Temperature detection method in a hydraulic arrangement

Abstract

Method for determining the temperature of a fluid in a hydraulic arrangement for a motor vehicle. The hydraulic arrangement has a pump arrangement, which is driven by means of a drive motor, and a pressure sensor, which is connected to a discharge port of the pump arrangement and is used to measure the pressure of the fluid. The pump arrangement is connected to a tank via a leakage point. The temperature of the fluid is determined on the basis of a relationship between a state variable of the drive motor and the temperature of the fluid at a predetermined pressure of the fluid, said relationship being specific to the hydraulic arrangement.

Claims

1. A method for assessing the determination of temperature in a hydraulic arrangement having variability, the hydraulic arrangement operating in conjunction with a motor vehicle drive train and the hydraulic arrangement operating a hydraulic load comprising an actuator involved with one of a friction clutch, brake system or continuously variable transmission arrangement, wherein the hydraulic arrangement comprises: an electric drive motor; a pump driven by the electric drive motor for pumping a fluid, the pump having an input port and a discharge port; a tank connected to the pump through the input port; a pressure sensor situated in a discharge line, the discharge line fluidly connecting the discharge port with the actuator; a leakage point connecting the discharge line with the tank; a control unit connected to the pressure sensor and electric drive motor, the control unit adjusting the rotational speed of the electric drive motor based on pressure feedback from the pressure sensor such that the actuator is actuated in a desired manner; wherein the control unit is further configured to control the electric drive motor by way of at least one characteristic curve or table stored in the control unit, the characteristic curve or table representing relationships between a state variable of the electric drive motor and the temperature of the fluid at predetermined pressures of the fluid; wherein the characteristic curve or table at least possesses one relationship between the state variable and temperature at a first predetermined pressure and an additional relationship between the state variable and temperature at a second predetermined pressure; wherein the method of assessing the determination of temperature in a hydraulic arrangement having variability comprises: determining relationships, specific to the hydraulic arrangement having variability, between the state variable of the electric motor and temperature, and checking or updating these relationships in the context of maintenance of the hydraulic arrangement.

2. Method according to claim 1, wherein a temperature determined from the at least one characteristic curve or table is used in the control unit to control the hydraulic arrangement.

3. Method according to claim 2, wherein the temperature determined is used to check the operation of a temperature sensor which measures the temperature of the fluid.

4. Method according to claim 1, wherein the state variable of the electric drive motor is the rotational speed thereof.

5. Method according to claim 1, wherein pressure of the fluid is regulated by adjusting the rotational speed of the electric drive motor.

6. Method according to claim 1, wherein the leakage point has an orifice plate, which is connected between the discharge port and the tank.

7. Method according to claim 1, wherein the leakage point comprises a leak in the hydraulic arrangement.

8. The method according to claim 1, wherein the method includes the step of: receiving, at the control unit, measured pressure of the fluid from the pressure sensor.

9. The method according to claim 1, wherein the leakage point is implemented by means of an orifice plate.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) Illustrative embodiments of the invention are shown in the drawing and are explained in greater detail in the description which follows. In the drawing:

(2) FIG. 1 shows a schematic illustration of a motor vehicle drive train having one embodiment of a hydraulic arrangement according to the invention;

(3) FIG. 2 shows two different relationships, specific to the hydraulic arrangement, between the rotational speed of a drive motor of a pump arrangement and the temperature of a fluid for a first predetermined pressure; and

(4) FIG. 3 shows an illustration corresponding to FIG. 2 for a second predetermined pressure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(5) A motor vehicle 10 having a drive train 11 is illustrated in schematic form in FIG. 1. The drive train 11 contains a vehicle motor 12, such as an internal combustion engine, a hybrid drive motor or the like. The drive train 11 furthermore has a friction clutch 14, the input of which is connected to the vehicle motor 12 and the output of which is connected to a transmission 16. An output of the transmission is connected to a differential 18, by means of which motive power is distributed between two driven wheels 20L, 20R.

(6) The drive train 11 furthermore has a hydraulic arrangement 24, which, in the present case, is used for automatic actuation of the friction clutch 14. However, a hydraulic arrangement 24 of this kind can also be used for other assemblies in the drive train, e.g. for brakes in converter-type automatic transmissions, for adjusting continuously variable transmissions or the like.

(7) In the case of dual-clutch transmissions, two such hydraulic arrangements are generally provided, one for each of the two friction clutches of the dual-clutch transmission.

(8) The hydraulic arrangement 24 has a pump 26, which, in the present case, is designed as a unidirectional pump. The pump 26 is driven by means of a drive motor 28 in the form of an electric motor. The corresponding driving rotational speed is indicated at n. As an option, it is also possible for the pump 26 to be designed as a bidirectional pump, this being indicated in FIG. 1 by a dashed-line symbol in the pump 26.

(9) An intake port of the pump 26 is connected to a tank 30, preferably via a fluid filter 32. The tank 30 is a region in which a fluid of the hydraulic arrangement is not under pressure. In the present case, the word “tank” is therefore any kind of reservoir or section of the hydraulic arrangement in which the fluid is present in substantially unpressurized form.

(10) A discharge port 34 of the pump 26 is connected to a hydraulic load 36. In the present case, the hydraulic load 36 contains an actuator 38 in the form of a single-acting piston/cylinder arrangement. The hydraulic actuator 38 has a single actuator port 40, which is connected directly to the discharge port 34, i.e. without the interposition of pressure control valves or other proportional valves. If appropriate, directional control valves can be present in the connection between the discharge port 34 and the actuator port 40.

(11) Also connected to the connecting line between the discharge port 34 and the actuator port 40 is a pressure sensor 42, which measures a pressure P of the fluid in said line. The discharge port 34 is furthermore connected to the tank 30 via an orifice plate 44.

(12) An optional temperature sensor, which measures the temperature T of the fluid, e.g. in the region of the tank 30, is indicated at 46.

(13) The drive train 11 furthermore has an electric or electronic control unit 50, which is connected to the pressure sensor 42. The control unit 50 is furthermore designed to control the drive motor 28, e.g. by means of a PWM signal. There can be a suitable power output element in the control unit, if required.

(14) As an option, the control unit 50 is furthermore connected to the optional temperature sensor 46.

(15) During operation, the friction clutch 14 is actuated by feed-back regulating the pressure P by adjusting the rotational speed n of the drive motor 28. As an alternative or in addition thereto, there can be a position sensor in the actuator 38 and/or in the friction clutch 14.

(16) The temperature T of the fluid furthermore plays a part in the regulation and/or other functions of the hydraulic arrangement.

(17) In the present case, at least one characteristic curve or table is stored in the control unit 50, representing the relationship between a state variable of the drive motor 28 and the temperature T of the fluid at a predetermined pressure P of the fluid (as indicated schematically at 52 in FIG. 1).

(18) If the predetermined pressure is determined by the pressure sensor 42, the temperature T of the fluid can be determined by accessing the characteristic curve or table 52. Consequently, the temperature sensor 42 is not absolutely essential for the operation of the control unit 50 and can therefore be dispensed with. As an alternative, the temperature sensor 42 can be provided, in which case the temperature determination function via the characteristic curve or via the table 52 in the control unit 50 can be used to check the operation of the temperature sensor 42, in particular for reasons of redundancy.

(19) The relationship between the state variable of the drive motor and the temperature is generally specific to each hydraulic arrangement owing to the various tolerances of the assemblies used in the hydraulic arrangement.

(20) The state variable can be an electric variable of the drive motor but is preferably the rotational speed n of the drive motor.

(21) Relationships of this kind are illustrated in FIGS. 2 and 3.

(22) FIG. 2 shows the relationship in the form of a characteristic curve 56 between the rotational speed n of the drive motor 28 and the temperature T of the fluid at a predetermined pressure P of 10 bar for a particular hydraulic arrangement 24, more specifically at 56. At 56′, this relationship is illustrated for a different hydraulic arrangement, in which the pump 26 has different axial play, for example.

(23) Characteristic curve 56 (or 56′) shows that the temperature T of the fluid is 90° C., for example, at a measured pressure P of 10 bar when it is necessary to operate the drive motor 28 at a rotational speed of 2600 revolutions in order to set this pressure of 10 bar. The temperature is furthermore 0° C., for example, when the drive motor has to be operated at a rotational speed of about 800 revolutions per minute in order to produce the pressure of 10 bar.

(24) In the other hydraulic arrangement, which is associated with characteristic curve 56′, the drive motor 28 is driven at a rotational speed of about 1800 revolutions per minute, for example, in order to achieve the pressure of 10 bar at a temperature of 90° C.

(25) The characteristic curves can be determined when commissioning the hydraulic arrangement of the drive train. As an alternative or in addition thereto, these characteristic curves 56, 56′ can be determined or updated during maintenance of the drive train and/or of the hydraulic arrangement 24.

(26) In general, it is possible to carry out the temperature determination function of the type described above by means of a characteristic curve 56 of this kind whenever the predetermined pressure is present.

(27) As an alternative, it is possible to store a plurality of such characteristic curves for a hydraulic arrangement, e.g. for different pressures. This is shown in FIG. 3.

(28) The hydraulic arrangement with which the characteristic curve 56 in FIG. 2 is associated has a characteristic curve 58 at a pressure of P=5 bar, where the temperature is 90° C., for example, when the drive motor is driven at about 1600 revolutions/minute. The other hydraulic arrangement has a characteristic curve 58′ for the same pressure of P=5 bar where the drive motor 28 is driven at a rotational speed of about 1200 revolutions/minute, for example, when the temperature T=90° C.