Analysis of the instrument panel display system and anti-skid control module of Toyota Prius

Analysis of the instrument panel display system and anti-skid control module of Toyota Prius

Prius is a hybrid car launched by Toyota Motor Corporation of Japan. This article will disassemble and analyze the dashboard display system and anti-skid control module of the body electronic part of this hybrid car.

Although many vehicle status information and vehicle control functions are displayed and implemented through a central touch screen panel, key information is provided by a dedicated display system that can be seen at a glance behind the steering wheel. The instrument panel module (DM) provides most of the read-only information, such as speed, oil level, gear, odometer / km, etc., through digital means and an icon-based vacuum fluorescent display (VFD) panel. VFD technology has been around for years, and Prius VFD may come from Futaba or Noritake. Toyota prefers the digital reading method. It does not use the analog pointer table that has recently been popular again in recent years.

For VFD, in automotive applications, the harsh external sunlight will reduce the resolution, so readability and contrast are more important. To further improve visibility, the driver actually sees the double-reflected VFD image instead of the direct image of the panel. The two mirrors under the instrument panel guide the output of the VFD to the light channel indicated to the driver, which filters out the scattered light of the VFD module and improves the driver's perception experience quality. Although the current required by the VFD is not particularly high, it requires high voltage. In addition, an MSC1162A 40-bit VFD display driver from Oki Semiconductor converts the output from the Fujitsu MB90583C 16-bit microcontroller to an appropriate level to Fluorescence is obtained in the driving electrodes in the vacuum chamber sealed by the panel.

A 5V regulator, a mysterious Toshiba chip (clock?) And a serial EEPROM are the main ICs soldered to the instrument panel. In addition to display control, Fujitsu's microprocessor forms a communication interface that supports the gear sensor and engine control module. It is unclear whether the speed and mileage information is calculated and stored in the DM, or is the DM only responsible for information display, and the display data comes from other Prius modules?

Two white modules are also connected to the DM, they are also somewhat unexpected. After opening, there is an oil-immersed V-shaped pendulum. The pendulum arm has a magnet at the end of the swing arm, which will be above a Hall effect sensor when swinging. My first thought was that it might constitute a yaw sensor as mentioned in the anti-skid control module (SCM), but its slow damping effect seems unlikely. Considering its structure, its more likely usage is used in conjunction with the DM circuit, and its orthogonal arrangement during installation makes it function as a tilt sensor to compensate for the displayed oil level. When the parking position makes one or both axles of the car angled, the sensor can be used to recalibrate the displayed oil level, so that even if the oil in the fuel tank is not within the sensing range of the fuel gauge built in the fuel tank, it can also ensure Accurate oil level reading. Once again, due to the complex design of Prius, sometimes it takes a lot of trouble to figure out the function of any module in its car.

Figure 1: As far as the instrument panel is concerned, Toyota Prius seems to appreciate the digital reading method rather than the analog pointer table.

Analog custom circuits are critical to SCM

We purchased a new Prius with a full configuration to decipher how its electronic system was implemented. Under the hood are hidden details of the power control system, power transmission / recovery electronic system, and infotainment / navigation system of the gas / electric hybrid car. Now, we will analyze its anti-skid control module (SCM)

SCM is used to control and correct traction losses. It works in conjunction with Prius's brake control system (driving hydraulic friction brakes and optimizing the use of regenerative braking as a fuel saving measure), and SCM controls which actions each wheel should take under what conditions. The module communicates with the drive loop control electronic system to adjust the power delivered. The basic input of SCM includes the wheel speed sensor on each wheel and the brake fluid pressure sensor on each wheel brake hub. Other inputs of SCM are yaw, deceleration rate and steering angle sensors.

To a certain extent, most of us are too enthusiastic about accelerators that compromise the friction of slippery roads. The Prius SCM compares the speed of the front (drive) wheel with the rear (driven) wheel. This allows it to detect the simple reciprocation of the tire under a given force to achieve the goal of uniform speed between the front and rear wheels.

Another task of SCM is to deal with and prevent the tire from locking under emergency braking conditions. At present, the anti-lock brake (ABS) system has actually become the standard for automobiles, and SCM has also included several tasks of ABS into its own jurisdiction. The SCM monitors the speed of the wheels to ensure that each wheel stops at the same rate. When the SCM finds that one wheel (or several wheels) is locked, it sends a command to the brake control system to suspend further braking,

To minimize side slip and maximize braking performance.

Figure 2: The anti-skid control module communicates with the drive loop control electronic system to adjust the power delivered. In the SCM function, overall friction and stability control are its most important tasks. When there may be insufficient steering control force (when the steering action is taken, the car will still "forward") or when the steering control force is too large (the car will turn backward), SCM will play a role. By monitoring the steering wheel angle, relative wheel speed, yaw and possible side g force, SCM can determine whether the situation of front wheel friction loss (steering force is insufficient) or rear wheel friction loss (steering force is too large) is about to occur during steering occur. In addition, the SCM works with the braking system to carefully guide the applied braking force to the wheels.

Like most of the key parts of the electronic system we found in the Prius spin-off, the implementation of this SCM still uses a conservative approach. There is a full cast iron part under the cover, and a PCB with lead seal auxiliary IC and a large number of devices densely covered under the instrument panel. Based on the diagonal split safety control concepts such as front right / rear left and front left / rear right wheels, I guess that the SCM is implemented symmetrically according to the center. With this method of redundancy implementation, even if a partial failure occurs, there is still a front wheel and a rear wheel that can be used in the control loop driven by the SCM.
Since the input signal modulation and the drive output of the brake transmission device are not essentially digital tasks, the analog circuit plays a key role in the realization of the SCM. The SCM's computing center is operated by a Toshiba TMP1984FDFG 32-bit microprocessor and a Mitsubishi M30620 16-bit microprocessor, which is a controller with built-in mask memory. It was 1995. This once again shows that in Prius's design, conservatism is the guiding principle. However, in addition to data processing, Toyota has adopted a customized strategy for its mixed-signal interface circuit. Simply looking at the chip itself, Toyota DA023 and DA034 are analog control or modulation devices. We did not find the common foundry marks on the die, but there is a small Toyota logo under the device label.
Although the number of devices behind the PCB is small, the large control current required for analog devices requires consideration of heat generation. The DA023 and DA034 symmetrically distributed on the left and right sides use a heat dissipation pad connected to the housing on the other side of the SCM board to dissipate the heat generated by the chip and keep the module temperature not too high.
In short, Prius's complex stability control relies on conservative processor selection and carefully crafted analog custom circuits.