The present disclosure relates generally to architectures for hydraulic systems. More particularly, the present disclosure relates to hydraulic systems having closed circuit hydraulic architectures.
Machines such as vehicles, for example, skid steer vehicles and transit mixers, often have closed circuit hydraulic systems (e.g., hydrostatic transmissions). In the case of skid steer vehicles, closed circuit hydraulic systems may be used for vehicle propulsion. In the case of transit mixers, closed circuit hydraulic systems may be used to provide concrete drum rotation.
Closed circuit hydraulic systems can be used for applications in which the systems are operated at low flow conditions to drive actuators at slower speeds, and high flow conditions to drive actuators at higher speeds. For some of these systems, such as a system for rotating a concrete drum for a transit mixer, the duration the system is operated at a low flow condition is much longer than the duration the system is operated at a high flow condition. During such low flow operations, a main pump of the system is operated at a reduced stroke length to provide reduced hydraulic fluid flow through the closed circuit. Prolonged operation at low speeds is not ideal from an efficiency perspective since variable piston pumps exhibit lower volumetric efficiencies when operated at reduced stroke lengths. In the case of a transit mixer, considerable energy losses result. Aspects of the present disclosure relate to architectures for addressing this issue.
During higher speed operation of a closed circuit hydraulic system, the main pump operates at full stroke and the charge pump is loaded by hot oil relief pressure. The hot oil relief valve is set at a pressure greater than the control pressure required for changing the displacement of the main pump, and energy losses proportional to the pressure margin will occur whenever the system is in use. Further, during idling operation of a closed circuit hydraulic system, the charge pump flow typically relieves over a charge pump relief valve causing energy losses the magnitude of which depends upon the relief setting of the charge pump relief valve. Aspects of the present disclosure relate to systems for reducing these types of losses.
Aspects of the present disclosure relate to a closed circuit architecture with intelligent control strategy adapted to allow charge pump flow to be used to satisfy low speed requirements. In this way, a main pump need not be used to satisfy low speed requirements and energy losses related to the inefficient volumetric efficiency of the main pump for low flow applications can be reduced.
Aspects of the present disclosure also relate to a closed circuit architecture with intelligent control strategy adapted to allow real-time pressure regulation of a relief pressure setting of a hot oil relief valve to minimize differences between the relief pressure setting and the pump control pressure during higher flow operation. In this way, energy losses related to the margin between the pump control pressure and the pressure relief setting can be reduced.
Aspects of the present disclosure also relate to closed circuit architecture with intelligent control strategy adapted to allow real-time regulation of a relief pressure setting of a charge pump relief valve to minimize energy losses during idling/no work conditions.
Aspects of the present disclosure also relate to closed circuit architecture with intelligent control strategy adapted to allow for the real-time regulation of a pressure relieve setting of a hot oil relief valve to provide for dynamic braking against equipment inertial movement.
Aspects of the present disclosure also relate to a hydraulic architecture that can switch between a closed loop circuit configuration where a charge pump provides charge flow to a main pump that drives an actuator, and an open loop circuit configuration where the charge pump drives the actuator.
Aspects of the present disclosure relate to a hydraulic circuit architecture for powering a hydraulic actuator such as a hydraulic motor for rotating a concrete drum of a transit mixer. During a first mode of operation, the hydraulic motor is driven at a first speed by hydraulic fluid pumped through a closed loop circuit by a main hydraulic pump powered by a power take-off of an engine. A charge pump, power by an electric motor, provides charge flow to a low-pressure side of the main hydraulic pump. During a second mode of operation, the main hydraulic pump is set to zero displacement, and charge pump is used to drive the hydraulic motor at a second speed that is less than the first speed. In the second mode of operation, the hydraulic circuit architecture is configured as an open loop hydraulic circuit.
Aspects of the present disclosure relate to hydraulic systems having hydraulic circuit architectures having features for enhancing the overall operating efficiencies of the hydraulic systems. One aspect of the present disclosure relates to hydraulic systems having hydraulic circuit architectures including features adapted to enhance the operating efficiencies of the systems during low speed operations. In one example hydraulic system, the hydraulic circuit architecture allows a charge pump to drive a hydraulic actuator of the system during low speed operations. Other examples relate to hydraulic systems having hydraulic circuit architectures that can be operated as closed circuits for high-speed operations, and can be operated as open hydraulic circuits for low speed operations. A further aspect of the present disclosure relates to hydraulic systems having a closed circuit architecture in which a hot oil relief valve of the system can be variably set at different pressures depending upon the control pressure of the system. In certain examples, the oil pressure relief setting of the hot oil relief valve is maintained at a pressure setting only slightly greater than the control pressure of the system. A further hydraulic system in accordance with the principles of the present disclosure utilizes a charge pump relief valve having a variable pressure relief setting in which the pressure relief setting is substantially reduced when the system is operating in an idling condition.
Another aspect of the present disclosure relates to a hydraulic drive system including a main hydraulic pump (e.g., a variable displacement pump or a fixed displacement pump), a hydraulic actuator (e.g., a hydraulic motor, hydraulic cylinder or the like) and a charge pump (e.g., an integral or auxiliary charge pump). The hydraulic system is operable in a first mode in which the main hydraulic pump drives the hydraulic actuator via a closed hydraulic circuit and the charge pump provides charge flow to the closed hydraulic circuit. The hydraulic system is also operable in a second mode in which the charge pump drives the hydraulic actuator via an open hydraulic circuit.
In one example, a hydraulic drive system for driving a vehicle component includes an electric motor, a variable displacement hydraulic pump driven by the electric motor, a variable displacement hydraulic motor driven by the main hydraulic pump, the hydraulic motor having an output shaft for driving the vehicle component, and a controller for controlling the speed of the electric motor and the displacement of the hydraulic pump, the controller being configured to meet an output demand of the hydraulic motor by selecting a combination of motor displacement, pump displacement and motor speed that results in the maximum efficiency of the system.
In some examples, the hydraulic component is one of a rotating drum and a propulsion system of a transit mixer.
In some examples, the controller is configured with a high speed mode and a low speed mode, wherein in the high speed mode the hydraulic motor and pump are operated at full displacement and the speed of the electric motor is varied to meet the output demand of the hydraulic motor.
In some examples, if an efficiency of the electric motor at low speeds is higher than an efficiency of the hydraulic pump at de-stroked conditions, the controller reduces the speed of the electric motor in order to achieve the output demand of the hydraulic motor. In some examples, if an efficiency of the electric motor at low speeds is higher than an efficiency of the hydraulic pump at de-stroked conditions, the controller reduces the speed of the electric motor in order to achieve the output demand of the hydraulic motor.
In some examples, the controller compares a rotational speed of the hydraulic component and compares the rotational speed with a reference speed, wherein the controller stops supply of power to the electric motor when the rotational speed matches the reference speed, wherein the controller supplies power to the electric motor when the rotational speed falls below the references speed.
In one example, a drive system for driving a vehicle component includes a first drive pathway including a hydrostatic transmission, a second drive pathway including an electric motor, a drive interface for transmitting power from the first or second drive pathway to the vehicle component, and a controller for selectively operating the hydrostatic transmission and the electric motor.
In some examples, the vehicle component is a drum of a transit mixer, the drum having a rotational speed demand.
In some examples, when a rotational speed demand of the drum is above a threshold, the controller operates the hydrostatic transmission to supply power to the vehicle component through the drive interface.
In some examples, the electric motor is driven by the hydrostatic transmission through the drive interface and acts as a generator.
In some examples, when a rotational speed demand of the drum is below a threshold, the controller operates the electric motor to supply power to the drum through the drive interface and controls the hydrostatic transmission to destroke at least one of a hydraulic pump and a hydraulic motor of the hydrostatic transmission.
In some examples, the controller compares a rotational speed of the drum and compares the rotational speed with a reference speed, wherein the controller stops supply of power to the electric motor when the rotational speed matches the reference speed, wherein the controller supplies power to the electric motor when the rotational speed falls below the references speed.
In some examples, the vehicle component is a propulsion system of a vehicle, for example a transit mixer, the propulsion system having a speed demand.
In some examples, when a rotational speed demand of the propulsion system is above a threshold, the controller operates the electric motor to supply power to the propulsion system through the drive interface and controls the hydrostatic transmission to destroke at least one of a hydraulic pump and a hydraulic motor of the hydrostatic transmission.
In some examples, when a rotational speed demand of the propulsion system is below a threshold, the controller operates the hydrostatic transmission to supply power to the vehicle component through the drive interface.
In some examples, the controller compares a rotational speed of the propulsion system and compares the rotational speed with a reference speed, wherein the controller stops supply of power to the electric motor when the rotational speed matches the reference speed, wherein the controller supplies power to the electric motor when the rotational speed falls below the references speed.
A variety of additional aspects will be set forth in the description that follows. The aspects can relate to individual features and to combinations of features. It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the examples disclosed herein are based.
The accompanying drawings, which are incorporated in and constitute a part of the description, illustrate several aspects of the present disclosure. A brief description of the drawings is as follows:
The main hydraulic pump 22 is preferably a variable displacement, bi-directional pump. The displacement of the main hydraulic pump 22 as well as the direction of hydraulic fluid flow through the closed hydraulic circuit 26 can be controlled by a controller 28. In the depicted example, the controller 28 interfaces with a pump control valve 30 used to control the displacement as well as the pumping direction of the main hydraulic pump 22. In one example, the pump control valve 30 can be actuated by a driver such as a solenoid controlled by the controller 28. The pump control valve 30 can be moved to different positions by the solenoid under the control of the controller 28 to control the displacement and pumping direction of the main hydraulic pump 22. In one example, the pump control valve 30 controls a pump control pressure provided to the main hydraulic pump 22 via pump control lines 32, 34 which provide hydraulic pressure for controlling the position of a swash plate 36. It will be appreciated that the angle of the swash plate 36 controls the displacement and pumping direction of the main hydraulic pump 22.
As indicated above, the main hydraulic pump 22 is preferably bi-directional. Thus, the main hydraulic pump 22 can be operated in a first directional setting in which hydraulic fluid flows in a first direction 38 through the closed hydraulic circuit 26. The main hydraulic pump 22 can also be operated at a second directional setting in which hydraulic fluid is pumped in a second direction 40 through the closed hydraulic circuit 26. When the hydraulic fluid is pumped in the first direction 38, the first portion 26a of the closed hydraulic circuit 26 represents a high-pressure side of the closed hydraulic circuit 26, and the second portion 26b represents a low-pressure side of the closed hydraulic circuit 26. As such, the first port 22a represents a high-pressure side of the main hydraulic pump 22 and the first port 24a represents a high-pressure side of the hydraulic motor 24. In addition, the second port 22b represents a low-pressure side of the main hydraulic pump 22 and the second port 24b represents a low-pressure side of the hydraulic motor 24. By contrast, when the main hydraulic pump 22 pumps hydraulic fluid in the second direction 40 through the closed hydraulic circuit 26, the second portion 26b represents the high-pressure line of the closed hydraulic circuit 26 and the first portion 26a represents the low-pressure line of the closed hydraulic circuit 26. As such, the second port 22b of the main hydraulic pump 22 represents the high-pressure side of the main hydraulic pump 22 and the second port 24b represents the high-pressure side of the hydraulic motor 24. As such, the first port 22a represents the low-pressure side of the main hydraulic pump 22 and the first port 24a represents the low-pressure side of the hydraulic motor 24.
The controller 28 can include one or more processors. The processors can interface with software, firmware, and/or hardware. Additionally, the processors can include digital or analog processing capabilities and can interface with memory (e.g., random access memory, read-only memory, or other data storage). In certain examples, the processors can include a programmable logic controller, one or more microprocessors, or like structures. The processors can also interface with displays (e.g., indicator lights, screens, etc.) and user input interfaces (e.g., control buttons, switches, levers, keyboards, touchscreens, control panels, dials, slide-bars, etc.). The user input interfaces can also a user to input a speed input signal to the controller which is representative of a desired rotational speed of the motor 24. In one example, the motor drives a concrete drum of a transit mixer.
Referring still to
The hydraulic circuit architecture of the hydraulic drive system 20 is preferably configured such that the hydraulic drive system 20 is operable in a first mode (see
It will be appreciated that the first mode is preferably activated for higher motor speed applications and the second mode is preferably activated for lower motor speed operations. The second mode allows the motor 24 to be efficiently driven at low speeds, while the main pump 22 is de-activated (e.g., set to zero displacement). In this way, the main pump 22 is not required to be used for low flow applications in which its volumetric efficiency is low. However, for higher motor speed applications which require higher hydraulic flow rates, the main pump 22 can efficiently be used to drive the motor 24. The controller 28 can switch the system between the first and second modes based upon the value of a motor speed input signal input to the controller from a user interface. The motor speed input signal corresponds to a desired drive speed of the hydraulic motor 24. If the desired drive speed of the hydraulic motor is above a predetermined speed, the controller 28 can set the system to the first mode. If the desired motor drive speed is at or below the predetermined speed, the controller 28 can set the system to the second mode.
Referring again to
The hydraulic circuit architecture of the hydraulic drive system 20 further includes a mode selector valve 54 movable between a first position (see
Referring again to
The hydraulic drive system 20 includes a charge flow line 64 that extends from the mode selector valve 54 to a location 66 along the charge pump flowline 58 that is between the first and second one-way check valves 60, 62. The hydraulic drive system 20 also includes a motor drive flow line 68 that extends from the mode selector valve 54 to the flow directional control valve 56. The flow directional control valve 56 can selectively couple the motor drive flow line 68 to a first directional flow control line 70 that couples to the charge pump flow line 58 at a location 71 between the first one-way check valve 60 and the first portion 26a of the closed hydraulic circuit 26, and a second directional flow control line 72 that couples to the charge pump flow line 58 at a location 73 between the second one-way check valve 62 and the second portion 26b of the closed hydraulic circuit 26.
Referring again to
Referring again to
Referring to
Referring to
The controller 28 is used to control the hydraulic proportional valves 50, 90 and other valves (e.g., pump control valve 30, mode selector valve 54, directional flow valve 56). The controller also interfaces with pressure sensors, user interfaces, electric motor controls, and other components to operate the hydraulic circuit architectures in the various modes described above. The controller will have digital and/or analog inputs and outputs for interfacing with the sensors, valves and other components.
With reference to
As shown at
In order to achieve different speeds of drum rotation, the speed of the electric motor 44 and the displacement of the hydraulic pump 22 is varied in such a way that the overall efficiency of the system is always maximum. For example, in a condition where high drum speed is desired, the hydraulic pump 22 and the hydraulic motor 24 used in hydrostatic transmission 100 works with full stroke displacement. During this time, the electric motor 44 should be operated at speed with maximum efficiency. Electric motor 44 draws power from battery 130 through controller 110 and performs the high speed drum rotation function.
Where a low drum speed is desired, the decision to either reduce the speed of electric motor 44 speed or de-stroking the hydraulic pump 22 used in hydrostatic transmission 100 will be based on the reference efficiency maps used in controller 110 such that maximum possible efficiency results. If the efficiency of the electric motor 44 at low speeds is higher than the efficiency of the hydraulic pump 22 at de-stroked conditions, then the controller 110 reduces the speed of the electric motor 44 in order to achieve the low speed drum rotation. If the efficiency of the electric motor at low speeds is lower than the efficiency of the hydraulic pump 22 at de-stroked conditions, then the controller 110 reduces the displacement of the hydraulic pump 22 in order to achieve the low speed drum rotation.
During battery powered drum rotation, the controller 110 receives the feedback of drum rotation speed, for example from a sensor or data input from the vehicle control system, and compares it with a reference speed derived from operator inputs and inverter output waveform. If the drum rotation speed matches the reference speed, the controller 110 stops the supply of power to electric motor 44. Once the drum rotation speed falls below the reference speed, then again controller 110 starts supplying power to electric motor 44.
As shown at
The drive interface 140 can be configured in any suitable form, such as a direct gear train, a planetary gear set, a belt-pulley drive system, etc. An example drive interface 140 is presented at
Where the drive system 300 is configured for drum rotation, the decision whether to use engine power via pathway 300a or battery power via pathway 300b for drum rotation is based on the speed requirements derived from operator input and the efficiency maps of hydrostatic transmission 100 and electric motor 44. With reference to
For high speed requirements of drum rotation derived from operator input, the control logic in the controller 110 uses engine power transferred through hydrostatic transmission 100. During this time, the controller 110 disconnects power to electric motor 44. In an example configuration where the electric motor 44 and hydrostatic transmission 100 are directly coupled to the drive interface 140 with the gear arrangement shown at
When the controller 110, derives the low speed drum rotation requirements based on operator input, the hydrostatic transmission 100 stops transferring power to drum rotation shaft 148 by de-stroking variable displacement motor 24 and pump 22. This allows shaft 142 to rotate with as little resistance as possible while the while the electric motor 44 supplies power to the output shaft 148 via drive interface 140.
During battery powered low speed drum rotation, the controller 110 receives the feedback of drum rotation speed and compares it with the reference speed derived from operator input. If the drum rotation speed matches the reference speed, the inverter of the controller 110 stops the supply of power to electric motor 44 during which the electric motor 44 would rotate due to the drum inertia. During this, the electric motor 44 works as a generator and electric charge/current generated flows from electric generator 44 to the battery 130 through the inverter/converter of the controller 110. When drum rotation speed drops below the reference speed in controller 110, then the inverter of the controller 110 again starts supplying power to electric motor 44 from battery 130.
Where the drive system 300 is configured for vehicle propulsion, the decision whether to use engine power via pathway 300a or battery power via pathway 300b for drum rotation is based on the speed requirements derived from operator input and the efficiency maps of hydrostatic transmission 100 and electric motor 44. With reference to
For low speed requirements of propulsion derived from operator input, the control logic uses engine power transferred through hydrostatic transmission 100. During this time controller 110 disconnects power to electric motor 44 and electric motor 44 works as a generator and supplies the current to battery 130.
When the controller 110, derives the high speed propulsion requirements based on operator input, the hydraulic transmission 100 stops transferring power to propulsion by de-stroking variable displacement motor 24 and pump 22. And then controller 110, supplies the electric power for propulsion using electric motor 44.
During battery powered high speed propulsion (mostly during constant speed mode with pedal-on), the controller 110 receives the feedback of propulsion speed and compares it with the reference speed derived from operator command and inverter output waveform. If the propulsion speed matches the reference speed, the inverter of the controller 110 stops the supply of power to electric motor 44 during which the electric motor 44 would rotate due to the kinetic inertia (kinetic regeneration) of the vehicle. During this, the electric motor 44 works as the generator and electric charge/current generated flows from electric generator 44 to the battery 130 through the inverter/converter of the controller 110. When propulsion speed drops below the reference speed in controller 110, then the inverter of the controller 110 again starts supplying power to electric motor 44 from battery 130.
During battery powered propulsion when the operator is not engaging pedal (pedal-off) and not yet applied the dynamic braking, the inverter is not supplying electric power as there is no operator command through pedal. During this, electric motor 44 works as a generator 44 due to vehicle kinetic inertia and electric current generated flows from generator 44 to battery 130 through inverter/converter device associated with the controller 110 to effectuate regenerative braking.
In one aspect of the above-referenced regeneration process, the controller 110 recognizes the constant speed requirement based on the operator pedal angle/input which is constant over the period of time. Once the controller 110 recognizes the constant speed mode, if the propulsion speed has matched the reference speed in the controller, then the controller 110 stops the power supply to electric motor 44 even though the operator is pressing the pedal at constant angle/input. During the period of power supply cut-off the electric motor 44 acts as a generator 44. During this, if propulsion speed falls below the reference speed, then again the power supply to electric motor 44 is resumed. During when constant speed mode is ON, if there is any change in pedal movement/angle, then this pedal movement input overrides the condition of constant speed mode and propulsion speed is regulated as per the operator input through pedal.
While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.
Number | Date | Country | Kind |
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201911016747 | Apr 2019 | IN | national |
This application is a National Stage application of International Patent Application No. PCT/EP2020/025188, filed on Apr. 24, 2020, which claims priority to Indian Application No. 201911016747 filed on Apr. 26, 2019, each of which is hereby incorporated by reference in its entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2020/025188 | 4/24/2020 | WO |