HYBRID DRIVE TRAIN

Abstract

A parallel hybrid drive train, in particular for a working machine, includes an internal combustion engine (1), an electrical machine (2) and hydraulic aggregates (3, 4, 5, 9) for driving working devices (6-8) and for moving the working machine. In order to increase the efficiency, the rotational speed of the internal combustion engine is lowered, that is to say the load point is moved. Increased power requirements are detected via a driver input and provide a desired rotational speed. The electrical machine assists the acceleration of the internal combustion engine to said desired rotational speed.

Claims

1-10. (canceled)

11. A method for the dynamic rotational speed reduction of an internal combustion engine in a mobile working machine, aided by an electric machine, the method comprising: ascertaining a nominal rotational speed of the internal combustion engine; using, aided by the electric machine, a dynamic rotational speed reduction of the internal combustion engine, the electric machine assisting acceleration phases of the internal combustion engine from lower rotational speeds to higher rotational speeds.

12. The method as recited in claim 11 wherein the ascertaining of the nominal rotational speed takes place by evaluating human machine interfaces.

13. A hybrid drive train for a mobile working comprising: an internal combustion engine; an electric machine; a hydraulic working machine; and a control unit configured for ascertaining a nominal rotational speed of the internal combustion engine, the hybrid drive train being configured to, aided by the electric machine, use a dynamic rotational speed reduction of the internal combustion engine, the electric machine configured for assisting acceleration phases of the internal combustion engine from lower rotational speeds to higher rotational speeds.

14. The hybrid drive train as recited in claim 13 wherein the hydraulic working machine includes an axial piston pump configured for requesting power from the internal combustion engine or the electric machine.

15. The hybrid drive train as recited in claim 13 further comprising a hydraulic motor interconnected with the hydraulic working machine.

16. The hybrid drive train as recited in claim 15 wherein the hydraulic motor is an axial piston motor.

17. The hybrid drive train as claim 13 further comprising at least one hydraulic actuating element, a lifting cylinder and/or a steering cylinder interconnected with the hydraulic working machine.

18. The hybrid drive train as recited in claim 17 wherein the at least one hydraulic actuating element is at least one working cylinder.

19. The hybrid drive train as recited in claim 17 wherein the at least one hydraulic actuating element, the lifting cylinder and/or the steering cylinder is interconnected with the hydraulic working machine via one or multiple proportional valves.

20. The hybrid drive train as recited in claim 13 wherein the drive train is configured for operating in a rotational speed-regulated manner.

21. The hybrid drive train as recited claim 13 wherein the hybrid drive train is controllable in the manner that a load point shift is settable at the internal combustion engine.

22. The hybrid drive train as recited claim 13 wherein the hybrid drive train is configured such that a load point shift up to the range of reaching the maximum torque of the internal combustion engine takes place, and the electric machine is then motor-driven.

23. The hybrid drive train as recited claim 13 wherein the electric machine is a mild hybrid drive.

Description

BRIEF SUMMARY OF THE DRAWINGS

[0041] Other advantageous embodiments of the present invention are apparent from the description of the drawings, which describes in greater detail an exemplary embodiment of the present invention illustrated in the figures.

[0042] FIG. 1 shows a schematic view of the arrangement and the interaction of the individual components;

[0043] FIG. 2 shows a characteristic map of the function of the load point shift with effect on the specific consumption (shell diagram);

[0044] FIG. 3 shows a characteristic map of the “load point shift” function;

[0045] FIG. 4 shows a system topology of a mild hybrid system of a construction machine, including an example of an electric machine and energy store;

[0046] FIG. 5 shows a schematic diagram for ascertaining the setpoint rotational speed of the internal combustion engine, including a dynamic rotational speed reduction and setpoint torque of the electric machine.

DETAILED DESCRIPTION

[0047] An internal combustion engine 1, in particular, a self-ignition combustion engine (diesel engine), is coupled directly with an electric machine 2, which is interconnected with the crankshaft of internal combustion engine 1 in place of a flywheel. The stator of this electric machine 2 is connected to the crankcase, and the rotor is interconnected with the crankshaft. The rotor is furthermore interconnected with a gear pump 3 and also with an axial piston pump 4. The output of gear pump 3 is interconnected (for example) with a working cylinder 6, a lifting cylinder 7 and a steering cylinder 8 via proportional valves 5. Gear pump 3 and axial piston pump 4 are hydraulic working machines.

[0048] Electric machine 2 is interconnected with an electrical energy store 13 via a four quadrant converter 12. A hybrid control unit 21 is also provided, with the aid of which all individual control units of the components, in particular of the drive train and the storage train, may be coordinated.

[0049] FIG. 2 shows a typical characteristic map of an internal combustion engine (torque as a function of rotational speed). In this characteristic map, the maximum torque Md.sub.max reachable by the internal combustion engine is plotted as the top curve. The lines of constant specific (fuel) consumption are displayed as shell curves below this top curve, the remaining lines characterizing a gradually increasing consumption, starting from the be.sub.min line. Finally, the curves of constant power P.sub.konst (power hyperbolas) of the internal combustion engine are plotted. In principle, the internal combustion engine, which is operated at a constant power P.sub.konst at point P1, may now be operated at the same constant power P.sub.konst at point P2, point P2, however, being situated in the be.sub.min field. Due to this adjustment, a consumption reduction of the internal combustion engine is achieved at the same power output.

[0050] In conventional drive trains of this type, however, it is problematic that, in an adjustment of this type—as shown in FIG. 3—the latter is always associated with an approach to the top curve of the reachable maximum torque. As illustrated in FIG. 3, if the top curve is approached at power point P2 during the adjustment, the internal combustion engine no longer has any more power reserves even at low load changes, and the internal combustion engine stalls, as shown at point 4. A profile having a dynamic rotational speed reduction but without assistance from the electric machine. Due to the embodiment according to the present invention, however, the power which may be provided by the electric machine may still be additively available. In other words, a power adjustment up to the Md.sub.max curve in the direction of reducing consumption may readily be carried out without any fear of the internal combustion engine stalling during load changes, since the additional power of the electric machine is available for this case.

[0051] P1-P2 corresponds to the dynamic rotational speed reduction when the load (power) remains stationary. Dynamic deflection of joystick (20) (HMI signal) thus precisely dynamically increases the load for the consumer.

[0052] P2-P3 corresponds to the profile having the dynamic rotational speed reduction and assistance from the electric machine (2).

[0053] P2-P4 corresponds to the profile having the dynamic rotational speed reduction but without assistance from electric machine (2).

[0054] P1-P2 corresponds to the profile having an abrupt load change without dynamic rotational speed reduction.

[0055] FIG. 4, in combination with FIG. 5, shows how the nominal rotational speed of the internal combustion engine of a construction machine may be highly dynamically accelerated during a working phase, despite dynamic load peaks. The internal combustion engine is expanded to a mild hybrid system for this purpose. The expansion includes an energy store 13 and an electric machine 2, which may be connected directly to the crankshaft as well as to a PTO (power takeoff). Electric machine 2, including associated energy store 13, may be provided with both an electric and a hydraulic design.

[0056] Electric machine 2 operates highly dynamically during the output or intake of energy, compared to internal combustion engine 1. Internal combustion engine 1 operates at a preferably low rotational speed during its working phases. In the case of load requests which demand a higher rotational speed of internal combustion engine 1, internal combustion engine 1 is assisted highly dynamically in parallel by electric machine 2 during the acceleration operation up to the higher setpoint rotational speed, e.g. in motor-driven operation of electric machine 2. The energy of electric machine 2 needed for this purpose comes from energy store 13. In phases of lower load demand, energy store 13 is recharged with the aid of electric machine 2, for example by the generator-driven operation of electric machine 2. The load demand must be detected as early as possible to be able to very quickly assist internal combustion engine 1 with the aid of electric machine 2 in the acceleration phase. This takes place the fastest by evaluating the signals of HMI interfaces 20, for example joystick 20, which is operated by the machine operator.

[0057] The required rotational speed of internal combustion engine 1—the nominal rotational speed—is ascertained with the aid of the ascertained load demand. This rotational speed is set via the control unit 22 of internal combustion engine 1. While internal combustion engine 1 now already tries to accelerate to the new nominal rotational speed on its own, it is assisted by electric machine 2 via a highly dynamic torque buildup. The setpoint torque of electric machine 2 is ascertained from the difference between the nominal and actual rotational speed.

[0058] The nominal rotational speed of internal combustion engine 1 is ascertained by evaluating HMI interfaces 20; a dynamic rotational speed reduction of internal combustion engine 1 in a construction machine with the aid of electric machine 2 is utilized. Electric machine 2 of the mild hybrid drive assists internal combustion engine 1 highly dynamically during the acceleration phases up to the desired higher nominal rotational speed. Electric machine 2 is connected directly to the crankshaft or to a PTO.

[0059] Electric machine 2, including its energy store 13, may be provided with both an electric and a hydraulic design. Batteries and/or capacitors and/or hydraulic stores may be considered for this purpose.

[0060] The method and the device are suitable, in principle, for all construction machines which are operated on the basis of the provision of power reserves upon dynamic load demands, presently at high nominal rotational speeds during the working phases. A special application takes place, for example, in a material handler.

[0061] The HMI signal is received by the hybrid control unit via the CAN bus; the transmission rate is in the range of approximately 10 m.sub.sec or less.

[0062] The HMI signal represents, e.g. the deflection of a joystick 20 from left to right and is transmitted via the CAN as a signal having a value range from −100% to +100%.

[0063] All HMI signals which result in an increase in the load on the internal combustion engine are thus read out by the hybrid control unit.

[0064] All HMI signals are evaluated in hybrid control unit 21, and a setpoint rotational speed for internal combustion engine 1 is calculated therefrom. The evaluation takes place via characteristic maps and a weighting factor for each HMI signal.

[0065] If an HMI signal changes rapidly, a rapid change in setpoint rotational speed (3) in FIG. 5 also results.

[0066] This initially results in a great difference (4) in FIG. 5 between the setpoint and actual rotational speed of internal combustion engine 1, since internal combustion engine 1

a) is unable to follow the setpoint rotational speed quickly enough, due to the comparatively low momentum;
b) the rapid change in the HMI signal always means a rapid load increase for internal combustion engine 1, which counteracts a rapid adaptation of the actual rotational speed to the setpoint rotational speed.

[0067] The rotational speed difference is used to calculate the setpoint torque of electric machine 2-(5) in FIG. 5.

[0068] If the setpoint/actual rotational speed quickly becomes very high, the setpoint torque of electric machine 2 also quickly increases. In the event that the actual rotational speed is greater than the setpoint rotational speed, no torque is requested from electric machine 2.

REFERENCE NUMERALS

[0069] 1 internal combustion engine [0070] 2 electric machine [0071] 3 gear pump [0072] 4 axial piston pump [0073] 5 proportional valves [0074] 6 working cylinder [0075] 7 lifting cylinder [0076] 8 steering cylinder [0077] 9 axial piston motor [0078] 10 gear stage [0079] 11 driving wheels [0080] 12 four quadrant converter [0081] 13 energy store [0082] 20 human-machine interfaces (HMI), joystick [0083] 21 hybrid control unit (ECU) [0084] 22 control unit of the internal combustion engine (ECU)