Conventional Automatic Transmission Research Articles

The Effectiveness of Using Continuous Variable Transmission (CVT) in 2WD Buggy Vehicles

Continuous Variable Transmission (CVT) is a transmission system that does not have gears like in manual transmission cars or conventional automatic transmission cars. CVT has the advantage of being able to maintain the proper rotational speed at any time in terms of engine efficiency by changing the speed ratio flexibly and continuously. A continuously variable transmission (CVT) is a transmission that can change steplessly through an infinite effective gear ratio between maximum and minimum. This is in contrast to other mechanical transmissions which only allow a few different gear ratios to choose. The flexibility of the CVT allows the drive shaft to maintain a constant angular speed over the output speed range. Torque is transmitted from the drive to the pulley which is driven by friction acting between the belt and pulley surfaces. Tests were carried out using a dynotest to obtain wheel rotation data and the resulting torque. The loading is given from 3 kg, 5 kg, 7 kg and 8 kg, the engine rpm used is 5500 rpm, 6000 rpm, 6500 rpm, 7000 rpm and 8000 rpm. Rear wheel rotation is inversely proportional to the load, the greater the load the rotation will decrease. Load is directly proportional to torque, the greater the load given the torque will increase. The CVT system is still effective for use as a power successor. The power that can be transmitted is still greater than 50%, namely 68%.

Development of Transaxle Fluid for Electrification Vehicles: Design of Novel Additive Formulation

<div class="section abstract"><div class="htmlview paragraph">To achieve carbon neutrality by reducing carbon dioxide (CO<sub>2</sub>) emissions, vehicles with an internal combustion engine have started to be replaced by electrification vehicles such as hybrid electric vehicles (HEVs), plug-in HEVs (PHEVs), and battery EVs (BEVs) worldwide, which have motors in their transaxles (T/As). Reducing transmission torque loss in the transaxles is effective to reduce CO<sub>2</sub> emissions, and lowering the viscosity of lubrication fluids in T/As is a promising method for reducing churning and drag loss. However, lowering viscosity generally leads to thin oil films and makes the lubrication condition severe, resulting in worse anti-fatigue and anti-seizure performance. To deal with these issues, we made improvements on the additive formulation of fluid, such as the addition of an oil-film-forming polymer, chemical structure change of calcium detergents, and an increase of anti-wear additives including phosphorus and sulfur. As a result, we succeeded in developing a novel fluid with greater lubricity than a conventional automatic transmission fluid (ATF), despite the fact that the viscosity of the new fluid was lowered by around 50% compared with that of the ATF. In addition, the electrical insulating and anti-foaming performance of this fluid, which are required for T/A fluid in electrification vehicles, were equal to or greater than those of the ATF. The fuel economy in the Toyota Hybrid System (THS) was improved by 1.0% and more compared with the ATF because of the significant viscosity decrease in the developed fluid. This fluid will be widely used for HEVs, PHEVs, BEVs, and fuel cell electric vehicles (FCEVs) and can contribute to the realization of a carbon-neutral society.</div></div>

Investigation of power split schemes for modern hybrid cars transmissions

The modes of operation of the transmissions for hybrid cars are studied in this work, using planetary gears for connecting the internal combustion engine (ICE) and the electric machines (motor-generators). The peculiarities of the two-stream variants with an electric branch – a closing block consisting of two electric machines is analysed. This achieves a stepless gear change and an increase in overall efficiency with respect to the efficiency of electrical machines. The theoretical formulation is based on the dependences between the losses of a two-stream circuit, which proves that this increase is a function of the relative share of power transmitted through the electrical branch. The characteristics of typical two-stream circuits with input differential and output differential with one mechanical and one electrical branch are determined. The aim is to evaluate not only the change in the total efficiency, but also the kinematic gear ratio and the ratio of the torques and their ranges for the whole circuit, as a function of the parameters of the electrical branch. The development of the schemes in order to improve their performance in different operating conditions is considered, which allows for combining the variants and modes of operation – serial hybrid and parallel hybrid in two variants, at low speed and high speed. Analytical and graphical methods are used to analyse and illustrate the results, which are more visual and suitable for composite planetary gears with more units. It is expected that cars with such transmissions will have better dynamics compared to conventional automatic transmissions and lower energy consumption or do less damage to the atmosphere, as a result of the optimal combination of the operating modes and dimensions of ICE and electric machines.

Electrified Drive-Unit Parametric Mechanical-Loss Model Development and Calibration

<div class="section abstract"><div class="htmlview paragraph">As the automotive industry vies to meet progressively more stringent global CO2 regulations in a cost-effective manner, electrified drive system cost and losses must be reduced. To this end, a parametric Drive Unit (DU) mechanical-loss model was developed to aid in the design and development of electrified propulsion systems, where the total propulsion system cost and DU losses can be directly linked (e.g., Hybrid Electric Vehicle (HEV) motor/inverter/engine content, or Battery Electric Vehicle (BEV) battery size).</div><div class="htmlview paragraph">Many DUs for electrified propulsion systems are relatively “simple” drive systems, consisting of gears, bearings, shafts, lip seals, and an electric motor(s), but without clutches, high-pressure lube systems, or chains/belts as found in conventional automatic transmissions. The DU loss model described in this paper studies these simple DUs, with the mechanical losses dissected into 10 loss components.</div><div class="htmlview paragraph">Analysis was conducted at the vehicle level to assess the relative loss contributions of the DU, motors, engine, etc. for the entire vehicle propulsion system to show the DU loss contribution to the total system. The DU loss model was used to deconstruct the total DU mechanical loss into subcomponents of Speed-Dependent (SD) and Load-Dependent (LD) losses. For each loss component, standard loss model equations were modified, or new equations were created, and calibrated based on loss data/trends of component-level bench tests, supplier data, and/or DU-level tests. Particular emphasis was placed on the LD components of the gear and bearing losses, as a function of load, speed and temperature, as they can represent a large portion of the total DU loss. DU-level tests were conducted at various positive and negative (regenerative braking) loads, speeds, fluid types, temperatures, and sump-fill levels to aid the development of the model. The model calibration methodology is described, where the calibrations of some of the individual component models were iterated, so that a universal set of loss model calibrations produced loss results that closely matched the test DU losses at the various operating conditions.</div></div>

Slope Shift Strategy for Automatic Transmission Vehicles Based on the Road Gradient

Motivated by the development of high-precision digital maps for advanced driver assistance system (ADAS) in recent years, this study provides a new approach to solve the problems of the conventional automatic transmission vehicle travelling on sloping roads. Based on vehicle dynamics, shift problems on hilly roads are analyzed. A novel intelligent shift strategy is proposed, which consists of a dynamic shift schedule for the uphill, a safety shift schedule for the downhill, and a comprehensive economical shift schedule for the gentle slopes. A set of driver-in-loop co-simulation tests was conducted in a driving simulator that is equipped with a MATLAB/Simulink dynamics simulation platform. The test results verified the effectiveness of the new intelligent shift strategy. With the road information provided by a high-precision digital map, busy shifting can be eliminated, and improved dynamic performance can be achieved for a vehicle travelling on the uphill roads; undesired upshift can be prevented, and engine traction resistance can be used to relieve the load of braking system when a vehicle travelling on the downhill roads; also, fuel consumption can be reduced for a vehicle travelling on a gently sloped road. Consequently, this novel intelligent shift strategy offers a reliable and effective solution for improving a vehicle’s driving performance on a hilly road.

Design and validation of clutch-to-clutch shift actuator using dual-wedge mechanism

Clutch-to-clutch shift technology is a key enabler for fast and smooth gearshift for multi gear transmissions. However, conventional hydraulic actuation systems for clutches have drawbacks of oil leakage and low efficiency. Electromechanical devices including wedge mechanism offer potential alternative actuators. The previous studies on the wedge emphasize on self-reinforcement, but neglect self-weakened phenomenon. In this paper, a novel dual-wedge mechanism is proposed to exert self-reinforcement and avoid self-weakened effect by selecting a correct working slope. The design concept and physical structure are thoroughly described. Dynamic models for the actuation system and vehicle powertrain are built for performance validation. The results show that the normal force generated by the wedge under self-reinforced case is 2.74 times that under self-weakened case. Using the same amount of the driving motor current, the upshift can be successfully completed in 0.78s when the correct slope is used; however, it fails to engage the clutch when the incorrect slope is used due to self-weakened effect. So does the downshift. Moreover, the experimental results of the dual-wedge mechanism using the correct slope are comparable to those from the hydraulic actuator of a conventional automatic transmission.

Laser structuring of printed layers on thick film ceramic substrates

The market for automatic transmissions continues to grow. In addition to what originally attracted interest to the product – enhanced driver convenience – the prospect of greater fuel efficiency is now a further factor in their favor. Continental has been offering transmission control units (TCU) since 1982, starting with those for simple three-gear conventional automatic transmissions, followed by all-wheel applications in 1985, CVT applications in 1999, truck applications in 2000, and arriving at the double clutch transmissions in widespread use today. At present Continental Business Unit Transmission is technology leader worldwide in the market for transmission controls for the full spectrum of automatic drives. Continental TCU's are divided in “Stand alone”, “Attached to” and “Integrated” TCU's. However the “Stand alone” and “Attached to” TCU's are normally equipped with standard PCB substrates. Because of the highest requirements in temperature, vibration and typical medias (aggressive Transmission oils – liquid & gaseous), standard organic substrates cannot be used, ceramic substrates are typically preferred. A common technology in that case is the ceramic based thick film technology, where conductor and resistor pastes are printed on the surface of a ceramic alumina substrate by using a common screen printing process. The printed layers (Au, Ag, AgPd, AgPt) have to be dried and thermally sintered after appliance. The increasing functionality of the TCU's and the increasing requirements due to miniaturization inherently show that thickfilm technology, as applied in a standard printing process, is not possible to reach those requirements. Continental has developed a concept to realize higher miniaturization of the circuit boards. Therefore a innovative laser structuring process has been installed for the newest generations of TCU's in cooperation with a leading machine and system manufacturer. By using the laser structuring of conductor lines it allows Continental to increase the connection density by keeping the substrate size unchanged. Typical common printing pitches in thickfilm production are 300μm, however pitches of 100μm are possible by laser structuring in mass production.

Modeling and validation of a hydraulic systems for an AMT

The automated manual transmission (AMT) offers the advantages of the high efficiency of manual transmissions and an operational convenience similar to conventional automatic transmissions. The AMT system is essentially a manual transmission with an added-on hydraulic and electronic control unit that automates the clutch and gear shift operation. Moreover, actuators for the AMT are installed directly on the existing manual transmission. For this reason, the development time and production costs of AMT systems are generally lower than those of other automated transmission technologies. This paper presents an analytical model for the simulation of a vehicle equipped with the AMT system and focuses on modeling the hydraulic system to control the clutch and gear shift during shift. The shift profiles for the clutch engagement are also simulated to evaluate shift quality.

Hybrid Transmission for Mobile Robot

This paper presents proposed designs of parallel hybrid transmissions with only one electric motor/generator (MG) and without any rotating clutches. The proposed motor/generator integrated hybrid transmission serves to regulate the engine’s effective gear ratio (engine rotational velocity versus vehicle velocity) by mixing the engine and electric motor powers through a power controlling device. The proposed design provides some of the benefits and flexibility of a power-split design but using conventional available components in a simpler mechanical layout that makes the design compact, mechanically simple, and operationally flexible. Three commonly used transmission gear sets are used for this purpose; Simpson, Ravigneaux, and Type-6206 gear sets. With an electronic control unit, eight major modes of operation including a regenerative braking capability are shown to be feasible in the proposed hybrid transmission; one electric motor mode, two engine modes, two engine/charge modes, and two power modes. Continuously variable transmission (CVT) capability is provided with the second engine/charge mode and with the second power mode. The second power mode can be further subdivided into three hybrid submodes that correspond to the direct drive, underdrive, and overdrive of a conventional automatic transmission. The feasibility of the proposed hybrid transmission is demonstrated with a numerical example employing conventional Ravigneaux gear train. The kinematics, static torque, and power flow relations for all operation modes are analyzed in detail.

Mode Control Strategy for a Two-Mode Hybrid Electric Vehicle Using Electrically Variable Transmission (EVT) and Fixed-Gear Mode

A mode control strategy for a two-mode hybrid electric vehicle (HEV) with a fixed-gear mode is proposed, considering wheel torque demand while minimizing fuel consumption. First, the dynamic equations of a power-split HEV are derived, and these equations consist of two electrically variable transmission modes and four fixed-gear modes. Using the dynamic equations, the optimal operation mode is selected from the viewpoint of the maximum available output torque with respect to the driver's demand and vehicle velocity. Next, an optimized mode selection map is constructed using optimization to minimize fuel consumption while satisfying the required wheel torque. We note that fixed-gear mode uses the fixed-gear mode 1 to implement a higher gear ratio if the vehicle speed is low and if the required output torque is large, as in a conventional automatic transmission shift map, and selects the fixed-gear mode 4 to implement a lower gear ratio if the vehicle speed is high and if the required output torque is low. A vehicle simulation was performed to verify the mode control algorithm of the two-mode HEV, and the results were compared with vehicle experimental results. The simulation results showed that the mode control strategy for the two-mode HEV gave satisfactory performance, similar to the experiment results.

On the intelligent slope shift strategy

The vehicle longitudinal dynamics was investigated and a slope recognition method based on reference tables was proposed, to overcome the problems encountered when a vehicle with conventional automatic transmission travels on slopes. Shift strategies on uphill and downhill slopes were also developed. The intelligent slope shift strategy is significant because it can improve the performance on slopes of not only conventional automatic transmissions, but also many other vehicle control systems, such as engine management systems, electric power steering, and shock absorbers.

A robust CVT for heavy-duty applications

Recently it has become increasingly apparent that continuously variable transmissions, or CVTs, are poised to replace conventional automatic transmissions in passenger car and truck applications. As is the case with any widely applicable innovation, CVTs are now going through the trial-and-selection process to determine which of the numerous designs are most suitable.

Adaptive shift scheduling strategy introducing neural network in automatic transmission

Abstract Conventional automatic transmissions, which have fixed shift patterns, sometimes show inconvenient shifting patterns, especially in uphill and downhill driving. In order to improve the driveability for these road conditions, Mitsubishi developed an adaptive shift logic called “Fuzzy shift” in 1992. Since then, further evolutional shift scheduling strategies has been developed to cover more extensive road conditions. This paper introduces neural network, learning and continuous variable shift patterns control incorporating this strategy.

Development of Transmission by 3K-Type CVT. (1st Report, Design of Transmission).

In the case of CVT (Continuously Variable Transmission), employing 3 K-type planetary gears, being manufactured, the speed of the output shaft of the CVT can be changed continuously from zero up to high speed. In this report, the construction of automatic transmission (RX-AT) has been designed incorporating this CVT, and the normal force has been set to make RX-AT transmit the power without slippage. After the equation of the rating life was determined by the experiments, the size of the RX-AT was determined by this equation and the normal force. Furthermore, from the result of manufacturing the experimental model RX-AT, a RX-AT more compact than conventional automatic transmission has been realized.

The Nutating Traction Drive

The unique torque speed characteristic of the single-shaft gas turbine requires that it have a continuously variable-ratio transmission for successful application to automotive use. This paper discusses the development of a novel mechanical transmission which has the power density required for highway vehicles. Cost and efficiency are competitive with conventional automatic transmissions.