GB1564635A

GB1564635A - Power unit

Info

Publication number: GB1564635A
Application number: GB46232/76A
Authority: GB
Original assignee: Renault SAS; Regie Nationale des Usines Renault
Current assignee: Renault SAS; Regie Nationale des Usines Renault
Priority date: 1975-11-07
Filing date: 1976-11-05
Publication date: 1980-04-10
Also published as: DE2650752A1; FR2330879A1; FR2330879B1

Description

(54) A POWER UNIT (71) We, REGIE NATIONALE DES USINES RENAULT, A French Body Corporate, of 8/10 Avenue Emile Zola. Boulogne-Billancourt. Hauts de Seine, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a power unit comprising at least two hydraulic motors and a pressure accumulator.

Hybrid vehicles provided with a hydraulic motor and an oloepneumatic accumulator are already known (Product Engineering, October 1973: transport conference in DENVER, September 1973). In this type of vehicle, energy is stored in the oleopneumatic accumulator in the form of fluid pressurised by a pump which is driven by a heat engine. The energy stored increases when the delivery of the pump exceeds the power output requirements of the unit. Conversely, the energy stored decreases when the delivery of the pump is less than the power output of the unit. It is possible to recover energy normally dissipated during braking of the vehicle by using the momentum of the vehicle to pump fluid into the accumulator.

With hybrid vehicles of this type there are difficulties in regulating the heat engine and in regulating the volumetric displacements of the pump and the motor. These difficulties are significant because the safety of the braking and quality of the acceleration of the hybrid vehicle depend on these features being regulated accurately.

Imperfect regulation makes it difficult to obtain satisfactory starting from a standstill and stable low speed running of the vehicle. In practice, the hydraulic motor must have a maximum power output substantially equal to the maximum braking power of the vehicle which itself is at least equal to four times the driving power provided in a traditional vehicle.

Even the minimum volumetric displacement of the hydraulic motor necessarily corresponds to a relatively high output torque which makes smooth starting from a standstill difficult.

According to the present invention there is provided a power unit comprising at leat two variable displacement hydraulic motors and a pressure accumulator for supplying fluid under pressure for driving the motors, one of the motors having a maximum displacement which is at least double that of the other motor, or one of the other motors, the output shafts of the motors being interconnected via a releasable coupling to drive a common shaft, the unit further comprising a control arrangement, connected to receive signals correspondin to the pressure in the accumulator and to the output torque required of the unit and adapted to control, in response to the said signals, the displacement of the motors and the operative condition of the coupling.

For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Figure I illustrates schematically a vehicle power unit; Figure 2 illustrates schematically a first part of a logic circuit for controlling the unit of Figure 1; Figure 3 illustrates schematically a second part of the logic circuit; Figure 4 illustrates schematically a third part of the logic circuit; and Figure 5 illustrates schematically a fourth part of the logic circuit.

As shown in Figure 1, an oleopneumatic accumulator 1 is connected to a first variable displacement hydraulic motor 3 and to a second variabe displacement hydraulic motor 4 whose maximum volumetric displacement is at least double, but preferably three to five times, that of the first. Output shafts 67 and 68 of these motors can be rotationally interconnected by gearing 69 and a coupling 2.

When the coupling 2 is engaged, a linear combination of the torques developed by the motors 3 and 4 is applied to a shaft 70 which drives a crown and pinion 71 forming part of a differential 72 and hence drives shafts 73 and 74 carrying driving wheels 75 and 76.

The operator of the vehicle controls the torque by a suitable control member, for example the acceleration pedal 8 of the vehicle, to which is connected a position sensor 9 applying to a logic circuit 90 a voltage ug proportional to the output torque desired by the operator. The logic circuit 90 is also connected to a sensor 5 which applies to it a voltage proportional to the pressure Pa in the accumulator 1.

The logic circuit 90 is connected via outputs to electrovalves 21, 31 and 41. The valves 31 and 41 are of the "pressure" type, i.e. they supply respectively pressures P3 and P4 which are proportional to the voltages U3 and U4 applied to them. The pressures act on the pistons of two actuators 32 and 42 which control the volumetric displacements of the hydraulic motors 3 and 4, respectively. These pistons are also subjected to the forces of two constant-force return springs. The mechanical connections between the rods of the pistons and the internal control members for the volumetric displacements of the motors 3 and 4 are such as to ensure the proportionality between the stroke of the respective piston and the volumetric displacement C3 or C4 of the motor concerned. For the motor 3: C3 = C30 + yu3 C30 is negative and corresponds to the maximum negative volumetric displacement of the motor 3 when it is acting as a pump, and u3 is the voltage applied by the logic circuit 90 to the electrovalve 31. y is a constant. C31 designates the maximum positive volumetric displacement of the motor 3. Similarly for the motor 4: C4 = C40 + 6u4 C40 is negative and corresponds to the maximum negative volumetric displacement of the motor 4 when it is acting as pump, and u4 is the voltage applied by the logic circuit 90 to the electrovalve 41. 5 is a constant. C41 denotes the maximum positive volumetric displacement of the motor 4. The electrovalves 21, 31, 41, like the hydraulic motors 3 and 4, are connected to a tank 12.

The coupling 2 is controlled by a third actuator 22 controlled by the electrovalve 21 to which is applied a voltage u2 from the logic circuit 90 and which is subjected to the force of a return spring.

The control arrangement described is designed to cut out the larger engine 4 by disengaging the coupling 2 when the smaller engine 3 is sufficient to supply the torque required by the operator taking into account the momentary pressure in the accumulator 1.

The basic equation of the system which is the sum of hydraulic torques developed by the motors 3 and 4 is in the form: Total Torque = ePa(C3 + qC4) E being a constant, and q being a constant dependent on the transmission ratio of the gearing 69.

This quantity should be equal to the torque required by the operator which is itself proportional to the displacement d of the control member, namely the acceleration pedal 8 of the vehicle. Thus: d = (pPa(C3 + qC4) or d C3 + qC4 = QPa The same total torque can be obtained with different combinations of the volumetric displacements of the motors 3 and 4.

To optimise the output the following conditions are imposed: 1) if d < C31, then C3 = d and C4 = 0.

Pa Pa Thus the required torque is supplied by the smaller motor 3 only, and the coupling 2 is disengaged.

2) if C31 < d l'6 qC4;, then C3 = ; C4 = d fPa qWFa Thus the torque is supplied by the larger motor 4 only, and the coupling 2 is engaged.

3) if qC41 < d < C31 + qC41 then C4 = C41 and C3 = d qC41 4)Pa Thus the torque is supplied by both motors, the larger 4 operating at maximum volumetric displacement. The coupling 2 is engaged.

Taking into account the relations: U5 = mPa m is a constant ug = nd n is a constant the preceding equations become:

2) if C31 < m. ug # qC4l, then u2 = 0; u3 = -C30 q)n U5 U4 = 1 (m . u9 - q(C40) qo (pn u5 3) if qC41 < m. u9 , then u2 = 0; U4 = 1C41 - C40) #n u5 # U3 = 1 (m . ug - C30 - qC41) Y cpn u5 One form of logic circuit 90 for obtaining these results will now be described.

In the part of the logic circuit shown in Figure 2 a logarithmic converter 101 is connected by its negative input to the sensor 9 to receive the voltage ug. Its positive input is earthed and the emitter-receiver junction of a transistor is in its feedback loop. In an analogous manner a second logarithmic converter 102 identical to the first is connected by its negative input to the sensor 5, to receive the voltage u5. The outputs of the logarithmic converters 1 1 and 102 are connected respectively to the negative and positive inputs of a differential amplifier 103 through resistances R1 and R3 respectively, this amplifier 103 having a resistance R2 in its feedback loop and also having its positive input earthed through a resistance R4 with R1/R2 = R3/R and R1 = R2.

The output of the differential amplifier 103 is connected to the input of an antilogarithmic converter 104 having the emitter-receiver junction of a transistor in its negative input, the base of the transistor being earthed and the positive input of the converter also being earthed, by way of resistance. A resistance R is disposed in the feedback loop of the converter 104. The output of the antilogarithmic converter 104 is connected to the negative input of an inverter amplifier 105 through a resistance R11. The inverter amplifier 105 has a resistance R21 in its feedback loop and its positive input is earthed through a resistance of the value: R11 . R21 Rll + F1 The output of the inverter amplifier 105 is connected in parallel to the negative inputs of two comparators 61 and 62. The positive input of the comparator 61 is connected to a point of a potential divider 611 at a potential corresponding to the maximum volumetric displacement C31 of the motor 3 and the positive input of the comparator 62 is connected to a point of another potential divider 621 at a potential corresponding to q.C41, C41 being the maximum volumetric displacement of the motor 4. The comparator 61 delivers an output signal Si which may be one zero, and the comparator 62 delivers an output signal S2 which may also be one or zero. One input of an AND-gate 107 is connected to the output S2 and the other input is connected to the output S1 through an inverter 106. The output of the AND-gate 107 delivers a signal S3 and is connected to one input of an OR-gate 109 of which the other input is connected to the output S2 of the comparator 62 through an inverter 108 delivering an output signal S2. The OR-gate 109 delivers a signal S4 at its output.

In Figure 3 the positive input of a non-inverting summating amplifier 111 is connected on the one hand through a resistance R1 to a point of a potential divider 110 which is at a potential corresponding to the volumetric displacement -C30, and on the other hand to a voltage u0 through a resistance R2. The negative input of the amplifier 111 is earthed through a reistance RA and the feedback loop of the amplifier has a resistance Rn. The output of the non-inverting summating amplifier 111 is connected on the one hand to one input of an analogue switch 301, controlled by the voltage Sl which is one of the outputs of Figure 2, and on the other hand to the positive input of a differential amplifier 113 by way of a series resistance R331. This positive input is also earthed through a resistance R43l. The negative input of the differential amplifier 113 has a resistance R131 and is connected to a point of a potential divider 114 which is at a potential equal to qC4l. The differential amplifier 113 has a resistance R231 in its feedback loop and the resistances are selected so that: R131 = R331 = 1 R231 R431 The output of the differential amplifier 113 its connected to one input of a second analogue switch 302 controlled by the voltage S2 which is one of the outputs of Figure 2.

The input of a third analogue switch 303, controlled by the voltage S3 which is also one of the outputs of Figure 2, is connected to a point of a potential divider 112 which has a positive potential corresponding to the quantity -C30 Y The outputs of the analogue switches 301, 302 and 303 are connected in parallel to supply the voltage u3 which controls the operation of the electrovalve 31 controlling the motor 3 through the actuator 32.

In Figure 4, a potential divider 116 provides a positive potential representing -C40 6 which constitutes the input voltage of a first analogue switch 401 which is controlled by the signal Sl which is one of the outputs of Figure 2.

A non-inverting, summating amplifier 115 has its positive input connected on the one hand to receive. through a resistance R143, a signal u0 which is delivered by the inverter amplifier 105 (Figure 2), and on the other hand, through a resistance R243, to a point of a potential divider 117 which is at a potential representing - qC40. The negative input of the amplifier 115 is earthed through a resistance RA43 and the feedback loop of the amplifier has a resistance Rn4.

The resistances are chosen such that: RA43 = R143 ; R143 = R243; RB43 = 1 RB43 R243 R143 q6 The output of the non-inverting summating amplifier 115 is connected to the input of a second analogue switch 402 controlled by the signal S3 which is one of the outputs of Figure 2.

Finally, a potential divider 108 provides a positive potential representing 1(C41 - C40) 6 which is applied to a third analogue switch 403 controlled by the signal S2 which is available at one of the outputs of Figure 2.

The outputs of the three analogue switches 401 402 and 403 are connected in parallel to supply at their common output the voltage u4 which controls the operation of the electrovalve 41 controlling the motor 4 through the actuator 42.

In Figure 5, a first analogue switch 201 has its input connected to the battery positive. It is controlled by the signal Sl which is available at one of the outputs of Figure 2. A second analogue switch 202 has its input earthed and it is controlled by the signal S4 which is available at one of the outputs of Figure 2.

The outputs of the two analogue converters 201 and 202 are connected in parallel to supply at their common output the voltage u2 which controls the operation of the electro-valve 21 controlling to the coupling 2 through the actuator 22.

When u2 = 0, the coupling 2 is engaged.

When u2 = +U, the coupling 2 is disengaged.

The electronic system illustrated in Figures 2 to 5 operates as follows: - at the input of the logarithmic converter 101, the signal is the voltage ug; - at the output the signal is equal to -kT log ug q ws - at the input of the logarithmic converter 102, the signal is the voltage u5; - at the output the signal is equal to -kT log u5 q RI5 The differential amplifier 103 is provided with resistances such that R1 = R3 R2 R4 and R1 = R2. Consequently the signal in output is equal to R2 . kT log u5 ~ -kT log u5 R1 q u9 - q u9 This last quantity is negative because u5 is always greater than u9. Us varied from U51 to u52 as the pressure of the accumulator 1 varied from P1 to P2 and ug varies from zero to U92 according to the displacement of the accelerator pedal 8. It is sufficient to choose u51 and u92 such that u5l < u92.

The signal at the output of the antilogarithmic converter 104 is equal to -RIs . ug u5 and the signal at the output of the inverter amplifier 105 is equalt to R21 RI5.. u9 S1 U5 If one chooses the magnitudes R11, R2l, R and Is such that R21 RI5 = m, The voltage uO = m . ug R11 #n w is obtained at the output of the inverter amplifier 105. The elements 101 to 105 disposed as indicated in fact constitute a potential divider.

In the comparator 61, the positive input is equal to C31 and the negative input is equal to Uo = m.u9 n u5 which was the signal u0 at the output of the inverter amplifier 105 as determined above.

The voltage S1 at the output of the comparator 61 is: S1 = 1 for C31 < m . u9 #n u5 S1 = 0 for C31 < m . u9 #n u5 S1 is the control voltage for the analogue switches 201 (Figure 5), 301 (Figure 3), 401 (Figure 4).

For the comparator 62, the signal at the positive input is equal to qC41; the signal at the negative input is equal to m . ug.

9n u5 The voltage S2 at the output of the comparator 62 is: = = for qC41 < m . ugS Tn = = 0 for qC41 < m . ug 4)n u5 From the voltage S2 the voltage S2 is produced by the inverter 108. The voltage S2 is the control voltage for the analogue switches 302 of Figure 3 and 403 of Figure 4.

From the voltages S2 and S 1 is produced by means of the AND-gate 197 the voltage S3 which is the control voltage for the switches 303 in Figure 3 and 402 in Figure 4.

Finally, from the voltages S3 and S 2is produced by means of the OR-gate 109 the voltage S4 which is the control voltage of the analogue switch 202 of Figure 5.

The position can be summarized in the following table: S1 S2 S1 S3 S2 S4 u0 < C31 1 1 0 0 0 0 C3l < uO < qc4l 0 1 1 1 0 1 u0 < qC41 0 0 1 0 1 1 In Figure 3 the potential divider 110 provides a potential corresponding to -C30.

In the non-inverting summating amplifier 111 the resistances are chosen such that RA = R1, R1 = R2 and Rn = 1.

RB R2 1 v Under these conditions the output voltage is equal to 1 (m . ug - C30).

α #n u5 This is the input voltage of the analogue switch 301 which is closed when S1 = 1 and open in other cases.

The potential divider 112 provides a potential representing -C30 -Y which is the input voltage of the analogue switch 303 which is closed when S3 = 1.

Finally, for the differential amplifier 113 the signal at the positive input is equal to 1 (M . u9 -C30).

u5 The signal at the negative input is equal to qC41, the voltage supplied by the potential divider 114.

Consequently the signal at the output amounts to 1 (m . ug -C30 - qC41) γ #n u5 which constitutes the feed voltage of the analogue switch 302 which is closed when S2 = 1 or S2 = 0.

In Figure 4 the potential divider 116 provides a potential representing -C40 Y which is the input voltage of the analogue switch 401 which is closed when S1 = 1 and open in other cases.

The non-inverting summating amplifier 115 receives as signals at its positive input on the one hand a voltage -qC40 supplied by the potential divider 117, and on the other hand the quantity = m m ug, fn u5 owing to the fact that it is connected to the output of the inverter amplifier 105 (Figure 2) through its resistance R143. The signal at its output is thus equal to 1 (u0 - qC40).

q6 This value is the feed voltage of the analogue switch 402 which is closed when S3 = 1 and opened in other cases.

Finally, the potential divider 118 supplies a voltage 1 (C41 - C40) # which constitutes the feed voltage of the analogue switch 403 which is closed when S2 = 1 or S2 = 0 and opened in other cases.

As far as Figure 5 is concerned it has already been seen before that when u2 = 0 the coupling 2 is engaged and when u2 = + U corresponding to the signal S1 = 1, the coupling 2 is disengaged.

By collecting the partial results indicating the signals transmitted by the different analogue switches illustrated in Figures 3, 4 and 5 when they are closed by the control signal which is applied to them, these conditions being summarised in the table above, it will easily be seen that the electronic system contained in the logic circuit 90 controls the mechanical, hydropneumatic and oleopneumatic parts of the apparatus in the desired manner.

WHAT WE CLAIM IS: 1. A power unit comprising at least two variable displacement hydraulic motors and a pressure accumulator for supplying fluid under pressure for driving the motors, one of the motors having a maximum displacement which is at least double that of the other motor, or one of the other motors, the output shafts of the motors being interconnected via a releasable coupling to drive a common shaft, the unit further comprising a control arrangement, connected to receive signals corresponding to the pressure in the accumulator and to the output torque required of the unit and adapter to control, in response to the said signals, the displacement of the motors and the operative condition of the coupling.

2. A power unit as claimed in claim 1, in which two of the hydraulic motors are provided.

3. A power unit as claimed in claim 2, in which the common shaft comprises the input of a differential which drives two wheels of a motor vehicle.

4. A power unit as claimed in any one of the preceding claims, in which the control arrangement comprises a logic circuit which produces signals which are applied to two flow control valves, for proportionately regulating the displacement of the motors, and to a further valve, for regulating the operative condition of the coupling.

5. A power unit as claimed in claim 4, in which the logic circuit comprises: a first part comprising a potential divider which produces at its output a voltage (uO) proportional to the ratio of voltages comprising the pressure and output torque signals; two comparators for comparing this voltage (u0) with a voltage proportional to the maximum volumetric displacement (C31) of the smaller motor and with a quantity (qC41) which is a multiple of the maximum volumetric displacement of the larger motor and for producing output signals having either the value 1 or the value zero depending on the relationship of the voltage (u0) to the quantities (C31) and (qC41); and a series of analogue switches the opening and closing of which are controlled by the said output signals which are grouped in parallel through

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. which constitutes the feed voltage of the analogue switch 302 which is closed when S2 = 1 or S2 = 0. In Figure 4 the potential divider 116 provides a potential representing -C40 Y which is the input voltage of the analogue switch 401 which is closed when S1 = 1 and open in other cases. The non-inverting summating amplifier 115 receives as signals at its positive input on the one hand a voltage -qC40 supplied by the potential divider 117, and on the other hand the quantity = m m ug, fn u5 owing to the fact that it is connected to the output of the inverter amplifier 105 (Figure 2) through its resistance R143. The signal at its output is thus equal to 1 (u0 - qC40). q6 This value is the feed voltage of the analogue switch 402 which is closed when S3 = 1 and opened in other cases. Finally, the potential divider 118 supplies a voltage

1 (C41 - C40) # which constitutes the feed voltage of the analogue switch 403 which is closed when S2 = 1 or S2 = 0 and opened in other cases.

their outputs so a to provide: a signal (U3) for controlling the volumetric displacement of the smaller motor; a signal (U4) for controlling the volumetric displacement of the larger motor; and a signal (u2) for controlling the operative condition of the coupling.

6. A power unit as claimed in claim 5, in which six of the said output signals are provided, of which the outputs of the comparators provide two signals (S1 and S2); a first inverter provides a signal S 1; an AND-gatereceiving the signals S2 and S 1 provides a signal S3; a second inverter provides a signal S 2; and an OR-gate connected to the output of the second inverter and to the output of the AND-gate produces a signal S4.

7. A power unit as claimed in claim 6, in which the signal (U3) for controlling the volumetric displacement of the smaller motor is produced at the common output conductor of three of the analogue switches: the first of which is controlled by the signal (S1) and provides, when closed, a signal 1 (uo - C30) w m which y is a constant and C30 is the maximum negative volumetric displacement of the smaller motor; the second of which is controlled by the signal (S3) and provides, when closed, a signal -C30; Y and the third of which is controlled by the signal (S2) and provides, when closed, a signal 1 (us - C30 - qC4l)

8. A power unit as claimed in claim 6 or 7, in which the signal (U4) for controlling the volumetric displacement of the larger motor is produced at the common output conductor of three of the analogue switches: the first of which is controlled by the signal (S1) and provides, when closed, a signal -C40, in which 6 is a constant and C40 is the maximum negative volumetric displacement of the larger motor; the second of which is controlled by the signal (S3) and provides, when closed, a signal 1 (uo - qC40); q6 and the third of which is controlled by the signal (S2) and provides, when closed, a signal 1 (C41 - C40).

9. A power unit as claimed in any one of claims 3 to 8, in which the signal (u2) for controlling the coupling is produced at the common output conductor of two of the analogue switches the inputs of which are connected respectively to the battery positive and to earth and which are controlled respectively by the signals (Sl) and (S45.

10. A power unit substantially as described herein with reference to the accompanying drawings.