JP2019011045A - Method for calculating viscosity of pressure medium in pressure medium circuit - Google Patents

Abstract

To provide a method for calculating viscosity of a pressure medium in a pressure medium circuit.SOLUTION: A brake circuit of an electronic slip-controllable vehicle brake device includes a pressure supply device that can be loaded via an operation mechanism, a sensor providing an operation signal indicating operation of the operation mechanism, a pressure sensor providing a pressure signal indicating a dominant pressure in the pressure supplier, and an electronic control unit, and further processes the signal in the electronic control unit. The electronic control unit records the operation signal and the pressure signal so as to be time-synchronized with each other, calculates a quotient from the value, and determines viscosity corresponding to a pressure medium by the recorded characteristic curve. An electronic controllable actuator is controlled depending on the calculated value.SELECTED DRAWING: Figure 2

Description

  The invention relates to a method for calculating the viscosity of a pressure medium in a pressure medium circuit according to the features of the superordinate conceptual part of claim 1.

  Regenerative braking systems based on the standard ESP brake system are on the market to enable regenerative braking with as little change as possible in the hydraulic layout of existing brake systems. Patent Document 1 discloses such a brake system. In this case, in the regenerative braking operation, the brake fluid volume pushed by the driver from the master brake cylinder into the hydraulic device is not used to increase the brake pressure in the wheel brake, but instead of the hydraulic device. Moved into the pressure medium reservoir by appropriate control of the valve.

  After the brake operation is finished, the pressure medium reservoir is discharged. This draining is done passively at the low viscosity of the pressure medium, i.e. by overflow of a given valve of the hydraulic device without using a feed pump, or active when the pressure medium is highly viscous, That is, using a feed pump, an alternative flow path takes place. In a retrofit manner, the discharge gradient, ie the amount of pressure medium that can be discharged per time unit, is highly dependent on the temperature or viscosity of the pressure medium and the flow resistance in the flow path.

  High viscosity values can lead to a long extension to the inconvenience of the discharge time. However, the regenerative braking operation cannot be performed while the pressure medium reservoir is being discharged. Furthermore, the regenerative capacity of the brake device is also impaired if the pressure medium reservoir cannot be completely emptied. Eventually, either action adversely affects the energy efficiency of the vehicle drive. Accordingly, there is a need for as quick and complete discharge of the pressure medium reservoir as possible.

  To shorten the drain time, a feed pump may be used as described above. Of course, the operating time of the feed pump affects the wear characteristics of the feed pump and must be considered in the structural design of the feed pump. This increases the construction costs and costs for the feed pump.

  To avoid unnecessary control of the feed pump or excessively long operating times and to ensure complete discharge of the pressure medium reservoir, the pressure medium viscosity and the pressure medium reservoir fill level are as accurate as possible. Need to know. A reliable estimate of the filling level again depends on the viscosity of the pressure medium. This is because this filling level is not measured, for example, but is indirectly estimated from the existing measurement data of the filling level, such as the valve opening time and the pressure applied to the master brake cylinder.

  Conventionally, a direct measurement of the temperature of the brake fluid is not performed, but a relatively inaccurate estimate of the temperature or viscosity of the pressure medium is performed based on an existing electrical resistance measurement in the brake system. Moreover, the moisture of the pressure medium and the type of pressure medium used adversely affects the accuracy of this estimate, so that the feed pump is eventually controlled unnecessarily frequently and driven unnecessarily long. Both also affect the structural design and thus the cost of this feed pump.

German Patent Application Publication No. 19604134

  In contrast, the method according to the invention for calculating the viscosity of the pressure medium in the pressure medium circuit according to the features of claim 1 allows a more accurate estimation of the filling level of the pressure medium reservoir, Accordingly, there is an advantage that the operation request or operation time of the feed pump for completely emptying the pressure medium reservoir can be determined more accurately. Furthermore, the adapted pump operation allows the regenerative capacity of the brake device to be utilized over a wider operating range, thereby increasing the energy efficiency of the vehicle drive. In addition, the overall shortened operating time of the feed pump allows a cheaper structural design of the feed pump.

  Other advantages or preferred developments of the method according to the invention are evident from the dependent claims and the following description.

  According to claim 2, the output signal is generated or suppressed depending on the limit value for the viscosity of the electronic control unit stored in the electronic control unit. This limit value is appropriately determined depending on, for example, various fluid resistances of various hydraulic devices.

  Apart from suitable control of the discharge of the pressure medium reservoir using a feed pump (claims 3 and 4), the control signal may take into account many other brake control functions by means of an electronic control unit. In this connection, if an emergency stop is imminent, for example, the wheel brake must be instructed to be preloaded. This filling may also be performed by operating the feed pump.

  Basically, as accurate information as possible about the viscosity of the pressure medium is important for all brake operations where high pressure generation dynamics are important. The brake pressure control in the wheel brake can also be carried out more accurately by knowing the viscosity of the pressure medium, for example, the control time and the necessary current supply to the switching valve and the regulating valve can be adjusted accordingly.

1 is a hydraulic circuit diagram of a brake device known from the prior art, which forms the basis of the present invention. 4 is a flow chart specifically illustrating a sequence of method steps of the method according to the invention.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a hydraulic circuit diagram known per se for an electronic slip-controllable brake device 10 of a motor vehicle. The brake device 10 has a master brake cylinder 14 which can be operated indirectly by the driver, preferably via an operating mechanism 12 in the form of a brake pedal. A brake booster 16 is disposed between the operation mechanism 12 and the master brake cylinder 14, and this brake booster 16 amplifies the braking force applied to the operation mechanism 12. The master brake cylinder 14 serves to detect a driver's braking request and supplies brake pressure to a brake circuit 18; 20 connected to the master brake cylinder 14. Therefore, the master brake cylinder 14 may be regarded as a pressure supply device that can be loaded from the outside. The master brake cylinder 14 is connected with a hydraulic device 22 that controls the open or closed loop of the brake pressure. The brake pressure loads a wheel brake 24 of the brake device 10 that is connected to the hydraulic device 22. The

  The closed-loop control of the brake pressure in the wheel brake 24 by the hydraulic device 22 is performed depending on the slip ratio prevailing at the wheel of the vehicle arranged corresponding to the wheel brake 24. This is detected using the difference in rotation speed between the wheels of the vehicle. Wheel rotation speed sensors 28 arranged corresponding to the wheels detect the respective rotation speeds and supply this measurement data to the electronic control unit 30 for evaluation in particular.

  The master brake cylinder 14 is configured in a typical two-line system, and therefore supplies a pressure medium under brake pressure to two brake circuits 18; 20 that are separate from each other. Each brake circuit 18; 20 is equipped with two of the four wheel brakes 24 in total in the brake device 10. Furthermore, each brake circuit 18; 20 has a feed pump 34 or a feed pump unit that can be driven by an electric motor 32. Furthermore, a pressure increasing valve 36 is connected to the front side of each wheel brake 24 of the brake circuit 18; 20 in terms of fluid technology, and a pressure reducing valve 38 is connected to the rear side in terms of fluid technology. The pressure increasing valve 36 controls the flow of pressure medium from the master brake cylinder 14 into the respective wheel brake 24 in a general manner, thereby determining the brake pressure rise, whereas the pressure reducing valve 36 is used for the wheel brake. The pressure medium outflow from 24 to the return line 40 is controlled, thereby determining brake pressure drop. A common pressure medium reservoir 42 is connected downstream of each of the plurality of pressure reducing valves 38 of the brake circuit 18; 20, and the pressure medium reservoir 42 has a feed pump 34 in which the pressure medium flowing out is disposed. This outflowing pressure medium is first buffered before it is sucked in again and returned into the respective brake circuit 18; 20. The switching valve 44 in each brake circuit 18; 20 controls the pressure medium connection between the master brake cylinder 14 and the wheel brake 24, and as a result, a brake pressure source (master brake cylinder 14 according to the operation mode of the brake device 10). Alternatively, the feed pump 34) is determined. The switching valve 44 is arranged directly downstream of the master brake cylinder 14 and upstream of the point where the pressure medium pumped by the feed pump 34 joins the brake circuit 18; 20 again. Further, a so-called suction valve 46 is provided, and the suction valve 46 is disposed in a pressure medium connection portion that connects the suction side of the feed pump 34 to the master brake cylinder 14. Via this pressure medium connection, the feed pump 34 adjusts the required brake pressure in the brake circuit 18; 20, for example, in which the pressure medium volume present in the pressure medium reservoir 42 is correspondingly adjusted by the feed pump 34. Therefore, when it is insufficient, the pressure medium can be supplied from the master brake cylinder 14 as necessary.

  The valves 36; 38; 44; 46 are configured as electronically controllable valves, in particular as electromagnetic valves. These valves can move from the basic position to the operating position. The pressure increasing valve 36 is open at the basic position and is shut off at the operating position, while the pressure reducing valve 38 is shut off at the basic position and can flow through at the operating position. The electronic control unit 30 includes various sensors 48 that indicate the movement of the operating mechanism 12, the pressure in one of the brake circuits 18; 20 directly downstream of the master brake cylinder 14 or the brake pressure in the wheel brake 24 of the brake circuit 18; 20. 50; 52 signals are detected, and these sensor signals, together with the signal of the wheel speed sensor 28, for the control signals that can be generated by the valves 36; 38; 44; 46, and the feed pump 34; Evaluate for possible control signals of the motor 32 to operate. In this case, the sensor that detects the movement of the operation mechanism 12 can evaluate the stroke of the operation mechanism 12, the acceleration of the operation mechanism 12, or the operation speed of the operation mechanism 12 and replace it with a corresponding operation signal.

  As already described at the beginning, the brake device 10 configured as described above is mounted on a vehicle that can convert the kinetic energy of the vehicle into electric energy during a brake operation (regenerative brake device). In this case, the adjusted vehicle deceleration no longer has to be provided by the brake system, only a correspondingly small hydraulic brake pressure is required to obtain the vehicle deceleration required by the driver. is there. However, the driver sets the braking request by operating the brake pedal and pushing the pressure medium correspondingly from the master brake cylinder 14 into the hydraulic device 22 as before. By correspondingly electronically controlling the elements, the hydraulic brake pressure increase in the wheel brake 24 must be suppressed or prevented at all. This is further sent to the pressure medium reservoir 42 through the pressure increasing valve 36 where the pressure medium displaced by the driver is released into the wheel brake 24 and through the pressure reducing valve 38 which is also released from the wheel brake 24. Is done. Corresponding control of the booster valve 36 and the pressure reducing valve 38 is performed by the electronic control unit 30 during regenerative braking operation, and therefore the pressure between the master brake cylinder 14 and the pressure medium reservoir 42 that is otherwise shut off. A media connection is formed. As a result, the pressure medium pushed away from the master brake cylinder 14 does not contribute at all to increase the brake pressure in the wheel brake 24 of each brake circuit 18; is there.

  After each operation of the regenerative brake, it is necessary to empty the pressure medium reservoir 42 in order to restore the complete regenerative function of the brake device 10 for future brake operations. The evacuation of the contents may be performed utilizing the feed pump 34 if the pressure medium viscosity and / or the filling level of the pressure medium reservoir 42 is too high to effect evacuation within the desired maximum time interval. . In the case of active discharge, the electronic control unit 30 determines the required operating time of the feed pump 34 until the pressure medium reservoir 42 is completely emptied.

  According to the method of the present invention, the viscosity of the pressure medium is determined from the operation signal of the sensor that detects the operation of the brake pedal 12 and the pressure signal of the pressure sensor 50 that detects the brake pressure of the brake circuit. If the determined viscosity exceeds the limit value stored in the electronic control unit 30, an active drainage of the pressure medium reservoir 42 is carried out, otherwise the drainage is in a passive manner, i.e. the feed pump 34. Done without involvement.

  As shown in FIG. 2, the method according to the invention consists in that the operating signal B and the pressure signal D are first recorded in time synchronization by the electronic control unit 30 in a first step S1. Next, in step S2, the electronic control unit determines the quotient Q from the pair of values. Next, in step S3, the dominant viscosity V is determined using the characteristic curve K stored in the electronic control unit 30 and describing the viscosity of the pressure medium depending on the quotient Q. The characteristic curve K is calculated in advance by a series of experiments with a corresponding hydraulic device 22 empirically and stored in the electronic control unit 30 in digital form.

  Further, a limit value G for the viscosity V is stored in the electronic control unit 30. When the limit value G is exceeded, the contents of the pressure medium reservoir 42 are discharged using the feed pump 34 in order to maintain the critical discharge continuation. Accordingly, the calculated viscosity V is compared with the limit value G in step S4 by the electronic control unit 30, and the determined viscosity V of the pressure medium is higher than the stored limit value G in step S5. Or when it is greater, a control signal A is output to the motor 32 to drive the feed pump 34. In the opposite case, that is, below the limit value G, the supply of the control signal A to the electric motor 32 is suppressed, and the discharge of the contents of the pressure medium reservoir 42 is performed passively.

  For passive discharge, the pressure medium reservoir 42 is provided with a return member, for example a return spring, which causes the spring to push, for example, a reservoir piston that pushes the pressure medium out of the pressure medium reservoir 42. To load. The discharge is performed along the discharge path via the pressure reducing valve 38 controlled to the open position by the electronic control unit 30, that is, flows through the wheel brake 24 and is opened at any basic position. The suction valve 36 and the switching valve 44 that can be passed through are likewise guided back into the master brake cylinder 14 or into the pressure medium reserve tank 54 connected to the master brake cylinder 14.

  Of course, modifications or supplements to the above embodiments are possible without departing from the basic idea of the invention. In this context it is pointed out that the method is preferably used only to empty the pressure medium reservoir 42 based on a regenerative braking operation. Knowledge of the viscosity of the pressure medium is taken into account by the electronic control unit 30, for example for adjusting the brake pressure or for controlling the highly dynamic brake operation.

DESCRIPTION OF SYMBOLS 10 Brake device 12 Operation mechanism 14 Pressure supply device, master brake cylinder 18, 20 Pressure medium circuit, brake circuit 30 Electronic control unit 34 Feed pump or feed pump unit 42 Pressure medium reservoir 48 Sensor 50 Pressure sensor A Output signal B Operation signal D pressure signal G limit value K characteristic curve Q quotient V viscosity

Claims (7)

A method for calculating the viscosity (V) of a pressure medium of a pressure medium circuit (18; 20), in particular a brake circuit of an electronic slip-controllable brake device (10) of an automobile,
The pressure medium circuit (18; 20) comprises a pressure supply (14) which can be loaded via an operating mechanism (12);
A sensor (48) that provides an operation signal (B) indicating an operation stroke, an operation speed or an acceleration of the operation mechanism when the operation mechanism (12) is operated;
A pressure sensor (50) that, in operation, provides a pressure signal (D) representative of the prevailing pressure at the pressure supply (14);
In a method comprising an electronic control unit (30), wherein the operating signal (B) and the pressure signal (D) are supplied to the electronic control unit (30) for further processing,
The electronic control unit (30) records the operation signal (B) and the pressure signal (D) in time synchronization with each other,
Calculate the quotient (Q) from a pair of values,
The viscosity (V) of the pressure medium is determined using at least one characteristic curve (K) stored in the electronic control unit (30) representing the viscosity (V) depending on the quotient (Q). To
A method for calculating the viscosity (V) of a pressure medium in a pressure medium circuit. Comparing the calculated viscosity (V) of the pressure medium with a limit value (G) for viscosity stored in the electronic control unit (30);
Method according to claim 1, characterized in that an output signal (A) is output from the electronic control unit (30) when the limit value (G) is exceeded.   3. The output signal (A) controls an electronically controllable actuator, in particular a motor-driven feed pump (34) of the pressure medium circuit (18; 20). the method of.   By controlling the electronically driveable feed pump (34), the pressure medium reservoir (42) of the pressure medium circuit (18; 20) filled with pressure medium is emptied, The method of claim 3.   The quotient (Q) comprising the operating signal (B) and the pressure signal (D) of the electronic control unit (30) is used to determine a possible filling amount of the pressure medium reservoir (42); The method according to claim 1, characterized in that it is characterized in that   The pressure medium reservoir (42) is emptied from the fixed discharge amount per time unit of the feed pump (34), the possible filling amount of the pressure medium reservoir (42), and the quotient (Q). The operation time of the feed pump (34) required for the calculation is calculated, and control of the feed pump (34) that can be driven electronically is interrupted after the calculated operation time has elapsed. Item 6. The method according to Item 5.   7. The method according to claim 1, wherein the method is used for controlling a brake operation in a regenerative braking device of a motor vehicle.

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