Method for Operating a Vehicle Drive and Device for Carrying Out Said Method

Abstract

The invention relates to a method for operating a vehicle drive comprising at least one internal combustion engine and at least one electric machine that is mechanically coupled to the internal combustion engine, in addition to an energy accumulator that is actively coupled to the electric machine and/or the internal combustion engine. According to the invention, the internal combustion engine and the electric machine or machines generate a required drive target torque at approximately the same time, a required optimum target torque of the internal combustion engine being limited to an optimized minimum torque lying above a minimum torque of an internal combustion engine or being limited to an optimized maximum torque lying below a maximum torque of an internal combustion engine and/or a modification speed of the optimum target torque of the internal combustion engine.

Description

STATUS OF THE TECHNOLOGY

The invention is based on a method to operate a vehicle drive and a device to carry out this method according to the generic terms of claim 1 and claim 13.

Hybrid vehicles are known to reduce emission and fuel consumption. It is their goal to operate the combustion engine in the range of more beneficial efficiency, to turn off the combustion engine in case of a standstill of the vehicle or in case of a low vehicle speed and to drive electrically impelled and to use braking energy by recuperation. With parallel hybrids an addition of the torques of the combustion engine and of one or several electric machines happens. The electric machines are, for example, coupled as starter generator with the belt drive or with the crankshaft of the combustion engine.

In the case of modern combustion engines different working points can be problematic with regard to exhaust emissions and fuel consumption.

In the case of a gasoline engine high torques can, for example, require a deviation from a stoichiometric air-fuel-mix, just as a wide-open-throttle enrichment can be necessary to keep the temperature of the components in the allowed limits. To adjust very little torques, a deviation of the firing angle in the direction late is common, which is also applied to reach a torque rate action, to, for example, enable a fast torque build-up in an idle motion. But with the firing angle deviation the efficiency deteriorates. In conjunction with thrust activations increased nitrogen oxide-emissions can generate in the catalyst because of oxygen surplus. In exactly the same way it has to be counted with increased blackening rates and nitrogen oxide-emissions when operating a diesel motor with high torques, with low torques there is the danger that the catalyst cools down.

From DE 101 60 480 A1 a method and a device to operate a vehicle drive is known, which includes a combustion engine and an electric machine among others.

ADVANTAGES OF THE INVENTION

The invention takes as starting point a method to operate a vehicle drive with at least one combustion engine and at least one electric machine, which is mechanically coupled with the at least one combustion engine, and with one energy accumulator actively coupled with the electric machine and/or the combustion engine.

It is recommended, that at least one combustion engine and at least one electric machine produce a requested drive target torque essentially together, with a requested optimum target torque of the combustion engine being limited to an optimized minimum torque above a combustion engine-minimum torque and/or an optimized maximum torque below a combustion engine-maximum torque and/or a modification speed of the optimum target torque of the combustion engine being limited. With the help of one or several electric machines inappropriate torques, i.e. very low or very high torques and just as inappropriate high modification speeds of the optimum target torque, can be avoided in a positive or negative direction, which influences favorable the fuel consumption and the exhaust emission of the combustion engine. The combustion engine and the one or several electric machines can be coordinated in regard to the torques in such a way, that the requested total drive target torque is generated at least approximately by the combustion engine and electric machine together with high dynamics. In doing so, it is of advantage, that an engine timing of a modern combustion engine can calculate a momentary actual torque on the basis of measured and estimated sizes. With a gasoline engine with intake-manifold fuel injection the actual torque can be gained, for example, from the motor speed, intake-manifold pressure, ignition time and excess air coefficient. In exactly the same way a governing/control system of a modern electric machine can calculate a momentary actual torque of the electric machine based on its electric sizes. The suggested method can therefore fall back favorable and without a big effort on easy to identify sizes. Beside that, high modification speeds or gradients of the torques can be avoided advantageously in positive and also in negative direction, which is problematic in regard to exhaust emission and fuel consumption, for example, in the case of the lambda-regulation of intake-manifold injecting gasoline engines in conjunction with their wall film problems or in connection with the “turbo lag” of diesel engines, where otherwise increased blackening rates could perform.

In an advantageous design the at least one electric machine is controlled according to a difference of the unlimited combustion engine-target torque and an actual torque of the combustion engine. With that, limitations of the optimum combustion engine-target torque, limitations for its modification speed and physically caused delays of the torque build-up of the combustion engine can be compensated totally or partly by the or those electric machines, contributing to high dynamics of the system. A torque rate action by means of a firing angle shifting is not necessary. Are allowed operation ranges of the electric machine or of the energy accumulator, like for example, torque range or charge state, left due to the corresponding triggering, the limitation for the optimum combustion engine-target torque and/or the limitation for its modification speed can be taken back.

In a further favorable design an electric machine is used to operate the combustion engine in a consumption favorable and/or emission favorable torque range between the optimized minimum torque and the optimized maximum torque. This range or the optimized minimum torque and the optimized maximum torque depend on the motor speed and further sizes and lies within the minimum and maximum combustion engine-torque limits of the combustion engine. An inappropriate wide-open-throttle enrichment in the range between the optimized maximum torque and the maximum combustion engine-torque and/or an inappropriate firing angle rearrangement or transmission to a thrust cut-off in the range between the optimized minimum torque and the minimum combustion engine-torque, which is inappropriate for the exhaust emission, can be avoided by the corresponding triggering of the electric machine.

In an advantageous further development, the optimized minimum torque and/or the optimized maximum torque and/or the modification speed of the optimum combustion engine-target torque are adjusted subject to the working conditions of the combustion engine. Alternatively or additionally, the optimized minimum torque and/or the optimized maximum torque and/or the modification speed of the optimum target torque can be adjusted subject to the working conditions of the electric machine. Alternatively or additionally, the optimized minimum torque and/or the optimized maximum torque and/or the modification speed of the optimum target torque can also be adjusted subject to the working conditions of the energy accumulator. Alternatively or additionally, the optimized minimum torque and/or the optimized maximum torque and/or the modification speed of the optimum target torque can be adjusted subject to a timely process of target torques.

Conveniently, the target torque derives from a position of the accelerator pedal and/or the position of the brake pedal. The maximum permitted modification speed of the optimum target torque can be derived from a modification speed of the position of the accelerator pedal and/or a position of the brake pedal.

It is favorable, if the drive target torque is determined subject to an idle motion-regulator and/or an active vibration damping and/or a gear control, so that essential factors of influences can be considered in regard to the operating behavior of the vehicle. Furthermore, an intervention of an operating strategy with a charge-target torque is advantageous to ensure a supply of an on-board supply and an energy accumulator, particularly a battery, and to improve a total efficiency of the drive line with a specific loading or unloading. The energy accumulator can, for example, be loaded in case of low performance requirements, as a result of which the torque of the combustion engine raises and the combustion engine arrives at a working point with a favorable specific consumption.

Conveniently, the torque range and/or the torque dynamics of the combustion engine are increased in case of inadmissible working conditions and/or insufficient performance of the energy accumulator and/or of the electric machine. It is of advantage, if an intervention in the limits of the torque range and/or the torque dynamics of the combustion engine does not occur in cases of temporary dynamic processes, like a delayed torque build-up of the electric machine.

Furthermore, the invention takes as starting point a device to carry out a method to control the torque of a drive with at least one combustion engine and at least one electric machine in the vehicle, which is mechanically coupled with the at least one combustion engine, and with an energy accumulator, being actively coupled with the electric machine and/or the combustion engine.

It is recommended, that a limitation unit is designed to limit a requested optimum target torque of the combustion engine to an optimized minimum torque above a combustion engine-minimum torque and/or an optimized maximum torque below a combustion engine-maximum torque and/or to limit a modification speed of the optimum target torque of the combustion engine. Preferably, a unit is designed to stop an intervention in the case of inadmissible working conditions and/or an inadmissible performance of the energy accumulator and/or the electric machine in the limits of the torque range and/or the torque dynamics of the combustion engine.

DRAWING

Further designs, aspects and advantages of the invention result also independently from their summary in the claims without restrictions of the generality from the following design example of the invention, shown on the basis of a drawing.

In the following the only FIGURE illustrates schematically the method according to the invention.

DESCRIPTION OF THE DESIGN EXAMPLE

On the basis of the FIGURE, the method according to the invention is explained exemplary at a parallel hybrid vehicle. A drive line exhibits a combustion engine 10 with a intake-manifold fuel injection (not shown), which is designed with a electronic accelerator pedal (not shown) and a catalyst (not shown). A balance wheel of the combustion engine 10 is coupled with an electric machine 15, which is formed as a crank axle starter generator. The combustion engine 10 and the electric machine 15 generated torques are added up as a drive torque. One target torque M_Driver, specified by the driver through the accelerator pedal, is low-pass filtered by means of a pre filter 22 to avoid a stimulus of power train vibrations through the driver or to reach a damping of Ferraria effect. Behind the pre filter 22 an intervention occurs by a idle motion-regulator (not shown) and optionally an active vibration damping and/or a gear control with an additional target torque M_together. The sum of that torques result in the total drive target torque M_target, which presents a nominal value for the sum torque M_actual of the combustion engine 10 and the electric machine 15.

Beside that, an intervention of a working strategy with a charge-target torque M_Charge is designed, ensuring the supply of an on-board supply and a not shown electric energy accumulator and improving a total efficiency of the drive line by directly loading or unloading the energy accumulator. With that, the energy accumulator can be loaded in case of low performance requirements, for example in city traffic, as a result of which the torque of the combustion engine 10 increases and the combustion engine 10 reaches typically a working point with beneficial specific consumption.

The behavior of the combustion engine 10 with a torque triggering depends on the dynamics of the air path and is described approximately with a series connection of a lag element 12 and a PT1-delay element 13 first order. A limiter unit 11 limits the by the combustion engine 10 requested optimum target torque M_{VM target opt} to a combustion engine-maximum torque M_{VM max} and a combustion engine-minimum torque M_{VM min} in the case of a thrust cut-off. The combustion engine-maximum torque M_{VM max} depends on different operating parameters, like motor speed, charge pressure of a possible turbo charger and such things.

The behavior of the electric machine 15 with a torque triggering can also be described approximately by means of a PT1-delay element 17 first order. But due to its smaller time constant in comparison with the combustion engine 10 the electric machine 15 exhibits much higher dynamics in the case of a torque control.

A torque treatment unit 18 for the combustion engine 10 includes a gradient limiter unit 19, providing for a limited rate of increase or modification speed of the optimum combustion engine-target torque M_{VM target opt}. A further limiter unit 20 limits to an optimum torque range between an optimized minimum torque M_{VM min opt} and an optimized maximum torque M_{VM max opt}. By that, this optimum torque range characterizes the most convenient working area of the combustion engine 10, which depends on operating parameters like the motor speed, the charge pressure of a possible turbo charger of a turbocharged engine and such things.

The optimum torque range lies within the torque limitations M_{VM max} and M_{VM min} of the combustion engine 10. The optimized maximum torque M_{VM max opt} is smaller than the combustion engine-maximum torque M_{VM max}. In the range between both maximum torques M_{VM max opt} and M_{VM max} an inappropriate wide-open-throttle enrichment of the combustion engine 10 would happen in the design example. The optimized minimum torque M_{VM min opt} is higher than the combustion engine-minimum torque M_{VM min}. In the range in-between, an inappropriate rearrangement of the firing angle in direction late or a transmission to a thrust cut-off, inappropriate for the exhaust emission, would occur to the fuel consumption.

The not shown control device of the combustion engine 10 calculates the momentary combustion engine-actual torque M_{VM actual}.

The difference torque M_{VM delta} of the unlimited target torque M_{VM target} and the actual torque M_{VM actual} of the combustion engine 10 are added on to the electric machine 15.

In the dynamics operation, the electric machine 15 balances the delayed torque build-up or torque removal of the combustion engine 10 and provides for high dynamics of the drive system. A torque rate action by means of a firing angle shifting is not necessary.

Beside that, the electric machine 15 is used to operate the combustion engine 10 in the optimum torque range between M_{VM min opt} and M_{VM max opt}. If, for example, the charge state or the performance of the energy accumulator do not allow that, the intervention of the electric machine 15 is taken back by modification of the torque limits M_{E min} and M_{E max} of the electric machine 15. By that or with a limitation because of physical characteristics of the electric machine 15 a deviation M_{E delta} develops between a target torque M_{E target} and an actual torque M_{E actual} of the electric machine 15.

The deviation M_{E delta} has an effect on the limiter unit 20 and/or the gradient limiter unit 19. If the rate of the deviation M_{E delta} increases, the limits for the optimum combustion engine-target torque M_{VM target opt} are expanded and/or higher modification speeds of the optimum combustion engine-target torque M_{VM target opt} are allowed. In that case, the combustion engine 10 can leave the optimum torque range.

An inserted filter unit or logic unit 21 prevents a corresponding intervention in the limiter unit 20 and/or the gradient limiter unit 19 in the torque treatment unit 18 at temporary, dynamic processes, for example due to a delay in the torque build-up of the electric machine 15.

In the design example a realization of the total drive target torque M_target to the actual value M_actual occurs, demonstrating the sum torque of the combustion engine 10 and the electric machine 15 with the high dynamics of the electric machine 15. Thereby, the torque range and the torque dynamics of the combustion engine 10 are limited to reduce the exhaust emissions and the fuel consumption. If the characteristics of the electric machine 15 do not allow that, the torque range and/or the torque dynamics of the combustion engine 10 are increased.

Claims

1. A method of operating a vehicle drive with at least one combustion engine, at least one electric machine mechanically coupled with the at least one combustion engine, and an energy accumulator actively coupled with the electric machine and/or the combustion engine, the method comprising:

generating a requested drive target torque by the combustion engine and the electric machine, essentially together;

limiting a requested optimum target torque of the combustion engine to an optimized minimum torque above an optimized minimum torque of the combustion engine and/or an optimized maximum torque of the combusion engine; and

limiting a modification speed of the optimum target torque of the combustion engine.

2. A method according to claim 1, further comprising triggering at least one electric machine according to a difference of an unlimited target torque and an actual torque of the combustion engine.

3. A method according to claim 1, wherein the electric machine is used to operate the combustion engine in a consumption favorable and/or emission favorable torque between the optimized minimum torque and the optimized maximum torque.

4. A method according to claim 1, wherein the optimized minimum torque, the optimized maximum torque, or the modification speed of the optimum target torque is set up subject to the working conditions of the combustion engine.

5. A method according to claim 1, wherein the optimized minimum torque, the optimized maximum torque, or the modification speed of the optimum target torque is set up subject to the working conditions of the electric machine.

6. A method according to claim 1, wherein the optimized minimum torque, the optimized maximum torque, or the modification speed of the optimum target torque is set up subject to the working conditions of the energy accumulator.

7. A method according to claim 1, wherein the optimized minimum torque, the optimized maximum torque, or the modification speed of the optimum target torque is set up subject to a process of target torques.

8. A method according to claim 1, wherein the target torque is derived from a position of an accelerator pedal or a position of a brake pedal; or the modification speed of the optimum target torque is derived from a modification speed of the position of the accelerator pedal or the position of the brake pedal.

9. A method according to claim 1, wherein the target torque is determined depending on an idle motion regulator, an active vibration damping, or gear control.

10. A method according to claim 1, further comprising considering a charge target torque to ensure supply of an on-board supply and/or the energy accumulator.

11. A method according to claim 1, further comprising increasing a torque range or torque dynamics of the combustion engine in case of inadmissible working conditions or inadmissible performance of the energy accumulator or the electric machine.

12. A method according to claim 1, wherein in cases of temporary dynamic processes, an intervention in the limits of the torque range or the torque dynamics does not occur.

13. A device that carries out a method to control torque in a drive with at least one combustion engine, at least one electric machine, mechanically coupled with the at least one combustion engine and an energy accumulator, actively coupled with the electric machine or the combustion engine, the device comprising a limiter unit designed to limit a requested optimum target torque of the combustion engine to an optimized minimum torque above a combustion engine-minimum torque or an optimized maximum torque below a combustion engine-maximum torque, or to limit a modification speed of the optimum target torque of the combustion engine.

14. A device according to claim 13, wherein the limit unit is designed to stop an intervention in case of inadmissible working conditions or inadmissible performance of the energy accumulator or the electric machine in the limits of a torque range and/or torque dynamics of the combustion engine.