On 20 February 2012, Master Liu, the owner of Tianlong (the user name of the forum is “it’s really cold in winter”), posted a post on the truck home forum to reflect the problems of his Tianlong brake (post link: talk about Tianlong’s “incomparable” Brake). Seeing several traffic accidents related to Tianlong, he suspected that there were hidden dangers in the design of Tianlong’s braking system. In addition, some Tianlong car owners also replied that their Tianlong had similar problems of Tianlong brake.
Traffic safety concerns human life, which has aroused our great attention. With the attitude of being responsible for drivers, owners, pedestrians and other vehicles, we decided to find out the root cause of the problem. After more than two weeks of test and analysis, we finally solved the braking problem of “it’s really cold in winter”.
Starting from the post of “it’s really cold in winter” and the problems reflected by the majority of riders, we summarized the reasons. We made a preliminary analysis in principle, began to focus on the trailer valve, and first did some touch tests in Beijing.
In order to completely solve the braking problem of “really cold in winter”, we then came to Daixian County, Shanxi Province for actual inspection. By replacing key assemblies and optimizing the vehicle braking system, we solved the braking problem that “really cold in winter” has been worried about. Finally, through the test, the braking distance was 40.7m under the conditions of total weight of 55 tons and speed of 70 km / h!
Because braking is a systematic problem, and the causes of different models are also diverse. There may be multiple factors causing the “really cold winter” braking problem, so the focus of this paper is to record the process of solving the problem in Dai County, Shanxi Province.
The whole process has a long time span. We have made detailed records, hoping to provide reference and help for everyone to check the braking system. The following is the content of the article. You can click the corresponding link to view the details.
Let’s start with the car of “winter is really cold”. On March 8, we saw “winter is really cold” and his Tianlong in Daixian County, Shanxi Province.
The picture above shows Tianlong, which is “really cold in winter”. It is a 6×2 double front axle model, Cummins 340 HP engine, fast 9-speed transmission, and Dena rear axle speed ratio of 4.44. The lightweight trailer is 11 meters long and the heavy vehicle is fully loaded with 55 tons. All tests in this paper are carried out under the condition of heavy vehicle.
It has been four years since Tianlong bought the second-hand car “it’s really cold in winter”. Many changes have been made during this period. The brake system of the whole car, “it’s really cold in winter” has also explained to us:
In order to prevent the trailer from pushing the head, especially on rainy and snowy roads, canceling the front brake of the main vehicle is a common method used by many heavy truck users in China. Of course, for 6×2 double front axle models, the friction of four tires is less when braking.
We consulted the relevant instructions of Dongfeng Tianlong braking system. The 6×2 model is equipped with load sensing valve. The car with “cold winter” has been removed, which we didn’t see.
The brake master cylinder adopts the products produced by Hubei Shiyan Hailiang industry and Trade Co., Ltd., which should not be the original brand of Tianlong. The trailer valve is a product called “brake king” produced in Xingtai.
The relay valve of the trailer of “it’s really cold in winter” is a product named “health”. After our research, this is actually a combination of relay valve functions and adaptive valve functions.
As for the trailer adaptation valve, here is an introduction: “skillfully using the adaptation valve to easily solve the empty brake locking of the trailer”. Its function is to reduce the pressure at the initial stage of braking to prevent the empty tire locking.
In the following tests, we also found some problems in the braking system, which will be described in detail in the later tests.
After learning about the “cold winter” car, we began our testing and improvement.
According to the reflection of “it’s really cold in winter” that “the effect of pulling and hanging brake is much better than that of stepping on brake”, we compared the introduction data of Dongfeng brake system, and preliminarily suspected that the problem lies in Tianlong’s trailer valve (principle introduction). Therefore, the main detection method is to test the control pressure of trailer brake system.
Two barometers are connected to the air pressure of the trailer supply line (usually red) and the control line (usually yellow).
For comparison, “it’s really cold in winter” bought two kinds of trailer valves from Dongfeng science and technology and webco online. The original vehicle was changed to a trailer valve called “brake king”.
The trailer valve of the “brake king” installed on the original car was replaced in the roadside repair shop “it’s really cold in winter”.
We note that the trailer valve of Dongfeng technology has the adjustment description of the forward crossing amount of the trailer control valve. The forward crossing amount of clockwise rotation increases and the forward crossing amount of counterclockwise rotation decreases. The forward displacement in the supply state is 0-50kpa, that is, 0.5 atmospheric pressure.
Before coming to Beijing, we had conducted similar tests on several cars and had some impressions (click to view the test in Beijing). In addition to the air pressure test, we also conducted several road tests to better verify our inference.
Note: due to limited conditions, the travel of the brake pedal cannot be accurately positioned. In order to reduce the error, all the actions of stepping on the brake pedal are done by the editor of truck home. In addition, it is also affected by vehicle air pressure and other factors, so the test results are mainly to judge the change trend of trailer braking characteristics under the formation of different pedals.