DE102004035262A1 - Automatic transmission for controlling speed ratios between input shaft and output shaft of clutch of motor vehicle has transmission mechanism mounted on hollow shaft for air regulation to get absolute figure of number of revolutions - Google Patents

Abstract

The automatic transmission clutch assembly (1) has transmission mechanism (4) on the hollow shaft (6), which moves the piston (11) by air pressure according to transmission oil viscosity, temperature and difference in revolutions of clutch to get an absolute figure. The transmission mechanism has resetting element (10) and sealing element (8) with which friction plate moves to regulate the output speed.

Description

The The invention relates to a method for controlling an automatic transmission according to the generic term of claim 1

automatic transmission have been around for quite some time in different types of motor vehicles used. Count among them For example, automatic transmissions, dual-clutch transmission and stepless transmission. Generally, there is an automatic transmission through a variable gear ratio between the input speed and the output speed and an automatable Control of different transmission ratios out. Under gear here is independent of a possible structural division on different assemblies the whole the one at the change the translation ratio involved and at least temporarily involved in the flow of power Understood elements.

One Switching command for change the translation ratio is usually by means of pressure medium actuated switching elements such Clutches and / or brakes translated into gear shift positions. The clutches or brakes for synchronization are different Transmission elements and for controlling the power flow within the transmission used. In the following, clutches and brakes are common referred to as couplings. The couplings used usually have this as friction linings designed active surfaces on, which with a closed clutch by means of a mostly axial Force pressed against each other be able to transmit torque in this way.

to Control of the clutches are predominantly hydraulic actuators used, which when open Clutch are depressurized or at least one compared to the operation have low actuation pressure when the clutch is closed. at low actuation pressure become the active surfaces the clutch usually via a return spring apart and the piston of the actuator unit in the direction of his Starting position pressed. The return spring can, for example, a coil spring, a plate spring or a combination of different springs, wherein by a Combination of different springs different spring characteristics can be realized.

There Clutches that are currently not included in the power flow, in almost all cases are open, so the friction linings they are not planed on each other, they ideally transfer no moment. In practice, however, is located between the friction linings a medium, which is mostly a gear oil and also in open Clutch for a certain torque transmission ensures between the friction linings. The torque transmission when the clutch is open is referred to as drag torque, thereby resulting losses of usable torque as drag losses. The drag losses also affect by a reaction of kinetic Energy in heat energy potentially negatively impacting the transmission.

The Drag torque is of a variety of different parameters dependent. Among other things depends it is essential to the clearance from the sum of the distances the friction linings with each other when open Clutch. But there are a lot of other parameters besides, which depends on the size of the drag torque Have influence. This parameter space is available depending on the operating state a drag torque optimum with respect to Drag torque over the clearance. The drag torque initially increases with increasing clearance from. Further growing clearance However, it can favor a so-called lamella wobble, which clearly shows increased Drag torque results.

There in an automatic transmission with gear engaged mostly the same several couplings that are not in the power flow, open be operated with a certain differential speed, add the drag losses of the individual clutches. In a dual-clutch transmission when driving in a gear at least one clutch is not engaged and thus has a drag torque that reduces the efficiency of the transmission influenced accordingly adversely. In a continuously variable transmission For example, the efficiency is achieved by the reverse clutch or the forward clutch, of which at least one in each operating state of the transmission is open, adversely affected.

While with respect to the efficiency of the transmission, a clearance corresponding to the drag torque optimum is desirable, other requirements on the transmission often require a deviating clearance. In particular, the clearance has a significant influence on the switching reaction time of the transmission, ie the time span between a shift request and the execution of the shift request of the transmission. The switching reaction time between a command for engaging or changing a gear and the execution of the command should be as short as possible, for example, in a vehicle with a so-called tip level or "Tiptronic" ^TM circuit the default of the driver as quickly as possible in one for the driver implement noticeable reaction of the transmission.

Also with transmissions with automatic gear A short switching reaction time of the transmission is required in order to be able to activate the optimum driving speed as quickly as possible. In addition, a short switching reaction time of the transmission allows a quick change of gears, which can be switched in time, for example, in strong decelerations of a vehicle in the next gear. If the required synchronous rotational speed of the respective gear stage to be next activated is not available on time due to an excessively long gear reaction time, this leads to an undesirable engine speed for a given speed profile and / or to a perceptible jerk and generally to an impairment of shifting comfort.

ever bigger, however the clearance is, the bigger it is the path that goes back to the direct contact of the friction linings must become. Because the clutches of automatic transmissions predominantly hydraulically operated be, due to the same diameter of the clutch piston a larger volume to be introduced into the clutch piston hydraulic fluid and thus a longer operating time under otherwise identical conditions.

From the DE 100 35 479 A1 A method is known which improves the switching speed of successive automatic transmission circuits by preparing the switching element required for a subsequent second upshift or downshift during the first upshift or downshift already during a first upshift or downshift. As a result, when the synchronous speed of the current first upshift or downshift is reached, the immediate execution of the subsequent second upshift or downshift is made possible. It is also possible to prepare several or all switching elements for a possible sequential circuit. This preparation includes a pre-filling of the corresponding switching elements and thus a corresponding reduction in the ventilation clearance of the associated couplings. This method may be able to shorten the shift reaction time of the transmission. However, the reduced ventilation clearance causes an increased drag torque, which has a negative effect on the power available for driving the vehicle and on the thermal load of the transmission. An optimization of the ventilation clearance with regard to minimizing the resulting drag loss of the transmission does not take place.

The DE 100 60 724 A1 suggests to increase the clutch pressure of the clutches to engage the next higher and / or next lower gear even before the presence of a gear change command so far that the clearance is overcome. In this case, the friction elements of the clutches are applied to each other with a low contact pressure when a gear shift command is expected due to the presence of certain conditions. This complete abolition of the clearance, it comes to the affected couplings to a considerable drag loss with appropriate thermal load and increased wear of the friction linings. This document also discloses only a method for improving the gear shift time and makes no statement about measures to minimize the drag losses. An optimization of the clearance is made only with respect to the gear shift time.

In front In this background, the invention is based on the object Method for controlling a motor vehicle operatively connected To provide automatic transmission, wherein in operation at least one Coupling optionally engageable or open with a clearance can be switched and an adjustable clearance having. It should this clearance be optimized so that the gear shift time and the induced Towing losses are minimized, with the weighting of the target variables gear shift time and lag loss should be specifiable and variable. In addition, should a compensation resulting from a reduced clearance resulting tow losses allows become. Overall, so the shifting comfort in a shift be significantly improved.

The solution This object is apparent from the features of the main claim, while advantageous embodiments and developments of the invention the dependent claims are removable.

Of the Invention is based on the finding that the shifting comfort significantly improve in a shift and the efficiency of the transmission, if on the one hand the clearance in one possible low drag torque results to minimize drag losses and on the other hand the clearance the clutches to be switched as possible is greatly reduced by the switching reaction time of the transmission and, thirdly, the resulting total drag in the optimal case by an appropriate control of the input power of the transmission can be compensated in whole or in part.

Therefore The invention is directed to a method for controlling one with a Motor vehicle operatively connected to automatic transmission, during operation at least one clutch selectively engageable or with a clearance is open switchable and has an adjustable clearance

to solution the task is provided that the clearance the at least one clutch is adjusted so that an optimum between the minimization of the switching reaction time of the clutch and minimizing the drag loss of the clutch, and the weighting between minimizing the switching reaction time and minimizing the drag loss of the at least one clutch dependent on of operating parameters of the clutch and / or the operating state of the Motor vehicle and / or environmental conditions of the motor vehicle automatically selected becomes.

By This control of a switching operation can be an optimum for the clearance determine which the opposite Optimization goals of a low clearance to improve the switching reaction time and one possible low drag loss and thus improved overall efficiency the transmission agreed in a balanced compromise, taking all important influencing parameters, which are detailed below explained be included.

In a preferred embodiment The invention is the clearance in principle limited to one size, in the case of a further enlargement of the air play still no substantial increase in the Drag torque occurs. If the clearance is increased, so decreases first the drag torque with increasing distance of the friction linings. Especially for clutches whose friction linings at least partially axially displaceable on an axle or shaft However, it comes from a certain, of the other Dependent on operating conditions Distance to a lamella called lameness, in the at least some friction linings by tumbling movements an increased friction against the surrounding Medium and / or generate against adjacent friction linings. This increases the tow loss. An enlargement of the clearance in the area of lamellae would therefore no advantages in with respect to the drag torque and at the same time disadvantages with respect on the switching reaction time with it. The maximum to be set clearance can be determined by type of gear or by type of gear fixed value can be specified. It is also possible the maximum clearance dependent on certain factors, in particular the rotational speed of the friction linings and / or the viscosity of the transmission oil or to calculate.

According to one Another variant of the method can be provided that for the determination of the optimal clearance to be set a transmission oil temperature and / or a transmission oil viscosity and / or as operating parameters of the clutch a differential speed of the clutch and / or an absolute speed the clutch and / or a torque load of the clutch and / or a local temperature of the clutch and / or a ratio of a transmission input speed to a transmission output speed and / or a hysteresis of the clearance concerning the Actuator input value for be used the clutch actuator. By considering a or more of these influencing factors whose influence in terms of to the clearance to be set below is described the internal gear conditions, which on the optimal clearance Exert influence, considered become. Which of these influencing factors in the concrete design for the Determination of the desired release distance used must, on a case by case basis, on the basis of the data available, the costs for one Capture or estimate data and their processing, as well as considerations of required Calculation time and desired accuracy are decided.

Stands the temperature of the transmission oil based on measurement data or calculations available, so can advantageously at a low temperature of the transmission oil, the clearance the clutch is enlarged and as the temperature of the transmission oil increases, the ventilation clearance is reduced. This allows the influence of changing with the temperature viscosity of the transmission oil be compensated. The higher the temperature of the oil is, the thinner it is it, and the lower is the drag loss under otherwise identical conditions at the clutch. In place of a sole reduction in drag loss However, it may be useful to the switching reaction time by a Reduction of the clearance to reduce and so the positive influence of a higher transmission oil temperature on the tow loss at least partially in favor of a shortened switching reaction time to compensate.

something similar when there is a reduction in the dynamic viscosity of the gear oil, For example, due to aging of the transmission oil or can occur by changing to another gear oil. A reduction the dynamic viscosity of the transmission oil also has the effect that under otherwise identical conditions the Drag torque of the clutch is reduced. This effect can now also be used in whole or in part instead of one lower drag torque by reducing the clearance the clutch to shorten the switching reaction time.

Increases under otherwise identical conditions, the differential speed between the input side and the output side of the clutch, it may be advantageous to increase the clearance, since the drag torque depends significantly on this differential speed and it is therefore often advisable to compensate for this increase at least partially and consciously accept a corresponding increase in the switching reaction time. This applies even more so than in many types of transmission, the differential speed of those clutches is particularly high, whose associated gear stages have a particularly deviating from the currently selected gear ratio ratio. Activation of these couplings within the next period, however, is usually unlikely. Therefore, an extended shift response time can be accepted here.

at an increase the absolute speed at the transmission input or transmission output of Clutch may also be advisable to increase the clearance to at least, the rising losses with increasing absolute speed partially compensate.

Becomes through calculations or measurements exceeding an upper limit a local temperature of the clutch detected at another Increasing the temperature permanent damage, greatly increased wear or even a destruction the clutch or excessive aging of the transmission oil would result so it is advantageous the clearance to increase the oil flow to cooling and to increase lubrication in this area.

Stands Immediate and short-term damage due to excessive temperature to fear, so is one by the enlargement of the Clearance game conditional increased switching reaction time Compared to the protection of the transmission unimportant, and the controller should be based solely on the effective cooling of the gearbox concerned be aligned. In a Temperaturgrenzbe rich, where indeed an elevated one Wear or a reinforced one Aging takes place, but no immediate damage is to be feared, can, however, between the goal of the most effective cooling and the goal of one at the same time as possible weighed short switching response time and the clearance are selected accordingly.

by virtue of of friction influences There may be a hysteresis of the clearance in terms of an actuator input value, for example, a hydraulic Clutch pressure come. This hysteresis has no consideration in determining the setpoint value for the actuator input value as a result, depending on from the adjustment direction of the clearance an equal absolute value of the actuator input value to different Lüftspielen leads. It It is therefore advisable to include the hysteresis in the determination of the actuator input value involve that the hysteresis at least largely compensated becomes. Since the friction is often temperature-dependent, it can make sense for this purpose be a temperature-dependent Provide hysteresis correction.

Further It may be advantageous if immediately after a successful opening of a Clutch the clearance is enlarged. At the opening The coupling occurs briefly to a sliding friction of the friction linings together and thus to a greatly increased Transformation of kinetic energy into heat energy. For fast normalization the temperature of the coupling and in particular of local temperature peaks It is therefore advantageous if for a certain time the air play and thus the transmission oil quantity and the transmission oil flow rate between the friction linings elevated becomes. In this case, the amount and the duration of the increase in the clearance be fixed or depending on Parameters selected which are related to the local maximum Temperature stand. These parameters can in particular the moment load the clutch, the transmission oil temperature, the duration of the sliding friction, and the time span since the last one clutch Control be.

At Place or preferably in addition to the previously explained Influencing factors can to determine a clearance to be set also operating states of Motor vehicle are used. As operating condition of the motor vehicle can in particular the operating temperature of a drive motor and / or an operating time of the drive motor and / or a speed of the Drive motor and / or an operating mode of the motor vehicle used become. These parameters in part allow the use of customary available anyway Information in place of transmission parameters, the possible Way only by extra for it provided sensors or complex Models can be obtained. Besides this possibility the substitution of special status data of the transmission by generally available Condition data of the motor vehicle, however, is also their additional consideration possible and even more advantageous.

There is a correlation between the operating temperature of a drive motor and the temperature of a transmission connected to this drive motor for many operating states. Both have the same starting temperature during a cold start, and the degree of heating of the drive motor can be used to infer the temperature of the transmission at least to a certain extent. This is especially true if additional information, for example, about the number of switching operations and / or the duration between the individual switching operations and / or the respective time-related torque load of the transmission taken into account and evaluated, for example by means of a model. In place of the control function of the temperature of the transmission oil can therefore control in an equivalent manner Based on a known drive motor temperature and the calculated or estimated transmission temperature. Accordingly, it is advantageous if at a low operating temperature of the drive motor, the clearance is increased.

Around ensure that in the most critical phase shortly after an engine start or a cold engine start the transmission drag as possible is low, can be over before a predetermined operating time of the drive motor, the clearance be enlarged.

Further it is advantageous if falling below a predetermined Speed of the drive motor, the clearance is increased. In this way, for example, at the start of the engine or in the Idle mode set a particularly low drag torque become.

In In recent years, it is particularly automatic Driven usual become available to the driver various operating modes put. these can Among other things, different tuning of the chassis and / or the motor control and the switching behavior of the automatic Gear include. Often Here is a switch option between a "sporty" mode, for example on performance, acceleration, cornering and the like can be optimized and an "economic" mode, for example optimized for fuel consumption and comfortable handling can be offered. Here it is now particularly advantageous if various operating modes can be set, which each have a priority of the driver over the Switching reaction time of the gearbox in relation to a minimization Express the drag losses in the gearbox.

Corresponding these priorities can the air play be set correspondingly smaller to shorter switching response times to reach or set larger be to the tow losses and thus the fuel consumption to minimize. It can the different modes in the simplest case by a additive correction value of the clearance differ. It makes sense, however, the provision of each appropriate Calculation rules or models for each mode, as to this Way all factors optimally weighted according to the respective priorities can be.

A particularly simple choice of the operating mode to be used, which It also has the advantage of giving the driver direct control over the choice to enable can be realized by the mode by the driver through a direct Input is specified. Therefor For example, a two-or multi-level switch in the grip area be provided by the driver, or a corresponding indication in a Personalization file are stored. In this case, the operating mode be set separately, or from the setting of another directly derived value, for example, from a usual choice between a "sporty" or "economic" attitude of Engine and / or chassis parameters.

A Alternative to the direct selection of the above described Operating mode consists in an automatic selection of the operating mode due an evaluation of driving parameters in the past. there can different data such as acceleration values, engine speeds, pedal travel and similar to be used to a mode appropriate to the driving style of the driver select.

At Place or preferably in addition to the previously explained Parameters of the transmission and the motor vehicle can environmental conditions of the motor vehicle and in particular the change of a slope of the Roadway and / or the detection of obstacles in the track and / or Traffic sign and / or the road for the election of the ventilation game be used. Are such ambient conditions known, can out You chances for an impending shift will be determined and the transmission for example, in a likely upcoming shift be prepared in such a way that the clearance is reduced to to shorten the switching reaction time. On the other hand, the clearance can enlarged and so that the drag torque can be reduced when the environmental conditions expect no imminent switching operation.

Becomes for example, by a tilt sensor or by stored Map data in conjunction with a navigation system that detects itself the slope of the road changes, so can if exceeded a predetermined change of Slope of the road ahead or under the vehicle the clearance be reduced to the gearbox on a likely forthcoming Change of gear ratio prepare.

If the vehicle is equipped with obstacle detection, for example by means of a radar device, the clearance can be reduced when obstacles are detected in the travel path of the vehicle and the transmission can thus be prepared for the likelihood of imminent deceleration of the vehicle and the associated change in transmission ratio. A vehicle follower, which it a driving makes it possible to drive behind a different vehicle at a fixed distance, is in this case the same as obstacle detection with respect to its mode of operation. In this context, if the preceding vehicle reduces the speed so much that a gear ratio change is indicated, it effectively presents an obstacle to which the vehicle responds by automatic or manual deceleration and gearshift.

Does the vehicle have a System that allows the detection of traffic signs, so may be the clearance in the recognition of certain traffic signs be reduced to an expected upcoming change of Transmission ratio prepare. It does not matter if the traffic sign physically detected, for example by means of image evaluating method will, or if the information is about the validity of a Traffic sign for the currently traveled or imminent section, for example transmitted by electromagnetic waves or due to Position data of the vehicle is taken from a database.

is the vehicle is equipped with a system that provides information about the in the near future to be traveled road course, so can This information can be used to advantage in recognition a street course, which expect an upcoming shift to reduce the clearance and that Transmission such as in front of a sharp turn or an intersection to prepare for the switching process.

above became a multiplicity of possible influencing factors on the clearance and the respective advantages of their consideration explained. there can the directions of action and resulting difference sizes for the clearance in many cases additively linked become. For example, the transmission oil against a dünnflüssigeres This can be done by reducing the clearance be taken into account. If at the same time the temperature of the transmission oil is low, this can be done by an enlargement of the air play considered become. An additive merge, possibly including weighting factors is in this Case makes sense.

It However, on the other hand, there can be influencing factors which are associated with a relative or absolute priority should be treated and therefore in a hierarchical relationship to other influencing factors. For example, for a clutch a Critical temperature measured or otherwise determined, which without countermeasures to injury of the transmission oil or even the clutch lead would, So all the other aspects go back to the protection of the transmission and the Magnification of the air play due to the high local temperature for optimal cooling absolute priority.

It is therefore particularly advantageous if the for determining the air play Factors used in a hierarchical relationship to each other stand. It can several influencing factors are on the same hierarchical level. The hierarchy can be given in an absolute priority Influencing factors before others and / or in a different one Weighting for example by means of weighting factors and / or in one Definition of limit values by factors of a higher hierarchical level consist of the regulatory or tax area due to influencing factors limit a lower hierarchy level.

As already mentioned It is particularly advantageous if when exceeding a predetermined transmission temperature and / or a predetermined local temperature in the transmission clearance independently is magnified by other influencing factors, as much as possible good cooling to enable the local area or by a reduction in drag losses in the transmission introduced heat output the cooling off to allow the transmission.

So far were a variety of factors influencing the game of play named and explained by gear couplings, but not on Differences between different clutches within a transmission enter into. Usually are in an automatic transmission several clutches in the open Status. For example, any fixed gear ratio with be provided a clutch and one or more additional couplings for one Reversal of direction for a reverse drive be provided. The probability of a clutch actuation in immediate future for different couplings dependent different from the currently set gear ratio large. In most cases come for this only the clutches into consideration, which associated with the currently engaged gear adjacent courses are, starting from the idle both the first forward gear as well as the reverse gear selectable are.

However, there are also known transmission controls, which can be switched over several courses, for example, from the fifth to the third gear. Furthermore, there are a variety of special gearboxes, for example, for off-road vehicles and work vehicles with the drive of work machines or auxiliary equipment. In general, therefore, it is desirable that to adjust the clearance of several clutches each un Different weightings of the influencing factors are used to determine the clearance to be set, and thereby different weightings of the objectives of a low drag torque and a short gear reaction time can be provided.

For the mentioned Case that, for example, in a third-gear operation only the clutches of the gears two and four for an immediate following operation For example, it is appropriate only for this Gears that Clearance to shrink when an imminent shift is expected will, while the other open clutches remain set to a value, which represents an optimum in terms of the respective drag torque. In this case, for example the weighting factors for the above explained Ambient conditions are set equal to zero.

In Certain cases It may also be advantageous, those courses, which after a successful Switching process next are switchable, also in a switch preparation to include Optimal switching response times for fast sequential switching operations to enable. Generally speaking are used to adjust the clearance several couplings these couplings into a plurality of groups assigned for the in each case different weights of the to determine the clearance to be set provided influencing factors and the groups a different weighting of the goals of a low drag torque and a short gear reaction time is assigned.

Especially the assignment of couplings to groups can not be static, but according to the calculated or estimated Probability of their integration into the power flow within a predetermined period.

A particularly simple realization is that for those Clutches which are not immediately for a next upcoming shift actuated can be the clearance in Is selected for a minimum drag torque. This can be the simplest Case by a fixed specification of the clearance for the respective couplings will be realized. However, a corresponding is particularly advantageous Calculation of the clearance under Inclusion of the above Influencing factors.

So far was the determination of the setpoint to be set for the clearance explained in detail using relevant input variables. to Control of the clutch and actual setting of the determined Setpoint, however, must have a specific default value for the control the clutch can be generated. Because clutches in automatic transmissions almost exclusively hydraulically operated It is particularly advantageous when adjusting the clearance a setpoint for a clutch actuating hydraulic actuator and in particular a desired pressure for a Hydraulic cylinder is calculated. This value can then, for example, via controllable Valves are easily adjusted. Of course, but also for others Actuators, such as electric motors and pneumatic actuators, Generate and use a setpoint accordingly.

Indeed In the generation of the setpoint for the actuator, there may be the risk that for example, due to a friction hysteresis of the pressure-displacement curve the exact target position is not always reached. To solve the problem can Of course the hysteresis and, if necessary, other influencing factors in the calculation the target pressure taken into account become. Especially easy and accurate is the clearance however, adjust; if the target position is one to the clearance in a direct and at least short-term fixed relationship Elementes is determined and the associated actuator in a way is activated, leading to a movement of the element in the direction leads to the target position. Upon reaching the desired position of the actuator is controlled so that the element remains in its nominal position.

For example a displacement sensor on the hydraulic cylinder unit or on the Connection between hydraulic cylinder unit and the clutch or also be provided on the clutch itself. That way you can the air gap in the form of a direct distance measurement and the hydraulic unit can be controlled so that the target clearance is set exactly. Of course can also with this procedure if necessary further influence factors such as about thermal expansions or a through wear of the friction linings increasing clearance over time considered at the same set distance of the actuator become.

Finally, it should be noted that by means of the method presented so far, the clearance can be adjusted to a respective overall optimum with regard to the drag torque and the switching reaction time. However, this may still result in a drag torque on the transmission, which may adversely affect the driving behavior of the vehicle due to its absolute size, but above all due to short-term size variations. It is therefore also proposed that the sum of the drag torques of several clutches is measured, calculated or estimated, and that the resulting total drag torque or its change value is used to act on the drive device (drive motor) of the transmission in such a way that the total drag torque is fully or partially compensated by an increase in the input power of the drive device.

there may be in place of a full compensation of the total drag torque, only that part of the drag torque prefers completely or partially compensated, which on the minimum drag torque or a mean drag torque, since this proportion in the practice of a driver noticeable change in the drive characteristics of the vehicle leads. The compensation of the drag torque can for example via a appropriate control of an engine control unit to increase an engine speed and / or an increase in the Motor torque done.

Especially in a change of the clearance through the control to prepare one or more clutches on one for the near future suspected or already started switching operation It may be one for the driver unpredictable variation of the drag torque of the Gearboxes come. Therefore, in the context of Invention provided that a from a change of the clearance in preparation for a for the change expected in the near future or already initiated of the drag torque and by increasing the input power of Drive motor is fully or partially compensated.

In conclusion, be mentioned, that the inventive method Of course not on motor vehicles in the sense of combustion-powered road vehicles limited is, but independent on the type of motor drive and the type of propulsion all Vehicles can be applied in which an engine power by means of an automatic transmission in a jacking or otherwise usable moment is converted.

The Invention leaves itself with reference to an embodiment further explain. For this purpose, the description is accompanied by a drawing. This shows in

1 an exemplary clutch, as used in automatic transmissions, in the open position,

2 the same clutch in a position with zero clearance,

3 a graph showing the relationship between piston stroke or clearance and drag torque, and

4 a clutch pressure piston stroke hysteresis in a diagram.

In 1 is therefore a clutch 1 with several on a Abriebswelle 2 non-rotatably but displaceably mounted friction linings 3 shown which of the likewise non-rotatably and axially displaceably mounted Gegenreibbelägen 4 are spaced, which on a sleeve or hollow shaft 5 are stored. In the illustrated state is one with a hydraulic cylinder 6 , the here in the end of the hollow shaft 5 is formed, active-connected hydraulic pressure P equal to zero, so that by a hydraulic, not shown, no axial force on a piston 7 is exercised, which by a sealing element 8th against pressure loss in the direction of the friction linings 3 . 4 is sealed.

The spring element 9 exercises over the return element 10 a restoring force on the piston 7 off, which holds this in the position shown. In particular, under the influence of different speeds N_1 and N_2 of the hollow shaft 5 and the output shaft 2 distribute the friction elements 2 . 3 largely uniform on the between the piston outer surface 11 and the stop serving as travel limit 12 , The sum of the free spaces forming between the friction linings is necessarily equal to the difference between the position of the piston outer surface 11 according to 1 and the position of the piston outer surface in one in the 2 shown position in which the friction linings 3 . 4 completely abut each other. This difference is called a clearance.

2 thus shows the same coupling 1 under an impact of the piston 7 with a hydraulic pressure P> 0, which the piston 7 against the restoring force of the spring element 9 towards the output shaft 2 shifts until the friction pads 3 and the Gegenreibbeläge 4 plan to come together to the plant. In the state shown, there is no clearance between the friction linings 3 and the Gegenreibbelägen 4 available. By a corresponding adjustment of the hydraulic pressure P, the position of the piston outer surface can now 11 against the restoring force of the spring element 9 be continuously adjusted, which at the same time also the clearance of the clutch 1 is set.

In this case, the spring element 9 as indicated in the drawing, a coil spring. Coil springs are characterized by a rising force over the spring travel. Of course, it is also possible to use other springs such as disc springs, which can be characterized by a constant force over a certain way or even a decreasing force with increasing distance. Finally, by a comm bination of different springs, the spring characteristic can be designed almost arbitrarily.

3 shows a graph A, which illustrates the relationship between piston stroke KW and drag torque MS. The friction linings and Gegenreibbeläge off 1 and 2 are summarized here under the term lining slats. On the X-axis here is the piston stroke KW and on the Y-axis, the drag torque MS or fully applied lining plates, the transmissible torque of the clutch 1 plotted.

In a first area between the piston position with pressureless hydraulics 13 and a piston stroke to the piston position 14 , on which the lining plates abut each other, but not yet abut plane, the drag torque MS steadily increases with the piston stroke KW (solid line A).

Will the piston 7 continue towards the with 15 method described piston position at which the lining plates lie flat against each other and the clearance of the clutch is zero, so the drag torque MS per unit route increases more than before, which is reflected in a greater slope of the graph. From here, the moment increases strongly with further increasing piston stroke KW, so that at the piston position 17 that at the input side of the clutch 1 offered moment is also completely transferred to the output side of the same.

The one with 16 designated and dotted traced torque curve when occurring Lamellum wobble shows qualitatively that in a piston stroke KW, which corresponds to a large clearance, a local maximum of the drag torque MS can form considerable height. In this area occurs a so-called lamella wobble, leave in the individual or all friction linings or Gegenreibbeläge due to the large available space the plane of rotation of the associated axis and thereby come into contact with each other, which can lead to considerable wear, or at least one increased entrainment of the located between the slats transmission oil effect. In both cases, caused by the lamellar wobble and the drag torque caused thereby power losses of the transmission are largely translated into heat, which can lead to a significant heat input into the transmission and the coupling damage.

In 4 the clutch pressure piston stroke hysteresis B is illustrated by a diagram. On the X-axis, in turn, the piston stroke KW is plotted here, while the clutch pressure PK is plotted on the Y-axis.

Will the clutch piston 7 after "right", that is moved in the positive X direction, so that clutch pressure PK must be applied to the piston 7 against the return spring force of the spring 9 and the seal friction on the sealing elements 8th Accordingly, this pressure PK multiplied by the piston area must give a force that is greater than the sum of the opposing forces.

On the other hand, if the piston is to be moved "left", the pressure PK must be lowered to a level of the piston force that is smaller than the restoring force minus the frictional force The friction force has a significant temperature influence below a threshold temperature, which is typically about 10 ° C For exact positioning of the piston 7 and thus the exact setting of the Lüftwegs it is therefore advantageous if the influence of the hysteresis B is taken into account or compensated.

1

clutch

2

output shaft

3

friction linings

4

Gegenreibbeläge

5

hollow shaft

6

hydraulic cylinders

7

piston

8th

sealing element

9

spring element

10

Return element

11

Outer piston surface

12

attack

13

Piston position, with pressureless hydraulics

14

Piston position, in which the lining plates abut each other

15

Piston position, where the lining lamellae abutted flat against each other

gene

16

Drag torque curve in the event of lamella wobble

17

piston position at complete closed clutch

B

hysteresis

KW

piston travel

MS

drag torque

N-1

rotation speed the output shaft

N_2

rotation speed the hollow shaft

P

Hydraulic pressure, clutch pressure

Claims (32)

Method for controlling an automatic transmission operatively connected to a motor vehicle, in which at least one clutch by means of an actuator is selectively engageable or openly openable with a clearance during operation and has an adjustable clearance, characterized in that the clearance of the at least one clutch is adjusted to achieve an optimum between minimizing the clutch response time of the clutch and minimizing the drag loss of the clutch and weighting between minimizing the shift response time and minimizing the drag loss of the at least one clutch Operating parameters of the clutch and / or the operating condition of the motor vehicle and / or environmental conditions of the motor vehicle is automatically selected. Method according to claim 1, characterized in that that the clearance is limited to one size, in the case of a further enlargement of the clearance no significant increase yet the drag torque occurs. Method according to one of claims 1 or 2, characterized that for determining the clearance to be set as the operating parameter the clutch has a transmission oil temperature and / or a transmission oil viscosity and / or a differential speed of the clutch and / or an absolute speed the clutch and / or a torque load of the clutch and / or a local temperature of the clutch and / or a ratio of a transmission input speed to a transmission output speed and / or a hysteresis of the clearance in terms of an actuator input value are used. Method according to claim 3, characterized that at a low temperature of the transmission oil increases the clearance of the clutch and as the temperature of the transmission oil increases, the ventilation clearance is reduced. Method according to claim 3, characterized that with a reduction in the dynamic viscosity of the transmission oil, the clearance the coupling is reduced. Method according to claim 3, characterized that at an increase the differential speed between the input side and the output side the clutch the clearance is enlarged. Method according to claim 3, characterized that at an increase the absolute speed at the transmission input or transmission output of the clutch the clearance is enlarged. Method according to claim 3, characterized that when exceeded an upper limit of a local temperature of the clutch, the clearance is increased. Method according to claim 3, characterized that immediately after a successful opening of a clutch, the clearance is enlarged. Method according to claim 3, characterized that a hysteresis (B) of the clearance in terms of an actuator input value so in the determination of the Aktuatoreingwertes is included that the hysteresis compensated at least largely becomes. Method according to one or more of the preceding Claims, characterized in that for determining the to be set Clearance as Operating condition of the motor vehicle, an operating temperature of Drive motor and / or an operating time of the drive motor and / or and / or a rotational speed of the drive motor and / or an operating mode of the motor vehicle is used. Method according to claim 11, characterized in that that at a low operating temperature of the drive motor the clearance is enlarged. Method according to claim 11, characterized in that that before exceeding a predetermined operating time of the drive motor, the clearance is enlarged. Method according to claim 11, characterized in that that falls below a predetermined speed of the drive motor the clearance is increased. Method according to claim 11, characterized in that that different operating modes can be set, which each a priority of Driver over the shift reaction time of the transmission relative to a minimization Express the drag losses in the gearbox. Method according to claim 15, characterized that the operating mode is set by the driver by direct input becomes. Method according to claim 15, characterized that the operating mode based on an evaluation of driving parameters and / or operating parameters of the vehicle in the past becomes. Method according to one or more of the preceding Claims, characterized in that as ambient conditions of the motor vehicle a change a slope of the road and / or the detection of an obstacle in or on the track and / or the detection of a traffic sign and / or the course of the road considered become. A method according to claim 18, characterized in that when exceeding a predetermined change in the slope of the road immediately before or under the vehicle, the clearance is reduced. Method according to claim 18, characterized that upon detection of obstacles in or on the track of the vehicle reduces the clearance becomes. Method according to claim 18, characterized that when certain traffic signs recognize the clearance is reduced. Method according to claim 18, characterized that upon detection of a road course, which can expect an upcoming shift, the clearance is reduced. Method according to one or more of the preceding Claims, characterized in that the to be set for determining the air play Factors used in a hierarchical relationship to each other stand. Method according to claim 23, characterized that when exceeded a predetermined transmission temperature and / or a preselected local Temperature in the gearbox the clearance independent of other influencing factors is increased. Method according to one or more of the preceding Claims, characterized in that for adjusting the clearance several clutches each have different weightings of the influencing factors be used to determine the clearance to be set, and that different weights of the objectives of a small Schleppmomentes and a short gear reaction time provided can be. Method according to one or more of the preceding Claims, characterized in that for adjusting the clearance several couplings these couplings into a plurality of groups be assigned for the respective different weights of the to be set to determine the air play Factors used are provided. Method according to claim 26, characterized in that that the assignment of clutches to groups according to the calculated or estimated probability their involvement in the power flow within a predetermined Period takes place. Method according to one or more of the preceding Claims, characterized in that for those couplings which are not directly for a Switching operation actuated can be the clearance is selected with regard to a minimum drag torque. Method according to one or more of the preceding Claims, characterized in that for adjusting the clearance a setpoint for a clutch actuating Actuator and in particular a target pressure for a hydraulic cylinder calculated becomes. Method according to one or more of the preceding Claims, characterized in that for adjusting the clearance the target position of a to the clearance in a direct and at least short-term fixed relationship Elementes is determined, and the associated actuator in one Way is activated, leading to a movement of the element in the direction leads to the target position, and that when the desired position is reached, the actuator is controlled in such a way that that the element remains in its desired position. Method according to one or more of the preceding Claims, characterized in that the sum of the drag torques of several clutches calculated or estimated and that the resulting total drag momentum is used is to the drive device of the vehicle or the transmission act in such a way that the total drag torque by increasing the Drive power of the drive device compensated in whole or in part becomes. Method according to one or more of the preceding Claims, characterized in that a result of a change of the clearance to the Preparing for a for the change expected in the near future or already initiated of the drag torque, and by increasing the Drive power of the drive device compensated in whole or in part becomes.