[0012] According to the invention, the temperature-dependent adjustment of the speed setting is carried out in such a way that the speed setting of the drive motor is increased as the temperature of the pressure medium increases. Since the volume flow of the hydraulic pump decreases with increasing pressure medium temperature at a constant speed and constant load pressure of the consumer, increasing the speed setting of the drive motor with increasing pressure medium temperature can reliably ensure that the hydraulic pump delivers a constant volume flow at a specific actuator displacement, regardless of the pressure medium temperature.

[0013] For this purpose, the characteristic map of the volumetric efficiency of the hydraulic pump is advantageously determined, several characteristic curves for constant volume flows are determined, and the viscosity-dependent factor is determined from these several characteristic curves for constant volume flows. The characteristic map of the volumetric efficiency of the hydraulic pump is preferably determined for target operating points, including the load pressures occurring at the consumer and the desired constant volume flows at which the consumer is to be operated. If several characteristic curves for constant volume flows are also determined, each of which is a function of the volumetric efficiency of the hydraulic pump, the viscosity-dependent factor can be determined from these characteristic curves, which is used for the temperature-dependent adjustment of the speed setting.

[0014] The temperature of the pressure medium is preferably measured with a temperature sensor that detects the temperature of the pressure medium in a tank of the hydraulic system.

[0015] Further advantages and details of the invention are explained in more detail with reference to the embodiment shown in the schematic figures. Figure 1 shows a circuit diagram of a hydraulic system of an industrial truck according to the invention, Figure 2 shows a diagram of the volumetric efficiency of the hydraulic pump of the hydraulic system of the Figure 1 about the viscosity of the pressure medium, Figure 3 a diagram of the viscosity of the pressure medium of the hydraulic system of the Figure 1 about the temperature and Figure 4 a diagram of the volume flow Q of the hydraulic pump of the hydraulic system of the Figure 1 about the temperature T of the pressure medium.

[0016] In the Figure 1A circuit diagram of a hydraulic system 1 of an industrial truck according to the invention is shown. The hydraulic system 1 has a hydraulic pump 3 driven by a drive motor 2 and at least one consumer 4 driven by the volume flow Q of the hydraulic pump 3.

[0017] The hydraulic pump 3 is operated in an open circuit and sucks in pressure medium from a tank 6 via a suction line 5 and delivers the volume flow Q into a delivery line 7, which is connected to the consumer 4. When the consumer 4 is activated, ie when the consumer 4 moves, the load pressure p of the consumer 4 is established in the delivery line 7.

[0018] In the illustrated embodiment, the hydraulic pump 3 is designed as a constant pump with a constant delivery volume.

[0019] The drive motor 2 driving the hydraulic pump 3 is designed, for example, as an electric motor.

[0020] An electronic control device 10 is connected on the input side to an actuator 11, for example a joystick or a manual control lever, and is connected on the output side to the drive motor 2 in order to specify a speed n for driving the hydraulic pump 3. When controlling the consumer 4, the electronic control device 11 specifies a speed n set for the drive motor 2 based on the control signal generated by the actuated actuator 11 in order to generate a corresponding volume flow Q of the hydraulic pump 3 for actuating the consumer 4 depending on the control signal of the actuator 11. The drive motor 2 thus provides the speed n and a corresponding torque M for driving the hydraulic pump 3.

[0021] The hydraulic pump 3, designed as a constant pump, delivers a volume flow Q according to the following equation: Q = V * n * η vol / 1000 where Q is the volume flow in l / min, V is the displacement in cm 3< , n is the speed in 1 / min and η vol is the volumetric efficiency of the hydraulic pump 3.

[0022] In the hydraulic pump 3 designed as a fixed-displacement pump, the delivery volume V is constant. Therefore, the volumetric efficiency η vol of the hydraulic pump 3 is the variable for determining the volumetric flow Q. The volumetric efficiency η vol of the hydraulic pump 3 depends on the speed n and the viscosity of the pressure medium, which varies depending on the temperature T of the pressure medium and the type of pressure medium and is thus a function of the temperature T of the pressure medium and the type of pressure medium.

[0023] In the Figure 2 is a diagram of the volumetric efficiency η vol of the hydraulic pump 3 of the Figure 1The ordinate represents the volumetric efficiency η vol of the hydraulic pump 3 and the abscissa represents the viscosity of the pressure medium. Figure 2 The dependence of the volumetric efficiency η vol of the hydraulic pump 3 on the viscosity of the pressure medium can be seen. At high viscosity of the pressure medium, the volumetric efficiency η vol of the hydraulic pump 3 is low, with decreasing viscosity of the pressure medium, the volumetric efficiency η vol of the hydraulic pump 3 increases. Figure 2 The range X also represents an optimal viscosity range for the operation of the hydraulic pump 3, which is not equal to, but smaller than, the entire temperature operating range of the pressure medium of the hydraulic system 1.

[0024] In the Figure 3 is a diagram of the viscosity of the pressure medium of the hydraulic system 1 of the Figure 1over the temperature T. The ordinate represents the viscosity of a pressure medium and the abscissa represents the temperature T. In the Figure 3 The dependence of the viscosity of a pressure medium on the temperature T can be seen. The viscosity of the pressure medium decreases with increasing temperature T. The viscosity of the pressure medium is therefore a function of the temperature T.

[0025] According to the diagram of the Figure 4 , in which the volume flow Q of the hydraulic pump 3 of the Figure 1is plotted against the temperature T of the pressure medium, with the volume flow Q of the hydraulic pump 3 being plotted on the ordinate and the temperature T of the pressure medium being plotted on the abscissa, it can be seen that the hydraulic pump 3, at constant speed n and constant load pressure p, delivers a volume flow Q which changes due to the dependence of the volumetric efficiency η vol of the hydraulic pump 3 on the viscosity over the temperature T of the pressure medium. With increasing temperature T of the pressure medium, the volume flow Q decreases. The hydraulic pump 3 thus delivers according to the diagram of the Figure 4depending on the temperature T of the pressure medium at a constant speed n and constant load pressure p a varying volume flow Q, whereby for the speed n specified for a specific actuation (deflection) of the actuator 11, different movement speeds of the consumer 4 are to be set at different temperatures T.

[0026] In the hydraulic system 1 according to the invention, a temperature sensor 12 is provided which detects the temperature T of the pressure medium in the container 6 and is connected on the input side to the electronic control device 10.

[0027] In order to provide a constant volume flow Q for the consumer 4 over the entire temperature operating range of the pressure medium for the control signal of the actuator 11 and thus to achieve that the same movement speed of the consumer 4 always results regardless of the temperature T of the pressure medium for a specific control signal of the actuator 11, according to the invention the volume flow Q of the hydraulic pump 3 is controlled as a function of the temperature T of the pressure medium when controlling the consumer 4 in such a way that when controlling the volume flow Q of the hydraulic pump 3 the influences of the temperature T of the pressure medium on the volume flow Q delivered by the hydraulic pump 3 are compensated.For this purpose, according to the invention, when controlling the consumer 4, the volume flow Q of the hydraulic pump 3 is controlled as a function of the actuating signal from the actuator 11 by means of a speed specification (setpoint speed) n setpoint of the drive motor 2, and in order to compensate for the influences of the temperature T of the pressure medium on the volume flow Q delivered by the hydraulic pump 3, a temperature-dependent adjustment of the speed specification (setpoint speed) n setpoint of the drive motor 2 is carried out. According to the invention, the speed n setpoint of the drive motor 3 and thus the speed n setpoint of the hydraulic pump 2 are thus adjusted as a function of the temperature T of the pressure medium measured by the temperature sensor 12 in such a way that, regardless of the temperature T of the pressure medium, a constant volume flow Q is generated to supply the consumer 4 for a specific deflection and thus a specific actuating signal from the actuator 11.Thus, at a specific deflection of the actuator 11, a volume flow Q that is independent of the temperature of the pressure medium and thus a volume flow Q that is constant over the temperature is made available to the consumer 4 by an individual speed n of the hydraulic pump 3 as a function of the respective temperature of the pressure medium.

[0028] In order to carry out the temperature-dependent adjustment of the speed specification (target speed) n soll of the drive motor 2 and to compensate for the influences of the fluctuating temperature T of the pressure medium on the volume flow Q in order to achieve a volume flow Q that is constant over the temperature T for a specific deflection of the actuator 11, the exact data for the hydraulic pump 3 with regard to the volume flow Q, which is a function of the speed n, the load pressure p and the volumetric efficiency η vol, as well as the temperature T of the pressure medium are required.

[0029] The temperature T of the pressure medium is measured by the temperature sensor 12 and made available to the electronic control device 10.

[0030] In the invention, the characteristic map of the volumetric efficiency η vol of the hydraulic pump 3 is to be determined. The characteristic map is to be determined, in particular, for target operating points, including the occurring load pressures p and the desired constant volume flows Q1, Q2, Q3 to Qn with which the consumer 4 is to be operated. The following equations are relevant for this purpose: Viskosität des Druckmittels = Funktion von Druckmittel

[0031] For this purpose, the viscosities of the pressure medium can be determined for different temperatures, for example -10°C, -5°C, 0°C, +5°C, +15°C, +35°C, +65°C, +85°C and +95°C.

[0032] With the provided characteristic curves for each volume flow Q = constant = function of displacement volume V, speed n, viscosity of the pressure medium, volumetric efficiency η vol (according to equation 3), a viscosity-dependent factor k can then be determined.

[0033] This viscosity-dependent factor k, which is stored in the electronic control device 10, is used for the temperature-dependent adjustment of the speed specification (target speed) n soll according to the following formula: n soll = n ideal + n ideal * k where n soll is the speed specification (setpoint speed) for the drive motor 2, n ideal is the speed specification value corresponding to the deflection of the actuator 11 and k is the viscosity-dependent factor.

[0034] By means of factorization (n ideal *k) it is thus achieved that with increasing temperature T of the pressure medium, which is measured by means of the temperature sensor 12, the speed specification (target speed) n soll for the drive motor 2 is increased by the electronic control device 10 in such a way that for a specific deflection of the actuator 11, the volume flow Q is independent of the temperature T and is constant over the temperature T. As a result, the consumer 4 is always operated at the same (constant) movement speed regardless of the temperature T of the pressure medium for a specific deflection of the actuator 11.

[0035] In the invention, a constant volume flow Q is thus provided to the consumer 4, independent of the temperature, upon a corresponding deflection of the actuator 11 by means of the individual speed of the hydraulic pump 3 as a function of the temperature T of the pressure medium.

[0036] If the hydraulic system 1 comprises several consumers 4, a viscosity-dependent factor k can be determined for each consumer 4 and stored in the electronic control device 10 so that each consumer 4 is parameterized separately.

[0037] Alternatively, in a hydraulic system 1 with several consumers 4, a generally valid viscosity-dependent factor k can be stored in the electronic control device 10, which can be used for all consumers 4 if the consumers 4 are justifiably oversupplied with the volume flow Q.

[0038] In addition, the load pressure p of the consumer 4 can be detected by a pressure sensor and made available to the electronic control device 10, whereby the effects of the load pressure p on the volumetric efficiency η vol of the hydraulic pump 3 can also be compensated.

[0039] The method according to the invention has a number of advantages.

[0040] With the method according to the invention, the driver of the industrial truck receives the same actuation speed of the consumer 4 across the entire temperature operating range of the pressure medium for the same deflection of the actuator 11, i.e., a specific deflection point of the actuator 11, for example, a joystick or a manual control lever. This leads to increased comfort, as consumer movements are executed optimally. In addition, reproducible actuation speeds of the controlled consumer 4 are achieved across the entire operating range. With the method according to the invention, the driver of the industrial truck is no longer forced to readjust the deflection on the actuator in order to achieve an expected actuation speed of the controlled consumer 4.

[0041] The hydraulic pump 3 is always operated in the optimal speed range and thus always results in the lowest noise levels at the operating point.

[0042] When the hydraulic pump 3 is operating outside the Figure 2 Within the optimal viscosity range X illustrated in Figure 1, an extended service life (running time) of the hydraulic pump 3 can be achieved by reducing the nominal speed of the hydraulic pump 3 and / or by reducing the speed dynamics. Cavitation in the hydraulic pump 3 at low starting temperatures and thus a high viscosity of the pressure medium, as well as a lubricating film break in the hydraulic pump 3 at high operating temperatures and thus a low viscosity of the pressure medium, can be prevented in this way. This can be achieved in the method according to the invention by implementing a warm-up phase and / or a cooling phase.

Claims

1. Method for operating a hydraulic system (1) of an industrial truck, which hydraulic system (1) has a hydraulic pump (3) which is driven by a drive motor (2), and at least one consumer (4) which is driven by the volume flow (Q) of the hydraulic pump (3), wherein when the consumer (4) is actuated the volume flow (Q) of the hydraulic pump (3) is controlled as a function of the actuating signal of an actuator element (11), in particular of a joystick or of a manual operator lever, wherein the hydraulic pump (3) is configured as a fixed displacement pump with a fixed delivery volume (V), and when the consumer (4) is actuated the volume flow (Q) of the hydraulic pump (3) is controlled as a function of the actuating signal of the actuator element (11), in particular of a joystick or of a manual operator lever, by means of a rotational speed specification (nsoll) of the drive motor (2), characterized in that the temperature (T) of the pressure medium is measured with a temperature sensor (12), and when the consumer (4) is actuated the volume flow (Q) of the hydraulic pump (3) is controlled as a function of the temperature (T) of the pressure medium in such a way that when the volume flow (Q) of the hydraulic pump (3) is controlled, the influences of the temperature (T) of the pressure medium on the volume flow (Q) which is delivered by the hydraulic pump (3) are compensated, as a result of which a fixed volume flow (Q) for the consumer (4) is made available over the entire temperature operating range of the pressure medium for the actuating signal of the actuator element (11), wherein in order to compensate the influences of the temperature (T) of the pressure medium on the volume flow (Q) which is delivered by the hydraulic pump (3) a temperature-dependent adaptation of the rotational speed specification (nsoll) of the drive motor (2) is carried out, and the temperature-dependent adaptation of the rotational speed specification (nsoll) is carried out in such a way that as the temperature (T) of the pressure medium rises the rotational speed specification (nsoll) of the drive motor (2) is increased, wherein the temperature-dependent adaptation of the rotational speed specification (nsoll) is carried out by factorizing (nideal*k) with a viscosity-dependent factor (k).

2. Method according to Claim 1, characterized in that the characteristic diagram of the volumetric efficiency (ηvol) of the hydraulic pump (3) is determined, a plurality of characteristic curves for fixed volume flows (Q) are determined, and the viscosity-dependent factor (k) is determined from the plurality of characteristic curves for fixed volume flows (Q).

3. Method according to either of Claims 1 and 2, characterized in that the temperature sensor (12) senses the temperature (T) of the pressure medium in a container (6) of the hydraulic system (1).

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