WO2009066129A1

WO2009066129A1 - Construction equipment machine with hydraulic transmission circuit

Info

Publication number: WO2009066129A1
Application number: PCT/IB2007/004365
Authority: WO
Inventors: Gilles Florean; David Lazzaro
Original assignee: Volvo Compact Equipment Sas
Priority date: 2007-11-22
Filing date: 2007-11-22
Publication date: 2009-05-28

Abstract

The invention relates to a construction equipment machine comprising a main engine ( 1) and a main hydraulic circuit (2) with at least a main hydraulic power pump (20) and at least one hydraulic power consumer (21), characterized in that said main engine ( 1) drives the main hydraulic power pump (20) through a hydraulic transmission circuit (3) comprising a hydraulic transmission pump (30) which is driven by said main engine ( 1) and which supplies hydraulic pressurized fluid to a hydraulic transmission motor (31), said hydraulic transmission motor (31) being connected to drive the main hydraulic power pump (20), and in that the hydraulic transmission motor (31) is of a variable capacity type.

Description

Construction equipment machine with hydraulic transmission circuit

Technical field

The invention relates to the field of construction equipment machinery, including but not limited to excavators, loaders, and road construction machinery. The invention can be implemented on any such machine comprising a main engine and a main hydraulic circuit with at least a main hydraulic power pump and at least one hydraulic power consumer.

Background art Construction machines of the type above have at least one work implement which is hydraulically powered, such as a back-hoe, a loader bucket installed at the extremity of a loader arm, etc... Most of these machines are also mobile machines where the machine is driven by a driveline which, in some cases, is also hydraulically powered. The driveline may also comprise hydraulically powered steering systems, and the machine may also comprise many auxiliary systems driven by hydraulic power.

Therefore, a construction equipment machine is typically equipped with a main hydraulic circuit which is supplied with pressurized hydraulic fluid by a main hydraulic power pump. This pressurized hydraulic fluid is consumed by hydraulic actuators incorporated in the work implement, driveline, steering system and/or auxiliaries.

Most construction equipment machines, especially machines such as excavators and loaders, have very fluctuating load cycles, meaning that there are big variations in the power to be supplied by the main hydraulic circuit to the various power consumers on board.

In conventional machines, the main hydraulic power pump is driven directly by the machine's main engine, usually an internal combustion engine such as a diesel engine. Therefore, the engine has to be driven to adjust as closely as possible to the instant power, torque and speed requirements of the main power pump. As explained above, since those requirements may vary very suddenly, very frequently, and over a wide range, this leads to the need to operate the engine over a wide range of operating conditions. Even though diesel engines are now capable of operating quite efficiently over broad ranges, it derives from the varying load cycle that the engine often needs to be oversized to be able to cope with such varying demands. A larger engine means an overall increased fuel consumption, more toxic emissions which need to be dealt with, more cooling power which reduces the overall efficiency, and more space on the machine, etc.... And even though, those varying demands mean that the engine is rarely used at its optimum operating conditions, and moreover, is often used in transient conditions which are usually not favorable, especially in terms of fuel economy and in terms of toxic emissions.

Therefore, there is a need for a new concept of hydraulic power generation in a construction equipment machine which can lead to a more efficient use of the machine's engine.

Summary of the invention

In view of the above objective, the invention provides for a construction equipment machine comprising a main engine and a main hydraulic circuit with at least a main hydraulic power pump and at least one hydraulic power consumer, characterized in that said main engine drives the main power hydraulic pump through a hydraulic transmission circuit comprising a hydraulic transmission pump which is driven by said main engine and which supplies hydraulic pressurized fluid to a hydraulic transmission motor, said hydraulic transmission motor being connected to drive the main hydraulic power pump.

Description of figures Figure 1 is a schematic diagram showing most of a hydraulic power installation of a construction equipment machine according to the invention, including an innovative hydraulic transmission circuit.

Figure 2 is a schematic diagram of a first embodiment of a transmission circuit according to the invention.

Figure 3 is a schematic diagram of a second embodiment of a transmission circuit, also shown in Figure 1.

Description of the invention

On figure 1 is represented schematically the hydraulic power installation of a construction equipment machine such as a backhoe-loader. On this diagram, one can see a main engine 1, a main hydraulic power circuit 2, and between them, a hydraulic transmission circuit 3.

The hydraulic power circuit 2 represented here is conventional and purely illustrative of one example of such a circuit as it can be found in a backhoe loader. Of course, different types of construction equipment machines would show different hydraulic power circuits, and even machines of the same type could have different such circuits, depending amongst other things on the number and sort of hydraulically powered equipments on the machine. Nevertheless, in all cases, such a hydraulic power circuit would exhibit a main hydraulic power pump 20. In the pictured example, the hydraulic power circuit comprises a series of hydraulic power consumers 21 which are here depicted as hydraulic cylinders, but which could also be embodied as hydraulic motors, hydraulic accumulators, etc... Conventionally, the actuators are used to control the movement and operation of various work implements of the machine, such as, in the case of a backhoe loader, the lowering and raising of a loader arm, the tilting of a loader bucket, the lowering and raising of a back-hoe arm and of a backhoe dipper, the tilting of a backhoe bucket, etc.. Other actuators could be provided for other movements and other work implements, but also for accessories such as actuators for stabilizer legs or power take-offs. On figure 1 is also shown that the main hydraulic power circuit feeds the machine's steering actuator 22, here through a steering wheel 23 by which the machine's driver or user can control the steering of the machine. Although not shown, the machine could also be equipped with a hydraulically powered driveline deriving its hydraulic pressurized fluid from the same main hydraulic power circuit 20.

The main hydraulic power circuit 2 also comprises control systems 24 for controlling each of the actuators 21. These control systems can comprise hydraulic components, such as hydraulic lines, valves, distributors, check-valves, pressure and flow regulators, including also man/machine interface devices such a levers, switches, joystick controllers, to allow for the proper control of the actuators. The control systems will ideally comprise also electrical and electronic devices to achieve enhanced control functions.

The main hydraulic power pump 20 is pressure regulated following the pressure in the main hydraulic circuit 2. In the shown embodiment, the main hydraulic power pump is a variable capacity pump, the capacity of which is regulated following the pressure in the main hydraulic circuit.

The main hydraulic power circuit 2 will not be detailed any further here inasmuch the skilled man in the art is able to conceive a circuit suitable for the contemplated machine.

The engine 1 can be of any type. Of course, the invention will be most beneficial with a conventional turbocharged diesel engine. Nevertheless, other kinds of engines could be contemplated, including petrol engines, gas turbines, electrical motors, or hybrid power sources combining a combustion engine and an electrical motor/generator.

The hydraulic transmission circuit 2 as shown on Figure 1 will be detailed in relation to Figure 3 where the same hydraulic transmission is shown in an enlarged view.

On Figure 2 is shown a first embodiment of a hydraulic transmission circuit for a construction equipment machine according to the invention. The transmission circuit 3 comprises a hydraulic transmission pump 30 which supplies pressurized hydraulic fluid to a hydraulic transmission motor 31 through a transmission fluid line 32. The transmission pump 30 is operatively coupled to be driven by the engine 1. The transmission motor 31 is operatively coupled to drive the main hydraulic power pump 20. In the example shown, the engine and the transmission pump are directly mechanically coupled through a clutch 4, while the transmission motor 31 is directly mechanically coupled through a clutch 5. Nevertheless, both couplings, which perform the transfer of rotating motion from one element to the other, could also be embodied by different devices, including for example fluid couplers, gearings, gearboxes, etc...

The transmission pump 30 is preferably a variable flow pump, for example a variable displacement axial piston pump with variable swash-plate. Nevertheless, it is contemplated that the invention can also be implemented with other types of pumps, even with fixed displacement.

The transmission motor 31 is of a variable capacity type, for example a variable displacement axial piston motor with variable swash-plate. Its capacity is controlled by a control system whereby, for a given flow and pressure of the hydraulic fluid in the transmission fluid line 32, it will be possible to control the motor's speed. The control system 33 shown on Figure 2 comprises a hydraulic two-way cylinder 331, a proportional

4-way solenoid switch valve 332, a feed line 333, and an electronic control unit 334. The feed line 333 is branched-off the transmission fluid line 32 and comprises a check valve

335 and a flow restrictor 366. The feed line 333 supplies one or the other of the two fluid chambers of the hydraulic two-way cylinder 331 through the solenoid valve 332 which is controlled by the ECU 334, so as to achieve a positive displacement of the rod of the cylinder in one way or the other depending on the position of the switch valve. The rod of cylinder 331 is mechanically coupled to the variable capacity control mechanism 311 of the variable motor 31. In practice, the actuator 331 can be incorporated in the variable displacement motor. Also, other control system designs could be used which are known to the man in the art.

The control system 33 is designed to allow the driver of the machine to control the rotating speed of the hydraulic transmission motor. Therefore, it also comprises a man/machine interface device by which the driver can input a target speed to the ECU 334. In figure 2, the interface device is shown as a pedal 337, which can be equipped with an angle transducer to provide the ECU 334 with an electronic analog or digital signal representative of the angle by which the pedal 337 is depressed by the driver, which in turn is indicative of the target speed. Other interface devices could also be used, either of a similar lever/joystick type, or of a turn-button type, of even of an indirect type comparable to cruise-control setting device. The control system 33 further comprises a speed sensor 338 capable of transmitting to the ECU 334 a signal indicative of the rotational speed of the hydraulic motor 31. Additionally, the transmission fluid line 32 could be equipped with a pressure and/or a flow sensor to provide the corresponding information to ECU 334 to achieve optimum control of the motor 31.

Thanks to the hydraulic transmission circuit 3 comprising a variable capacity motor 31, it is possible to supply the main hydraulic power pump with the requisite torque and speed to match the machine's demands without having to constantly adjust the operating conditions of the engine 1, at least to a certain extent. Indeed, at least for a certain range of torque and power demand around a given operating point, it will be possible to adjust to the demand without substantially modifying the engine's operating parameters, simply due to the possibility to adjust the hydraulic motor's capacity so as to adjust its torque output and its operating speed.

Of course, this adjustability has its limits, notably linked to the ability for the transmission pump 30 to deliver the right flow of hydraulic fluid at the right pressure when operated by the engine 1 at a given speed.

On Figure 3 is shown an enhanced embodiment of a transmission circuit for a construction equipment machine according to the invention. The difference with the previous embodiment of Figure 2 lies only in the presence of a pressure accumulating system 34 which is located between an upstream part 321 and a downstream part 322 of the transmission fluid line 32, between the transmission pump 30 and the transmission motor 31. In this embodiment, the transmission circuit 3 comprises two fluid pressure accumulators 341, 342 which are connected each to one of two parallel intermediate conduits 343, 344 each having an upstream and a downstream extremity. The accumulating system 34 is connected to the upstream 321 and downstream 322 parts of the transmission fluid line 32 through, respectively, an upstream solenoid switch valve 345, and a downstream solenoid switch valve 346 which are both electrically controlled by an ECU. In the shown embodiment, the ECU controlling the accumulating system switch valves 345, 346 is the ECU 334 of the motor speed control system 33, but it could be a different ECU. The upstream switch valve 345 can be switched between a first position, where it connects the upstream part 321 of transmission fluid line 32 to the upstream extremity of a first intermediate conduit 343 while the upstream extremity of the second intermediate conduit 344 is closed, and a second position, where it connects the upstream part 321 of transmission fluid line 32 to the upstream extremity of the second intermediate conduit 344, while the upstream extremity of the first intermediate conduit 343 is closed. The downstream switch valve 346 can be switched between a first position, where it connects the downstream part 322 of transmission fluid line 32 to the downstream extremity of the second intermediate conduit 34 while the downstream extremity of the first intermediate conduit 343 is closed, and a second position, where it connects the downstream part 322 of transmission fluid line 32 to the downstream extremity of the first intermediate conduit 343, while the downstream extremity of the second intermediate conduit 344 is closed.

The ECU 334 controls both switch valves 345, 346 simultaneously so that they are both either in their first position or in their second position.

When the valves 345, 346 are in their first position, the first accumulator 341 is therefore in fluid communication with the transmission pump 30 and is isolated from the downstream part 322 of the transmission . fluid.. line 32. Therefore, the pressurized hydraulic fluid which is supplied by the transmission pump 30 is accumulated under pressure in the first accumulator. During the same time, the second accumulator 342 is isolated from the pump 31 but is connected to the downstream part 322 of the transmission fluid line 32 and is therefore able to supply the transmission motor 31, and its speed control system 33, with previously accumulated hydraulic fluid under a substantially uniform pressure. Conversely, when the valves 345, 346 are both in their second position, the first accumulator 341 supplies fluid to the hydraulic motor 31 and the second accumulator 342 is in communication with the transmission pump 30 to as to be refilled with pressurized fluid.

One advantageous feature of the accumulating system 34 is to provide the transmission motor 31 with hydraulic fluid under a substantially constant pressure whatever the flow of fluid in the motor 31, which of course will depend on the instant capacity of the motor 31 and on the load on the main pump 20.

Another advantageous feature of the accumulating system is to be able smoothen the ups and downs in hydraulic fluid flow in the transmission line 32 with respect to the transmission pump. This means that, at least to a certain degree, it becomes possible to operate the transmission pump at a substantially constant speed, pressure and flow, which means that the engine will also run at a substantially constant speed and load. It is then possible to choose and rate the various components of the transmission circuit, as well as the engine, so that this substantially constant speed and load imposed on the engine, to meet the torque, power and speed needed by the main hydraulic pump, are close to the engine's optimal operational parameters.

The extent to which the accumulator system will be able to keep a constant pressure and compensate the ups and downs in terms of flow will be largely dependent on the technology of the accumulator(s), and most of all, of their dimensions. Of course, the larger the accumulator(s) will be, the more efficient will the accumulator system be.

In the system of Figure 3, each of the of two intermediate lines 341, 342, and/or the accumulators, are preferably equipped with a pressure and/or a flow sensor to provide the corresponding information to ECU 334 which can then control the switching of switch valves in order to manage the volume of fluid accumulated in each accumulator, and to connect them at the right time to the pump 30 or to the motor 31. Advantageously, since the ECU 334 which drives the switch valves 345, 346 also controls the motor 31, the switching strategy for the valves 345, 346 can take into account the instant capacity of the motor 31 and its rotating speed. In all cases, the downstream part 322 of the transmission fluid line 32 could be equipped with a pressure and/or a flow sensor to provide the corresponding information to ECU 334 to achieve optimum control of the motor 31 and of the pressure accumulating system 34. It will now be given an approximate outlook on the advantages of the various embodiments of the invention, hereinafter referred to as configuration B for the embodiment of Figure 2 and configuration C for the embodiment of Figure 3, versus the prior art, hereinafter called configuration A, where the main hydraulic power pump is directly driven by the engine. We will consider the case of a wheel loader (or any equivalent machine, such as a backhoe loader or a skid-steer loader) when performing different sets of operations which are typical of its work cycle. Set I of operations corresponds to the loading of the bucket. Set II of operations corresponds to the loader reversing, lowering its loader arm, and forwarding towards a truck. Set III of operations corresponds the loader forwarding towards the truck and raising its loader arm.

A prior art machine corresponding to configuration A has been equipped with measurement sensors in order to determine the engine power, engine torque and engine speed, as well as the pressure and flow of hydraulic fluid in the main hydraulic circuit. The capacity of the main hydraulic pump was also monitored. These parameters were recorded while the machine was performing its standard work cycle, including the set of operations defined above. For each of the said set of operations, it was then determined a representative peak value of the parameters, which are shown in tables A-I to A-III below.

Derived from the above, it has been calculated what would be the major operating parameters of a machine in configurations B and C for each of the set of operations I, II, and III described above. These figures are shown in tables B-I to B-III and C-I to C-III below. For these calculations, it was chosen to predetermine the optimum engine regime to be 1800 rpm and the capacity of the accumulator(s) to be 40 liters for configuration C, the accumulator system 34 being able to deliver at least 30 1/min under a pressure of 150 bars.

From the above tables, it can be seen that, in configuration A, there is simply no choice other than controlling the engine to provide exactly the torque and speed needed by the main pump.

In configuration B, the transmission circuit 3 allows to operate the engine 1 at a different speed than that of the main pump 20, with a different torque, while still satisfying the overall power requirement.

In configuration C, there is the supplemental advantage that the accumulator system 34 can provide part of the power needed.

In this set of operations, it is seen that, for configuration C, the engine 1 does not need to supply power to the main hydraulic circuit 2. Nevertheless, rather than simply idling the engine, it can be provided that the engine 1 is then used to refill the accumulator system 34 by driving the pump 30.

In this set of operations, with high power demand, it appears clearly that configuration C is advantageous in that it allows not only to operate the engine at its optimum speed/torque regime, which is also true for configuration B, but also to have an engine of lesser power rating since the additional peak power needed can be provided by the accumulator system 34. Of course, the accumulator system can only provide power to the extent that its capacity is sufficient to meet the duration of the peak power demand, but, depending on the work cycle, it is possible to adapt the capacity of the accumulators, and/or their storing pressure to increase or decrease the ability of the accumulator system to provide the adequate duration of peak power.

The above figures have been calculated in the context of configurations B and C where the engine would be controlled according to a very simple strategy which is to keep, if possible, the engine 1 at a constant optimum speed. Of course, other strategies for controlling the engine, and of course controlling the transmission circuit accordingly, could be implemented, taking into consideration not the only an optimum engine speed, but an optimum set of engine speed / engine load data points. Of course, for configuration C, it would in any case be preferable to integrated into these strategies the control of the accumulating system state of charge. Preferably, the transmission speed control system 33, the transmission pump 30, the main power pump 20, the engine 1, and, in the case of embodiment 2, the accumulator system 34, will be electronically controlled either through a common electronic unit, or through several inter-communicating electronic units in order to achieve the optimum control of these elements.

Claims

1. A construction equipment machine comprising a main engine (1) and a main hydraulic circuit (2) with at least a main hydraulic power pump (20) and at least one hydraulic power consumer (21), characterized in that said main engine (1) drives the main hydraulic power pump (20) through a hydraulic transmission circuit (3) comprising a hydraulic transmission pump (30) which is driven by said main engine (1) and which supplies hydraulic pressurized fluid to a hydraulic transmission motor (31), said hydraulic transmission motor (31) being connected to drive the main hydraulic power pump (20), and in that the hydraulic transmission motor (31) is of a variable capacity type.

2. A construction equipment machine according to claim 1, characterized in that the machine comprises a transmission motor control system (33) by which a user of the machine can control the capacity of the hydraulic transmission motor (31).

3. A construction equipment machine according to claim 2, characterized in that the transmission motor control system (33) controls the speed of the hydraulic transmission motor by varying the capacity of the motor.

4. A construction equipment machine according to claims 2 or 3, characterized in that the control system (33) comprises a speed sensor (338) for sensing the speed of the transmission motor (31).

5. A construction equipment machine according to any preceding claim, characterized in that the main hydraulic power pump (20) is pressure regulated following the pressure in the main hydraulic power circuit (2).

6. A construction equipment machine according to claim 5, characterized in that the main hydraulic power pump (20) is a variable capacity pump the capacity of which is regulated following the pressure in the main hydraulic power circuit (2).

7. A construction equipment machine according to any preceding claim, characterized in that the hydraulic transmission pump (30) has a variable capacity.

8. A construction equipment machine according to any preceding claim, characterized in that the hydraulic transmission circuit (3) comprises at least one hydraulic pressure accumulator (34, 341, 342).

9. A Construction equipment machine according to claim 8, characterized in that the hydraulic transmission circuit (3) comprises at least two hydraulic pressure accumulators (341, 342), and in that when one accumulator is hydraulically connected to the transmission pump (30), the other accumulator is hydraulically connected to the transmission motor (31).

10. A construction equipment machine according to any preceding claim, characterized in the main engine (1) is an internal combustion engine.