Method for operating a pneumatic positioning system of a transmission and control unit for carrying out the method

Abstract

Method for operating a pneumatic actuating system (1) of a transmission, wherein the actuating system (1) has an air reservoir (5) in which a first pressure prevails, wherein the air reservoir (5) is coupled to an actuator chamber (6) of the actuating system (1) in which a second pressure prevails, and wherein the actuator chamber (6) is coupled to switching cylinders (2, 3) via switching valves (7, 8, 9, 10), wherein, when a shift is performed in the transmission, an air mass supplied to the active switching cylinders (2, 3) via the corresponding switching valves (7, 8, 9, 10) and an air mass sum from a target air mass required to perform the shift in the active switching cylinders (2, 3) and a current base leakage of the activated switching cylinders (2, 3) are determined, wherein a fault leakage in the pneumatic actuating system (1) is then inferred if the air mass supplied to the active switching cylinders (2, 3) The supplied air mass is greater than the total air mass, characterized by:that the mass of air supplied to the active switching cylinders (2, 3) via the switching valves (7, 8, 9, 10) is determined as a function of the mass flow rate through the active switching valves (7, 8, 9, 10), wherein the mass flow rate through an active switching valve (7, 8, 9, 10) is determined as a function of the pressure prevailing in the actuator chamber (6) and as a function of a maximum mass flow rate through the respective switching valve (7, 8, 9, 10).

Description

[0001] The invention relates to a method for operating a pneumatic actuating system of a transmission. Furthermore, the invention relates to a control unit configured for carrying out the method and a corresponding computer program.

[0002] It is common practice to actuate the switching elements of a transmission, such as the shift cylinders, using a pneumatic actuator system. Such a system has an air reservoir connected to the actuator chamber via at least one primary switching valve. From this chamber, each shift cylinder can be supplied with air via at least one secondary switching valve. Leakage in the actuator system or the transmission can prevent the shift cylinders from functioning correctly, potentially making it impossible to reliably shift gears. This can, in some cases, lead to a complete standstill of the vehicle containing the transmission.It is therefore important to reliably detect any fault leakage that may occur in a pneumatic actuation system of a transmission in order to initiate a replacement reaction if necessary, such as a modified shifting sequence, in order to maintain the operational readiness of the vehicle.

[0003] From DE 10 2011 075 168 A1 a method for detecting a leak in an actuating device of a pressure-medium actuated clutch is known, wherein according to this prior art the actuating travel of a piston of the actuating cylinder is determined over time with the clutch open and the valves closed, and the degree of leakage of the actuating cylinder over time is determined from this.

[0004] DE 10 2015 210 668 A1 discloses a method for detecting a fault leakage in a pneumatic actuating system of a gearbox and a control unit for carrying out the method.

[0005] Based on this, the present invention aims to provide a novel method for operating a pneumatic actuating system of a transmission. In particular, a novel method for detecting a fault leak in the pneumatic actuating system of the transmission and a method for reacting to a fault leak detected in such a system are to be proposed. Furthermore, a corresponding control unit and a computer program for carrying out the methods are to be specified.

[0006] From a process engineering perspective, this problem is solved starting from the preamble of claim 1 or from the preamble of claim 5 in conjunction with its characterizing features. A control unit is also the subject of the further independent claim 8. Advantageous embodiments are the subject of the dependent claims and the following description.

[0007] According to a first embodiment of the invention, a method for operating a pneumatic actuating system of a transmission is proposed, in which the pneumatic actuating system has an air reservoir in which a first pressure prevails. The air reservoir is coupled to an actuator chamber of the pneumatic actuating system in which a second pressure prevails. The actuator chamber of the pneumatic actuating system is coupled to switching cylinders of the transmission via switching valves.

[0008] It is intended that when a shift is performed in the transmission, an air mass supplied to the active shift cylinders via the corresponding shift valves and an air mass sum are determined from a target air mass required to perform the shift in the active shift cylinders and a current basic leakage of the activated shift cylinders, whereby a fault leakage in the pneumatic actuating system is then inferred if the air mass supplied to the active shift cylinders is greater than the air mass sum.

[0009] The first embodiment of the invention presented here proposes a method for balancing the air mass consumed in the active switching cylinders during a switching operation. In the event of a fault leak indicating a malfunction, the air mass supplied to the active switching cylinder via the corresponding switching valves is significantly higher than the total air mass, which depends on the air mass in the active switching cylinder and the air mass of any underlying leakage from the active switching cylinders that occurs even when the actuator system is functioning correctly. Such a balancing method allows for the simple and reliable detection of a fault leak in the actuator system.

[0010] According to a further advantageous development, a fault leak in the pneumatic actuating system can be inferred if, during the execution of a shift in the transmission, the air mass supplied to the shift cylinder is greater than the total air mass for a defined period. This allows for a particularly advantageous conclusion to be drawn about a fault leak in the pneumatic actuating system.

[0011] The air mass supplied to the active switching cylinders via the switching valves is determined based on the mass flow rate across the active switching valves. This mass flow rate is determined based on the pressure prevailing in the actuator chamber and a maximum mass flow rate across the respective switching valve. This method of determining the air mass supplied to the switching cylinders via the switching valves is simple and reliable.

[0012] Preferably, the target air mass in the active switching cylinders for the total air mass is determined based on the piston area and switching travel of each active switching cylinder. This allows for a simple and reliable determination of the air mass in the switching cylinders for the total air mass.

[0013] The current baseline leakage of each active switching cylinder for the total air mass is preferably determined based on a previous baseline leakage of the respective active switching cylinder. This allows the natural baseline leakage of the active switching cylinders, which also occurs in the case of a non-faulty leakage of the pneumatic actuating system, to be determined simply and reliably.

[0014] According to a second embodiment of the invention, a method for operating a pneumatic actuating system of a transmission is proposed, in which the pneumatic actuating system has an air reservoir in which a first pressure prevails. The air reservoir is coupled to an actuator chamber of the pneumatic actuating system in which a second pressure prevails. The actuator chamber of the pneumatic actuating system is coupled to switching cylinders of the transmission via switching valves.

[0015] It is designed that, in the event of a detected leak in the pneumatic actuator system, the switching valves of the pneumatic actuator system, which are connected to the actuator chamber of the pneumatic actuator system and the switching cylinders of the transmission, are deactivated for a configurable period of time. This prevents air from flowing uncontrollably from the actuator chamber of the pneumatic actuator system in the event of a detected leak.

[0016] With the switching valves of the pneumatic actuator system deactivated, air is introduced into the system by a pump or air compressor. This air mass rebuilds pressure in the actuator chamber of the pneumatic actuator system, as the deactivated switching valves interrupt the connection between the actuator chamber and the transmission's switching cylinders.

[0017] After the parameterizable shutdown time has elapsed, the switching valves required for the execution of a switching operation in the gearbox are finally activated, thereby pressurizing the gearbox's switching cylinders assigned to the switching valves.

[0018] Thus, the method according to the invention proposes a substitute reaction in the event of a detected fault leak in the pneumatic actuating system, by means of which a gear in the transmission can be reliably shifted even in the event of a detected fault leak. The shutdown time of the switching valves in the event of a detected fault leak can, for example, be between 400 and 600 milliseconds.

[0019] Furthermore, claim 8 specifies a control unit for operating a pneumatic actuator system of a motor vehicle, which is adapted to carry out the method according to the invention. The control unit can, for example, be designed as a transmission control unit.

[0020] The solution according to the invention can also be embodied as a computer program product which, when running on a processor of a control device, instructs the processor by means of software to carry out the associated process steps relating to the invention. In this context, a computer-readable medium on which a computer program product described above is stored and retrievable is also part of the subject matter of the invention.

[0021] The invention is not limited to the specified combination of features of the dependent or suffixed claims. Furthermore, it is possible to combine individual features, even those apparent from the claims, the subsequent description of embodiments, or directly from the drawings. References in the claims to the drawings by means of reference numerals are not intended to limit the scope of protection of the claims.

[0022] To illustrate the invention, a drawing with exemplary embodiments is attached to the description. This drawing shows: Fig. 1. A block diagram of a pneumatic actuating system of a gearbox; and Fig. 2. A diagram illustrating details of the procedure for operating the pneumatic positioning system.

[0023] The invention relates to a method for detecting excessive or faulty leakage in a pneumatic actuating system of a transmission, which can lead to improper gear changes in the transmission. Such leakage is referred to as fault leakage. Furthermore, the invention relates to a method by which, upon detection of fault leakage in the pneumatic actuating system, a substitute reaction is executed by means of which a gear in the transmission can be reliably engaged even with a detected fault leakage. The invention further relates to a control unit for carrying out the method.

[0024] Fig. Figure 1 shows, by way of example, the basic structure of a pneumatic positioning system 1 for a gearbox, namely in Fig. 1 for a group transmission, wherein at least one pneumatically actuated switching cylinder 2, 3 is installed in each transmission section of the group transmission. In the case of the Fig. The switching cylinder 2 shown in Figure 1 is a pneumatically actuated switching cylinder of a pre-selector group of the transmission, which can be actuated via two switching valves 7 and 8. The switching cylinder 3 is a pneumatically actuated switching cylinder of a main transmission of the transmission, which can be actuated via four switching valves 9, 10, 11, and 12. A position sensor 14 is assigned to switching cylinder 2, which controls the pre-selector group, and with the aid of this sensor, the positions of an actuating piston 16 of switching cylinder 2 can be measured. A position sensor 13 is assigned to switching cylinder 3, which controls the main transmission, and with the aid of this sensor, the positions of an actuating piston 15 of switching cylinder 3 can be measured.

[0025] The pneumatic positioning system 1 of the Fig. The pneumatic actuator 1 comprises an air reservoir 5. A first pressure, namely pressure p1, prevails in the air reservoir 5. Furthermore, the pneumatic actuator 1 includes a so-called actuator chamber 6, in which a second pressure, namely pressure p2, prevails. The actuator chamber 6 is coupled to the air reservoir 5 via a pressure reducing valve 4. The pressure reducing valve 4 reduces the pressure p1 of the air reservoir 5 to an adjustable, constant pressure p2.

[0026] The switching cylinders 2, 3 can be supplied with compressed air from the actuator chamber 6, with each switching cylinder 2, 3 being coupled to the actuator chamber 6 via switching valves 7, 8, 9, 10. In the exemplary embodiment of the Fig. 1 Each of the switching cylinders 2, 3 is coupled to the actuator room 6 via two switching valves 7, 8 or 9, 10.

[0027] For example, in the Fig. To reliably detect a fault leak in the exemplary pneumatic actuating system 1 of a transmission shown in Figure 1, the following procedure is used when a shift is performed in the transmission, in which one or both shift cylinders 2, 3 of the transmission are supplied with compressed air and in which one or more shift valves 7, 8, 9, 10 are active: the mass of air supplied to the active shift cylinders 2, 3 via the corresponding shift valves 7, 8, 9, 10 is determined. Furthermore, a total air mass is calculated from the target air mass required to perform the shift in the active shift cylinders 2, 3 and the current baseline leakage of the active shift cylinders 2, 3. The baseline leakage is also referred to as natural leakage and always occurs during the operation of the pneumatic actuating system 1.Then, if the air mass supplied to the active switching cylinders 2, 3 is greater than the air mass sum, a fault leak in the pneumatic actuating system 1 is concluded, namely when, during the execution of a shift in the transmission, the air mass supplied to the switching cylinders 2, 3 is greater than the air mass sum for a defined period of time.

[0028] According to the invention, the air mass consumed in the pneumatic actuating system 1 during a switching operation is balanced. In the event of a fault leak, the air mass supplied to the active switching cylinder 2, 3 via the corresponding switching valves 7, 8, 9, 10 is significantly higher than the total air mass, which depends on the air mass in the active switching cylinders 2, 3 and the air mass due to any current baseline leakage of the active switching cylinders 2, 3. If the difference between the air mass flowing through the switching valves 7, 8, 9, 10 into an active switching cylinder 2, 3 and the total air mass consisting of the target air mass in the active switching cylinders 2, 3 during an active switching operation and the air mass due to the natural leakage of the active switching cylinders 2, 3 is greater than a defined limit, a fault leak of an active switching cylinder 2, 3 is detected.Leakage detection is performed separately for each of the switching cylinders 2 and 3.

[0029] Assuming that all gear changes are performed at a supercritical pressure ratio, the mass of air supplied to the active shift cylinder via an active shift valve 7, 8, 9, 10 is calculated according to the following equations: mist=∫m˙ist⋅dt m˙ist=ψMAX ψMAX=C∗p2∗ρ∗(T0T) C=k∗αD∗Q∗ψMAX∗(2∗RS∗T0)p0 where m ist the mass of air supplied to the active switching cylinder via the respective active switching valve 7, 8, 9, 10, where m ist the mass flow through the respective active switching valve 7, 8, 9, 10, where p2 is the pressure prevailing in the actuator chamber 6, where ψ MAXthe maximum mass flow through the respective active switching valve 7, 8, 9, 10, where C is a pneumatic conductance of the respective active switching valve 7, 8, 9, 10, where ρ is the air density, where T0 is the absolute air temperature under standard conditions, where T is the current air temperature, where no adaptation factor of the respective active switching valve 7, 8, 9, 10 is given, where α D a pneumatic correction factor of the respective active switching valve 7, 8, 9, 10, where R S is the specific gas constant of air, where p0 is the air pressure of the air under standard conditions and where Q is the valve cross-section of the respective active switching valve 7, 8, 9, 10.

[0030] According to the formulas above, the air mass flowing from the actuator chamber 6 through the respective active switching valve 7, 8, 9, 10 into the switching cylinder 2, 3 is therefore obtained by integrating the mass flow through the respective active switching valve 7, 8, 9, 10.

[0031] When determining the air mass supplied to the active actuator cylinder 2, 3 via the respective active switching valve 7, 8, 9, 10, according to Fig. 2. A distinction is made between the control of the switching valve 7, 8, 9, 10 in a supercritical region 18 with a constant mass flow rate and the control of the switching valve 7, 8, 9, 10 in a subcritical region 19 with a non-constant mass flow rate. As shown by the curve 17 of the Fig. The mass flow rate through the switching valves 7, 8, 9, 10 in the subcritical region 19, which can be determined from the diagram, is approximated by an ellipse. Assuming that all gear changes are performed at a supercritical pressure ratio, a constant mass flow rate through the switching valves 7, 8, 9, 10 results. This constant mass flow rate is also the maximum mass flow rate 15 through the switching valves 7, 8, 9, 10.

[0032] The target air mass required for a successful execution of a shift in the transmission in the respective active shift cylinder 2,3 is determined depending on a piston area of ​​the respective active shift cylinder 2, 3 and depending on shift paths of the respective active shift cylinder 2, 3.

[0033] The target air mass of the respective active switching cylinder 2, 3 for the air mass sum is preferably calculated according to the following equation: mSetpoint=ρ∗VSetpoint VSolt=V1+V2 V1=A1∗(x−lMIN) V2=A2∗(lMAX−x) where m Soll is the current target air mass of the active switching cylinder, where V Sollthe current target volume of the active switching cylinder, where ρ is the air density, where V1 is the active volume in the first actuation direction of the actuating piston, where V2 is the active volume in the second actuation direction of the actuating piston, where A1 is the active piston area in the first actuation direction of the actuating piston, where A2 is the active piston area in the second actuation direction of the actuating piston, where x is the current piston position, where I max the maximum switching range is and where I min the minimum shift distance.

[0034] For example, the first actuation direction of the actuator piston can be understood as actuating the actuator piston in a direction towards increasing position values. The second actuation direction of the actuator piston is opposite to the first actuation direction and thus corresponds to actuating the actuator piston in a direction towards decreasing position values.

[0035] Thus, the target air mass m can be calculated from the active volume in the first actuation direction V1 and the active volume in the second actuation direction V2. soll The area is calculated in the shift cylinder during an active shift. In the main transmission, a distinction is made between shifts to and from neutral, as the active piston areas differ in these cases.

[0036] The above volumes V1, V2 can also be additively superimposed with a dead volume of the switching cylinders.

[0037] The current basic leakage of the respective active switching cylinder 2, 3 for the air mass sum is preferably calculated according to the following equation: mL(k)=mL(k−1)+VSollRS∗T∗p˙∗tS where m L(k) the current base leakage of the respective active switching cylinder, where m L(k-1) the preceding base leakage of the respective active switching cylinder, where V Sollthe current target volume of the active switching cylinder, where Rs is the specific gas constant of air, where T is the current air temperature, where ṗ is the rate of change of air pressure, and where t S a sampling rate. The equation above applies under the assumption that the volume V Soll and the rate of change of air pressure ṗ is constant.

[0038] For each switching cylinder that is active during the circuit execution, the air mass m ist and the base leakage was determined separately using the formulas above.

[0039] As already explained, a fault leakage of the pneumatic actuating system 1 is detected when, over a defined time during the execution of a shift in the transmission, the air mass m supplied to the active shift cylinder 2, 3 via the corresponding shift valves 7, 8, 9, 10 ist greater than the sum of the air masses from the target air mass required to carry out the circuit. sollin the active switching cylinder 2, 3 and the current basic leakage m Leak of the activated switching cylinder 2, 3 is: mActual > mTarget + mLeak.

[0040] If a fault leak is detected in the actuator system 1, countermeasures can be initiated to enable the transmission to operate in a defined manner. According to the present invention, if a fault leak is detected in the pneumatic actuator system 1, the switching valves 7, 8, 9, 10 of the pneumatic actuator system 1, which are connected to the actuator chamber 6 and the switching cylinders 2, 3, are deactivated for a configurable period of time. This prevents air from flowing uncontrollably from the actuator chamber 6 of the pneumatic actuator system 1 in the event of a detected fault leak.

[0041] With switching valves 7, 8, 9, 10 switched off, air can be introduced into the pneumatic actuating system 1 by means of an air compressor, which causes a pressure p2 to be built up again in the actuator chamber 6, since the connection between the actuator chamber 6 and the switching cylinders 2, 3 is interrupted by the switched-off switching valves 7, 8, 9, 10.

[0042] After the parameterizable shutdown time has elapsed, the switching valves 7, 8, 9, 10 required for the execution of a switching operation are activated, whereby a gear in the transmission can be switched using the pressure p2 built up in the actuator chamber 6.

[0043] When a circuit is executed, the mass of air supplied to the respective switching cylinders 2, 3 via the switching valves 7, 8, 9, 10 is determined depending on a mass flow via the respective switching valve 7, 8, 9, 10.

[0044] The invention further relates to a control unit for carrying out the method according to the invention. The control unit comprises means that serve to carry out the method according to the invention. These means are hardware-related means and software-related means. The hardware-related means are data interfaces for exchanging data with the assemblies involved in carrying out the method according to the invention. For example, the control unit exchanges data with position sensors 13, 14, which are installed on the switching cylinders 3, 2 and sensing the positions of the actuating pistons 15, 16. The hardware-related means of the control unit also include a processor for data processing and a memory for data storage. The software-related means are program modules for carrying out the method according to the invention. Reference sign 1 Positioning system 2 actuator cylinders 3 actuator cylinders 4 Pressure reducing valve 5 air reservoir 6 Control room 7 switching valve 8 switching valve 9 switching valve 10 switching valve 11 Switching valve 12 switching valve 13 Position sensor 14 Position sensor 15 actuating pistons 16 actuating pistons 17 Curve pattern 18 supercritical region 19 subcritical region

Claims

Method for operating a pneumatic actuating system (1) of a transmission, wherein the actuating system (1) has an air reservoir (5) in which a first pressure prevails, wherein the air reservoir (5) is coupled to an actuator chamber (6) of the actuating system (1) in which a second pressure prevails, and wherein the actuator chamber (6) is coupled to switching cylinders (2, 3) via switching valves (7, 8, 9, 10), wherein, when a shift is performed in the transmission, an air mass supplied to the active switching cylinders (2, 3) via the corresponding switching valves (7, 8, 9, 10) and an air mass sum from a target air mass required to perform the shift in the active switching cylinders (2, 3) and a current base leakage of the activated switching cylinders (2, 3) are determined, wherein a fault leakage in the pneumatic actuating system (1) is then inferred if the air mass supplied to the active switching cylinders (2, 3) The supplied air mass is greater than the total air mass, characterized by this.that the mass of air supplied to the active switching cylinders (2, 3) via the switching valves (7, 8, 9, 10) is determined as a function of the mass flow rate through the active switching valves (7, 8, 9, 10), wherein the mass flow rate through an active switching valve (7, 8, 9, 10) is determined as a function of the pressure prevailing in the actuator chamber (6) and as a function of a maximum mass flow rate through the respective switching valve (7, 8, 9, 10). Method according to claim 1, characterized in that a fault leakage in the pneumatic actuating system (1) is inferred if, during the execution of a switching operation in the transmission, the mass of air supplied to the switching cylinder (2, 3) is greater than the sum of the air masses for a defined period of time. Method according to one of claims 1 or 2, characterized in that the target air mass for the active switching cylinders (2, 3) is determined depending on a piston area of ​​the respective active switching cylinder (2, 3) and depending on switching paths of the respective active switching cylinder (2, 3). Method according to one of claims 1 to 3, characterized in that the current basic leakage of the respective active switching cylinder (2, 3) is determined depending on a previous basic leakage of the respective active switching cylinder (2, 3). Method for operating a pneumatic actuating system (1) of a transmission, wherein the actuating system (1) has an air reservoir (5) in which a first pressure prevails, wherein the air reservoir (5) is coupled to an actuator chamber (6) of the actuating system (1) in which a second pressure prevails, and wherein the actuator chamber (6) is coupled to switching cylinders (2, 3) via switching valves (7, 8, 9, 10), characterized in that in the event of a detected fault leakage in the pneumatic actuating system (1), the switching valves (7, 8, 9, 10) of the pneumatic actuating system (1) connected to the actuator chamber (6) and the switching cylinders (2, 3) are switched off for a parameterizable period of time. Method according to claim 5, characterized in that when switching valves (7, 8, 9, 10) of the pneumatic actuating system (1) are switched off, a pressure is built up in the actuator chamber (6) of the pneumatic actuating system (1) by a mass of air introduced into the pneumatic actuating system (1) by an air compressor. Method according to claim 6, characterized in that after the parameterizable time period has elapsed, the switching valves (7, 8, 9, 10, 11, 12) required for the execution of a switching operation in the transmission are actuated and the switching cylinders (2, 3) assigned to the switching valves (7, 8, 9, 10, 11, 12) are pressurized. Control unit for operating a pneumatic actuating system (1) of a transmission, wherein the actuating system (1) has an air reservoir (5) in which a first pressure prevails, wherein the air reservoir (5) is coupled to an actuator chamber (6) of the actuating system (1) in which a second pressure prevails, and wherein the actuator chamber (6) is coupled to switching cylinders (2, 3) via switching valves (7, 8, 9, 10), characterized in that, when a shift is executed in the transmission, the control unit actuates switching valves (7, 8, 9, 10) and determines an air mass supplied to the active switching cylinders (2, 3) via the corresponding switching valves (7, 8, 9, 10) and an air mass sum from a target air mass required to execute the shift in the active switching cylinders (2, 3) and a current basic leakage of the activated switching cylinders (2, 3), wherein the control unit then a fault leakage in the pneumatic positioning system (1) is detected when the active switching cylinders (2,3) the supplied air mass is greater than the total air mass, wherein, in the event of a detected fault leakage, the control unit triggers a substitute reaction in the pneumatic actuating system, and wherein the control unit is configured to perform a method according to one of the preceding claims.

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