Energy efficient electric vehicle control system

Abstract

An electric vehicle comprises an electrical system and a hydraulic system. The electrical system comprises an electric power supply and an electric motor-generator connected to the drive train of the vehicle. The hydraulic system includes a pump, and a hydraulic actuator. At least one of the electrical system and the hydraulic system includes energy recovery means arranged to convert kinetic energy from the drive train to electrical energy or to convert kinetic energy from the hydraulic actuator into hydraulic pressure respectively. The electrical and hydraulic systems are connected such that the recovered energy may be converted from electrical to hydraulic energy and/or vice versa. The hydraulic system may further include a hydraulic accumulator.

Claims

1. A lift truck comprising: an electrical system comprising an electric power supply and an electric motor-generator connected to a drive train of the lift truck; and a hydraulic system for causing lifting of and additional auxiliary movements of a lift of the lift truck, the hydraulic system including a hydraulic pump/motor, a main hydraulic actuator configured to raise and lower the lift, and one or more auxiliary hydraulic actuators configured to cause the additional auxiliary movements of the lift; wherein the hydraulic system is configured to selectively redirect hydraulic power from the main hydraulic actuator to hydraulically power the one or more auxiliary actuators without redirection of said hydraulic power first to the hydraulic pump/motor.

2. The lift truck of claim 1, wherein the hydraulic system further includes a hydraulic accumulator.

3. The lift truck of claim 2, wherein the hydraulic system includes another motor-generator connected to the hydraulic pump/motor and arranged such that hydraulic power stored in the hydraulic accumulator may be converted to electrical energy.

4. The lift truck of claim 3, wherein the electrical energy generated from the hydraulic accumulator may be selectively directed to the electric motor-generator of the electrical system to provide motion to the drive train and/or to charge the battery.

5. The lift truck of claim 1, wherein the electric motor-generator is configured to convert kinetic energy from the drive train to electrical energy and is connected to the hydraulic system such that said electrical energy may be converted to hydraulic power via the hydraulic pump/motor.

6. The lift truck of claim 5, wherein the electrical power supply is a battery and said electrical energy converted from the drive train may be selectively used to charge the battery.

7. The lift truck of claim 1, wherein the hydraulic system includes another motor-generator connected to the hydraulic pump/motor and an inverter drive connected to the another motor-generator of the hydraulic system.

8. The lift truck of claim 1, further comprising an inverter drive connected to the electric motor-generator of the electrical system.

9. The lift truck of claim 1, wherein the electric motor-generator of the electrical system is connected to a traction drive, and is configured to apply a braking force to the lift truck and to convert the kinetic energy generated during said braking to electrical energy.

10. A lift truck comprising: a battery; an inverter drive electrically connected to the battery and connected to a first motor/generator, a traction drive/brake coupled to the first motor/generator; a second inverter drive electrically connected to the battery and connected to a second motor/generator; and a hydraulic pump/motor coupled to the second motor/generator and hydraulically connected to a hydraulic lift circuit for causing lifting of and additional auxiliary movements of a lift of the lift truck, the hydraulic lift circuit including a main hydraulic actuator configured to raise and lower the lift, and one or more auxiliary hydraulic actuators configured to cause the additional auxiliary movements of the lift; wherein hydraulic power from actuation of the main hydraulic actuator is selectively redirected to hydraulically power the one or more auxiliary actuators without redirection of said hydraulic power first to the hydraulic pump/motor.

11. The lift truck of claim 10, wherein hydraulic power from actuation of the main hydraulic actuator is alternatively selectively converted into electrical power and stored in the battery or converted into torque to move the lift truck.

12. The lift truck of claim 10, wherein kinetic power from the traction drive/brake is converted to electrical energy and is selectively stored in the battery or further converted to hydraulic power and used to actuate the main hydraulic actuator.

13. The lift truck of claim 12, wherein the hydraulic lift circuit further includes a hydraulic accumulator, and wherein electrical power converted from the traction drive/brake is alternatively selectively converted into hydraulic power and stored in the accumulator.

14. The lift truck of claim 10, wherein the hydraulic lift circuit further includes a hydraulic accumulator, and wherein hydraulic power from actuation of the main hydraulic actuator is alternatively selectively stored in the accumulator.

Description

(1) The present invention will now be described by way of example only with reference to the following illustrative figures in which:

(2) FIG. 1 is a schematic of a first embodiment of a system constructed in accordance with the present invention utilizing a first motor/generator to drive the traction drive/brake and a second motor/generator for the hydraulic pump/motor.

(3) FIG. 2 illustrates a second exemplary schematic embodiment of a system constructed in accordance with the present inventionthe system utilizing a single motor/generator to drive the traction drive/brake and the hydraulic pump/motor.

(4) FIG. 3 illustrates a third exemplary schematic embodiment of a system constructed in accordance with the present inventionthe system utilizing a single motor/generator and at least two hydraulic pump/motors.

(5) FIG. 4 illustrates a fourth exemplary schematic embodiment of a system constructed in accordance with the present inventionthe system utilizing two motor/generators and at least two hydraulic pump/motors.

(6) FIG. 5 is the system of FIG. 4 showing a first operating condition of the system.

(7) FIG. 6 is the system of FIG. 4 showing a second operating condition of the system.

(8) FIG. 7 is the system of FIG. 4 showing a third operating condition of the system.

(9) FIG. 8 is the system of FIG. 4 showing a fourth operating condition of the system.

(10) Referring now to FIG. 1, a schematic for a work vehicle such as a lift truck or fork lift. The system 10 comprises a battery 20 electrically connected to a first inverter drive 30 which is electrically connected to a first motor/generator 40 and a second inverter drive 32 which is electrically connected to a second motor/generator 42. The first motor/generator 40 is mechanically connected to the traction drive/brake 50 or wheel of system 10. The second motor/generator 42 is mechanically connected to a hydraulic pump/motor 60 which is connected to a hydraulic circuit 70 which includes a plurality of valves for the operation of cylinders to operate the functions of the lift truck. These functions include the raising and lowering of the lift, and also the tilt, reach, and side shift. The circuit 70 also includes an accumulator 80 which is selectively connected to the pump/motor 60, lift cylinder 72, and other cylinders 74, 76, 78 which operate the function of the lift.

(11) The battery 20 is typically a DC battery which is electrically connected to provide and receive DC power to and from the inverter drives 30, 32. The inverter drives 30, 32 are electrically connected to each other via a common bus 34, which enables the inverter drives 30, 32 to pass electric power from one to the other, enabling the power to bypass the battery 20 for either immediate use or storage in the accumulator 80. The inverter drives 30, 32 are electrically connected to provide and receive AC power to and from the motor/generators 40, 42, which operate both as motors and generators. The first motor/generator 40 is mechanically connected to the traction drive/brake 50 which operates as a traction drive during acceleration of the work vehicle and as a traction brake during deceleration of the vehicle. The second motor/generator 42 is connected to the hydraulic pump/motor 60 which operates as a pump when charging the accumulator 80 or powering the hydraulic cylinders 72, 74, 76, 78 and as a motor when hydraulic pressure from the hydraulic accumulator 80 or from the hydraulic lift cylinder 72 is used to power the traction drive 50 or to provide power for storage in the battery 20. The motor/generators 40, 42 are variable speed drives. The inverter drives 30, 32 are PMAC drives or other appropriate inverter drives.

(12) The operation of the system is as follows:

(13) In stand by mode, the second motor/generator 42 is run off of the battery 20 at an optimum speed and torque to turn the hydraulic pump/motor 60 to charge the accumulator 80.

(14) In accelerating drive mode, the motor/generator 40 will take power from the battery 20, the motor drive operation can be assisted by running the motor/generator 42 using flow from the accumulator 80 to drive the hydraulic pump/motor 60 with electrical power transfer direct through the common bus 34 (not back to the battery).

(15) In decelerating drive mode, the first motor/generator 40 will create power as a generator, this power can go back to the battery 20, or it can be more efficiently routed to the second motor/generator 42 to charge the accumulator 80 as required.

(16) In lift mode, the accumulator 80 is used for fast movement of the hydraulic actuator 72 with motor 42 assist as required. Precision movements may be made with the motor/generator 42 only. Power for the lift actuator 72 is also available from battery 20, and power from motor/generator 40 may also be used if available (during braking).

(17) In lower modethe speed is set by the motor/generator 42, by the load motor if accumulator needs charge, and to generate electricity if the accumulator 80 is fully charged. Regenerative power from lowering the lift actuator 72 is available to the accumulator 80, traction motor 40, or battery 20 (the battery being lowest efficiency regeneration).

(18) Auxiliary functions 74, 76, 78 are powered by accumulator 80 with motor/generator 42 assist as required.

(19) The intention is to run the motor/generators 40, 42 in their optimum power/torque mode, and regenerate as much brake or lowering energy as possible. It's more efficient to transfer recovered electrical power to the opposite motor/generator, than back into the battery 20.

(20) For example during deceleration the traction motor/generator 40 can create electrical power, which is used to drive the motor/generator 42 and charge the accumulator 80 during transport mode. Running the motor/generator 42 during transport mode will help balance out the peak demands. Acceleration and lifting can be boosted by the accumulator 80 that has been charged during less demanding parts of the machine cycle.

(21) In a second embodiment shown in FIG. 2, a schematic shows one motor/generator 40 to drive and be driven by both the traction drive/brake 50 and the hydraulic pump/motor 60. Accordingly, the system 10 utilizes a single inverter drive 30 between the battery 20 and the motor/generator 40. The second embodiment is otherwise similar to the first embodiment, but with a significant reduction in component cost. Some simultaneous operations will need to be compromised, but this will be compared to the cost reduction trade off.

(22) In a third embodiment shown in FIG. 3, a schematic shows one motor/generator 40 to drive and be driven by both a first hydraulic pump/motor 60 and a second hydraulic pump/motor 62 which is coupled to the traction drive/brake 50. The second pump/motor 62 and the first pump motor 60 are selectively connected by the hydraulic circuit 70 to each other and to the hydraulic actuator 72, and the hydraulic accumulator 80. Accordingly, the system 10 utilizes a single inverter drive 30 between the battery 20 and the motor/generator 40. The third embodiment is otherwise similar to the first embodiment, but with a significant reduction in component cost. Some simultaneous operations will need to be compromised, but this will be compared to the cost reduction trade off.

(23) In FIG. 4, another embodiment is shown which saves battery power consumption by re-generating kinetic energy and using this energy to drive either the traction or hydraulic implement motors. The advantage is to keep the motors running in their most optimum torque and speed curve and to balance out the peaks and troughs of the overall power demand from the battery. The most efficient energy recovery is by either transferring the recovered electrical energy directly to the opposite motor drive, or if this motor does not need additional power use this to run the hydraulic pump to charge the accumulator. This approach will yield an overall power consumption benefit. An additional advantage is to reduce the size of the main power components (battery motor & drive).

(24) The system of FIG. 4 is shown in operational conditions in FIGS. 5-8. In FIG. 5, the motor draws energy from the battery to run the pump at the optimum speed to charge the accumulator (during transport mode). Any brake energy can be used to generate electrical power and avoid the need to draw power from the battery. The accumulator is sized to operate the tilt reach and side shift cylinders during the normal operating cycle, the pump flow can also be used to assist if required.

(25) In FIG. 6, during lifting, brake energy generated by the traction motor can be used to assist the hydraulic motor, and again reduce the current draw from the battery. Speed and fork position control is achieved by varying the motor speed.

(26) In FIG. 7, for gravity lowering with no weight on the forks we can by-pass oil to the tank via the proportional RV. To slow the cylinder we ramp the RV pressure and drive the pump to generate electricity. This can assist the traction motor drive, and avoid current draw from the battery. With a heavy load more energy is recovered, while speed and fork position control is achieved by varying the motor speed.

(27) In FIG. 8, the accumulator can be used to drive the pump motor to generate power to assist the traction drive during acceleration, and again reduce power consumption from the battery. Reach, tilt, and side shift functions are normally operated by the accumulator, as this is more efficient, and allows simultaneous operation during lift and lower.

(28) Although not shown, a disk brake may be utilized for auxiliary braking and to act as a parking brake. A fail-safe interlock can be utilized for the disk brake if no driver is at the cab/seat.

(29) Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.