Hydraulic operating device for a cooling fan of a commercial vehicle

Abstract

Hydraulic operating device (12) for a cooling fan (14) of a commercial vehicle (10), comprising a hydraulic motor (16) and a fan unit (18) driven by the hydraulic motor (16) for generating a cooling airflow (20), a hydraulic supply (38) adjustable according to a pressure feedback with respect to its delivery volume for providing pressurized hydraulic fluid, and a control valve (44) for adjusting a volume flow passing through the hydraulic motor (16) depending on a control signal representing a cooling requirement (46), wherein a sensor line (52) branched off in a supply line (50) between the control valve (44) and the hydraulic motor (16) leads to a pressure control input (54) of the hydraulic supply (38).

Description

[0001] The invention relates to a hydraulic operating device for a cooling fan of a commercial vehicle.

[0002] Such an operating device is used, among other things, in agricultural tractors manufactured by John Deere for cooling charge air compressed by a turbocharger and supplied to a supercharged diesel engine. This known operating device comprises a hydraulic motor that drives a fan impeller to generate an axial air flow passing through an intercooler. The hydraulic motor is operated by a dedicated hydraulic pump with a constant displacement. In order to be able to adapt the speed of the fan impeller and thus the intensity of the axial air flow to the respective cooling requirements in such a case, a bypass valve in the form of an electrically controllable pressure control valve is connected in parallel to the hydraulic motor.The arrangement created in this way enables flexible placement of the intercooler within the agricultural tractor and thus improved use of the available installation space.

[0003] In addition, agricultural tractors are typically equipped with a (main) hydraulic system that operates various vehicle- or work-related functions. The hydraulic system, in turn, includes a hydraulic pump in the form of a variable-displacement hydraulic pump fed from a hydraulic fluid reservoir. The variable-displacement hydraulic pump has a pressure control input that allows the discharge volume to be adjusted as desired based on a feedback hydraulic pressure.

[0004] The presence of two hydraulic pumps naturally requires more space within the agricultural tractor. Furthermore, the usual use of a hydraulic pump with a constant displacement for cost reasons inevitably results in compromises in energy efficiency, which is particularly true when the hydraulic motor is operated at partial load.

[0005] The document US6314729 B1 shows a hydraulic operating device for a cooling fan of a commercial vehicle according to the preamble of claim 1.

[0006] The object of the present invention is therefore to design a hydraulic operating device for a cooling fan of a commercial vehicle with a view to optimizing the required installation space and energy efficiency.

[0007] This object is achieved by a hydraulic operating device having the features of patent claim 1.

[0008] The hydraulic operating device for a cooling fan of a commercial vehicle comprises a hydraulic motor and a fan unit driven by the hydraulic motor for generating a cooling air flow, a hydraulic supply adjustable in accordance with a pressure feedback with regard to its delivery volume for providing pressurized hydraulic fluid, and a control valve for adjusting a volume flow passing through the hydraulic motor depending on a control signal representing a cooling requirement, wherein a sensor line branched off in a supply line between the control valve and the hydraulic motor leads to a pressure control input of the hydraulic supply provided for pressure feedback.

[0009] To adjust the speed of the hydraulic motor and thus the cooling capacity of the fan unit, the control valve is opened or closed depending on the control signal, resulting in a corresponding increase or decrease in the flow rate passing through the hydraulic motor. The resulting change in hydraulic pressure in the supply line is fed back via the sensor line to the pressure control input of the hydraulic supply, which responds with a corresponding increase or decrease in the flow rate.

[0010] This results in the fan unit operating in a manner that is adapted to the actual cooling requirements and is therefore particularly efficient.

[0011] The cooling air flow generated by the fan unit passes, for example, through an intercooler, which serves to cool the charge air compressed by a turbocharger and supplied to a turbocharged diesel engine. The fan unit is designed as an axial or radial fan.

[0012] The sensor line intended for load reporting can contain a constant throttle element in the form of an orifice or nozzle, which limits hydraulic losses toward the pressure control input of the hydraulic supply to non-critical values. Depending on the specific design of the hydraulic system, however, the throttle element may also be omitted.

[0013] In principle, the operating device according to the invention is suitable for use in all commercial vehicles equipped with a hydraulic system for operating various vehicle- or work-related functions and that have a hydraulic supply for this purpose (e.g., formed by a hydraulic variable-displacement pump). This applies not only to agricultural tractors, but also to most other commercial vehicles in the agricultural and forestry sectors or the construction machinery sector. The need for a separate hydraulic pump is unnecessary under such circumstances.

[0014] Advantageous further developments of the operating device according to the invention emerge from the subclaims. The control valve is preferably a 2 / 2-way proportional valve. The 2 / 2-way proportional valve can be electrically or pressure-operated. Accordingly, based on the control signal, electrical valve actuation can be provided by means of a solenoid or stepper motor associated with the 2 / 2-way proportional valve, but also hydraulic valve actuation by applying a pilot pressure to a pressure control input of the 2 / 2-way proportional valve. The pilot pressure is generated by means of a pilot valve that can be electrically actuated as a function of the control signal and is located between the hydraulic supply and the pressure control input of the 2 / 2-way proportional valve.

[0015] Furthermore, it is possible for the control valve to be pressure-compensated. Due to pressure compensation, the control valve maintains the volume flow specified by the control signal, and thus the speed of the fan unit, largely constant even in the event of load fluctuations in the hydraulic motor and / or operational pressure fluctuations in the hydraulic supply.

[0016] In an example not according to the invention, a one-way or check valve permeable toward the pressure control input of the hydraulic supply can be arranged in the sensor line. This prevents undesirable speed fluctuations of the fan unit due to pressure feedback caused at the pressure control input of the hydraulic supply by superimposed load signals from other hydraulic consumers.

[0017] According to the invention, a pressure relief valve opening toward the pressure control input of the hydraulic supply is arranged in the sensor line. To prevent undesirable pressure feedback via the sensor line, the pressure relief valve behaves like a one-way or check valve, but additionally reduces the hydraulic pressure fed back to the pressure control input of the hydraulic supply by an amount corresponding to its respective switching threshold. This ultimately deceives the hydraulic supply into believing a reduced hydraulic load, which, with a suitable design of the hydraulic motor, allows for an additional improvement in energy efficiency without compromising the cooling capacity provided by the fan unit.

[0018] The hydraulic operating device according to the invention for a cooling fan of a commercial vehicle is described in more detail below with reference to the accompanying drawings. Identical reference numerals refer to identical or functionally comparable components. They show: Fig. 1 a schematically illustrated example of a hydraulic operating device not according to the invention, and Fig. 2 a schematically illustrated embodiment of the hydraulic operating device according to the invention.

[0019] Fig. 1 shows in a simplified representation a circuit diagram of a hydraulic operating device not according to the invention according to an example.

[0020] The hydraulic operating device 12 for a cooling fan 14 located in a commercial vehicle 10 comprises a hydraulic motor 16 and a fan unit 18 driven by the hydraulic motor 16 to generate a cooling air flow 20. For example, the fan unit 18 is designed as an axial fan 22; however, it can also be a radial fan. The axial fan 22 has a plurality of fan blades 26 projecting along an outer circumference of a fan hub 24, wherein the fan hub 24 is connected to an output 30 of the hydraulic motor 16 via a drive shaft 28. The fan unit 18 and the hydraulic motor 16, in combination, form the cooling fan 14.

[0021] The cooling air flow 20 generated by the fan unit 18 passes through a charge air cooler 32, which serves to cool charge air compressed by a turbocharger 34 and supplied to a supercharged diesel engine 36.

[0022] Furthermore, the operating device 12 comprises a hydraulic supply formed by a hydraulic variable-displacement pump 38 for providing pressurized hydraulic fluid. The hydraulic variable-displacement pump 38 draws this fluid from a reservoir 42.

[0023] The hydraulic variable displacement pump 38 is part of a (main) hydraulic system 40 of the commercial vehicle 10 and serves to operate various vehicle- and work-related functions. The commercial vehicle 10 is, for example, an agricultural tractor or any other commercial vehicle from the agricultural and forestry sectors or the construction machinery sector.

[0024] A control valve 44 serves to adjust a volume flow passing through the hydraulic motor 16 depending on a control signal representing a cooling requirement 46. The (here electrical) control signal is generated by a control unit 48, which serves to monitor a cooling requirement requested by the charge air cooler 32.

[0025] Furthermore, a sensor line 52 branched off in a supply line 50 between control valve 44 and hydraulic motor 16 leads to a pressure control input 54 of the hydraulic variable displacement pump 38, which serves for pressure feedback.

[0026] To adjust the speed of the hydraulic motor 16 and thus the cooling capacity of the fan unit 18, the control valve 44 is opened or closed depending on the control signal, which leads to a corresponding increase or decrease in the volume flow passing through the hydraulic motor 16. The change in hydraulic pressure occurring in the supply line 50 is fed back via the sensor line 52 to the pressure control input 54 of the hydraulic variable displacement pump 38, whereupon the pump responds with a corresponding increase or decrease in the delivery volume.

[0027] According to Fig. 1 In the sensor line 52 intended for load reporting, there is a throttle element 56 designed as a constant throttle in the form of an orifice or nozzle, which limits hydraulic losses in the direction of the pressure control input 54 of the hydraulic variable displacement pump 38 to non-critical values. Depending on the specific design of the hydraulic system 40, however, the throttle element 56 may also be omitted.

[0028] Furthermore, a one-way or check valve 58 is arranged in the sensor line 52, which is permeable in the direction of the pressure control input 54 of the hydraulic variable displacement pump 38. This valve is located within the sensor line 52 in series with the throttle element 56. The one-way or check valve 58 prevents undesirable speed fluctuations of the fan unit 18 due to pressure feedback caused at the pressure control input 54 of the hydraulic variable displacement pump 38 by superimposed load signals from other hydraulic consumers.

[0029] For example, the control valve 44 is a 2 / 2-way proportional valve 60 which can be electrically actuated by means of an associated solenoid 62 on the basis of the control signal generated by the control unit 48.

[0030] The control valve 44 is designed to be pressure-compensated. For this purpose, a pressure control valve 64 is located between the hydraulic variable displacement pump 38 and the 2 / 2-way proportional valve 60. This pressure control valve compares an output-side hydraulic pressure with an input-side hydraulic pressure at the 2 / 2-way proportional valve 60 and adjusts it to a fixed differential pressure. In this way, the 2 / 2-way proportional valve 60 maintains the volume flow specified by the control signal and thus the speed of the fan unit 18 largely constant, even in the event of load fluctuations of the hydraulic motor 16 and / or operational pressure fluctuations in the hydraulic supply. The pressure control valve 64, together with the 2 / 2-way proportional valve 60, can be a structural component of the control valve 44.

[0031] If the requirements for the constancy of the cooling capacity are lower, pressure compensation can be omitted, and the additional pressure control valve 64 is then omitted.

[0032] To achieve fail-safe operation, the 2 / 2-way proportional valve 60 is designed, for example, such that it automatically assumes a fully open position in the event of a fault in the control unit 48, thus maintaining the required cooling of the charge air cooler 32. However, it is also possible for the 2 / 2-way proportional valve 60 to be biased toward a closed position, so that in the event of a failure of the control unit 48, the operation of the hydraulic motor 16 is deliberately interrupted. A correspondingly designed 2 / 2-way proportional valve 60 is representatively shown in Fig. 2 reproduced.

[0033] Fig. 2 shows a simplified diagram of the hydraulic operating device according to the invention according to an exemplary embodiment. This differs from the previously mentioned design of the 2 / 2-way proportional valve 60 in Fig. 1The example shown further differs in that, instead of a one-way or check valve 58, a pressure relief valve 66 opening in the direction of the pressure control input 54 of the hydraulic variable displacement pump 38 is arranged in the sensor line 52. With regard to avoiding undesirable pressure feedback via the sensor line 52, the pressure relief valve 66 behaves like a one-way or check valve, but additionally reduces the hydraulic pressure fed back to the pressure control input 54 by an amount corresponding to its respective switching threshold. This ultimately deceives the hydraulic variable displacement pump 38 into thinking there is a reduced hydraulic load, which, with a suitable design of the hydraulic motor 16, allows an additional improvement in energy efficiency to be achieved without impairing the cooling capacity to be provided by the fan unit 18.

Claims

1. Hydraulic operating device for a cooling fan of a utility vehicle, comprising a hydraulic motor (16) and a fan assembly (18), which can be driven by the hydraulic motor (16), for generating a cooling air stream (20), comprising a hydraulic supply (38), which is adjustable in terms of its delivery volume in accordance with pressure feedback, for providing pressurized hydraulic liquid, and comprising a control valve (44) for setting, in a manner dependent on a control signal that represents a cooling demand (46), a volume flow that passes through the hydraulic motor (16), with a sensor line (52) that is branched off in a supply line (50) between control valve (44) and hydraulic motor (16) leading to a pressure control inlet (54) of the hydraulic supply (38), characterized in that, in the sensor line (52), there is arranged a pressure-limiting valve (66) which opens in the direction of the pressure control inlet (54) of the hydraulic supply (38).

2. Operating device according to Claim 1, characterized in that the control valve (44) is a 2 / 2 directional proportional valve (60).

3. Operating device according to Claim 1 or 2, characterized in that the control valve (44) is of pressure-compensated configuration.

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