Method for monitoring the gear ratio of an automatic transmission

Abstract

Method for monitoring the gear ratio of an automatic transmission, wherein a change from an output gear ratio (i_A) to a target gear ratio (i_Z) is implemented by switching on at least one switching element and by switching off at least one further switching element, wherein a monitoring function checks whether, during a gear ratio change, the gear ratio (i) is below a monitoring upper limit (1) and above a monitoring lower limit (2), characterized by the fact that At a defined time (T4), a time monitoring function is started and it is additionally checked whether the translation is equal to or less than an additional monitoring upper limit (3) or equal to or greater than an additional monitoring lower limit (4) by the end of a predefined period (t1). wherein the additional monitoring upper limit (3) is below the one monitoring upper limit (1) and the additional monitoring lower limit (4) is greater than the one monitoring lower limit (2) and where, if a translation (i) is present after the defined period (t1) is less than the additional monitoring upper limit (3) and greater than the additional monitoring lower limit (4), a torque reducing the speed of the transmission output shaft and present in the area of ​​the transmission output is detected and / or expected.

Description

[0001] The present invention relates to a method for monitoring a gear ratio of an automatic transmission according to the preamble of patent claim 1.

[0002] With the increasing complexity of automatic transmissions used in motor vehicles, the demands on monitoring systems are also growing. In modern automatic transmissions, shift stages are realized by switching several shift elements in combination according to a defined shift logic.

[0003] When switching from one gear to another, the gear ratio changes. If the gear ratio change proceeds correctly, switching from one gear to another occurs by engaging one switching element and disengaging at least one other switching element.

[0004] However, in automatic transmissions, an error can occur during a gearshift process where a switching element involved in the shift remains closed and does not open, contrary to the specified switching logic of the selected gear. The cause of this could be, for example, a valve jamming in the hydraulic control of a switching element that is to be deactivated.

[0005] As a result, it is possible that, in addition to the shift element failing to open, the shift element to be engaged as part of the shift logic reaches a certain transmission capacity, resulting in over-determination of the transmission gear set. This results in a torque that reduces the speed of the transmission output shaft and is present in the area of ​​the transmission output. During unfavorable operating conditions, such a torque causes discontinuities in the output torque curve and may then impair driving comfort.

[0006] In order to ensure safe operation of the motor vehicle, it is therefore necessary to ensure that it is detected as early as possible whether a switching element that is to be opened is incorrectly not opening during a gear change.

[0007] In monitoring methods known in the state of the art, software-based evaluation of the control of the switching elements ensures that no overdetermination of the gear set occurs.

[0008] Secondly, conventional automatic transmissions continuously monitor the current gear ratio. The monitoring function used checks at defined intervals whether the current gear ratio is below a certain upper monitoring limit and simultaneously above a certain lower monitoring limit at a given time.

[0009] The monitoring upper limit and the monitoring lower limit define a monitoring tolerance band around the calculated and expected gear ratio. They are set depending on the operating state of the automatic transmission in such a way that even minor deviations from the expected gear ratio profile do not falsely lead to fault detection by the monitoring function. If there is currently no requirement for a gear ratio change, the tolerance band is selected to be narrower than during a change from an initial gear ratio to a target gear ratio. This allows for the detection of any transmission faults within short operating times during normal driving conditions outside of a gear ratio change.On the other hand, this procedure is intended to avoid error messages and gearshift interruptions if deviations occurring during a gear change between the actual curve of the current gear ratio of the transmission and an idealized target curve of the gear ratio of the transmission are below tolerable defined threshold values, since such deviations only have an insignificant impact on driving comfort, for example.

[0010] Potential overdetermination of the transmission gear set is detected when the gear ratio of the automatic transmission remains at the level of the initial gear ratio during a gear change. A fault occurring in an automatic transmission and characterized by overdetermination of the gear set is detected at the time at which the transmission ratio curve of the automatic transmission, which remains constant at the level of the initial gear ratio over time, crosses one of the monitoring limits or falls below it in the case of a requested upshift or exceeds it in the case of a requested downshift.

[0011] Since, for the reason stated above, the tolerance band during a change from an initial gear ratio to a target gear ratio is set at a greater distance around the target gear ratio curve of an automatic transmission than during operating states of the automatic transmission in which no gear ratio change is performed, there is a possibility that an over-determined gear set may not be detected until after an undesirably long operating period. Furthermore, calculation errors can impair the functioning of the monitoring function, since a wide range of information from the gearshift sequence is fed to the gear ratio monitoring system as input values ​​and evaluated.

[0012] A safety system for an automatic transmission is known from the applicant's DE 195 25 867 A1. The applicant's publications DE 195 27 414 A1, DE 103 13 483 A1, and DE 103 18 519 A1 disclose methods for monitoring a shift sequence or gear monitoring in an automatic transmission.

[0013] The present invention is therefore based on the object of creating an improved method for monitoring a gear ratio of an automatic transmission based on the cited prior art.

[0014] According to the invention, this object is achieved by the method according to the features of patent claim 1.

[0015] Accordingly, a method for monitoring a gear ratio of an automatic transmission is proposed, in which a change from an initial gear ratio to a target gear ratio is implemented by engaging at least one shifting element and disengaging at least one further shifting element. A monitoring function checks whether the gear ratio is below an upper monitoring limit and above a lower monitoring limit during a gear ratio change. At a defined point in time, time monitoring is started via the monitoring function and an additional check is carried out to determine whether the gear ratio is equal to or less than an additional upper monitoring limit or equal to or greater than an additional lower monitoring limit by the end of a predefined period of time. The additional upper monitoring limit is below one of the upper monitoring limits and the additional lower monitoring limit is greater than the lower monitoring limit.If, after the expiry of the predefined period, a gear ratio is smaller than the additional monitoring upper limit and greater than the additional monitoring lower limit, a torque that reduces the speed of the transmission output shaft and is present in the area of ​​the transmission output is detected and / or expected.

[0016] Since the additional monitoring upper limit and the additional monitoring lower limit are not used for general gear ratio monitoring during a gear change, these additional monitoring limits make it possible to implement a narrower monitoring tolerance band around the currently engaged gear ratio during a change from an initial gear ratio to a target gear ratio than the monitoring tolerance band known from the prior art.

[0017] In addition to this additional monitoring tolerance band, which is formed by the additional monitoring upper limit and the additional monitoring lower limit, the time monitoring ensures that after a predefined period of time has elapsed, it is detected at a defined, early point in time whether the requested gear change or gear ratio change has erroneously not taken place, which in particular makes it easy to avoid safety-critical driving conditions.

[0018] In a variant of the method according to the invention, the predefined period of time is, on the one hand, selected such that the detection of an incorrect gear ratio change characterized by an expected overdetermination of the gear set already occurs at a time at which actuations of switching elements can be carried out which counteract a torque present in the area of ​​a transmission output and resulting from the overdetermination of the gear set, which actuate, for example, an interruption of the power flow in the area of ​​the automatic transmission, and, on the other hand, is at least specified in such a way that it is ensured that a properly running gear ratio change is completed within this period of time.

[0019] If there is a request to change from one gear stage to another gear stage and thus to change from an initial gear ratio to a target gear ratio and the gear ratio remains approximately constant at the level of the initial gear ratio despite the activation of one or more shifting elements, this is detected by the method according to the invention in that the gear ratio is smaller than the additional monitoring upper limit and greater than the additional monitoring lower limit until the expiry of the predefined period of time.

[0020] From this, the monitoring function of the method according to the invention concludes that the switching element to be switched off is erroneously not switched off and that a torque reducing the speed of the transmission output shaft and present in the area of ​​the transmission output is already present or is to be expected.

[0021] Thus, by means of the method according to the invention, it is advantageously possible to detect at a much earlier point in time, in comparison to the monitoring method known from the prior art, whether a switching element to be switched off has erroneously not been transferred into its open operating state during a gear change, and appropriate countermeasures can be taken in good time.

[0022] According to an advantageous variant of the method according to the invention, the additional monitoring upper limit lies below a section of the one monitoring upper limit present before a request for a gear change and the additional monitoring lower limit is arranged above the section of the one monitoring lower limit present before the request for a gear change.

[0023] A tolerance band that is even tighter around a current gear ratio has the advantage that a torque that reduces the speed of the gearbox output shaft and is present in the area of ​​the gearbox output can be excluded before the end of the predefined period and at an even earlier point in time, since the narrower the additional monitoring tolerance band, the sooner a gear ratio exceeds or falls below the additional monitoring upper limit or the additional monitoring lower limit when the gear ratio is changed correctly.

[0024] According to a further variant of the method according to the invention, a distance between the additional monitoring upper limit and a section of the one monitoring upper limit present before a request for a gear ratio change is approximately equal to the distance between the additional monitoring lower limit and a section of the one monitoring lower limit present before the request for the gear ratio change.

[0025] Such an arrangement of the additional monitoring upper limit or the additional monitoring lower limit ensures that, during both upshifts and downshifts within short, preferably equally long operating times, incorrect gear ratio changes characterized by an expected overdetermination of the gear set can be excluded.

[0026] According to a further variant of the method according to the invention, the time monitoring is started via the monitoring function at the latest when the at least one switched-on switching element has a defined transmission capability.

[0027] If, in this variant, the gear ratio is smaller than the additional monitoring upper limit and larger than the additional monitoring lower limit after the expiry of the predefined period, the monitoring function can advantageously rule out the possibility that the gear ratio change does not take place because the corresponding switching element to be switched on is not switched on or cannot provide the transmission capacity required for a proper gear ratio change, and at the same time reliably determine that a switching element to be switched off is incorrectly not switched off or can be switched off.

[0028] According to a further variant of the method according to the invention which can be carried out with little effort, the time monitoring is started via the monitoring function when a current supplied to a switched-on switching element is equal to or greater than a defined threshold value.

[0029] Starting the time monitoring depending on the current supplied to a switched switching element is therefore easy to implement, since the current set for switching a switching element is monitored anyway as part of other monitoring functions or the control of the automatic transmission.

[0030] According to a further variant of the method according to the invention, the time monitoring is started via the monitoring function when a request for a translation change is present.

[0031] This has the advantage that time monitoring is started at the earliest possible point in time, thus detecting any premature or premature gear ratio change and thus a departure from the additional monitoring tolerance band. This prevents the possibility of such a departure from the additional monitoring tolerance band remaining undetected by the gear ratio, both by the monitoring function and by the time monitoring implemented by it, and thus leading to incorrect conclusions.

[0032] Both the features specified in the patent claims and the features specified in the following exemplary embodiment of the subject matter according to the invention are suitable, either individually or in any combination with one another, for further developing the subject matter according to the invention.

[0033] Further advantages and advantageous embodiments of the subject matter according to the invention emerge from the patent claims and the exemplary embodiment described in principle below with reference to the drawings.

[0034] It shows: Fig. 1 an exemplary switching matrix; and Fig. 2 schematic curves of various operating and monitoring parameters of an automatic transmission over time t.

[0035] In Fig. Figure 1 shows an example shift diagram of an automatic transmission (not shown in detail). The automatic transmission can accommodate eight forward gears (1 to 8) and one reverse gear (R). Those shift elements A to E marked with a dot in the shift diagram are closed to represent the respective gears (1 to R).

[0036] To represent all gear ratios "1" to "R," three of the five shift elements A, B, C, D, and E must be closed or kept in the closed operating state. For example, to represent the first forward gear "1," shift elements A, B, and C must be closed, while shift elements A, B, and D are closed when reverse gear "R" is engaged in the automatic transmission. The other shift elements D, E, or C, E must each be fully opened.

[0037] When changing from an output gear stage to a target gear stage or from an output ratio i_A to a target ratio i_Z, depending on the respective output gear stage and the respective target gear stage, the corresponding switching elements A, B, C, D and / or E must be switched on or certain other switching elements A, B, C, D and / or E must be switched off. Thus, switching back from the fifth to the fourth gear stage requires switching element C to be switched off and switching element E to be switched on, while switching elements A and D are kept in the closed operating state.

[0038] In Fig. 2 shows a schematic curve of a gear ratio i over time t as an example. In addition to the curve of the gear ratio i, the associated monitoring limits 1, 2, 3 and 4 as well as current and pressure curves I_S and p_S are shown over time t, all of which can preferably be varied depending on the operating state and / or over the running time of the automatic transmission. The curve of the current I_S required to actuate a shift element A, B, C, D or E to be engaged as required and the curve of the pressure p_S to be applied in the area of ​​the shift element A, B, C, D or E to be engaged correspond to one another. Due to the system, the curve of the pressure p_S has a certain time offset compared to the leading curve of the current I_S at the beginning of the requested shift sequence.

[0039] The curve of gear ratio i, shown as an example and schematically, occurs during a faultless downshift. If the curve V has the value 1, a shift request is present or a downshift is currently being performed. If, however, the curve V has the value 0, there is no shift request, no downshift is being performed, or the requested downshift has been completed.

[0040] At a time T0, the output gear ratio i_A is engaged in the automatic transmission and there is no request for a gear ratio change.

[0041] A request to change from the currently engaged output ratio i_A to a requested target ratio i_Z is made at a time T1. With this request, the current I_S to be applied to the switching element A, B, C, D or E to be switched on is determined in the Fig. 2. With the certain system-related time offset, the pressure p_S, which must be applied to the switching element A, B, C, D, or E to be activated in order to carry out the requested switching operation, also rises abruptly at a time T2, ideally to the level of the rapid filling pressure, and remains at this pressure level until a time T3, at which point the pressure equalization phase begins, lasting until a time T4.

[0042] During operation of the automatic transmission, a monitoring function is used to monitor whether the currently engaged gear ratio i or a gear ratio to be engaged corresponds to a requirement and whether the gear ratio i is below a monitoring upper limit 1 and above a monitoring lower limit 2.

[0043] If there is a request to change the gear ratio at time T1, one monitoring upper limit 1 is shifted upwards and one monitoring lower limit 2 is shifted downwards and one monitoring tolerance band is thus widened compared to a period before time T1.

[0044] At time T4, at which the pressure equalization phase ends and at which the frictional switching element A, B, C, D or E to be switched on has an operating state in which the transmission capacity of the switching element A, B, C, D or E is zero and from which an increase in the actuating force of the switching element A, B, C, D or E results in an immediate increase in the transmission capacity, the current I_S reaches a defined threshold value I1.

[0045] During the in Fig.Based on the operating state curve of the automatic transmission underlying the curves shown in Figure 2, a time monitoring function is started at time T4. Furthermore, an additional monitoring upper limit 3, which is lower than the monitoring upper limit 1, and an additional monitoring lower limit 4, which is higher than the monitoring lower limit 2, are set. These additional monitoring limits 3 and 4 run parallel above and below the level of the output gear ratio i_A from time T4 onwards and form an additional, narrower monitoring tolerance band surrounding the curve of the gear ratio i.

[0046] During a correct gearshift sequence, the gear ratio i leaves the level of the initial gear ratio i_A from time T5 after a ramp-like increase in the pressure p_S applied to the gearshift element A, B, C, D or E to be engaged, beginning at time T4, and a related increase in the transmission capacity of the gearshift element A, B, C, D or E to be engaged. With a further increase in the pressure p_S, the gear ratio i increases in a ramp-like manner until the desired level of the target gear ratio i_Z is reached at a time T8. This is the case when, within the scope of a so-called overlap shift, the transmission capacity of the gearshift element A, B, C, D or E to be disengaged is reduced to the extent required for this purpose or the gearshift element A, B, C, D or E to be disengaged is opened as required.From a time T6 and before the expiry of the predefined period t1, which in this case ends at a time T7, the transmission ratio i exceeds the additional monitoring upper limit 3 and thus the additional monitoring tolerance band.

[0047] The monitoring function detects at time T6 that the shift element A, B, C, D or E to be disengaged has a transmission capability at which the gear ratio i of the automatic transmission increases towards the target gear ratio i_Z and there is no overdetermination of the transmission gear set. As long as the progression of the gear ratio i of the automatic transmission with increasing operating time t remains within the broader monitoring tolerance band limited by monitoring limits 1 and 2, the monitoring function detects a properly proceeding gear ratio change which includes a corresponding load transfer from the shift element A, B, C, D or E to be disengaged within predefined operating times towards the shift element A, B, C, D or E to be engaged. The load transfer ultimately leads to the gear ratio i assuming the value of the target gear ratio i_Z orthe requested gear ratio is engaged in the automatic transmission and the requested gear change is completed.

[0048] The additional monitoring tolerance band makes it possible to detect, within a short operating time and to the extent explained in more detail below, an improper shifting sequence during which the transmission capacity of the shift element A, B, C, D, or E to be disengaged is not reduced to the required extent, or the shift element A, B, C, D, or E to be disengaged is not opened. This is intended because the progressive engagement of the frictionally engaged shift element A, B, C, D, or E to be engaged causes an increasing over-determination of the gear set of the automatic transmission, which generates a braking torque in the output area that counteracts the output torque. The braking torque depends on the current transmission capacity of the shift element A, B, C, D, or E to be engaged.However, such braking torque results in undesirable power losses, which increase the fuel consumption of a vehicle equipped with an automatic transmission. Furthermore, such braking torque may impair driving comfort if it causes an abrupt deceleration of the vehicle that is incomprehensible to the driver.

[0049] If an overdetermination of the transmission gear set occurs during the execution of a requested gear ratio change, the gear ratio i is known to remain constant at the level of the initial gear ratio i_A. Thus, with the present procedure in conjunction with the narrower, additional monitoring tolerance band, an overdetermination of the transmission gear set is already detected at time T7 if the profile of the gear ratio i of the automatic transmission lies within the narrower, additional monitoring tolerance band at time T7 and at the end of the predefined period t1.

[0050] In contrast, an overdetermination of the transmission gear set without the narrower, additional monitoring tolerance band over the monitoring tolerance band comprising a significantly larger gear ratio range can only be determined at time T9, at which the gear ratio i of the automatic transmission, which has the level of the output gear ratio i_A when a previously described faulty gear shift sequence occurs, intersects or falls below the monitoring lower limit.

[0051] With the monitoring method according to the invention, an incorrect gear ratio change is detected as early as the expiration of the predefined period t1 or at time T7, and thus considerably earlier than with conventional monitoring methods. This allows appropriate countermeasures to be initiated much earlier. In particular, to avoid safety-critical driving conditions caused by an overdetermined transmission gear set, it can be provided, for example, that the opening of all shift elements A to E is requested at time T7, and the automatic transmission is transferred to a so-called safe operating state.If the inventive procedure is implemented, for example, in the actuation sequence of transmission systems designed with positive-locking shifting elements that are to be transferred to an open operating state to represent a requested gear ratio during vehicle operation, undesirable operating states, such as an over-determined gear set of an automatic transmission, can be detected to the desired extent after only a short period of operation. This is advantageous because defined operating states of an automatic transmission must be established for the proper actuation of positive-locking shifting elements.

[0052] Furthermore, with the procedure according to the invention, upshifts can also be monitored to the extent described above, wherein a proper shift sequence of a requested upshift is detected if the gear ratio i of the automatic transmission leaves the narrower, additional monitoring tolerance band by falling below the additional monitoring lower limit before the end of the predefined period t1.

[0053] In contrast, a faulty shift sequence of a requested upshift characterized by an overdetermined gear set is determined using the procedure according to the invention if the gear ratio i of the automatic transmission is still within the narrower, additional monitoring tolerance band at the end of the predefined period t1.

[0054] Depending on the respective application, the defined period t1 can be varied over the running time of the automatic transmission and / or the respective operating state curve. Reference symbol 1 Surveillance ceiling 2 Monitoring lower limit 3 additional monitoring limit 4 additional monitoring lower limit A to E switching elements I_S supplied current I1 defined threshold of the supplied current i Translation i_A Output translation i_Z target translation p_S pressure T0 to T9 discrete time t1 predefined period V Course

Claims

[1] Method for monitoring a gear ratio of an automatic transmission, wherein a change from an initial gear ratio (i_A) to a target gear ratio (i_Z) is implemented by switching on at least one switching element and by switching off at least one further switching element, wherein a monitoring function checks whether the gear ratio (i) is below a monitoring upper limit (1) and above a monitoring lower limit (2) during a gear ratio change, characterized by , that at a defined time (T4) a time monitoring is started via the monitoring function and additionally checked whether the translation is equal to or less than an additional monitoring upper limit (3) or equal to or greater than an additional monitoring lower limit (4) until the end of a predefined period (t1), wherein the additional monitoring upper limit (3) is below the one monitoring upper limit (1) and the additional monitoring lower limit (4) is greater than the one monitoring lower limit (2) and wherein, in the case of a transmission ratio (i) which is smaller than the additional monitoring upper limit (3) and greater than the additional monitoring lower limit (4) after the expiry of the defined period (t1), a torque which reduces the speed of the transmission output shaft and is present in the region of the transmission output is detected and / or expected. [2] Method according to claim 1, characterized bythat the predefined period (t1) is, on the one hand, selected such that the detection of a faulty gear ratio change characterized by an expected overdetermination of the gear set already takes place at a time (T7) at which actuations of switching elements (A to E) of the automatic transmission can be carried out which counteract a torque present in the area of ​​a transmission output and resulting from the overdetermination of the gear set, and, on the other hand, is at least specified such that it is ensured that a properly running gear ratio change is completed within this period (t1). [3] Method according to claim 1 or 2, characterized bythat the additional monitoring upper limit (3) is below a section of the one monitoring upper limit (1) present before a request for a gear ratio change and the additional monitoring lower limit (4) is above the section of the one monitoring lower limit (2) present before the request for a gear ratio change. [4] Method according to one of claims 1 to 3, characterized by that a distance between the additional monitoring upper limit (3) and a section of the one monitoring upper limit (1) present before the request for a gear ratio change is approximately equal to the distance between the additional monitoring lower limit (4) and a section of the one monitoring lower limit (2) present before the request for a gear ratio change. [5] Method according to one of claims 1 to 4, characterized bythat the time monitoring is started via the monitoring function when at least one switched-on switching element has a defined transmission capability. [6] Method according to one of claims 1 to 4, characterized by that the time monitoring is started via the monitoring function when a current (I_S) supplied to a switched-on switching element is equal to or greater than a defined threshold value (11). [7] Method according to one of claims 1 to 4, characterized by that the time monitoring is started via the monitoring function when a request for a translation change occurs.

Images