The function of the controller is to regulate the speed and direction of motion of the vehicle. This is accomplished by altering the amount and direction of current supplied to the motor. The current is increased by decreasing the resistance in series with the armature, and by passing successively through several arrangements of field strength. Modern controllers are designed to operate with continuous torque, throughout their range. This means that while changing from one speed to another the pulling power of the motor is not interrupted, thus avoiding a jerk with each increase of speed and burning of the controller contacts from breaking the current at each step. Reversing the current is accomplished by reversing the relative position (polarity) of the connecting leads from the battery.
The control may be either manual or actuated by a foot pedal according to the requirements of the manufacturer. Usually the controller is located under the seat in a suitable compartment at the driver’s left (Fig. 143), in a front hood, or under the car floor. In the latter instance, the control is combined with a wheel steering head and is manipulated by the left hand (Fig. 144), so that the right may be used for the more strenuous duty of steering. A form of control which has been recently introduced is known as the remote control type of controller. In this a small handle or dial regulates, according to its position, the motion of a number of plunger electro-magnets, which in turn open and close the connections between the battery, resistance and motor. The advantage claimed is ease and simplicity of operation.
Each type and style of control has its advocates and all are safe, positive in action and reliable. The differences are dictated by the requirements of location and the range of speed to be regulated. The prime consideration in each controller is for the utmost simplicity, both in construction and operation. Great study and much experiment has been expended toward that end, having efficiency of operation and positive action clearly in mind.
Structurally, the simple drum controller (Fig. 144, consists of a cylinder, or section of one, rotated by a handle. The drum is provided with copper segments upon its surface, upon which rest copper contact fingers under slight pressure. To the fingers are attached the leads from the battery, motor and resistance. The segments on the drum connect the fingers electrically in a similar manner to the closing of a switch. When the controller handle is in the "neutral" position no contact is made by the segments and the fingers so that no current flows from one lead to another. This is the normal position of the controller for current "off” and should always be left so when the operator brings the car to a standstill and leaves it. A number of designs of this type of controller are arranged so that when the handle is brought into this position and is to be left there for a time an auxiliary handle or safety switch may be released, discontinuing any connections between the battery and controller, so that an accidental movement of the controller handle may not start the vehicle and cause damage. As the drum is rotated the segments are brought under the fingers making a combination of connections between the battery, resistance, and motor field and armature terminals.
The first position is one designed to give low speed and high starting torque so that the vehicle may be started from rest easily, without jerk, but surely and positively under any condition. Providing that the motor be powerful enough and there be sufficient capacity in the battery, the car will start under practically all conditions. The limiting conditions, however, are when the wheels are either firmly secured in deep mud or sand, etc., or cannot, make use of the tractive effort because of their excessive slipping, as on a sleety pavement. In order to exert the maximum torque, the fields of the motor are arranged in series with each other and with the armature. The motor is then known as a series motor and is capable of exerting a very powerful turning effort. In order to limit the current supplied to the motor so that the starting will not be too violent, a resistance is inserted in series with the motor allowing only a smooth slow start.
When the vehicle has once been put in motion, acceleration may be increased more rapidly. It is accomplished through the successive steps of the controller. The second step or point of the controller maintains the same connections as before, with the exception that the resistance in series with the motor is decreased, and in the third step the resistance is omitted. To further increase the speed, the fields are arranged in parallel with a little resistance placed in series with the armature. The next speed omits the resistance of the preceding. Further increased speed may be gained by further weakening of the field.
It is obvious that, as the speed is increased, more power is used, and that, as the voltage of the battery is practically constant, the current must increase, and, at high speed and in climbing severe hills, it follows that high current will be used. The amount available depends upon the battery capacity. If the battery has a capacity of 150 ampere hours and a current of 100 amperes be drawn continuously, then the vehicle could be operated for approximately one and one-half hours, while if the operation demanded but 20 amperes approximately seven and one-half hours of steady running might be obtained. The greater the current the greater will be the heating of the motor, controller, resistance, etc., and, while each of these is designed to operate under adverse circumstances, they should not be abused where it can be avoided as explained below.
In the explanation just given it was assumed that the cells were connected in series during the speed changes. While this is the case in a number of makes of commercial vehicles, it is not universal, as a parallel arrangement is used with several types of passenger car. The motor combinations remain relatively the same. The method usually employed in paralleling the battery is to divide the battery in half, thus starting with resistance and half the total battery voltage available. The second and third speeds reduce the resistance in the armature circuit, while the fourth speed operates with all the cells in series with resistance. Thus by combining increasing voltage from the battery, decreased external resistance and weakened motor field, a considerable number of steps of speed increase may be efficiently secured. Up to the present time a range of five or six speed steps has been considered sufficient for smooth acceleration, but some manufacturers are now furnishing controllers having as many as ten steps, augmented by a planetary gear shift for slow running in traffic, or more efficient hill climbing.
A form of controller which is flat and has but two contact making segments, is shown in Fig. 134. The leads are brought to the segments of the stationary sector and those from the battery to the movable contact piece. The advantage claimed for this type of controller is the small number of movable parts and the large contact surfaces.
In the operation of trucks of high capacity it is necessary to have a controller which will handle considerable current without overheating and with small wear of parts so that operation may not be interrupted by the frequent need of renewal. Fig. 135 shows a type of controller similar to that made use of in railway practice where severe service is also met. This controller is of the drum type and provided with insulation and auxiliary features which prevent sticking or burning of the contact making members.
A controller which has been introduced into electric automobile service recently is known as the "electro-magnetic type." The principle involved consists in making and breaking the contacts of the controller by means of a secondary electrical circuit. The operator of the car, by means of a small dial or lever placed in a comfortable position, regulates the current in this secondary circuit. The primary circuit is that passing through the motor, battery and controller. A number of plunger electromagnets operated by the small current in the secondary circuit are opened and closed according to the position of the dial. The arrangement effected by the opened and closed position of these magnets determines the direction and magnitude of the current in the motor circuit in a similar manner to that negotiated by the segments and fingers of the drum controller. By means of this dial, therefore, all the speed combinations required may be effected, and the advocates of this type claim simplicity of operation and flexibility as its features inasmuch as the dial is very easily moved and the magnets or controller proper may be located in any suitable part of the vehicle. The essential difference distinguishing this controller from those heretofore mentioned is that it is electrically and not mechanically operated. A handle or lever does not operate it positively so that its location does not depend upon any arrangement of links, gears or chains.
Figure 147 shows a developed diagram of connections effected by the controller in the successive positions or speed points. These points are accomplished by the attaching of a star-wheel to the axis of the control drum which registers with a pawl having a roller end. Thus, as the drum is rotated, the spring of the pawl forces the end of the latter to roll into the slots of the star-wheel with a sudden movement which can readily be felt by the hand of the operator and usually (distinguished by a clicking sound. In this manner, as the controller is passed from speed to speed, the steps or notches are separate and distinct.
When an auxiliary or safety switch is combined with the controller, it is designed to be placed in the "off" position when the vehicle is brought to rest, and allowed to stand unattended. By this means accidental throwing of the controller into a running position is avoided and when combined with a Yale lock, prevents unauthorized use of the vehicle. In some instances three-point switches are provided, one position for "running," the second for “off” and the other for charging. Practically every make of car has distinctive features in connection with its control and safety devices, but the principles are identical in each case. The differences are in the details designed toward simplicity in the operation of the particular vehicle in question.
In some control methods, the designers have seen fit to utilize the impetus for retarding the motion of the car by adding a notch to the controller which short circuits the armature through resistance, the motor fields being excited from the battery. The motor is then acting as a generator, absorbing the energy of the moving vehicle transmitted through the gears to the motor shaft for the generation of electricity. This action gradually retards the motion and is, therefore, known as an “Electric Brake.” When a controller of the side lever type (Fig. 145) is thus equipped, the handle of the controller is pressed forward for the forward speeds, and back past the neutral or "off" position for electric braking. Pressing the handle further back beyond the electric brake notch, usually tightens a small band brake operating upon a pulley on an extension of the motor shaft. This method of braking is very powerful and is convenient for those who find the operation of brake pedals difficult.
The remarks in the preceding paragraphs on the subject of controllers have been confined to the control of single motor drives. The same principles are applied, however, to the operation of two or four motor equipments, with slight changes in the wiring.
Owing to the simplicity and the ease with which variations of speed and maneuvering may be accomplished, the electric drive has reached high favor in a great number of heavy duty vehicle applications. Among these may be mentioned tractors for heavy materials such as lumber, coal, machinery, building materials, etc., as well as coaches and omnibuses.
Care. The arcing at the points of a knife switch when slowly opened is no doubt familiar to most readers, and the appearance of the scarred metal is evidence that the switch was carelessly opened. This action takes place to a certain extent in the controller if the drum is held between the notches. The fingers are held onto the segments of the drum by a moderate pressure and are faced to make good contact. Should the contact be poor, however, touching at only a few points, or the finger slowly drawn from the segment, then there will be an arc between them causing a blistered surface. This can easily be avoided by having the contact surfaces well faced with proper pressure and the spring of the pawl tightened sufficiently to cause the drum to stop exactly in the notch. When working on the controller it is well to disconnect the battery leads so as to avoid burns or short circuits.
Lubrication should be frequent, regular and moderate. About once a week when in daily service, inspection should be made and the fingers adjusted to an even, moderate tension. They should be run parallel with the drum and faced with sandpaper so as to make good contact. Badly burned fingers should be replaced and fitted into position. The drum segments should be kept bright and clean and lubricated by being wiped with a linen rag and a small amount of vaseline. If they are blistered or pitted, they should be smoothed down with sandpaper. When it is necessary to face fingers to the drum, the sandpapering should be done upon the fingers rather than the drum segments as the latter are not as easily replaced as the fingers.