Radial piston pump

An electric motor driven radial piston pump for a motor vehicle brake system with slip control is disclosed wherein the radial piston pump includes two parallel working circuits drivable by the drive motor. The working pressure of the first working circuit is limited to a preset value. Above the preset value only the second working circuit is effective.

BACKGROUND OF THE INVENTION 
The present invention relates to an electric motor driven radial piston 
pump for use in a motor vehicle with brake slip control. 
A radial piston pump of this kind is disclosed in the German patent 
specification DE-OS No. 32 19 513. If such a pump is to be used in a motor 
vehicle brake system having slip control, a relatively high delivery rate 
of the pump is required in the low braking pressure range. This 
requirement leads to high power consumption of the electric drive motor, 
whereas higher pressures require lower delivery rates. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide for a radial piston pump 
which provides for lower power consumption. 
This object is achieved according to the present invention wherein a radial 
piston pump is provided with two parallel working circuits drivable by the 
same drive motor and wherein the working pressure of the first working 
circuit is limited to a preset value. 
According to the invention, the two working circuits jointly assure the 
high delivery rate required in the low pressure range. When the preset 
working pressure of the first working circuit is exceeded, the second 
working circuit alone provides the entire delivery rate. Advantageously, 
since the effective delivery rate of the first working circuit is zero 
above the preset working pressure, the power consumption due to the first 
working circuit decreases so that the total power consumption increases at 
a lower rate as the pressure increases. 
According to an important feature of the invention, a throttle channel is 
arranged between the pressure side and the suction side of the first 
working circuit. 
According to an important feature of the invention, a throttle channel is 
arranged between the pressure side and the suction side of the first 
working circuit. 
According to another important feature, a check valve is arranged between 
the pressure side of the first working circuit of the throttle channel and 
the connecting point on the pressure side of the two working circuits. 
Advantageously, the throttle channel provides means for gradually reducing 
the output pressure of the first working circuit towards the suction side 
as the output pressure increases. Initially, only part of the pressure 
fluid flows back to the suction side through the throttle channel when the 
pressure is low, whereas as the pressure increases the entire pressure 
fluid finally flows back from the pressure side of the first working 
circuit is its suction side. Accordingly, the first working circuit no 
longer contributes to the effective total delivery rate. In order to 
assure that, from the moment the preset limit value of the first working 
circuit is reached, the pressure fluid does not flow back the output side 
of the second working circuit through channel of the first working circuit 
to the latter's suction side, the check valve shuts off the connection 
from the first working circuit to the second working circuit. 
According to an important feature of the invention, the throttle channel is 
a clearance space of a preset width between a piston and cylinder wall of 
the first working circuit. 
A still further important feature of the invention provides for the check 
valve to be arranged in a channel in a control journal on which the pump 
motor is rotatably mounted. The two working circuits are connected 
together dependant on the angle of rotation of the rotor which is common 
to both working circuits. 
According to another embodiment, a valve is arranged on the suction side of 
the first working circuit which is switchable from its open position to 
its closed position at a preset output pressure of both working circuits. 
When the valve closes upon reaching the preset output pressure of the 
first working circuit, the second working circuit cannot take in any more 
working fluid. Thus, the delivery rate of the first working circuit is 
completely interrupted and the power consumption of the drive motor is 
further reduced. 
According to the invention, the pressure-controlled valve is a check valve 
on which the suction pressure of the first working circuit operates in its 
opening direction. Below the preset output pressure, the check valve is 
opened automatically by the suction pressure of the first working circuit. 
Advantageously, each piston of the first working circuit is in the shape of 
a ball and the second working circuit includes at least one cylinder 
having one ball-shaped piston and one cylindrical piston. A ball-shaped 
piston has the advantage that, if the throttle channel is designed as a 
clearance between the piston and cylinder, the flow through the throttle 
channel is largely independent of the viscosity of the liquid used as the 
working fluid. The combination of ball and cylindrical piston in the 
second working circuit on the other hand assures fluid tightness between 
the piston and cylinder and thus allows high working pressures to build up 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Shown in FIGS. 1 and 3 is a radial piston pump according to the invention, 
including a first working circuit 1 and a second working circuit 2. Both 
working circuits 1 and 2 have a common stator including cam rings 3 and 4 
and a common rotor 5 which is driven by an electric motor 6 as shown in 
FIG. 3. The rotor is rotatably mounted on a control journal 7 which is 
common to both working circuits. The cam rings 3, 4 are disposed 
eccentrically relative to the control journal 7 and to the rotor 5. In 
each working circuit 1 and 2 the rotor 5 is provided with two 
diametrically opposed cylinders 8, 9 and 10, 11, respectively. Each 
cylinder pair is formed as two continuous aligned radial bores. The 
cylinder pair 8, 9 is orientated from the pair 10, 11 by 90 degrees. Each 
cylinder 8, 9, 10, 11 accommodates a piston 12, 13, 14, 15 shaped as a 
ball. The cylinders 10 and 11 each include an additional cylindrical 
piston 16 and 17 which are shaped as a sleeve having a conical seat for 
receiving the ball-shaped pistons 14 and 15. 
The cylinders 8 and 9 and the ball-shaped pistons 12 and 13 have a large 
diameter than the cylinders 10 and 11 and the corresponding pistons 14, 
15, 16 and 17. 
Between the ball-shaped pistons 12 and 13 and the inside wall of their 
cylinders 8 and 9, there is a clearance space of preset width which forms 
a throttle channel connecting the pressure of the working circuit with the 
suction side of the working circuit 1. The pistons 14, 15, 16 and 17, on 
the other hand, are largely fluid-tight and slidingly mounted in the 
cylinders 10, 11. 
The control journal 7 is provided with two channels 18 and 19 in the form 
of parallel bores. One portion of the channel 18 associated with the 
working circuit 1 is disposed on the pressure side of the working circuit 
1 and is connected by a check valve 20 with a portion of the channel 18 
associated with the pressure side of the working circuit 2 and is also 
connected with an outlet port 21. The channel 19,. however, is in constant 
communication with an inlet port 22 disposed on the suction side, which 
inlet port 22 in turn communicates with a reservoir 23 for a brake 
pressure fluid. 
The check valve 20 shuts off in the direction of the pressure side of the 
working circuit 1. 
As FIG. 3 shows in more detail, the cam rings 3 and 4 are mounted in a 
stator ring 24 which is mounted in a stator housing 25. The electric drive 
motor is flanged coaxially to the rotor 5. The shaft 26 of the drive motor 
6 is connected with the rotor 5 by means of a coupling 27 and is sealed at 
the housing 29 of the drive motor 6 by means of a packing 28 in the form 
of a radial packing ring. The inlet port 22 communicates by way of 
ring-shaped filter 30 with an inlet chamber 31, which in turn communicates 
by way of an opening 32 in a retaining ring 33 and the clearances between 
the rotor 5 and the cam rings 3, 4 and an adjoining longitudinal bore 34 
and radial bores 35 and 36 in the control journal 7 with an axial channel 
19 of the control journal 7. 
The channels 18 and 19 are also alternately connectable with the cylinders 
8, 9, 10 and 11 by way of radial bores by rotation of the rotor 5. The 
channel 18 includes the check valve 20 and communicates through radial 
channels 37 and 38 with the bearing surfaces between the rotor 5 and the 
control journal 7 for the purpose of lubricating the connection. The 
channel 18 is connected through a radial bore 39 with the outlet port 21. 
During operation of the two-circuit pump according to FIGS. 1 and 3, the 
delivery rates Q.sub.1 and Q.sub.2 of the two working circuits 1 and 2, as 
shown in FIG. 2, decrease linearly as the output pressure P or the load of 
the pump increases, the delivery rate Q.sub.1 of the working circuit 1 is 
initially higher than the delivery rate Q.sub.2 of the working circuit 2. 
The delivery rate Q.sub.1 of the working circuit 1, however, decreases 
faster than the delivery rate Q.sub.2 of the working circuit 2, because 
the working circuit 1 conveys the pressure fluid through the throttle 
channel, as defined by the piston to cylinder wall clearance space, back 
to the suction side. The total delivery rate Q.sub.1 +Q.sub.2 of both 
working circuits 1 and 2 therefore also decreases according to the dotted 
line in FIG. 2. Upon reaching a preset value P.sub.g, the working circuit 
1 conveys the entire pressure fluid back through the throttle channel. The 
delivery rate Q.sub.1 above the value P.sub.g therefore is zero, while the 
total delivery rate Q.sub.1 +Q.sub.2 equals the delivery rate Q.sub.2 due 
solely to the working circuit 2. At this point in the operation the check 
valve 20 is closed so that the working circuit 2 cannot convey any 
pressure fluid through the working circuit 1 to the suction side. Up to 
the pressure limit value P.sub.g, at which the delivery rate Q.sub.1 of 
the working circuit 1 reaches zero, the operating current J of the drive 
motor 6 increases at constant speed as the pressure P increases. Upon 
exceeding the pressure limit value P.sub.g, however, the increase of the 
operating current J is lower, as is shown by the dashed line in FIG. 2. 
The lower rate of increase of the operating current J is a result of the 
decreasing speed of the drive motor 6 as the load of the working circuit 2 
increases due to the cessation of delivery by the working circuit 1. 
Thus, the two-circuit pump described has a relatively high delivery rate 
Q.sub.1 +Q.sub.2 in the low pressure range, and a relatively low delivery 
rate in the high pressure range, as is particularly desirable in brake 
systems with slip control (antiskid brake systems). 
The embodiment shown in FIG. 4 differs from the embodiment illustrated in 
FIGS. 1 and 3 only in that on the suction side of the first working 
circuit a valve 40, such as a check valve, which is switchable in 
dependance on the output pressure of both working circuits is arranged 
between the inlet port 22 and the inlet channel 19. The check valve 40 
shuts off in the direction of the reservoir 23 upon reaching a preset 
output pressure lower than the value P.sub.g according to FIG. 2, so that 
the working circuit 1 cannot take in brake fluid from the reservoir 23 and 
the delivery rate of the working circuit 1, independent of any tolerances 
of the throttle channel, is completely interrupted at a precisely defined 
value of the output pressure.