Vehicle management systems


Vehicle management system

Control systems with braking systems are one of the most important on-board systems from a safety perspective. The control systems have the task of precisely maintaining and changing the direction of movement of the vehicle. When driving, the driver's command is transmitted via the control system to the vehicle's steering wheels.

Modern management systems should meet the following requirements:

- ensuring stable movement of the vehicle when driving in the direction and at the same time the steering wheel should have as little idling as possible
- providing adequate force on the steering wheel when turning while driving
- Appropriate kinematics of the steering system that allows the steering wheels to roll in a curve with as little lateral sliding as possible
- spontaneous return of the steering wheels from the curvilinear position to the rectilinear position
- as little impact transmission as possible from the wheels on the steering wheel
- maintaining proportionality between the steering wheel turning moments and the steering wheel turning moments (feeling "on the steering wheel", feedback on tire contact with the ground)

The driver can change the angle at which the steering wheels are using various elements that are connected and make up the steering system. In the general case, passenger vehicle control systems consist of the following units:
- control mechanism (steering wheel with associated, usually articulated shaft)
- steering gear (rack and pinion, worm gear, combined mechanism ()
- transmission mechanism (clamps, joints (.)
- steering wheels


Figure 1. Deformable steering column

Command mechanism
With technological advances, the steering wheel shafts have become increasingly complex assemblies. Modern steering shafts include a variety of additional systems, including telescopic depth adjustment for the driver to find the ideal position behind the wheel, shafts that collide during a collision to avoid or mitigate the effects of a crash on the driver, and locks with the steering lock .

The steering wheel is usually mounted on the shaft using a tapered, grooved and threaded connection and secured with a nut. The shaft is located in the shaft housing (pipe) that is attached to the vehicle body. The upper link of the body to the body of the body is designed on modern vehicles so that it is separated from the body during a collision. In some embodiments, the lower link between the shaft housing and the body is designed to deform in a collision such that the shaft and the steering wheel move together downwards and forwards. The lower part of the shaft is attached to the steering gear by means of a universal joint which allows the steering shaft to be at a certain angle relative to the steering gear and reduces the transmission of shock from the ground.

There are a number of different control shaft solutions that are deformed during a collision, and this article will describe one possible solution. Independent of performance, the role of such systems is to reduce the loads acting on the driver in a collision. In a collision, drivers usually grab the steering wheel firmly, thus transferring most of their mass to the steering wheel (often distorted upper sections of the steering wheel can be seen in photo and video materials from the scene of an accident). The principle of operation of the deformable steering columns is simple: in the initial phase of the collision, the force is transmitted from the steering gear to the steering shaft, which begins to move upwards, and thus does not cause the steering wheel to move axially. As the deceleration continues, the driver's body presses the steering wheel and the steering shaft housing, whose upper bracket disengages and it detaches from the body and moves downwards, and then to the front thanks to a deformable lower steering shaft housing bracket.


Figure 2. Variable Transmission Gear Design (Top Right)


In modern vehicles, the most commonly used are two gearbox solutions, which have proven to be the most suitable for many aspects. The first solution is with a toothed rack and the second solution is a gearbox with a coiled spindle and balls. The worm gearbox is less commonly used on passenger cars today.


The dominant solution for gearboxes today is a gear rack, most often backed by a hydraulic or electric power steering. The shaft of the steering wheel is connected by a PTO joint to the gear that drives the toothed rack. The gear is permanently coupled to the rack. When the driver turns the steering wheel, the steering wheel turns, and with it the steering wheel gear that transmits movement to the rail itself. Turning the steering wheel translates into moving the gear bar to the left or right. The toothed rack is connected to the wheels by a system of levers and clamps and their rotation achieves the desired direction of movement of the vehicle.

To reduce the forces the driver must develop during steering wheel rotation, there is a reduction in transmission, usually between 18-20: 1, between the steering wheel shaft gears and the rack. Transmission ratio is a trade-off between the force a driver has to develop on the steering wheel to spin the wheels (the higher the gear ratio - the steering wheel is easier) and the number of steering wheel turns relative to the steering wheel speed (the higher the gear ratio, the more it takes steering wheel for the same wheel deflection). To solve this problem, control gears without servo assisted gears with variable gear ratio are used. With fixed transmission systems, the steering wheel becomes more difficult as the steering wheels rotate more than the straight line position. Variable gear ratios are used to correct this phenomenon. To achieve a higher gear ratio, the gear pair step is reduced and thus easier to rotate the steering wheel, but more steering wheel rotation is required to reach the end positions. Toothed rack solution is the most commonly used solution in passenger vehicles today.

Figure 3. Gearbox with spindle and balls with variable gear ratio (below)

Figure 3. Gearbox with spindle and balls with variable gear ratio (below)

Advantages over gearbox with coiled spindle and balls:
- simple construction
- cheap and simple production
- easy to use and high efficiency
- there is no gap between the rack and pinion
- toothed racks and clamps are connected directly
- compactness
- easy adjustment of the travel of the rack, and thus the maximum angle of rotation of the wheels

- sensitivity to shocks
- if the clamps are at an angle, the loads are higher
- limited clamp length
- the dependence of the angle of rotation of the wheels on the travel of the rack, which is why a smaller lever must be used and thus increase the forces in the control system
- reducing the gear ratio increases the forces on the steering wheel, which due to the absence of power steering can be annoying (eg when parking)

Fig. 4. Gearbox with control gear (gear rack)

Fig. 4. Gearbox with control gear (gear rack)

Gearbox with spindle and balls

Nowadays, it is less common for steering gears, but still quite prevalent on larger passenger and commercial vehicles, especially when there is no power steering, because the steering forces are relatively small. Generally, this type of gearbox is nowadays often present in commercial vehicles and rarely on SUVs and pick-up vehicles. The higher cost of making this type of gear in the beginning raises the price of the vehicle, but on the other hand it is extremely robust and suitable for harsh operating conditions.

The principle of operation is similar to the older type of gearbox with coil and nut, but in this case balls were placed between the coil spindle and nut to increase efficiency. Instead of threading, there are spiral-shaped ball bearings on the steering wheel spindle and nuts. When the steering wheel is rotated, it also rotates the coil spindle, which drives the balls that transfer their motion to the nut, which moves axially with respect to the coil spindle. The movement of the nut causes the steering segment to rotate, which further transfers its movement to the transmission and to the wheels. Variable transmission ratios are also available with this system.

The advantages of gearboxes with coiled spindles over gears are:
- the possibility of transmitting forces of higher intensity
- the possibility of a large angle of rotation of the wheels
- the possibility of using longer clamps
- the possibility of choosing different lengths of the transmission mechanism, which reduces the load when parking


Figure 5. Gears and joints of the transmission

Transmission mechanism

The transmission consists of various clamps and joints and is tasked with transferring movement from the steering gear to the steering wheels. The movement of the movement must be precise regardless of the vertical movement of the wheels. The complexity of the transmission depends on the type of steering gear and some other parameters of the vehicle structure. Toothed gearbox requires the smallest number of clamps, but is effective in transmitting movement.

Controllability can be achieved through the trapeze of steering. The control trapezoids according to their position relative to the axis of the steering wheels can be front or rear, and according to the design parameters of the steering trapezoids, they can be with one or more cross-sectional links. In the case of a dependent bearing, the steering trapezoid is made of clamps and transverse beams, and in the case of an independent one reliance the trapeze is made up of clamps and a thoughtful line connecting the steering wheel hubs or hub mounts.

Management trapezoidal pattern most commonly applied to the dependent reliance control wheels are shown in FIGS. a), b) and c), and trapezoids used in the independent system reliance are shown in Figures d) and e), and the solution in Fig. f) is used with a pinion gearbox. If the control wheels are dependent on the suspension, the transverse one-piece clamp is usually used, though there are different solutions. In the case of independent support, the cross member consists of two or more articulated parts.


Figure 6. Management trapezoid scheme

Text by Vanja Dragosavljevic

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