By wire control of braking and acceleration
View Patent ↗A rider surface maintenance vehicle with variable dynamic braking, in contrast to a mechanically-engaged braking system that uses a brake cable. A brake pedal engages a sensor that encodes the pedal position as an electronic signal. The electronic signal, along with the vehicle velocity, determines a machine deceleration rate, or braking rate, either by calculation, lookup table, or a combination of the two. The braking rate may be tuned so that the of the brake mimics or approximates the feel of a conventional mechanically-engaged brake that uses a brake cable. During stopping, once the vehicle passes below a threshold velocity, a parking brake is automatically engaged. The braking rate is converted to a duty cycle, and the braking is preferably accomplished by pulse width modulation (PWM) of an electrical load applied in parallel to the motor.
1. A method of providing an electrical braking function through an electrical motor in a surface maintenance vehicle to approximate the feel of a mechanical braking system, comprising the steps of:
a. engaging a brake pedal to initiate braking function;
b. sensing the position of the brake pedal and encoding the pedal position as an electronic signal;
c. sensing the vehicle velocity;
d. using said vehicle velocity and said signal, determining a desired machine deceleration rate to approximate the sensation of mechanical braking;
e. determining the desired conductance applied in parallel to the motor to create a dynamic braking force from the motor;
f. generating a series of pulses of frequency at least as great as the response frequency of the motor and creating an effective conductance;
g: applying the effective conductance in parallel with the motor to cause machine deceleration by dynamic braking, and
h. re-adjusting the conductance in response to deceleration to proximate the feel of mechanical braking, whereby the vehicle is decelerated.
2. A method of providing an electrical braking function through an electrical motor in a surface maintenance vehicle to proximate the feel of a mechanical braking system, comprising the steps of:
a. engaging a brake pedal to initiate braking function;
b. sensing the position of the brake pedal and encoding the pedal position as an electronic signal;
c. sensing the vehicle velocity;
d. using said vehicle velocity and said signal, determining a desired machine deceleration rate to approximate the sensation of mechanical braking;
e. generating a series of pulses of frequency greater than the response frequency of the motor;
f. within each pulse defining the desired duty cycle to create an effective conductance;
g. applying the effective conductance in parallel with the motor to cause machine deceleration by dynamic braking; and
h. iteratively checking vehicle velocity and brake pedal position and correspondingly altering duty cycle to respond to demand for greater or lesser braking.
3. The method of claim 2 , wherein the determining step is performed by calculation.
4. The method of claim 2 , wherein the determining step is performed by lookup table.
5. The method of claim 2 , wherein the determining step is performed by a combination of calculation and lookup table.
6. The method of claim 2 , wherein the amplitude of each pulse is essentially constant and does not vary with duty cycle.
7. The method of claim 6 , wherein if the sensed vehicle velocity is below a predetermined threshold velocity, then a parking brake is engaged.
8. The method of claim 7 , wherein the parking brake is a solenoid-driven spring-loaded caliper brake pad.
9. An electrically powered surface maintenance machine with dynamic braking capable of proximating mechanical braking response, comprising:
a. an electric motor;
b. a brake pedal having a position sensor;
c. an encoder for converting the pedal position to an electrical pedal position signal;
d. a machine velocity sensor;
e. a braking rate controller capable of determining braking force tuned to approximate mechanical braking, in response to the electrical pedal position signal and the machine velocity;
f. a converter to translate braking rate to an effective electrical load to be applied in parallel to the motor;
g. an updater for iteratively checking the machine velocity and the pedal position and repeatedly adjusting the braking rate and thereby adjusting the effective electrical load applied in parallel to the motor; and
wherein the effective electrical load is determined by a series of pulses of frequency greater than the response frequency of the motor.
10. The machine of claim 9 , wherein the effective electrical load is determined by the duty cycles of the pulses.
11. The machine of claim 10 , wherein the amplitude of the pulses is essentially constant and independent of the duty cycle.
12. The machine of claim 9 , wherein if the sensed machine velocity is below a predetermined threshold velocity, then a parking brake is engaged.
13. The machine of claim 12 , wherein the parking brake is a solenoid-driven spring-loaded caliper brake pad.