#How VP37 electronic rotary pump works

04 / February 2022
How VP37 electronic rotary pump works

Seletron Performance

Chip tuning additional units for diesel engines with VP37 electronic rotary injection pumps.

As you may know, we conducted a survey via newsletter to see what topics our readers are most interested in, so we can best align our content to your interests. As a result of this survey, we realized (with pleasure) that a number of people are particularly interested in very technical topics related to the detailed operation of our chip tuning units. We were happily surprised that not only mechanics and tuners are interested in these topics, but also private individuals that, perhaps like you who are reading this, are thirsty for information to satisfy their curiosity related to the automotive sector, and especially the world of engines.


Among the various, more technical requests that go beyond the desire to know about power and torque increases achievable for engines of various car models were targeted and specific requests for how our chip tuning units function for particular injection systems. The requests weren't limited to this, but we have to start somewhere. Given the complexity of the topic, we will be forced to divide it into several sections. We have decided to begin in chronological order, starting with the first electronically controlled injection system employed on modern diesels, or for clarity, those produced since the mid-1990s when electronically controlled fuel injection first appeared on a turbodiesel. Here then is the first topic in the series which we hope will be of interest to you:


How our chip tuning units for Diesel engines with VP37 electronic rotary pumps work.

The demand arose in the 1990s, and around the middle of this decade, the first turbodiesels with electronic injection control appeared. Some competitors sold chip tuners that were really unrefined, and the worst one was made with a simple pressure switch that connected to a small pressure line in the turbo that was tripped at a certain pressure threshold, about 0.5 bar. This involved interjecting a trimmer (a variable resistor screw) into the injection pump circuit. The result? With low or partial loads, the module wouldn't trip at all. Then, at some point, the pressure switch would trip and create a sharp rise. Absolute performance was there, but there was an annoying step down, no progression, and worst of all, with a steady gait at medium loads, the modules continually turned on and off. The result was bad, and the cost wasn't exactly cheap (some cost as much as 360 Euros).


Another competitor used a similar system but instead of a pressure switch used a relay that generated an annoying step increase with the pressure of the accelerator pedal. Another manufacturer created a version with two relays to make the step less noticeable. The results? The boost absolutely was there, but in addition to the steps, another problem arose: with the engine off and the ignition on, if you accidentally pressed the accelerator pedal, a yellow light appeared on the ignition, indicating an error in the electronic management. Some customers with BMW 325tds and 525tds wanted to increase the power of their 6-cylinder engine but were unwilling to accept these huge limitations and problems. Other requests came to us to solve similar problems plaguing the (then widespread) VW-Audi 1900TDI 90 and 110-hp engines.


Introduction: How do electronically controlled rotary injection pumps work?

These pumps are a modern (more accurately robotic) version of traditional rotary pumps, i.e., those that have two functions implemented by the same pumping element. In fact, the piston rotates and functions as a distributor (i.e., deciding which injectors to send pressurized diesel fuel to) and as a pump(i.e., the actual function of compressing the diesel fuel). Initially, these pumps had control of diesel delivery through a steel cable connected to the accelerator pedal. To manage the injection timing (it is necessary to advance the injection timing by a few degrees as the engine speed goes up), rotary pumps incorporate a centrifugal variator that, as the rpm goes up, rotates the cam-holder plate connected to the pump by a few degrees.


Ultimately, the amount of diesel fuel is determined by the position of the accelerator pedal, and the timing is adjusted via a centrifugal variator that varies the phase according to the speed of rotation onnly. Calibration of the maximum delivery of the pump is done by a screw locked by lock nut. Early diesel engines either have this type of pump or in-line type pumps that have a very different architecture but have basically the same limitations. Perhaps we will discuss these separately because they are very uncommon on car engines.


On the VP37 electronic rotary pumps, there are major differences. The EDC controller decides the timing, or phase, which operates in PWM to control an electro-hydraulic actuator that shifts the injection phase. The timing is no longer tied directly to the engine speed alone, but the ECU decides (based on the internal mapping contained in the EPROMs) which timing value to hold. In order to have a feedback signal of the actual injection timing, one of the 4 (or more) injectors has an electromagnetic sprayer lift sensor (called an instrumented injector).


Through this signal, the EDC control unit adjusts the PWM control of the advance injection valve actuator accordingly.

The second command is determined by the diesel fuel delivery (amount injected for each individual cycle). Here again, the EDC control unit operates on a PWM-controlled delivery actuator. However, the feedback signal here is represented by a resistive delivery position encoder. That encoder is a potentiometer connected to the discharge regulator spool and is embedded in the injection pump housing and lambasted by the diesel fuel itself.


Our CHIPBOX chip tuner intervenes on this sensor. Inside the injection pump, there is a diesel temperature sensor that functions as a reference for its density, a value that the ECU uses to decide the duration of the diesel delivery. All chip tuning units for these injection systems connect to one of the wires of the diesel delivery encoder potentiometer. Increasing the ohmic resistance reduces the feedback to the ECU, and the ECU, in compensation, changes the PWM drive of the diesel delivery slider to increase the amount of diesel sent to the atomizing injectors.


The first point of focus is the hated delivery step. We, therefore, decided to create four ohmic resistance increment steps (not linear but roughly logarithmic). To do this, we employ four micro-relays using its normally closed contacts ( with two each relay, we connect them in parallel to increase reliability over time). The other key aspect is that to avoid having fault lights come on in the engine diagnostic system, and we need to make the relays activate with a certain delay, even if we press the accelerator pedal with the engine off and the ignition on. This gives rise to the need to use a microcontroller, specifically, a PIC, which we will outline along with other internal components.


The microprocessor cannot directly drive the four micro-relay coils, so we use a driver that incorporates the current amplifiers and load dump protection diodes for the over-voltage of the relay coils within it. The microprocessor has the four control outputs connected to the driver chip, and the driver outputs are directed to the four micro relays. Each normally closed contact of the relays has a resistor of different values in parallel, which are then connected in series with each other and in parallel to the maximum power adjustment trimmer.


To make the tripping even smoother and to reduce exhaust fumes, the processor always switches on the four relays in sequence with a certain delay.

The two wires connected to the ends of the power adjustment trimmer and in parallel with the resistor assembly are connected in series to wire number 1 of the Bosch rotary injection pump connector.


An alternative system to the series resistor that we developed was to insert a transistor in parallel to the measurement circuit, thus between the common and the position signals.

By acting on the base (in the case of a BJT transistor) or on the gate (in the case of a MOSFET transistor), the transistor acts as a variable resistor placed in parallel with the measurement inductance, thus lowering the impedance of the circuit (as if the pump were more closed than it is) so that the ECU will open the pump more to compensate.

As in the previous case, a microcontroller is used both to properly manage the various engine conditions because the control of this variable resistor is not linear, and it is easier correct the response with a microcontroller.


Let us come to the inputs: to proportion the ohmic increment implemented on the encoder signal directed to the EDC control unit, we take the accelerator pedal potentiometer signal as the main reference. This signal has a voltage value ranging from about 0.4V to about 4V. We take this signal, pass it through a variable resistor voltage divider ("throttle sensitivity" adjustment) and send it to the micro-controller after passing it inside an RCZ filter branch. The micro-controller converts this signal from a DC voltage to a binary code. This signal will determine when and how much to change the signal, thus determining the ohmic value that we are going to put in series with the injection pump encoder signal, i.e., the percentage of diesel injection delivery increment that we are going to create.


Some engines, however, have a tendency to trigger oscillations on the transmission around the maximum torque speed. This phenomenon can be accentuated when there are large increases in engine torque around 2000 rpm. We then introduce a second parameter reading: the signal from the air mass meter (debimeter). This signal is related to the amount of air intake and thus also to the engine speed. We created a second input that reads the MAF signal (which also passes through a variable resistive divider or curve adjustment) and sends it to the micro-controller after passing it inside another RCZ filter branch.


Thanks to this signal, it is possible to adjust the chip tuning additional unit to provide the maximum boost only after a certain rpm, i.e., only after moving off the back of the torque curve. This way, we avoid oscillation triggers and increase the torque more where it normally tends to drop, i.e., after the maximum torque speed. Since, on certain engines, this connection to the air mass meter is not needed, we inserted two dip-switches connected to 2 other digital inputs of the processor, and one of these switches determines whether or not the trip map should take this signal into account. The second switch activates or deactivates the "Overboost" function. When activated, the Overboost function allows adjustments of larger increments because a part of this increment remains active only for a few seconds.


The circuit is composed of the operating status LED, the input signal for the ON-OFF switch, and another signal is sent to a logic input of the microprocessor, again after passing it inside an RCF filter branch. Except for the wire to be physically connected to the accelerator pedal, this chip tuner already has original connectors for almost all car models on which it could be installed (BMW, Audi, Seat, Skoda, Renault, Rover, etc.).


With this first article, we hope we have satisfied your curiosity. Come back and read us regularly because later on, we will also talk about chip tuners for engines with radial piston pump injection systems, and also about chip tuning units for engine tuning with injector-pump engines... and more!


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