1 Introduction

The automobile power steering hydraulic pump is the heart of the power steering system. Its performance has an important impact on the performance of the automobile power steering system, and will directly affect the steering and handling stability of the automobile. In addition, with the continuous application of new materials, new technologies, and new structures, as well as the introduction of a large number of high-speed steering hydraulic pumps for cars, the performance of steering hydraulic pumps is more urgent. Therefore, it is necessary to conduct in-depth testing methods for steering hydraulic pumps. Discuss, put forward effective test methods, perfect test methods, and deeply study the characteristics of steering hydraulic pumps.

In the test process of the power steering hydraulic pump, the main parameters that need to be measured are temperature, flow, pressure, speed, torque and other characteristic parameters of the general hydraulic pump. Due to the special structure and use requirements of the power steering hydraulic pump, it has Because of its specific performance, how to accurately and conveniently measure the performance parameters of the steering hydraulic pump is the most critical issue when developing the power steering hydraulic pump test bench.

2. Test method of power steering hydraulic pump

The steering hydraulic pump test standard "ZBT 23002 Automotive Power Steering Hydraulic Pump Bench Test Method" was formulated in 1984, promulgated and implemented in 1987, and has been used for more than ten years. At that time, domestic automobile power steering hydraulic pump products were gear pumps, while car steering hydraulic pumps were still blank.

With the rapid development of the automobile industry in recent years, the power steering hydraulic pump industry has also made great progress. The steering vane pump has almost replaced the gear pump. The car steering hydraulic pump has been widely used, especially the introduction of a large number of foreign technologies. The original test method It has fallen behind and cannot fully and accurately detect existing products. Especially in the first quarter of 1997, the Chongqing Automobile Research Institute undertook the task of spot-checking the product quality of automotive steering hydraulic pumps issued by the State Technical Supervision Bureau and found that the original test method was far from meeting the testing requirements of existing products, and it was difficult to perform the test. Operation, it is difficult to make a comprehensive, fair and accurate evaluation of product quality.

Therefore, in order to meet the development needs of my country's automotive industry products and effectively control product quality, it is necessary to conduct in-depth discussion and research on test methods.

2.1, 0.85pmax pressure concept

The original test method requires that the product is performed under high working pressure pmax when performing performance tests such as running-in and flow detection. At this time, the safety valve of the steering hydraulic pump is fully opened and is in a flow-off state with a flow rate of 0. Test and burn the pump easily. In order to prevent the safety valve of the steering hydraulic pump from opening during the test, the safety valve of the steering hydraulic pump must be locked before the test. This approach is equivalent to adjusting the hydraulic pump, so this method is neither scientific nor in line with the loading conditions, and at the same time it cannot detect the product performance more comprehensively and accurately. Therefore, the 0.85 pmax pressure concept is proposed, that is, the product performs performance testing such as running-in and flow detection under the condition of 0.85 times the high pressure. At this time, the safety valve of the steering hydraulic pump will not be opened, so that the detected performance accurately reflects the steering hydraulic pressure. The real situation of the pump.

2.2. Air tightness test

The original test method has no airtightness test requirements. A large number of tests show that the airtightness test can accurately and reliably reflect the sealing performance of the steering hydraulic pump seal and the assembly quality between the parts, and the test is simple, feasible, and cost-effective. Low cost, easy to promote and apply.

2.3. Oil temperature for reliability test

The operating conditions of steering hydraulic pumps are much more complicated than those of general engineering pumps. When in use, the steering hydraulic pump is often in complex working conditions with variable speed and pressure, and the oil temperature changes drastically and has a large range. In addition, a small orifice orifice is installed at the outlet of the steering hydraulic pump to overflow the excess flow and directly return to the oil inlet cavity to form a small circulation in the steering hydraulic pump, which makes the steering hydraulic pump heat up The phenomenon is much more serious than ordinary pumps. At the same time, due to structural limitations, the steering hydraulic pump is generally installed next to the engine on the whole vehicle, and the ambient temperature is high, so the steering hydraulic pump heats up more seriously. Moreover, there is very little oil in the power steering system, generally 1 to 3 L, and its heat is not easy to dissipate.

Therefore, in order to accurately assess the performance and life of the steering hydraulic pump, the test oil temperature should be around 70°C.

2.4, cut-off test

In the original test method, referring to the general pump test method, a cut-off test is proposed. Since the power steering gear assembly generally has a stroke unloading valve, when it turns to the limit position, the stroke unloading valve opens, so that the steering hydraulic pump is in an unloaded state. Even if there is no stroke unloading valve, there will inevitably be a certain amount of internal leakage in the power steering assembly, so the steering hydraulic pump will not be in a cut-off state. Especially the vane pump has almost no cut-off capability. Therefore, the interruption test project should be cancelled.

2.5. Variable speed impact test

As we all know, due to the special operating conditions of the steering, the steering hydraulic pump cannot be continuously overloaded during the driving process of the car. On the contrary, the speed of the car is constantly changing during the driving process, and the steering system is always ensuring that the car is driving on a certain trajectory. Due to the road surface, the steering wheel is constantly impacted by the road surface, so the car driving process The middle steering hydraulic pump is constantly subjected to shock loads.

In order to make the test conditions consistent with the actual operating conditions and make the test data truly and accurately reflect the service life of the steering hydraulic pump, it is proposed to change the continuous overload test in the original test method to the variable speed impact test.

3. Introduction to the structure of the test bench

The driving device adopts AC frequency conversion speed regulation, and the AC motor directly drives the tested pump through the connecting sleeve and slider. For test pieces with different installation forms, only the connecting flange and slider need to be replaced.

The fuel tank is installed on the work surface with a volume of about 150 L. A 3 kW heater is installed in the fuel tank. The bottom of the fuel tank is about 200 mm from the center of the drive shaft. The oil suction port pipe diameter is 30 mm, which can ensure that the tested hydraulic pump sucks oil well. The fuel tank panel is equipped with a vacuum gauge and a pressure gauge to monitor the vacuum degree of the suction port and the loading pressure of the oil outlet.

4. Test bench hydraulic system

The test bench uses a proportional relief valve to load. The computer controls the proportional solenoid valve through electrical signals to load, and uses the pressure sensor feedback signal to fine-tune the proportional relief valve. The loading is accurate and the loading process is automated.

Due to the constant replacement of the test piece, it will inevitably bring a large amount of pollutants to the entire system, and the proportional relief valve requires high oil cleanliness. Therefore, in order to ensure the normal operation of the entire system. Two-stage high-pressure filtration is used in the design. Its filtration accuracy reaches 5μm, and a fully enclosed oil tank is used.

The viscosity of the oil is greatly affected by the oil temperature. In order to ensure the accuracy of the flow test, the system uses a water cooler to strictly control the oil temperature to make the variation range within ±2°C.

5. Test bench test system

The test parameters of the test bench include four parameters: speed, flow, pressure, and temperature.

The speed sensor is an inductive sensor. Its output is a sine wave signal. After being amplified by a transistor, it is shaped by a Schmitt circuit (4093 chip), and is divided by a resistor and input to the input terminal of the inverter (4011) The output terminal of the inverter is connected to the G2 terminal of the computer 7210 board. Since the reliable trigger level of the 4093 chip is above 6V, the voltage applied to the transistor and the 4093 are all 12 V, so the high level output after 4093 shaping is 12 V, the low level is 0 V, and the computer input The voltage should not be higher than 5 V, so the 5 V voltage pulse signal is sent to the computer after the resistor divides the voltage, and then the reverse circuit.

The output of the flow sensor itself is a 12 V pulse signal, and each pulse represents 0.1 L. When counting flow pulses, if the number of pulses is counted in a fixed time, the number of pulses can be approximately lost. Moreover, because the test time is short, the number of lost pulses will be amplified, which will inevitably produce larger measurement errors. Therefore, when counting the number of flow pulses, it is more accurate to use fixed pulses to measure time.

In order to reduce interference, the pressure and temperature signals are all 4-20 mA analog quantities, and the signals are directly sent to the 5411 board for A/D conversion through the HK16-pin plug.

The correct grounding of the test bench can prevent external interference signals. Because the inverter is used, if the grounding method is wrong, it will cause serious interference to the computer system. After extensive exploration of the grounding problem of the test system, the interference problem was finally solved satisfactorily. Regardless of whether the protection method is grounding protection or zero connection protection, the direction of the line must be as follows: the zero (ground) wire first enters the ground terminal of the inverter, then leads to the test bench, and then connects to the control cabinet (be careful not to use a single Core wire). Since the inverter is hung on the control cabinet, the enclosure of the inverter must be insulated from the cabinet when installing the converter.

6. Test bench computer system

The control software is an advanced multi-task industrial control configuration software based on the MS-DOS operating system. The software has the advantages of full Chinese graphic prompts, simple and reliable operation, and good interface. Proved by practice is an industrial control configuration software.

6.1, hardware system

The host is IPC486DX4/100

NA5411 and ACL7120 control template

EPSON 300K printer

6.2, software system

Industrial control configuration software can display working conditions graphically, print reports online, and provide manual and automatic operation screens. In manual operation, it has a graphical prompt function.

The industrial control configuration software consists of the following files:

CHZHI.EXE executable software

SYS.DAT configuration data file

CQHI16J.116 dot matrix font library

CBTYPE.DAT model data file

7. Conclusion

Through a large number of experiments, a feasible test method for steering hydraulic pump is proposed. After more than a year of production and actual use, the test method is easy to operate, and the test results can truly and accurately reflect the performance of the steering hydraulic pump. It is proved by use that the ZYBT-Ⅱ automobile steering hydraulic pump test bench is safe and reliable, with stable performance, fully automated test process, simple operation, strong adaptability, accurate and credible test results, and greatly improves test efficiency, and is widely popularized The value of use.