Control unit for a transmission and corresponding operating method

The invention relates to a control unit for setting the transmission ratio of a transmission arranged together with a motor in a drive train according to the preamble of claim 1 and a method for operating such a control unit according to claim 9.

It is, for example, from the German patent application <patcit id="pcit0001" dnum="DE4230101A1"><text>DE 42 30 101 A1</text></patcit> Known to generate a predetermined braking torque in a motor vehicle on the one hand by the braking torque of a service brake and on the other hand by the braking torque (drag torque) of the engine, whereby the service brake is relieved, which is particularly advantageous in the case of long-lasting braking operations, since otherwise there is a risk that the service brake is overheated and therefore loses its optimal braking effect.

From the German published application <patcit id="pcit0002" dnum="DE4330391A1"><text>DE 43 30 391 A1</text></patcit> a control unit for a drive train of a motor vehicle is also known, in which a desired braking effect is determined from the actuation of the brake pedal, which in turn leads to a downshifting of the automatic transmission in order to increase the braking effect of the engine. This takes advantage of the fact that the braking effect of the engine increases with increasing speed, so that the braking effect at a given speed is greater in a small gear than in a larger gear.

A disadvantage of the known arrangements described above, however, is the fact that the braking torque of the motor increases with the speed, so that relatively high speeds are required to achieve a good braking effect of the motor, which is disturbing with regard to noise, wear and tear and comfort.

From the publication <patcit id="pcit0003" dnum="EP0800949A"><text>EP 0 800 949 A23 </text></patcit>a generic control unit for a transmission arranged with a motor and an electrical generator in a drive train is known, the generator feeding a battery. In the event of a braking request, depending on the state of charge of the battery, either an operating mode "regenerative braking" or an operating mode "engine braking" is selected.

The invention is therefore based on the object of providing an arrangement which, in addition to the service brake and the engine braking torque, generates an additional braking torque even at relatively low speeds. Furthermore, the invention has for its object to provide an operating method for such an arrangement.

Starting from the known control unit according to the preamble of claim 1, the invention is solved by the characterizing features of claim 1 or - with regard to the operating method - by the features of claim 9.

The invention encompasses the general technical teaching of utilizing the braking torque generated by an electric generator arranged in the drive train, it being advantageous that the braking torque of an electric generator is maximum at a given electrical power at low speeds. The efficiency of the generator is also better under these conditions.

The electrical generator is preferably an integrated starter generator (ISG) which supplies the electrical system of the motor vehicle with power when the vehicle is in motion and can be used to start the engine when the engine is not running. However, the term generator is to be understood here in general and in the following and can include all units which are coupled to the drive train and can generate a braking torque from the rotating drive train.

When utilizing the braking effect of an electrical generator to relieve the service brake, it should be noted that the braking torque generated by the generator not only depends on the speed in the manner described above, but also on the electrical voltage or the state of charge of the battery fed by the generator depends. On the one hand, the braking torque generated by the generator is lower at low battery voltage than at nominal voltage, which is particularly noticeable at low speeds between 1000 and 3000 revolutions per minute. On the other hand, with a fully charged battery, the generator cannot reload any further energy into the battery, so that the generator may not be operated as a generator in this state of the battery.

The braking torque generated to relieve the service brake is therefore composed on the one hand of the braking torque of the engine and on the other hand of the braking torque of the generator, the sum of these two braking torques also being speed-dependent and initially decreasing with increasing speed, so that a good one is achieved Braking effect low speeds must be aimed for as long as the battery is not fully charged and the generator can therefore contribute to the braking effect. If, on the other hand, the battery is fully charged, the generator must not be operated as a generator and consequently cannot contribute to the braking effect, so that the braking torque relieving the service brake is generated exclusively by the engine. In this case, however, higher speeds should be aimed for in order to achieve a good braking effect, since the braking torque generated by the motor alone increases with the speed when viewed.

The control unit according to the invention therefore detects the state of charge of the battery by means of a measuring unit and adjusts the transmission ratio of a transmission arranged in the drive train as a function of the state of charge of the battery in such a way that the best possible recuperative braking effect is achieved.

This means that in an automatic transmission, the downshift points are at lower speeds in order to keep the speed in a low range for as long as possible, in which the generator has a good braking effect.

In a variant of the invention, the generator is connected on the output side to the battery via a controllable switching element in order to separate the generator from the battery when the battery is fully charged. This is advantageous for protecting the battery, since the generator cannot feed electrical energy into the battery when the battery is fully charged and therefore must not be operated as a generator. The term switching element is to be understood generally here and includes, for example, discrete switching elements such as relays or power semiconductors.

In a further variant of the invention, the switching element connects the generator either to the battery or to a load resistor arrangement (for example electrical auxiliary heating, rear window heating), in order to enable generator operation of the generator even when the battery is fully charged.

According to a variant of the invention, a further clutch is arranged in the drive train between the generator and the engine, which makes it possible to lower the speed of the generator, for example, below the idling speed of the engine, as a result of which the braking torque of the generator can be maximized.

In a variant of the invention, it is also provided that the engine is switched off during a braking operation in order to save fuel and avoid emissions. However, this means that the engine must be started quickly after the braking process has ended. In a variant of the invention, the generator is therefore preferably provided on the output side with highly dynamic electrical energy stores (for example Supercaps), from which the electrical energy for quick engine start can be taken after braking.

Other advantageous variants of the invention are described in the subclaims or are explained in connection with the following description of the preferred exemplary embodiment of the invention with reference to the drawings. Show it:<dl id="dl0001" compact="compact"><dt>Figure 1</dt><dd>the drive train of a motor vehicle and auxiliary systems and the control unit according to the invention,</dd><dt>Figure 2</dt><dd>the control unit according to the invention as a block diagram,</dd><dt>Figure 3</dt><dd>the calculation unit contained in the control unit according to the invention for calculating the switch-back points of the automatic transmission,</dd><dt>Figure 4</dt><dd>the downshift speed as a function of the desired braking torque as well</dd><dt>Figure 5</dt><dd>a flowchart of the operating method according to the invention.</dd></dl>

In the <figref idref="f0001">Figure 1</figref> The arrangement shown shows a drive train of a motor vehicle which is driven by an internal combustion engine 1, the internal combustion engine 1 being constructed conventionally and therefore being shown only schematically.

The internal combustion engine 1 is controlled by an electronic engine control (EMS) 2, which receives, among other things, the position of an accelerator pedal 3 as an input signal.

On the output side, the internal combustion engine 1 is connected via a shaft to a clutch 4, which makes it possible to separate the internal combustion engine 1 from the drive train. This enables the speed of rotation of an integrated starter generator (ISG) 5 arranged in the drive train to be decoupled, as a result of which the braking effect of the starter generator (ISG) 5 is improved.

In the closed state, however, the clutch 4 connects the internal combustion engine 1 to the integrated starter generator (ISG) 5, which works as a generator when driving and charges an electric battery 6. When the engine is at a standstill, on the other hand, the integrated starter generator 5 can be used to start the internal combustion engine 1.

Furthermore, a clutch 7 for a torque converter 8 is arranged in the drive train, wherein the clutch 7 can be designed, for example, as a wet or dry clutch. The clutch 7 and the torque converter 8 are controlled by an electronic transmission control (EGS) 9, the electronic transmission control 9 being able to set five different transmission ratios ü of the torque converter 8. Switching between the individual gears according to the different gear ratios is carried out automatically by the electronic transmission control (EGS) 9 by appropriately actuating the clutch 7 and the torque converter 8. As an alternative to the gearbox shown with fixed gear steps, a gearbox with continuously adjustable gear ratio can also be used become.

Furthermore, a speed sensor 10 is arranged in the drive train, which continuously measures the current speed n of the drive train and provides it for signal processing purposes, as will be described in detail.

Finally, the drive train is connected to a wheel 11 of the motor vehicle, a brake actuator 12 being arranged on the wheel 11, which enables the wheel 11 to be braked. The brake actuator 12 can, for example, be a component of a piston brake or a disc brake and is controlled by a brake control system (BSS) 13, the brake control system (BSS) 13 having the desired braking torque M_Brake receives the service brake from a control unit 14. In the context of the invention, the brake system can be designed either as a conventional hydraulic brake system or as an electronic brake system ("Brage by Wire").

The desired total braking torque M_should is determined by an evaluation unit 15 as a function of the actuation of a brake pedal 16, taking into account, for example, the pedal position, the pedal force, the duration of the pedal actuation and the speed of the pedal actuation. The desired braking torque M_should is made up of the braking torque M according to the following formula_v the internal combustion engine, the braking torque M_ISG of the integrated starter generator (ISG) 5, the braking torque M_Brake the service brake and the gear ratio ü together: <maths id="math0001" num=""><math display="block"><msub><mi mathvariant="italic">M</mi><mi mathvariant="italic">should</mi></msub><mo mathvariant="italic">=</mo><msub><mi mathvariant="italic">M</mi><mi mathvariant="italic">Brake</mi></msub><mo>+</mo><msub><mi>M</mi><mi mathvariant="italic">ISG</mi></msub><mo>⋅</mo><mover><mi>u</mi><mo>¨</mo></mover><mo>+</mo><msub><mi>M</mi><mi>V</mi></msub><mo>⋅</mo><mover><mi>u</mi><mo>¨</mo></mover></math><img file="EP1301366B1_D0001.tif" /></maths>

The control unit 14 therefore first calculates the braking torque M._v the internal combustion engine 1 and the maximum possible braking torque M_ISG of the integrated starter generator (ISG) 5, around the brake actuator 12 for generating the remaining braking torque M_Brake to control, as in the detailed representation of the control unit 14 in <figref idref="f0002">Figure 2</figref> is shown.

For this purpose, the control unit 14 has a characteristic element 17 which has the current speed n on the input side_Is receives from the speed sensor 10 and from it according to a predetermined functional relationship M_v= f₁ (n_IS) the braking torque M_v the internal combustion engine 1 calculated.

In addition, the control unit 14 has a second characteristic element 18, which is connected on the input side to the speed sensor 10 on the one hand and to a calculation unit 34 on the other side, the calculation unit 34 being connected on the input side to the battery 6 and from the battery voltage U_B determines the state of charge SOC of the battery 6. The characteristic curve element 18 determines M from a predetermined characteristic curve field_ISG= f₂(SOC, n_IS) depending on the state of charge SOC of the battery and the speed n_IS the braking torque of the integrated starter generator (ISG) 5 is calculated. The braking torques M determined in this way_v and M_ISG are fed to an adder 19 which calculates the braking torque which enables the service brake to be relieved and is connected on the output side to a subtractor 20 which is derived from the predetermined total braking torque M_should and the sum of the braking torques of the integrated starter generator (ISG) 5 and the internal combustion engine 1, taking into account the gear ratio ü, the required braking torque M_Brake the service brake calculated and forwarded to the brake control system (BSS) 13.

In addition, the control unit 14 has a comparator unit 21, which is connected on the input side to the speed sensor 10 and the current speed n_IS continuously with specified downshift speeds n₅₄, n₄₃, n₃₂, n₂₁ compares in order to control the electronic transmission control (EGS) 9 when a downshift speed is reached so that the torque converter 8 shifts down a gear. The current speed drops n_Is during braking, for example, down to the downshift speed n₅₄, the torque converter 8 shifts from fifth to fourth gear. The downshift speeds are calculated dynamically as a function of the state of charge of the battery 6 by a calculation unit 22, which is detailed in FIG<figref idref="f0003">Figure 3</figref> is shown.

To detect the state of charge of the battery 6, the calculation unit 22 first has a characteristic element 23 which is connected on the input side to the state of charge calculation unit 34, which on the output side generates a signal SOC representing the state of charge of the battery 6. A multiplicative factor then appears at the output of the characteristic element 23, which is subsequently limited to a maximum value in a limiter 23.

To calculate the four downshift speeds n₅₄, n₄₃, n₃₂, n₂₁ the calculation unit 22 has four essentially matching assemblies, so that in <figref idref="f0003">Figure 3</figref> the same reference numerals are used for matching components and only one of the matching modules is described below.

Each of the corresponding assemblies has two characteristic elements 25, 26, which have the desired total braking torque M on the input side_should record and the respective switching speed n_{i, i-1} determine regardless of the current state of charge of the battery 6. The characteristic curves stored in the characteristic curve members 25, 26 are shown by way of example in FIG. 6, the right characteristic curve in FIG. 6 representing the switching speed without the involvement of the integrated starter generator (ISG) 5 (ie with SOC = max.), Whereas the left characteristic curve represents the switching speed with optimum participation of the integrated starter generator (ISG) (ie with SOC = min.). Depending on the current state of charge of the battery 6, the actual switching speed lies between the two characteristic curves shown in FIG. 6. The shift speeds calculated by the two characteristic curve members 25 and 26 thus represent extreme values ​​and limit the bandwidth within which the shift speed actually lies. The characteristic elements 25, 26 are therefore connected on the output side to a subtractor 27, which calculates the bandwidth Δn within which the switching speed lies. The output signal of the subtractor 27 is fed to a multiplier 28 which multiplies the bandwidth Δn by the signal which is dependent on the state of charge of the battery 6. The product produced in this way is in turn fed to a subtractor 29, which is connected on the input side to the characteristic element 26 and therefore absorbs the switching speed resulting from the predetermined braking torque M_Should without considering the braking effect of the integrated starter generator (ISG) 5. The output signal of the multiplier 28 is then subtracted from this “static” switching speed, so that the actual switching speeds are reduced compared to the “static” switching speeds without taking into account the integrated starter generator (ISG) 5. If the battery 6 is completely discharged, for example, the output signal of the limiter 24 assumes the value 1. Correspondingly, the multiplier 28 completely forwards the speed bandwidth Δn to the subtractor 29, so that the switching speed results from the characteristic curve shown on the left in FIG. 6. If, on the other hand, the battery 6 is fully charged, the output signal of the limiter 24 assumes the value zero, so that the switching speed appearing at the output of the subtractor 29 results from the characteristic curve shown on the right in FIG.

In addition, the in <figref idref="f0001">Figure 1</figref> Arrangement shown on a controllable switching element 30, which connects the integrated starter-generator (ISG) 5 either with the battery 6 or with a load resistor arrangement 31. This enables generator operation of the integrated starter generator (ISG) 5 even when the battery 6 is already fully charged and therefore can no longer absorb electrical energy. The switching element 30 is activated by an evaluation unit 32 arranged in the control unit 14, which detects the charge state SOC of the battery 6 on the input side and the integrated starter generator (ISG) 5 when the switching element 30 exceeds a predetermined maximum value of the battery charge SOC Battery 6 disconnects and switches to load resistor arrangement 31.

For load-free switching, there is the option of torque M_{ISG, SHOULD} to reduce temporarily. For this purpose, a switching element 35 is provided which, like the switching element 30, is controlled by the control unit 14. Depending on the control, the switching element 35 either outputs the setpoint M calculated by the control unit_{ISG, SHOULD} or the value zero as a setpoint to the generator 5.

Finally, the integrated starter generator 5 is connected via a further switching element 36, the switching element 30 to a highly dynamic energy store in the form of a supercap 33, which absorbs electrical energy in generator operation and, after the internal combustion engine 1 is switched off during a braking operation, the internal combustion engine 1 is started quickly enables.

The following is now based on the in <figref idref="f0005">Figure 5</figref> The flowchart shown explains the operating method according to the invention for the control unit described above, it being assumed for simplification that the torque converter 8 is operated in the highest gear stage at the beginning of the braking process. At the beginning of the braking process, the engine is first switched off. The battery voltage is then measured to determine the interpolated downshift speeds n₅₄, n₄₃, n₃₂, n₂₁ depending on the state of charge SOC of the battery 6 and the predetermined braking torque M._should to calculate as in <figref idref="f0003">Figure 3</figref> is shown. Then the current speed n is then from the speed sensor 10_Is measured and with the previously calculated switching speeds n₅₄, n₄₃, n₃₂, n₂₁ compared.

As long as the specified switching speeds are not undershot during the braking process, the switching speeds are again dynamically calculated and with the current speed n_Is compared.

When one of the predetermined shift speeds is reached, the torque converter 8 then shifts down a gear, whereupon the shift speeds are dynamically calculated again.

At the end of the braking process, the engine may then be started, for which purpose the energy stored in the highly dynamic energy store 33 is used.

The invention is not restricted to the exemplary embodiments described above. Rather, a multitude of variants and modifications are conceivable that make use of the idea according to the invention and therefore also fall within the scope of protection.