Patent Application
20090192018
This application claims the priority, under 35 U.S.C. ยง119, of German application DE 10 2008 006 194.8, filed Jan. 26, 2008; the prior application is herewith incorporated by reference in its entirety.
1. Field of the Invention
The invention relates to a method for controlling the drivetrain of a motor vehicle which has a dual-clutch transmission with a first partial transmission and a first clutch and with a second partial transmission and a second clutch. The drivetrain is operated with a gear being engaged in the first partial transmission and a gear being engaged in the second partial transmission at the same time and with the first clutch and the second clutch being operated with slip at the same time. The invention also relates to a control unit which is set up for carrying out the method.
A method of this type and a control unit of this type are each known from series-produced motor vehicles. The division of the dual-clutch transmission into a first partial transmission and a second partial transmission which can be connected, independently of one another, to the drive engine of the drivetrain by the first and second clutch respectively, permits a change in transmission ratios without an interruption in tractive force. During starting, the drive motor drives the motor vehicle generally first via the first clutch and the first partial transmission. Here, when the (second) clutch of the second partial transmission is open, the second gear can already be engaged in the second partial transmission. During the transfer of the transmission of torque from a transmission via the first partial transmission to a transmission via the second partial transmission, the two clutches are briefly operated with slip at the same time, with the transmission of torque via the first clutch decreasing and via the second clutch increasing. The torques which are transmitted via the two clutches at the same time in the transfer phase are added in the dual-clutch transmission. After the transfer has taken place, the second clutch is completely closed. After the transfer is complete, the motor vehicle is accelerated further in the second gear. On account of the change in transmission ratio, the relationship between the engine rotational speed and driving speed changes. The opening and closing of the clutches and the resulting rotational speed changes incite oscillations in the drivetrain.
During driving at low speeds in the lowest part-load range, that is to say with only a very low torque demand by the driver, comfort plays a greater role than other properties, for example a sporty driving behavior. In particular at a walking pace between approximately 5 and 15 km/h, longitudinal oscillations of the vehicle, which are caused by the shifts, or perceptible jolts, which are caused by load changes, or vibrations, which are caused by the charge exchange during the charging of combustion chambers of the drive engine, are perceived to be disturbing.
For example, overrun and part-load shifts during coasting (stopping) lead to uncomfortable longitudinal vibrations and traction/overrun load changes. A late opening of the clutch of the first gear shortly before stopping also leads, as a result of the resulting relief of load from the drivetrain, to a perceptible change in the longitudinal deceleration. If appropriate, downshifts are carried out even with an intermediate application of the throttle, and increase fuel consumption.
During driving at constant speed at very low speeds of for example 5 km/h-15 km/h, as typically occurs in stop-and-go operation, shifts lead to changes in speed and to uncomfortable longitudinal oscillations which the driver must compensate by throttle pedal corrections. Furthermore, jolt effects and/or acceleration effects caused by mass inertia effects, changes in torque and changes in transmission ratio can be perceived during the shifts. As a result of the rotational speed influence, both the engine torque and also the engine power are varied, as a result of which the driver is forced to correct the throttle pedal angle. Frequent upshifts and downshifts are undesirable on account of the low level of hysteresis (speed interval), and yet are likely.
It is accordingly an object of the invention to provide a method and a control unit for controlling a drivetrain which has a dual-clutch transmission which overcomes the above-mentioned disadvantages of the prior art methods and devices of this general type, by which the driving comfort under the stated conditions is improved.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for controlling a drivetrain of a motor vehicle having a dual-clutch transmission with a first partial transmission and a first clutch and with a second partial transmission and a second clutch. The method includes operating the drivetrain with a gear engaged in the first partial transmission and a further gear engaged in the second partial transmission at a same time; and operating the first clutch and the second clutch with slip at a same time. The first clutch and the second clutch are activated in a manner coordinated with one another such that a rotational speed of an internal combustion engine one of assumes a predetermined value and maintains the predetermined value.
Here, the first and the second clutch are each activated in a manner coordinated with one another in such a way that a rotational speed of the internal combustion engine assumes or maintains a predetermined value. In other words, instead of completely closing the one clutch in the present gear and completely opening the other clutch, the two clutches are operated with slip, preferably with regulated slip, in order to obtain a comfortable driving behavior.
By this features, it is achieved that, when driving slowly, the engine rotational speed, following a nominal rotational speed, smoothly aligns with a target rotational speed without pronounced local rotational speed minima and rotational speed maxima. When stopping, the target rotational speed may for example be the idle rotational speed. In contrast, in the case of a permanently closed clutch, as is conventional in the prior art, the engine rotational speed could, specifically when driving slowly in 1st and 2nd gear, fall below a target rotational speed. To prevent this, it is known to allow an upshift to take place later and to allow the downshift, for example into first gear, to take place earlier, which increases fuel consumption and is associated with losses in comfort. In contrast, the low engine rotational speeds of for example 700 rpm to 1200 rpm obtained with the invention help to reduce fuel consumption.
It is self-evident that the features specified above and the features yet to be explained below can be used not only in the respectively specified combination but also in other combinations or individually without departing from the scope of the present invention.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and a control unit for controlling a drivetrain which has a dual-clutch transmission, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now to the figures of the drawing in detail and first, particularly, to
The dual-clutch transmission 14 has a first partial transmission TG1 and a second partial transmission TG2. A torque flow between an input shaft 28 of the first partial transmission TG1 and a crankshaft 30 of the internal combustion engine 12 takes place via a first controllable clutch K1. A torque flow between an input shaft 32 of the second partial transmission TG2 and the crankshaft 30 of the internal combustion engine 12 takes place via a second controllable clutch K2. In one embodiment, the first partial transmission TG1 provides transmission stages (gears) with odd numbering, such as the first gear, the third gear and so on, while the second partial transmission TG2 provides the transmission stages (gears) with even numbering, such as the second gear, the fourth gear and so on.
Both a main shaft 34 of the first partial transmission TG1 and also a main shaft 36 of the second partial transmission TG2 is rotationally fixedly connected to the shaft 20. The shafts 34 and 36 therefore rotate at the same rotational speed which, when the motor vehicle is driving in a straight line without slip at the drive wheels 16, 18, is linearly dependent on the rotational speed of the drive wheels 16, 18 and therefore linearly dependent on the driving speed v of the vehicle. In the schematic illustration of
In the embodiment of
To control the drivetrain 10, the control unit 40 processes signals from a multiplicity of sensors which measure operating parameters of the drivetrain 10. Here, in connection with the invention, the following operating parameters are of particular significance: a throttle pedal angle Wped, which is provided by a driver demand transducer 42 and which represents a torque demand by the driver, a rotational speed nMot of the crankshaft 30 of the internal combustion engine 12, which rotational speed nMot is measured by a rotational speed sensor 43, and a vehicle speed v which is measured by a driving speed transducer 44. In one embodiment, the driving speed transducer 44 is realized as a rotational speed sensor which measures a rotational speed at the outlet of the dual-clutch transmission 14, that is to say a rotational speed of one of the shafts 34, 36 or 20. Alternatively or in addition, a rotational speed signal is measured at one or more of the wheels 16, 18, for example by the sensor arrangement of an anti-lock brake system.
With the knowledge of the transmission ratios set in each of the partial transmissions TG1 and TG2, the rotational speed nK1 of the input shaft 28 of the first partial transmission TG1 and the rotational speed nK2 of the input shaft 32 of the second partial transmission TG2 are each given by a linear function of the driving speed v.
As a function of the operating parameters of the drivetrain 10, and if appropriate as a function of further operating parameters, in particular as a function of operating parameters of the internal combustion engine 12, the control unit 40 forms actuating signals S_Mot, S_K1, S_K2, S_TG1 and S_TG2. Here, the actuating signal S_Mot serves to set a torque of the internal combustion engine 12. The actuating signal S_TG1 serves to engage a gear in the first partial transmission TG1 and therefore to set its transmission ratio. Similarly, the actuating signal S_TG2 serves to set a transmission ratio in the second partial transmission TG2. With the actuating signal S_K1, the torque flow via the first clutch K1 is controlled. Similarly, the torque flow via the second clutch K2 is controlled with the actuating signal S_K2.
The relationship of the actuating signals S_K1, S_K2 to the torque transmitted in each case via each of the two clutches K1, K2 at certain rotational speed differences is preferably stored in the control unit 40 in the form of characteristic curves or characteristic maps. This is prior art. The rotational speed differences are likewise known in the control unit 40 by evaluating the rotational speed values nMot and nK1, nK2. The engine torque is also known, the engine torque being calculated continuously by the control unit 40 from characteristic operating variables of the internal combustion engine 12, since modern engine controllers determine all actuating variables on the basis of torque demands which are calculated for example as a function of the throttle pedal angle Wped.
The control unit 40 determines, from the sign of the rotational speed difference at each of the clutches K1, K2, the direction of the torque being transmitted in each case, and from the actuation signal S_K1, S_K2 which is ultimately reproduced in the contact pressure of the clutch friction surfaces, the value of the torque being transmitted via each of the two clutches K1, K2.
The control unit 40 can therefore distribute the torque flow via the two clutches K1, K2 in a controlled manner, and thereby control the direction and magnitude of the resultant total torque flow, in order to set the engine rotational speed nMot to a nominal value, or nominal value profile over time or over the driving speed v, by coordinated activation of the two clutches K1, K2.
The control unit 40, or a corresponding combination of control units, is otherwise set up, in particular programmed, to carry out the method according to the invention, or one of its embodiments. Here, to carry out is to be understood to mean to control the method processes described here.
Until the time t0, the vehicle decelerates in the third gear with the clutch K1 closed. The clutch K2 is open. The engine rotational speed nMot corresponds there to the rotational speed nK1_Gang 3. In parallel, with the clutch K2 open, the second gear in the second partial transmission TG2 is engaged. Between the times t0 and t1, the first clutch K1 is opened to an increasing extent and the clutch K2 is closed to an increasing extent until, at the time t1, the clutch K1 is fully open and the clutch K2 is fully closed. The rotational speed nMot correspondingly rises while the clutches K1, K2 are slipping until the time t1, before then falling again during the further deceleration of the vehicle with the clutch K2 closed and the clutch K1 open.
With the clutch K1 open, after the time t1, the first gear in the first partial transmission TG1 is engaged. Between the times t2 and t3, the second clutch K2 is opened to an increasing extent and the first clutch K1 is closed to an increasing extent. As a result, the rotational speed nMot of the internal combustion engine 12 rises to a value predefined by the curve 47. The rotational speed nMot then falls again during the further deceleration of the vehicle, until the value of the idle rotational speed is reached at the time t4.
To prevent the rotational speed nMot falling below the idle rotational speed of the internal combustion engine, the clutch K1 is opened at the time t4. The rotational speed nMot is then held at a constant value by known idle rotational speed regulation. The change between local rotational speed minima and local rotational speed maxima which can be seen in the profile 48 before the time t4 are generated in that the rotational speed of the internal combustion engine 12 is raised between the times t0 and t1 and the times t2 and t3, in each case at the expense of the kinetic energy of the vehicle. The braking action of the internal combustion engine 12 therefore varies and incites the oscillations in the drivetrain 10, which are reproduced in undesired longitudinal oscillations of the vehicle. Similarly, the jolt as the clutch K1 is opened at the time t4 is a disturbance which can incite oscillations or which can be perceived as a jolt.
From the main program HP(B=0), a step 52 is repeatedly reached in which operating parameters BP of the drivetrain 10 are read in, which operating parameters BP are evaluated for an activation of the comfort-oriented control of the drivetrain proposed here. Details of the comfort-oriented control are explained in more detail further below with reference to
The evaluation is represented in
If the evaluation in step 54 yields that the comfort-oriented control should not be carried out, B is set to the value B=0. The response to the query in the subsequent step 56 is then negative, and the main program HP(B=0) in step 50 is then executed again. This means that the drivetrain 10 is controlled in the manner known from the prior art (
In contrast, if the evaluation in step 54 yields that a comfort-oriented control of the clutches K1, K2 should take place, B is set to the value B=1. In one embodiment B is set to 1 if the vehicle is travelling with a low torque demand from the driver, that is to say with a small pedal angle Wped and a low speed in a low gear, for example in first or second gear. In one embodiment, it is for this purpose checked whether the throttle pedal angle Wped is smaller than a lower threshold value Wped_low and at the same time both the engine rotational speed nMot is lower than a threshold value nMot_Grenz and the driving speed v is also lower than a threshold value v_Grenz. In a further embodiment, the threshold value nMot_Grenz and/or the threshold value v_Grenz is dependent on a modulation factor MF which represents the roadway inclination and which is provided for example by an inclination sensor:
B=1 if:
Typical values, to which the invention is not restricted, are:
If the conditions are met, the response to the query in the subsequent step 56 is positive and the program branches into the step 58 in which a modified main program HP(B=1) is executed to control the drivetrain 10 in a comfort-oriented manner.
From step 58, a step 60 is repeatedly reached in which operating parameters BP of the drivetrain 10 are read in, which operating parameters BP are evaluated for a deactivation of the comfort-oriented control of the drivetrain proposed here. The evaluation is represented in
In one embodiment, B is set to 0 in step 62 if the clutch K1 in the first gear or the clutch K2 in the second gear is no longer slipping, that is to say if there is no longer a difference between the engine rotational speed nMot and the rotational speed of the input shaft of the associated partial transmission, and at the same time the vehicle speed v exceeds a threshold value v_Grenz or lies above the threshold value. The threshold value is preferably lower than 20 km/h and, in one embodiment, is dependent on the modulation factor MF in such a way that a higher limit value is generated when the vehicle is travelling on a hill than when the vehicle is travelling on a flat road.
Alternatively, B is set to 0 if the torque demand Wped from the driver exceeds a threshold value Wped_Grenz_Zug and the clutch which is to be closed is no longer slipping. Here, too, one embodiment provides that the threshold value Wped_Grenz_Zug is dependent on the driving speed v and the modulation factor in such a way that the threshold value Wped_Grenz_Zug likewise increases with increasing values of v and/or MF. Without restricting the generality of the invention, values for Wped_Grenz_Zug preferably lie between 50% and 70% of the maximum pedal angle.
A further embodiment provides that B is set to 0 if the driver manually downshifts from the second gear into the first gear. The first clutch K1 is then closed. If the clutch K1 is no longer slipping, and the engine rotational speed nMot exceeds a threshold value nMot_Grenz (v, MF) which is possibly further increased by a hysteresis offset, B is set back from B=1 to B=0. Without restricting the generality of the invention, the hysteresis offset is of the order of magnitude of 50 rpm.
From the time t0, at which the threshold value nMot_Grenz is reached, the first clutch K1 is successively opened and the second clutch K2 is successively closed. In contrast to the prior art, the opening of the clutch K1 and the closing of the clutch K2 take place in a manner coordinated with one another, such that the engine rotational speed nMot, falling in a monotonous fashion, aligns with the idle rotational speed nLL of the internal combustion engine 12 as a target rotational speed. Here, the rotational speed nMot is set, alternatively or in addition to interventions into the control of the internal combustion engine 12, by coordinated control of the torque flows via the two clutches K1, K2. Up to the time t0, the clutch K2 was open and therefore transmitted no torque, while the clutch K1, as the vehicle decelerates in the overrun mode, transmits an overrun torque with which the internal combustion engine 12 is driven by the kinetic energy of the decelerating vehicle.
The gradual opening of the clutch K1 from the time t0 permits slip at the clutch K1. The gradual closure of the clutch K2 which takes place in parallel transfers the transmission of the overrun torque which is driving the internal combustion engine 12 to the clutch K2. As a result, after the time t0, the engine rotational speed nMot lies between values on the curve 68 of the second gear and the curve 66 of the third gear. The engine rotational speed nMot is too high for the third gear and too low for the second gear. Therefore the engine rotational speed nMot can be reduced by closing activation of the clutch K1 of the third gear and can be increased by closing activation of the clutch K2.
As a result of closing activation of in each case one of the two clutches K1, K2, the rotational speed nMot can thereby be increased or reduced. Here, in one embodiment, the activation preferably takes place in a regulated fashion. For this purpose, the actual value of the engine rotational speed nMot is compared with a nominal value, and from the regulating error, actuating variables S_K1 and S_K2 are formed, with which the torque transmission via the clutches K1 and K2 is individually controlled.
In
At the time t2, the rotational speed nMot crosses the curve 68. At this time, the briefly-closed clutch K2 temporarily transmits all of the overrun torque, while the clutch K1 is temporarily fully opened. When the clutch K1 is open, the first gear is engaged. From now on, a closure of the clutch K1 has the effect of increasing nMot and holding the clutch K2 closed has the effect of reducing nMot. Similarly to the process between the times t0 and t2, the engine rotational speed nMot is subsequently aligned, in a monotonously falling fashion, with the target rotational speed by corresponding activation of the clutches K1, K2.
The target rotational speed in the form of the idle rotational speed nLL is reached at the time t4 by virtue of the curve 70 intersecting the value of the target rotational speed. To prevent the engine rotational speed nMot falling below the target rotational speed, not only the second clutch K2 but also the first clutch K1 is increasingly opened as the point of intersection 76 is approached.
When the speed v1 is reached, the rotational speed nMot corresponds to the rotational speed nK1_Gang 1 of the input shaft 28 of the first partial transmission TG1. In the desired profile, which is dependent on the vehicle speed v, of the engine rotational speed nMot, the first clutch K1 can no longer transmit traction torques with the first gear engaged for speeds of v>v1. The first clutch K1 can instead only transmit overrun torques. The clutch K2, in contrast, initially continues to transmit a traction torque. Similarly to stopping, the two clutches K1, K2 are initially operated with continued slip with increasing speed v, and at speeds of v>v1, the rotational speed nMot of the internal combustion engine 12 is set to a nominal value by suitable activation of the clutches K1, K2 with gears simultaneously engaged in both partial transmissions TG1, TG2. The setting preferably takes place by regulation.
In the speed range v1<v<v2, in the illustrated profile of nMot, the clutch K1 transmits an overrun torque while the clutch K2 transmits a traction torque. In the speed range v2<v<v3, in the illustrated profile of nMot, the clutch K1 transmits a traction torque while the clutch K2 transmits an overrun torque. If the traction torque prevails, the rotational speed nMot decreases. If the overrun torque prevails, the rotational speed nMot increases. When the speed v3 is reached, the engine rotational speed nMot corresponds to the rotational speed nK1_Gang3 of the input shaft 28 of the first partial transmission TG1, such that there is no rotational speed difference at the clutch K1. In the illustrated embodiment, at this time, the clutch K1 is activated in such a way that it is fully opened. Here, the complete opening of one clutch need not coincide precisely with the complete closure of the other clutch. It is essential merely that, when gears are simultaneously engaged in both partial transmissions TG1, TG2, at least one of the two clutches K1, K2 is operated with slip in order that the dual-clutch transmission 14 does not lock.
From the speed v3, which in the illustration of
The smooth nMot profiles 64 in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 006 194.8 | Jan 2008 | DE | national |
