Hydraulic retarder heat balance performance test method
By introducing an aerodynamic equivalent and thermal inertia delay model of the chassis onto the hydraulic retarder test bench and dynamically adjusting the cooling system, the problem of aerodynamic and thermal management simulation distortion in existing bench test methods is solved, and higher precision thermal balance performance testing is achieved.
Patent Information
- Application Number
- CN202610512301.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-17
- Publication Date
- 2026-07-10
AI Technical Summary
Existing hydraulic retarder bench testing methods cannot realistically simulate the aerodynamic environment and thermal management system of a real vehicle chassis, resulting in large errors in thermal balance performance test results and affecting test accuracy and reliability.
Using an equivalent aerodynamic model and a thermal inertia delay model of the chassis, the aerodynamic state and thermal influence environment of the actual vehicle chassis are reconstructed on a test bench. The cooling system is dynamically adjusted to simulate the actual vehicle conditions, including adjusting the cooling fan and coolant flow rate, and real-time correction of simulated vehicle speed and braking torque to ensure the accuracy of the test.
It improves the accuracy and reliability of hydraulic retarder thermal balance performance testing, reduces heat transfer error between open test benches and closed vehicle chassis, and provides test data support with real vehicle reference value.
Smart Images
Figure CN122360959A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of vehicle auxiliary braking technology, specifically to a test method for the thermal balance performance of a hydraulic retarder. Background Technology
[0002] Hydraulic retarders, as efficient auxiliary braking devices for vehicles, generate braking torque through the hydrodynamic friction of the working fluid between the stator and rotor. Under sustained high-load conditions, such as long downhill slopes in heavy commercial vehicles, the hydraulic retarder converts the absorbed kinetic energy into heat, causing a sharp rise in the temperature of the working fluid. Therefore, thermal balance capability is a core indicator for evaluating the performance of hydraulic retarders, directly affecting the vehicle's downhill safety and the risk of thermal runaway.
[0003] The industry primarily relies on two methods for testing the thermal balance performance of hydraulic retarders: real-vehicle road tests and indoor bench tests. While real-vehicle road tests best reflect actual operating conditions, they are greatly affected by external factors, making it difficult to reproduce the test conditions. Indoor bench tests, although solving the problems of controllable and repeatable testing environments, still suffer from physical environment distortion when simulating thermal balance on long downhill slopes. Existing bench tests typically use the cooling fan speed to simply map the vehicle's speed. However, in real vehicle operation, air must pass through complex flow-obstructing components such as the front grille, intercooler, and radiator before reaching the surface of the hydraulic retarder located behind the chassis. By then, the airflow speed has significantly decreased and turbulence has formed. The direct-blowing air cooling on the test bench results in a convective heat transfer coefficient on the surface of the hydraulic retarder housing that is much higher than that of a real vehicle, causing the thermal equilibrium temperature measured on the test bench to be falsely low. Furthermore, in real vehicles, during the initial braking phase or when the vehicle speed changes, due to the long cooling system piping and the large heat capacity of the water tank, there is a significant lag effect in the transfer and dissipation of heat, i.e., thermal delay. The independent cooling system of traditional test benches often responds too quickly and cannot truly simulate the thermal delay characteristics of the entire thermal management system of a real vehicle under dynamic operating conditions. This will also cause the transient temperature rise measured on the test bench to be inconsistent with that of the real vehicle, affecting the test results and accuracy. Summary of the Invention
[0004] In view of this, the present invention provides a test method for the thermal balance performance of a hydraulic retarder, which can improve the accuracy and reliability of the test and reflect the thermal balance performance of the hydraulic retarder under actual vehicle operating conditions.
[0005] To achieve the above objectives, the present invention provides a method for testing the thermal balance performance of a hydraulic retarder, comprising: Construct a test bench that includes a drive motor, a hydraulic retarder under test, a cooling water pump, a cooling fan, an environmental monitoring device, and a measurement and control system; Drive the hydraulic retarder to the set initial speed and start the cooling system circulation; Maintain a constant rotation speed and apply a braking command to the hydraulic retarder to simulate the vehicle's long downhill driving conditions, while collecting braking torque, hydraulic retarder oil temperature and coolant parameters in real time. The measurement and control system acquires the set simulated vehicle speed, corrects the simulated vehicle speed through a pre-made aerodynamic equivalent model and thermal inertia delay model of the vehicle chassis, calculates the target effective wind speed, and adjusts the operation of the cooling fan accordingly, so as to reconstruct the surface aerodynamics and thermal influence environment that matches the actual vehicle chassis on the test bench. Based on the deviation between the real-time oil outlet temperature of the hydraulic retarder and the preset target equilibrium temperature, the measurement and control system dynamically adjusts the circulation flow rate of the coolant and / or the medium temperature. The system continuously monitors the changing trend of the oil outlet temperature and the heat exchange status of the system. When the preset dynamic stability criteria are met, it is determined that thermal equilibrium has been reached, and the thermal equilibrium performance index of the hydraulic retarder is recorded and output.
[0006] Furthermore, the chassis aerodynamic equivalent model corrects the simulated vehicle speed by including: Based on the aerodynamic drag reduction mapping relationship between the front grille of the actual vehicle and the flow obstruction effect of the chassis tunnel, the set simulated vehicle speed is converted into the effective frontal speed actually acting on the surface of the hydraulic retarder, so as to reduce the forced convection heat transfer error caused by the difference in spatial layout between the open test bench and the closed actual vehicle chassis.
[0007] Furthermore, the thermal inertia delay model corrects the simulated vehicle speed by including: When the measurement and control system receives a simulated vehicle speed change or braking power step signal, it controls the cooling fan speed to change according to a smooth delay response curve based on the preset lag time and first-order inertial response period. The delay response curve is used to simulate the time difference and physical inertia of heat transfer required for air to flow from the front air intake grille through the radiator core and finally reach the surface of the hydraulic retarder when the vehicle is in motion.
[0008] Furthermore, it also includes environmental temperature difference compensation logic based on convective heat transfer equivalence: The actual ambient temperature in the laboratory is obtained in real time through environmental monitoring devices and compared with the set target road condition ambient temperature of the actual vehicle. When there is a deviation between the laboratory ambient temperature and the actual target road condition ambient temperature, the measurement and control system adjusts the speed of the cooling fan based on the principle of equal heat exchange flow.
[0009] Furthermore, the measurement and control system dynamically adjusts the circulation flow rate of the coolant and / or the temperature of the medium, including: Adjusting the speed of the cooling water pump changes the circulation flow rate of the coolant, thereby changing the inlet temperature of the coolant and thus bringing the outlet temperature to the target medium temperature.
[0010] Furthermore, the dynamic stability criterion is a steady-state determination based on a time window, including: Within a continuous set time window If the fluctuation range of the hydraulic retarder outlet oil temperature does not exceed the set allowable temperature deviation... If the fluctuation range of the braking torque at a constant speed does not exceed the set threshold, then the hydraulic retarder and its cooling system are determined to have reached thermal equilibrium.
[0011] Furthermore, during the test, the oil outlet temperature of the hydraulic retarder is monitored in real time. If the real-time oil outlet temperature has reached or exceeded the maximum safe temperature of the hydraulic retarder before the measurement and control system determines that the thermal equilibrium state has been reached, the measurement and control system will trigger an over-limit alarm and reduce the braking force, while adjusting the cooling water pump and cooling fan to the maximum output power.
[0012] Furthermore, the thermal balance performance indicators include the oil outlet temperature when the system actually reaches thermal balance, the response time from the start of applying braking load to the determination of reaching thermal balance, and the average braking power that the hydraulic retarder can continuously and stably output during the thermal balance period.
[0013] Furthermore, after completing the thermal balance test under the set conditions, the initial speed of the hydraulic retarder was changed, and the test was repeated to obtain multiple sets of thermal balance test data of the hydraulic retarder under different vehicle speed simulations.
[0014] Furthermore, after completing the thermal balance test under the single set conditions, the braking load of the hydraulic retarder was changed, and the test was repeated to obtain multiple sets of thermal balance test data of the hydraulic retarder under different braking gears.
[0015] Compared with the prior art, the advantages and positive effects of this invention are: To address the issues of distorted convective heat transfer intensity and difficulty in reproducing thermal delay characteristics caused by the difference in airflow resistance between the open laboratory environment and the enclosed environment of the actual vehicle chassis in existing hydraulic retarder bench testing methods, this invention introduces a chassis aerodynamic equivalent model and a thermal inertial delay model. During dynamic testing under applied braking load, the measurement and control system no longer uses mechanical direct air cooling. Instead, it first uses the aerodynamic equivalent model to reduce and correct the simulated vehicle speed based on the preset resistance characteristics of the front-end airflow obstruction components and chassis air ducts, calculating the effective frontal velocity that can actually act on the retarder housing surface. Simultaneously, the thermal inertial delay model simulates the time difference required for airflow through the radiator core to reach the retarder surface and the heat transfer of the coolant in the pipes. By leveraging inertia to delay or smooth the response commands of the cooling fan and water pump, and through dynamic reconstruction of cooling wind speed and flow commands in two dimensions—spatial resistance and time response—the complex aerodynamic environment of the real vehicle chassis and the actual heat exchange process of the vehicle's thermal management system can be realistically reproduced in a test bench environment. This effectively reduces the excessive forced air cooling error caused by the open test bench, making the thermal cycle and heat accumulation state of the hydraulic retarder on the test bench closer to the real long downhill heavy load conditions. Consequently, it significantly improves the test accuracy of key performance indicators such as thermal equilibrium temperature, transient response time, and continuous braking power, providing reliable and real-vehicle-reference-value test data support for the refined matching design of the vehicle's thermal management system and the thermal capacity calibration of the hydraulic retarder. Attached Figure Description
[0016] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0017] Figure 1 This is a schematic flowchart of the hydraulic retarder thermal balance performance test method in an embodiment of the present invention. Detailed Implementation
[0018] In a typical embodiment of the present invention, such as Figure 1 As shown, a test method for the thermal balance performance of a hydraulic retarder is presented.
[0019] Traditional methods for testing the thermal balance performance of hydraulic retarders suffer from difficulties in replicating external conditions during real-vehicle road tests, while indoor bench tests face the technical bottleneck of distorted physical environments. Existing bench tests typically use controlled cooling fan speeds to simply map vehicle speed, resulting in a forced convection heat transfer coefficient on the surface of the hydraulic retarder housing that is much larger than that of a real vehicle, leading to falsely low measured thermal balance temperatures. Simultaneously, traditional independent cooling systems respond too quickly, failing to realistically simulate the thermal delay characteristics of a real vehicle's complex thermal management system under dynamic conditions. To address these issues, this embodiment proposes a new method for testing the thermal balance performance of hydraulic retarders. By realistically reconstructing aerodynamic conditions and thermally affected environments matching those of a real vehicle on a test bench, this method highly simulates the complex aerodynamic environment of the real vehicle chassis and the actual heat exchange process of the vehicle's thermal management system, simulating long downhill driving conditions and thus improving test accuracy.
[0020] In this embodiment, the test method for the thermal balance performance of the hydraulic retarder specifically includes the following steps: Construct a test bench that includes a drive motor, a hydraulic retarder under test, a cooling water pump, a cooling fan, an environmental monitoring device, and a measurement and control system; Drive the hydraulic retarder to the set initial speed and start the cooling system circulation; Maintain a constant rotation speed and apply a braking command to the hydraulic retarder to simulate the vehicle's long downhill driving conditions, while collecting braking torque, hydraulic retarder oil temperature and coolant parameters in real time. The measurement and control system acquires the set simulated vehicle speed, corrects the simulated vehicle speed through a pre-made aerodynamic equivalent model and thermal inertia delay model of the vehicle chassis, calculates the target effective wind speed, and adjusts the operating status of the cooling fan accordingly. Based on the deviation between the real-time oil outlet temperature of the hydraulic retarder and the preset target equilibrium temperature, the measurement and control system dynamically adjusts the circulation flow rate of the coolant and / or the medium temperature. The system continuously monitors the changing trend of the oil outlet temperature and the heat exchange status of the system. When the preset dynamic stability criteria are met, it is determined that thermal equilibrium has been reached, and the thermal equilibrium performance index of the hydraulic retarder is recorded and output.
[0021] In the test bench setup, the drive motor is connected to the hydraulic retarder via a coupling to provide power input; the cooling water pump and cooling fan serve as the core heat dissipation actuators, receiving real-time commands from the measurement and control system. During simulated long downhill driving conditions, the drive motor maintains a constant speed, and the measurement and control system generates braking torque by applying different control signals to the hydraulic retarder. A large amount of kinetic energy is converted into heat energy, causing the oil temperature to rise rapidly. Controlling the braking torque of the hydraulic retarder can be achieved through common control methods such as changing the filling rate.
[0022] The spatial layout of an open test bench differs significantly from that of a closed real-vehicle chassis. In a real vehicle, air must pass through complex components such as the front grille and intercooler, and by the time it reaches the retarder surface, the wind speed has significantly decreased and turbulence has formed. If the fan is directly controlled to blow air at the simulated vehicle speed on the test bench, it will lead to heat transfer errors. To address this, in this embodiment, the chassis aerodynamic equivalent model corrects for the simulated vehicle speed. The correction process is based on the aerodynamic drag reduction mapping relationship between the front grille of the real vehicle and the tunnel obstruction effect of the chassis, converting the set simulated vehicle speed into the effective frontal speed acting on the surface of the hydraulic retarder, thereby reducing the forced convection heat transfer errors caused by the difference in spatial layout between the open test bench and the closed real-vehicle chassis.
[0023] The aerodynamic drag reduction mapping relationship can be obtained through prior wind tunnel testing, computational fluid dynamics simulation, or actual road test data analysis of real vehicles. This allows us to obtain the changes in air velocity and pressure as air flows through areas such as the front grille, engine compartment, and chassis tunnel at different vehicle speeds, and the impact of these changes on the airflow velocity on the surface of the hydraulic retarder. For example, the front grille may obstruct and divert airflow, while the chassis tunnel effect may accelerate airflow in certain areas. The aerodynamic drag reduction mapping relationship reflects the nonlinear transformation from the overall vehicle speed to the local effective frontal velocity of the hydraulic retarder.
[0024] In this embodiment, the measurement and control system performs mapping calculations based on the following nonlinear aerodynamic drag and wake coupling attenuation function: (1) In formula (1), The target effective wind speed is the compensation wind speed command that the cooling fan of the test bench needs to output, in m / s. The simulated vehicle speed set for the test, in m / s; This is the maximum design speed of the vehicle model, expressed in m / s. The wind penetration coefficient, ranging from 0.3 to 0.6, characterizes the primary obstruction effect of the vehicle's front grille, condenser, etc., on natural windward flow. and This is the airflow obstruction reduction factor for the chassis duct, where... The value ranges from 0.1 to 0.3, and the exponent is... The value is 1.5-2.0, which is used to characterize the physical phenomenon that the airflow is caused to flow around the narrow chassis space at high speed, resulting in a nonlinear decrease in the internal wind speed. Real-time simulated rotational speed of the active cooling fan at the front of the actual vehicle, in rpm; This is the fan exhaust conversion constant, used to convert the rotational speed into the initial airflow speed; This refers to the residual airflow velocity when the exhaust from the front-end fan reaches the rear retarder. The equivalent fluid distance from the front-end fan of the actual vehicle to the installation location of the hydraulic retarder is expressed in meters (m). The chassis space kinetic energy dissipation coefficient represents the impact of chassis structural roughness on airflow consumption.
[0025] Furthermore, during the initial braking phase or speed changes of a real vehicle, the complex airflow path and the heat capacity of the cooling system's pipes and water tank cause a significant lag effect in heat transfer. To address this, this embodiment introduces dynamic response control using a thermal inertia delay model. When the monitoring and control system receives a simulated speed change or braking power step signal, it controls the cooling fan speed to change smoothly according to a preset lag time and first-order inertial response period.
[0026] The delay response curve is used to simulate the time difference and physical thermal inertia required for air to flow from the air intake grille through the radiator core and finally reach the retarder surface during actual vehicle operation. The system no longer responds to signals with instantaneous abrupt changes, but instead undergoes a process of initial delay followed by a smooth transition, thus making the transient temperature rise curve consistent with actual vehicle operating conditions.
[0027] Specifically, the measurement and control system calculates the effective wind speed of the target using an aerodynamic equivalent model. Subsequently, to overcome the physical distortion caused by the excessively fast response of the test bench fan, the measurement and control system introduced a thermal inertia delay model to dynamically correct the final output of the cooling fan. When a simulated vehicle speed change or braking power step signal is received, the measurement and control system calculates the real-time control command for the fan based on the following first-order inertial and pure time-delay differential equations: (2) To facilitate the measurement and control system in using digital controllers (such as PLCs or industrial PCs) according to the sampling period By implementing discretization programming, the above physical model can be transformed into the following difference iteration formula: (3) In formulas (2) and (3), (or the first) Step The current dynamic wind speed command output to the cooling fan of the test bench is in m / s. (or the first) Step () represents the effective wind speed calculated in real time from the underlying aerodynamic equivalent model, in m / s; (In discrete form, the corresponding step difference) () represents the preset airflow pure lag time, in seconds. It is used to accurately simulate the physical time difference required for external cold air to pass through the front air intake grille, flow through the radiator core, travel through the long chassis passage, and finally reach the surface of the hydraulic retarder when the vehicle is in motion. The first-order inertial response period of the system heat transfer is denoted as , and is a time constant in seconds. It is used to characterize the inherent thermal resistance and smooth, gradual inertia of temperature change in the vehicle cooling system when absorbing or dissipating heat. The control sampling period of the measurement and control system is expressed in seconds (s).
[0028] Even with accurate simulations of airflow velocity and thermal inertia, the indoor ambient temperature in the laboratory often fails to perfectly match the set target road condition ambient temperature. To eliminate the interference caused by this temperature difference, this embodiment also includes an ambient temperature difference compensation logic based on convective heat transfer equivalence. The actual ambient temperature in the laboratory is acquired in real time through an environmental monitoring device and compared with the set target road condition ambient temperature. When a deviation exists, the control system adjusts the cooling fan speed based on the principle of equal heat transfer flow. If the laboratory temperature is higher than the target road condition temperature, the control system increases the fan speed to compensate for the heat loss due to the temperature difference, ensuring that the effective heat dissipation load is equivalent to the actual vehicle operating conditions.
[0029] During the dynamic adjustment of the cooling system, it is necessary to ensure that the oil outlet temperature of the hydraulic retarder steadily approaches the target equilibrium temperature. In this embodiment, the dynamic adjustment of the coolant circulation flow rate and / or medium temperature by the monitoring and control system specifically includes: on the one hand, adjusting the speed of the cooling water pump through a frequency converter to change the coolant circulation flow rate, thereby quickly responding to large changes in heat load; on the other hand, changing the inlet temperature of the coolant before it enters the retarder by controlling the auxiliary heater or chiller unit, thereby ensuring that the oil outlet temperature accurately reaches the target medium temperature. This dual adjustment mechanism effectively avoids control lag or temperature overshoot that may result from single adjustment.
[0030] In order to objectively and quantitatively determine whether the system has truly reached stability and avoid errors caused by subjective judgment or instantaneous disturbances, this embodiment proposes a clear dynamic stability criterion. This criterion is a steady-state determination based on a time window. Within a continuous set time window Δt, if the fluctuation range of the hydraulic retarder outlet oil temperature does not exceed the set temperature allowable deviation ΔT, and the fluctuation range of the braking torque at a constant speed does not exceed the set threshold, then the measurement and control system automatically determines that the hydraulic retarder and its cooling system have reached a thermal equilibrium state.
[0031] Specifically, the monitoring and control system collects oil outlet temperature data in real time and calculates its fluctuation range within Δt. Simultaneously, it monitors braking torque data in real time and calculates its fluctuation range within Δt. When both conditions are met simultaneously—the fluctuation range of the hydraulic retarder's oil outlet temperature does not exceed the set allowable temperature deviation ΔT, and the fluctuation range of the braking torque at constant speed does not exceed the set threshold—within a continuous set time window Δt, the monitoring and control system will determine that the hydraulic retarder and its cooling system have reached thermal equilibrium. At this point, the system will record and output the hydraulic retarder's thermal equilibrium performance indicators.
[0032] During the initial stage of a high-power braking simulation on a long downhill slope, the internal temperature of the hydraulic retarder may spike rapidly. To prevent equipment damage and ensure test safety, this embodiment monitors the oil outlet temperature of the hydraulic retarder in real time during the test. If the real-time oil outlet temperature reaches or exceeds the maximum safe temperature of the hydraulic retarder before the monitoring and control system determines that thermal equilibrium has been reached, the monitoring and control system will trigger an over-limit alarm. Simultaneously, the system will immediately and automatically reduce the applied braking load and forcibly adjust the cooling water pump and cooling fan to their maximum output power, forming an active overheat protection mechanism.
[0033] Once the system smoothly enters thermal equilibrium, the monitoring and control system records and outputs the thermal equilibrium performance indicators of the hydraulic retarder. These indicators include, but are not limited to, the oil outlet temperature when the system actually reaches thermal equilibrium, the response time from the start of applying braking load to determining that thermal equilibrium has been reached, and the average braking power that the hydraulic retarder can continuously and stably output during the thermal equilibrium period.
[0034] The oil outlet temperature value when the system actually reaches thermal equilibrium refers to the stable temperature of the hydraulic retarder oil flowing out of its outlet when the hydraulic retarder and its cooling system reach the preset dynamic stability criterion, that is, the thermal equilibrium state. It is collected in real time by a temperature sensor placed at the oil outlet of the hydraulic retarder and recorded at the moment when the measurement and control system determines that the thermal equilibrium state has been reached.
[0035] The response time from the start of applying the braking load to the determination of reaching thermal equilibrium refers to the length of time elapsed from the moment the measurement and control system issues a braking command to the hydraulic retarder and begins applying the braking load, until the moment when the hydraulic retarder and its cooling system first meet the preset dynamic stability criteria and are determined to have reached thermal equilibrium. This time is timed and recorded by the measurement and control system.
[0036] The average braking power that a hydraulic retarder can stably output during thermal equilibrium refers to the average braking power that the hydraulic retarder can stably output during the duration during which the hydraulic retarder and its cooling system are in thermal equilibrium. Braking power is the product of braking torque and rotational speed. The measurement and control system continuously collects braking torque and rotational speed data during thermal equilibrium and calculates the average braking power.
[0037] To comprehensively evaluate the overall performance of the hydraulic retarder throughout the vehicle's entire lifecycle, after completing the thermal balance test under single set conditions, further multi-condition testing can be conducted. By adjusting the frequency converter of the drive motor to change the initial speed of the hydraulic retarder, the above test steps are repeated to obtain multiple sets of thermal balance test data for the hydraulic retarder under different vehicle speeds. Furthermore, by changing the braking command applied to the hydraulic retarder, simulating the driver engaging different retarder braking gears, the braking load is changed, and the above test is repeated to obtain multiple sets of thermal balance test data for the hydraulic retarder under different braking gears. By obtaining cross-test data under different vehicle speeds and different braking gears, a complete thermal balance performance profile of the hydraulic retarder can be constructed, providing comprehensive and accurate data support for vehicle thermal management matching and retarder structure optimization.
[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for testing the thermal balance performance of a hydraulic retarder, characterized in that, include: Construct a test bench that includes a drive motor, a hydraulic retarder under test, a cooling water pump, a cooling fan, an environmental monitoring device, and a measurement and control system; Drive the hydraulic retarder to the set initial speed and start the cooling system circulation; Maintain a constant rotation speed and apply a braking command to the hydraulic retarder to simulate the vehicle's long downhill driving conditions, while collecting braking torque, hydraulic retarder oil temperature and coolant parameters in real time. The measurement and control system acquires the set simulated vehicle speed, corrects the simulated vehicle speed through a pre-made aerodynamic equivalent model and thermal inertia delay model of the vehicle chassis, calculates the target effective wind speed, and adjusts the operation of the cooling fan accordingly, so as to reconstruct the surface aerodynamics and thermal influence environment that matches the actual vehicle chassis on the test bench. Based on the deviation between the real-time oil outlet temperature of the hydraulic retarder and the preset target equilibrium temperature, the measurement and control system dynamically adjusts the circulation flow rate of the coolant and / or the medium temperature. The system continuously monitors the changing trend of the oil outlet temperature and the heat exchange status of the system. When the preset dynamic stability criteria are met, it is determined that thermal equilibrium has been reached, and the thermal equilibrium performance index of the hydraulic retarder is recorded and output.
2. The test method for thermal balance performance of a hydraulic retarder as described in claim 1, characterized in that, The chassis aerodynamic equivalent model corrects for the simulated vehicle speed by including: Based on the aerodynamic drag reduction mapping relationship between the front grille of the actual vehicle and the flow obstruction effect of the chassis tunnel, the set simulated vehicle speed is converted into the effective frontal speed actually acting on the surface of the hydraulic retarder, so as to reduce the forced convection heat transfer error caused by the difference in spatial layout between the open test bench and the closed actual vehicle chassis.
3. The test method for thermal balance performance of a hydraulic retarder as described in claim 1, characterized in that, The thermal inertia delay model corrects for the simulated vehicle speed by including: When the measurement and control system receives a simulated vehicle speed change or braking power step signal, it controls the cooling fan speed to change according to a smooth delay response curve based on the preset lag time and first-order inertial response period. The delay response curve is used to simulate the time difference and physical inertia of heat transfer required for air to flow from the front air intake grille through the radiator core and finally reach the surface of the hydraulic retarder when the vehicle is in motion.
4. The test method for thermal balance performance of a hydraulic retarder as described in claim 2 or 3, characterized in that, It also includes ambient temperature difference compensation logic based on convective heat transfer equivalence: The actual ambient temperature in the laboratory is obtained in real time through environmental monitoring devices and compared with the set target road condition ambient temperature of the actual vehicle. When there is a deviation between the laboratory ambient temperature and the actual target road condition ambient temperature, the measurement and control system adjusts the speed of the cooling fan based on the principle of equal heat exchange flow.
5. The test method for thermal balance performance of a hydraulic retarder as described in claim 1, characterized in that, The monitoring and control system dynamically adjusts the circulation flow rate and / or medium temperature of the coolant, including: Adjusting the speed of the cooling water pump changes the circulation flow rate of the coolant, thereby changing the inlet temperature of the coolant and thus bringing the outlet temperature to the target medium temperature.
6. The test method for thermal balance performance of a hydraulic retarder as described in claim 1, characterized in that, The dynamic stability criterion is a steady-state determination based on a time window, including: Within a continuous set time window If the fluctuation range of the hydraulic retarder outlet oil temperature does not exceed the set allowable temperature deviation... If the fluctuation range of the braking torque at a constant speed does not exceed the set threshold, then the hydraulic retarder and its cooling system are determined to have reached thermal equilibrium.
7. The test method for thermal balance performance of a hydraulic retarder as described in claim 6, characterized in that, During the test, the oil outlet temperature of the hydraulic retarder was monitored in real time. If the real-time oil outlet temperature reached or exceeded the maximum safe temperature of the hydraulic retarder before the measurement and control system determined that the thermal equilibrium state had been reached, the measurement and control system would trigger an over-limit alarm and reduce the braking force, while adjusting the cooling water pump and cooling fan to the maximum output power.
8. The test method for thermal balance performance of a hydraulic retarder as described in claim 1, characterized in that, The thermal balance performance indicators include the oil outlet temperature when the system actually reaches thermal balance, the response time from the start of applying braking load to the determination of reaching thermal balance, and the average braking power that the hydraulic retarder can continuously and stably output during the thermal balance period.
9. The test method for thermal balance performance of a hydraulic retarder as described in claim 1, characterized in that, After completing the thermal balance test under the set conditions, the initial speed of the hydraulic retarder was changed, and the test was repeated to obtain multiple sets of thermal balance test data of the hydraulic retarder under different vehicle speed simulations.
10. The test method for thermal balance performance of a hydraulic retarder as described in claim 9, characterized in that, After completing the thermal balance test under the set conditions, the braking load of the hydraulic retarder was changed, and the test was repeated to obtain multiple sets of thermal balance test data of the hydraulic retarder under different braking gears.