CN110986404B

CN110986404B - High-precision oil cooler and control method

Info

Publication number: CN110986404B
Application number: CN201911120623.1A
Authority: CN
Inventors: 毕增利; 赵成寅; 杨爱玲; 陈桂福
Original assignee: Gree Electric Appliances Inc of Zhuhai
Current assignee: Gree Electric Appliances Inc of Zhuhai
Priority date: 2019-11-15
Filing date: 2019-11-15
Publication date: 2021-06-18
Anticipated expiration: 2039-11-15
Also published as: CN110986404A

Abstract

The invention discloses a high-precision oil cooler and a control method, wherein the high-precision oil cooler comprises a refrigerating system and a circulating oil path system, and the refrigerating system comprises a main flow path system and a bypass flow path system; the main flow path system comprises a variable frequency compressor, a condenser, a fan, an electronic expansion valve and an evaporator which are sequentially communicated end to end; the fan is arranged on the condenser; the bypass flow path system comprises a bypass flow regulating valve, and the bypass flow regulating valve is connected with the condenser and the electronic expansion valve in parallel; the circulating oil circuit system comprises an oil tank and an oil pump; the oil inlet of the oil tank is communicated with the oil outlet of the machine tool, the oil outlet of the oil tank is communicated with the oil inlet of the oil pump, the oil outlet of the oil pump is communicated with the oil inlet of the evaporator, and the oil outlet of the evaporator is communicated with the oil inlet of the machine tool. The high-precision oil cooler can realize accurate temperature control and save energy sources.

Description

High-precision oil cooler and control method

Technical Field

The invention relates to an oil cooler, in particular to a high-precision oil cooler and a control method.

Background

The oil cooler utilizes the principle of evaporation and heat absorption of a refrigerant to carry out cooling work, the oil pump pumps oil from the oil storage tank of the machine tool to the refrigerating system for heat exchange treatment, and cooled hydraulic oil returns to the oil storage tank of the machine tool through the oil outlet pipeline of the oil cooler.

The existing oil cooler generally uses a fixed-frequency compressor to be matched with a bypass flow regulating valve to unload the redundant cold, thereby achieving the purpose of accurate temperature control, for example, the patent number ZL02294103.7 discloses a control device of a mechanical cooling system, and the patent number ZL200820088306.7 discloses a liquid cooling temperature control device, the control device of the mechanical cooling system and the liquid cooling temperature control device can unload the cold through a bypass valve (such as an electric flow regulating valve or an electronic flow regulating valve) used by the fixed-frequency compressor, thereby achieving the purpose of temperature control, but the defects that:

the control device of the cooling system for machinery and the liquid cooling temperature control device both realize temperature control through the fixed-frequency compressor and the bypass flow regulating valve, in the process, the fixed-frequency compressor always operates at a fixed frequency, the power consumption is high, and although temperature control can be realized through the bypass flow regulating valve, the energy is not enough saved.

Disclosure of Invention

The invention provides a high-precision oil cooler for overcoming the defects in the prior art, which can realize accurate temperature control and save energy sources.

Another object of the present invention is to provide a method for controlling a high-precision oil cooler.

The technical scheme of the invention for solving the technical problems is as follows:

a high-precision oil cooler comprises a refrigeration system and a circulating oil path system, and is characterized in that the refrigeration system comprises a main flow path system and a bypass flow path system,

the main flow path system comprises a variable frequency compressor, a condenser, a fan, an electronic expansion valve and an evaporator, wherein the air suction end of the variable frequency compressor is communicated with the outlet end of the evaporator, and the air exhaust end of the variable frequency compressor is communicated with the inlet end of the condenser; the fan is arranged on the condenser, and the outlet end of the condenser is communicated with the inlet end of the electronic expansion valve; the outlet end of the electronic expansion valve is communicated with the inlet end of the evaporator;

the bypass flow path system comprises a bypass flow regulating valve, wherein the bypass flow regulating valve is connected with the condenser and the electronic expansion valve in parallel; the inlet end of the bypass flow regulating valve is communicated with the exhaust end of the variable frequency compressor, and the outlet end of the bypass flow regulating valve is communicated with the outlet end of the electronic expansion valve;

the circulating oil circuit system comprises an oil tank and an oil pump, wherein an oil inlet of the oil tank is communicated with an oil outlet of the machine tool, an oil outlet of the oil tank is communicated with an oil inlet of the oil pump, an oil outlet of the oil pump is communicated with an oil inlet of the evaporator, and an oil outlet of the evaporator is communicated with an oil inlet of the machine tool;

when the inverter compressor is at the lowest frequencyRate F_minAnd the highest frequency F_maxWhen the bypass flow regulating valve works, the bypass flow regulating valve is in a closed state; when the inverter compressor is at the lowest frequency F_minWhen the refrigeration capacity is larger than the refrigeration capacity required by the cooling object during working, the bypass flow regulating valve is in an open state, and the more the refrigeration capacity is, the larger the opening of the bypass flow regulating valve is.

Preferably, a capillary tube is further arranged between the exhaust end of the variable frequency compressor and the inlet end of the bypass flow regulating valve.

Preferably, an inlet oil temperature bulb is arranged between the oil pump and the evaporator.

Preferably, an outlet oil temperature bulb is arranged between the evaporator and an oil inlet of the machine tool.

Preferably, a gas suction temperature sensing bulb is arranged between the outlet end of the evaporator and the gas suction end of the variable frequency compressor.

Preferably, an exhaust temperature sensing bulb is arranged between the exhaust end of the variable frequency compressor and the inlet end of the bypass flow regulating valve and the inlet end of the condenser.

Preferably, a filter is arranged between the outlet end of the condenser and the inlet end of the electronic expansion valve, the outlet end of the filter is communicated with the inlet end of the electronic expansion valve, and the inlet end of the filter is communicated with the outlet end of the condenser.

Preferably, a condensation temperature sensing bulb is further arranged between the outlet end of the condenser and the filter.

A control method of a high-precision oil cooler comprises the following steps:

(1) determining the frequency operating range (F) of the inverter compressor_min-F_max)；

(2) Determining the maximum opening E of the bypass flow control valve_max；

(3) By controlling the frequency conversion compressor at 0-F_maxPID calculation is carried out on the current target frequency within the range, and the calculation formula is as follows:

F＝F_(k-1)+Kp×(e_(k)-e_(k-1))+Ki×e_(k)+Kd×(e_(k)-2×e_(k-1)+e_(k-2))

in the formula:

f, calculating the target frequency of the current compressor;

F_(k-1)-variable frequency compressor frequency at the (k-1) th sampling instant;

kp is a proportional coefficient, and a fixed value is taken;

ki is an integral coefficient, and a fixed value is taken;

kd is a differential coefficient, and a fixed value is taken;

e_(k)deviation value at kth sampling instant, e_(k)＝T_(k)-T_{_set}；

e_(k-1)Deviation value at (k-1) th sampling instant e_(k-1)＝T_(k-1)-T_{_set}；

e_(k-2)Deviation value at (k-2) th sampling instant e_(k-2)＝T_(k-2)-T_{_set}；

T_{_set}-setting a target oil temperature; t is_(k)-actual oil temperature at the kth sampling instant;

T_(k-1)-actual oil temperature at the (k-1) th sampling instant; t is_(k-2)-actual oil temperature at the (k-2) th sampling instant;

(4) the opening degree of the bypass flow regulating valve is controlled according to the current compressor target frequency F, if the current compressor target frequency F is within (F)_min-F_max) The opening degree of the bypass flow regulating valve is 0B; if the current compressor target frequency F is less than or equal to F_minWherein, when the target frequency F of the current compressor is 0Hz, the opening degree of the bypass flow regulating valve is the maximum opening degree E_maxThe current compressor target frequency F is F_minWhen the target frequency F of the compressor is F, the opening degree of the bypass flow regulating valve is 0B_minBetween-0 Hz, E_maxIs equally divided into F_minThe opening degree of the bypass flow regulating valve is between 0 and E_maxBetween and current compressor target frequency at F_min-0Hz is in a one-to-one correspondence;

(5) and selecting the opening parameter of the bypass flow regulating valve corresponding to the calculated current compressor target frequency F according to the PID calculation result as a basis for opening the bypass flow regulating valve.

Preferably, the steps (1) - (5) are applied in a controlled outlet oil temperature mode, wherein the controlled outlet oil temperature mode comprises the steps of:

s1: starting oil pump and detecting outlet oil temperature T_{-an outlet}Setting outlet oil temperature T_{Set outlet}When the outlet oil temperature reaches the set target temperature, i.e. T_{-an outlet}＝T_{Set outlet}(ii) a The existing state is maintained;

s2: when the outlet oil temperature is lower than the set target temperature, i.e. T_{-an outlet}＜T_{Set outlet}(ii) a If the variable frequency compressor is not started, the existing state is kept;

s3: when the outlet oil temperature is lower than the set target temperature, i.e. T_{-an outlet}＜T_{Set outlet}；

If the inverter compressor is started and the frequency of the (k-1) th sampling moment of the inverter compressor is greater than the lowest frequency F of the inverter compressor_minI.e. F_(k-1)＞F_min(ii) a Reducing the frequency of the variable frequency compressor according to the PID calculation result;

if the inverter compressor is started, and the frequency of the (k-1) th sampling moment of the inverter compressor is more than 0HZ and less than the lowest frequency F of the inverter compressor_minI.e. 0 < F_(k-1)≤F_min(ii) a Increasing the opening degree of the bypass flow regulating valve according to the PID calculation result;

if the inverter compressor is started and the (k-1) th sampling time rate of the inverter compressor is equal to 0, F _(k-1)0; if the running time of the variable frequency compressor is more than the preset time t0, closing the variable frequency compressor and the fan, and closing the bypass flow regulating valve after 60s, otherwise, keeping the existing state;

s4: when the outlet oil temperature is higher than the set target temperature, i.e. T_{-an outlet}＞T_{Set outlet}；

If the inverter compressor is started, and the frequency of the (k-1) th sampling moment of the inverter compressor is less than or equal to the lowest frequency F of the inverter compressor_minI.e. F_(k-1)≤F_min(ii) a And reducing the opening degree of the bypass flow regulating valve according to the PID calculation result, otherwise increasing the frequency of the variable frequency compressor according to the PID calculation result.

And if the variable frequency compressor is not started and the stop time of the variable frequency compressor is more than 120s, starting the fan and the variable frequency compressor.

Preferably, the steps (1) - (5) are applied to an inlet oil temperature control mode, wherein the inlet oil temperature control mode comprises the following steps:

t1: starting oil pump and detecting inlet oil temperature T_{-an inlet}Setting inlet oil temperature T_Setl-inletWhen the inlet oil temperature reaches the set target temperature, i.e. T_{-an inlet}＝T_Setl-inlet(ii) a The existing state is maintained;

t2: when the inlet oil temperature is lower than the set target temperature, i.e. T_{-an inlet}＜T_Setl-inlet(ii) a If the variable frequency compressor is not started, the existing state is kept;

t3: when the inlet oil temperature is lower than the set target temperature, i.e. T_{-an inlet}＜T_Setl-inlet；

if the inverter compressor is started and the frequency of the (k-1) th sampling moment of the inverter compressor is equal to 0, F _(k-1)0; if the running time of the variable frequency compressor is more than the preset time t0, closing the variable frequency compressor and the fan, and closing the bypass flow regulating valve after 60s, otherwise, keeping the existing state;

t4: when the inlet oil temperature is higher than the set target temperature, i.e. T_{-an inlet}＞T_Setl-inlet；

The working principle of the high-precision oil cooler is as follows:

when the refrigeration system works, the circulating oil way system and the refrigeration system are started. In the refrigerating system, a variable frequency compressor works to drive a refrigerant to circularly flow. In the circulating oil circuit system, the oil pump drives the engine oil to circularly flow, so that heat in the machine tool is brought to the evaporator. In the evaporator, heat exchange is realized between the refrigerant and the engine oil, and the refrigerant absorbs heat in the engine oil, so that the engine oil is cooled. The refrigerant which completes heat exchange reaches the condenser through the variable frequency compressor and works through the fan, so that the heat in the refrigerant is discharged into the air through the condenser. The variable frequency compressor is continuously driven to perform refrigerant circulating motion, so that the engine oil is continuously cooled.

When the engine oil temperature of an oil inlet of the evaporator or the engine oil temperature of an oil outlet of the evaporator is detected to be less than a specific value, the fact that the refrigerating capacity in the refrigerating system is surplus is indicated, therefore, the frequency of the variable frequency compressor is firstly reduced, the refrigerating capacity is reduced, when the frequency of the variable frequency compressor is reduced to the lowest frequency, if the refrigerating capacity in the refrigerating system is surplus, the refrigerating capacity is reduced by opening the bypass flow regulating valve, and because the refrigerant passing through the bypass flow path system does not participate in cooling the engine oil, and the bypass flow path system is connected with the main flow path system in parallel, the refrigerant passing through the bypass flow path system is increased, the refrigerant participating in cooling the engine oil in the main flow path system is reduced, and the refrigerating capacity of the whole refrigerating system is reduced. Therefore, the opening degree of the bypass flow regulating valve is controlled, so that accurate temperature control is realized. After the bypass flow regulating valve is opened, the refrigerant entering the bypass flow path system does not participate in cooling the engine oil, so that the high-low pressure difference of the system is reduced, the compression amount of the variable frequency compressor can be reduced, and the energy consumption of the variable frequency compressor is further reduced.

In addition, when the refrigerating capacity of the traditional oil cooler is too large, the refrigerating capacity is generally reduced by opening the bypass flow regulating valve, but the frequency of the compressor is still kept unchanged, and the high-precision oil cooler provided by the invention further reduces the refrigerating capacity by reducing the frequency of the variable-frequency compressor until the frequency is minimum and then opening the bypass flow regulating valve, so that the energy consumption of the variable-frequency compressor can be further reduced, and the energy is saved.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. the high-precision oil cooler provided by the invention utilizes the variable-frequency compressor to replace a fixed-frequency compressor in the traditional oil cooler, and controls the frequency of the variable-frequency compressor in real time according to the difference of the temperature of the engine oil, thereby controlling the refrigerating capacity. And the bypass flow regulating valve is matched, under the condition that the refrigerating capacity is surplus, the refrigerating capacity is firstly reduced by reducing the variable frequency compressor, and then the refrigerating capacity is further reduced by opening the bypass flow regulating valve, so that the linkage control of the variable frequency compressor and the bypass flow regulating valve is simplified, and the continuous high-precision energy-saving control of the unit from 0-100% of load is realized.

2. In the traditional compressor start-stop control, the high-low pressure difference between the suction end and the exhaust end of the compressor is balanced, so that the limitation of stopping for 3min is met when the compressor is stopped and then started again. If the oil temperature of the engine oil rises within 3min after the engine is stopped, the restarting condition of the compressor is achieved, but the compressor cannot be started, so that the oil temperature exceeds the target temperature too much, and the temperature control precision of the oil cooler is influenced. According to the invention, the bypass flow regulating valve is closed in a delayed manner after the frequency conversion compressor is stopped, and the pressure difference of gas at the gas inlet end and the gas outlet end of the frequency conversion compressor is balanced by the refrigerant in the bypass flow path system, so that the high-low pressure balancing time of the system is shortened, the time interval of stopping and restarting is reduced from 3min to 2min, the temperature control response speed of the oil cooler is improved, and the temperature control precision is improved.

3. When the refrigerating capacity of the traditional oil cooler is too large, the refrigerating capacity is generally reduced by opening the bypass flow regulating valve, but the frequency of the compressor is still kept unchanged, and the high-precision oil cooler provided by the invention reduces the frequency of the variable frequency compressor until the frequency is minimum, and then further reduces the refrigerating capacity by opening the bypass flow regulating valve, so that the energy consumption of the variable frequency compressor can be further reduced, and the energy is saved.

Drawings

FIG. 1 is a schematic configuration diagram of a first embodiment of a high-precision oil cooler according to the present invention.

FIG. 2 is a flowchart of a method for controlling the high-precision oil cooler according to the present invention.

Fig. 3 is a flowchart of a control method in a second embodiment of the high-precision oil cooler of the present invention.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.

Example 1

Referring to fig. 1 to 2, the high-precision oil cooler of the present invention includes a refrigerating system and a circulating oil path system, wherein,

the refrigeration system includes a main flowpath system and a bypass flowpath system, wherein,

the main flow path system comprises a variable frequency compressor 1, a condenser 2, a fan 3, a filter 4, an electronic expansion valve 5 and an evaporator 6, wherein the air suction end of the variable frequency compressor 1 is communicated with the outlet end of the evaporator 6, and the air exhaust end of the variable frequency compressor is communicated with the inlet end of the condenser 2; the fan 3 is arranged on the condenser 2, and the outlet end of the condenser 2 is communicated with the inlet end of the filter 4; the outlet end of the filter 4 is communicated with the inlet end of an electronic expansion valve 5, and the outlet end of the electronic expansion valve 5 is communicated with the inlet end of an evaporator 6;

the bypass flow path system comprises a capillary tube 7 and a bypass flow regulating valve 8, wherein the capillary tube 7 and the bypass flow regulating valve 8 are connected with the condenser 2 and the electronic expansion valve 5 in parallel, one end of the capillary tube 7 is communicated with the outlet end of the variable frequency compressor 1, and the other end of the capillary tube is communicated with the inlet end of the bypass flow regulating valve 8; the outlet end of the bypass flow regulating valve 8 is communicated with the outlet end of the electronic expansion valve 5;

the circulating oil path system comprises an oil tank 12 and an oil pump 13, wherein an oil inlet of the oil tank 12 is communicated with an oil outlet of the machine tool, an oil outlet of the oil tank 12 is communicated with an oil inlet of the oil pump 13, an oil outlet of the oil pump 13 is communicated with an oil inlet of the evaporator 6, and an oil outlet of the evaporator 6 is communicated with an oil inlet of the machine tool;

when the inverter compressor 1 is at the lowest frequency F_minAnd the highest frequency F_maxWhen the bypass flow control valve works, the bypass flow control valve 8 is in a closed state; when the inverter compressor 1 is at the lowest frequency F_minWhen the refrigeration capacity is larger than the refrigeration capacity required by the cooling object during working, the bypass flow regulating valve 8 is in an open state, and the more the refrigeration capacity is, the larger the opening of the bypass flow regulating valve 8 is.

The evaporator 6 in this embodiment adopts a double-pipe or shell-and-tube heat exchanger, and the evaporator 6 does not need to be placed in the oil tank 12, so that the heat exchange effect is better compared with an immersion fin heat exchanger.

Referring to fig. 1-2, an inlet oil temperature bulb 14 is arranged between the oil pump 13 and the evaporator 6; an outlet oil temperature bulb 15 is arranged between the evaporator 6 and an oil inlet of the machine tool. By arranging the inlet oil temperature bulb 14 and the outlet oil temperature bulb 15, the inlet oil temperature and the outlet oil temperature are detected, and data support is provided for follow-up linkage control of the variable frequency compressor 1 and the bypass flow regulating valve 8.

Referring to fig. 1-2, a suction temperature sensing bulb 10 is arranged at the outlet end of the evaporator 6 and the inlet end of the inverter compressor 1; and an exhaust temperature sensing bulb 11 is arranged between the outlet end of the variable frequency compressor 1 and the inlet ends of the bypass flow regulating valve 8 and the condenser 2. Through setting up exhaust bulb 11 and the temperature sensing bulb 10 of breathing in, can detect the temperature of the gas of frequency conversion compressor 1's suction end and discharge end to for follow-up to frequency conversion compressor 1 and bypass flow control valve 8's coordinated control provides data support.

Referring to fig. 1-2, a condensing bulb 9 is further disposed between the outlet end of the condenser 2 and the filter 4. The temperature of the refrigerant passing through the condenser 2 can be detected by providing the condensation bulb 9.

Referring to fig. 1-2, the outlet ends of the bypass flow regulating valve 8 and the electronic expansion valve 5 and the inlet end of the evaporator 6 are provided with throttling thermal bulbs 16, and the throttling thermal bulbs 16 are used for detecting the temperature of the refrigerant entering the evaporator 6.

Referring to fig. 1 to 2, the high-precision oil cooler of the present invention operates on the principle that:

when the refrigeration system works, the circulating oil way system and the refrigeration system are started. In the refrigeration system, the inverter compressor 1 works to drive a refrigerant to flow circularly. In the circulating oil system, the oil pump 13 circulates the engine oil, thereby bringing heat in the machine tool to the evaporator 6. In the evaporator 6, heat exchange is realized between the refrigerant and the engine oil, and the refrigerant absorbs heat in the engine oil, so that the engine oil is cooled. And the refrigerant after heat exchange reaches the condenser 2 through the inverter compressor 1, and is driven by the fan 3, so that the heat in the refrigerant is discharged to the air through the condenser 2. The variable frequency compressor 1 is continuously driven to circularly move the refrigerant, so that the engine oil is continuously cooled.

In the process, one end of the capillary 7 in the bypass flow path system is communicated with the exhaust end of the variable frequency compressor 1, and the other end of the capillary is communicated with the inlet end of the bypass flow regulating valve 8, so that the temperature at the valve body of the bypass flow regulating valve 8 can be reduced, when the bypass flow regulating valve 8 is closed, the pipe diameter of the capillary 7 is small, the heat dissipation area is large, and the heat conducted through a pipeline and a refrigerant in the pipe can be reduced; when the bypass flow regulating valve 8 is opened, the high-temperature and high-pressure exhaust gas at the exhaust end of the variable frequency compressor 1 is throttled by the capillary 7 and then is changed into a state of relatively low temperature and low pressure, and then flows through the valve body of the bypass flow regulating valve 8, so that the reliability of the valve body can be improved. The temperature model selection limit of the bypass flow regulating valve 8 is reduced, so that the cost is reduced.

When the engine oil temperature of an oil inlet of the evaporator 6 or the engine oil temperature of an oil outlet of the evaporator is detected to be less than a specific value, the refrigerating capacity of the refrigerating system is indicated to be surplus, the frequency of the variable frequency compressor 1 is reduced firstly, so that the refrigerating capacity is reduced, after the frequency of the variable frequency compressor 1 is reduced to the lowest frequency, if the refrigerating capacity is still surplus, the bypass flow regulating valve 8 is opened, and since the refrigerant passing through the bypass flow path system does not participate in cooling the engine oil and the bypass flow path system is connected with the main flow path system in parallel, the refrigerant participating in cooling in the main flow path system is reduced due to the increase of the refrigerant passing through the bypass flow path system, so that the refrigerating capacity of the whole refrigerating system is reduced. Therefore, the opening degree of the bypass flow regulating valve 8 is controlled, so that accurate temperature control is realized. After the bypass flow regulating valve 8 is opened, the refrigerant entering the bypass flow path system does not participate in cooling the engine oil, so that the high-low pressure difference of the system is reduced, the compression amount of the inverter compressor 1 can be reduced, and the energy consumption of the inverter compressor 1 is further reduced.

In addition, when the refrigerating capacity of the traditional oil cooler is too large, the refrigerating capacity is generally reduced by opening the bypass flow regulating valve 8, but the frequency of the compressor is still kept unchanged, and the high-precision oil cooler provided by the invention further reduces the refrigerating capacity by reducing the frequency of the inverter compressor 1 to the minimum frequency and then opening the bypass flow regulating valve 8, so that the energy consumption of the inverter compressor 1 can be further reduced, and the energy is saved.

Referring to fig. 2, the method for controlling the high-precision oil cooler of the present invention comprises the steps of:

(1) determining the frequency operating range (F) of the inverter compressor 1_min-F_max) I.e. (20Hz-80Hz)

(2) Determining the maximum opening E of the bypass flow control valve 8_max(ii) a Wherein, E is_max＝500B；

(3) By means of a pair of frequency conversion compressors 10-F_maxPID calculation is carried out, the control of the frequency of the variable frequency compressor 1 and the bypass flow regulating valve 8 can be completed, the control calculation is simple, and the variable frequency compressor 1 is ensured to be at the lowest frequency F_min(20 Hz), the bypass flow regulating valve 8 is opened to avoid the inverter compressor 1 from being at the non-lowest frequency F_minThe bypass flow control valve 8 is opened at (20 Hz), which results in energy waste. Wherein, the calculation formula is:

F＝F_(k-1)+Kp×(e_(k)-e_(k-1))+Ki×e_(k)+Kd×(e_(k)-2×e_(k-1)+e_(k-2))

in the formula:

f, calculating the target frequency of the current compressor, namely a theoretical value;

F_(k-1)-frequency of the variable frequency compressor 1 at the (k-1) th sampling moment; kp is a proportional coefficient, and a fixed value is taken;

ki is an integral coefficient, and a fixed value is taken; kd is a differential coefficient, and a fixed value is taken; e.g. of the type_(k)-a deviation value at the kth sampling instant,

e_(k)＝T_(k)-T_{_set}；e_(k-1)deviation value at (k-1) th sampling instant, where e_(k-1)＝T_(k-1)-T_{_set}；

e_(k-2)Deviation value at (k-2) th sampling instant, where e_(k-2)＝T_(k-2)-T_{_set}；

T_{_set}-setting a target oil temperature;

T_(k)-actual oil temperature at the kth sampling instant;

T_(k-1)-actual oil temperature at the (k-1) th sampling instant;

T_(k-2)-actual oil temperature at the (k-2) th sampling instant;

(4) maximum opening degree E when fully opening the bypass flow control valve 8_max(i.e., 500B) is used as the frequency 0Hz control of the inverter compressor 1, and 0B when the bypass flow regulating valve 8 is fully closed is used as F_min(i.e., 20HZ) control; will E_max(i.e., 500B) is equally divided into F_minParts, namely 20 parts; 0 to E_maxOther opening degree parameters and the frequency conversion compressor 1F_min-frequency parameters between 0Hz one to one; as shown in the following table:

(5) through the PID calculation result, the opening parameter of the corresponding bypass flow regulating valve 8 is selected according to the calculated current compressor target frequency F, and is used as the basis for opening the bypass flow regulating valve 8, for example, after F is calculated to be 10HZ, because the lowest frequency of the inverter compressor 1 is not lower than 20HZ, the bypass flow regulating valve 8 is opened to the position with the opening of 250B, so that the refrigerating capacity of the whole refrigerating system is equivalent to the refrigerating capacity of the inverter compressor 1 working under the frequency of 10HZ, and the accurate control of the refrigerating capacity can be realized.

The control method of the high-precision oil cooler comprises an outlet oil temperature control mode and an inlet oil temperature control mode. The two control modes are distinguished in that the set oil temperature is different from the detected oil temperature. In the outlet oil temperature control mode, the oil temperature set and detected by the unit is the outlet oil temperature; and when the inlet oil temperature is controlled, the oil temperature set and detected by the unit is the inlet oil temperature.

In the outlet oil temperature control mode, the frequency control of the inverter compressor 1 and the opening control of the bypass flow regulating valve 8 are performed according to the following steps (see fig. 2 in detail):

(S1) the oil pump 13 is started, and the outlet oil temperature T is detected_{-an outlet}Setting outlet oil temperature T_{Set outlet}When the outlet oil temperature reaches the set target temperature, i.e. T_{-an outlet}＝T_{Set outlet}(ii) a The existing state is maintained;

(S2) when the outlet oil temperature is lower than the set target temperature, i.e. T_{-an outlet}＜T_{Set outlet}(ii) a If the variable frequency compressor 1 is not started, the existing state is kept;

(S3) when the outlet oil temperature is lower than the set target temperature, i.e. T_{-an outlet}＜T_{Set outlet}；

If the inverter compressor 1 is started and the frequency of the (k-1) th sampling moment of the inverter compressor 1 is greater than the lowest frequency F of the inverter compressor 1_minI.e. F_(k-1)＞F_min(ii) a Reducing the frequency of the variable frequency compressor 1 according to the PID calculation result;

if the inverter compressor 1 is started and the frequency of the (k-1) th sampling moment of the inverter compressor 1 is more than 0 and less than the lowest frequency F of the inverter compressor 1_minI.e. 0 < F_(k-1)≤F_min(ii) a Increasing the opening degree of the bypass flow regulating valve 8 according to the PID calculation result;

if the inverter compressor 1 is started and the frequency of the (k-1) th sampling moment of the inverter compressor 1 is equal to 0, F _(k-1)0; if the running time of the variable frequency compressor 1 is more than the preset time t0, closing the variable frequency compressor 1 and the fan 3, and closing the bypass flow regulating valve 8 after 60s, otherwise, keeping the existing state;

(S4) when the outlet oil temperature is higher than the set target temperature, i.e. T_{-an outlet}＞T_{Set outlet}；

If the inverter compressor 1 is started and the frequency of the (k-1) th sampling moment of the inverter compressor 1 is not more than the lowest frequency F of the inverter compressor 1_minI.e. F_(k-1)≤F_min(ii) a The opening degree of the bypass flow regulating valve 8 is reduced according to the PID calculation result, otherwise, the frequency of the variable frequency compressor 1 is increased according to the PID calculation result.

Example 2

Referring to fig. 3, the present embodiment is different from embodiment 1 in that the control method of the high-precision oil cooler of the present invention is applied to the inlet oil temperature control mode, and the frequency control of the inverter compressor 1 and the opening degree control of the bypass flow regulating valve 8 are performed according to the following steps (see fig. 3 in detail):

(T1) the oil pump 13 is turned on, and the inlet oil temperature T is detected_{-an inlet}Setting inlet oil temperature T_Setl-inletWhen the inlet oil temperature reaches the set target temperature, i.e. T_{-an inlet}＝T_Setl-inlet(ii) a The existing state is maintained;

(T2) when the inlet oil temperature is lower than the set target temperature, i.e., T_{-an inlet}＜T_Setl-inlet(ii) a If the variable frequency compressor 1 is not started, the existing state is kept;

(T3) when the inlet oil temperature is lower than the set target temperature, i.e., T_{-an inlet}＜T_Setl-inlet；

(T4) when the inlet oil temperature is higher than the set target temperature, i.e., T_{-an inlet}＞T_Setl-inlet；

If the inverter compressor 1 is started and the frequency of the (k-1) th sampling moment of the inverter compressor 1 is not more than the lowest frequency F of the inverter compressor 1_minI.e. F_(k-1)≤F_min(ii) a And reducing the opening degree of the bypass flow regulating valve 8 according to the PID calculation result, or increasing the frequency of the variable frequency compressor 1 according to the PID calculation result.

And if the inverter compressor 1 is not started and the shutdown time of the inverter compressor 1 is more than 120s, starting the fan 3 and the inverter compressor 1.

The remaining steps are performed with reference to example 1.

Example 3

The present embodiment is different from embodiment 1 in that, in step (4) of the method for controlling a high-precision oil cooler of the present invention, the maximum opening E when the bypass flow rate control valve 8 is fully opened_max(i.e., 500B) is used as the frequency 0Hz control of the inverter compressor 1, and 0B when the bypass flow regulating valve 8 is fully closed is used as F_min(i.e., 20HZ) control; will E_max(i.e., 500B) determining the opening degree by dividing the flow rate based on the flow rate curve of the bypass flow rate control valve 8；0-E_maxOther opening degree parameters and the frequency conversion compressor 1F_minThe frequency parameters sequentially correspond between-0 Hz; as shown in the following table:

the remaining steps are performed with reference to example 1.

In the embodiment, the change of the bypass flow regulating valve 8 aiming at the nonlinear flow curve is close to linearity, and the stability of the control target temperature is facilitated.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the protection scope of the present invention, although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A control method of a high-precision oil cooler is characterized by comprising the following steps:

(1) determining the frequency operation range (Fmin-Fmax) of the variable frequency compressor;

(2) determining the maximum opening Emax of the bypass flow regulating valve;

(3) by means of a pair of frequency conversion compressors 0-F_maxPID calculation is carried out, and the calculation formula is as follows:

F＝F_(k-1)+Kp×(e_(k)-e_(k-1))+Ki×e_(k)+Kd×(e_(k)-2×e_(k-1)+e_(k-2))

in the formula: f, calculating the target frequency of the current compressor; f_(k-1)-variable frequency compressor frequency at the (k-1) th sampling instant; kp is a proportional coefficient, and a fixed value is taken; ki is an integral coefficient, and a fixed value is taken; kd is a differential coefficient, and a fixed value is taken; e.g. of the type_(k)Deviation value at kth sampling instant, e_(k)＝T_(k)-T_{_set}；e_(k-1)Deviation value at (k-1) th sampling instant e_(k-1)＝T_(k-1)-T_{_set}；e_(k-2)Deviation value at (k-2) th sampling instant e_(k-2)＝T_(k-2)-T_{_set}；T_{_set}-setting a target oil temperature; t is_(k)-actual oil temperature at the kth sampling instant; t is_(k-1)-actual oil temperature at the (k-1) th sampling instant; t is_(k-2)-actual oil temperature at the (k-2) th sampling instant;

(5) selecting the opening parameter of the bypass flow regulating valve corresponding to the calculated current compressor target frequency F as the basis for opening the bypass flow regulating valve according to the PID calculation result;

under the mode of controlling the oil temperature at the outlet, the frequency control of the variable frequency compressor and the opening control of the bypass flow regulating valve are carried out according to the following steps:

(S1) the oil pump is started, and the outlet oil temperature T is detected_{-an outlet}Setting outlet oil temperature T_{Set outlet}When the outlet oil temperature reaches the set target temperature, i.e. T_{-an outlet}＝T_{Set outlet}(ii) a The existing state is maintained;

(S2) when the outlet oil temperature is lower than the set target temperature, i.e. T_{-an outlet}＜T_{Set outlet}(ii) a If the variable frequency compressor is not started, the existing state is kept;

if the inverter compressor is started and the (k-1) th sampling time rate of the inverter compressor is equal to 0, F_(k-1)0; if the running time of the variable frequency compressor is more than the preset time t0, closing the variable frequency compressor and the fan, and closing the bypass flow regulating valve after 60s, otherwise, keeping the existing state;

If the inverter compressor is started, and the frequency of the (k-1) th sampling moment of the inverter compressor is less than or equal to the lowest frequency F of the inverter compressor_minI.e. F_(k-1)≤F_min(ii) a Reducing the opening degree of the bypass flow regulating valve according to the PID calculation result, otherwise increasing the frequency of the variable frequency compressor according to the PID calculation result;

if the variable frequency compressor is not started and the stop time of the variable frequency compressor is more than 120s, starting the fan and the variable frequency compressor;

under the mode of controlling the oil temperature at the inlet, the frequency control of the variable frequency compressor and the opening control of the bypass flow regulating valve are carried out according to the following steps:

(T1) the oil pump is started, and the inlet oil temperature T is detected_{-an inlet}Setting inlet oil temperature T_Setl-inletWhen the inlet oil temperature reaches the set target temperature, i.e. T_{-an inlet}＝T_Setl-inlet(ii) a The existing state is maintained;

(T2) when the inlet oil temperature is lower than the set target temperature, i.e., T_{-an inlet}＜T_Setl-inlet(ii) a If the variable frequency compressor is not started, the existing state is kept;

if the inverter compressor is started and the frequency of the (k-1) th sampling moment of the inverter compressor is equal to 0, F_(k-1)0; if the running time of the variable frequency compressor is more than the preset time t0, closing the variable frequency compressor and the fan, and closing the bypass flow regulating valve after 60s, otherwise, keeping the existing state;

2. A high-precision oil cooler to which the method of controlling a high-precision oil cooler of claim 1 is applied, characterized by comprising a refrigeration system including a main flow path system and a bypass flow path system, and a circulating oil path system, wherein,

when the inverter compressor is at the lowest frequency F_minAnd the highest frequency F_maxWhen the bypass flow regulating valve works, the bypass flow regulating valve is in a closed state; when the inverter compressor is at the lowest frequency F_minWhen the refrigeration capacity is larger than the refrigeration capacity required by the cooling object during working, the bypass flow regulating valve is in an open state, and the more the refrigeration capacity is, the larger the opening of the bypass flow regulating valve is.

3. The oil cooler of claim 2, wherein a capillary tube is further disposed between the discharge end of the inverter compressor and the inlet end of the bypass flow control valve.

4. The high-precision oil cooler according to claim 2, wherein an inlet oil temperature bulb is provided between said oil pump and said evaporator.

5. The high-precision oil cooler of claim 2, wherein an outlet oil temperature bulb is disposed between the evaporator and an oil inlet of the machine tool.

6. The oil cooler of claim 2, wherein a suction bulb is disposed between the outlet end of the evaporator and the suction end of the inverter compressor.

7. The oil cooler of claim 2, wherein an exhaust bulb is disposed between the exhaust end of the inverter compressor and the inlet ends of the bypass flow control valve and the condenser.

8. The high-precision oil cooler of claim 2, wherein a filter is disposed between an outlet end of the condenser and an inlet end of the electronic expansion valve, an outlet end of the filter is communicated with the inlet end of the electronic expansion valve, and an inlet end is communicated with an outlet end of the condenser.