CN112896291B - Composite gear and rack type active steering system and control method thereof - Google Patents
Composite gear and rack type active steering system and control method thereof Download PDFInfo
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- CN112896291B CN112896291B CN202110356571.9A CN202110356571A CN112896291B CN 112896291 B CN112896291 B CN 112896291B CN 202110356571 A CN202110356571 A CN 202110356571A CN 112896291 B CN112896291 B CN 112896291B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D3/00—Steering gears
- B62D3/02—Steering gears mechanical
- B62D3/12—Steering gears mechanical of rack-and-pinion type
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D5/00—Power-assisted or power-driven steering
- B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D5/00—Power-assisted or power-driven steering
- B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
- B62D5/0457—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such
- B62D5/046—Controlling the motor
Abstract
The invention discloses a composite rack and pinion type active steering system and a control method thereof, wherein the system comprises: the device comprises a steering wheel, a steering shaft end gear, a power-assisted motor reducer, a gear rack system, a corner superposition motor reducer, a sliding rail seat, a steering tie rod, a steering knuckle, a steering wheel and a control module; according to the invention, the composite gear-rack system device is designed, and the superposition of the steering angle of the driver is realized by adopting a driving mode of the main transmission rack and the auxiliary transmission rack with higher reliability, so that the active steering function is realized, the cost of the system is saved, and the reliability of the steering system is ensured.
Description
Technical Field
The invention belongs to the technical field of vehicle steering transmission, and particularly relates to a composite rack and pinion type active steering system and a control method thereof.
Background
Since the invention of automobiles, the transmission ratio of a transmission for steering a vehicle is usually fixed, namely, whether the vehicle runs at low speed at a narrow lane or intersection or runs at high speed on a highway, the ratio of the steering wheel angle input by the vehicle to the front wheel steering angle output by the vehicle is always constant. This is also a difficult problem for large enterprises. If direct steering is adopted, a driver does not need to greatly rotate the steering wheel when the driver is in a sharp bend, but the fine action of the steering wheel can influence the driving stability when the driver is in high-speed driving; conversely, the more indirect the steering system, the greater the stability of the vehicle on a motorway, but at the expense of maneuverability in cornering. Therefore, conventional steering systems must make a tradeoff between safety and comfort. Therefore, all vehicle enterprises are currently designing a steering system capable of achieving sensitive steering at a low speed and stable steering at a high speed.
For the above problems, the existing solution is to add a device capable of changing the steering transmission ratio in the steering system, and implement low-speed sensitive and high-speed stable steering through a certain control, i.e. an active steering technique, specifically a steering system that retains the conventional power-assisted steering function and can apply an active additional steering angle to the steering system based on the input of the driver. Such as the planetary gear train based active steering system designed by pomma and the harmonic gear based active front wheel steering system designed by audi both achieve the above-mentioned functions. In addition, the newly proposed steer-by-wire system can actually realize the above functions by a disconnected structural design.
In summary, a steering system capable of implementing an active steering function includes: a planet gear type active steering system of the BMW, an Audi harmonic gear type active steering system and a steer-by-wire system. However, these systems have certain disadvantages, and although the active steering system of planetary gear type can achieve the above functions, the high cost makes it difficult to be popularized in a large scale. The harmonic gear type active steering system is easy to generate fatigue failure and poor in heat dissipation condition due to the existence of the harmonic gear type, cannot be used in occasions with transmission speed ratio smaller than 35, and is difficult to achieve low-speed portability, instantaneous transmission ratio is very high, and system performance is not stable enough. The steer-by-wire system is difficult to perfectly solve the reliability problem of the system because a mechanical connection structure is cancelled. Therefore, there is a need for an active steering system that can safely and reliably realize active steering, and has low cost, good heat dissipation, and easy control performance.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention provides a compound rack and pinion type active steering system and a control method thereof, so as to solve the problem that the shortcomings of various active steering technical schemes in the prior art are obviously difficult to be popularized in a large scale. According to the invention, the composite gear-rack system device is designed, and the superposition of the steering angle of the driver is realized by adopting a driving mode of the main transmission rack and the auxiliary transmission rack with higher reliability, so that the active steering function is realized, the cost of the system is saved, and the reliability of the steering system is ensured.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention relates to a composite rack and pinion type active steering system, which comprises: the device comprises a steering wheel, a steering shaft end gear, a power-assisted motor reducer, a gear rack system, a corner superposition motor reducer, a sliding rail seat, a steering tie rod, a steering knuckle, a steering wheel and a control module;
the input end of the steering shaft is connected with the output end of the steering wheel, and the output end of the steering shaft is fixedly connected with the input end of the steering shaft end gear;
the steering shaft end gear is connected with the input end of the gear rack system;
the power-assisted motor is fixed on one side of the steering shaft and is connected with the steering shaft through the power-assisted motor reducer;
the rack and pinion system includes: the main transmission rack, the auxiliary transmission rack, the central gear shaft bearing and the corner superposition gear;
the input end of the main transmission rack is meshed with the shaft end gear of the steering shaft, and the output end of the main transmission rack is meshed with one side of the central gear;
the auxiliary transmission rack is parallel to the main transmission rack, the input end of the auxiliary transmission rack is meshed with the corner superposition gear, and the output end of the auxiliary transmission rack is meshed with the other side of the central gear, which is parallel to the main transmission rack;
the central gear shaft is fixedly connected to the steering tie rod and is provided with the central gear shaft bearing;
the central gear is sleeved on the central gear shaft bearing;
the output end of the corner superposition motor reducer is fixedly connected with the corner superposition gear;
the corner superposition motor is fixed on a frame of the vehicle, and the output end of the corner superposition motor is connected with the input end of the reducer of the corner superposition motor;
the main and auxiliary transmission gear bars are arranged on the slide rail seat, and the slide rail seat is fixedly arranged on a frame of a vehicle;
the input end of the steering knuckle is connected with the output end of the steering tie rod, and the output end of the steering knuckle is connected with the steering wheel;
the control module includes: the device comprises a torque sensor, a corner superposition motor corner sensor, a power-assisted motor torque sensor, a vehicle speed sensor, a steering wheel corner sensor and an electronic control unit;
the input end of the electronic control unit is respectively connected with a torque sensor, a corner superposition motor corner sensor, a power-assisted motor torque sensor, a vehicle speed sensor, a steering wheel corner sensor and a steering wheel corner sensor, and the output end of the electronic control unit is respectively connected with a power-assisted motor corner superposition motor; when the vehicle is turned, the power-assisted motor is controlled to assist power according to vehicle parameters obtained from the sensors, and the steering angle superposition motor is controlled to adjust the steering transmission ratio.
Furthermore, the torque sensor is arranged on the steering shaft, and is used for acquiring a torque signal of the steering shaft and transmitting the torque signal to the electronic control unit;
the vehicle speed sensor is arranged in a drive axle housing or a transmission housing of the vehicle and is used for obtaining the vehicle speed of the vehicle and transmitting a signal to the electronic control unit;
the steering wheel angle sensor is arranged on a steering wheel and used for obtaining the steering wheel angle when a vehicle turns and transmitting a signal to the electronic control unit;
the corner superposition motor corner sensor is arranged at the output end of the corner superposition motor and used for acquiring a corner signal of the corner superposition motor and transmitting the signal to the electronic control unit;
the power-assisted motor torque sensor is arranged at the output end of the power-assisted motor and used for acquiring a power-assisted motor torque signal and transmitting the signal to the electronic control unit;
the steering wheel corner sensor is arranged on the steering wheel and used for obtaining an actual output corner signal of the steering wheel and transmitting the signal to the electronic control unit.
Furthermore, the main transmission rack and the auxiliary transmission rack are arranged on the slide rail seat in a sliding groove mode.
Furthermore, one side of the main transmission rack opposite to the tooth space of the auxiliary transmission rack is provided with a semi-cylindrical sliding groove, the number of the sliding rail seats is two, and the upper ends of the sliding rail seats are provided with semi-cylindrical protruding parts used for installing the main transmission rack and the auxiliary transmission rack.
Furthermore, the corner superposition motor is arranged on the frame in the middle of the two slide rail seats, so that the integration level of the system is further improved.
Further, the rack and pinion system is mounted to an upper end of the tie rod and is parallel to a frame of the vehicle.
Furthermore, the diameter of the central gear is larger than the diameter of the corner superposition gear and the diameter of the steering shaft end gear, and only the central gear is meshed with the main transmission rack and the auxiliary transmission rack simultaneously.
Furthermore, the tooth profiles of the main transmission rack, the auxiliary transmission rack, the steering shaft end gear, the corner superposition gear and the central gear are all helical teeth.
Furthermore, the reducer of the corner superposition motor is a worm gear reducer, so that structural self-locking is realized when the corner superposition is not carried out or the fault of the corner superposition motor occurs.
Further, when the steering is not performed, the installation position of the central gear is at the middle position of the main transmission rack and the auxiliary transmission rack, the installation position of the corner superposition gear is at the right side 1/4 of the auxiliary transmission rack, and the installation position of the steering shaft end gear is at the left side 1/4 of the main transmission gear.
The invention also provides a control method of the composite rack and pinion type active steering system, which comprises the following steps based on the system:
(1) during steering, collecting a steering wheel corner signal, a corner superposed motor corner signal, a power-assisted motor torque signal, a vehicle speed signal, a torque signal and a steering wheel corner signal of a vehicle, and transmitting the collected signals to an electronic control unit;
(2) respectively calculating the steering transmission ratio and the steering assistance torque required under the current speed and the steering angle of the vehicle according to the steering wheel steering angle signal, the vehicle speed signal, the torque signal and the steering wheel steering angle signal acquired in the step (1);
(3) and (3) respectively controlling the transmission ratio and the steering assistance of the corner superposition motor and the power-assisted motor according to the corner superposition motor corner signal and the power-assisted motor torque signal acquired in the step (1) and the steering transmission ratio and the steering assistance torque calculated in the step (2).
Further, the method further comprises the step (4): the output of the power-assisted motor acts on the steering shaft, the input of the steering wheel acts on the central gear through a shaft end gear of the steering shaft and a main transmission rack, the output of the corner superposition motor also acts on the central gear through an auxiliary transmission rack, and the central gear drives the steering wheel through a tie rod and a steering knuckle to complete steering.
Further, the steering transmission ratio calculation formula in the step (2) is as follows:
wherein i is a steering transmission ratio; i.e. imaxThe expected maximum steering gear ratio; i.e. iminTo expect the smallest turnTo a gear ratio; u is the vehicle speed of the vehicle; e is a natural logarithm; k is an element of [55-60 ]]And λ ∈ [8-12 ]]To adjust the parameters; e is an adjusting function related to the steering wheel angle; thetawIs the steering wheel corner, and is positive anticlockwise; thetaw0And thetawmThe threshold value is adjusted for the steering wheel angle.
Further, the calculation formula of the steering assist torque in the step (2) is:
K(u)＝D2eau+b (4)
in the formula, TapThe steering assisting moment; t iswInputting torque for a steering wheel; t isw0Inputting torque for a steering wheel of a reference driver for starting power assistance; t iswmaxThe maximum steering assisting moment; k (u) is the gradient of the power-assisted characteristic curve; e. a and b are both constants; d1And D2The factors are adjusted for the characteristics of the drivers, and different drivers have different assistance characteristics.
Further, the step (3) of controlling the rotation angle superposition motor comprises the following steps:
(31) calculating an expected steering wheel angle theta according to the steering transmission ratio in the current vehicle state obtained in the step (2)f：
(32) Calculating a target additional rotation angle required to be output by the rotation angle superposition motor according to the expected rotation angle of the steering wheel obtained in the step (31) and the current rotation angle of the steering wheel;
(33) and (4) controlling a corner superposition motor to track the target additional corner according to the target additional corner value obtained by calculation in the step (32), so as to realize accurate control of the steering transmission ratio.
Further, the calculation formula of the target additional rotation angle in the step (32) is as follows:
in the formula, rwThe gear radius of the gear at the end of the steering shaft; thetamAdding a corner for the target, namely, superposing the corner output by the motor by the corner, wherein the anticlockwise direction is positive; g is the steering gain ratio of the tie rod to the steered wheels; gmThe reduction ratio of the motor reducer is superposed for the corner; r isoThe radius of the gear is superimposed for the corner.
Further, in the step (33), a fuzzy PID control method is adopted to control the corner stacking motor to track the target additional corner, the error and the error change rate between the target additional corner and the actual output corner of the corner stacking motor are used as control inputs, and the control current of the corner stacking motor is used as an output to control the corner stacking motor.
Further, the control steps of the power assisting motor in the step (3) are as follows:
(34) calculating the target torque T required to be output by the power-assisted motor according to the steering power-assisted torque required in the current vehicle state obtained in the step (2)p：
In the formula, GpThe reduction ratio of the reducer of the power-assisted motor;
(35) and (4) according to the target torque of the power-assisted motor calculated in the step (34), taking the error between the target torque and the torque actually output by the power-assisted motor as control input, taking the control current of the power-assisted motor as output, and adopting a robust synovial controller to control the power-assisted motor to track the target torque so as to realize accurate control of the steering power-assisted torque.
The invention has the beneficial effects that:
compared with the existing active steering system, the active steering system has the advantages that the original mechanical connection from the steering wheel to the steering wheel is kept, the active steering function is realized by utilizing a rack and pinion structure with lower cost and more reliability, the cost of the active steering system can be further reduced, the reliability and the safety of the vehicle steering system are improved, the application of the active steering system in an actual vehicle can be better promoted, and the active steering system has high market value and practical significance.
The invention improves the concrete structure on the basis of the unchanged friction and rigidity conditions of the original rack-and-pinion steering gear, is beneficial to keeping the original control feeling for a driver, and simultaneously, the acting counter torque generated by the composite rack-and-pinion system can be compensated by using the original power-assisted motor.
The corner superposition motor reducer adopted by the invention is a worm gear reducer, so that structural self-locking can be realized when an additional corner is not output, and the system can normally steer under the condition that the corner superposition motor does not work or fails.
Drawings
FIG. 1 is a schematic diagram of the active front wheel steering system of the present invention;
FIG. 2 is a detailed block diagram of the rack and pinion system of the present invention;
FIG. 3 is a flow chart of a control method of the present invention;
in the figure: 1-steering wheel, 2-steering wheel angle sensor, 3-torque sensor, 4-power-assisted motor, 5-power-assisted motor torque sensor, 6-power-assisted motor reducer, 7-steering shaft, 8-steering wheel, 9-steering knuckle, 10-rack-and-pinion system, 11-steering shaft end gear, 12-electronic control unit, 13-vehicle speed sensor, 14-central pinion shaft, 15-angle superimposed motor, 16-angle superimposed motor angle sensor, 17-steering wheel angle sensor, 18-angle superimposed motor reducer, 19-tie rod, 20-slide rail seat, 21-secondary drive rack, 22-main drive rack, 23-central gear, 24-central pinion shaft bearing, 25-angle superimposed gear.
Detailed Description
In order to facilitate understanding of those skilled in the art, the present invention will be further described with reference to the following examples and drawings, which are not intended to limit the present invention.
Referring to fig. 1 and 2, a multiple rack and pinion type active steering system according to the present invention includes: the device comprises a steering wheel 1, a steering shaft 7, a steering shaft end gear 11, a power-assisted motor 4, a power-assisted motor reducer 6, a gear-rack system 10, a corner superposition motor 15, a corner superposition motor reducer 18, a sliding rail seat 20, a steering tie rod 19, a steering knuckle 9, a steering wheel 8 and a control module;
the input end of the steering shaft 7 is connected with the output end of the steering wheel 1, and the output end of the steering shaft is fixedly connected with the input end of the steering shaft end gear 11;
the steering shaft end gear 11 is connected with the input end of the gear rack system 10;
the power-assisted motor 4 is fixed on one side of the steering shaft 7 and is connected with the steering shaft through the power-assisted motor reducer 6;
the rack and pinion system 10 includes: a main transmission rack 22, a secondary transmission rack 21, a central gear 23, a central gear shaft 14, a central gear shaft bearing 24 and a corner superposition gear 25; the rack and pinion system is arranged at the upper end of the steering tie rod 19 and is parallel to the frame of the vehicle;
the input end of the main transmission rack 22 is meshed with the steering shaft end gear 11, and the output end of the main transmission rack is meshed with one side of the central gear 23;
the auxiliary transmission rack 21 is parallel to the main transmission rack 22, the input end of the auxiliary transmission rack is meshed with the corner superposition gear 25, and the output end of the auxiliary transmission rack is meshed with the other side of the central gear 23 which is parallel to the main transmission rack;
the central gear shaft 14 is fixedly connected to the steering tie rod 19, and the central gear shaft bearing 24 is mounted on the central gear shaft 14;
the central gear 23 is sleeved on the central gear shaft bearing 24; the diameter of the central gear 23 is larger than that of the corner superposition gear 25 and that of the steering shaft end gear 11, so that only the central gear 23 is meshed with the main transmission rack and the auxiliary transmission rack simultaneously;
the output end of the corner superposition motor reducer 18 is fixedly connected with the corner superposition gear 25; the corner superposition motor reducer 18 is a worm gear reducer, so that structural self-locking is realized when corner superposition is not performed or a fault occurs in the corner superposition motor, and the normal operation of a steering system is ensured.
The corner superposition motor 15 is fixed on the frame of the vehicle, and the output end of the corner superposition motor is connected with the input end of the corner superposition motor reducer 18; the corner superposition motor is arranged on the frame in the middle of the two slide rail seats, so that the integration level of the system is further improved.
The main transmission gear rack and the auxiliary transmission gear rack are arranged on the slide rail seat 20 in a sliding groove mode, and the slide rail seat 20 is fixedly arranged on a frame of a vehicle; the opposite surfaces of the tooth grooves of the main transmission rack and the auxiliary transmission rack are provided with semi-cylindrical sliding grooves, the number of the sliding rail seats is two, and the upper ends of the sliding rail seats are provided with semi-cylindrical protruding parts for mounting the main transmission rack and the auxiliary transmission rack;
the tooth profiles of the main transmission rack, the auxiliary transmission rack, the steering shaft end gear 11, the corner superposition gear 25 and the central gear 23 all adopt helical teeth, so that the steering stability is improved, the impact force is reduced, and the working noise is reduced.
The input end of the steering knuckle 9 is connected with the output end of the tie rod 19, and the output end of the tie rod is connected with the steering wheel 8;
the control module includes: a torque sensor 3, a steering angle superposition motor steering angle sensor 16, an assist motor torque sensor 5, a vehicle speed sensor 13, a steering wheel steering angle sensor 2, a steering wheel steering angle sensor 17 and an Electronic Control Unit (ECU) 12.
The input end of the electronic control unit is respectively connected with the torque sensor 3, the corner superposition motor corner sensor 16, the power-assisted motor torque sensor 5, the vehicle speed sensor 13, the steering wheel corner sensor 2 and the steering wheel corner sensor 17, and the output end of the electronic control unit is respectively connected with the power-assisted motor 4 and the corner superposition motor 15; during steering, the assist motor 4 is controlled to assist power according to vehicle parameters obtained from the sensors, and the steering gear ratio is adjusted by controlling the steering angle superposition motor 15.
The torque sensor 3 is mounted on the steering shaft 7, acquires a torque signal of the steering shaft 7 and transmits the torque signal to the electronic control unit 12;
the vehicle speed sensor 13 is mounted in a transaxle case or a transmission case of the vehicle, and is used for obtaining the vehicle speed of the vehicle and transmitting a signal to the electronic control unit 12;
the steering wheel angle sensor 2 is mounted on the steering wheel 1 and used for obtaining the steering wheel angle when the vehicle turns and transmitting a signal to the electronic control unit 12;
the corner superposition motor corner sensor 16 is installed at the output end of the corner superposition motor 15, and is used for acquiring a corner signal of the corner superposition motor 15 and transmitting the signal to the electronic control unit 12;
the power-assisted motor torque sensor 5 is arranged at the output end of the power-assisted motor 4 and used for acquiring a power-assisted motor torque signal and transmitting the signal to the electronic control unit 12;
the steering wheel steering angle sensor 17 is mounted on the steering wheel 8 and is used for obtaining an actual output steering angle signal of the steering wheel 8 and transmitting the signal to the electronic control unit.
In addition, when the steering is not performed, the installation position of the central gear is in the middle position of the main transmission rack and the auxiliary transmission rack, the installation position of the corner superposition gear is at the right side 1/4 of the auxiliary transmission rack, and the installation position of the steering shaft end gear is at the left side 1/4 of the main transmission gear.
Referring to fig. 3, the invention further provides a control method of a compound rack and pinion type active steering system, based on the system, comprising the following steps:
(1) during steering, collecting a steering wheel corner signal, a corner superposed motor corner signal, a power-assisted motor torque signal, a vehicle speed signal, a torque signal and a steering wheel corner signal of a vehicle, and transmitting the collected signals to an electronic control unit;
(2) respectively calculating the steering transmission ratio and the steering assistance torque required under the current speed and the steering angle of the vehicle according to the steering wheel steering angle signal, the vehicle speed signal, the torque signal and the steering wheel steering angle signal acquired in the step (1);
the steering transmission ratio calculation formula is as follows:
wherein i is a steering transmission ratio; i.e. imaxThe maximum steering gear ratio expected; i.e. iminA desired minimum steering gear ratio; u is the vehicle speed of the vehicle; e is a natural logarithm; k is an element of [55-60 ]]And λ ∈ [8-12 ]]To adjust the parameters; e is an adjusting function related to the steering wheel angle; thetawIs the steering wheel corner, and is positive anticlockwise; thetaw0And thetawmThe threshold value is adjusted for the steering wheel angle.
The calculation formula of the steering assist torque is as follows:
K(u)＝D2eau+b (4)
in the formula, TapIs a steering assisting torque; t iswInputting torque for a steering wheel; t isw0Inputting torque for a steering wheel of a reference driver for starting power assistance; t iswmaxThe maximum steering assisting moment; k (u) is the gradient of the power-assisted characteristic curve; e. a and b are both constants; d1And D2The factors are adjusted for the characteristics of the drivers, and different drivers have different assistance characteristics.
(3) Respectively controlling the transmission ratio and the steering assistance of the corner superposition motor and the power-assisted motor according to the corner superposition motor corner signal and the power-assisted motor torque signal acquired in the step (1) and the steering transmission ratio and the steering assistance torque calculated in the step (2);
the control steps of the corner superposition motor are as follows:
(31) calculating an expected steering wheel angle theta according to the steering transmission ratio in the current vehicle state obtained in the step (2)f：
(32) Calculating a target additional rotation angle required to be output by the rotation angle superposition motor according to the expected rotation angle of the steering wheel obtained in the step (31) and the current rotation angle of the steering wheel;
(33) and (4) controlling a corner superposition motor to track the target additional corner according to the target additional corner value obtained by calculation in the step (32), so as to realize accurate control of the steering transmission ratio.
The calculation formula of the target additional rotation angle in the step (32) is as follows:
in the formula, rwThe gear radius of the gear at the end of the steering shaft; thetamAdding a corner for the target, namely, superposing the corner output by the motor by the corner, wherein the anticlockwise direction is positive; g is the steering gain ratio of the tie rod to the steered wheels; gmThe reduction ratio of the motor reducer is superposed for the corner; r isoThe radius of the gear is superimposed on the corner.
And (3) controlling the corner superposition motor to track the target additional corner by adopting a fuzzy PID control method in the step (33), and controlling the corner superposition motor by taking the error and the error change rate of the target additional corner and the actual output corner of the corner superposition motor as control input and the control current of the corner superposition motor as output.
Wherein, the control steps of the booster motor in the step (3) are as follows:
(34) calculating the target torque T required to be output by the power-assisted motor according to the steering power-assisted torque required in the current vehicle state obtained in the step (2)p：
In the formula, GpThe reduction ratio of the reducer of the power-assisted motor;
(35) and (4) according to the target torque of the power-assisted motor calculated in the step (34), taking the error between the target torque and the torque actually output by the power-assisted motor as control input, taking the control current of the power-assisted motor as output, and adopting a robust synovial controller to control the power-assisted motor to track the target torque so as to realize accurate control of the steering power-assisted torque.
(4) And (4) in the step (3), the output of the power-assisted motor acts on the steering shaft to reduce the steering load of a driver, meanwhile, the input of a steering wheel acts on the central gear through a steering shaft end gear and a main transmission rack, the output of the corner superposition motor also acts on the central gear through a secondary transmission rack, and the central gear drives the steering wheel through a steering tie rod and a steering knuckle to complete steering.
While the invention has been described in terms of its preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (1)
1. A control method of a compound rack and pinion type active steering system is based on the compound rack and pinion type active steering system, and the system comprises the following steps: the device comprises a steering wheel, a steering shaft end gear, a power-assisted motor reducer, a gear rack system, a corner superposition motor reducer, a sliding rail seat, a steering tie rod, a steering knuckle, a steering wheel and a control module;
the input end of the steering shaft is connected with the output end of the steering wheel, and the output end of the steering shaft is fixedly connected with the input end of the steering shaft end gear;
the steering shaft end gear is connected with the input end of the gear rack system;
the power-assisted motor is fixed on one side of the steering shaft and is connected with the steering shaft through the power-assisted motor reducer;
the rack and pinion system includes: the main transmission rack, the auxiliary transmission rack, the central gear shaft bearing and the corner superposition gear;
the input end of the main transmission rack is meshed with the shaft end gear of the steering shaft, and the output end of the main transmission rack is meshed with one side of the central gear;
the auxiliary transmission rack is parallel to the main transmission rack, the input end of the auxiliary transmission rack is meshed with the corner superposition gear, and the output end of the auxiliary transmission rack is meshed with the other side of the central gear, which is parallel to the main transmission rack;
the central gear shaft is fixedly connected to the steering tie rod and is provided with the central gear shaft bearing;
the central gear is sleeved on the central gear shaft bearing;
the output end of the corner superposition motor reducer is fixedly connected with the corner superposition gear;
the corner superposition motor is fixed on a frame of the vehicle, and the output end of the corner superposition motor is connected with the input end of the reducer of the corner superposition motor;
the main transmission rack and the auxiliary transmission rack are arranged on the slide rail seat, and the slide rail seat is fixedly arranged on a frame of a vehicle;
the input end of the steering knuckle is connected with the output end of the steering tie rod, and the output end of the steering knuckle is connected with the steering wheel;
the control module includes: the device comprises a torque sensor, a corner superposition motor corner sensor, a power-assisted motor torque sensor, a vehicle speed sensor, a steering wheel corner sensor and an electronic control unit;
the input end of the electronic control unit is respectively connected with a torque sensor, a corner superposition motor corner sensor, a power-assisted motor torque sensor, a vehicle speed sensor, a steering wheel corner sensor and a steering wheel corner sensor, and the output end of the electronic control unit is respectively connected with a power-assisted motor corner superposition motor; when the vehicle is turned, the power-assisted motor is controlled to assist power according to vehicle parameters obtained from each sensor, and the steering angle superposition motor is controlled to adjust the steering transmission ratio;
the method is characterized by comprising the following steps:
(1) during steering, collecting a steering wheel corner signal, a corner superposed motor corner signal, a power-assisted motor torque signal, a vehicle speed signal, a torque signal and a steering wheel corner signal of a vehicle, and transmitting the collected signals to an electronic control unit;
(2) respectively calculating the steering transmission ratio and the steering assistance torque required under the current speed and the steering angle of the vehicle according to the steering wheel steering angle signal, the vehicle speed signal, the torque signal and the steering wheel steering angle signal acquired in the step (1);
(3) respectively controlling the transmission ratio and the steering assistance of the corner superposition motor and the power-assisted motor according to the corner superposition motor corner signal and the power-assisted motor torque signal acquired in the step (1) and the steering transmission ratio and the steering assistance torque calculated in the step (2);
further comprising the step (4): the output of the power-assisted motor acts on a steering shaft, the input of a steering wheel acts on a central gear through a steering shaft end gear and a main transmission rack, the output of a corner superposition motor also acts on the central gear through an auxiliary transmission rack, and the central gear drives a steering wheel through a steering tie rod and a steering knuckle to complete steering;
the steering transmission ratio calculation formula in the step (2) is as follows:
wherein i is a steering transmission ratio; i.e. imaxThe maximum steering gear ratio expected; i.e. iminA desired minimum steering gear ratio; u is the vehicle speed of the vehicle; e is a natural logarithm; k is an element of [55-60 ]]And λ ∈ [8-12 ]]To adjust the parameters; e is an adjusting function related to the steering wheel angle; thetawIs the steering wheel corner, and is positive anticlockwise; thetaw0And thetawmAdjusting a threshold for a steering wheel angle;
the calculation formula of the steering assist torque in the step (2) is as follows:
K(u)＝D2eau+b (4)
in the formula, TapThe steering assisting moment; t iswInputting torque for a steering wheel; t isw0Inputting torque for a steering wheel of a reference driver for starting power assistance; t iswmaxThe maximum steering assisting moment; k (u) is the gradient of the power-assisted characteristic curve; e. a and b are both constants; d1And D2Adjusting factors for the characteristics of drivers to realize that different drivers have different power-assisted characteristics;
the control steps of the corner superposition motor are as follows:
(31) calculating an expected steering wheel angle theta according to the steering transmission ratio in the current vehicle state obtained in the step (2)f：
(32) Calculating a target additional corner to be output by the corner superposition motor according to the expected steering wheel corner obtained in the step (31) and the current steering wheel corner;
(33) controlling a corner superposition motor to track the target additional corner according to the target additional corner value obtained by calculation in the step (32), and realizing accurate control of the steering transmission ratio;
the calculation formula of the target additional rotation angle in the step (32) is as follows:
in the formula, rwThe gear radius of the gear at the end of the steering shaft; theta.theta.mAdding a corner for the target, namely, superposing the corner output by the motor by the corner, wherein the anticlockwise direction is positive; gIs the steering gain ratio of the tie rod to the steered wheel; gmThe reduction ratio of the motor reducer is superposed for the corner; r isoThe radius of the gear is superposed for the corner;
and (3) controlling the corner superposition motor to track the target additional corner by adopting a fuzzy PID control method in the step (33), and controlling the corner superposition motor by taking the error and the error change rate of the target additional corner and the actual output corner of the corner superposition motor as control input and the control current of the corner superposition motor as output.
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