This application claims the benefit of the filing date under 35 U.S.C. § 119(a)-(d) of European Patent Application No. 19170851.0, filed on Apr. 24, 2019.
The present invention relates to a compressor control module and, more particularly, to a compressor control module for controlling the operation of a variable displacement swash plate compressor.
In general, air-conditioning systems for vehicles are equipped with a refrigerant compression cycle system for cooling and/or heating. The heart of the refrigerant compression cycle is a compressor that compresses and circulates refrigerant in the refrigerant cycle. The compressor is typically configured to keep the pressure in the evaporator at a low level. The pressure in the evaporator directly relates to the temperature of saturated refrigerant throttled into the evaporator, and hence, by keeping the pressure low, the compressor keeps the temperature low in the evaporator.
The variable displacement swash plate type compressor is popular for vehicle air-condition systems. The variable displacement swash plate compressor is typically driven by a belt driven by the vehicle engine. The compressor output (such as compressor load or compressor work done on fluid) can be adjusted by shifting an angle of a swash plate.
The variable displacement swash plate compressor is configured so that a rotating swash plate's inclination angle affects the reciprocation length of compression pistons. The inclination angle of the swash plate, in turn, is typically regulated by varying a pressure difference between a crank chamber of the variable displacement swash plate compressor and suction chamber thereof. That is, when the pressure in the crank chamber is increased by directing high-pressure working fluid from the discharge chamber to the crank chamber, the pressure difference between the crank chamber and the suction chamber (Pc−Ps) increases, and the swash plate angle decreases (i.e. is moved perpendicular to a main shaft), so the stroke of the piston is reduced. Accordingly, when the pressure in the crank chamber is decreased, the swash plate angle is increased and the stroke of the piston is increased, leading to increased compressor mass flow rate.
The crank chamber of the variable displacement swash plate compressors in the prior art is in constant communication with the suction chamber via a fixed orifice, often termed “bleed port”. With a control valve closing the passage between the crank chamber and the discharge chamber, the pressure in the crank chamber, due to the bleed port, decreases until it reaches the pressure in the suction chamber. This will increase the inclination angle of the swash plate to maximum, and consequently, the strokes of the pistons, increasing the compressor mass flow.
The prior art control of swash plate angle is done by regulating the flow of the high-pressure working fluid from the discharge chamber to the crank chamber. Mainly the pressure difference between the resulting crank case pressure and suction pressure (Pc−Ps) defines the swash plate angle. This configuration of the prior art is well known and simple but has disadvantages. The bleed port between suction chamber and the crank chamber leads to pressure losses that could otherwise be used for cooling. Another disadvantage is that the prior art control tends to be unstable in certain conditions.
The electronic control valve used by a so-called “externally controlled variable compressor” typically includes an actuating rod driven by an electronic actuator such as a solenoid. The actuating rod moves valve bodies, depending upon the turning on/off of the solenoid. The externally controlled variable compressor can adjust the temperature at the outlet of an evaporator, for example, within a range of up to 12° C. By adjusting the temperature in the evaporator, the AC system can be optimized for cooling load, leading to more efficient cooling, and reduced power consumption.
Further, since the electrical control valve in some embodiments may control the swash plate to be perpendicular to the main shaft, setting the compressor output/load to a minimum, the mechanism for otherwise turning the compressor on/off (usually a clutch) can be dispensed with, simplifying the construction and reducing manufacturing costs.
The prior art typically involves an open-loop regulation of the suction pressure. A Heating Ventilation and Air Conditioning (HVAC) system sets a desired suction pressure for the compressor. The desired suction pressure is translated into a certain drive signal for the electronic control valve of the compressor which sets the swash plate position, and hence the compressor output/load. The suction pressure is typically not measured. The HVAC control only uses vehicle cabin temperature and evaporator air outlet temperature as control values. The construction is mostly stable but due to the suction pressure not being measured, there is no feedback that the actual suction pressure is achieved. The system is hence prone to static errors and hysteresis effects due to friction.
A compressor control module (CCM) controls an output of a variable displacement swash plate compressor. The CCM directly calculates, or receives from an external source, a signal indicating a desired or required output from the compressor, receives a current value of the desired or required output, and receives or calculates a current rotation speed and angle, with respect to a rotation axis, of a swash plate, or a current piston stroke length and a reciprocating frequency of the compressor. The CCM determines a difference between the desired or required output from the compressor and the current value and outputs a signal to a valve driving unit which will adjust an angle of a swash plate such that the actual value becomes closer to, or the same as, the desired or required output, taking into account the additional values received or calculated in the receives or calculates step.
The invention will now be described by way of example with reference to the accompanying Figure, of which:
Exemplary embodiments of the present invention will be described hereinafter in detail with reference to the attached drawings, wherein like reference numerals refer to like elements. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. According to the description of the various aspects and embodiments, elements shown in the drawings can be omitted if the technical effects of those elements are not needed for a particular application, and vice versa: i.e. elements that are not shown or described with reference to the figures but are described above can be added if the technical effect of those particular elements is advantageous in a specific application.
A variable displacement swash plate compressor according to an embodiment is shown in
A front housing 20, as shown in
As shown in
The control valve 100 selectively opens and closes the first communication passage P1 and the second communication passage P2, so that the bleed port can be closed, or substantially closed. By allowing pressure to be regulated in both directions, the bleed port can be reduced or closed, substantially improving efficiency. However, closing the bleed port makes the system less stable and small variation of control valve opening may lead to large change in swash plate angle. Closing or substantially closing the bleed port improves efficiency but makes the system complex to control. This invention describes a solution how to precisely control a compressor where the bleed port is closed or substantially reduced.
The variable displacement swash plate compressor might not comprise a bleed port or bleed valve between any of the suction chambers and crank chamber, or at least comprises a bleed port or bleed valve with reduced diameter. By removing the bleed port or bleed valve or reducing its diameter, the efficiency of the compressor is increased due to reduction of inner pressure loss and hence fuel can be saved.
A rotary shaft 40 may be rotatably disposed through the center bore 11 of the cylinder housing 10 and a shaft hole 23 of the front housing 20, as shown in
A rotor 44 having the rotary shaft 40 passing through the center thereof to integrally rotate with the rotary shaft 40 is disposed in the crank chamber 21. The rotor 44 is formed substantially in a disc shape and fixed on the rotary shaft 40 and a protrusive hinge arm may be formed on a side the rotor 44.
The swash plate 48, in the embodiment shown in
In
When the first communication passage P1 is opened, the crank chamber 21 and the suction chamber 31 communicate with each other, so the pressure in the crank chamber 21 decreases. Accordingly, the inclination angle of the swash plate 48 is increased, and consequently, the strokes of the pistons 15 are increased. Further, when the second communication passage P2 is opened, the crank chamber 21 and the discharge chamber 33 communicate with each other, so the pressure in the crank chamber 21 is increased. Accordingly, the inclination angle of the swash plate 48 is decreased and the strokes of the pistons 15 are decreased.
In the embodiment, the control valve 100 does not use the entire section shown in
The control of the control valve 100 may be targeted at achieving a certain suction chamber pressure requested by a Heating Ventilation and Air Conditioning (HVAC) system. In order to improve the precision of achieved suction pressure with the bleed port closed, a pressure sensor may be included on an evaporator side of the refrigeration cycle, for example, in the suction chamber 31 of the compressor. The sensor measures the suction pressure. A control unit including a controller (such as a PI/PID controller) may further be included and configured to adjust the control valve 100 so as to close the gap between target and actual suction pressure. Feedback from suction pressure in closed loop increases stability and accuracy of the suction pressure control. However, the rather long delay in the refrigeration cycle may lead to controllability issues and make the control complex.
The HVAC system, for example of a vehicle, is shown in
For the calculation of the target value, other external signals may be taken into account, like outside air conditions (such as temperature and humidity), sun load on the vehicle, and target and actual value of the evaporator air outlet temperature.
The control unit then applies control input to the electrical control valve 100 by applying a current to the electromagnetic actuator, so the opening level of the first communication passage P1 is increased. When the first communication passage P1 is increased, the crank chamber 21 and the suction chamber 31 communicate with each other, so the pressure in the crank chamber 21 decreases. The inclination angle of the swash plate 48 is increased, and consequently, the strokes of the pistons 15 are increased. This increases the load of the compressor (assuming constant rotation speed of the swash plate 48) and leads to pressure decrease in the evaporation side of the refrigeration cycle. Measured suction pressure is decreased and using a control algorithm of the controller, the control unit is configured to adjust the input to the control valve so that the target suction pressure is kept.
The above relates to a solenoid actuator. The skilled person would easily adjust the invention for using a stepped actuator, or any other suitable actuator.
If P2 channel is open long enough, the pressure in the crank chamber 21 becomes the same as the discharge pressure, so the inclination angle of the swash plate 48 is decreased to its minimum value. Without the compressor keeping the suction pressure low, the pressure in the evaporator will increase due to heating and additional refrigerant entering via the thermal expansion valve. When the suction pressure reaches the target value a current will again be applied to the actuator in order increase the stroke lengths to maintain an appropriate suction pressure.
As shown in
Example sensors providing information that can be used to calculate current compressor mass flow rate, include sensors providing information on swash plate rotation speed and angle. Another example of sensors providing information that can be used to calculate current swash plate angle and/or compressor mass flow rate, includes sensors providing information on piston reciprocation frequency and stroke length. Current swash plate angle and/or compressor mass flow rate may be measured and/or calculated in other ways. The swash plate rotation speed may be the same as the piston reciprocation frequency. The swash plate angle may be derived from the piston stroke length from pre-set data on compressor construction including the swash plate and piston structure.
a) either directly calculate, or receive 610 from an external source, for example the HVAC control unit, a signal indicating the desired or required output from the variable displacement swash plate compressor, for example, but not limited to, a suction pressure, a piston stroke length, an evaporator outlet air temperature, a refrigerant mass flow and/or a work done on fluid;
b) receive 620 the current/actual value of the value described in a)
c) receive or calculate 630 the current rotation speed and angle, with respect to the rotation axis, of the swash plate 48, or the current piston stroke length and its reciprocating frequency, respectively, of the variable displacement swash plate compressor;
d) optionally receive or calculate 640 additional current values of the compressor, the air conditioning system or from the vehicle, like the discharge pressure, the crank case pressure, the delta pressure between suction pressure and crank case pressure, the evaporator outlet air temperature, the engine speed, but not limited to,
e) determine 650 the difference between the desired or required output from the variable displacement swash plate compressor and the current output of the variable displacement swash plate compressor; and
f) output 660 a signal to the valve driving unit which will adjust the angle of the swash plate 48 such that the actual output of the variable displacement swash plate compressor becomes closer to, or the same as, the desired or required output as obtained in step a), also taking into account the additional values received or calculated in c) and d).
The present CCM may drive the control valve to adjust pressure ratio between Pc and Ps to regulate the swash plate angle and output of the compressor in a closed loop control which may include the use of input signals from additional sensors. The signal output from the CCM at step f) may affect the valve driving unit that drives the actuator that drives the valve body to open one of the communication passages. The first passage opens PcPs and increases the angle. The second opens PdPc to decrease the swash plate angle.
The variable displacement swash plate compressor might comprise at least one delta pressure sensor that measures the pressure difference between the crank case pressure and the suction pressure, wherein the CCM is (optionally) adapted to use this information for step d).
In one example, the CCM contains automated control algorithms including an inner loop that is regulating the control valve actuator in order to achieve a certain swash plate angle and/or compressor discharge rate as set by an outer control loop in a cascade manner. The inner loop may be closed by input from sensors providing measurements that may be used to determine the swash plate angle or current compressor discharge rate. The delay may be relatively small compared to the delay from a suction pressure sensor, such as a delay well below one second.
One embodiment of a regulation of suction pressure with an inner loop regulating the swash plate angle is shown in
The delay in the outer loop is longer than in the inner loop shown in
In addition, the swash plate position can be monitored before and/or during operation and certain failure detected if the swash plate 48 is not responding as expected to change in control valve changes.
A CCM according to an embodiment may also comprise a piston reciprocating speed sensor. Measurement from the piston reciprocating speed sensor may provide information on the piston reciprocation frequency to the inner and/or outer controller in a feedforward manner in order to pre-empt changes in engine rpm, allowing the control valve to be adjusted so that the stroke length compensate for the increased piston reciprocation frequency in order to keep the work load placed on the fluid constant. If the engine speed is increased suddenly, the increased compressor speed will be feedforward for example to the inner loop, and the stroke length decreased, so that a spike in compressor output is prevented. The spike would otherwise lead to torque peaks and to unnecessary cooling, and a waste of energy. As an example, the piston reciprocation cycle frequency and the piston stroke length of pistons 15 might be calculated by signals received from at least one speed-stroke sensor, such as speed-stroke sensor descried in European patent application 19159899.4.
Without using information on the rotation speed of the swash plate 48, such as the feedforward swash plate rotation speed, changes of compressor speed are only recognized by the controller after the suction pressure has changed. In such case, if the speed of the compressor is increased due a change of the engine rpm, the cooling effect of the air-conditioning system will be too high until the suction pressure has settled around the higher, desired level/value, leading to passenger discomfort and wasted energy. By sensing and responding to changes in compressor rotation speed (such as by feedforward), the CCM may react on speed variations earlier. In one embodiment, the compressor RPM and/or its derivative is used as input for the feed forward function in order to adjust the target piston stroke length value, e.g. by adding or subtracting certain values. In one embodiment, the adjustment may also take place at a different location of the control circuit, e.g. at the controller output value.
Examples of piston positioning sensors and piston speed sensors include eddy current sensor, cylinder pressure sensor, hall sensor, magneto-resistive sensor, capacity based sensor, and inductive based sensor.
By using the piston stroke length information, which corresponds to the swash plate angle, in an inner control circuit of a cascaded controller, the piston stroke length can be controlled directly. This significantly improves the control quality. It is also possible to use a difference between crank chamber pressure and suction chamber pressure (Pc−Ps) value instead of the piston length information for the 2nd controlling loop.
The input to the 1st controller in
The output signal of the 2nd controller shown in
At the time when the SWP angle changes, meaning its derivative is different from zero, or different from a certain tolerance band around zero, the corresponding Pc−Ps value is logically either the current lower Pc−Ps threshold or the current upper Pc−Ps threshold, and is stored in a “lower threshold variable” or a “upper threshold variable”. This can be done permanently, meaning that the Pc−Ps threshold values are updated constantly. The “2nd controller” uses these thresholds for precisely controlling SWP angle movement.
The feed forward function may also be used in relation to
If the piston stroke length is low, the P-parameter and/or I-parameter and/or D-parameter can be higher compared to higher stroke situations. Depending on the control deviation of the outer control loop, it might be advantageous to adjust the I-parameter in order to increase the response of the controller. For example, if the control deviation is larger than a pre-defined limit, the I-Parameter can be set to larger values than for smaller control deviations.
Further, in order to improve controllability, for any embodiment described herein, a feed-forward function can be advantageous. This is because fast RPM changes cause the Ps to either increase or decrease. Without using these RPM changes as input value for the controller, the controller response to such RPM changes is very slow, because the suction pressure response is very slow (system related). In this case, the Ps pressure logically varies, which cause increases energy consumption because of unintended ramping of the Ps level/mass flow.
The compressor RPM value is used as input for the controller in order to improve the dynamic behavior in case of compressor RPM changes. For example, the compressor RPM and/or its derivative may be used as input for the feed forward function in order to adjust the input and/or the output of one and/or more than one controller loops.
Although exemplary embodiments were described above, the scope of the present disclosure is not limited to the specific embodiments and the present disclosure may be appropriately changed within the scope described in claims. For example, the suction pressure sensor may be disposed at one of the suction chamber 31 of the compressor, the outlet end of the evaporator, and a working fluid pipe between the evaporator and the compressor.
Although cascade control, PI, PID are mentioned in examples, any other type or construction of control mechanism may be used by the skilled person as the case may be, such as Model Predictive Control (MPC), Internal Model Controller (IMC), online predictive controller like neural network, Multi-Input-Single-Output (MISO) controller.
A thermostatic expansion valve (TXV) may control evaporator superheat temperature by adjusting mass flow. The compressor controls suction pressure that may be strongly linked to the evaporator temperature.
The control algorithm of the CCM may be located on a PCBA including a microcontroller, a valve driving unit, power supply, input units to read sensors and communication units to deliver and/or receive information to/from AC ECU and/or Engine ECU.
Number | Date | Country | Kind |
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19170851.0 | Apr 2019 | EP | regional |