Self-propelling work machine and method for braking such a work machine

Abstract

Methods and systems are provided related to a self-propelling work machine in the form of a tracked vehicle having an electric drive, with a generator drivable by an internal combustion engine, an auxiliary unit connected to the engine, and a braking apparatus for braking the work machine. The braking apparatus provides regenerative braking by the electric drive and comprises a feedback apparatus for feeding back electrical motor braking power of the electric motor to the generator to apply the motor braking power on the engine and on the auxiliary unit. A controller automatically increases or decreases the electrical load of the auxiliary unit based on the electrical motor braking power fed back to the engine and/or based on an engine speed.

Claims

1. A self-propelling work machine, comprising: an internal combustion engine; an electric drive having at least one electric motor, a generator drivable by the internal combustion engine and supplying the electric drive with electrical energy, and at least one auxiliary unit coupled to the internal combustion engine; a braking apparatus configured to provide a regenerative braking by the electric drive; a feedback apparatus for feeding back electrical motor braking power from the electric motor to the internal combustion engine via the generator; and a controller with computer readable instructions stored on non-transitory memory for adjusting an electrical load of the at least one auxiliary unit of the internal combustion engine based on the electrical motor braking power fed back to the internal combustion engine via the generator.

2. The machine of claim 1, wherein the controller includes further instructions for further adjusting the electrical load of the at least one auxiliary unit of the internal combustion engine based on an engine speed while the internal combustion engine receives the fed back electrical motor braking power.

3. The machine of claim 1, wherein feeding back electrical motor braking power from the electric motor to the internal combustion engine via the generator includes transferring an electrical current corresponding to the electrical motor braking power from the electrical motor to the generator.

4. The machine of claim 3, wherein the electrical motor braking power is fed back to the internal combustion engine via the generator until a retard capacity of the internal combustion engine is reached.

5. The machine of claim 4, wherein the controller includes further instructions for: reducing a fuel supplied to the internal combustion engine while maintaining a substantially constant engine speed while the electrical motor braking power is fed back to the internal combustion engine via the generator, and; after the fuel supplied has been reduced to below a threshold amount of fuel, increasing the engine speed via the electrical motor braking power fed back into the internal combustion engine until an upper threshold engine speed is reached.

6. The machine of claim 4, wherein the controller includes further instructions for: after the retard capacity of the internal combustion engine is reached, feeding back the electrical motor braking power to the at least one auxiliary unit while increasing the electrical load of the at least one auxiliary unit on the internal combustion engine.

7. The machine of claim 1, further comprising an engine speed sensor, wherein the controller adjusts the electrical load of the at least one auxiliary unit on the internal combustion engine to maintain a substantially constant engine speed, the adjusting including: estimating an engine speed based on an output of the engine speed sensor, and increasing the electrical load of the at least one auxiliary unit on the engine as the engine speed exceeds a predefined engine speed, and decreasing the electrical load of the at least one auxiliary unit on the internal combustion engine as the engine speed falls below the predefined speed of the engine.

8. The machine of claim 7, wherein the at least one auxiliary unit includes a hydraulic pump which is not required for propulsion of the machine, the hydraulic pump conveying fluid in idle circulation when actuated or the hydraulic pump being swiveled to convey a quantity of zero.

9. The machine of claim 8, wherein the electrical load of the hydraulic pump conveying fluid in idle circulation when actuated is increased by a control apparatus via actuation of a pressure relief valve such that a flow resistance in the idle circulation is gradually increased, and wherein the electrical load of the hydraulic pump swiveled to convey the quantity of zero when actuated can be increased by the controller to successively swivel out the hydraulic pump against a constant flow resistance in circulation, against the pressure relief valve set to a fixed setting.

10. The machine of claim 1, wherein the feedback apparatus comprises at least one motor inverter coupled to the at least one electric motor, at least one generator inverter coupled to the generator, and at least one DC voltage intermediate circuit coupling the at least one motor inverter to the at least one generator inverter.

11. The machine of claim 4, further comprising a mechanical brake and an electrical braking resistor, wherein the controller includes further instructions for: after the retard capacity of the internal combustion engine has been reached and the electrical load of the at least one auxiliary unit has been increased up to a threshold load, providing further braking corresponding to a deficit in desired braking via one or more of the mechanical brake and the electrical braking resistor, the mechanical brake actuated after a braking capacity of the electrical braking resistor is exhausted.

12. A method for braking a work machine, comprising: operating an electric motor during regenerative braking to generate electrical motor braking power; feeding the generated electrical motor braking power to a generator coupled to an engine via a feedback apparatus; applying a mechanical drive power generated at the generator via the electrical motor braking power on the engine via the generator; and varying an electrical load of an auxiliary unit coupled to the generator based on one of the electrical motor braking power fed back to the engine via the generator, and an operating state of the engine while the electrical motor braking power is fed to the engine via the generator.

13. The method of claim 12, further comprising: reducing a fuel supply to the engine while maintaining an engine speed as the electrical motor braking power fed back to the engine increases until the fuel supply is cut off; then, with the fuel supply to the engine cut off, increasing the engine speed via the fed back electrical motor braking power until a predefined threshold engine speed is reached; and when the engine speed is at the predefined threshold engine speed and the electrical motor braking power is less than a desired braking force requested by an operator, increasing the electrical load of the auxiliary unit.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a schematic side view of a self-propelling work machine which can be configured as a bulldozer in accordance with an advantageous embodiment of the present disclosure and which comprises an electric drive as a traction drive which is supplied with current from a generator which can be driven by an internal combustion engine, for example in the form of a diesel engine.

(2) FIG. 2 shows a schematic representation of the components of the drive system of the work machine of FIG. 1 and of a control apparatus comprising a retard regulation assistant which distributes the electrical motor braking power generated on the braking of the work machine to different modules of the drivetrain and controls them.

(3) FIG. 3 shows a flowchart for presenting the method steps executed on the braking of the work machine of FIGS. 1-2.

(4) FIG. 4 shows a flowchart of an example method for using engine speed feed-back control for adjusting engine fueling and for regulating the amount of motor braking effort that can be fed back to a generator coupled to the engine.

DETAILED DESCRIPTION

(5) FIG. 1 shows a self-propelling work machine 1 which in the depicted example is configured as a bulldozer. Machine 1 comprises a tracked chassis as the undercarriage 2. It is understood that the work machine can also be configured in different forms, for example as a construction machine or as a mining machine having a wheel undercarriage, for example in the form of a dump truck or truck.

(6) The drive system of the work machine 1 comprises at least one electric drive 3 having at least one electric motor 4 which can serve as a traction drive and can drive the chain drive of the bulldozer of FIG. 1 or a wheel of the undercarriage. As FIG. 2 shows, a plurality of electric motors 4 can also be provided, for example as an individual wheel drive or for driving a plurality of axles.

(7) As FIG. 2 shows, the electric drive 3 is supplied with electric current from a generator 5, the generator 5 being driven by an internal combustion engine 6 which can be formed, for example, as a diesel engine.

(8) The work machine 1 can furthermore comprise at least one hydraulic unit 7 which can, for example, in the embodiment of the work machine 1 in the form of a bulldozer serve for adjusting the dozer blade 8 and can for this purpose comprise at least one hydraulic actuator 9, for example in the form of a hydraulic cylinder of the bulldozer.

(9) The hydraulic unit 7 can comprise a pressure source actuatable by the internal combustion engine 6 or in the form of a hydraulic pump to supply the operating hydraulics with hydraulic fluid and hydraulic pressure.

(10) Alternatively or additionally to the named hydraulic unit 7, the work machine 1 can also comprise one or more additional auxiliary units such as a cooling apparatus or a cooling fan (not shown in the drawings) and which can likewise be coupled to the internal combustion engine 6 such that they can receive power from the engine.

(11) A braking apparatus 10 for braking the work machine 1 can comprise mechanical brakes for braking the chain drive or the wheel drive and can be configured, for example, in the form of spring pre-loaded brakes which can be hydraulically ventilated.

(12) The braking apparatus 10 furthermore comprises the use of the at least one electric motor 4 as the generator in order to provide the desired braking power by the electric drive 3 by way of regenerative braking. The electrical motor braking power provided by the electric motors 4 is controlled and distributed by a control apparatus 11, which comprises a feedback regulator or retard regulation assistant 12.

(13) As FIG. 2 shows, power electronics 13 can be associated with the electric drive 3 or with each electric motor 4. By means of the power electronics 13, during a motor operation (wherein power is output from the motor and is used to assist the engine output), power supplied to the electric motor 4 is varied and, conversely, during a retard operation (wherein excess power generated by the engine or via regenerative braking is absorbed by the motor), the returned motor braking power can be controlled. Further power electronics 14 can also be provided in a higher-ranking manner between the electric drive 3 and the generator 5 and can be connected to a braking resistor 15 so as to be able also to reduce fed back motor braking power dissipatively at this braking resistor 15, as required.

(14) Retard regulation assistant 12 is connected to the named power electronics 14 to regulate the fed back motor braking power. Herein, the fed back motoring power is the power absorbed during a retard operation that is then fed back to the engine via the generator of the drive system. The retard regulation assistant 12 is furthermore connected to the internal combustion engine 6 and to the hydraulic unit 7 in order to monitor their operating states by means of a suitable sensor system and conversely optionally also to influence their working parameters or operating parameters via control modules. A monitoring sensor system 16 may, for example, comprise a speed sensor for monitoring the speed of the internal combustion engine 6 and a pressure sensor for monitoring the hydraulic pressure in the hydraulic unit 7.

(15) Retard regulation assistant 12 can have engine control means 17 for controlling the internal combustion engine 6, in particular for reducing the fuel supply, and/or can have hydraulic control means 18 for controlling the hydraulic unit 7, in particular for varying the power pick-up, for example via changing the flow rate and/or the conveying pressure of the pump of the hydraulic unit 7, as previously explained. For example, engine control means 17 may include one or more engine torque actuators, such as an intake throttle, valve timing, spark timing, cam timing, fuel injector, etc., and the retard regulation assistant 12 may send a command signal to the actuator to control the engine. In one example, the retard regulation assistant 12 may send a command signal (e.g., pulse width or duty cycle signal) to a cylinder fuel injector to reduce the fuel supply to the engine.

(16) If a machine operator desires a specific braking force, for example by actuating a brake pedal or a brake lever or by actuating a braking request button, the retard regulation assistant 12 can control or regulate the regenerative motor braking, as is illustrated in the method of FIG. 3.

(17) If a braking request is present the retard regulation assistant first checks whether the internal combustion engine 6 is already running at its upper speed limit, at step 100 in FIG. 3. If this is not the case, e.g. if the internal combustion engine can still provide or pick-up retard power, the retard regulation assistant controls the power electronics to generate regenerative motor braking power at the electric motors and feed the generated braking power back to the generator, at steps 110 and 120 of FIG. 3. This feeding back of the motor braking power to the generator results in an increase of the speed of the internal combustion engine. This can initially advantageously be compensated or reduced or limited in that the fuel supply is reduced, which results in a particularly efficient operation of the work machine. The fuel supply can in this respect advantageously be reduced by the retard regulation assistant such that initially no speed change of the internal combustion engine occurs even as the braking power is applied, with the reduction of the fuel supply being able to be increased step-wise or continuously until no more fuel at all is supplied.

(18) If such a compensation by reducing the fuel supply is no longer possible, the speed of the internal combustion engine increases, which the retard regulation assistant generally permits, at step 130 in FIG. 3.

(19) If the motor braking power to be supplied due to the desired braking force is still smaller than the retard power which can be picked up at the internal combustion engine, the feedback regulation works in a loop, as shown at branch 140 in the flowchart of FIG. 3. That is, branch 140 is taken when Pmot<Pret, e.g. the motor braking power is smaller than the retard power applied by the internal combustion engine.

(20) If, based on the monitored speed of the internal combustion engine, it is determined in step 130 that the internal combustion engine is working at its upper speed limit, e.g. the engine can no longer take up any further retard power, the retard regulation assistant checks in step 150 whether further motor braking power can be applied in the hydraulic unit. For example, it may be determined if the conveying volume or the conveying pressure can be changed, if the pump can be swiveled out further and/or if a restriction resistance can be increased. If the motor braking power corresponding to the desired braking force can be taken up via such adjustments, e.g. if the motor braking power does not exceed the retard power which can be provided by the internal combustion engine and by the work hydraulics, the regulation in turn takes the branch 140.

(21) If, on the other hand, the retard power of the hydraulic unit and of optionally present further auxiliary units such as fans is reached, the retard regulation assistant controls the power electronics which are connected to the braking resistor to dissipatively reduce further motor braking power at the braking resistor at steps 160 and 170 in FIG. 3. If the braking resistor cannot take up the motor braking power which cannot be applied any more at the internal combustion engine and at the hydraulic unit, the regulation again returns via the step 140 since Pmot<Pret, at step 140 in FIG. 3.

(22) If the motor braking power or the portion exceeding the retard capacity of the internal combustion engine and of the hydraulic unit, however, exceeds the retard capacity of said braking resistor, the retard regulation assistant reduces the motor braking power by a corresponding control of the power electronics 14, at step 180 in FIG. 3.

(23) In this case, the desired braking force of the machine operator can no longer be satisfied by regenerative braking by means of the electric drive so that the work machine would be braked more slowly or less powerfully than is desired by the machine operator. In other words, the desired braking force would not be provided. To address this issue, when the maximum retard power of the retard system has been reached, a mechanical brake can be connected, which can advantageously take place gently with an increasingly rising braking force so that the net braking force is as close as possible to the desired braking force.

(24) Turning now to FIG. 4, an example method 400 is shown for adjusting engine fueling and for regulating the amount of motor braking effort that can be fed back to a generator coupled to the engine.

(25) At 402, the method includes estimating and/or measuring vehicle and engine operating conditions. For example, parameters assessed may include engine speed, engine load, vehicle speed, operator torque demand, battery state of charge, ambient conditions such as ambient temperature, barometric pressure, and ambient humidity, manifold pressure and flow, engine dilution, etc. At 404, the method includes determining if braking has been requested. For example, it may be determined if the operator has actuated a brake device, such as a brake pedal, a brake lever, or a braking request button. If no braking request has been received, at 406, the method includes maintaining engine settings and then the routine ends.

(26) If braking is requested, at 408, the method includes determining an amount of braking power (or braking force) requested. For example, based on a degree of actuation (or displacement) of the brake pedal, or a position of the brake lever, an amount of braking power requested may be determined. In addition, a requested rate of braking force application may also be determined.

(27) At 410, it may be determined if the engine speed is at below upper limit. For example, it may be determined if the engine speed is below a limit above which regenerative braking effort cannot be received at the engine. If not, that is if the engine is at the upper speed limit, then at 412, the method includes actuating mechanical brakes and/or braking resistors of the vehicle system to provide the requested braking effort. For example, a degree of actuation of the mechanical brakes may be adjusted to provide the requested braking effort. Herein, a regenerative motor braking effort is not fed back to the engine because the engine does not have retard capacity.

(28) If the engine speed is below the upper limit, then at 414, the controller may infer that the engine is capable of receiving regenerative braking effort. That is, the engine does have retard capacity. The controller may infer the magnitude of the engine's retard capacity based on the engine speed relative to the upper limit. Then, the controller may generate or enable regenerative braking power at the electric motor(s) of the electric drive system. For example, the controller may enable the electric motor(s) to be driven using wheel torque during regenerative braking. Further, the controller may feed the generated motor braking power to the engine via the generator. In particular, as the electric motor(s) is driven by regenerative braking, the electric motor may be used to supply an electric current to the generator which is coupled to the engine. As such, in the absence of motor braking effort, an electric current is provided at the generator using engine torque generated by combustion of fuel at the engine. The electric current provided at the generator is used to support auxiliary loads of the engine such as auxiliary fans and pumps. By using the electric current provided at the generator via the motor braking effort, the load on the engine is reduced, enabling the engine to run more efficiently (e.g, at a higher speed or with lower fuel consumption). The controller may also measure or infer the amount of power being fed back into the engine via one or more sensors. For example, the motor braking effort fed back into the engine may be inferred based on the output of a speed sensor, based on the output of a torque sensor coupled to a shaft of the engine and/or generator, etc.

(29) At 416, the method includes reducing fuel delivered to the engine based on the fed motor braking power while maintaining the engine speed. Herein the engine is operated with speed control (at a constant speed) and fueling is adjusted to maintain the engine speed. By using the electric current provided at the generator via the motor braking effort, the load on the engine is reduced, enabling the engine to run at the same speed with lower fuel consumption. Thus as the motor braking effort that is fed back to the engine is increased, the fuel delivered to the engine to maintain the engine speed may be correspondingly reduced. In one example, the engine fueling is gradually ramped down as the motor braking power fed into the engine is ramped up.

(30) At 418, the method further includes adjusting the output of one or more auxiliary units of the electric drive system based on the motor braking power fed into the engine. In one example, the output of the one or more auxiliary units of the electric drive system may be increased so that the motor braking power fed into the engine can match the requested braking power (requested at 404). Increasing the output includes, for example, increasing a speed of an auxiliary cooling fan, increasing a pump speed, flow, or pressure of an auxiliary hydraulic pump, actuating an auxiliary device, etc. In some examples, the output of the auxiliary unit(s) may be increased selectively only after the engine fueling has dropped to below a threshold amount of fuel, such as to an amount of fuel required for idling, or when engine fueling has been cut off. In still other examples, the output of the auxiliary unit(s) may be increased only after the retard capacity of the engine is reached and the engine is not capable of accepting any further motor braking power on its own without the adjustment to the auxiliary unit. In other examples, such as where the engine speed is increased while maintaining engine fueling as the motor braking power fed back to the engine increases, the output of the auxiliary units may be increased only after the engine speed has increased to an upper limit above which the engine is not capable of accepting further motor braking power. In one example, the output of the auxiliary units may be increased above settings required for nominal (or current) conditions.

(31) At 420, it may be determined if the requested braking power has been met via the regenerative motor braking power fed back to the engine. If yes, then at 424, the controller may maintain mechanical brakes (and braking resistors) disabled. In this way by meeting the braking needs using motor braking power fed back to the engine, wear and tear of mechanical brakes is reduced, and component life is extended.

(32) If the requested braking power has not been met via only the regenerative motor braking power fed back to the engine, at 422, the method determines if further motor braking power can be fed to the engine. If one example, the engine can continue to receive power while the engine speed is below an upper speed limit. In another example, the engine can continue to receive power while engine fueling is above a threshold amount. If further feeding of motor braking power to the engine (via the generator) is possible, then the method returns to 414 to feed regenerative motor braking power to the engine while adjusting engine fueling, engine speed, and/or auxiliary unit load applied on the engine via the generator.

(33) If further feeding of motor braking power to the engine (via the generator) is not possible, then at 426, the controller may provide a deficit to the requested braking effort via the mechanical brake and/or braking resistor. For example, the controller may calculate a deficit between the requested braking power and the braking power available via the regenerative motor braking fed into the engine. Then, the controller may adjust a degree and/or duration of actuation of the mechanical brake and/or braking resistor to meet the deficit. This includes adjusting a rate of ramping in actuation of the mechanical brake and/or braking resistor to provide the requested braking power.

(34) In this way, engine performance in an electric drive system can be improved. By feeding power generated during regenerative motor braking via an electric motor into a generator coupled to an engine, the load applied on the engine can be reduced. This enables fuel-based engine speed control to reduce the amount of fuel delivered to an engine while maintaining engine speed. By increasing the output of one or more auxiliary units responsive to the engine reaching a retard capacity, regenerative braking can be used to meet the desired braking with reduced need for applying mechanical brakes or braking resistors. As a result, component lift is also extended.