Summary of vehicle adjustment principle of extreme racing horizon 4
Chapter I Engine
1. Natural suction and pressurization
Natural inhalation is a form of forcing air into the combustion chamber by atmospheric pressure. When the piston of the cylinder moves down, it sucks in air so that fuel can be burned in the cylinder. The common turbocharging technology is to use the exhaust gas generated by the operation of internal combustion engine to drive the air compressor. From the structural point of view, the difference between turbocharging and self-priming is that an air compressor is added to increase the intake air by compressing air, so that the turbocharged engine can suck more air into the cylinder and support more fuel combustion under the same cylinder volume, thus improving the power. The principle is similar to that of mechanical supercharging, except that the air compressor is directly driven by the engine crankshaft.
With the increase of speed, the power and torque of naturally aspirated engine will increase in a relatively stable trend. Mechanical supercharging is similar, because the air compressor will provide compressed air to the engine as long as the crankshaft is moving. However, at low speed, the exhaust gas can't provide enough energy to drive the air compressor, so the turbocharged engine doesn't perform well at low speed, and it needs to maintain a certain speed to provide powerful torque and power. Especially in cross-country and frequent acceleration and deceleration rally, special attention should be paid to shifting gears to ensure the engine speed. Compared with turbocharging, mechanical supercharging will become the burden of the engine at high speed, because the mechanical structure is difficult to adapt to the extremely high speed.
2. Parts modification
More importantly, the camshaft and turbine. Camshaft can increase the limit speed, so that the engine can provide more power at high speed and shift gears more smoothly. The turbine just increases horsepower, and if it is not enough, it will be modified.
Unless the engine horsepower is too poor, the modification is basically shared.
Chapter II Clutch and Gearbox
1. Hold on
The clutch affects the shift speed. For rally and cross-country races with frequent gear shifting and constant acceleration and deceleration, accelerating gear shifting will improve acceleration and deceleration performance.
2. Gearbox
By adjusting the transmission ratio of the speed change gear, the gearbox can output the power output by the engine crankshaft to the driving wheels with different combinations of torque and speed. Generally, it is only necessary to adjust the final transmission ratio so that the acceleration performance and speed of the vehicle can reach the required balance. If the transmission ratio of each gear is uneven, it needs to be adjusted separately. The final effect should be that when accelerating, the engine speed of each gear is basically the same, so as to achieve the best torque output and the smoothest acceleration. For rally, if the maximum speed is not high, you can downshift to minimize the time loss caused by upshift and downshift.
The modification of the transmission system is also used together ~
Chapter III Car Body
1. Roller cover
Increasing the strength of the car body is helpful to cross-country and rally at any time, and can improve the stability of the vehicle when landing. But increase the weight of the car, and the road car will not be installed.
Step 2 lose weight
After the weight is reduced, the maneuverability can be greatly improved. After the car body is lightweight, the inertia will be reduced and the speed of acceleration and braking will be accelerated. For a bend, the centripetal force F = MV 2/R, that is, the square of the speed v is equal to Fr/m, that is, the greater the radius of the bend, the greater the limit speed; The greater the centripetal force, the greater the limit speed; The smaller the mass, the greater the limit speed. The source of centripetal force in the case of horizontal pavement is friction. As we all know, the friction force F is directly proportional to the friction coefficient K and the positive pressure P. When the friction coefficient is constant, the greater the pressure, the greater the friction force. That is f=kP. The downforce of the vehicle mainly comes from two aspects, namely, the gravitational force mg and the downforce A caused by aerodynamic force. At this time, f=k(mg+A). Substituting into the formula, v 2 = kgr+ka/m. Without considering the air pressure a at high speed, the mass has no effect on the limit speed of the curve. But in the real situation, the lighter the mass, the better the curve performance.
It is always said that the weight of the car does not affect the steering performance. There is a rumor here.
3. Aerodynamic kit
The main aerodynamic kits are the front lip and tail wing, which can provide additional downforce at high speed to increase friction, thus improving cornering performance and stability. Take the wing as an example, its lift is generally proportional to the square of velocity. Similarly, at low speed, the aerodynamic package will basically not work, and it will only start to work after the speed increases and the air flow increases. Therefore, for low-speed corners, as well as cross-country and rally competitions, aerodynamic kits will increase the weight of the car and affect its performance. For expressway bend, it can be greatly improved. Increasing the pressure under the front lip will increase the friction of the front wheel and improve the lateral driving force of steering. The tail wing can increase the downward pressure of the rear wheel, increase the transmission efficiency between the tire and the ground, and prevent the vehicle from turning too sharply at high speed. (Oversteering and rear wheel slipping are called tail flick; Under-steering, the front wheel slipping is called pushing the head), but excessively increasing the downforce will increase the rotating friction and resistance of the tire when the vehicle is driving, reduce the limit speed of the vehicle, and increase fuel consumption and tire wear.
Chapter IV Tires and Suspension
1. Fatigue
The higher the tire pressure, the greater the rigidity and the closer the connection between the hub and the ground. If the tire pressure is high, steering and acceleration will respond quickly. However, the maximum friction will be reduced and the tire will slip easily. Reducing the tire pressure will increase the contact area between the tire and the ground, make the tire soft and make the responsiveness worse, but it will increase the friction. Generally, the tire pressure of a pulling car is lower than that of a road car. Similarly, increasing the wheel hub diameter makes the tire sidewall thinner, and the effect is similar to increasing the tire pressure.
2. Tire positioning
Track, that is, the width of the distance between the front/rear tires. The wheelbase is the distance between the front and rear axles. Wider track can improve the stability when rolling, such as sharp turns, but when the track increases, the wheelbase decreases in proportion, and the stability of the vehicle will become worse when pitching, that is, leaning forward and backward, and the center of gravity will move back and forth. Generally speaking, the wheelbase cannot be changed. Vehicles with long wheelbase have better linear stability, while vehicles with short wheelbase are more flexible and have better stability when cornering.
The caster angle is the angle of the steering shaft. Just like the front wheel of a bicycle, when turning, the axis of rotation forms a certain angle with the ground. When the caster angle of the kingpin is 0, the steering shaft is perpendicular to the ground. If the tire is simplified as a circular plane, the intersection line between the tire plane and the ground plane, that is, the straight line in the rolling friction direction, is completely consistent with the rotation direction of the steering shaft. How many degrees the steering shaft rotates, how many degrees the tire rolling direction changes. At this time, the pressure in the vertical direction of the vehicle does not affect the steering of the tire. Assuming the limit case, when the inclination angle is 90 degrees, that is, the steering shaft is parallel to the ground, it can be imagined that no matter how the steering shaft rotates at this time, the intersection line between the tire plane and the ground plane is horizontally forward, no steering will occur, and the height of the steering shaft will become lower. Therefore, the greater the inclination angle, the lower the steering sensitivity.
When the car is driving in a straight line, if the steering wheel is slightly deflected by external force (for example, it is deflected to the right as shown by the arrow in the figure), the driving direction of the car will be shifted to the right. At this time, due to the centrifugal force of the car itself, at the contact point B between the wheel and the road surface, the road surface acts this lateral reaction force Fy on the wheel. The reaction force Fy forms a moment FyL acting on the wheel around the kingpin axis, and its direction is just opposite to the wheel deflection direction. Under the action of this torque, the wheels will return to the original middle position, thus ensuring the car to run stably in a straight line, so this torque is called stable torque. It is helpful for the stability of vehicles on bumpy roads.
Toe angle refers to the angle between the tire and the central axis of the vehicle when we look at the vehicle directly above.
If toe-in is set, the steering is sensitive; Setting toe-in at too large an angle is easy to oversteer; If it is set to toe-in, the steering will be slow; If the toe-in is set too high, the vehicle will understeer.
Ackerman Angle is designed to prevent the vehicle from slipping when turning. When designing the steering mechanism, the rotation angle of the inner wheel (relative to the bending center) is slightly larger than that of the outer wheel, so that the angles of the two wheels are one big and one small, forming an included angle, thus forming the Ackerman angle. This design can make the steering wheel keep the rolling direction consistent with the actual displacement direction when the vehicle turns quickly, and maintain a more stable grip. Therefore, the tire toe angle in the outer picture is stable, and the straight-line driving is unstable. For the rear wheel of the vehicle, most of the wheel tracks are set to the inner eight. Because when the vehicle turns, the weight of the vehicle body will press on the tire outside the vehicle. If the outer eight settings are set at this time, the wheels will point to the outside of the vehicle and pull the rear of the vehicle outward, which is easy to drift and shake the tail and increase instability.
Tire inclination is the angle formed between the wheel and the vertical line on the ground when viewed from the front of the car.
When the car turns a corner, the body will lean to the outside, and our wheels will also lean to the outside. Assuming that the camber angle of the four wheels of our vehicle is 0, only the outer side of our tire will contact the ground because of inclination in the curve, thus reducing the contact area with the ground and reducing the grip. Then, when the camber is set to a negative value, the struggling wheels on the outside of the vehicle will get the largest area contact with our ground in the curve, so as to obtain better grip on the curve.
When adjusting the inclination angle, it can be judged by the tire temperature. When the temperature of the outer tire and the inner tire is basically the same during continuous steering, it shows that the tire has the most complete contact with the ground, the largest contact area and the best grip performance.
3. Spring and damping
Track adjustment is equivalent to improving the overall geometric balance of the car, and improving the overall handling of the car from the grip and load. Wheel attitude adjustment is equivalent to improving the handling on the grip track. Suspension adjustment will improve the load transfer handling of the four tires.
Load transfer is the transfer of center of gravity and weight, just like physical inertia. When a car brakes, it leans forward because of its own weight, and most of the load is applied to the front wheel, which is load transfer. When accelerating, the load is concentrated on the rear wheel; When turning, it is the front outer side and the rear outer side (the front outer side wheel bears more load than the rear outer side). Because the road surface is uneven and suspended, there is load transfer, which makes the grip of the four wheels change constantly. F 1 adopts a light body with a low center of gravity and a mid-engine to make the weight distribution more reasonable and minimize the load transfer. The function of suspension is to make the load transfer less violent and less sensitive.
Therefore, the softer the suspension performance, the more balanced the load transfer, and the load transfer of the car can be controlled very accurately when driving, and the maximum four-wheel grip can be obtained. But relatively speaking, too soft suspension will also make the car roll too much, losing control sensitivity and tracking. The harder the suspension performance, the more accurate and sensitive the vehicle handling and tracking, but the load transfer becomes more intense, thus reducing the fault tolerance rate, the ultimate grip and the adaptability to the road.
Spring is the foundation of suspension, and it will produce resilience with compression. The longer the compression length, the greater the resilience. Therefore, the car will press the spring to a certain extent, and the elasticity of the spring will gradually increase until it is equal to the pressure given by the car, maintaining a certain height and supporting the car body. The flatter the spring is pressed, the greater the elastic force is.
Damping is a component that limits and controls the spring. It is different from spring. It is installed next to the spring, which will only give the spring resistance to continuous compression or rebound, so that the spring is gentle when it is compressed, less violent when it rebounds, and will not let the car jump around. With the cooperation of spring and damping, the weight of front and rear tires is well shared when the car is fully loaded. For example, when the car accelerates, the rear wheel is compressed and the load is slowly transferred to the rear wheel, but the front wheel is not directly inclined, but slowly extended with the slow compression of the rear wheel spring to help the car transfer the load backwards, and the grip of the front wheel will not be lost quickly. Specifically, when decelerating into a corner, assuming that the rebound damping of the rear wheel is large, the load is transferred to the front wheel when braking, the pressure of the rear wheel is reduced, and the spring is elongated. However, due to the existence of rebound damping, the spring can not be stretched quickly, the tire will leave the ground, and the rear wheel will lose its grip, leading to tail flick. Similarly, when the compression damping of the front suspension is reduced, the front suspension will be compressed quickly, the front of the car will sink faster, and the rear of the car will rise faster, which will also reduce the grip of the rear wheel and cause tail flick.
The anti-roll bar is used to tighten the suspension on both sides. It will restrain the suspension from moving in different directions on both sides. For example, when turning, the inner suspension is elongated and the outer suspension is compressed, and the anti-roll bar will tighten the car body to prevent the car body from tilting too much.
The anti-roll bar can adjust the hardness. The harder the anti-roll bar is, the stronger the connection between the suspension and the car body is. However, when turning sharply, the inner wheels may be off the ground, and the total grip of the inner and outer sides will become smaller. However, the softer anti-roll bar will make the body roll and the tires will keep scratching the ground. The limit case is that the inner and outer tires do not transfer load at all when turning, and still maintain the same ground pressure. Therefore, the front and rear suspension anti-roll bars can adjust the grip of the front and rear inner and outer tires respectively to achieve the effect of adjusting the total grip of the front and rear sides, thus adjusting the oversteer and understeer.
To sum up, the car needs to sacrifice some load transfer to maintain flexibility when turning sharply. On the one hand, it is the adjustment of tire positioning, on the other hand, it is the anti-roll bar and suspension rebound. These parameters have their own division of labor:
Toe angle affects the trajectory when turning and continuously affects the posture of the front and rear wheels; Springback affects the initial load transfer, and the anti-roll bar affects the grip balance inside and outside the curve. In addition, hard springs and compression damping can also make the load transfer process from straight line to curve more flexible;
The details of the grip are composed of tires and inclination. The wider the tire, the lower the tracking performance when lifting on a curve, and the tire pressure will make the slipping process silky (soft) or simply (hard); The inclination is in charge of the best grip area, and it is necessary to observe the fit state between the wheel and the track; Ackerman angle and caster angle will affect the steering performance of wheels. Ackerman angle affects the direction of inner wheel, and caster angle of kingpin affects steering wheel support.
The pitch of wheels will affect the attitude of the whole vehicle, including the transmission of load, the direction of wheels and the body movement of the whole vehicle.
In short, the adjustment must comprehensively observe the movements of all parts, make the posture of the car more coordinated through the cooperation of all parts, make the car cooperate with the track and drivers, and finally achieve perfect dynamic balance through distinct movement changes.
Chapter IV Transmission System
1. limited slip differential
When turning, there is a speed difference between the inner and outer tires. Because of the weight transfer, the downward pressure of the inner tube is small, and the downward pressure of the outer tire is large, that is, the grip of the outer tire is greater than that of the inner tube, and the resistance of the upper tire and the outer tire is also greater than that of the inner tube. When the transmission shaft outputs power, if the power is too large, the inner wheel will slip first and lose its grip, while its resistance will be further reduced when slipping, and the transmission shaft will output all the power to the slipping tire, so that the outer tire that really grasps the ground will lose power. On the whole, the reduction of the driving force of the automobile tire will lead to insufficient steering force, which will lead to insufficient steering. So it is necessary to add a limited slip differential. Structurally, several friction plates are added to the differential to connect the left and right shafts to a certain extent. The higher the locking rate of limited slip differential, the closer the connection between inner and outer tires. When it reaches 100%, it means that there is no differential and the inner and outer tires have the same speed. At this time, excessive steering and slipping will be serious. Limited slip differential is divided into acceleration differential and deceleration differential. The former controls the locking degree of the inner and outer tires when stepping on the accelerator, and the latter controls the locking degree of the inner and outer tires when the engine is braked by loosening the accelerator. The principle of deceleration difference is similar. When decelerating, the braking oil pressure of the inner and outer tires, that is, the braking resistance, is the same, while the ground friction of the outer tire is larger. Assuming that the locking rate is 100%, the pressure between the outer tire and the ground is high and it does not slip, but its stroke is greater than the actual stroke of the inner tire. If the inner tube and the outer tire are completely locked, the rotation stroke of the inner tube is greater than the actual stroke, so it slips and loses grip. When cornering and decelerating, the main steering torque of the whole vehicle comes from the braking friction of the inner tube (it is conceivable that the vehicle will turn left only when the left tire is braked), so the higher the locking rate, the more serious the understeer is.
2. Driving wheel
Firstly, according to the position of the driving wheel, it is divided into front-wheel drive (FWD), rear-wheel drive (RWD) 4WD (four-wheel drive) or AWD (all-wheel drive).
The characteristic of FWD is that the engine installed in front directly transmits power to the front wheels, which improves the traction efficiency. 60% ~ 70% of the weight is concentrated in the front of the car, which provides better stability. However, the front wheels have to bear 75% of the braking, and the center of gravity of the car moves backward during the rapid acceleration, which will cause acceleration delay and insufficient steering. Because the center of the transmission shaft is too close to the center of gravity of the vehicle, it is difficult to provide enough steering torque.
RWD is characterized by sensitive steering, but it is difficult to maintain a stable posture when the rear wheel slips, because the front wheel does not provide power. Moreover, the rear wheel is very easy to slip when the high-power rear wheel drive is started. The starting performance is not good, so it is necessary to add additional traction control system to prevent excessive traction. But because of its simple structure, high transmission efficiency and higher speed.
AWD has the best mobility, because the traction distribution is relatively uniform, all traction can be completely transferred to the ground. And the front wheel also has driving force when turning, so the steering stability is better. AWD models are equipped with a central differential, which can independently adjust the power distribution of the front and rear wheels. The more power the rear wheels distribute, the more inclined they are to RWD, which will increase the oversteer.
Intuitively look at the tire downforce, taking Volkswagen idr as an example.
This is a tire under pressure in the parking state, and the size of the green circle represents the downward pressure.
Next, the tire states are 50km/h, 1 10km/h and 230km/h respectively. It can be clearly seen that at 1 10km/h, the green belt begins to become slightly larger and the downforce becomes larger, but the downforce does not increase obviously at low speed, and only at high speed will there be a strong downforce.
By the way, tire pressure and sidewall thickness can be understood by shoes, just like football shoes and basketball shoes. The soles of football shoes are hard, but they feel strong when running, especially on the hard plastic playground track. Basketball shoes with air cushions bounce comfortably, but they feel bouncing when running, but they are not so strong.
Brakes
There is basically no need to make major changes when abs is turned on, and the introduction text next to the training interface is very clear, because the braking action before turning is very simple, which only involves the load distribution of the front and rear wheels and the resulting grip change. The keyboard player can reduce the oil pressure, and the player who can control the handle linearly can increase it appropriately. If you turn off abs, you need to look at it according to your personal feeling.
The so-called understeer and oversteer, I personally think it is necessary to distinguish between attitude problems and out-of-control problems. If it is an attitude problem, the car is still in a controllable state, because the steering system will automatically adjust the direction of the front wheels with the change of vehicle speed. In other words, even if the steering is killed, the front wheel will not lose its grip and the car will go straight ahead. If it is not out of control, it will not directly lose control of the tail, but it will turn to bending center because it is too sensitive. If the turning radius is enlarged by increasing the speed, it may lose its lateral grip. At this time, it was out of control.
To sum up, training can adjust more the posture of the car body, so that the maximum speed can match the maximum steering ability when cornering. At most, the control force is achieved by adjusting the tire inclination angle and suspension height. The simplest is the transverse G force, which really affects the maximum speed of bending center. Adjusting it depends more on the modification of tire tread and body weight reduction, and the adjustment only plays a icing on the cake.
There is another important factor whether it is out of control. Unless the skills are in place and you have a deep understanding of the characteristics of the car, it is recommended to turn on abs and turn on traction control after driving. It's really different from these.
For example, there is an ATV cross-country race on Fortune Island. The basic weight of ATV varies from 700-900kg, and there are even more than 600. This weight is easy to get out of control when it lightly touches obstacles in cross-country running. The map is still raining at night and the ground is extremely slippery. At this time, unless you are lucky enough not to hit the stone wall, it is really difficult to run. If the stability control system is turned on, everything will be different, and the ATV can be easily saved by swinging its tail.