EV.4.7 APPS / Break Pedal Plausibility Check

EV.4.7 APPS / Brake Pedal Plausibility Check

EV.4.7.1 Must monitor for the two conditions:

The mechanical brakes are engaged EV.4.6, T.3.2.4
The APPS signals more than 25% Pedal Travel EV.4.5

This rule requires that programmable logic be used to verify that the driver is not pressing the brakes and accelerator synchronously. In an emergency situation where the driver loses control, they might simultaneously step on the accelerator and brake pedals by instinct. At this time, the brake system cannot slow the car down immediately. So according to the rules, if the accelerator pedal travel is more than 25%, and at the same time the brake pedal is hardly pressed, those situations must be detected.

Additionally, EV.4.6 offers guidance for the brake system encoder, and T.3.2.4 stipulates further rules about the mechanical brakes with regard to the Electric Vehicle class. This rule states that while a majority (90%) of the brake travel can be used for regenerative braking without directly activating the hydraulics, the last area of exertion (10%) must directly activate the hydraulics so that an emergency braking signal is not interrupted.

Rules Reference - T.3.2.4

T.3.2 Brake Pedal, Pedal Box and Mounting

T.3.2.4 (EV only) Additional requirements for Electric Vehicles:

a. The first 90% of the Brake Pedal travel may be used to regenerate energy without actuating the hydraulic brake system.

b. The remaining Brake Pedal travel must directly actuate the hydraulic brake system. Brake energy regeneration may stay active.

Rules Reference - EV.4.5

EV.4.5 Accelerator Pedal Position Sensor - APPS

Refer to T.4.2 for specific requirements of the APPS

Rules Reference - EV.4.6

EV.4.6 Brake System Encoder - BSE

Refer to T.4.3 for specific requirements of the BSE

EV.4.7.2 If the two conditions in EV.4.7.1 occur at the same time:

a. Power to the Motor(s) must be immediately and completely shut down

b. The Motor shut down must stay active until the APPS signals less than 5% Pedal Travel, with or without brake operation

The team must be able to demonstrate these actions at Technical Inspection

Given that both conditions above are true, the power to the motor(s) must be cut off instantly and entirely (note that this does not require implementation within the shutdown circuit). Furthermore, the power to the motor(s) must remain shut down until the accelerator pedal travel is a minimal 5%, whether the brakes are still engaged or not. Often, the implementation of these programmable rules utilizes CAN Bus Serial Communication.

But what is CAN?

The Controller Area Network (CAN Bus) is essentially a nervous system, enabling communication between interconnected 'nodes' or 'electronic control units' (ECU's). Information sensed by one part can be shared with another. The CAN Bus system enables each ECU's to communicate without complex dedicated wiring.

Specifically, an ECU can prepare and broadcast information (e.g. sensor data) via the CAN Bus (consisting of two wires, CAN low and CAN high). The broadcasted data is accepted by all other ECU's on the CAN network - and each ECU can then check the data and decide whether to receive or ignore it.

Graphic - CAN Bus Broadcast

Article - CAN for APPS/BPPC

wevj-12-00001.pdf

In the case of the APPS/Brake Pedal Plausibility Check (BPPC), there needs to be a signal detection node which compounds the Brake and APPS input. A model of this is shown below, implemented by students at the Mechanical and Automotive Engineering, Xiamen University of Technology.

In order to establish a combined control model of acceleration and brake pedals that meets the special requirements of the rules and design, while keeping the mechanical structure unchanged, this paper takes the accelerator and brake pedal of the Xiamen University of Technology electric racing car as a research object and proposes a simple and reliable control strategy. According to the rules of the competition, the voltage signals of the accelerator pedal position sensor (APPS) and brake pedal sensor (BPS) are detected and processed accordingly, and the acceleration and brake pedals are prevented from being depressed at the same time. The control model that meets the requirements is established in Matlab/Simulink and verified by experimental test.

Diagram - Top Level Structure

The electric accelerator pedal consists of mechanical structure, two independent displacement sensors and relevant circuits. Its essence it converts the driver’s torque request to corresponding voltage signals and transfers them to the vehicle control unit (VCU). As shown above, voltage signals are sent to the motor control unit (MCU) by controller area network (CAN) bus after processing in the VCU and the MCU controls the torque output of the motor.

Diagram - Global Control Model

The signals of the acceleration and brake pedals, first enter the filter model. The APPS limits and consistencies are then output from the filter model to the amplitude limit check and consistency check models. APPS and Brake are respectively the accelerator and brake pedal opening position. Signal APPS and Brake are output to the APPS/Brake plausibility check model. After their detection, all three outputs are sent to the arbitration model. The APPS output then flips from 0 to 1. Then the actual opening of the accelerator pedal will be converted into a torque demand value and sent to the motor controller by the CAN bus.

Spreadsheet - EV Technical Inspection (Active)

Furthermore, this process must be demonstrated in full at the Technical Inspection. With the procedure shown to the left, teams must press the brake pedal while requesting at least a quarter of acceleration pedal travel and see the axle stop. It must remain stopped even as brakes are disengaged, and only turn again once the driver returns the accelerator pedal to a minimal (5%) travel.

Note that this test is completely separate from the Brake System Plausibility Device (BSPD) inspection.

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