Method for operating a pneumatic actuating system of a transmission and control device for carrying out the method

Abstract

A method for operating a pneumatic actuating system of a transmission. The actuating system has an air reservoir at a first pressure. The reservoir couples an actuating space of the actuating system which is at a second pressure, and the actuating space couples, via control valves, shifting cylinders. When conducting a transmission gearshift, an air mass delivered to the active shifting cylinders via corresponding control valves, and an air mass sum including a nominal air mass in the active cylinders required for accomplishing the gearshift and an actual basic leakage from the activated shifting cylinder are determined. A defect leak in the pneumatic actuating system is recognized, if the air mass delivered to the active shifting cylinders is larger than the air mass sum. If a defect leak is recognized, the control valves coupling the actuating space and the shifting cylinders are shut off for a period of time.

Claims

1. A method of operating a pneumatic actuating system of a transmission, the actuating system having an air reservoir in which a first pressure is present, the air reservoir being coupled to an actuating space of the actuating system in which a second pressure is present, and the actuating space being coupled, by way of control valves, to shifting cylinders, the method comprising: when a gearshift is carried out in the transmission, determining an air mass delivered to the active shifting cylinders, via the corresponding control valves, and an air mass sum which comprises a nominal air mass in the active shifting cylinders required for carrying out the gearshift and an actual basic leakage from the activated shifting cylinder; and if the air mass delivered to the active shifting cylinders is larger than the air mass sum, concluding that there is a defect leak in the pneumatic actuating system.

2. The method according to claim 1, further comprising concluding that the defect leak in the pneumatic actuating system exists if, while a gearshift is being carried out in the transmission, the air mass delivered to the shifting cylinder remains larger than the air mass sum over a defined time period.

3. The method according to claim 1, further comprising determining the air mass delivered via the control valves to the active shifting cylinders as a function of a mass flow through the active control valves; and determining a mass flow through an active control valve as a function of the pressure present in the actuating space and as a function of a maximum mass flow through the shifting valve concerned.

4. The method according to claim 1, further comprising determining the nominal air mass for the active shifting cylinders as a function of a piston area of the active shifting cylinder concerned and as a function of shifting paths of the active shifting cylinder concerned.

5. The method according to claim 1, further comprising determining an actual basic leakage from the active shifting cylinder concerned as a function of a previous basic leakage from the active shifting cylinder concerned.

6. A method for operating a pneumatic actuating system of a transmission, the actuating system having an air reservoir in which a first pressure is present, the air reservoir being coupled to an actuating space of the actuating system in which a second pressure is present, and the actuating space being coupled to shifting cylinders by way of control valves, the method comprising: when a defect leak is recognized in the pneumatic actuating system, shutting off the control valves of the pneumatic actuating system connected to the actuating space and the shifting cylinders for a parameterizable period of time.

7. The method according to claim 6, further comprising, when the control valves of the pneumatic actuating system are shut off, building up a pressure in the actuating space of the pneumatic actuating system by an air mass delivered by an air compressor.

8. The method according to claim 7, further comprising, after a lapse of the parameterizable time period, actuating the control valves required for carrying out a gearshift in the transmission, and acting upon the shifting cylinders associated with the control valves by pressure.

9. A control unit for operating a pneumatic actuating system of a transmission, the actuating system comprising an air reservoir in which a first pressure is present, the air reservoir being coupled to an actuating space of the actuating system in which a second pressure is present, and the actuating space being coupled to shifting cylinders by way of control valves, and, when a gearshift is carried out in the transmission, the control unit actuates the control valves and determines an air mass delivered to active shifting cylinders via the corresponding control valves and an air mass sum consisting of a nominal air mass in the active shifting cylinders required for carrying out the gearshift and an actual basic leakage from the activated shifting cylinder, and, if the air mass delivered to the active shifting cylinders is larger than the air mass sum, the control unit detecting a defect leak in the pneumatic actuating system, and, if a defect leak is determined, the control unit initiates a compensatory reaction in the pneumatic actuating system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) To clarify the invention drawings with example embodiments are attached to the description. The drawings show:

(2) FIG. 1: A block circuit diagram of a pneumatic actuating system of a transmission; and

(3) FIG. 2: A diagram to make clear details of the method for operating the pneumatic actuating system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) The invention relates to a method for recognizing a leak that is too large, or is incorrect, in a pneumatic actuating system of a transmission, which leak can lead to the fact that gearshifts can no longer be carried out properly in the transmission. Such a leak is termed a defect leak. Furthermore, the invention relates to a method by which, if a defect leak in the pneumatic actuating system has been recognized, a compensatory reaction is initiated by means of which a gear can be reliably engaged in the transmission even when a defect leak has been recognized. In addition the invention relates to a control unit for carrying out the method.

(5) FIG. 1 shows, as an example, the basic structure of a pneumatic actuating system 1 for a transmission, namely in FIG. 1 for a group transmission such that each part of the group transmission comprises a shifting cylinder 2, 3 that is to be actuated pneumatically. The shifting cylinder 2 shown in FIG. 1 is a pneumatically actuated shifting cylinder of a splitter group of the group transmission, which can be actuated by two control valves 7, 8. The shifting cylinder 3 is a pneumatically actuated shifting cylinder of a main transmission of the group transmission, which can be actuated by four control valves 9, 10, 11, 12. Associated with the shifting cylinder 2, which serves to actuate the splitter group, there is a position sensor 14 with the help of which the position of an actuating piston 16 of the shifting cylinder 2 can be detected by measurement-technological means. Associated with the shifting cylinder 3, which serves to actuate the main transmission, there is a position sensor 13 with the help of which the position of an actuating piston 15 of the shifting cylinder 3 can be detected by measurement-technological means.

(6) The pneumatic actuating system 1 of FIG. 1 comprises an air reservoir 5. In the air reservoir 5 there is present a first pressure, namely a pressure p.sub.1. Furthermore the pneumatic actuating system 1 comprises a so-termed actuating space 6 in which there is a second pressure, namely a pressure p.sub.2. The actuating space 6 is connected to the air reservoir 5 by way of a pressure-reducing valve 4. By means of the pressure-reducing valve 4, the pressure p.sub.1 in the air reservoir 5 is reduced to an adjustable constant pressure p.sub.2.

(7) Starting from the actuating space 6, the shifting cylinders 2, 3 can be supplied with compressed air, each shifting cylinder 2, 3 being coupled to the actuating space 6 by way of control valves 7, 8, 9, 10. In the example embodiment of FIG. 1 each of the shifting cylinders 2, 3 is coupled to the actuating space 6 via two respective control valves, 7, 8 and 9, 10.

(8) In order, now for example, to be able to reliably recognize a defect leak in the pneumatic actuating system 1 of a transmission shown as an example in FIG. 1, when a gearshift is carried out in the transmission during which one or both of the shifting cylinders 2, 3 of the transmission are supplied with compressed air and in which one or more of the control valves 7, 8, 9, 10 is/are active, an air mass delivered to the active shifting cylinders 2, 3 via the corresponding control valves 7, 8, 9, 10 is determined. In addition an air mass sum consisting of a nominal air mass required for carrying out the gearshift in the active shifting cylinders 2, 3 and a current basic leakage from the active shifting cylinder 2, 3 is determined. The basic leakage is also referred to as the natural leakage and always occurs during the operation of the pneumatic actuating system 1. If the air mass delivered to the active shifting cylinders 2, 3 is larger than the air mass sum, it is concluded that there is a defect leak in the pneumatic actuating system 1, namely if while a gearshift is being carried out in the transmission the air mass delivered to the shifting cylinders 2, 3 remains larger than the air mass sum for a defined period of time.

(9) Accordingly, according to the invention a comparative balancing of the air mass consumed in the pneumatic actuating system 1 while a gearshift is taking place is carried out. In the event of a defect leak, the air mass delivered to the active shifting cylinders 2, 3 by way of the corresponding control valves 7, 8, 9, 10 is substantially larger than the air mass sum which consists of the air mass in the active shifting cylinders 2, 3 added to the air mass of a current basic leakage from the active shifting cylinders 2, 3. If the difference between the air mass flowing via the control valves 7, 8, 9, 10 into an active shifting cylinder 2, 3 and the air mass sum consisting of the nominal air mass in the active cylinders 2, 3 during an active gearshift and the air mass attributable to the natural leakage from the active shifting cylinders 2, 3 is larger than a defined limit value, a defect leak in an active shifting cylinder is recognized. Leak detection is carried out separately for each of the shifting cylinders 2, 3.

(10) On the assumption that all gearshifts in the transmission are carried out with a supercritical pressure ratio, the air mass delivered to the active shifting cylinder via an active control valve 7, 8, 9, 10 is calculated from the following equations:

(11) ${\stackrel{.}{m}}_{\mathrm{ist}}={\stackrel{.}{m}}_{\mathrm{ist}}*\mathrm{dt}$${\stackrel{.}{m}}_{\mathrm{ist}=}{}_{\mathrm{MA}X}$${}_{\mathrm{MA}X}=C*p_2**\sqrt{\left(\frac{T_0}{T}\right)}$$C=\frac{k*{}_D*Q*{}_{\mathrm{MA}X}*\sqrt{\left(2*R_S*T_0\right)}}{p_0}$
in which m.sub.ist is the air mass delivered to the active shifting cylinder via the active control valve 7, 8, 9, 10 concerned, m.sub.ist is the mass flow through the active control valve 7, 8, 9, 10 concerned, p.sub.2 is the pressure present in the actuating space 6, .sub.MAX is the maximum mass flow through the active control valve 7, 8, 9, 10 concerned, C is a pneumatic conductance value of the active control valve 7, 8, 9, 10 concerned, is the air density, T.sub.0 is the absolute air temperature in the normal condition, T is the current actual air temperature, k is an adaptation factor of the active control valve 7, 8, 9, 10 concerned, .sub.D is a pneumatic correction factor of the active control valve 7, 8, 9, 10 concerned, R.sub.S is the specific gas constant, p.sub.0 is an air pressure of the air in the normal condition and Q is the valve cross-section of the active control valve 7, 8, 9, 10 concerned.

(12) Thus, according to the above formulas the air mass flowing through the active control valve 7, 8, 9, 10 concerned, starting from the actuating space 6 and into the shifting cylinder 2, 3, is obtained by integrating the mass flow through the active control valve 7, 8, 9, 10 concerned.

(13) According to FIG. 2, in the determination of the air mass delivered to the active shifting cylinder 2, 3 via the active control valves 7, 8, 9, 10 concerned, there is a distinction between actuating the control valves 7, 8, 9, 10 in a supercritical range 18 in which the mass flow is constant, and actuating the control valves 7, 8, 9, 10 in a below-critical range 19 in which the mass flow is not constant. As can be seen from the shape of the curve 17 in FIG. 2, the mass flow through the control valves 7, 8, 9, 10 in the below-critical range 19 is approximated by an ellipse. On the assumption that all gearshifts in the transmission are carried out at a supercritical pressure ratio, the mass flow through the control valves 7, 8, 9, 10 will be constant. This constant mass flow is likewise also the maximum mass flow through the control valves 7, 8, 9, 10.

(14) The nominal air mass in the active shifting cylinder 2, 3 concerned, required for carrying out a successful gearshift in the transmission, is determined as a function of a piston area of the active shifting cylinder 2, 3 concerned and as a function of shifting paths of the active shifting cylinder 2, 3 concerned.

(15) The nominal air mass of the active shifting cylinder 2, 3 concerned for the air mass sum is preferably calculated from the following equations:
m.sub.Soll=*V.sub.Soll
V.sub.Soll=V.sub.1+V.sub.2
V.sub.1=A.sub.1*(xl.sub.MIN)
V.sub.2=A.sub.2*(l.sub.MAXx)
in which m.sub.Soll is the actual nominal air mass of the active shifting cylinder, V.sub.Soll is the actual nominal volume of the active shifting cylinder, is the air density, V.sub.1 is the active volume in the first actuation direction of the actuating piston, V.sub.2 is the active volume in the second actuation direction of the actuating piston, A.sub.1 is the active piston area in the first actuation direction of the actuating piston, A.sub.2 is the active piston area in the second actuation direction of the actuating piston, x is the current piston position, l.sub.max is the maximum shifting path and l.sub.min is the minimum shifting path.

(16) For example, the first actuation direction of the actuating piston can be understood to mean an actuation of the actuating piston in the direction toward increasing position values. The second actuation direction of the actuating piston is opposite to the first actuation direction and corresponds to an actuation of the actuating piston in the direction toward decreasing position values.

(17) Thus, from the active volume V.sub.1 in the first actuation direction and the active volume V.sub.2 in the second actuation direction, the nominal air mass m.sub.Soll in the shifting cylinder during an active gearshift can be calculated. In doing this, in the main transmission there is a difference between gearshifts away from and toward neutral since the respective active piston areas are different.

(18) To the above volumes V.sub.1, V.sub.2, a dead volume of the shifting cylinder can also be additively superimposed.

(19) The actual basic leakage of the active shifting cylinder 2, 3 concerned for the air mass sum is preferably calculated from the following equation:

(20) $m_{L\left(k\right)}=m_{L\left(k-1\right)}+\frac{V_{\mathrm{soll}}}{R_S*T}*\stackrel{.}{p}*t_S$
in which m.sub.L(k) is the actual basic leakage from the active shifting cylinder concerned, m.sub.L(k-1) is the previous basic leakage from the active shifting cylinder concerned, V.sub.Soll is the actual nominal volume of the active shifting cylinder concerned, R.sub.S is the specific gas constant of air, T is the current air temperature, {dot over (p)} is the rate of change of the air pressure and t.sub.S is a scanning rate. The above equation applies on the assumption that the volume V.sub.Soll and the rate of change of the air pressure {dot over (p)} are constant.

(21) For each shifting cylinder that is active while carrying out a gearshift, the air mass m.sub.ist and the basic leakage according to the above formula are determined separately.

(22) As already stated, a defect leak in the pneumatic actuating system 1 is recognized when, over a defined time period while a gearshift is being carried out in the transmission, the air mass m.sub.ist delivered via the corresponding control valves 7, 8, 9, 10 to the active shifting cylinder 2, 3 is larger than the air mass sum consisting of the nominal air mass m.sub.Soll required for carrying out the gearshift in the active shifting cylinder 2, 3 and the actual basic leakage m.sub.Leak from the active shifting cylinder 2, 3:
m.sub.ist>m.sub.Soll+m.sub.Leak

(23) When it is concluded that there is a defect leak in the actuating system 1, countermeasures can be initiated to nevertheless enable a defined operation of the transmission. According to the present invention it is provided that when a defect leak is recognized in the pneumatic actuating system 1 the control valves 7, 8, 9, 10 of the pneumatic actuating system 1 connected to the actuating space 6 and the shifting cylinders 2, 3 are shut off for a parameterizable time period. When a defect leak is recognized, this can prevent air from flowing out of the actuating space 6 of the pneumatic actuating system 1 in an uncontrolled manner.

(24) When the control valves 7, 8, 9, 10 are shut off, air can be supplied to the pneumatic actuating system 1 by means of an air compressor, whereby in the actuating space 6 a pressure p.sub.2 is built up again, since by virtue of the shut-off control valves 7, 8, 9, 10 the connection between the actuating space 6 and the shifting cylinders 2, 3 is interrupted.

(25) After the lapse of the parameterizable shut-off duration, the control valves 7, 8, 9, 10 required for carrying out a gearshift are actuated so that by means of the pressure p.sub.2 built up in the actuating space a gear can be engaged in the transmission.

(26) When a gearshift is carried out, the air mass delivered via the control valves 7, 8, 9, 10 to the shifting cylinders 2, 3 concerned is determined as a function of a mass flow by way of the control valve 7, 8, 9, 10 concerned.

(27) The invention also 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 include hardware means and software means. The hardware means are data interfaces for the exchange of data between the assemblies involved in carrying out the method according to the invention. For example, the control unit exchanges data with the position sensors 13, 14 which are built into the shifting cylinders 3, 2 and which sense the positions of the actuating pistons 15, 16. The hardware means of the control unit also include a processor for data processing and a memory for data storage. The software means consist of program modules for carrying out the method according to the invention.

INDEXES

(28) 1 Actuating system 2 Actuating cylinder 3 Actuating cylinder 4 Pressure-reducing valve 5 Air reservoir 6 Actuating space 7 Control valve 8 Control valve 9 Control valve 10 Control valve 11 Control valve 12 Control valve 13 Position sensor 14 Position sensor 15 Actuating piston 16 Actuating piston 17 Curve shape 18 Supercritical range 19 Below-critical range