1. Power steering
DEFINITIONS
Power steering power (Power Steering) used in automotive steering systems, is substantially modified by the manual steering system, the main thing is to add a booster (Power booster), to help the driver.
Category
automobile steering systems can be divided into mechanical energy steering system and a steering power steering system types. Mechanical steering systems rely on manipulation of a steering wheel steering force of a steering wheel of the driver is achieved; the power steering system is implemented under the control of the driver’s steering wheel by means of fluid pressure or an electric motor drive force generated by the automobile engine. Therefore, the power steering system is also called steering power amplifying means.
Since the power steering system, the steering flexible, lightweight, selection of a diverter structure in the form of increased flexibility in the design of cars, the front wheels can absorb the impact generated road surfaces, etc., it has States widely used in automobile manufacturing. However, the major drawback of having a fixed magnification power steering system is: if the fixed magnification power steering system is designed to reduce the force to turn the steering wheel of cars in the parking state or the low speed, when the vehicle is traveling at high speed when this fixed magnification power steering force of the steering wheel causes rotation of the system is too small, is not conducive to high-speed car directional control; the other hand, if the power of the fixed magnification steering system is designed to increase the car steering force at high speeds, when the vehicle is suspended or low speed, turn the steering wheel will be very difficult. Electronic control technology in automotive power steering system, the driveability of the car to reach a satisfactory level. Electronically controlled power steering system during low-speed driving can turn light and flexible; when steering in the high speed region, but also to ensure the best power magnification and stable steering feel, thereby enhancing the steering stability at high speeds .
The electronically controlled power steering system
The electronically controlled power steering system (EPS-Electronic Control Power Steering), depending on the power source can be divided into hydraulic power electronic control steering system (hydraulic EPS) and electronic control electric power steering system (electric EPS). Hydraulic EPS is the addition of a solenoid valve controlling liquid flow rate, a vehicle speed sensor and an electronic control unit or the like on the basis of conventional hydraulic power steering system, the electronic control unit according to the detected vehicle speed signal, controlling the solenoid valve, the steering power magnification continuous adjustable to meet high power requirements of the low-speed steering. EPS electric motor is a direct current as a power source, the electronic control unit in accordance with the vehicle speed and the steering parameters and the like signals, controls the motor torque magnitude and direction. After the torque of the motor speed reduction mechanism reduction by twisting, applied to the steering mechanism of the automobile so as to obtain a condition compatible with the steering effort by an electromagnetic clutch.
a hydraulic electronically controlled power steering system
The electronically controlled power steering system (EPS) can reduce the steering force at a low speed to increase the maneuverability of the steering system; high-speed when the steering force may be appropriately increased to improve the steering stability. Electronically controlled hydraulic power steering system is added an electronic control device on the basis of a conventional hydraulic power steering system constituted on. Depending on the mode of control, the electronic control hydraulic power steering system can be divided into flow control formula, formula and reaction force control valve sensitivity controlled three forms.
(a) flow control formula EPSTOP
The system consists of the vehicle speed sensor, solenoid valve, the overall power steering control valve and power steering pump and an electronic control unit, etc. composition. A solenoid valve installed between the oil passage leading to the power steering on both sides of the cylinder piston oil chamber when the valve needle of the solenoid valve is fully opened, the two oil passage to the bypass solenoid valve. Flow controlled power steering system is based on a signal of the vehicle speed sensor, the opening degree of the control solenoid valve needle, thereby controlling the steering power cylinder bypass flow of hydraulic oil on both sides of the oil chamber of the piston to change the steering force on the steering wheel. The higher the speed, the larger the average current flowing through the solenoid coil of the solenoid valve, electricalThe greater the degree of opening of the magnetic valve needle, the greater the bypass flow of hydraulic oil, the smaller the hydraulic booster effect, turn the steering wheel a force also increases. This is the working principle of flow-controlled power steering system.
the pulse frequency of the current signal driving the electromagnetic solenoid of the valve is substantially constant, but increases as the vehicle speed, the current duty ratio of the pulse signal gradually increases, so that the average value of the current flowing through the electromagnetic coil with the vehicle speed the rise increases.
(ii) reaction force control formula EPSTOP
The system is mainly composed of a steering control valve, the diverter valve, a solenoid valve, a steering power cylinder, a steering pumps, storage tanks, vehicle speed sensor and an electronic control unit and other components.
In a conventional steering control valve is a rotary valve integral type power steering control valve based on the addition of the reaction force chamber constituting the hydraulic pressure. The upper end of the torsion bar by a pin and the rotary valve stem is connected to the lower end of the pinion shaft are connected by pins. An upper end portion of the pinion shaft is connected by a pin to the control valve body. When steering, the steering force on the steering wheel is transmitted to the pinion shaft via a torsion bar. When the steering force increases, the torsional deformation of the torsion bar, relative rotation between the control valve and the rotary valve stem will occur, so it changes on, off, and the relationship between the working fluid and the oil passage between the valve stem flow direction, thereby achieving steering action.
The diverter valve is a steering pump oil from the shunt valve to one side of the control valve and the solenoid valve side. According to the vehicle speed and steering requirements, the control oil pressure changing valve side electromagnetic valve side, the side of the solenoid valve to ensure a stable oil flow.
Function fixed orifice is supplied to the steering portion of the flow control valve assigned to the hydraulic reaction force chamber side.
electromagnetic valve is required to flow back into the oil tank the electronic control unit side of the hydraulic reaction force chamber (ECU) controls the opening area of the linear solenoid valve according to the level according to the vehicle speed. When the stopped vehicle speed or lower, the energizing current of the electromagnetic coil the ECU is increased, the solenoid valve opening area is increased, through the oil bypass diverter valve, flow back to the reservoir through a solenoid valve, acting on the plunger back pressure (pressure in the hydraulic reaction force chamber) decreases. Thus the push force of the valve plunger of the rotary valve stem (reaction force) is small, so only a small steering force can cause torsional deformation of the torsion bar, the valve body and the valveSteering lever effect is achieved relative rotation.
When the vehicle turns in the high speed region, the ECU energizing current so that the electromagnetic coil is reduced, the solenoid valve opening area is reduced, the hydraulic oil pressure chamber is increased the reaction force acting on the back of the plunger pressure increases, so the force pushing the plunger stem of the rotary valve is increased, a large steering force is required at this time to make the relative rotation between the valve body and the valve stem (equivalent to increasing the torsional stiffness of the torsion bar), is achieved steering effect, so the driver can obtain good steering characteristics and steering feel at high speed.
(c) the sensitivity of the control valve of formula EPSTOP
type EPS sensitivity control valve is a solenoid valve according to the vehicle speed control, the power steering control valve directly change the gain of the oil pressure (the valve sensitivity) to control the oil pressure method. Such a steering system is simple, less part, inexpensive, and has a large degree of freedom in selecting a steering force, the steering feel can be obtained a natural and good steering characteristics.
The system were partially improved steering control valve rotor valve, solenoid valve and increases the vehicle speed sensor and an electronic control unit or the like.
variable orifice
of the rotary valve into a low-speed dedicated orifice (lR, 1L, 2R, 2L), and high-speed dedicated orifice (3R, 3L) are two, arranged on the lower side of the variable orifice a high speed dedicated bypass solenoid circuit.
The working process is as follows:
When the vehicle is stopped, the solenoid valve is completely closed, if the steering wheel is rotated to the right at this time, the high sensitivity and low specific 1R 2R smaller apertures under the action of steering torque to turn off, turning the high-pressure oil pump lL flows through the power steering cylinder right chamber, the oil through the left chamber 3L, 2L flow back into the storage tank. So in this case it has a lightweight steering characteristics. And the greater the applied steering torque on the steering wheel, lL variable orifice, the larger the opening area of 2L, the smaller the throttle effect, the more obvious the effect steering.
With the increase of the vehicle speed, under the action of the electronic control unit, the opening degree of the solenoid valve is also linearly increases, if the steering wheel is rotated to the right, the steering pump high pressure oil through lL, 3R bypass solenoid valve to flow back into the tank. At this time, the right steering power cylinder chamber depending on the power steering oil pressure is low sensitivity and high bypass solenoid valveSpeed dedicated opening degree of the variable orifice 3R. The higher the vehicle speed, under the control of the electronic control unit, the larger the opening degree of the solenoid valve, the greater the bypass flow, the smaller the steering action; when the vehicle speed constant, the smaller the steering force exerted on the steering wheel , the greater the degree of opening of the high speed dedicated orifice 3R, the smaller the effect steering, when the steering force increases, the degree of opening is gradually reduced 3R, steering effect also increases. Thus, the sensitivity control valve type power steering system allows the driver to get a natural steering feel very good speed and steering characteristics.
The electric power steering electronic control system
Since the hydraulic power steering system work stress and high sensitivity, small outside dimensions, thereby to obtain a wide range of application. In large vehicles with air suspension or air brake, but also the use of pneumatic power steering. However, a common disadvantage of such a power steering system structure is complicated, power consumption, prone to leakage, difficult to effectively control the steering force. In recent years, with the wide application of computer in the car, there was an electric power steering electronic control system, referred to as electric EPS.
Composition (a) an electric-type EPS, the principles and characteristics of the TOP
The electric EPS usually by a torque sensor, a vehicle speed sensor, an electronic control unit (the ECU), the motor an electromagnetic clutch and so on. EPS is the use of electric motor as power sources, vehicle speed and steering parameters, the electronic control unit performs the assist control, the principle can be summarized as follows:
When manipulating the steering wheel, steering wheel mounted on the shaft the torque sensor continuously measure the steering shaft torsion short signal, vehicle speed signal and the signal input to the electronic control unit simultaneously. The electronic control unit according to the input signals, determining the magnitude and direction of the assist torque, i.e., the motor current and a steering selected, adjusting the size of the steering assisting power. After the torque of the motor speed reduction mechanism reduction by twisting, applied to the steering mechanism of the automobile so as to obtain a fit with the vehicle condition by the steering force by an electromagnetic clutch.
The electric EPS many hydraulic power steering advantage of the system do not have:
(1) the motor, clutch, gear, steering the components lever or the like assembled as a whole, and alreadyDuctless no control valve, so that a compact structure and weight saving. Usually the quality of the electric lighter than hydraulic EPS EPS about 25 mass percentage.
(2) no hydraulic power steering systems must often operate steering pump, motor only need to turn to when power is turned on, the power consumption and fuel consumption can be reduced to a minimum.
(3) eliminates the need for a hydraulic system, there is no need to supplement steering oil pump, there is no fear oil.
(4) can be more easily provided as required vehicle performance, modified steering characteristics.
structure and working principle of (two) main part of an electric EPS
1. The torque sensor
Function
is to measure a steering wheel torque sensor and relative torque between the diverter, as one of the basis of electric power. View of the structure and working principle of non-contact torque sensor of FIG. 9, FIG. Respectively, wound on the output shaft of the pole pieces A, B, C, D four coils, the steering wheel is in the neutral position (straight ahead), the torsion bar is in the longitudinal plane of symmetry just illustrated output shaft pole piece AC, BD’s plane of symmetry. When both ends of the U, T plus successive input pulse voltage signal Ui equal due to the magnetic flux through each pole shoe, so that the V, W both ends of the detected output signal voltage Uo = 0. Steering, since the torsion bar between the pole piece and the output shaft relative torsional deformation, the pole piece A, to increase magnetic resistance between the D, to reduce the magnetic resistance between the B, C, each pole piece of the magnetic flux change, so in V, W appeared between the potential difference. Potential difference which twist angle of the torsion bar. And proportional to the input voltage Ui. If the scale factor is K, there Uo = KUitheta; therefore, by measuring the V, W potential difference can be measured across the twist angle of the torsion bar, and then also know the rotational torque applied to the steering wheel. 10 shows a structure of a sliding-type variable resistor of the torque sensor. It is the angular displacement of the torsion bar is converted into the load torque caused by a change in the potentiometer resistance, and pass out as the torque signal slip rings.
2. Motor
The electric motor and EPS started with the DC motor is basically the same principle, but is generally used a permanent magnetic field. The maximum current is generally about 3OA,Voltage of DC12V, rated torque is 1ONmiddot; about m.
steering DC motor reversing control need for a relatively simple application of the control circuit shown in FIG. 11. a1, a2 trigger signal terminal. When the input signal to obtain an end a1, transistor T3, T2 to give base current conduction, the current through T2, the motor M, T3, Ground circuit is configured, then the motor is transferred; a2 terminal obtained when the input signal, the current through T1, M, T4, and to ground circuit configuration, the motor is reversed due to the opposite current direction. Trigger control signal terminal current magnitude can be controlled by the size of the motor current.
3. The electromagnetic clutch
variable resistor sliding torque sensor when the slip ring into the structure of the current coil through the electromagnetic clutch, electromagnetic attraction generated driving wheel, splined platen is attracted to the driving wheel pressed, then the power of the motor is transmitted to the actuator through the shaft, the drive wheel, the pressure plate, splined driven shaft.
The electric EPS typically set a working range, for example, when the vehicle speed reaches 45km / h, it does not require auxiliary power steering, then the motor stops working, not to the electromagnetic clutch and the motor inertial effects work steering system, the clutch should be separated in time, to cut off the auxiliary power. In addition, when the motor fails, the clutch is automatically detached, then still use manual control steering.
4. The reduction mechanism
EPS electric reduction mechanism is indispensable member. There are practical reduction mechanism in various combinations, generally the steering shaft worm gear drive combination, and some with the two-stage planetary gear drive combination. To suppress noise and improve the durability of the reduction gear mechanism and some special tooth, some use a resin material.
(iii) Examples of the TOP type EPS motor
The system consists of a torque sensor, a vehicle speed sensor, an electronic control unit, the motor and the reduction mechanism. The torque sensor (slide type variable resistor), and a speed reduction mechanism made of a motor integrally mounted on the steering column, the electromagnetic clutch mounted next to the output end of the motor, the electronic control unit installed in the driver seat.
When the steering system is working, is applied on the steering wheel steering force via the input shaft, the output shaft is transmitted to the torsion bar, the torsion bar is twisted so that the deformation between the input shaft and the output shaft relative rotation, while the slider in the axial direction movement, axial movement of the control arm of the slider into a rotation angle of the potentiometer, i.e. the amount of the torque value into a voltage, and input to the electronic control unit.
When the steering wheel is in the neutral position, the sensor output voltage is 2.5V; when the steering wheel is rotated to the right, the output voltage is greater than 2.5V; when the steering wheel is rotated left, the output voltage is less than 2.5 V, the output characteristic of the torque sensor 16 shown in FIG. Thus, the electronic control unit according to the level of the output voltage of the sensor, and can determine the rotational direction of the rotation angle of the steering wheel.