Honda's hybrid/turbo technology analysis: a complete overtake of its rivals

At the 2016 FUNTEC TURBO+HYBRID Technology Experience Camp, Honda officially released three turbocharged engines and a new generation of hybrid systems, named SPORT TURBO and SPORT HYBRID. The newly released powertrains will gradually be installed in new models, such as the new hybrid Accord/Spiri, the tenth-generation Civic, and the upcoming mid-size SUV of GAC Honda. And at this test drive meeting, I will be able to test drive these new models (still in the development stage).

Although the manufacturer released these new powertrains in this event, in fact, many specific parameters have not been announced to the public. There is neither manufacturer data nor our actual test data. Does this mean that we have surpassed our opponents in all aspects? You must think I am fooling you. No, the main basis is the following two points: Toyota, the main competitor, once issued a statement expressing its high recognition of Honda's new i-MMD dual-motor hybrid system. The original meaning is probably, "The throne of the mid-size car with the lowest fuel consumption has been taken away by Honda Accord. If we want to surpass its performance, we can only redevelop a new hybrid system." (According to official website data, the fuel consumption rate of the hybrid Accord is 30km/L, 158kW, and the fuel consumption rate of the hybrid Camry is 23.4km/L, with a comprehensive output power of 151kW). As for several turbocharged engines, after comparing the test drive of the test model and the same level model, I also think that the former performs better. Next, let's take a look at what is so great about these new powertrains.

■ New generation sports dual-motor hybrid system i-MMD

Honda also has a series of hybrid powertrain products. The i-MMD system released this time is for mid-size cars. The first to be equipped with this system are the current American and Japanese versions of the hybrid Accord, and the new Accord and Spirior hybrid models that will be launched in China will also be equipped with this system. In the world of hybrid powertrains, Toyota has always been the leader, but it has such a high evaluation of Honda's i-MMD system, which must have its unique features. The i-MMD system has two motors and is simpler in structure than Toyota's THS-II system.

"The picture shows the current US version of the hybrid Accord"

What we experienced on site was the upcoming new Accord hybrid model, but unfortunately we were not allowed to take photos of the new car, which is still in the confidentiality stage, so we could only use the pictures of the current US version instead. We first test drove the hybrid version of the Camry, and then the hybrid Accord, so that the difference between the two cars was more obvious. Let's talk about the power performance first. The hybrid Accord, which is mainly driven by an electric motor, accelerates significantly faster than the Camry, and both the stamina and the responsiveness of repeated acceleration are better, and even feel half a level higher. The powerful torque advantage of the electric motor is obvious. In addition, the performance in terms of driving quality cannot be ignored. The noise of the power system, the sound insulation of the cabin, and the vibration reduction effect of the suspension are much better than those of the hybrid Camry. It is definitely one of the most anticipated models this year. Let's take a look at what is unique about this i-MMD system.

According to the manufacturer, there is an essential structural difference between Honda's i-MMD system and Toyota's THS-II system. Honda's i-MMD system continuously switches power sources when working, while Toyota's THS-II continuously adjusts the mixing ratio of each power source.

The advantage of the i-MMD system is that the various components in the system are connected by a fixed gear ratio, and no speed change mechanism is required (speed change mechanisms often make the system more complex and increase weight), and the engine can directly drive the vehicle forward, reducing energy loss in the transmission components, and having higher fuel efficiency and saving more fuel. At the same time, the high-power drive motor used in the i-MMD system has a stronger power output, which makes the power performance of the entire system better, which is one of the main reasons why it is called a sports hybrid system. The i-MMD system has three modes, namely EV driving mode, hybrid driving mode, and engine driving mode. Next, let's take a look at the working principle.

●  EV driving mode: Actually, we all like to use electric mode

The original intention of the hybrid system is to save fuel, and the vehicle is equivalent to an electric car in EV mode, and the engine is turned off and does not burn fuel. Therefore, when driving a hybrid vehicle, many people tend to use EV mode as much as possible. For a Virgo user like me, it is more likely to develop into obsessive-compulsive disorder. Under certain conditions (in fact, EV is not the most fuel-efficient mode, which will be explained later), I think this approach is reasonable.

The benefit of the electric mode is that it can reduce the power loss of the transmission system when driving the vehicle forward, and can make more efficient and full use of energy. Therefore, in Honda's i-MMD system, the EV driving mode plays an important role. The working principle is very simple, that is, to use the electricity stored in the battery to drive the vehicle forward. There is a key point here. The clutch in the system is disconnected and the engine is idle. It has nothing to do with the operating parts and will not cause any energy loss. The maximum speed of the EV mode is 120km/h. If the battery is fully charged, it can travel about 2km (20-30km/h). After all, this is not a pure electric system. The role of the EV mode is just to make better use of the remaining energy.

When braking or decelerating, the wheels drive the drive motor to rotate (the active and passive relationship between the drive motor and the vehicle is reversed, but the direction of rotation of the motor remains unchanged), generating electrical energy and storing it in the battery. In EV mode, the drive motor also plays the role of a generator, being both a father and a mother. In this state, the vehicle is equivalent to a traditional electric vehicle, while utilizing the powerful power output of a high-power electric motor to achieve a smooth and powerful acceleration experience.

● Engine driving mode: The most fuel-efficient way is to burn the oil just right

Although the electric mode is the most fuel-efficient, think about it, the vehicle is not plug-in, the only energy source is gasoline, and it still depends on the engine burning oil to provide energy. So the question is back to square one, how can the engine be more fuel-efficient? The i-MMD system has a 2.0L Atkinson cycle engine, and the fuel efficiency of the engine is the highest at about 2000rpm. If the output power of the engine at this time is exactly equal to the power required to drive the vehicle forward, then this is the most fuel-efficient state of the i-MMD system in theory.

In reality, the chances of achieving a perfect state are not high, so the engine needs to rotate with the generator to store excess energy in the battery by generating electricity. In the engine driving mode, the engine directly drives the vehicle forward, and the engine speed will increase accordingly with the vehicle speed. However, at this time, the vehicle state is equivalent to a traditional car driving in the highest gear, so the change in speed will not cause the engine speed to be too high and deviate from the economic fuel consumption zone (the vehicle's maximum speed is set to 180km/h), and the engine can still maintain a relatively ideal fuel efficiency (although the instrument does not display the engine speed, it should not be too high).

● Hybrid driving mode: Is it a better way to save the country from the curve?

The hybrid driving mode mainly occurs when accelerating or the battery is low. The engine is started to drive the generator to generate current, which is then combined with the current from the battery to power the electric motor, providing a stronger power output. If the accelerator is floored, assuming that the battery has enough power, plus the current from the engine, it should be the strongest power output state. The maximum comprehensive output power of the i-MMD system is 158kW. But if the battery is dead, the acceleration will be discounted accordingly.

Honda's i-MMD system is a bit of a roundabout way of saving the country. It generates electricity first and then drives the vehicle through the drive motor. The hybrid mode allows the engine to maintain power generation within the 2000 rpm economic fuel consumption zone, so that the engine can generate electricity at the most efficient working condition to reduce fuel consumption. At the same time, the drive motor also has an advantage in torque (drive motor 135kW/315N·m). This is a perfect match and becomes the efficient hybrid mode of i-MMD.

● What is the basis for the vehicle to determine which driving mode to use?

The vehicle needs to consider three factors when deciding which driving mode to use: the remaining power SOC, the current vehicle speed, and the power required to maintain the vehicle speed/accelerate. The i-MMD system can achieve high fuel efficiency in both EV driving mode and engine driving mode, so both are the preferred modes for the i-MMD system.
 

     ■ VTEC TURBO series engine

The three VTEC TURBO engines released this time actually made their debut at the Honda Conference in 2013. The engine power parameters announced at that time were very high, giving everyone a very high expectation, but many internal details were actually reserved at that time. This official release is closer to mass production, and both 1.5T and 2.0T have road test vehicles (models that will be launched in China soon will also have the opportunity to test drive this time.)

The three models in the VTEC TURBO series have similar technologies, such as dual VTC variable valve timing technology for intake and exhaust, direct injection technology, cylinder head cooling system, etc. However, due to the different positioning of the models and the planned models, there are also differences in details, such as VTEC valve lift technology. The 1.0T engine has VTEC on the intake side, the 1.5T engine does not have VTEC, and the 2.0T engine has VTEC on the exhaust side.

● VTEC TURBO 1.0T

Honda's 1.0T engine uses a three-cylinder structure, and the intake valve is equipped with Honda's unique VTEC variable valve lift control system, which can increase the intake valve lift at high speeds, thereby reducing intake resistance and increasing intake volume, thereby increasing engine output power. In addition, the engine has intake and exhaust variable valve timing technology, and the timing regulator is driven by a belt. The new long-lasting timing belt can achieve the same life as the engine.

Since the 1.0T engine has a small displacement, in order to improve the intake efficiency, the manufacturer has equipped it with VTEC variable valve lift technology on the intake side. The VTC variable valve timing system on both the intake and exhaust sides can effectively reduce the turbo lag phenomenon. The 1.0T adopts a direct injection system in the cylinder, and the direct injection nozzle is side-mounted. With the high tumble intake duct unique to the engine, it can form a strong mixture tumble, improve combustion efficiency, and reduce the engine fuel consumption rate.

The key to the above-mentioned tumble intake duct is the shape and optimization of the cylinder head opening. Combined with the shape of the piston top, a strong tumble can be generated in the cylinder to achieve rapid combustion of the mixture.

The engine's turbine system uses a wastegate valve controlled by an electric actuator. Compared with the traditional wastegate valve controlled by a vacuum tank, this electrically controlled wastegate valve can control the wastegate opening more accurately and quickly, thereby achieving accurate and rapid control of boost pressure.

In addition, in order to reduce losses during engine operation, the engine uses a variable displacement oil pump, which can control the displacement of the oil pump according to the engine speed, thereby reducing the energy loss of pumping oil under low engine speed and low load conditions.

According to the manufacturer's engineers, the balance block of the middle cylinder of the crankshaft is actually also heavier, and if it is as far away from the crankshaft axis as possible, the engine vibration will be smaller and the vibration reduction effect will be better, but in order to reduce weight, it was not increased in the end. The 1.0T engine uses forged crankshafts and connecting rods to achieve a better lightweight effect, and the pistons are cast. The 1.0T engine has a fuel consumption reduction of about 10% compared to the 1.5T engine.

● VTEC TURBO 1.5T

Honda's 1.5T engine will be installed in many domestic Jade and other models in the future. The design goal of this engine is to maintain good fuel economy while enhancing torque output.

It is worth noting that Honda's 1.5T engine is not equipped with VTEC valve lift control technology, but only uses intake and exhaust variable valve timing technology, and the timing regulator is driven by a chain. The intake and exhaust variable valve timing technology realizes dynamic control of the intake and exhaust valve overlap angle (intake and exhaust valves open at the same time), uses the intake airflow to drive the exhaust gas out of the cylinder, reduces the combustion chamber temperature, and suppresses the knock phenomenon.

The 1.5T engine is positioned to balance fuel economy and power performance. Without VTEC variable valve lift technology, the output power is about 150 horsepower, but the specific number has not been announced and is expected to be announced in April. Compared with the same level of models, this is already a good level, but people are greedy and want to get stronger power. The hardware of the 1.5T engine of the US version of Civic should be very close to the 1.5T released this time, but the maximum power reaches 176 horsepower, which is a big gap. When it was released in 2013, it was as high as 200 horsepower.

Like Honda's 1.0T engine, the 1.5T engine also uses a side-mounted nozzle layout, combined with high-tumble intake duct technology to improve the engine's fuel efficiency.

In order to balance fuel economy, the 1.5T engine optimizes the shape of the cylinder head intake hole and piston surface, achieving high longitudinal tumble flow for more complete combustion. The 1.5T engine uses a forged crankshaft and connecting rod, and the lightweight design helps improve the engine's responsiveness.

Like mainstream small-displacement engines, Honda's 1.5T engine uses an exhaust manifold integrated in the cylinder head. By improving the heat exchange efficiency between the exhaust manifold and the engine coolant, the engine warm-up speed and exhaust temperature under high-load conditions are increased.

The Civic that will be launched in China will be equipped with a 1.5T engine, matched with CVT or 6MT. The American version of the Civic tested on site is equipped with a CVT gearbox, with very good power performance, small turbo lag, and high responsiveness of the engine and gearbox. Compared with a certain 1.4T model of Volkswagen tested on site, the power advantage is quite obvious, and the latter is equipped with a 6MT gearbox. The tenth-generation Civic tested on site has shift paddles, but the version introduced into China is still uncertain. In addition, the 1.5T engine is relatively noisy. The manufacturer said that it has been included in the optimization and improvement plan, but it is still uncertain whether the domestic version will be adjusted. In addition, the new Civic Si is also under development.

● VTEC TURBO 2.0T

Honda's 2.0T engine adopts a four-cylinder structure with variable valve timing technology for intake and exhaust and VTEC valve lift control technology. The VTEC system of this engine is not set on the intake side, but on the exhaust side. The exhaust side VTEC system can speed up the scavenging speed, thereby reducing the temperature of the combustion chamber to suppress knocking.

Increasing the compression ratio is an effective way to improve the thermal efficiency of the engine, but suppressing the knock phenomenon caused by the increase in compression ratio is a difficult problem encountered during development. The 1.0T, 1.5T and 2.0T engines all control the valve overlap angle to enhance the scavenging effect, reduce the combustion temperature, suppress the knock phenomenon, and ultimately achieve an increase in compression ratio.

Honda's 2.0T engine uses a small and lightweight turbine, which can improve the turbo hysteresis phenomenon to a certain extent, allowing the peak torque to be output at a lower speed, so that the vehicle has better acceleration performance. The electric control pressure relief valve can accurately and quickly control the exhaust pressure relief valve opening, thereby achieving accurate and rapid adjustment of the boost pressure, achieving a balance between power and fuel economy.

Honda's 2.0T engine uses an exhaust manifold integrated in the cylinder head, which increases the engine warm-up speed and exhaust temperature under high load conditions. In addition, the engine also has an annular cooling oil channel inside the piston to enhance the cooling of the piston and significantly reduce friction.

In order to reduce the engine's operating inertia and overall weight, Honda's 2.0T engine uses lightweight connecting rods and crankshafts. The engine's connecting rods and crankshafts are manufactured using a forging process, which ensures strength while achieving maximum lightness.

At the scene, the 2.0T engine was equipped on a camouflaged medium-sized SUV, which will be put into production and listed by GAC Honda this year. Judging from the on-site test vehicle, the vehicle configuration is very rich, with panoramic sunroof, rear electric side window sunshades, rear seat heating, LED headlights, LED fog lights, front and rear right cameras, etc., and the gear control is button-type. Although the test drive in a limited venue is very short, the acceleration performance of the vehicle still left a deep impression on everyone. Compared with the 2.0T Highlander tested in comparison, the acceleration of this camouflaged test drive car is obviously stronger, and the matching 9AT gearbox tuning is also very good, and the smoothness is quite good. The overall driving texture of the vehicle is also much stronger than that of the Highlander. In addition, the vehicle is equipped with air suspension, with three driving modes: standard, sport, and comfort. The difference in suspension damping between different modes is obvious, which can better take into account the needs of sportiness and comfort.

Summarize:

In just one day, we could only experience four new powertrains in a hurry, but the short experience has aroused everyone's interest. As a veteran technology geek, Honda has finally brought out its secret weapon. The comprehensive level of the four powertrains is very high, and they are better than the current products of the same level on sale. Three of the four powertrains have been confirmed to be launched in China this year, and the performance of the new models is worth looking forward to.