Hydraulic gearbox for an SMA motor used in an energy recovery device

Description

Field

[0001] The present application relates to the field of energy recovery and in particular to the use of Shape-memory alloys (SMAs) or Negative Thermal Expansion materials (NTE) for same.Background

[0002] Low-grade heat, which is typically considered less than 100 degrees, represents a significant waste energy stream in industrial processes, power generation and transport applications. Recovery and re-use of such waste streams is desirable. An example of a technology which has been proposed for this purpose is a Thermoelectric Generator (TEG). Unfortunately, TEGs are relatively expensive. Another largely experimental approach that has been proposed to recover such energy is the use of Shape-memory Alloys.

[0003] A Shape-memory Alloy (SMA) is an alloy that "remembers" its original, cold-forged shape which once deformed returns to its pre-deformed shape upon heating. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems.

[0004] The three main types of Shape-memory Alloys are the copper-zinc-aluminium-nickel, copper-aluminium-nickel, and nickel-titanium (NiTi) alloys but SMAs can also be created, for example, by alloying zinc, copper, gold and iron.

[0005] The memory of such materials has been employed or proposed since the early 1970's for use in heat recovery processes and in particular by constructing SMA engines which recover energy from heat as motion. Recent publications relating to energy recovery devices include PCT Patent Publication number WO2013 / 087490, assigned to the assignee of the present invention. It is desirable to translate the contraction of the SMA or NTE material into a mechanical force in an efficient manner. It is not a trivial task and generally is complicated and involves significant energy losses, as disclosed in patent publication numbers DE3014560 and US2008 / 034750. US patent publication number US2016 / 138575 and US patent No. 5,079,920 discloses the option of having a simple hydraulic system to harvest the output of a SMA material. PCT Patent publication number WO2018 / 002182 discusses a solution in which a low pressure accumulator can prevent the over-stressing of SMA wires when they are not ready to be subjected to the full force developed by a hydraulic system, which in effect provides a protection mechanism to allow the SMA wires to have a long fatigue life. US-A-4955196 describes a machine that uses the shape memory effect of shape memory alloy members to generate force on a movable part when its transformation is constrained while undergoing temperature changes. The generated high pressure or high speed fluid can be used to drive a generator. US 2016 / 0138575 describes an energy recovery device with a shape memory alloy (SMA) engine housed in an immersion chamber. The engine has a length of SMA material fixed at a first end and connected at a second end to a drive mechanism. The immersion chamber is sequentially filled to activate the SMA and there is an output transmission for coupling to and being driven by a gear based or hydraulic based transmission system.

[0006] A problem with the systems disclosed is that it is very difficult to transfer large reciprocating forces from contraction / expansion of the SMA or NTE material into steady rotary motion.

[0007] It is therefore an object to provide an improved system and method in an energy recovery device.Summary

[0008] An energy recovery system according to claim 1 is provided.

[0009] In one embodiment, a plurality of check valves are configured to create a unidirectional main drive circuit for the fluid to flow.

[0010] In one embodiment, a hydraulic motor is configured to transfer the energy gained from the SMA core to a generator.

[0011] In one embodiment, a low pressure side is adapted to provide an applied force to the core and a high pressure side takes the flow with the energy gained to a generator.

[0012] In one embodiment, a reciprocating motion of the power stroke is configured to be smoothed out through the use of at least one accumulator.

[0013] In one embodiment, a steady flow rate through a motor is provided, such that the motor is configured to operate at a speed which suits a higher efficiency output.

[0014] In one embodiment, the core comprises a plurality of Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) elongated wires arranged in parallel with each other.

[0015] The advantage of the invention is to be able to allow a multistage variable force application regime on a SMA core or engine to increase the system efficiency. The system provides a method of transferring large reciprocating forces into a steady rotary motion.

[0016] The back force on the SMA is generated by the electrical load demand put on the generator which transfers into a hydraulic system, through a hydraulic motor for example. This can be enabled using a power pack system. The key function of the power pack is to create a minimum relaxation pressure for resetting the core or engine, replenish lost fluids, through a series of valves and keep the oil healthy through cleaning and cooling.Brief Description of the Drawings

[0017] The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a known energy recovery system; Figure 2 illustrates a first embodiment of the invention showing a basic schematic of an energy recovery system; Figure 3 illustrates a hydraulic circuit according to a second embodiment run in a configuration shown in Figure 1; and Figure 4 illustrates a hydraulic circuit according to a third embodiment of the invention and a variation of Figure 2 operating in a closed loop system. Detailed Description of the Drawings

[0018] The invention relates to a heat recovery system under development which can use either Shape-Memory Alloys (SMAs) or Negative Thermal Expansion materials (NTE) to generate power from low-grade heat.

[0019] An exemplary known embodiment of an energy recovery device will now be described with reference to Figure 1 which provides an energy recovery device employing a SMA engine indicated by reference numeral 1. The SMA engine 1 comprises an SMA actuation core. The SMA actuation core is comprised of SMA material clamped or otherwise secured at a first point which is fixed. At the opposing end, the SMA material is clamped or otherwise secured to a drive mechanism.

[0020] Thus whilst the first point is anchored the second point is free to move albeit pulling the drive mechanism 3, generating a power stroke. An immersion chamber 4 is adapted for housing the SMA engine and the chamber is adapted to be sequentially filled with fluids, at different temperatures, to allow heating and / or cooling of the SMA engine. Fluid can enter the top of the chamber 4 in the direction of the arrow and exit via an outlet near the bottom of the chamber 4. Accordingly, as heat is applied to the SMA core it is free to contract. Suitably, the SMA core comprises a plurality of parallel wires, ribbons or sheets of SMA material. It will be appreciated that in the context of the present invention the term 'wire' is used and should be given a broad interpretation to mean any suitable length of SMA or NTE material that can act as a core.

[0021] Typically, a deflection in and around 4% is common for such a core. Accordingly, when a 1m length of SMA material is employed, one might expect a linear movement of approximately 4cm to be available. It will be appreciated that the force that is provided depends on the mass of wire used. Such an energy recovery device is described in PCT Patent Publication number WO2013 / 087490, assigned to the assignee of the present invention.

[0022] For such an application, the contraction of such material on exposure to a heat source is captured and converted to usable mechanical work. A useful material for the working element of such an engine has been proven to be Nickel-Titanium alloy (NiTi). This alloy is a well-known Shape-Memory Alloy and has numerous uses across different industries. It will be appreciated that any suitable SMA or NTE material can be used in the context of the present invention.

[0023] Force is generated through the contraction and expansion of the SMA material, presented as a plurality of wires (or bundle), within the working core, via a piston and transmission mechanism. Accordingly, depending on the requirements of a particular configuration and the mass of SMA material needed a plurality of SMA wires may be employed together, spaced substanitally parralell to each other, to form a single core.

[0024] It is desirable to transfer large reciprocating forces from contraction / expansion of the SMA or NTE material into steady rotary motion.

[0025] In one embodiment the invention provides a multistage variable force application regime on an SMA engine to increase the system efficiency. A method of transferring large reciprocating forces into a steady rotary motion is now described with reference to Figure 2. The system provides a variable force application regime to bundles of SMA (Shape Memory Alloy) wires in a SMA engine or core.

[0026] During the relaxation stage of a cycle a hydraulics transmission module is adapted to apply a multistage force application. The pattern includes a base force for a certain time frame and after the time frame has passed; the transmission should be able to provide an increasing force over another set time frame.

[0027] The design can allow for varying time frames.

[0028] On the power stroke from the engine, a back force is applied to the SMA material with a force higher than the maximum relaxation force. The energy gain in the transmission generated from the SMA can then be transferred to a generator G.

[0029] Figure 2 illustrates a basic schematic of a circuit 10 showing a number of cores 11 connected to a hydraulic system 12 and a power pack system 13. The functionality of the control valves CV in a manifold supply the hot and cold water to the SMA engine 11 to provide a controlled temperature change to provide expansion and contraction of the SMA engine 11 to generate a power stroke for power generation.

[0030] The abbreviations used in figure 2 are set out below: BV is Ball / Shut Off Valve; CV is Check Valve; FL is Filter; HA is Hydraulic Accumulator; HM is Hydrostatic Motor; INT is Intensifier; PRF is Pressure Relief Valve; 16 is Recharge Motor; RP is Recharge Pump; and SV is Solenoid Operated Valve.

[0031] The power pack system 13 comprises a tank T, a recharge motor 16, and pump RP and filtration circuit 17 which provides the minimum force on the SMA material for the initial relaxation phase and allows a minimum flow to run through a filter and cooler for oil conditioning.

[0032] A series of check valves CV can be used to create a unidirectional main drive circuit for the fluid flow and a hydraulic motor HM is used in this circuit to transfer the energy gained in the circuit from the SMA to be transferred to the generator G. This circuit is then split down into two key sections. A low pressure side which supplies the cores and a high pressure side which takes the flow with the energy gain to the motor and generator G.

[0033] To supply an increasing pressure regime for the second phase of the relaxation stroke, an intensifier INT can be incorporated to take a small amount of flow from the high side of the main drive circuit to boost the pressure on a stored amount of oil volume taken from the low side and pump it into a piston which is applying a force to the SMA engine. The flow and pressure into the piston is regulated through a pilot operated valve. The activation time frames is dictated by solenoid valves SV.

[0034] The reciprocating motion of the pistons is smoothed out through the use of accumulator 12 which facilitates a steady flow rate through the motor and allows the generator G and motor to operate at a speed which suits a higher efficiency output.

[0035] The fluid delivery system valve operation can be operated by additional solenoids and variable flow restrictors.

[0036] In one embodiment a cascade arrangement involves the serial connection of cores such that water flowing from the outlet of one core can be sent to the inlet of another core.

[0037] Figure 3 illustrates how the hydraulic circuit can run in a basic configuration indicated by the reference numeral 30 and uses the same reference numerals as Figure 2 for common elements. This circuit 30 pumps a low pressure volume of oil into the core and when the cores are activated, the piston will increase the pressure in the actuator to pump it out through a check valve system and into the motor. This creates a pressure differential between the inlet of the motor and the outlet going to the tank T. This differential creates a torque on the motor shaft which can then be used to turn a generator G.

[0038] Figure 4 illustrates a variation of the embodiment shown in Figure 3 where the circuit can be converted into a closed loop system, indicated by the reference numeral 40. The outlet of the motor does not drop the pressure back to atmospheric in the tank T but rather matches the low pressure being pumped into the cores. This reduces the pressure drop across the motor but also reduces the flow rate that needs to be pumped in from the tank T. The system subsequently has less power out at the motor shaft but a reduced parasitic load on the pump. The low-pressure pump will serve to keep a minimum low pressure on the cores and send the minimum amount of fluid through a filtration or cooling system to ensure the oil remains in good condition. It will also replace any losses through the relief valves. This flow rate is typically a lot less than the main driveline flow being pumped from the core actuators and therefore creates a net gain in power output across the full system.

Claims

1. An energy recovery system (10,30,40) comprising: a Shape-Memory Alloy (SMA) core (11) or Negative Thermal Expansion (NTE) core (11) and adapted to convert movement of the core (11) into energy in response to a change in temperature, and a fluid is configured to communicate with the core (11) to provide a temperature change to cyclically activate the core (11), and generate a power stroke, characterised in that a hydraulics transmission module (12,HM) is configured to apply a back force to the core that is higher than a maximum relaxation force of the core during a relaxation stage of a cycle by applying a base force for a certain time frame, and after said time frame has passed the transmission module (12,HM) is configured to provide an increasing force over another set time frame.

2. The energy recovery system (10,30,40) as claimed in claim 1 wherein a plurality of check valves (CV) are configured to create a unidirectional main drive circuit for the fluid to flow.

3. The energy recovery system (10,30,40) as claimed in any preceding claim wherein a hydraulic motor (12) is configured to transfer the energy gained from the SMA core to a generator.

4. The energy recovery system (10,30,40) as claimed in any preceding claim comprising a low pressure side adapted to provide loading to the core and a high pressure side which takes the flow with the energy gained to a generator.

5. The energy recovery system (10,30,40) as claimed in any preceding claim wherein reciprocating motion of the power stroke is configured to be smoothed out through the use of at least one accumulator so that a steady flow rate through a motor is provided.

6. The energy recovery system (10,30,40) as claimed in any preceding claim wherein the core comprises a plurality of Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) elongated wires arranged in parallel with each other.