Impulse start in a hybrid drivetrain

Abstract

A hybrid drive device includes an internal combustion engine, an electric machine and an impulse start module which comprises two clutches and a flywheel mass. A method for operating the hybrid device includes opening the first clutch of the impulse-start module and establishing a start-up requirement for the internal-combustion engine. The method also includes closing the first clutch with the second clutch in an open or closed position for a start of the internal-combustion engine.

Claims

1. A method for operating a hybrid-drive device of a motor vehicle, wherein the hybrid-drive device comprises: an internal-combustion engine, an electric machine, and an impulse-start module, wherein the impulse-start module comprises a first clutch, a second clutch, and a centrifugal mass coupled to the internal-combustion engine solely via the first clutch and to the electric machine solely via the second clutch, the method comprising: opening the first clutch; establishing a start-up requirement for the internal-combustion engine; closing the first clutch, so as to couple the centrifugal mass to the internal-combustion engine, while opening the second clutch to an open position and thereby decoupling the centrifugal mass from the electric machine, when the start-up requirement is a first start-up requirement, and while maintaining the second clutch in a closed position, coupling the centrifugal mass to the electric machine, when the start-up requirement is a second start-up requirement, so as to start the internal-combustion engine in accordance with the start-up requirement; selecting a speed of the centrifugal mass such that, during the start of the internal-combustion engine, the speed of the centrifugal mass lies above an idling speed of the internal-combustion engine prior to closing the first clutch; and shifting the electric machine at least one gear higher after opening the second clutch and prior to closing the first clutch.

2. The method according to claim 1, wherein the start of the internal-combustion engine is performed with the aid of a reciprocal actuation of the first clutch and the second clutch of the impulse-start module.

3. The method according to claim 1, wherein the start of the internal-combustion engine is executed as an initial start.

4. The method according to claim 2, wherein the start of the internal-combustion engine is executed as an initial start.

5. The method according to claim 1, wherein the impulse-start module starts the internal-combustion engine during electric starting, whereby the centrifugal mass of the impulse-start module is coupled with the electric machine by the second clutch in the closed position.

6. The method according to claim 2, wherein the impulse-start module starts the internal-combustion engine during electric starting, whereby the centrifugal mass of the impulse-start module is coupled with the electric machine by the second clutch in the closed position.

7. The method according to claim 1, wherein the impulse-start module starts the internal-combustion engine during engine-off coasting or during electric driving.

8. The method according to claim 2, wherein the impulse-start module starts the internal-combustion engine during engine-off coasting or during electric driving.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts a drivetrain;

(2) FIG. 2 depicts a hybrid drivetrain;

(3) FIG. 3 depicts a first variant of an electric starting on the basis of speed and clutch status;

(4) FIG. 4 depicts a second variant of an electric starting on the basis of speed and clutch status;

(5) FIG. 5 depicts an engine-off coasting on the basis of speed and clutch status;

(6) FIG. 6 depicts a start-up of the internal-combustion engine from electric driving on the basis of speed and clutch status;

(7) FIG. 7A depicts a first variant of an initial start of the internal-combustion engine in the case of a stationary vehicle on the basis of speed and torque;

(8) FIG. 7B depicts a second variant of an initial start of the internal-combustion engine on the basis of speed and torque;

(9) FIG. 7C depicts a third variant of an initial start of the internal-combustion engine on the basis of speed and torque.

DETAILED DESCRIPTION OF THE DRAWINGS

(10) In FIG. 2 a hybrid drivetrain is shown schematically. The hybrid-drive device HA comprises an internal-combustion engine VM, an electric machine EM and an impulse-start module IM which is arranged between the internal-combustion engine VM and the electric machine EM and comprises a first clutch KS and a second clutch K0. A rotation-inequality-reducing element DU is arranged between the clutches KS and K0. Instead of the rotation-inequality-reducing element DU, in some embodiments a flywheel is used. The start of the internal-combustion engine VM is undertaken with the aid of a reciprocal actuation of the first KS and second K0 clutch of the impulse-start module IM.

(11) The figures described in the following each relate to an operating strategy for the method for operating a hybrid-drive device HA of a vehicle with P2-mild-hybrid drivetrain, as shown in FIG. 2. The first clutch KS separates the rotation-inequality-reducing element DU (dual-mass flywheel, torsion-vibration damper, speed-adaptive absorber, . . . ), also called DU element in the following, from the internal-combustion engine VM.

(12) The lower axis in each figure specifies the change of the clutch or the rotational speeds over time. The transitions from one state to the other or from one speed to another are within the milliseconds (ms) range. The states in which the vehicle has been represented as electric or as a hybrid (that is to say, with engaging of the internal-combustion engine) encompass a range of seconds. The speed specified by LL corresponds to an idling speed of the internal-combustion engine and is between 600-900 revolution per minute.

(13) FIG. 3 shows a first variant of an electric starting on the basis of speed and clutch status, also called electric creep. In this first variant, the vehicle is at the beginning, the speeds of VM and EM are zero. During or shortly before the starting, the electric machine EM is brought to a certain speed. The second clutch K0 in this case has been closed, so that the DU element is also accelerated concomitantly. By virtue of the torque of the electric machine EM, the vehicle is accelerated. The starting element here is located in the transmission iAE. If creeping is effected without accelerator pedal and at constant vehicle speed, the electric machine EM rotates at elevated rate, so that an impulse start of the internal-combustion engine is possible at any time. The iAE is in a state of slippage.

(14) In this variant of the start-up, in the case of a start requirement at first the first clutch KS is closed. The internal-combustion engine VM is started and accelerated to an ensuing synchronous speed which lies above the speed at the iAE. Consequently no change of arrangement takes place at the iAE, which would be clearly noticeable at the output. Subsequently the slippage in the iAE is reduced and the internal-combustion engine VM takes over the propulsion.

(15) This start-up can be put into operation so long as the speed at the internal-combustion engine VM arising upon closing of the first clutch KS lies above the speed at the transmission iAE. The speed at the transmission iAE is considered to be directly proportional to the vehicle speed (in a fixed gear).

(16) FIG. 4 depicts a second variant of an electric starting on the basis of speed and clutch status. In the case where the limiting speed for the first start variant, in FIG. 3, is exceeded in creep, the start-up is undertaken in a manner analogous to FIG. 4. At start-up here, at first the centrifugal mass of the DU element is decoupled by opening of the second clutch K0. The electric machine EM can provide the full available power for propelling the vehicle. Subsequently the internal-combustion engine VM is started by closing of the first clutch KS. The still missing speed-range up to the coupling speed the internal-combustion engine VM executes by combustion of fuel. When the transmission input speed is attained, a speed control begins to regulate the internal-combustion engine VM to the target speed, and the second clutch K0 can be closed. Subsequently the internal-combustion engine VM takes over the propulsion, and the electric machine EM reduces its torque.

(17) FIG. 5 shows an engine-off coasting on the basis of speed and clutch status. “Engine-off coasting” means that the internal-combustion engine VM has been separated from the drivetrain, and the first clutch KS is open. No accelerator pedal is being actuated by the driver, and the electric machine EM consequently is not providing a positive torque. The vehicle can consequently roll more or less freely. All the clutches within the transmission are closed; the gears are adjusted in accordance with the vehicle speed. The second clutch K0 is closed. The centrifugal mass of the DU element DU consequently always has the same speed as the transmission input.

(18) The free rolling is represented by the decrease of the speed of nJ. In the case of a start requirement, the second clutch K0 is opened quickly. The centrifugal mass can rotate freely. By virtue of the closing of the first clutch KS, the internal-combustion engine VM is started and dragged to a synchronous speed. Subsequently the internal-combustion engine VM builds up speed by combustion of fuel. When the transmission input speed is attained, a speed control begins to regulate the internal-combustion engine VM to the target speed, and the second clutch K0 can be closed. Subsequently the internal-combustion engine VM takes over the propulsion, and the electric machine EM reduces its torque.

(19) The start-up from the engine-off recuperation proceeds in identical manner, with the difference that in the recuperation the vehicle speed decreases more intensely by reason of the negative torque on the electric machine EM.

(20) FIG. 6 shows a start-up of the internal-combustion engine from electric driving on the basis of speed and clutch status. The start-up from electric driving proceeds like the start-up from the engine-off coasting (cf. FIG. 5). During the start-up, the electric machine EM can make the full power available for the propulsion of the vehicle. A first vehicle reaction can consequently be represented.

(21) During electric driving, the second clutch K0 has been closed; the centrifugal mass DU consequently rotates at transmission input speed. By virtue of an adapted transmission-shift strategy, this speed can always be kept within a speed-band suitable for the impulse start.

(22) By reason of some boundary conditions (low outside temperature, low state of charge of the battery, etc.), it may happen that a start of the internal-combustion engine is initiated at the beginning of the journey at standstill. Since an additional start device is dispensed with, here too an impulse start of the internal-combustion engine is undertaken. For this purpose, three start variants are conceivable, which are shown in FIGS. 7A-7C. The designations of the curves are:

(23) niAE: speed of the starting clutch iAE within the transmission,

(24) nVM: speed of the internal-combustion engine VM,

(25) nJ: speed of the centrifugal mass J,

(26) nEM: speed of the electric machine EM,

(27) MEM: torque of the electric machine EM and

(28) KS, K0 and iAE: status of the corresponding clutch.

(29) FIG. 7A shows a first variant of a cold start of the internal-combustion engine on the basis of speed and torque. At the beginning, the first clutch KS and the second clutch K0 are closed. The internal-combustion engine VM is started with the aid of the torque of the electric machine.

(30) FIG. 7B shows a second variant of a cold start of the internal-combustion engine on the basis of speed and torque. The centrifugal mass DU is brought to a certain starting speed by the torque of the electric machine. Subsequently the internal-combustion engine VM is started by closing of the first clutch KS. Here, the inertia of the DU element and of the electric machine acts on the crankshaft in order to start the internal-combustion engine VM.

(31) FIG. 7C shows a third variant of a cold start of the internal-combustion engine on the basis of speed and torque, and may be regarded as a combination of the first and second variants (FIGS. 7A, 7B): the electric machine and the centrifugal mass DU are racing at the beginning. As soon as a certain speed has been attained, the first clutch KS is closed. Under the action of torque of the electric machine EM and the inertia of the centrifugal mass and the electric machine EM, the internal-combustion engine VM is started.

(32) It should be borne in mind that the methods, devices and systems described in this document can be used both on their own and in combination with other methods, devices and systems described in this document. Furthermore, any aspects of the methods, device and systems described in this document can be combined with one another in diverse ways. In particular, the features of the claims can be combined with one another in diverse ways.

(33) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.