214 & 224 WHEEL-TYPE EXCAVATORS Regulator For Motor (BMR Series) Caterpillar


Regulator For Motor (BMR Series)
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1.1. General
2.1. Function of the Regulator

Fig. WH 143


(Typical Example)

The hydraulic motor is an axial piston motor with a pressure controlled, infinitely variable angle of pivot in the range between the minimum intake volume (limitation by means of adjusting screw, depending on vehicle type and technical data) and the maximum intake volume in cm3/revolution.

In conjunction with the total-capacity-controlled double pump, the regulator for the motor guarantees a particularly smooth startup, e.g. when used as a running gear motor. Moreover, in the individual transmission stages during travel, top speeds can be achieved with only one pump delivery, whereas if fixed displacement motors were used, either one or a second pump delivery would be required.

The motor is equipped with a pressure-controlled switching device, which automatically alters the intake volume towards maximum:

214 - BMR 105 - minimum 48 cm3/rev., max. 105 cm3/rev - 260 bar (26 000 kPa) 224 - BMR 140 - minimum 55 cm3/rev., max. 140 cm3/rev. - 260 bar (26 000 kPa)

General

The oil quantity supplied determines, as a function of the actual intake volume, the output speed and the alternate pressurization of connections A and B determines the direction of rotation.

The output torque arises from the force (resulting from pressure and piston area) applied at the drive shaft and is dependent on the actual angle of pivot.

Function of the Regulator

Shuttle valve (1) is joined to main connections A and B, and screens are built into the shuttle valve feed line, the function of which is to protect the entire regulation unit from dirt particles.

Shuttle valve (1) joins the connection which has the greater pressure with the regulators (2) and channel (3), which in turn is connected to the small area of the regulating piston (4). In the example shown, the high pressure is at connection B. The large area of the regulating piston (4) is connected to the unpressurized motor casing via a channel (5) and annular channel (6), whereupon the piston moves to that end position, which corresponds to the minimum working volume of the regulating motor and stays there.

The spring (7) determines the response pressure of the regulator. If this is exceeded, the valve element (8) lifts. The small valve piston (9) stays in position as reaction element, supported by means of its mushroom-shaped base on the compressed bottom of the casing of the valve (2). During upward motion, the control edges of the valve element (8) close the connection between channel (5) and annular channel (6) and open the connection between annular channel (10) and channel (5). This allows pressure to reach the large area of the regulating piston (4), moving the piston towards Vmax. Adaptation to the required torque is stepless and the motor comes to a perfect standstill in any position between Vmin and Vmax.

The pressue interval, in which the motor regulates from Vmin to Vmax, is 10 to 15 bar (1000 to 1500 kPa).

The purge valve combination can be seen at the bottom of the drawing. Discharge valve (11) opens the connection with the lower pressure (in this case A) so that oil can flow out of this channel. The amount of oil flowing out is limited to a specific quantity (approximately 8 l/min), regardless of the pressure from the low pressure side, in the 2-way flow-regulating valve (12).

Valve (12) opens at approximately 5 bar (500 kPa).