| With the rapid development of China’s economy,the transportation industry is also making continuous progress,and the number of heavy trucks in China is increasing,which also brings many road safety issues.Especially when heavy trucks descend long slopes,frequent use of brake pads is required to keep the vehicle within a safe speed range.Due to the heat attenuation characteristics of brake pads,frequent use of brake pads for braking can easily lead to a rapid increase in the temperature of the brake friction pads,a sharp decline in braking performance,and potential safety hazards.Engine assisted braking can reduce dependence on brake pads,while achieving good braking effects and ensuring the safety of vehicles and personnel.Therefore,engine assisted braking technology has become a research hotspot.Currently,there is a lack of research on engine compression release braking.In order to improve the braking effect of compression release braking,this paper studies the impact of brake gas recirculation(BGR)on braking power during compression release braking;The influence of brake valve operating parameters and BGR valve operating parameters on the braking process;The influence of valve opening resistance on hydraulic oil leakage.The research results can provide theoretical guidance on how to improve the braking effect of engine compression release braking.This study takes a six-cylinder four stroke turbocharged diesel engine as the research object and builds a simulation platform.The main research contents and conclusions are as follows:1)Study the influence of BGR on braking power during compression release braking.The study found that when the rotational speed is lower than 1500 r/min,the braking power without BGR is relatively high;when the rotational speed is higher than1500 r/min,the braking power with BGR is relatively high,and the increase amplitude increases as the rotational speed increases.2)The influence of brake valve operating parameters on the braking process is studied.The effects of different brake valve opening times,brake valve closing times,brake valve maximum lift,brake valve opening speed,and brake valve clearance on brake power are analyzed.The research shows that there are optimal brake valve opening time,brake valve closing time,and brake valve maximum lift at different rotational speeds,which maximize the brake power.Among them,the maximum brake valve lift has the greatest impact on the brake power.During the process of changing the maximum brake valve lift from 0.5 mm to 3 mm,the brake power changes by about twice;The effect of brake valve opening speed on brake power is affected by the brake valve opening time.When the opening time is near the top dead center,the brake power when the brake valve opening speed is first fast and then slow is greater than the brake power when the brake valve opening speed is first slow and then fast,while when the opening time is far from the top dead center,the result is exactly the opposite;The brake valve clearance has a greater impact on the brake power at high rotational speeds with BGR.When the rotational speed is lower than 1700r/min,the brake power first increases and then decreases as the brake valve spacing increases.When the rotational speed is higher than 1700r/min,the brake power decreases inversely as the brake valve clearance increases.3)The influence of BGR valve operating parameters on the braking process is studied.The influence of different BGR opening time,BGR closing time,and BGR maximum lift on brake power is analyzed.Research shows that the BGR opening time has a small impact on braking power,and there is an optimal BGR closing time at high rotational speeds to maximize braking power.As the BGR opening height increases,braking power significantly increases.The higher the rotational speed,the greater the braking power increase.4)A hydraulic valve model of a brake valve actuator is established,and the influence of valve opening resistance on hydraulic oil leakage is discussed.A onedimensional simulation model of hydraulic valve during compression release braking is established;The corresponding relationship between plunger fit clearance and hydraulic oil leakage is analyzed.The research shows that the hydraulic oil leakage tends to increase with the increase of fit clearance;The influence of valve opening resistance on hydraulic oil leakage was compared.As the rotational speed increased,the brake valve opening resistance increased,and the leakage also showed an increasing trend.At 2100 r/min,the valve opening resistance was about 8000 N,and at 1000 r/min,the valve opening resistance was about 4300 N,with the former leaking about twice as much as the latter. |
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