Cooling system and control method of medium and heavy-duty engine

Abstract

The invention provides a cooling system and a control method of a medium and heavy-duty engine, a thermostat comprises a wax thermostat and an electric control rotary valve thermostat which are arranged on a cooling water path of the engine in parallel, and the engine is provided with a first cooling water path and a second cooling water path. The second cold water path is communicated with the hydraulic retarder and then converged with the first cold water path to form a water path which is communicated with a thermostat inlet, an electric control thermostat and wax type thermostat parallel connection structure is formed, the working temperature of engine cooling liquid is increased, oil consumption of an engine is reduced, meanwhile, the fault that a traditional engine cooling system is prone to water return is reduced, and the service life of the engine is prolonged. The fault that water is prone to return when the hydraulic retarder is used is greatly reduced, and flexible control can be achieved according to the temperature, the temperature rising rate and working conditions or loads.

Description

Technical Field

[0001] The invention belongs to the technical field of engines and relates to a cooling system and a control method for a medium and heavy-duty engine. Background Art

[0002] With the increase in logistics volume and the improvement in transportation efficiency, heavy-duty vehicles now require diesel engines with greater power and torque. In order to ensure safe driving, heavy-duty vehicles are generally equipped with retarders as high-speed auxiliary brake components. The retarder will generate a lot of heat when working, which requires the engine's water tank cooling system to dissipate heat together. In order to reduce the engine friction work, the maximum torque operating speed of medium and heavy-duty diesel engines tends to develop at a low speed. The thermostat of the cooling system is mostly a wax thermostat. When the water temperature rises to a certain temperature (set temperature), the thermostat opens. When the water temperature of the engine is lowered, the thermostat closes. Whether it is an ordinary thermostat, an electronically controlled rotary valve (ball valve), or an electrically heated thermostat, it is controlled in this way.

[0003] In the prior art engine cooling system, the thermostat is designed to be connected in parallel with an electric ball valve or a rotating cylinder (barrel or can) and a wax thermostat. When the outlet water temperature is low or the load is low, the thermostat is closed; when the outlet water temperature of the engine internal circulation rises and the temperature reaches the set thermostat opening temperature, the wax thermostat opens; if the engine is heavily loaded, the water temperature rises rapidly and reaches the opening temperature set by the wax thermostat, or exceeds the opening temperature of the wax thermostat, the wax thermostat opens; but the above scheme still has disadvantages: when the vehicle goes downhill, the engine load becomes smaller, because the vehicle is in a higher gear (12 gear) and the speed is 60km / h~70km / h, the engine speed is low (1000rpm), the engine flow is low, and at this time the wax thermostat is in a small opening, or in a closed state. If a hydraulic retarder is used, it is difficult to meet the cooling demand due to the relatively large heat generated by the hydraulic retarder and the slow response of the wax thermostat, and the engine is prone to overheating and water return.

[0004] There are also technical solutions in the prior art to prevent water from returning to the engine cooling system, such as the engine cooling system disclosed in Chinese patent CN215633286U, which is waterproof by regulating air pressure. The disadvantages are that the water temperature channel is small, the resistance is large, the return water control has a certain lag, and the cooling effect is not good, which cannot meet the heat dissipation requirements of vehicles with retarders as high-speed auxiliary brake components. Summary of the invention

[0005] The present invention provides a cooling system and control method for medium and heavy-duty engines. The electronically controlled thermostat and the wax-type thermostat are connected in parallel, which improves the operating temperature of the engine coolant and reduces the fuel consumption of the engine. At the same time, the problem of water return in the traditional engine cooling system is reduced, and the problem of water return when using a hydraulic retarder is greatly reduced. The system can be flexibly controlled according to the temperature, the temperature rise rate, the working condition or the load.

[0006] To achieve the above-mentioned object, the present invention provides a cooling system for a medium and heavy-duty engine, which is used for the coordinated cooling of the engine and the hydraulic retarder, including a water pump, an engine, a thermostat, and a radiator water tank which are connected end to end in sequence to form a water circulation, and also includes a transmission and a hydraulic retarder which are arranged in sequence at the output end of the engine, the thermostat includes a wax thermostat and an electronically controlled rotary valve thermostat which are arranged in parallel on the cooling water path of the engine, the engine is provided with a first cooling water path and a second cooling water path, and the second cooling water path is connected to the hydraulic retarder and then merged with the first cooling water path to form a water path which is connected to the inlet of the thermostat.

[0007] The main cooling water route of the engine flows from the water pump to the engine, and the secondary cooling water route flows from the engine to the hydraulic retarder and then back to the thermostat. At the same time, a part of the first cooling water route is throttled through the throttle plate and directly goes to the thermostat.

[0008] If the thermostat is open, the water will flow to the water tank radiator after passing through the thermostat, and then return to the water pump inlet after passing through the radiator water tank. At this time, it is in a large circulation condition.

[0009] If the thermostat is in the closed state, the water flows to the water pump inlet through the small circulation hole of the thermostat, and it is in the small circulation working condition.

[0010] The thermostats used in the cooling system of medium and heavy-duty vehicles are mostly wax-type thermostats. When the water temperature rises to the set temperature (generally 83℃~85℃), the thermostat opens (generally increases by 0.1mm). When the temperature continues to rise to 95±2℃, it reaches the maximum lift (generally the lift is 10±2mm). When the water temperature of the engine is lowered, the thermostat closes.

[0011] Preferably, the present invention further comprises a temperature sensor, and the temperature sensor is arranged on the water path at the inlet of the thermostat.

[0012] Preferably, an engine controller is further included, the temperature sensor and the engine are electrically connected to the engine controller, and the engine controller issues instructions to control the opening of the electronically controlled rotary valve thermostat according to the engine outlet water temperature and the engine operating condition data. The engine controller can identify the engine operating condition and the engine outlet water temperature, accurately control the opening of the electronically controlled rotary valve thermostat, and has a fast control speed, thus avoiding the shortcoming of the slow response of the wax thermostat.

[0013] Preferably, the present invention further comprises an expansion water tank, wherein the expansion water tank is provided with two inlets, one inlet is connected to the position after the first cooling water circuit and the second cooling water circuit merge, and the other inlet is connected to the expansion water tank; the outlet of the expansion water tank is connected to the inlet of the water pump. The expansion water tank of the present invention is used for degassing, and the degassing water circuit has two branches. One branch flows from the engine to the expansion water tank, and then returns to the water inlet of the water pump from the expansion water tank. The other branch flows from the heat dissipation water tank to the expansion water tank, and then returns to the water inlet of the water pump from the expansion water tank. The use of two degassing branches ensures that there are no bubbles in the cooling water circuit, thereby ensuring the cooling effect.

[0014] The present invention also provides a control method for a cooling system of a medium-heavy engine, using the above-mentioned cooling system of a medium-heavy engine, comprising the following steps:

[0015] S1: Identify the vehicle working condition and detect the engine water outlet temperature. If the vehicle is in a normal driving condition, proceed to step S2; if the vehicle is in a long downhill condition, proceed to step S3; if the vehicle is in a climbing condition, proceed to step S4;

[0016] S2: When the engine outlet water temperature reaches the cut-off temperature of the wax thermostat, the wax thermostat opens and the electric control rotary valve thermostat closes;

[0017] S3: The vehicle is in the high-speed range, the hydraulic retarder is used, the engine outlet water temperature is between 80 and 87°C, and the engine controller issues a command that the opening of the electronically controlled rotary valve thermostat is 25%; at this time, the vehicle speed is getting higher and higher, and the driver starts to use the hydraulic retarder. Due to the downhill section, the engine load is low, and the outlet water temperature is between 80 and 87°C. The use of the hydraulic retarder triggers the control rotary valve thermostat to open 25%. The cooling water passes through the electronically controlled rotary valve thermostat and enters the water tank, reducing the occurrence of water return failure due to the large heat dissipation generated by the use of the hydraulic retarder. On the contrary, if the vehicle is not equipped with a control rotary valve thermostat, the engine speed is low, the engine flow is low, and at this time the wax thermostat is at a small opening, and the large heat dissipation generated by the use of the hydraulic retarder causes the wax thermostat to respond slowly and fail to meet the cooling requirements, which is prone to overheating and water return failure.

[0018] S4: When the engine outlet water temperature reaches the range of 92-98°C, the wax thermostat and the electric control rotary valve thermostat are opened at the same time, and the wax thermostat and the electric control rotary valve thermostat work in parallel.

[0019] In step S4, the wax thermostat and the electric control rotary valve thermostat work in parallel. The reason is:

[0020] If only ordinary wax thermostat is used, if the thermostat opening is designed to be high, such as 85℃ for initial opening, it will not be able to respond, the water temperature will easily increase at the opening speed, and water backflow will occur; if the opening temperature is set lower, such as 78℃ for initial opening, the coolant will take away more heat, resulting in higher fuel consumption.

[0021] If only an electric rotary valve thermostat is used, a relatively large flow electric rotary valve thermostat is required. Although the system cooling performance can meet the requirements, the cost is relatively high. The use of wax thermostats working in parallel can not only ensure sufficient cooling flow but also reduce costs.

[0022] Preferably, the initial opening temperature of the wax thermostat is set to 87°C. In step S4, considering the opening work of the electric control rotary valve thermostat, a wax thermostat with a high initial opening temperature can be used, because the higher the opening temperature of the wax thermostat, the more fuel-efficient it is, which can reduce fuel consumption and take into account both fuel consumption and cost.

[0023] Preferably, in step S4, the engine controller controls the opening of the electric rotary valve thermostat according to the engine outlet water temperature, when the engine outlet water temperature is 88°C, the opening of the electric rotary valve thermostat is 25%, when the engine outlet water temperature is 90°C, the opening of the electric rotary valve thermostat is 50%, when the engine outlet water temperature is 92°C, the opening of the electric rotary valve thermostat is 75%, and when the engine outlet water temperature is 94°C, the opening of the electric rotary valve thermostat is 100%. This setting reduces the flow resistance through the wax thermostat, reduces the water temperature rise rate, and reduces the occurrence of water return failures.

[0024] In the present invention, the electric control rotary valve thermostat can be flexibly controlled by the engine. The engine outlet water temperature is not the only factor of the electric control rotary valve thermostat, and it can be flexibly controlled according to the temperature, temperature rise rate and working conditions or loads.

[0025] Specifically, in step S3 of the present invention, the long downhill working condition of the vehicle is: the gear is 12 gears, the vehicle speed is 60-70km / h, the engine speed is 900-1100rpm, and the hydraulic retarder is working. At this time, the engine load becomes smaller, and the wax thermostat may be in a closed state. At this time, if hydraulic retarding is used, since the hydraulic retarding generates relatively large heat, and the engine is in the internal circulation of the engine, the antifreeze capacity of the engine is small, and the heat capacity is also small, resulting in a sharp increase in the temperature of the engine antifreeze, and the wax thermostat has a slow response time, and the engine overheats and returns water. If the cooling system of the present invention is used, the electronically controlled rotary valve thermostat can be forced to open according to the use of a hydraulic retarder to trigger the electronically controlled rotary valve thermostat. Since the electronically controlled rotary valve thermostat is opened, the antifreeze takes a large circulation, avoiding the occurrence of engine return water.

[0026] Specifically, in normal driving conditions, the hydraulic retarder does not work, the engine outlet water temperature is between 80 and 95°C, and the opening of the wax thermostat in step S2 is controlled according to the engine outlet water temperature. In normal driving conditions, the hydraulic retarder is not used, the engine outlet water temperature is between 80 and 90°C, and the ordinary wax thermostat is controlled according to the aforementioned working temperature. At this time, the engine ECU does not issue any instructions, and the electronically controlled rotary valve thermostat is in a closed state.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The parallel structure of the electronically controlled rotary valve thermostat and the wax-type thermostat increases the working temperature of the engine coolant, reduces the fuel consumption of the engine, and reduces the fault of the traditional engine cooling system that is prone to water backflow;

[0029] 2. The parallel structure of the electronically controlled rotary valve thermostat and the wax-type thermostat greatly reduces the fault of water backflow when using the hydraulic retarder.

[0030] 3. The electronically controlled rotary valve thermostat can be flexibly controlled by the ECU, with a fast reflection speed. Water temperature is not the only factor of the electronically controlled rotary valve thermostat, and it can be flexibly controlled according to temperature, temperature rise rate, working conditions or load. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of a cooling system for a medium and heavy-duty engine according to the present invention.

[0032] Figure 2 It is a structural diagram of the thermostat described in the present invention.

[0033] Figure 3 It is a structural schematic diagram of the wax type thermostat described in the present invention.

[0034] Figure 4 It is a structural schematic diagram of the electronically controlled rotary valve thermostat of the present invention.

[0035] Figure 5 The present invention discloses a coolant flow diagram of a cooling system of a medium- and heavy-duty engine when the vehicle is in a normal driving condition.

[0036] Figure 6 The present invention discloses a coolant flow diagram of a cooling system of a medium- and heavy-duty engine when the vehicle is in a long downhill condition.

[0037] Figure 7 The present invention discloses a coolant flow diagram of a cooling system of a medium- and heavy-duty engine when the vehicle is in a climbing condition.

[0038] Figure 8 The present invention discloses a coolant flow diagram of a cooling system of a medium-heavy duty engine in a degassing working state.

[0039] In the figure: 1-water pump, 2-engine, 3-thermostat, 31-wax thermostat, 32-electrically controlled rotary valve thermostat, 4-radiator water tank, 5-transmission, 6-hydraulic retarder, 7-temperature sensor, 8-engine controller, 9-expansion water tank. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0041] In the description of the present invention, it is necessary to understand that the terms "left", "right", "up", "down", "front", "back", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or structure referred to must have a specific direction, be constructed and operate in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0042] Example 1:.

[0043] like Figures 1-2 As shown, this embodiment is applied to a vehicle with a hydraulic retarder 6, and the hydraulic retarder 6 serves as a high-speed auxiliary brake component. The retarder generates a lot of heat when working, and the water tank cooling system of the engine 2 needs to dissipate the heat together, which is used for the coordinated cooling of the engine 2 and the hydraulic retarder 6. The cooling system of a medium and heavy-duty engine described in this embodiment includes a water pump 1, an engine 2, a thermostat 3, and a radiator water tank 4, which are connected end to end to form a water circulation, and also includes a transmission 5 and a hydraulic retarder 6 arranged at the output end of the engine 2 in sequence.

[0044] like Figure 2 As shown, in this embodiment, the thermostat 3 includes a wax thermostat 31 and an electronically controlled rotary valve thermostat 32 arranged in parallel on the cooling water circuit of the engine 2. The engine 2 is provided with a first cooling water circuit and a second cooling water circuit. The second cooling water circuit is connected to the hydraulic retarder 6 and then merges with the first cooling water circuit to form a water circuit connected to the inlet of the thermostat 3.

[0045] The structure of the wax thermostat 31 is as follows: Figure 3 As shown, the structure of the electronically controlled rotary valve thermostat 32 is as follows Figure 4 shown.

[0046] The main cooling water route of the engine 2 flows from the water pump 1 to the engine 2, and the secondary cooling water route flows from the engine 2 to the hydraulic retarder 6, and then returns to the thermostat 3;

[0047] At the same time, the first cooling water path directly reaches the thermostat 3 after being throttled by the throttle plate.

[0048] If the thermostat 3 is open, the water flows to the water tank radiator after passing through the thermostat 3, and then returns to the water inlet of the water pump 1 after passing through the radiator water tank. At this time, it is in a large circulation working condition.

[0049] If the thermostat 3 is in the closed state, the water flows to the water inlet of the water pump 1 through the small circulation hole of the thermostat 3, and is in the small circulation working state at this time.

[0050] The thermostat 3 used in the cooling system of medium and heavy-duty vehicles is mostly a wax thermostat 31. When the water temperature rises to the set temperature (generally 83℃~85℃), the thermostat 3 opens and generally increases by 0.1mm. When the temperature continues to rise to 95±2℃, the maximum lift is reached (generally the lift is 10±2mm). When the water temperature of the engine 2 is reduced, the thermostat 3 is closed.

[0051] This embodiment further includes a temperature sensor 7, which is arranged on the water path at the inlet of the thermostat 3. The temperature sensor 7 is used to obtain the engine outlet water temperature and transmit it to the engine controller 8.

[0052] The present embodiment further includes an engine controller 8, the temperature sensor 7 and the engine 2 are electrically connected to the engine controller 8, and the engine controller 8 issues instructions to control the opening of the electronically controlled rotary valve thermostat 32 according to the engine outlet water temperature and the engine 2 working condition data. The engine controller 8 can identify the engine 2 working condition and the engine outlet water temperature, accurately control the opening of the electronically controlled rotary valve thermostat 32, and has a fast control speed, thereby avoiding the shortcoming of the slow response of the wax thermostat 31.

[0053] like Figure 8 As shown, this embodiment further includes an expansion water tank 9, which is provided with two inlets, one of which is connected to the position where the first cooling water circuit and the second cooling water circuit merge, and the other inlet is connected to the expansion water tank 9; the outlet of the expansion water tank 9 is connected to the inlet of the water pump 1. Figure 8 As shown, the expansion water tank 9 of this embodiment is used for degassing, and the degassing water path has two branches. One branch flows from the engine 2 to the expansion water tank 9, and then returns to the water inlet of the water pump 1 from the expansion water tank 9. The other branch flows from the radiator water tank 4 to the expansion water tank 9, and then returns to the water inlet of the water pump 1 from the expansion water tank 9.

[0054] In this embodiment, the cooling water circuit of the cooling system of the engine 2 with the hydraulic retarder 6 using the electronically controlled rotary valve thermostat 32 is substantially the same as the cooling system of the engine with the hydraulic retarder 6, except that an additional electronically controlled rotary valve thermostat 32 is connected in parallel. The electronically controlled rotary valve thermostat 32 and the wax type thermostat 31 can work individually or in parallel. In addition to the same temperature control principle, they can also be flexibly controlled to be opened and closed according to the working conditions of the engine 2.

[0055] Embodiment 2:

[0056] This embodiment is a control method for a cooling system of a medium-heavy engine, which is used to control the cooling system of the medium-heavy engine in the above embodiment, and includes the following steps:

[0057] S1: Identify the vehicle working condition and detect the engine water outlet temperature. If the vehicle is in a normal driving condition, proceed to step S2; if the vehicle is in a long downhill condition, proceed to step S3; if the vehicle is in a climbing condition, proceed to step S4;

[0058] S2: Figure 5 As shown, when the engine outlet water temperature reaches the removal temperature of the wax thermostat 31, the wax thermostat 31 opens and the electronically controlled rotary valve thermostat 32 closes; the coolant circulation path is: engine 2, first cooling water circuit, wax thermostat 31, radiator water tank 4, water pump 1.

[0059] S3: Figure 6 As shown, the vehicle is in the high-speed range, the hydraulic retarder 6 is used, the engine outlet water temperature is between 80 and 87°C, and the engine controller 8 issues a command that the opening of the electronically controlled rotary valve thermostat 32 is 25%; there are two coolant circulation paths, the first path is: engine 2, the first cooling water path, the electronically controlled rotary valve thermostat 32, the radiator water tank 4, and the water pump 1; the second path is: engine 2, the second cooling water path, the hydraulic retarder 6, the electronically controlled rotary valve thermostat 32, the radiator water tank 4, and the water pump 1.

[0060] S4: Figure 7 As shown, when the engine outlet water temperature reaches the range of 92-98°C, the wax thermostat 31 and the electric control rotary valve thermostat 32 are opened at the same time, and the wax thermostat 31 and the electric control rotary valve thermostat 32 work in parallel. There are two coolant circulation paths, the first one is: engine 2, first cooling water path, electric control rotary valve thermostat 32 and wax thermostat 31, radiator water tank 4, water pump, and the second one is: engine 2, second cooling water path, hydraulic retarder 6, electric control rotary valve thermostat 32 and wax thermostat 31, radiator water tank 4, water pump 1.

[0061] In this embodiment, the initial opening temperature of the wax thermostat 31 is set to 87°C.

[0062] In this embodiment, in step S4, the engine controller 8 controls the opening of the electronically controlled rotary valve thermostat 32 according to the engine outlet water temperature. When the engine outlet water temperature is 88°C, the opening of the electronically controlled rotary valve thermostat 32 is 25%, when the engine outlet water temperature is 90°C, the opening of the electronically controlled rotary valve thermostat 32 is 50%, when the engine outlet water temperature is 92°C, the opening of the electronically controlled rotary valve thermostat 32 is 75%, and when the engine outlet water temperature is 94°C, the opening of the electronically controlled rotary valve thermostat 32 is 100%.

[0063] In this embodiment, in step S3, the long downhill condition of the vehicle is: the gear is 12th gear, the vehicle speed is 60k~70km / h, the speed of the engine 2 is 900~1100rpm, and the hydraulic retarder 6 is working.

[0064] In this embodiment, in normal driving conditions, the hydraulic retarder 6 does not work, the engine outlet water temperature is between 80° C. and 95° C., and the opening of the wax thermostat 31 in step S2 is controlled according to the engine outlet water temperature.

Claims

1. A cooling system for a medium and heavy-duty engine, characterized in that: The invention comprises a water pump (1), an engine (2), a thermostat (3), and a radiator water tank (4) which are connected end to end to form a water circulation, and also comprises a transmission (5) and a hydraulic retarder (6) which are arranged in sequence at the output end of the engine (2); the thermostat (3) comprises a wax-type thermostat (31) and an electric-controlled rotary valve thermostat (32) which are arranged in parallel on the cooling water path of the engine (2); the engine (2) is provided with a first cooling water path and a second cooling water path; the second cooling water path is connected to the hydraulic retarder (6) and then merges with the first cooling water path to form a water path which is connected to the inlet of the thermostat (3).

2. A cooling system for a medium and heavy-duty engine according to claim 1, characterized in that It also includes a temperature sensor (7), which is arranged on the water path at the inlet and outlet of the thermostat (3).

3. A cooling system for a medium and heavy-duty engine according to claim 2, characterized in that It also includes an engine controller (8), the temperature sensor (7) and the engine (2) are electrically connected to the engine controller (8), and the engine controller (8) issues instructions to control the opening of the electronically controlled rotary valve thermostat (32) according to the engine water outlet temperature and the engine (2) operating condition data.

4. A cooling system for a medium and heavy-duty engine according to claim 3, characterized in that: It also comprises an expansion water tank (9), wherein the expansion water tank (9) is provided with two inlets, one inlet being connected to the position after the first cooling water circuit and the second cooling water circuit merge, and the other inlet being connected to the expansion water tank (9); the outlet of the expansion water tank (9) is connected to the inlet of the water pump (1).

5. A method for controlling the cooling system of a medium and heavy-duty engine, characterized in that A cooling system for a medium-to-heavy engine according to any one of claims 3 to 4 comprises the following steps: S1: Identify the vehicle working condition and detect the engine water outlet temperature. If the vehicle is in a normal driving condition, proceed to step S2; if the vehicle is in a long downhill condition, proceed to step S3; if the vehicle is in a climbing condition, proceed to step S4; S2: When the engine outlet water temperature reaches the cut-off temperature of the wax thermostat (31), the wax thermostat (31) is opened and the electric control rotary valve thermostat (32) is closed; S3: The vehicle is in the high gear range, the hydraulic retarder (6) is used, the engine outlet water temperature is between 80 and 87° C., and the engine controller (8) issues a command to open the electronically controlled rotary valve thermostat (32) to 25%; S4: When the engine outlet water temperature reaches the range of 92-98° C., the wax type thermostat (31) and the electric control rotary valve thermostat (32) are opened at the same time, and the wax type thermostat (31) and the electric control rotary valve thermostat (32) work in parallel.

6. The control method of a cooling system of a medium-to-heavy engine according to claim 4, characterized in that: The initial opening temperature of the wax thermostat (31) is set to 87°C.

7. The method for controlling a cooling system of a medium- and heavy-duty engine according to claim 4, characterized in that: In step S4, the engine controller (8) controls the opening of the electronically controlled rotary valve thermostat (32) according to the engine outlet water temperature; when the engine outlet water temperature is 88° C., the opening of the electronically controlled rotary valve thermostat (32) is 25%; when the engine outlet water temperature is 90° C., the opening of the electronically controlled rotary valve thermostat (32) is 50%; when the engine outlet water temperature is 92° C., the opening of the electronically controlled rotary valve thermostat (32) is 75%; and when the engine outlet water temperature is 94° C., the opening of the electronically controlled rotary valve thermostat (32) is 100%.

8. The method for controlling the cooling system of a medium- and heavy-duty engine according to claim 4, characterized in that In step S3, the long downhill working condition of the vehicle is: the gear position is 12th gear, the vehicle speed is 60-70 km / h, the engine (2) speed is 900-1100 rpm, and the hydraulic retarder (6) is working.

9. The method for controlling a cooling system of a medium- and heavy-duty engine according to claim 4, characterized in that: In normal driving conditions, the hydraulic retarder (6) does not work, the engine outlet water temperature is between 80° C. and 95° C., and the opening of the wax thermostat (31) in step S2 is controlled according to the engine outlet water temperature.

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