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[YesAuto Electric Vehicle Technology] In the domestic hybrid mid-size car market, the Camry Shuangqing is a well-known product. With the launch of the domestic hybrid Accord within this year, Camry Shuangqing (hereinafter referred to as “Hybrid Camry”) will face a strong opponent. The domestic hybrid Accord will continue to use the i-MMD hybrid system of the US version of the Hybrid Accord, and there will not be much change in the corresponding performance indicators. Friends who follow the Autohome website may have seen my colleague Huang Rongjia’s introduction to the hybrid Accord i-MMD hybrid system and the difference in daily use between the American version of the hybrid Accord and the domestic version of the ordinary Accord written by Huang Rongjia not long ago. . If the above two articles still cannot satisfy your curiosity about Hybrid Accord technology, then the technical analysis and actual measurement of this article will reveal more secrets about Hybrid Accord for you.

● The same hybrid, but not the same as Toyota

Although the hybrid systems of Honda Hybrid Accord and Toyota Hybrid Camry both use dual motors and Atkinson cycle naturally aspirated gasoline engines, the hybrid systems of the two vehicles are quite different in the power transmission path. According to the measured data of Autohome, the hybrid Accord equipped with a larger output power motor has a slight advantage in acceleration performance, while the hybrid Camry with a more ingenious transmission system structure has better fuel economy.

The i-MMD hybrid system adopted by the Hybrid Accord is generally more inclined to use electric motors to drive the vehicle. Only in high-speed cruising conditions, the system will switch to engine mode. At this time, the engine drives the wheels through the mechanical transmission mechanism to push the vehicle forward, and the motor plays an auxiliary role.

The THS-II hybrid power system adopted by the Hybrid Camry uses a planetary gear mechanism to mechanically couple the power of the engine, generator, and drive motor together, and realizes the “mixed flow” of power without the use of a mechanical clutch.

Comparison table of parameters of Hybrid Accord and Hybrid Camry
Model 2012 Camry Zunrui American Hybrid Accord
engine capacity 2.5L 2.0L
engine model 4AR-FXE LFA1
Engine compression ratio 12.5 13
Engine maximum horsepower 160Ps (118kW)/5700rpm 143Ps (105kW)/6200rpm
Peak engine torque 213N·m/4500rpm 165N·m/3500-6000rpm
Maximum power of drive motor 105kW (143Ps) 124kW (169Ps)
Peak torque of drive motor 270N·m 307N·m
Comprehensive power of power system 202Ps (151kW) 199Ps (146kW)
battery capacity 1.6kWh 1.3kWh
Battery Type NiMH batteries Lithium Ion Battery
Car home measured acceleration time to 100 kilometers 8.12s 7.99s
Car home measured average fuel consumption 5.41L/100km 5.7L/100km
Note: The measured fuel consumption level and acceleration time are related to the test environment, and the data is for reference only.

Neither car has a gearbox in the traditional sense. Hybrid Accord is because the engine only directly drives the wheels when cruising at high speed, which is equivalent to only working in the highest gear. The driving problems at low vehicle speeds are all handled by high-power motors, which simplifies the driving structure. The hybrid Camry uses a planetary gear mechanism to distribute the power output of the engine/motor.

If you want to use one sentence to explain the difference in the working logic of the hybrid power system of the two cars, I think the hybrid Accord's i-MMD hybrid system is more inclined to use the electric motor to drive the vehicle under normal circumstances, while the Hybrid Camry's THS -II hybrid power system under normal circumstances is more focused on using the engine to drive the vehicle.

● How far can the pure electric mode go?

The lithium battery capacity of the Hybrid Accord is only 1.3kWh, which is relatively small. In actual use, how far can the Hybrid Accord go in pure electric mode? Below we illustrate through actual measurement data.

Obviously, the pure electric mode is not suitable for high-speed driving. This is related to the torque output characteristics of the motor. The peak torque of the permanent magnet synchronous motor appears in the low-to-medium-speed region, and its torque output is reduced in the high-speed region, and it cannot efficiently output the torque to achieve vehicle cruise and speed increase. The high-speed power output performance of the engine is higher, and the fuel economy is better in the cruising state of the vehicle, which just makes up for the shortcomings of the motor. The cooperation of the engine and the electric motor makes the Hybrid Accord have good power performance and fuel economy in the full speed range.

● How does the engine work in hybrid mode?

In the hybrid mode, the engine does not output power to the wheels. It only drives the generator to generate electricity. The generated electric energy and the electric energy from the lithium battery drive the motor to drive the wheels to increase the speed of the vehicle. Since the engine speed information is not displayed on the vehicle dashboard, the general user cannot know the working status of the engine.

The depth of the driver's accelerator pedal will be reflected on the POWER indicator on the instrument panel. When the accelerator pedal is depressed about 40% of the full stroke, the number of POWER indicator bars is about 6 bars, and the engine speed will increase to about 3000rpm. In the hybrid mode, the engine speed is related to the number of POWER indicator lights. The more the number of POWER indicator lights, the higher the target speed of the engine, so as to generate more electric energy to meet the needs of the motor-driven vehicle.

● Why the engine mode can only be used at medium and high speeds?

In addition to pure electric mode and hybrid power mode, the hybrid Accord also has an engine mode that uses the engine to directly output power to drive the vehicle. However, the engine mode is automatically triggered by the system only when the vehicle speed is medium to high. Why can I enter the engine mode at medium and high speeds? To answer this question, we first understand the knowledge of the engine's economic fuel consumption area.

By using the above two working logics, the hybrid Accord i-MMD system can make the engine work in areas with lower fuel consumption rates as much as possible, thereby achieving the goal of fuel saving.

The relationship between vehicle speed and engine speed in hybrid Accord engine mode
Vehicle speed (km/h) Engine speed (rpm)
80 1837
100 2296
120 2755
140 3214

It can be seen that the engine speed range corresponding to the 80-140km/h vehicle speed range is 1837-3214 rpm. The above speed range is consistent with the engine fuel consumption rate distribution diagram shown above. Since the Hybrid Accord transmits power to the wheels through a fixed gear ratio in the engine mode, it is impossible to control the engine speed through a shift operation similar to a traditional gearbox. This makes the car must enter the engine mode near 80km/h, making the engine work in the economic fuel consumption area, so that the engine's fuel consumption advantage can be fully utilized.

● Is the electronically controlled hydraulic brake assist system reliable?

In addition to electric air-conditioning compressors, electric water pumps, and electric power steering, the hybrid Accord also uses an electronically controlled hydraulic brake booster system for its braking system. The use of electric air-conditioning compressors, electric water pumps, and electric power steering are mainly to reduce the burden on the engine. The traditional air-conditioning compressor, mechanical water pump, and mechanical hydraulic booster pump driven by the crankshaft pulley will increase the load of the engine and consume the power of the engine. The hybrid Accord has more considerations when it comes to configuring an electronically controlled hydraulic brake assist system.

Hybrid Accord is a hybrid model. Due to the existence of pure electric mode, the engine is not always in operation. This makes it impossible for the vehicle to provide continuous and stable negative pressure for the vacuum booster of the traditional brake booster system in the intake manifold or through the mechanical vacuum pump to achieve the brake boost function when the engine is turned off. After the electric control power booster pump is configured, even if the engine on the hybrid Accord is in a stalled state, the vehicle still has a brake boost function to meet the driving safety requirements of the vehicle.

If the electric control power booster pump fails, it is just like the situation after the vacuum booster pump fails. Although the brake has lost the boost, when the driver presses the brake pedal hard, it can also generate a certain braking force on the wheels through hydraulic transmission. , This is the same as the traditional hydraulic braking system, which can play the role of emergency braking.

● The difference between D block and B block

In addition to the four gears P, R, N, and D configured on general automatic models, the Hybrid Accord also has a B gear to enhance the intensity of kinetic energy recovery. The function of the B gear is to enhance the kinetic energy recovery intensity of the electric motor through the comprehensive control of the hybrid power system control unit, so as to convert more vehicle kinetic energy into electric energy for storage within a unit time. So what is the difference between B gear and D gear? Below we will further illustrate through actual measurement.

The B gear of the Hybrid Accord will only increase the energy recovery intensity of the system and increase the vehicle deceleration. Its speed-up performance is no different from that of the D gear. I usually use the B block to collect the fuel for a certain distance in front of the traffic lights, and use the energy recovery function to stably decelerate the vehicle, so that it can be decelerated without stepping on the brakes and can also charge the lithium battery, which is more fuel efficient. In downhill road conditions, the B block can also be used to increase the traction resistance of the vehicle, reduce the working strength of the braking system, and avoid overheating and performance degradation.

The D gear of the hybrid Camry stops the engine when the vehicle is decelerating, MG1 idling, and all the electric energy generated by MG2 is used to charge the power battery, thereby achieving the maximum kinetic energy recovery effect and accelerating the charging speed of the power battery.

● Where is the lithium battery? How does it dissipate heat?

The power battery of the Hybrid Accord is a lithium battery, which is actively cooled by a blower located in the trunk. There is an air vent on each side of the back of the rear seat. The air in the passenger compartment will be drawn into the lithium battery to cool the internal battery cells, and then exhausted outside the car through the vent in the trunk.

Since pure electric vehicles do not have the engine to charge the lithium battery, the lithium battery will have a “loss of electricity” in the low temperature environment. This is caused by the drop in discharge current of lithium batteries at low temperatures. In order to weaken the above-mentioned “power loss” phenomenon, pure electric vehicles will install a thicker insulation layer for the battery to isolate the cells from heat exchange with the external environment; if the insulation is good, the cooling cannot be neglected. When pure electric vehicles are running, lithium The battery will be charged and discharged frequently and generate a lot of heat. At this time, an efficient cooling system is required to cool the lithium battery to ensure that the lithium battery is always at a suitable working temperature. In comparison, the battery temperature control system on the Hybrid Accord is much simpler than that used on pure electric vehicles.

● Is it possible to cool and heat when driving in pure electric mode?

As we mentioned earlier, the hybrid Accord uses an electric compressor, so it can theoretically be cooled by a lithium battery in a pure electric mode. And how long the power of the lithium battery can support the work of the electric compressor is our concern. At the same time, if pure electric heating is used, the power consumption is very large. Only pure electric vehicles will consider electric heating; hybrid vehicles generally start the engine to increase the temperature of the coolant, and then pass the warmed coolant through The radiator in the passenger compartment allows the air-conditioning system to blow hot air. What is the heating method of the air-conditioning system of the Hybrid Accord?

In addition, the hybrid Accord will start the engine when a cold car starts to allow the engine coolant to reach a certain temperature. In addition to preparing for air conditioning and heating, it is more important to allow the engine lubricating oil to reach a suitable working temperature (reduce viscosity and improve fluidity) and allow the three-way catalytic converter to reach working temperature as soon as possible (reduce emissions).

Full text summary:

Whether the Hybrid Accord can surpass the Hybrid Camry is really hard to say, after all, the two are relatively close in terms of fuel consumption and power performance. In China, the sales of hybrid models are also closely related to local subsidy policies. The pricing of domestically-made hybrid Accords and whether local subsidies will be provided will be the focus of the majority of Honda fans. If the domestic hybrid Accord’s pricing strategy and subsidies are similar to those of the hybrid Camry, then the domestic hybrid Accord will become the biggest competitor of the hybrid Camry. (Photo/Text/Car House Chang Qinglin/Car House Chang Qinglin/Liang Haiwen)