Research On Flow Status Under Low Oil Charging Ratio Operating Condition And Idling Power Loss Mechanism In A Hydrodynamic Retarder

Hydrodynamic retarders can produce certain braking torque and cause the idle power loss under non-braking operating conditions,only with air existing in the flow passages.The idle power loss can cause the low efficiency when the vehicle driving,because the hydrodynamic retarders work under non-braking operating conditions in most of time.In order to reduce the idle power loss,it is necessary to do some research on flow fields and the idling power loss mechanism under low oil charging ratio operating conditions.In this paper,the research on idling power loss mechanism in a hydrodynamic retarder was conducted based on the analysis of flow field and the methods of reducing the power loss were carried out finally.The main contents are as follows:Firstly,the numerical models of the flow passages of the hydrodynamic retarder were built.The accuracy of the model was verified by comparing the results of numerical simulations and the experimental results under full oil-filling conditions.In order to compare the internal and external characteristics of a hydrodynamic retarder with spoilers and without spoilers,numerical analyses of the retarders in the stators were constructed under non-braking conditions.The results show that the spoilers impede the air circulation flow and the idling power loss of the hydrodynamic retarder can reduce to 38% of the original one,which means that the vehicle power utilization will be enhanced efficiently.Secondly,numerical simulations under low oil-filling ratio operating conditions were conducted to investigate the action process of the spoiler among cascades.And the variations of the braking torque and pressure difference of spoiler baffle with input rotating speeds and oil-filling ratios were analyzed.The results show that braking torque changes significantly around the oil-filling ratio of 20%.Combining with the analysis of flow field parameter,the working factor was also verified,which provides the theory basis for the designation of spoiler and spring.Thirdly,the mechanism of drag reduction and efficiency improvement was researched by building and calculating the model with bionic non-smooth surface on spoilers.The results show that the spoilers with bionic non-smooth surface can reduce idling loss obviously through changing the distribution of flow field.Compared with ordinary spoilers,the idling loss of hydraulic retarder can be reduced around 15% at the rotary speed of 4200r/min.Finally,the influence of size,number and distribution of spoiler baffles on idling loss and flow field characteristics was analyzed for the ordinary spoiler.And then the influence of size and distribution of convex tubercles was also studied for the spoiler with non-smooth surface.Through the study of this article,the mechanism of idling power loss reduced by spoiler was explained and the working factor was also verified.What’s more,the drag reduction technology of bionic non-smooth surface was applied to the optimization of spoiler and the influence of spoiler’s structure parameters on idling power loss was analyzed.All of them play significant guiding role to the actual engineering application.