Discuss the development history and trends of chassis

The "Smart Chassis" series of articles focuses on the current development trend of chassis intelligence and introduces mainstream chassis products.

As an introduction, this article will explore the development history of the chassis and detail the development trends of the intelligent chassis.

1

The development of the chassis

Since the birth of automobiles more than 100 years ago, the development of chassis has been deeply tied to the development of automobiles. The chassis system determines the dynamic behavior of the six degrees of freedom of the automobile in the longitudinal, lateral and vertical directions, and is a necessary condition for the operation of the automobile. According to the broad definition, the chassis system has many components, including the body, throttle, clutch and other components in addition to the drive, steering and braking systems; but if we only look at the six degrees of freedom control, the chassis system can be refined into the following four subsystems.

Looking at the development history of chassis systems, it can be summarized into three periods:

Mechanical Age

Electromechanical hybrid era

Smart Era

Mechanical period of chassis

In the early days, the vehicle mass was relatively small and the speed was relatively low, so the mechanical chassis could meet the driver's control needs. The driver directly controlled the six-component force of the tire by operating the steering wheel and pedals, thereby indirectly changing the vehicle's three-way translation and three-way rotation degrees of freedom.

With the development of science and technology and the development of the automobile industry, especially the development of military vehicles and military technology, the chassis system has also made new breakthroughs. For example, the introduction of hydraulic steering and hydraulic braking is a major technological innovation for the chassis in the mechanical era. At the same time, as vehicles become heavier, boosters have begun to be widely used in chassis control to provide steering or braking assistance to the driver.

Typical products in this stage include mechanical hydraulic power steering systems and vacuum boosters. The mechanical hydraulic power steering system uses the power of the engine to drive the oil pump to provide hydraulic assistance to the mechanical steering, making it easier to operate the steering wheel. However, since the engine power is used as the oil pump power, the engine power used for driving will be partially lost.

Mechanical hydraulic power steering system, picture from the Internet

The working principle of the brake booster vacuum booster is:

When the driver steps on the brake pedal, the pedal force is amplified by the first stage due to the lever action and transmitted to the vacuum booster; the vacuum booster transmits the braking force to the master cylinder after the second stage amplification; the brake fluid in the master cylinder is pushed into the wheel cylinder and generates a greater braking force under the action of pressure, pushing the wheel-end caliper to tighten the brake disc, thereby achieving braking.

Working principle of vacuum booster, picture from the Internet

The key to the normal operation of the vacuum booster is a stable vacuum source. Vehicles equipped with gasoline engines can generate a higher vacuum pressure in the intake manifold because the engine uses a spark ignition type, which can provide a sufficient vacuum source for the vacuum booster brake system. For vehicles driven by diesel engines, since the engine uses a compression ignition CI (Compression Ignition cycle), the same level of vacuum pressure cannot be provided at the intake manifold, so a vacuum pump that provides a vacuum source needs to be installed.

Although the introduction of hydraulic systems provided assistance to the driver, in essence, the control of vehicle motion during the chassis mechanical era depended entirely on the driver's input.

The era of electromechanical hybrid chassis

In the era of electromechanical hybrid, the traditional mechanical hydraulic design is combined with single-chip microcomputer control, which not only further reduces the driver's driving burden, but also assists the driver to better control the vehicle through software control. The vehicle's fuel economy, safety and comfort are greatly improved.

During this period, one of the most well-known revolutionary products is the Anti-lock Brake System (ABS). For passenger cars, emergency braking is sometimes used to avoid danger during daily driving, but the brake caliper exerts too much force on the brake disc during emergency braking, which can cause the wheels to lock. Improper vehicle performance caused by wheel locking (such as failure to stop within a safe distance during emergency braking or vehicle tailspin during emergency braking) often leads to serious traffic accidents.

As early as the 1930s, automotive engineers began to study the anti-lock braking system ABS (Anti-lock Brake System, ABS) to solve the problem of wheel locking during emergency braking. ABS is a closed-loop control device in the braking system that can prevent wheel locking during braking and ensure the braking performance and stability of the vehicle.

ABS working principle, picture from the Internet

In the late 1970s, due to the development of digital electronic computer technology and the progress of hydraulic control technology, German Bosch launched ABS based on hydraulic control, which had a very ideal control effect. Therefore, Bosch officially mass-produced ABS products in 1978. The advent of Bosch ABS officially kicked off the development of chassis electronic stability systems. Since then, many companies such as Bosch, ITT Automotive, Kelesy-Hayes, and Wabco have continuously strengthened their research on ABS. Various new ABS have emerged one after another, with performance being continuously optimized and prices gradually reduced. Today, ABS has become a standard feature of cars and commercial vehicles.

Bosch ABS explosion, picture from the Internet

Smart chassis era

Under today's wave of automobile electrification and intelligence, traditional power has been upgraded to a three-electric system, traditional mechanical components on the chassis system have been streamlined, and the degree of electronic control has become increasingly higher; at the same time, with the increasing popularity of assisted driving systems (such as ACC, AEB, etc.) and the gradual implementation of autonomous driving systems, new demands for more and more intelligent scenarios have emerged.

On the other hand, the consumer market's positioning of cars is also changing. End consumers no longer view cars as just a means of transportation, but have turned them into a carrier and space for improving the quality of life. This consumption trend means that while the industry is pursuing car intelligence, it also needs to further improve the comfort and driving quality of cars to provide consumers with a more pleasant car experience.

Driven by this trend, automobiles have also put forward higher requirements for chassis systems. Only a more intelligent chassis can adapt to the development needs of automobile electrification and intelligence.

The new requirements for smart chassis can be summarized into four categories:

Personalized: Provide personalized customization according to customers' driving habits

High performance: The system responds more accurately and quickly

Growable: The system has self-learning capabilities and supports OTA upgrades

High security: multiple security guarantees for product safety and information security

According to the definition of Professor Zhang Junzhi of Tsinghua University, the intelligent chassis still retains the two major functions of the chassis:

Loading

Driving

But the objects carried and the means of completing the journey have changed.

First, the intelligent chassis provides a platform for the autonomous driving system, cockpit system, and power system, which is a change in the object of the load. Secondly, in terms of the realization of driving tasks, we have sorted out the new capabilities of the intelligent chassis from the relationship between people, vehicles, and roads. In the relationship between the car and the road, the intelligent chassis has the ability to recognize, predict, and control the interaction between the wheels and the ground. In the relationship between the car and the person, after the car becomes unmanned, the original perception and adaptive manipulation of the abnormal state of the chassis by the person disappears, and the intelligent chassis should have the ability to manage its own operating status. These are several new capabilities of the chassis, all of which serve the driving task, so in the end the intelligent chassis is still a system that specifically realizes the intelligent driving task of the vehicle.

Professor Zhang Junzhi of Tsinghua University defines intelligent chassis. Image from the Internet

2

The development trend of intelligent chassis

Although the chassis system is still in the electromechanical hybrid stage judging from the current market share, a trend towards an intelligent chassis can already be seen.

Trend 1: Wire control

First, the popularity and evolution of wire control technology in automobiles. Wire control technology originated from aircraft control systems. It converts the pilot's control commands into electrical signals and transmits them directly to the autonomous servo through cables. The biggest advantage of wire control technology is its precise and rapid response, which is inherited by automobile wire control technology.

At present, all chassis control subsystems have achieved wire control, but chassis wire control technology is more reflected in the control decision-making level, and the driver input level still relies on the driver's direct input (steering or pedaling). With the evolution of autonomous driving, the role of the driver has been weakened, the role of the steering wheel and pedals has gradually weakened, and the wire-controlled chassis has a trend towards true wire control. The most obvious case that confirms the trend is the implementation of regulations for wire-controlled steering products. As early as a few years ago, car companies launched wire-controlled steering products, but they were unable to mass-produce due to regulations. Now regulations are gradually no longer an obstacle. Take China as an example. GB 17675-2021 "Basic Requirements for Automobile Steering Systems" deleted the requirement that full power steering mechanisms must not be installed (3.3 in 1999), that is, the domestic regulatory level has allowed the physical decoupling between the steering wheel and the steering gear of the steering system. The hot sales of Cybertruck in many countries also mean that the relevant regulations in other countries are also in the same trend.