WO2022017561A1

WO2022017561A1 - Method for controlling a drivetrain

Info

Publication number: WO2022017561A1
Application number: PCT/DE2021/100585
Authority: WO
Inventors: Frederic Pfister; Marc Rambert
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2020-07-22
Filing date: 2021-07-06
Publication date: 2022-01-27
Also published as: DE102021117344A1; CN116194692A

Abstract

The invention relates to a method for controlling a wheel drive of a motor vehicle, having an electric motor, having an at least two-speed planetary transmission connected downstream of said electric motor, and having at least one drive wheel connected downstream of the planetary transmission, wherein gears of the planetary transmission are shifted by means of two hydrostatically operated friction clutches which immobilize a respective component of the planetary transmission so as to be static relative to a housing. In order to be able to shift gears in the planetary transmission synchronously and without NVH influences on the occupants of the motor vehicle, the friction clutches are each operated by means of a hydraulic unit (200) with a pressure supply device (201), with a slave cylinder (206) which acts on the friction clutch counter to the action of a spring element (209), with a pressure relief valve (201) arranged in a pressure line (205) between the pressure supply device (201) and the slave cylinder (206), and with a pressure sensor (211) arranged in the pressure line (205) between the pressure relief valve (204) and the slave cylinder (206), and a biting and release point (TP, AP) of the friction clutches are each determined in the course of a pressure change which changes owing to the operation of the pressure relief valve (204) and which is detected by the pressure sensor (211) while the motor vehicle is at a standstill.

Description

Process for controlling a power train

The invention relates to a method according to the preamble of claim 1 . Wheel drives in which a drive unit, for example an electric motor drives a drive wheel of a motor vehicle with the interposition of a switchable gear such as a planetary gear, are known, for example, from the publications DD 278 307 A and EP 2 597 336 B1. For example, to switch a planetary gear, components of the planetary gear such as ring gear and/or carrier are fixed to the housing by means of a brake band, so that different translations can be switched from the different translations with and without a rotating ring gear or carrier. The brake band can be actuated in different ways by means of electric or hydraulic actuators, for example by means of hydrostatically actuated friction clutches. Such planetary gears are controlled by a control unit which controls the corresponding actuators.

The object of the invention is the further development of a method for controlling a wheel drive of a motor vehicle. In particular, the object of the invention is to precisely control friction clutches and to adapt them neutrally for the vehicle occupants with regard to vibrations and noise.

The object is solved by the subject matter of claim 1. The claims dependent on claim 1 provide advantageous embodiments of the subject-matter of claim 1.

The proposed method is used to control a wheel drive arranged, for example, on two or all drive wheels of a motor vehicle wise wheel drives. For this purpose, a central and/or several decentralized control units are provided, which control a drive unit and a gear each of a wheel drive. It goes without saying that a wheel drive controlled by the method is also covered by the inventive concept and can be claimed as an additional subject matter if necessary.

The respective wheel drive contains a drive unit, preferably an electric motor. The electric motor can be provided in a driving or recuperative manner. An at least two-speed planetary gear is connected downstream of the electric motor or its rotor. The planetary gear is designed at least in one stage, preferably in two stages. As components of the planetary gear, at least one sun gear, a ring gear and at least one web with rotatable and distributed over the circumference arranged planetary gears are provided. The planet gears are each meshed with a sun gear and the associated ring gear. Depending on how the components are interconnected, one component of the planetary gear, for example a sun wheel of a first stage, serves as the drive and is firmly connected to the rotor. For example, two webs of different stages can be connected to the output, so that without reversing the direction of rotation, both a ring gear and a web can be connected to the housing, preferably in an intersecting manner and in opposite directions, in order to set two different transmission ratios between input and output. In each case two of the components can be fixed to the housing of the planetary gear for switching the planetary gear, that is to say they can be connected to the housing.

Serve for this purpose hydrostatically actuated friction clutches, which are arranged between the housing and the corresponding component so that they can be effectively switched. For example, the ring gear can be connected to the housing by means of a first friction clutch and the web can be connected to the housing by means of a second friction clutch. the friction Couplings are designed, for example, as forcibly closed friction clutches, that is, the friction clutches are closed under hydrostatic pressure and are thus connected to the housing. In the non-actuated state of the friction clutches, the ring gear or web are arranged such that they can rotate relative to the housing. To achieve a large translation, the friction clutches are alternately closed and opened. When the planetary gear is shifted, the friction clutches are actuated in an overlapping manner, ie one friction clutch is opened and the other friction clutch is closed.

The hydrostatic actuation of the friction clutches takes place by means of a hydraulic unit controlled by a control unit. The hydraulic unit contains a pressure supply device, for example an electrically operated pump. Both Hy draulic units of the two friction clutches can be fed from a common pressure supply device. The hydraulic unit contains a slave cylinder which actuates the friction clutch and is connected to the pressure supply device by means of a pressure line. Under pressure, the slave cylinder is shifted axially against the action of a spring element, for example a return spring. If the pressure is released from the slave cylinder, the slave cylinder piston, which is prestressed by the spring element, moves to its rest position and the frictional engagement of the friction clutch is released. To control the pressure in the slave cylinder, a pressure valve controlled by the control unit, for example electromagnetically actuated, is installed in the pressure line between the pressure supply device and the slave cylinder. relief valve switched. The pressure relief valve connects the slave cylinder in a first switching position with the pressure supply device. In a second switching position, the slave cylinder is connected to an unpressurized sump.

The pressure relief valve is preferably actively switched from the second switch position to the first switch position, contrary to a return spring.

Exact knowledge of the contact points of the friction clutch, i.e. the exact switching pressure or filling level of the slave cylinder, is required to engage the planetary gear using friction clutches that are precisely matched to one another. It has been shown here that due to the system hysteresis, the touch point at which the friction clutch begins to transmit torque and a detachment point at which the friction clutch begins to no longer transmit torque fall apart, so that according to the invention both pressure points, namely the touch and the detachment point can be continuously determined and adapted.

The touch and release point of the friction clutches are preferably determined in the course of a change due to the actuation of the pressure relief valve while the motor vehicle is stationary using a pressure change detected by a pressure sensor arranged in the pressure line behind the pressure relief valve. The touch and release point is adapted when the motor vehicle is stationary, ie when the wheels are stationary, so that the influence of this is excluded. The method can be carried out essentially without vibrations and noise for the occupants.

In this case, the contact point is advantageously determined at a first pressure value with the pressure of a slave cylinder piston of the slave cylinder changing significantly from a lower gradient to a greater gradient when the slave cylinder is currently connected to the pressure supply device by means of the pressure relief valve. placed. This means that the contact point is determined when the friction clutch closes after the pressure relief valve has closed.

The detachment point is defined at a second pressure value with the pressure of a slave cylinder piston of the slave cylinder changing significantly from a higher slope to a lower slope when the pressure relief of the slave cylinder is currently switched by means of the pressure relief valve. The release point is determined with the friction clutch opening after the pressure relief valve has been opened.

The contact and release points of the two friction clutches are each determined separately after switching on the pressure reducing valve by the pressure changes in the pressure line being recorded by the pressure sensor over time and evaluated. The individual pressure values are preferably recorded and evaluated at fixed time intervals, for example interrupts of the recording and evaluating control unit.

For example, the pressure values are allocated during a determination of the contact or detachment point, for example at each interrupt, in a clocked manner in a FIFO data register with a fixed number of storage locations. The pressure values are gradually read in serially and shifted on, with the sum of the pressure values of the register being determined at each time cycle. The totals are each compared with a predetermined total value of the contact or separation point and the pressure value that is essential for the contact or separation point is determined for a predetermined total value.

The pressure values located at the storage locations can each be loaded with a coefficient that is specifically predetermined for the storage location. For example, a data value located in the register at a centrally arranged memory location can have the smallest coefficient in terms of magnitude and the an Pressure values located in both chronological directions from this spaced memory locations can be subjected to increasing coefficients in terms of amount. This serial determination of cumulative values makes it possible to determine breakpoints in the pressure behavior at the touch point or at the detachment point, at which compression of the disks and counter-disks of the friction clutches begins at the touch point and is released at the detachment point. This results in a steep rise in pressure at the contact point during the filling of the slave cylinder after a flat increase in bridging an idle travel of the slave cylinder piston when the contact point is reached at this break point, with a beginning transmission of torque to the friction clutch and a fixing of the relevant component of the planetary gear on its housing with a corresponding circuit. At the detachment point, while the slave cylinder is being emptied, there is a steep drop in pressure until the lamellae and counter lamellae separate, with the torque applied to them dissipating with a release of the relevant component from the housing and at the break point of the detachment point, the transition to the idle travel of the Slave cylinder piston with a flat slope of the pressure drop.

The invention is explained in more detail with reference to the game shown in Figures 1 to 4 Ausführungsbei. These show:

Figure 1 shows a crossover shift of a planetary gear by means of two pressurized slave cylinders over time,

FIG. 2 shows a schematically illustrated hydraulic unit for actuating one of the two friction clutches,

FIG. 3 Pressure curves of the pressurized slave cylinders to determine the touch and release points of the friction clutches and

FIG. 4 shows an evaluation scheme for determining the tactile and detachment points by means of FIR.

FIG. 1 shows the schematically illustrated diagram 100 of the rotational speed n of an output of a planetary gear or of the pressure p acting on two slave cylinders, each of which actuates a friction clutch, over time t. Ge shows an overlap circuit of the two friction clutches for the control of a planetary gear, in that one friction clutch com- ponents of the planetary gear—here a floating wheel and a carrier—is alternately connected to the housing. The overlapping shift takes place from fast to slow with the speed n(1) present at the output of the planetary gearbox at the beginning of the overlapping shift and the speed n(2) present after the overlapping shift. The curve 101 shows the course of the speed n over time t during the overlap shift. Curve 102 shows the progression of pressure p(K1) of the slave cylinder actuating the first friction clutch and curve 103 shows pressure p(K2) of the slave cylinder actuating the second friction clutch over time t during the overlapping shift.

At the start of the overlapping shift, the first friction clutch is closed by the pressure value p(K1,1) applied, which means that the component actuated by this friction clutch, for example the ring gear, is braked firmly in the housing. There is no pressure on the slave cylinder of the second friction clutch, so that it is open and the web transfers the applied torque to the output. After the initiation of the overlap shift by a responsible Steuerein unit, the slave cylinder of the first friction clutch is relieved of pressure and the slave cylinder of the second friction clutch is pressurized by appropriate switching on of pressure relief valves.

After a short reaction time after opening the pressure relief valve, the curve 102 shows the steeply falling branch 104 until the preload on the disk pack of disks and counter disks of the first friction clutch is reduced at the release point AP and no more torque is transmitted via the first friction clutch. As time t increases, the slave cylinder piston is displaced along the flat branch 105 by means of the spring element acting on it, up to the end position. The position of the detachment point is determined by evaluating the two gradients of the branches 104, 105.

The curve 103 shows a slowly increasing pressure along the branch 106 on the slave cylinder of the second friction clutch after a short reaction time after the pressure relief valve has been closed. When contact point TP is reached, the lamellae and counter lamellae of the lamellar set of the second friction clutch come into contact and are preloaded. This results in the steep rise in pressure in branch 107 until the second friction clutch is fully engaged. The touch point TP is determined by evaluating the slopes of the branches 106, 107.

In the period At between the time t(2) of the detachment point AP and the time t(1) of the contact point TP, the torque transmitted to the output is slackened. In order to be able to shift the planetary gear exactly, the contact point TP and the release point AP are continuously determined and adapted according to FIGS. FIG. 2 shows schematically the hydraulic unit 200 for one of the two friction clutches. A hydraulic unit 200 is provided for each of the friction clutches. hen. The hydraulic unit 200 contains the pressure supply device 201, which is designed here as a pump 203 driven by the electric motor 202. The pressure supply device 201 can be available to both hydraulic units of the friction clutch.

The pressure relief valve 204 is arranged in the pressure line 205 between the pressure supply device 201 and the slave cylinder 206 and switches between the slave cylinder 206 on the one hand and on the other hand optionally between the pressure supply device 201 and the unpressurized sump 207, so that the slave cylinder 206 is pressurized or relieved of pressure can be.

The slave cylinder piston 208 is displaced under pressure against the action of the spring element 209 and, after overcoming the idle travel As, prestresses the lamellar pack 210 of the friction clutch.

If the pressure relief valve 204 shown here open is closed, first the slave cylinder 206 is filled and the slave cylinder piston 208 is displaced against the action of the spring element 209 to the touch point TP, the pressure in the pressure line 205 increases slowly but steadily. When the slave cylinder piston 208 or a component connected to it reaches the disk set 210 at the contact point TP, the pressure in the pressure line increases with a steeper gradient, since the disk set 210 is prestressed. The friction clutch begins to transmit torque at touch point TP by means of the beginning frictional contact between the disks and counter disks of disk set 210, so that the transition between the pressure with a small gradient and the pressure with a large gradient can be assigned the pressure value at the touch point.

The pressure sensor 211 is provided for detecting the pressure in the pressure line 205 . The detachment point of the friction clutch is determined in a similar manner after the pressure relief valve 204 opens, by evaluating the steeply falling pressure up to the detachment of the disks and counter-disks of the disk set 210 and the pressure dropping with a slight incline when the spring element 209 is relieved.

The friction clutch is designed according to the normally open principle. This means that the friction clutch is opened when there is no pressure in the pressure line 205 and is closed under pressure. This means that the component of the planetary gear set assigned to this friction clutch is connected to the housing under pressure.

With reference to the hydraulic unit 200 of Figure 2, Figure 3 shows the diagram 300 with the pressure p over the travel s of the slave cylinder piston 208 after a switching of the pressure relief valve 204. Here, the curve 301 shows the pressure behavior of the pressure line 205 when the pressure relief valve 204 is currently closed with the branch 302 rising with a slight incline and the branch 303 rising steeply after the touch point TP.

The curve 304 shows the pressure behavior of the pressure line 205 shortly after the opening of the pressure relief valve 204 with the steep branch 305 up to the separation point AP and the branch 306 with a lower gradient until the pressure line is completely depressurized.

The touch point TP is determined in the direction of the increasing travel s of the slave cylinder piston 208 by register 307 with five memory locations c4, c3, c2, c1, cO according to the FIFO principle (first-in-first-out) with pressure values in Time intervals of interrupts of the control unit filled and according to the principle of a filter with a finite impulse response (FIR; finite impulse response filter) is evaluated. In the same The detachment point AP is determined in the direction of the decreasing path s of the slave cylinder piston 208 by means of the register 308. The touch point TP or separation point AP is recognized when the value resulting from the FIR filter corresponds to a calibrated value. The corresponding pressure value is then assigned to touch point TP or release value AP.

The pressure hysteresis of the hydraulic unit 200 can be determined from the pressure difference Dr between the curves 301 and 304 or the branches 302, 306 with the contact point TP and the separation point AP.

FIG. 4 shows the principle of the FIR filter for determining the touch point TP of FIG. 3, for example. The coefficients k4, k3, k2, k1, k0 with the values -6, -3, 0, 3, 6 are assigned to the pressure values briefly stored at the memory locations c4, c3, c2, c1, c0 of the FIFO register 307 . The sum is formed from the pressure values p(cn) of the storage locations c4, c3, c2, c1, c0 according to the given formula. If this sum corresponds to a calibrated value, the pressure value p(C2) is accepted as the pressure value for the contact point TP.

Reference List

100 chart

101 curve

102 curve

103 curve

104 branch

105 branch

106 branch

107 Ast 00 Hydraulic unit 01 Pressure supply device

202 electric motor

203 pump

204 pressure relief valve

205 pressure line

206 slave cylinder

207 swamp

208 slave cylinder piston

209 spring element

210 plate pack

211 pressure sensor

300 diagram

301 curve

302 ast

303 Ast

304 curve

305 branch

306 branch

307 registers

308 registers

AP detachment point co storage space c1 memory location c2 memory location c3 memory location c4 memory location kO coefficient k1 coefficient k2 coefficient k3 coefficient k4 coefficient n speed ⁿ (1 ) speed ⁿ (2) speed

P pressure

P(cn) pressure value

P(K1) pressure p(K1,1) pressure value

P(K2) pressure s path

TP touch point t time t(1) time t(2) time

Dr pressure difference

As empty path

At period

Claims

patent claims

1. A method for controlling a wheel drive of a motor vehicle with an electric motor, an at least two-speed planetary gear set downstream of this and at least one drive wheel connected downstream of the planetary gear set, with gears of the planetary set being switched by means of two hydrostatically actuated friction clutches each fixing a component of the planetary set to the housing characterized in that the friction clutches are each operated by means of a hydraulic unit (200) controlled by a control unit, with a pressure supply device (201), with a slave cylinder (206) which applies the friction clutch against the action of a spring element (209), with a pressure line in a pressure line (205) between the pressure supply device (201) and the slave cylinder (206) arranged pressure relief valve (204) and between the pressure relief valve (204) and the slave cylinder (206) arranged in the pressure line pressure sensor or (211) and a touch and release point (TP, AP) of the friction clutches in the course of a change due to the actuation of the pressure relief valve (204) while the motor vehicle is stationary based on a pressure sensor (211) detected Pressure change can be determined.

2. The method according to claim 1, characterized in that the touch point (TP) at a first pressure value with a pressure of a slave cylinder piston (208) of the slave cylinder (206) that changes significantly from a lower to a greater slope at currently by means of the pressure relief valve ( 204) is fixed to the slave cylinder (206) connected to the pressure supply device (201).

3. The method according to claim 1 or 2, characterized in that the detachment point (AP) at a second pressure value with the pressure of a slave cylinder piston (208) of the slave cylinder (206) changing significantly from a higher to a lower slope at currently by means of the pressure relief valve (204) switched pressure relief of the slave cylinder (206) is fixed.

4. The method according to any one of claims 1 to 3, characterized in that after the pressure-reducing valve (204) has been switched on, the pressure changes are recorded and evaluated over time.

5. The method according to claim 4, characterized in that during a determination of the contact or detachment point (TP, AP), pressure values are clocked in a register (307, 308) according to the FIFO principle with a fixed number of storage locations (cO, c1, c2, c3, c4) are read in and shifted on, with the sum of the pressure values of the register (307, 308) being determined at each time cycle and a pressure value essential for the touch or release point (TP, AP) being determined for a predetermined sum value will.

6. The method as claimed in claim 5, characterized in that the pressure values located at the storage locations (c0, c1, c2, c3, c4) are each provided with a coefficient ( kO, k1, k2, k3, k4) are applied.

7. The method according to claim 6, characterized in that for a data value located in the register (307, 308) at a centrally arranged memory location (c2) with the smallest coefficient (k2) in terms of amount and at a distance from this in both temporal directions Pressure values located in storage locations are charged with the amount according to increasing coefficients (k0, k1, k3, k4).

8. The method according to any one of claims 1 to 7, characterized in that the friction clutches are closed when pressure is applied and the associated component of the planetary gear is connected to the housing.

9. The method according to any one of claims 1 to 8, characterized in that the friction clutches are actuated with overlapping torque.

10. The method according to any one of claims 1 to 9, characterized in that the two friction clutches are operated by means of a common pressure supply device (201), preferably an electrically operated pump (203).