Hydraulic transmission

Patent metadata

Field	Value
Publication number	US-9976641-B2
Application number	US-201415022397-A
Country	US
Kind code	B2
Filing date	Feb 25, 2014
Priority date	Sep 18, 2013
Publication date	May 22, 2018
Grant date	May 22, 2018

Abstract

A hydraulic transmission comprising a variable displacement pump and motor, at least one having cylinders having valves which are controllable on each cycle of cylinder working volume to determine the net displacement of working fluid by the cylinder. The transmission has a valve control module which determines a displacement of the pump and the motor by specifying a displacement demand. The pump and/or motor valve control module determine the frequency of intensity peaks in the frequency spectrum of the pattern of cylinders carrying out active and inactive cycles of cylinder working volume using a first procedure and, if these will fall within disallowed frequency bands including the resonant frequency of components with which the transmission is in mechanical communication, the displacement demand, or another input, is periodically modified to suppress generation of those frequencies. The hydraulic transmission is useful for example in a wind turbine generator, or a vehicle.

First claim

The invention claimed is:

1. A hydraulic pump or motor comprising:
a rotatable shaft,
a shaft sensor which measures the position or speed of rotation of the rotatable shaft,
at least one cam having at least one lobe,
a plurality of cylinders having working volumes which vary cyclically with rotation of the rotatable shaft,
a low pressure working fluid line and a high pressure working fluid line,
a plurality of valves regulating the flow of working fluid between each cylinder and the low and high pressure working fluid lines, at least one said valve associated with each cylinder being an electronically controlled valve,
wherein the hydraulic pump or motor comprises a valve control module configured to generate command signals to actively control the said electronically controlled valves in phased relationship to cycles of cylinder working volume, to thereby determine whether each cylinder carries out an active cycle in which there is a net displacement of working fluid or an inactive cycle in which there is no net displacement of working fluid, for each cycle of cylinder volume,
the valve control module having a demand input which receives a displacement demand signal representative of a target net displacement of working fluid by the plurality of cylinders,
wherein the valve control module is configured to generate said command signals so that the time averaged net displacement of the plurality of cylinders meets the displacement demand represented by the displacement demand signal, while selecting the pattern of command signals so that the frequency of one or more intensity peaks of the frequency spectrum of the pattern of active and inactive cycles of cylinder working volume carried out by the cylinders do not remain within one or more ranges of undesirable frequencies, taking into account the speed of rotation of the rotatable shaft.

2. A hydraulic pump or motor according to claim 1 , wherein the said frequency of one or more intensity peaks comprises the fundamental frequency of cylinders carrying out active cycles, or a harmonic thereof, or the fundamental frequency of cylinders carrying out inactive cycles, or a harmonic thereof.

3. A hydraulic pump or motor according to claim 1 , wherein the valve control module is configured to execute a displacement determination algorithm at each of a plurality of time steps to process the displacement demand signal and the net displacement of working fluid during previous cycles of cylinder working volume and to cause at least one said cylinder to undergo an active cycle in which it makes a net displacement of working fluid when the difference between the total amount of working fluid which has been displaced and the total amount of working fluid which has been demanded, exceeds a threshold.

4. A hydraulic pump or motor according to claim 3 , wherein the valve control module is configured to vary the threshold to thereby reduce the intensity of one or more undesirable frequency components of the pattern of active and inactive cycles of cylinder working volume of the one or more said cylinders.

5. A hydraulic pump or motor according to claim 4 , wherein the threshold is alternately raised and lowered to reduce the intensity of one or more said undesirable frequency components.

6. A fluid working machine according to claim 5 , wherein the threshold is alternately raised and lowered at a frequency between half and one tenth of the frequency of an undesirable frequency within a said range of undesirable frequencies within which at least one intensity peak of the frequency spectrum would otherwise fall.

7. A fluid working machine according to claim 4 , wherein the valve control module receives a rotatable shaft speed signal and is configured to take into account the rotatable shaft speed signal when determining whether the threshold should be varied.

8. A fluid working machine according to claim 1 , wherein the displacement demand signal received by the valve control module is selectively modulated so that the frequency of one or more said intensity peaks of the frequency spectrum does not remain within one or more said ranges of undesirable frequencies.

9. A fluid working machine according to claim 8 , wherein the displacement demand signal is selectively modulated by a periodic modulation waveform.

10. A hydraulic pump or motor according to claim 3 , wherein the valve control module comprises an accumulator which stores an accumulated displacement error value and an adder which at each time step adds the displacement demand represented by the displacement demand signal to the accumulated displacement error value and a subtractor which subtracts a value representative of the amount of working fluid which has been displaced under the active control of the valve control module on the same or the previous time step.

11. A hydraulic pump or motor according to claim 1 , wherein the valve control module comprises a frequency determination module which determines the frequency of one or more intensity peaks of the frequency spectrum of the pattern of active and inactive cycles of cylinder working volume which would be generated if the valve control module selected the pattern of active and inactive cycles of cylinder working volume using a first procedure, taking into account the displacement demand and the speed of rotation of the rotatable shaft, and compares the determined one or more frequencies with one or more range of undesirable frequencies, and if at least one determined frequency falls within at least one range of undesirable frequencies, normally causes the pattern of active and inactive cycles of cylinder working volume to be selected using a second procedure instead of the first procedure, thereby reducing the intensity of said frequency spectrum in at least one said range of frequencies.

12. A hydraulic pump or motor according to claim 1 , comprising a resonance determining module which determines one or more of the ranges of undesirable frequencies in dependence on one or more measured parameters.

13. A hydraulic pump or motor according to claim 1 , comprising a resonance determining module which is operable to determine one or more of the ranges of undesirable frequencies by analyzing a signal to identify one or more oscillations, and to identify the resonant frequency of the one or more oscillations, and to set one or more ranges of undesirable frequencies to include the determined one or more frequencies.

14. A hydraulic pump or motor according to claim 12 , wherein the resonance determining module determines one or more of the ranges of undesirable frequencies in dependence on one or more measured parameters which are independent of the speed of rotation of the rotatable shaft.

15. A hydraulic pump or motor according to claim 1 , wherein at least some of the undesirable frequency components include resonant frequencies of at least one component of a or a machine including the hydraulic transmission.

16. A hydraulic transmission comprising
a variable displacement hydraulic pump,
a variable displacement hydraulic motor,
a drive shaft coupled to the hydraulic pump, for driving the hydraulic pump, and
an output shaft coupled to the hydraulic motor, for coupling to a load,
wherein at least one of the hydraulic pump and the hydraulic motor is a hydraulic pump or motor according to claim 1 .

17. A wind turbine generator comprising a hydraulic transmission according to claim 16 , a turbine coupled to the hydraulic pump and comprising a plurality of blades, and an electricity generator coupled to the hydraulic motor.

Assignees

• Artemis Intelligent Power Ltd

Inventors

• Caldwell Niall
• Abrahams Daniel
• Dumnov Daniil

Classifications

• F03D9/28

  the apparatus being a pump or a compressor · CPC title

• F03D15/00

  Transmission of mechanical power · CPC title

• F04B17/02

  driven by wind motors · CPC title

• F04B1/0531

  with cam-actuated distribution members · CPC title

• F04B1/06

  Control · CPC title