CREEPING (2-PEDALS)

The creeping mode of a car with AT is a mode in which the car begins to move slowly forward (or backward in R mode) immediately after releasing the brake pedal, without pressing the AP. This mode allows you to start smoothly and makes it easier to drive at low speeds, for example, in traffic jams or parking.

The following basic parameters are used to compare and evaluate different cars according to the convenience of the crawling mode:

• the speed of the car without pressing the AP is usually 3-7 km/h – low speed is better for traffic jams and maneuvers.
• the smoothness of the creeping mode – the absence of jerks, jerks, delays at the start of movement — the smoother, the more convenient
• the speed control possibility – some modern cars (electric vehicles, hybrids) allow you to adjust the intensity of the creeping mode through the menu, which may be convenient for different drivers.
• the reaction to the transition between D and R - is how quickly and gently the car starts moving in the opposite direction when switching between D and R

The convenience of the crawling mode of a car with AT depends on:

• AT type – torque converter automatic transmission, variator, robotic automatic transmission – affects the smoothness and intensity of the transmission of torque
• AT calibrations – calibration regulates the box operation parameters and AT control algorithms.

Currently, the following types of automatic transmissions are used in passenger cars:

the torque converter automatic transmission is the earliest type of automatic transmission used. The use of this type of transmission is possible on vehicles with powerful engines – these transmissions can transmit high torques. The smoothness and switching speed are high.

CVT, continuous variation transmission – continuously variable transmission. Due to the design features, the transmission of high moments was initially impossible, which led to the use of this type of transmission on low-power subcompact cars. At the moment, manufacturers have resolved this issue and CVT is used on very powerful cars. The smoothness and speed of the moment change are the maximum possible.

The robotic automatic transmission – DCT, dual-clutch transmission – is the second generation of robotic gearboxes (previously, single-clutch transmissions were used, but currently they do not exist in mass production due to mediocre characteristics. It is the most advanced in terms of switching speed and smoothness. These gearboxes can transmit high torques.

A torque converter automatic transmission consists of:

• torque converter — an assembly connecting the engine to the gearbox and converting the torque – consists of a pump wheel (rigidly connected to the internal combustion engine), a turbine wheel (connected to the gearbox shaft), a stator — a fixed element (increases the efficiency of MOM transmission).
• torque converter locking mechanism is a locking plate with clutches and a piston, which, under the control of transmission fluid pressure, provides a tight connection between the pump and turbine wheels to increase efficiency in certain modes.
• hydraulic control unit is a system of channels and solenoids controlled by electronics, which regulates the pressure and fluid supply for gear shifting and control of the torque converter.
• planetary gearbox — provides the necessary gear ratios for the transmission
• electronic control unit (ECU/TCM) — controls the operation of the hydraulic unit and the torque converter locking mechanism based on data from numerous sensors – RPM, pressure, temperature.

CVT is a type of automatic transmission that allows you to smoothly change the gear ratio without mechanical steps. The most common type is the V—belt type. The main components of the V—belt variator are the:

• driving and driven pulleys, each consisting of two conical movable halves that can move closer and apart, changing the diameter of the pulley.
• belt (or chain) — connects the drive and driven pulleys. In V–belt CVTs, a metal wedge-shaped belt is used.
• hydraulic system — provides movement of the halves of the pulleys to change their diameters and, accordingly, the gear ratio.
• control unit (electronic control module) is the "brain" of the transmission, which controls the operating modes of the variator.
• reversing mechanism is a planetary gearbox to ensure reverse
• starting clutch module can be a friction package, a torque converter or an electromagnetic clutch.

In the early CVTs, the gears were continuously variable, but customers did not like this because the engine was humming at maximum power. The control system is currently being calibrated in such a way that stepwise switching is simulated.

DCT is a type of transmission that combines the advantages of "mechanics" in terms of dynamics and efficiency, and automatic in terms of convenience. The main structural blocks of DCT:

• two clutches – each with its own set of gears: the first one with odd gears (1, 3, 5, 7), the second is with even numbers (2, 4, 6, R).
• two primary shafts are located in each other – one inside the other. One transmits the torque to the odd gears, the other to the even gears.
• fork and gears – each "half" of the box has its own set of gears, synchronizers and forks. Everything works as in a regular manual transmission, but without driver intervention.
• hydro-electronic control module is a central electronic module with a set of sensors and actuators responsible for controlling gear shifting and clutch operation.
• actuators are electric or hydraulic drives that squeeze/spin the clutches and move the gearshift forks at the command of the control unit.

The first DCT production models did not have sufficient reliability and gained fame for being unpredictable in operation. But at the moment, manufacturers have solved this problem.